Functionalization Methods of Starch and Its Derivatives: From Old Limitations to New Possibilities PDF

polymers Review Functionalization Methods of Starch and Its Derivatives: From Old Limitations to New Possibilities Arkadiusz Zarski 1, *, Kamila Kapusniak 1 , Sylwia Ptak 1 , Magdalena Rudlicka 1 , Sergiu Coseri 2 and Janusz Kapusniak 1 1 Faculty of Scienc...

polymers Review Functionalization Methods of Starch and Its Derivatives: From Old Limitations to New Possibilities Arkadiusz Zarski 1, *, Kamila Kapusniak 1 , Sylwia Ptak 1 , Magdalena Rudlicka 1 , Sergiu Coseri 2 and Janusz Kapusniak 1 1 Faculty of Science and Technology, Jan Dlugosz University in Czestochowa, 13/15 Armii Krajowej Ave., 42-200 Czestochowa, Poland; [email protected] (K.K.); [email protected] (S.P.); [email protected] (M.R.); [email protected] (J.K.) 2 “Petru Poni” Institute of Macromolecular Chemistry, Romanian Academy, 41 A, Gr. Ghica Voda Alley, 700487 Iasi, Romania; [email protected] * Correspondence: [email protected] Abstract: It has long been known that starch as a raw material is of strategic importance for meeting primarily the nutritional needs of people around the world. Year by year, the demand not only for traditional but also for functional food based on starch and its derivatives is growing. Problems with the availability of petrochemical raw materials, as well as environmental problems with the recycling of post-production waste, make non-food industries also increasingly interested in this biopolymer. Its supporters will point out countless advantages such as wide availability, renewability, and biodegradability. Opponents, in turn, will argue that they will not balance the problems with its processing and storage and poor functional properties. Hence, the race to find new methods to improve starch properties towards multifunctionality is still ongoing. For these reasons, in the presented review, referring to the structure and physicochemical properties of starch, attempts were made to highlight not only the current limitations in its processing but also new possibilities. Attention was paid to progress in the non-selective and selective functionalization of starch to obtain materials with the greatest application potential in the food (resistant starch, dextrins, and maltodextrins) and/or in the non-food industries (hydrophobic and oxidized starch). Citation: Zarski, A.; Kapusniak, K.; Ptak, S.; Rudlicka, M.; Coseri, S.; Keywords: starch; dextrin; maltodextrin; modification methods; controlled and uncontrolled Kapusniak, J. Functionalization functionalization; food and non-food application Methods of Starch and Its Derivatives: From Old Limitations to New Possibilities. Polymers 2024, 16, 597. https://doi.org/10.3390/ 1. Introduction polym16050597 The existence of matter is closely related to the presence of polymer compounds in it. Academic Editor: Nicolas Sbirrazzuoli Natural polymers, i.e., those found in living organisms, both prokaryotic and eukaryotic, constitute the main building and reserve material. Due to the functions they perform and Received: 1 February 2024 their strategic importance, it is no wonder that these compounds are commonly found in Revised: 16 February 2024 nature. Biopolymers are therefore obtained from natural, renewable sources, unlike most Accepted: 17 February 2024 synthetic polymers produced from a non-renewable source such as petroleum. Moreover, Published: 21 February 2024 polymers of natural origin are biodegradable and therefore not harmful to the environment. In terms of chemical structure, they mainly include polysaccharides, polypeptides, polynu- cleotides (nucleic acids), and polyterpenes (rubbers). Over the centuries, humanity has Copyright: © 2024 by the authors. learned how to use these natural resources, developing newer methods and techniques for Licensee MDPI, Basel, Switzerland. processing them. Polysaccharides have particularly wide possibilities and application This article is an open access article potential. One of them, the most common next to cellulose and chitosan, is starch. Its main distributed under the terms and sources are primarily cereals—maize, wheat, and rice, as well as potatoes and cassava. conditions of the Creative Commons Thus, access to starch is practically unlimited all over the world, and the undemanding Attribution (CC BY) license (https:// agricultural cultivation of plants rich in it and simple methods of obtaining and extracting creativecommons.org/licenses/by/ it from plant material make it a relatively cheap polymer. In 2022, the value of the global 4.0/). starch market was estimated at approximately USD 60 billion (134.5 million metric tons), Polymers 2024, 16, 597. https://doi.org/10.3390/polym16050597 https://www.mdpi.com/journal/polymers Polymers 2024, 16, 597 2 of 46 and in the future, it may grow to even USD 90 billion by the end of the third decade (approx. 200 million metric tons). However, the unwavering interest in starch not only in the food industry but also in other industries results mainly from its functional properties. Analysts predict that the upward trend in the use of this biopolymer will continue in the coming years proportionally in all major industrial sectors. First place (over 60% of the market) is taken by the production of food for humans, both traditional (emulsifiers, thickeners, gelling agents, stabilizers, and antifoaming agents) and functional (e.g., prebiotic), as well as beverages and ethanol. The next places are taken by the production of animal feed, the production of medicines and dietary supplements, and the production of paper, textiles, and glue, as well as the increasingly trendy production of biodegradable packaging as an alternative to plastics. It is also expected that in the coming years the demand for modified starch will significantly increase compared to native starch. In the presented review, the most important issues regarding starch properties that make this biopolymer so attractive for many industrial applications and thereby multifunc- tional material have been discussed. Special attention was paid to the limitations in its use, as well as to new approaches and strategies proposed or implemented to solve the main problems related to its processing in recent years (Figure 1). The most promising methods and techniques for its further functionalization, as well as the prospects for the development of starch-based materials in the coming decades, have also been described. Figure 1. Old limitations and new possibilities in functionalization methods of starch and its derivatives. Polymers 2024, 16, 597 3 of 46 2. Structure of Starch In terms of chemical structure, starch is a polysaccharide. Due to the fact that it consists of only one type of mer, i.e., α-D-glucopyranose, it is classified as a homopolymer. Six-carbon closed rings of glucose units are connected to shorter or longer polysaccharide chains using glycosidic bonds. Such bonds are formed as a result of connecting neighboring molecules through the oxygen atom that forms the hydroxyl group. Chain extension is achieved by replacing the hemiacetal hydroxyl group at carbon C-1 of one glucose molecule with the oxygen atom of the hydroxyl group at carbon C-4 of the next unit, with the release of a water molecule. Therefore, instead of the term glucose unit, the term anhydroglucose unit (AGU) is often used. In this way, one end of the polymer chain, with a free hydroxyl group, is non-reducing, and the other end, with a free aldehyde group, is reducing. In addition to α-1,4-glycosidic bonds, α-1,6-glycosidic bonds also take part in glucose polymerization. While the former are responsible for the creation of chain forms, the latter are responsible for connecting these chains together, resulting in the formation of branched forms. So, basically, starch consists of two polyglucan fractions that differ in structure and, therefore, in properties: linear amylose and branched amylopectin (Figure 2) [6,7]. In amylose, apart from very long polysaccharide chains (average chain length, CL 270–525 AGU), there may be, although definitely few, branches (average CL 5–20 AGU). Amylopectin, in turn, is characterized by many branches but always with short chains. Figure 2. Structure of amylose and amylopectin in starch. The quantitative ratio of starch fractions is not a constant value and varies significantly depending on the botanical source of starch (Table 1) [6–8]. Typically, the main polysac- charide component of starch is amylopectin in a ratio of 3:1 to amylose, with exceptions, such as in the case of waxy starches, where amylopectin constitutes up to 100% of the polymer, or high-amylose starches, as in the case of maize starch with an amylose content of up to 70%. Genetically modified maize starch with an amylose content exceeding 90% is also known in the literature [9,10]. Polymers 2024, 16, 597 4 of 46 Table 1. Characteristics of different types of starch. Starch Type Barley Maize Potato Rice Wheat Tapioca Source Cereal Cereal Tuber Cereal Cereal Root Grain shape Lenticular, round Polyhedral, round Round, oval Polygonal, angular Lenticular, round Oval Grain diameter [µm] 2–40 2–30 5–100 1–35 1–40 4–45 Polymorphism type A A B A A A/C Amylose [%] ~22 23–32 18–29 ~22 23–29 17–30 Amylopectin [%] 78 75 78 78 77 80 Lipid [%] 0.6–0.9 0.8 0.01 0.3 0.9 0.02 Protein [%] 0.1 0.35 0.1 0.3 0.4 0.1 Phosphorus [%] 0.05 0.09 0.20 0.09 0.3 0.009 The polysaccharide components of starch also differ in molecular weight, which in turn also depends on the origin of the polymer [11–13]. Both fractions are identified with the molecular weight distribution throughout the polymer, so that its molecular weight is expressed as the average of the fraction masses. The molecular weight of amylose is much lower compared to that of amylopectin. It ranges from 105 to 106 Da for amylose and 107 to 108 Da for amylopectin. For example, the degree of polymerization (DP) of potato amylose is approx. 103 glucose residues, i.e., the average molecular weight is approx. 162 × 103 Da, while for wheat amylose, it is 4 × 103 glucose residues and 648 × 103 Da, respectively. The number average DP of amylose is between 9 × 102 and 3 × 103 and that of amylopectin is in the range of 5–17 × 103. In addition to polysaccharide compounds, starch may contain other components, including lipids, proteins, phosphorates, minerals, mainly in the form of oxides, and water—chemically bound or unbound. The content of the latter is very important from the point of view of many properties and applications of starch. In commercially available starches, its content ranges from 12 to 21% (including cereal starches up to 14%, root starches up to 17%, and tuber starches up to 21%). Due to the form in which water may appear in starch grains, it is classified as adsorbed, crystallized, or inclusionary (filling free spaces inside or intermolecularly). Depending on atmospheric conditions (mainly temperature and relative air humidity), its content may change significantly [5,11]. Both amylose and amylopectin do not occur in nature as separate compounds but in the form of water-insoluble, discrete, and semi-crystalline aggregates called starch granules. These granules, depending on their botanical origin, differ significantly in morphological terms, especially in terms of size (from 1 to 100 µm) and shape (round, oval, spherical, hull, or irregular). Changes in the appearance of starch granules also occur in the case of most of its modifications, which is particularly well seen in the example of potato starch and its acidically or enzymatically hydrolyzed derivatives—dextrins and maltodextrins, respectively (Figure 3). Starch granules have a semi-crystalline structure, with a degree of crystallization ranging from 15 to 45%, mainly related to the presence of a branched fraction, i.e., amylopectin. The general model of the crystalline parts of starch granules is based on a spherocrystalline assembly of amylopectin molecules, composed of double helices arranged radially in such a way that the non-reducing end of the polymer chain is directed towards the granule surface. The chains of the branched fraction layer on top of each other in two dimensions, and together with the chains of the unbranched fraction, they organize into three-dimensional micelles, forming radially spreading crystallites with a size of approx. 9 nm [5,16]. It is believed that α-1,6-glycosidic bonds in amylopectin, i.e., branching sites, are located in amorphous areas and, together with amylose, form amorphous fractions of the polymer. Both amylose and amylopectin molecules, through intra- and intermolecular hydrogen and hydrophobic bonds, lead to the formation of structures with an increasingly higher degree of organization—from lamellas, through clusters, blocklets, and growth rings, to the final product, i.e., water-insoluble granules with alternating crystalline and amorphous layers. Polymers 2024, 16, 597 5 of 46 Figure 3. Optical and scanning electron microscope images of potato starch, dextrin, and maltodextrin (Jan Dlugosz University in Czestochowa, 2023). Various arrangements of double helices are responsible for polymorphism in starch. Polymorphic variants of type A, B, C, and V are known. In type A, amylopectin double helices are short (DP 11–16) and densely packed into monoclinic unit cells with max. eight water molecules. This type is characteristic of cereal starches. In turn, in the type B polymorphic variant, amylopectin helices are long (DP 30–45) and loosely packed with hydration of up to 27%. Type B is often found in starches isolated from tubers and roots. The type C polymorph is a mixture of types A and B. It is characteristic of legume starch. Dehydration caused by high temperature and pressure may lead to changes in the double helical systems and thus polymorphic changes from type B to type A. In turn, type V is characteristic of amylose, fatty acids, and monoacylglycerols. It occurs in swollen granules and becomes visible during gelatinization. 3. Properties of Starch Although starch is a homopolymer in terms of structure, it is a highly differenti- ated compound in terms of its physical and chemical properties. The specific physico- chemical properties of this biopolymer depend on many factors, primarily the content of polysaccharide fractions and non-polysaccharide components, as well as the structure and structural features of starch granules. Such differences are dictated not only by genetic conditions—the species origin of the plants from which starch was isolated—but even by the growing conditions of these plants. Starch isolated from plant material after appropriate processing is a white or yellow powder—insoluble in cold water and most common organic solvents. Typically, espe- cially alkaline media used led to its partial hydrolysis and the formation of undesirable depolymerization products. Due to its chemical structure and the presence of many polar hydroxyl groups, it is a hydrophilic compound and should mix well with water, but it does not. It depends on the presence of an insoluble or sparingly soluble amylose fraction. However, starch is hygroscopic—it absorbs large amounts of moisture from the environ- Polymers 2024, 16, 597 6 of 46 ment. Swelling is a reversible and exothermic process during which starch granules can significantly increase their volume. When the aqueous starch suspension is heated, the starch granules usually swell spherically and crack above 50 ◦ C. Thus, the semi-crystalline structure is lost, and the amylose molecules flowing out from the damaged granules begin to co-create a network that retains water and increases the viscosity of the mixture and electrical conductivity. Gelatinization is often associated with starch pasting but incor- rectly so because these terms describe different stages of hydration and swelling of starch granules. It is an endothermic process taking place at a specific temperature or, more precisely, a certain temperature range. Moreover, it is characteristic for a given type of starch and depends not only on the presence of water but also on the pH or presence of ionic compounds, e.g., salt. Gelatinization mainly includes changes related to the melting of crystalline areas of amylopectin and partial washing out of amylose. All the changes taking place around the starch gelatinization temperature are called pasting. During it, intense swelling occurs, and the grains completely disintegrate. In the first phase, hydrogen bonds in the amorphous fraction are broken. In the second phase, water takes on the role of a plasticizer, which results in hydration and the swelling of the mentioned fraction. Ultimately, as a result, the starch loses its granular structure, amylose is intensely released, and the whole thing takes the form of a paste. Equally important parameters as the gelatinization temperature are the reduced vis- cosity values, which determine the rheological properties of starch, which are particularly important for the food industry. They are used as an indicator of retrogradation during storage. The higher final viscosity and higher degree of retrogradation are caused not only by amylose but also by proteins and the presence of disulfide bridges. If we take a closer look at the retrograde phenomenon, this is an irreversible process based on secondary crystallization. As a result of nonspecific reconstruction of hydrogen bonds between hydroxyl groups, the intermolecular spaces become narrowed, which is accom- panied by dehydration called syneresis. The endothermic transformations of retrograded starch may occur at lower temperatures than in the case of native starch. During retrogra- dation, the crystal lattice is not recreated, but a new one with a lower degree of order is created, which causes the structure to have lower thermal stability. In retrograding starch, amylose associates in a double helix (up to 70 AGU), and amylopectin recrystallization occurs by connecting the outermost and short branches of the polysaccharide chain. The functional properties of starch may change over time, under the influence of various biotic and abiotic factors that act directly or indirectly on the degree of granule ordering. The deformation or destruction of the crystalline structure of starch results in mostly irreversible changes in properties, not only corresponding to an increase in amor- phousness but also a loss of optical birefringence, gelatinization, and swelling. A high degree of crystallinity ensures structural stability, and thus, the granules become more resis- tant to various types of phase transitions. Also, differences in the degree of structural order of starch determine its different characteristics in relation to gelatinization temperatures, transition to the glassy state, or decomposition. The poor solubility of starch in water and organic solvents is the result of many intra- and intermolecular hydrogen bonds between its hydroxyl groups. When using water as a solvent, the modification is usually carried out in heterogeneous conditions, where we are dealing with a suspension rather than a solution. In a heterogeneous system, starch substitution reactions, for example, yield products with a low degree of modification and many byproducts. Therefore, in order to achieve a higher degree of function- alization, organic solvents and catalysts, such as dimethyl sulfoxide (DMSO), pyridine, N,N-dimethylacetamide (DMAc), or N,N-dimethylformamide (DMF), were quite often used. The problem with most organic solvents is that they can be dangerous to living organisms and the environment due to, for example, their flammability or toxicity. Already for the third decade now attention has been paid to new types of solvents—mainly ionic liquids (ILs) and supercritical fluids (SCFs) (Figure 4). And it is to them that the following considerations will be devoted. Polymers 2024, 16, 597 7 of 46 Figure 4. Popular solvents in starch functionalization: (1) scCO2 , (2) DMSO, and (3) imidazolium IL. ILs are compounds with an ionic structure where the cation is only organic, but the anion may also be inorganic. They owe their name to their low melting point, which is below the boiling point of water and often even close to room temperature. Due to their thermal and chemical stability, low volatility, and non-flammability, as well as designable polarity, they are used in various polymerization and derivatization techniques. So far, imidazolium ILs, mainly chlorides, have most often been used in starch modifications. They act not only as solvents but also as catalysts and have usually been used in substitution reactions. In recent years, ionic liquids have been quite often used not only as solvents in chemical and biochemical modifications but also as plasticizers or compatibilizers in physical modifications, mainly to obtain starch blends and TPS. Over the years of their use, some limitations have already arisen. The studies on the ecotoxicity of the ionic liquids known so far have confirmed that they are not as green solvents and reaction media as previously believed [29,30]. The high polarity of compounds used to modify starch, including ionic liquids, is advisable when dissolving or gelatinizing starch but undesirable in anhydrous and biocatalyzed reactions. The hygroscopicity of solvents may create problems with the removal of water as a byproduct of the reaction. This may, in turn, contribute to the inactivation of biocatalysts through the structural deformation of their active centers. A liquid or gas becomes a supercritical fluid (SCF) when the temperature and pressure at which they are located exceed critical values. Of all supercritical fluids, the most commercially available are water (scH2 O) and carbon dioxide (scCO2 ). The latter has most commonly been used in starch functionalization. For carbon dioxide, the supercritical state occurs above a temperature of 304.25 K and a pressure of 7.39 MPa, in which it retains a density similar to a liquid and a diffusion similar to a gas. Compared to traditional solvents used in starch processing, it is characterized by low viscosity, good permeability, and a high diffusion coefficient, which increase the dissolving capacity, making the mass transfer process simpler and the reaction rate higher. Among the physical modifications of starch, scCO2 has been used mainly to induce its gelatinization [32,33]. Chemical modifications of starch using scCO2 as a reaction medium include the synthesis of starch esters using methyl and vinyl esters or acetic anhydride, as well as the synthesis of pre-gelatinized starch grafted with poly(L-lactic acid) [34–36]. Dual physicochemical methods have also been performed, such as reactive supercritical fluid extrusion, mainly to crosslink starch [37–39]. The scCO2 has similar advantages to ILs, i.e., non-flammability, non-volatility, and multifunctionality. Additionally, for supercritical fluids, there is no problem with their recycling, as is the Polymers 2024, 16, 597 8 of 46 case with ILs. The one problem, which is quite significant, is the high cost of producing supercritical fluids. However, when comparing them with ionic liquids, the latter have many more limitations such as the difficulty in their purification and the increasing number of reports about their ecotoxicity. 4. Physical, Chemical, and Dual Modification of Starch Starch is a polymer compound that is sensitive to a lot of physical factors such as high temperature, very low and high pH, pressure, light, radiation, ultrasonic waves, and various types of mechanical stress. In general, the physical modifications of starch can be divided into two main groups, i.e., thermal and nonthermal, as shown in Figure 5. Figure 5. Physical modification of starch. In recent years, nonthermal physical modifications have become increasingly popular. Thanks to them, with low energy consumption, it is possible to introduce significant changes in the structure of starch and thus modulate some of its properties, mainly physical ones. Among them, for example, ozonation forces the loss of starch granulation, and treatment with high hydrostatic pressure affects its crystallinity and gelatinization [41,42]. Nonthermal methods can also induce certain chemical changes, e.g., in the case of plasma, which is able to induce crosslinking in starch molecules, thus introducing changes in the thermal properties of starch—melting temperatures and other phase transitions [43,44]. Among other nonthermal physical modifications, the use of ultrasound and microniza- tion, as well as high-pressure, γ-irradiation, or pulsed electric field treatment, is becoming increasingly popular. Apart from improving the properties of starch, their main advantage is that they are quick and simple and do not require complicated procedures. Moreover, they do not generate byproducts, so the problem of their disposal disappears, and they are not toxic. However, the problem is the high cost of devices and the lack of standardization and reproducibility. When using physical modification, however, as the leading method in dual modifica- tions, hydrothermal methods such as annealing or heat moisture treatment (HMT) were most often used (Table 2). Polymers 2024, 16, 597 9 of 46 Table 2. Examples of dual modification methods of starch based on hydrothermal treatments. Type of Starch Type of Dual Modification Changes in Starch Properties Reference Decrease thermal stability, pasting Corn Infrared HMT properties, and viscosity Decrease thermal stability, pasting Wheat Infrared HMT properties, and viscosity Increase resistant starch content; Corn Extrusion and HMT decrease solubility and swelling power Increase rheological properties, solubility, Barley Annealing and hydroxypropylation and freeze–thaw stability Increase resistant starch content, thermal Lactic, citric, and acetic acids Corn stability, and rheological properties; and HMT decreased crystallinity Decrease viscosity; Corn Lactic acid and HMT increase resistant content and thermal stability Decrease swelling power and Inclusion complexes with sodium retrogradation; Potato stearate and HMT increase thermal stability and resistant fraction content Annealing uses an excess of water (in the range of 40–70% v/v) and a temperature below the gelatinization temperature and has a long processing time. HMT is performed at a low water content (usually 10–30% v/v) and high temperatures of 100–120 ◦ C. In particular the products of combined hydrothermal treatment are promising candidates for resistant starch-based food, being a safer replacement of chemically crosslinked starch. Various methods of preparing blends based on starch or its derivatives are still fo- cused on good compatibility and efficient processing. Such blends have evolved quite dynamically over recent years, from systems with native starch, thermoplastic starch (TPS), or starch modified in various ways to nanostructured varieties. Initially, synthetic, non- degradable polymers were used as blend components. Finally, natural and biodegradable polymers were used. There is an equally wide range of available technologies for their preparation—from typical laboratory or traditional ones such as the solvent casting method, extrusion, molding, and the foaming process to reactive extrusion, 3D printing, or electro- and forcespinning (Figure 6). A definite trend should be to design materials with improved processing and utility properties while maintaining biodegradability and the nature of environmentally friendly materials. The combination of starch with synthetic or other natural polymers in the form of blends is carried out in order to eliminate limitations in its use, mainly such as brittleness, sensitivity to moisture, or poor mechanical properties. When a nondegradable polymer is a component of the mixture, there is a risk of greater environmental pollution with microplastics. It is not an ideal solution when we use other biodegradable polymers, such as aliphatic polyesters, in blends with starch. Its strength properties improve, its hydrophilicity decreases, and its resistance to biotic and abiotic factors increases. However, the problem is that these are low-starch mixtures, and their production costs are still high and therefore uncompetitive compared to traditionally used petroleum-based polymers. The evolution in obtaining such materials, opportunities, and challenges was recently reported by Zarski et al. and Muñoz-Gimena et al.. Also, the approach of using starch-based materials in the form of nanostructures is becoming more and more trendy every year. So far, their production has involved both physical processing—grinding, homogenization, ultrasound, and radiation—as well as chemical processing, such as hydrolysis, copolymerization, and crosslinking. It has been shown that the combination of chemical and physical methods makes it possible to Polymers 2024, 16, 597 10 of 46 achieve greater efficiency and uniformity of the obtained starch nanostructures. Mainly nanocrystals, nanofibers, nanogels, and starch nanomicelles were tested (Table 3). The purpose of producing such nanoparticles is to potentially use them as fillers to improve the barrier and mechanical properties of widely used polymeric materials. Figure 6. Systems and methods for preparing starch-based blends most frequently used in recent years. Table 3. Examples of preparation method of starch nanostructures. Starch Nanostructure Type of Starch Method of Preparation Min. Size [nm] Reference High-amylose maize Acid-catalyzed hydrolysis 118 Nanocrystal Waxy Acid-catalyzed hydrolysis 70 High-amylose maize Electrospinning 300 Nanofiber High-amylose maize Electrospinning 30 Corn Coaxial electrospinning 110 Potato Graft copolymerization 120 Nanogel α-starch Crosslinking 30 Starch octanoate Esterification 410 Nanomicelle Waxy maize Emulsification 60 Corn Graft copolymerization 20 Nanostructured forms of starch can be used as emulsion stabilizers, additives to films and gels to improve functional properties, forming agents in self-assembling structures, or as scaffold components in tissue engineering. Starch nanoparticles are biocompatible and non-toxic but also sensitive to changes in temperature and acidity. Their properties depend on hydrophobicity, charge, and surface morphology and, above all, size and shape. Polymers 2024, 16, 597 11 of 46 Based on the number of studies conducted in recent years, it seems obvious that of all the methods used in starch processing, typical chemical methods are the most important due to the scope of application (Figure 7) [69,70]. The most commonly used chemical func- tionalization of starch is based on classic organic chemistry reactions such as crosslinking, grafting, esterification, etherification, hydrolysis, or oxidation (Figure 8). Figure 7. Chemical modification of starch. All these reactions lead to starch derivatives, whose physicochemical properties differ substantially from those of the starting material. Due to its chemical structure, starch has characteristics typical of aldehydes, ethers, and especially alcohols. The ether bond (C-O-C) occurring in the glucopyranose ring of starch is quite stable and not very reactive. It is only susceptible to acid or base hydrolysis at elevated temperatures. The situation is similar with glycosidic bonds responsible for the formation of chains and branches in this polysaccharide. They undergo hydrolysis in the presence of hydrogen ions through the action of strong acid and increased temperature (uncontrolled method)—and hydro- lases during enzymatic decomposition (controlled method). The unbranched fraction, i.e., amylose, is more susceptible to hydrolysis. In turn, the glycosidic bonds of both fractions are stable in an alkaline environment, even at elevated temperatures. Therefore, the most susceptible to chemical interactions seem to be hydroxyl groups, of which starch has many, up to three free groups per AGU. These are primary groups at carbon C-6, the most reactive groups, and secondary groups at carbons C-2 and C-3. However, the reactivity of native starch is low due not only to the polymer structure but also to the multi-stage organization of starch granules. Accessibility to hydroxyl groups and glycosidic bonds is hampered by the presence of a dense network of intra- and intermolecular hydrogen bonds. Thus, starch reactions are determined not only by the reactivity of its functional groups and reagents. These are usually reactions at the phase boundary, which, given the complex structure of starch, prevents the effective penetration of the reagent into the potential reaction site. This explains the fact that the degree of starch conversion is usually Polymers 2024, 16, 597 12 of 46 not great, and a number of functional groups of glucose units remain intact. In turn, those functional groups that are available to the reagents do not always react selectively because local disturbances in the reagent concentration occur. Hence, there is a need not only to develop methods of loosening the starch structure and increasing the potential reaction sites but also to develop selective modifications. Therefore, an effective solution seems to be to conduct regioselective reactions based on one of three approaches: the use of protecting groups, regioselective replacement of -OH groups with other functional groups, or catalyzed selective functionalization of these groups without the use of a protecting group [73,74]. The selective functionalization of starch is discussed later based on the examples of starch oxidation. Figure 8. Cont. Polymers 2024, 16, 597 13 of 46 Figure 8. Mechanisms of basic reactions in chemical modification of starch: (1) acid-catalyzed hydrolysis; (2) etherification; (3) oxidation; (4) crosslinking; and (5) esterification. Based on current research, it can be concluded that today, single physical treatments or single-step chemical or enzymatic modifications of starch are used less and less frequently. Polymers 2024, 16, 597 14 of 46 Although it has been emphasized that physical modifications are a much simpler, cheaper, and greener alternative to starch functionalization than in the case of chemical or enzymatic modifications, after many decades of using both, it can be concluded that the truth lies somewhere in the middle because carrying out a more selective or controlled modification requires the use of catalysts, while many chemical or biochemical reactions of starch would not take place without simple or more complicated physical thermal or nonthermal pretreatments such as gelatinization, pH changes, or radiation treatment. Therefore, due to the awareness of the preponderance of potential benefits, especially when designing multifunctional starches, in recent years, more and more attention has been paid to dual or multi-stage modifications. In the following subsections, we decided to focus on and discuss in more detail recent reports on the non-selective and selective functionalization of starch towards obtaining materials with, in our opinion, the greatest potential in the food industry (resistant starch, dextrins, and maltodextrins) and/or in non-food industries (hydrophobic and oxidized starch). To the best of our knowledge, this is the first review to present such a summary of the studies from the last few years. 4.1. Development of New Resistant Starch and Pyrodextrins Starch is the largest energy source worldwide, but only part of the starch consumed in our diet is degraded by host or bacterial enzymes and absorbed in the form of glucose in the small intestine. Some dietary starch transits the colon as resistant starch (RS), where it is digested by specialized members of the microbiota [76,77]. Moreover, starch can be used as a raw material for the production of preparations with the properties and structure of RS, as well as resistant dextrins (RDex). Both of them may exhibit the characteristics of soluble (SDF) or insoluble dietary fiber (IDF). RS and RDex as dietary fiber (DF), due to its beneficial health effects, can also be considered as an important ingredient in the formulation of functional foods. Functional foods are industrially processed or natural foods that when regularly consumed within a diverse diet at efficacious levels have potentially positive effects on the health and/or well-being of people beyond basic nutrition. Moreover, some ingredients of DF, including part of RS and RDex, can be selectively utilized by the host microbiota and promote health, demonstrating a prebiotic effect. DF is a functional food ingredient that can be used easily in various functional foods like breakfast cereals, bread, cookies, cakes, yogurt, beverages, and meat. 4.1.1. Resistant Starch There are five known types of resistant starch: RS1—physically inaccessible starch mainly due to physical barriers formed by cell walls and protein matrices ; RS2—starch that forms compact granules that resist digestive enzymes ; RS3—retrograded starch formed during cooking and the subsequent cooling of starch or starchy products ; RS4—chemically modified starch, i.e., starches which have been etherized, esterified, or cross-bonded with chemicals ; RS5—natural or manufactured starch–lipid complexes. Based on the number of the most cited papers in recent years, more attention has been paid to the impact of the consumption of RS on the gut microbiota and short-chain fatty acid production [76,87–89]. However, some scientists are working on the development of new types of RS. In recent years, we have observed an increase in the number of publications and a constantly high number of patents devoted to resistant starch. The percentages of documents by subject area on resistant starches published over the last 10 years are presented in Figure 9. Polymers 2024, 16, 597 15 of 46 Figure 9. The percentages of documents by subject area on resistant starches published between 2013 and 2023, based on Scopus database. The progress in the work on their production over the last 10 years is summarized in Table 4. In the case of RS, depending on its type, its resistance may be the result of both its natural structure and the effect of heat/cold or chemical treatment. Table 4. Development of new RS preparations over last decade. Starch Source Modification Conditions/Reagent Type of RS Reference Unpeeled raw banana powder, peeled Fruits were sliced, dried, and milled; starch raw banana powder, and banana starch was extracted from peeled raw RS2 from Kluai Namwa Luang banana powder Native starch digested with protease, lipase, Lotus stem α-amylase, and amyloglucosidase and RS2 + modification subjected to ultrasonic treatment Native; acid hydrolysis and Pea starch RS2 and RS3 pullulanase debranching Wrinkled and round pea starches Heat–moisture treatment RS3 Autoclaving, debranching by pullulanase, Sago RS3 autoclaving, and cooling Debranching by pullulanase, autoclaving, Potato peels RS3 and cooling Autoclaving in citrate buffer, protease, and Maize flour amylase (+pullulanase in ) application, RS3 [96,97] second autoclaving, and cooling Acid thinning, debranching, Pea and normal maize starches RS3 and recrystallization Highly branched potato starch, waxy potato starch, amylomaltase-modified Debranching and recrystallization RS3 [99,100] potato starch, and waxy rice starch Cyperus esculentus (tiger nut) starch Debranching and nanoprecipitation RS3 Autoclaving, debranching by pullulanase, Sago starch autoclaving, and cooling (RS) and RS treated RS3 with 0.5 M hydrochloric acid Polymers 2024, 16, 597 16 of 46 Table 4. Cont. Starch Source Modification Conditions/Reagent Type of RS Reference Cowpea starch Autoclaving–cooling cycles (1, 3, and 5) RS3 Gelatinized starches were subjected to temperature cycling between 4 and 30 ◦ C Waxy and normal maize starch RS3 (1 day at each temperature) or isothermal storage (4 ◦ C) for 2 or 8 days Highland barley, oat, and Enzymatic hydrolysis (α-amylase and RS3 buckwheat starches pullulanase), autoclaving, and cooling Gelatinization, debranching by pullulanase, Waxy maize starch RS3 cooling, and self-assembly of nanoparticles Gelatinization, debranching by pullulanase, Potato starch RS3 autoclaving, and cooling Different types of bean starches and Autoclaving–cooling and α-amylase action RS3 maize starch or autoclaving and pullulanase Heating/cooling with or without Sorghum starch and waxy rice starch RS3 debranching gelatinized starch Extrusion cooking with different High-amylose maize starches RS3 moisture content Autoclaving or debranching Culinary banana starch RS3 with pullulanase Ultrasound-assisted annealing treatment of Waxy maize starch RS3 fractionated debranched starch Autoclaving–cooling and α-amylase and Fractionated lotus seed starch RS3 glucoamylase action Cassava starch Debranching by pullulanase and cooling RS3 Maize flour and maize starch Autoclaving–cooling treatments RS3 Amylase and isoamylase hydrolysis and Maize starch RS3 autoclaving–cooling Autoclaving–cooling or microwave Lotus seed starch heated/water bath heated, cooling, and RS3 [117,118] purified by amylase and glucoamylase Oat flour Dual autoclaving–retrogradation treatment RS3 1,4-maltotriohydrolase action, debranching Maize starch RS3 using pullulanase, and autoclaving–cooling Debranching using pullulanase and Faba bean starch RS3 retrogradation treatment Autoclaving in acetate buffer, debranching Sweet potato, cassava, and high-amylose by amylase and pullulanase, autoclaving, RS3 maize starches and cooling Maize and sorghum starches Extrusion and different storage time RS3 Pea starch Ultrasonic treatment and cooling RS3 Green banana flour Autoclaving and debranching by pullulanase RS3 Waxy proso millet grains Debranching and retrogradation RS3 Retrogradation of starch and acetylation by Potato, wheat, corn, and tapioca starch RS3/RS4 [127,128] acetic anhydride Retrograded and acetylated starch produced Potato starch via starch extrusion or starch hydrolysis RS3/RS4 with pullulanase Polymers 2024, 16, 597 17 of 46 Table 4. Cont. Starch Source Modification Conditions/Reagent Type of RS Reference Potato starch Retrograded and crosslinked by adipic acid RS3/RS4 Retrograded, acetylated by acetic acid Potato starch RS3/RS4 [131,132] anhydride, and crosslinked by adipic acid Cassava, potato, sweet potato, lentil, Octenyl succinic anhydride (OSA) RS4 [133,134] and banana Canna Acetic anhydride RS4 Sorghum starch Extrusion of phosphorylated starch RS4 Crosslinking starch with sodium Pea starch trimetaphosphate and RS4 sodium tripolyphosphate Crosslinking starch with sodium Three Korean rice varieties trimetaphosphate and RS4 sodium tripolyphosphate Cassava and sweet potato roots, unripe 20, 40, and 60% of citric acid RS4 banana, potato tubers, and lentil seeds Crosslinking starch with sodium trimetaphosphate and sodium Maize starch tripolyphosphate under sonication and RS4 conventional conditions at various levels of pH Extrusion combined with phosphorylation Potato starch RS4 or succinylation Nanoparticles prepared by acid hydrolysis, crosslinking with sodium trimetaphosphate Waxy rice starch and freeze drying, freeze drying after RS4 sonication, and ethanol dehydration after sonication Acetic anhydride, propionic anhydride, and High-amylose maize starch RS4 [143,144] butyric anhydride Microwave-assisted L-malic Sweet potato starch RS4 acid modification Lactic acid, phosphorylated, and Waxy rice starch RS4 dual-modified starch Maize starch Citric acid RS4 Acetic anhydride used for pulsed electric Wheat flour RS4 fields and conventional esterification Cassava starch Citric acid RS4 Rice starch Citric acid (10, 20, 30, 40%) RS4 Citrate esterification of debranched and Waxy maize starch RS4 non-debranched starch Phosphorylation by using sodium Rice starch trimetaphosphate and sodium RS4 tripolyphosphate Oat starch Acetic acid anhydride RS4 Rice starch Acetic acid anhydride RS4 Phosphorus chloride and sodium Field pea, faba bean, and maize starches trimetaphosphate/sodium tripolyphosphate RS4 in a semidry or aqueous state Maize starch L-malic acid RS4 Polymers 2024, 16, 597 18 of 46 Table 4. Cont. Starch Source Modification Conditions/Reagent Type of RS Reference Rice starch Pullulanase debranching and propionylation RS4 Addition of different lipids/fatty acids (10%, Brown lentil starch RS5 w/w) to both raw and cooked starch samples Rice was cooked with ghee, coconut oil, White, black, and red rice RS5 virgin coconut oil, and rice bran oil Butyric, lauric, stearic, and linoleic acid Brown rice flour complexation of amylose assisted RS5 by ultrasonication Lauric acid, stearic acid, and glycerol Wheat starch RS5 monolaurate; water bath or microwave oven Starch and linoleic acid or stearic acid Arrowhead tubers RS5 ultrasonic treatment Yam starch Palmitic acid RS5 Debranching using pullulanase and High-amylose maize starch RS5 + modification complexation with stearic acid 4.1.2. Pyrodextrins Pyrodextrins, also called resistant dextrins (RDex) or dextrins (Dex), are produced by roasting dry starch granules with or without acid catalysts , whereas resistant mal- todextrins (RMDex) are often produced by combined pyrodextrinization and subsequent treatment with amylolytic enzymes. Starch dextrinization causes a series of chemical reactions, including hydrolysis, transglucosidation, and repolymerization. Before Dex were found to be resistant to digestion with amylolytic enzymes, white dextrins, yellow dextrins, and British gums were used as binders, coatings, adhesives, and encapsulating agents. Currently, many studies have confirmed the branched structure of Dex and the formation of new glycosidic bonds (mainly α-1,6, β-1,6, α-1,2, and β-1,2 linkages), ensuring enzymatic resistance [169,170]. To further increase the digestive resistance, sequential appli- cation of pyroconversion and enzymatic hydrolysis with alpha-amylase is used [166,171]. RDex/RMDex can be obtained from starches of various botanical origins and are typically amorphous, highly soluble in water, and are characterized by low viscosity and cold storage stability [173,174]. In recent years, we have observed a significant increase in the number of publications and patents devoted to resistant dextrins. The percentages of documents by subject area on resistant dextrin published over the last 10 years are presented in Figure 10. The progress in the dextrinization of different types of starch over the last 10 years towards DF (and/or prebiotic preparations) is shown in Table 5. As shown in Table 5, for the purpose of dextrinization, typically acid concentrations of about 0.1% of starch dry basis, heating temperatures ≥ 90 ◦ C, and prolonged heating times ≥ 60 min are applied. The most frequently used catalyst for the dextrinization reaction is hydrochloric acid; however, acids such as acetic, citric, or tartaric acid are also used. Convectional heating is usually used for RDex preparation; however, unconventional methods such as microwave heating can also be successfully used. The latter allows for a reduction in heating time from hours to seconds. As described above, the resistance to enzymatic digestion of starch derivatives can result from carrying out chemical reactions, including dextrinization reactions. Polymers 2024, 16, 597 19 of 46 Figure 10. The percentages of documents by subject area on resistant dextrins published between 2013 and 2023, based on Scopus database. Table 5. Progress in the dextrinization of starch over the last 10 years towards fiber and/or prebiotic preparations. Type of Dextrin/Maltodextrin Heating Conditions Acid Catalyst Ref. Banana maltodextrin 90–110 ◦ C, 1–3 h 2.2 M HCl to 80:1, 120:1, or 160:1 (w/v) starch–acid proportion Banana maltodextrin 90 ◦ C, 1 h 2.2 M HCl to 160:1 (w/v) starch–acid proportion Barley dextrin 90 ◦ C, 1 h 2.2 M HCl 2.2 M HCl or 1.32 M CH3 COOH to 1.82 g of Breadfruit dextrin 140 ◦ C, 3 h acid/kg db starch ratio Cassava dextrin 100–120 ◦ C, 1–3 h 0.04–0.1% HCl Cassava dextrin and 120 ◦ C, 1–3 h 0.04–0.06% HCl cassava maltodextrin Cassava dextrin and Maltodextrin 90–110 ◦ C, 1–3 h 2.2 M HCl to 80:1, 120:1, or 160:1 (w/v) starch–acid proportion Cassava dextrin and Maltodextrin 90 ◦ C, 3 h 2.2 M HCl to 160:1 (w/v) starch–acid proportion Maize dextrin 140–200 ◦ C, 2 h 0.5 M HCl to pH 3.0 Maize dextrin 120–140 ◦C or 140–180 ◦ C, 3h 0.05–0.2% of HCl or 0.5–2.5% of acetic acid Maize dextrin 180 ◦ C, 0.5, 3 or 5 h 0.5 M HCl to pH 3.0 Maize dextrin 180 ◦ C, 1–4 h 0.5 M HCl to pH 3.0 Maize maltodextrin 140–160 ◦ C, 1.5–2 h 1 mL of 0.5% citric acid/20 g starch Normal and waxy tapioca dextrin 130–170 ◦ C, 1–4 h 0.5 M HCl to pH 3.0 [168,185] Potato dextrin 40–120 W, 1 or 10 cycles, 15–90 s 0.1% of HCl + 0.1% of citric acid Potato dextrin 130 ◦ C, 4h 0.1% of HCl + 0.1% of citric acid Potato dextrin 735–1050 W, 2–10 min 0.1% of HCl + 0.1% of citric acid Potato dextrin 105–630W, 2–10 min 0.1% of HCl + 0.1% of citric acid Potato dextrin 150 ◦ C, 3 h or 180 ◦ C, 1h 0.1% of HCl + 0.1% of citric acid Potato dextrin 130 ◦ C, 2 h 0.1% of HCl + 40% of tartaric acid [189,190] Polymers 2024, 16, 597 20 of 46 Table 5. Cont. Type of Dextrin/Maltodextrin Heating Conditions Acid Catalyst Ref. Potato dextrin 130 ◦ C, 3 h or 130 ◦ C, 2 h 0.1% of HCl + 0.1% of citric acid or 0.1% of HCl + 40% of tartaric acid Rice dextrin 170 ◦C for 350 min Without an acidic catalyst Sorghum dextrin 120 ◦ C, 6h 0.182% HCl Waxy maize dextrin 150–170 ◦ C, 1–10 h 0.036–0.144% HCl Waxy maize dextrin 170 ◦ C, 0.5–4 h 0.5 M HCl to pH 3.0 [194–196] Waxy maize dextrin 170 ◦ C, 4 h 0.5 M HCl to pH 3.0 Waxy maize dextrin 150 or 170 ◦ C, 0.5–4 h 0.5 M HCl to pH 3.0 or pH 2.0 Waxy maize dextrin 150 or 170 ◦ C, 4 h 0.5 M HCl to pH 3.0 or pH 2.0 Yam dextrin 140 ◦ C, mostly 1.5–4.5 h Mostly 0.99–2.65 g HCl/g starch db 4.2. Progress in Synthesis of Amphiphilic Derivatives of Maltodextrin Maltodextrins are the products of partial starch hydrolysis. They are composed of an- hydroglucose units, linked together mainly by α-1,4-glycosidic and, less frequently, α-1,6- glycosidic bonds. They are a mixture of molecules with different chain lengths character- ized by a common parameter—glucose equivalent (DE). It is defined as the percentage amount of reducing sugars converted to glucose in the dry weight of the sample. It is in- versely proportional to the molar mass and affects the viscosity, sweetness, solubility, and color of maltodextrin. Maltodextrins with different DE values show different properties, such as viscosity. However, also those whose DEs are identical may exhibit different properties. The reasons for this may be different procedures for the preparation of maltodextrins (a type of hydrolysis) or a botanical source of starch. Due to their properties, non-toxicity and a relatively low price, maltodextrins are often used as thickeners in the food industry and binders in the pharmaceutical industry [206,207]. Despite having many advantages, maltodextrins also possess some properties that are unattrac- tive for essential food applications. Due to their highly hydrophilic properties (absence of lipophilic groups), they do not have surface-active properties in emulsion systems. The stabilization of an emulsion with the addition of maltodextrins may be the result of a change in the viscosity of the system or continuous-phase gelling. It is then necessary to use a large amount of maltodextrin, even in the order of 25–40% by weight [200,205]. Such a high content of maltodextrin in food products could significantly change the properties of the final products, not only affecting their viscosity but also the subsequent sensory experience (deterioration of palatability). Moreover, the increase in water activity caused by the use of maltodextrins affects the microbiological stability. An effective solution to this problem could be the use of amphiphilic compounds as emulsifiers. Amphiphilic polymers have hydrophobic and hydrophilic subregions; therefore, they can act as low-molecular-weight surfactants. They may show good fat emulsifying capacity, possibly due to the steric stabilization associated with their macromolecular structure. Maltodextrins, in order to change their properties into amphiphilic ones, can undergo various types of modifications—chemical, physical, or enzymatic, e.g., esterification or gelation. The -OH groups at the 2, 3, and 5 carbon atoms are particularly susceptible to reactions. Esterification is currently one of the most popular methods of maltodextrin modification. The general scheme of the esterification reaction is shown in Figure 11. As a result of esterification, products can be obtained with properties depending on the type of acid used, the glucose equivalent of maltodextrin, and the degree of substitution of the finished product. Additionally, the use of enzymes as esterification catalysts offers an attractive alternative to the synthesis of oligo- and polysaccharide esters. Such reactions can be carried out under milder conditions (lower temperature and pressure), which prevents the depolymerization of polysaccharides. Enzymatic catalysis reduces the need to use toxic reagents (mainly solvents) and can also be carried out under milder pH conditions. Polymers 2024, 16, 597 21 of 46 These types of reactions are safer for health and may be of interest for biomedical and food applications (emulsifiers, stabilizers, targeted food). Figure 11. Schematic diagram of the process of converting maltodextrin and fatty acid to maltodextrin ester through esterification reaction using lipase enzyme. Maltodextrin fatty acid esters are non-ionic surfactants. Due to their amphiphilic character, they exhibit properties different to those of unmodified maltodextrins. They can be obtained as a result of lipase-catalyzed esterification with fatty acids in non-aqueous solvents in the presence of a small amount of water. The mentioned method is of great interest due to the lower amount of byproducts and the mild reaction conditions. Mal- todextrins esterified with fatty acids using enzymatic methods have potential applications in the food industry as emulsion stabilizing particles. Sun et al. obtained maltodextrin esters in a t-butyl alcohol environment, using immobilized lipase from Candida antarctica as a biocatalyst. In the reaction, they used maltodextrin and stearic acid in a molar ratio from 1:2 to 1:6. They received products with a degree of substitution (DS) ranging from 0.003 to 0.017. The process was carried out at temperatures from 60 to 70 ◦ C for 48–72 h. They considered the conditions as optimal, with the highest DS at a molar ratio of 1:4, a temperature of 60 ◦ C, and a time of 60 h. Udomrati and Gohtani esterified tapioca maltodextrin (DE = 16) with free fatty acids (decanoic, lauric, and palmitic) in the presence of immobilized lipase from Ther- momyces lanuginosus in a DMSO environment and with a molar ratio (D-glucose acid/fatty acid) equal to 1:0.1, 1:0.5, and 1:1. In the reaction, they used temperatures in the range of 50–70 ◦ C and incubation times from 2 to 8 h. The obtained products showed a DS of 0.002–0.084 and a solubility in the range of 84.8–87.2%. The highest DS results were ob- tained for the molar ratio of 1:0.5, at a temperature of 60 ◦ C and after 4 h of the reaction. Studies have also shown that the chain length used in the esterification of the fatty acid affects the degree of substitution obtained during the reaction. This is due to the lim- ited mobility of the longer-chain acids in the reaction system, which in this case leads to compounds with a lower degree of substitution. The obtained esters were used as emulsifying agents for hexadecane oil. Udomrati and Gohtani investigated their emulsification index as a function of the concentration of maltodextrin/esterified maltodextrin versus oil. They showed that as the concentration of esterified maltodextrins increased, the emulsification index increased, reaching the maximum at a concentration of 35%. The emulsifying activity also increased with the increase in the chain length of the fatty acid present in the ester molecule. Esterified maltodextrin showed surface, interfacial, and emulsifying activity. These results showed that esterified maltodextrins can be used as stabilizers for hydrophobic particles in an aqueous environment. Their absorption at the oil–water interface creates a dense layer of hydrophilic loops, ensuring steric repulsion between the surfaces of the particles. Udomrati and Gohtani expanded their research. They prepared maltodextrin esters, not only based on maltodextrin with DE = 16 but also with DE = 9. They used the esterification method described in. Maltodextrin (with DE = 16 or DE = 9) and fatty acid (decanoic, lauric, or palmitic) in a molar ratio of 1:0.5 were dissolved in DMSO. The reaction was catalyzed by lipase from Thermomyces lanuginosus (in a buffer solution). The Polymers 2024, 16, 597 22 of 46 samples were incubated for 4 h at 60 ◦ C. The obtained esters were tested for the ability to stabilize emulsions containing Tween 80. The emulsions were prepared on the basis of soybean oil, 1% aqueous Tween 80 solution, and aqueous solutions of esterified maltodextrins with various concentrations ranging from 0% to 35%. The results indicated that esters of long-chain maltodextrins with long-chain fatty acids had the best emulsion stabilizing properties at high concentrations. Compared to unmodified maltodextrins, maltodextrin esters proved to be more effective stabilizers for oil-in-water (O/W) emulsions containing Tween 80. They can also be expected to be good emulsion stabilizers of other types. The continuation of the research described above led to the recognition of the mechanism of emulsion stabilization. The emulsions were prepared on the basis of soybean oil, 1% aqueous solution of Tween 80, and 10% aqueous solutions of esterified maltodex- trins (maltodextrin palmitate with DE=16 and maltodextrin palmitate with DE = 9). The described emulsion stabilization mechanism may indicate that mainly Tween 80 has been adsorbed to the oil surface, and maltodextrin esters may interact with Tween 80 to form a double stabilizing layer. The esterified maltodextrin formed an outer dense layer providing steric stabilization between the surface molecules. Roczkowska et al. carried out the esterification of medium-saccharified potato maltodextrin with oleic acid in the presence of a lipase from Thermomyces lanuginosus (in a buffer solution) without the use of any organic solvent. Using the optimal reaction conditions, a molar ratio of maltodextrin to acid of 1:2, a reaction time of 1 h, and a temperature of 60 ◦ C, they obtained a product with a DS equal to 0.024 and reduced the solubility in relation to unmodified maltodextrin. In a further stage of research on the esterification of potato maltodextrins with oleic acid, a reaction with low- and high-saccharified maltodextrin was also carried out. Products with a DS of 0.038 for the low-saccharified maltodextrin ester and 0.017 for the high-saccharified maltodextrin ester were obtained. On the basis of the obtained esters, O/W emulsions were prepared with various volume ratios of the oil phase to the water phase and with different emulsifier concentrations (10–35%) in the water phase. The emulsions were visually inspected, and the creaming index (CI) was determined. The best results were obtained for low-saccharified maltodextrin ester, 1:1 and 3:2 volume ratios, and emulsifier concentrations in the range of 15–35%. Potato maltodextrin esters with oleic acid can play an important role in the preparation of stable O/W emulsions without the need for an additional stabilizer. One of the newer methods proposed by Park and Walsh is the synthesis of esteri- fied maltodextrins with fatty acids in food-grade ethanol. This distinguishes this method from the previous ones, where solvents such as DMSO or butanol were used. In addition, during the synthesis, two different fatty acid residues were used, both individually and in the form of a mixture. The acid residue donors were vinyl laurate and vinyl palmi- tate. In the synthesis of esters, corn maltodextrins with two different glucose equivalents, Maltrin 100 (M100) and Maltrin 250 (M250), were used. The reaction was carried out for 8 days in the presence of the immobilized enzyme—lipase from Thermomyces lanuginosus. The obtained products were characterized by determining, inter alia, their DS (ranging from 0.016 to 0.026), and solubility (ranging from 93.1% to 100.9%). The general scheme of the transesterification reaction is shown in Figure 12. It has been shown that the degree of substitution of esterified maltodextrins is closely related to the length of the fatty acid chain used in the reaction. Fatty acids with shorter chains make it possible to obtain derivatives with a higher DS. Esterified maltodextrins formed by a reaction with a fatty acid mixture show an intermediate DS. The solubility of the obtained compounds is not closely related to the DE of maltodextrins but to the type of fatty acid used. Esterified maltodextrins containing shorter-chain acids are more soluble. On the basis of the obtained products, O/W emulsions were prepared. Corn oil was used as the oil phase. It was mixed in a 1:4 weight ratio with an aqueous solution contain- ing esterified maltodextrins. The derivatives were added to the water in three different concentrations (0.125%, 0.25%, or 0.5%). For comparative purposes, emulsions based on Polymers 2024, 16, 597 23 of 46 unmodified maltodextrins (specimens M100 and M250), with the addition of sucrose ester, Tween 20, and a blank were also made. Emulsification was carried out at two different tem- peratures (4 and 22 ◦ C). The emulsions were subjected to stability assessment and droplet size analysis. It was shown that all the modified maltodextrins obtained showed a higher emulsion stabilizing ability than their unmodified counterparts. In particular, emulsions containing derivatives obtained by reacting M100 with vinyl laurate and a mixture of vinyl laurate and palmitate, as well as M250 with vinyl laurate at all tested concentrations and temperatures, showed better results than emulsions prepared on the basis of commercial equivalents. This confirms the validity of the statement that the esterified maltodextrins can be used in the food industry as emulsion stabilizers. The product resulting from the esterification of M100 with 0.5% vinyl laurate at a concentration of 0.5% may prove to be the most effective in this role, especially in the case of food emulsions stored at temperatures from 4 to 22 ◦ C. Figure 12. Schematic diagram of the process of converting maltodextrin and vinyl ester to maltodex- trin ester through transesterification reaction using lipase enzyme. An important aspect in food production is microbiological food safety. Limited knowl- edge of the antimicrobial properties of fatty acid-modified maltodextrins prompted scien- tists to undertake research in this field. Pantoa et al. investigated the surface-active and antimicrobial properties of three maltodextrin esterification products with fatty acids (in the concentration range from 0 to 20% by weight) obtained on the basis of decanoic, lauric, and palmitic acids. The products were obtained according to the procedure pro- posed by Udomrati and Gohtani. All products showed surface-active properties that depended on the length of the fatty acid chain and the concentration used. The analysis of antimicrobial properties was carried out on the basis of the ability to inhibit the growth of Gram-negative (Escherischa coli) and Gram-positive (Staphylococcus aureus) bacteria. The esterified maltodextrins containing the rest of the lauric acid showed the most effective inhibitory effect on the growth of Escherichia coli at a concentration of 20%. Unfortunately, none of the esters showed an inhibitory effect on the growth of Gram-positive bacteria. Subsequent studies on microorganisms by Park and Walsh proved that the es- terified maltodextrins obtained by them also have antimicrobial properties. The study used 11 types of microorganisms most often found in food products: yeasts (Zy- gosaccharomyces rouxii, Zygosaccharomyces bailii), Gram-positive bacteria (Bacillus subtilis, Streptococcus thermophilus, Lactococcus lactis, Lactobacillus plantarum, Geobacillus stearother- mophilus), Gram-negative bacteria (Escherischa coli, Pseudomonas fluorescens), and pathogenic Polymers 2024, 16, 597 24 of 46 Gram-positive bacteria (Bacillus cereus, Listeria monocytogenes). The antimicrobial activity of esterified maltodextrins was assessed based on the determination of the minimum in- hibitory concentration (MIC) and the minimum bactericidal and fungicidal concentration (MBC and MFC). Extracellular protein concentration tests and SEM analysis were also performed. After analyzing the results, it