Anthocyanin-Based pH-Sensitive Smart Packaging Films for Monitoring Food Freshness (Journal Article PDF)

Journal of Agriculture and Food Research 9 (2022) 100340 Contents lists available at ScienceDirect Journal of Agriculture a...

Journal of Agriculture and Food Research 9 (2022) 100340 Contents lists available at ScienceDirect Journal of Agriculture and Food Research journal homepage: www.sciencedirect.com/journal/journal-of-agriculture-and-food-research Anthocyanin-based pH-sensitive smart packaging films for monitoring food freshness Lei Zhao a, *, Yaqi Liu a, Liang Zhao a, Yong Wang b, ** a Beijing Advanced Innovation Center for Food Nutrition and Human Health, Beijing Engineering and Technology Research Center of Food Additives, Beijing Technology and Business University, Beijing, 100048, China b Academy of National Food and Strategic Reserves Administration, Beijing, 100037, China A R T I C L E I N F O A B S T R A C T Keywords: Anthocyanins are water-soluble natural pigments with good antioxidant and antibacterial properties, and their Anthocyanin colors are pH sensitive to the environment. At present, the use of plant anthocyanins to prepare active and smart Smart packing packaging film has attracted increasing attention in the field of food engineering. The use of anthocyanin-based pH sensitive pH-sensitive smart packaging films can not only effectively prolong the shelf life, but also monitor the freshness Freshness indicator of food. This review mainly summarizes the mostly used packaging materials, preparation, structural and physicochemical properties, and the applications of anthocyanin-based films as pH-sensitive smart packaging for monitoring food freshness. 1. Introduction incorporated with anthocyanins are useful for monitoring food fresh­ ness. The common biopolymers for the preparation of smart packaging Packaging plays a crucial role in maintaining food quality and food films are polysaccharides, proteins and lipids. safety in modern food industry. Consumers are very concerned about food freshness, which is the main indicator that guarantees both food 2. Anthocyanins quality and food safety. Nowadays, smart packaging films based on pH-sensitive indicators are able to monitoring food freshness in a timely Anthocyanins are the most remarkable pigments, which are manner that has been widely developed. Anthocyanin has responsible for the red, orange, pink and blue colors, and can be color-changing properties over a broad range of pH values, these natural extracted from natural resources of vegetables (e.g., red cabbage, purple sensors were developed to detect the freshness. Furthermore, an­ carrot, etc.), fruits (e.g., grape, pomegranate seed, etc.), and flower (e.g., thocyanins are safety, abundant availability, and delivering beneficial butterfly pea, red rose, etc.). Chemically, anthocyanins are plant sec­ health effects [4,5]. This review provides insights into the ondary metabolites belonging to a large subgroup of polyphenols, which anthocyanin-based pH-sensitive smart packaging films that are applied are based on a flavylium cation structure. More than 600 different types to monitoring food freshness. of anthocyanins have been identified in nature. The six most com­ Smart packaging, as an emerging technology in food industry, pro­ mon anthocyanidins (aglycone form) are cyanidin, pelargonidin, del­ vide readily visible and overall information relating to the quality and phinidin, petunidin, peonidin and malvidin. Specifically, freshness of the packaged foods to the consumers [6,7]. During micro­ cyanidin-3-glucoside is one of the most common anthocyanins in bial contamination or chemical changes on packaged food, consumers black rice, black bean, and many berries. can realize food freshness status via tracking chromatic change. Anthocyanins can be found as different chemical structures and Recently, food packaging trend has been driven towards more colors depending on the pH of the solution as shown in Fig. 1. In environmental-friendly and biodegradable materials by selecting natu­ general, anthocyanin displays red in acidic conditions, pink in neutral ral substances rather than synthetic ones [2,8]. In particular, biode­ conditions, and blue in basic conditions. This particular property of gradable polymer-based color indicator smart packaging films anthocyanins has been the one most used in the development of smart * Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (L. Zhao), [email protected] (Y. Wang). https://doi.org/10.1016/j.jafr.2022.100340 Received 11 June 2022; Received in revised form 7 July 2022; Accepted 7 July 2022 Available online 11 July 2022 2666-1543/© 2022 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by- nc-nd/4.0/). L. Zhao et al. Journal of Agriculture and Food Research 9 (2022) 100340 packaging films for monitoring food freshness based on pH indicators. Additionally, pH sensitive PVA-starch films fabricated with zinc-oxide Anthocyanins also have a variety of beneficial health effects, such as nanoparticle, nutmeg oil and Jamun extract were reported to exhibit antioxidant activity, anti-inflammatory activity, retinoprotective ef­ enhanced mechanical strength, water barrier, UV barrier and antimi­ fects, antimicrobial activity, anti-obesity and anti-diabetic effects crobial properties. [13–16]. Recent epidemiological studies suggest that consumption of anthocyanins reduces the risk of cardiovascular disease, diabetes, and 3.3. Starch cancer. Starch is considered as an ideal food packaging material due to its 3. Biodegradable packaging materials advantages of plentiful supply, low cost, good biodegradable, biocom­ patible and film-forming properties. However, the starch films have 3.1. Chitosan shortcomings of hydrophilicity, easy aging and poor mechanical prop­ erties, which can be improved by adding plasticizer or blending mate­ Chitosan (CS), a natural cationic polysaccharide with high molecular rials with complementary properties. CS and PVA are film-forming weight, is the product derived from deacetylation of chitin. It is materials with good biocompatibility and are often used to prepare biodegradable, biocompatible, non-toxic, and has good antimicrobial composite films with starch. Researchers found that CS was and film-forming property , and is widely used for food packaging. conducive to improve the extensibility of the CS/starch composite films Several additives such as essential oils and natural extracts have been. The additions of 10–20 wt% PVA to the maize starch/CS (70/30) incorporated into CS packaging to improve film properties such as matrix is essential to ensure the formation of the films with advanced antimicrobial ability against foodborne microorganisms. However, mechanical and functional properties. Starch has attracted exten­ the application of CS in food packaging is limited due to its brittle sive attention as a film-forming material for active and intelligent texture and poor mechanical property. Therefore, CS can be mixed with colorimetric packaging with the addition of anthocyanins. other polymers to broaden its application. A previous study observed that cellulose nanocrystal/CS composite films possessed enhanced ten­ 3.4. Alginate sile strength and water and UV barrier properties. In more recent studies, pH responsive smart films based on CS/methylcellulose and Alginate is a natural polyanionic polysaccharide extracted from CS/chitin nanocrystals integrated with anthocyanin extract exhibited various brown algae. It is composed of β-D-mannuronic acid and enhanced mechanical properties, and could be applied in food pack­ α-L-guluronic acids joined by 1,4-glycosidic bonds. Alginate has good aging as quality sensors [21,22]. colloidal, gel-forming and film-forming properties, and is often used as thickener, emulsifier and stabilizer of food. Alginate film has 3.2. Polyvinyl alcohol gas-selective permeability, which is beneficial to form an environment with low oxygen and high carbon dioxide, thus avoid unnecessary food Polyvinyl alcohol (PVA) is a water-soluble and biodegradable poly­ oxidation and extend food storage period. Alginate films incorpo­ mer joined by only carbon-carbon linkages and has high density of hy­ rated with tea polyphenol were reported to have enhanced tensile droxyl groups located on its side chains. It can be decomposed into CO2 strength and strong antioxidant and anti-inflammatory properties [36, and water by natural microorganisms thus possesses good biocompati­ 37]. However, alginate film is sensitive to water vapor, and this draw­ bility. Additionally, PVA has good gas barrier, film-forming, printability, back can be overcome by incorporating with other polymers to improve transparency and mechanical properties and is widely used as packaging its hydrophilicity. materials. In order to expand its application, polymer materials with different properties, such as starch, CS, tannin and cellulose were 3.5. Others used to mix with PVA to enhance the elasticity, mechanical strength and water resistance of PVA films [24,25]. An intelligent starch/PVA film Some other biodegradable polymers like gellan gum, pullulan and was prepared with anthocyanins and limonene as simultaneous colori­ gelatin with good film-forming and mechanical properties and oxygen- metric indicators. The film exhibited good antimicrobial activity on barrier characteristic were also applied in the preparation of edible, pasteurized milk and can be used to detect the freshness of milk. active and intelligent films for food packaging applications. They are Fig. 1. Chemical structures of anthocyanin at different pH values.Source:. 2 L. Zhao et al. Journal of Agriculture and Food Research 9 (2022) 100340 often combined with several other materials to prepare composite films properties of active and intelligent food packaging films. to enhance their mechanical properties for various applications. For In view of the poor thermal stability of anthocyanins, anthocyanin- example, a pullulan-based packaging film incorporated with nisin, lauric based films are usually prepared by solution casting technique, in alginate, thymol and polyethylene showed good antimicrobial activity which the anthocyanin extract is fully mixed with polysaccharide or against foodborne pathogens in meat and poultry products. In a protein polymers using a common solvent (Fig. 2). After degassing, the recent study, Ye et al. developed a semi-refined blueberry pectin resulting film-forming solution is poured onto a flat surface and allowed (SBP)/gelatin composite film and the incorporation of SBP enhanced the to air dry into a thin film at 20–60 ◦ C. Plasticizers such as glycerol tensile strength and thermal stability of the film. The composite film , sorbitol and polyethylene glycol are usually added to the could restrict the entry of air and moisture from outside and retard the film-forming solution to improve the water resistance and mechanical oxidation and photodegradation of food. properties of the film. Additionally, the anthocyanin-based film is usu­ ally prepared in a dark environment of 50–75% relative humidity at 4. Anthocyanin-based films 4–30 ◦ C in order to avoid anthocyanin degradation. 4.1. Preparation of anthocyanin-based films 4.2. Structural characteristics At present, anthocyanins have been used to prepare active intelligent food packaging films and were extracted from different plant sources The mechanical and barrier properties of anthocyanin-based films through various methods such as solvent extraction, soxhlet extraction, are closely related to intermolecular interactions between film compo­ supercritical fluid extraction, pressurized fluid supercritical fluid nents. Most researchers use instrumental analysis to study the structural extraction, pressurized fluid extraction, ultrasound and microwave characteristics of the films. Scanning electron microscopy (SEM) can be assisted extraction. used to analyze the morphology of film surface and cross section, which Various polysaccharides (e.g., starch, cellulose, CS, pectin and algi­ is helpful to understand the arrangement and interaction between nate) and proteins (e.g., gelatin, zein and soy protein isolate) were used different film components. Fourier transform infrared spectroscopy in the preparation of anthocyanin-based films [41,42]. Of which, starch (FTIR) can provide information about the interactions between different is the most widely used material, followed by CS. However, the me­ film components. X-ray diffraction (XRD) is often used to observe the chanical properties of starch films still need to be improved. crystallization characteristics of films, which can help us to better un­ Therefore, composite films were prepared by blending starch with other derstand the compatibility between different film components. The polymers (e.g., PVA, gelatin, agar and CS) to improve the mechanical SEM, FTIR and XRD results of anthocyanin-based films can be affected by the source and amount of anthocyanins. Generally, the addition of Fig. 2. Preparation process of anthocyanin-based pH-sensitive smart packaging films and the detection of color change of films at different pH conditions using colorimetric sensor labels or a smartphone camera. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.) 3 L. Zhao et al. Journal of Agriculture and Food Research 9 (2022) 100340 anthocyanins led to a smoother cross-sectional surface of the films [47, mechanical properties. Most importantly, the major disadvantage is that 48]. However, it has been reported that the excessive addition of Lycium the degradation of anthocyanins during time makes the films lost their ruthenicum Murr. extract destroyed the compact structure of ability to monitor food freshness. Therefore, more future studies should pH-sensitive κ-carrageenan film. FTIR spectra analysis showed that be carried out to overcome these drawbacks. some characteristic bands of anthocyanin-based films became broader and more intensive with the increase of anthocyanins. The change 5. Applications of anthocyanin-based films in FTIR spectra was attributed to molecular interactions between an­ thocyanins and film polymers including hydrogen bonds and electro­ Oxidation and microbial contamination are the main causes of food static interactions. Moreover, XRD results showed that deterioration. Anthocyanin extracts with excellent antioxidant and anthocyanin-rich extracts could affect the diffraction peak intensities antibacterial activities can be added to the films to develop active food of the films, which was probably attributed to the newly formed inter­ packaging. The antioxidant and antimicrobial activities of molecular hydrogen bonds between film polymers and anthocyanins anthocyanin-based films are closely related to the source and amount of [48,50,51]. anthocyanins, as well as the interactions between anthocyanins and film matrix [8,56–58]. Anthocyanin-based films have been reported to show 4.3. Physicochemical properties antimicrobial activity against several microorganisms, especially against Gram-positive bacteria. Therefore, anthocyanin-based films The physicochemical properties of anthocyanin-based films mainly can be used as active packaging for foods to prolong their shelf life. include optical characteristics, water vapor and gas barrier abilities, Generally, the pH value of meat gradually increased with the extension mechanical properties, thermal stability and pH sensitivity. Among of storage time. As shown in Fig. 3, anthocyanin-based films are them, the optical characteristics of the films directly affect consumers’ pH-sensitive and can realize real-time monitoring of food freshness, such acceptance of packaged food and the protection of light-sensitive food. as fish, pork, shrimp and cheese [3,7,22,33,46,60]. The The moisture and gas barrier performance of the film reflect its ability to anthocyanin-based pH-sensitive films have the potential to be used as prevent the transfer of water vapor, oxygen or carbon dioxide from the colorimetric sensor labels. However, no natural pigments have been surrounding environment to packaged food. The mechanical properties reported to be used as manufacture intelligent colorimetric pH-sensitive of the film including tensile strength, elongation and elastic modulus can products at present. Moreover, the RGB values of the films can be con­ reflect its ability to provide the effective protection for the packaged verted to total volatile base nitrogen (TVB-N) values and automatically food in food supply chain. Researches showed that the addition of an­ analyzed by a smartphone application to determine meat freshness thocyanins significantly improved the barrier and mechanical behavior (Fig. 2). The combined utilization of anthocyanin-based pH-sensitive of the films against UV/visible light, water vapor and oxygen, which films and smartphone will be an accurate and simple way to help con­ could be due to the adhesion of anthocyanins to the film matrix through sumers judge food quality easily and reliably [61,62]. the interface and the subsequent formation of a stable and dense membrane network structure. It was supposed that the presence of 6. Conclusions and future perspectives double bonds in the aromatic ring of anthocyanins could absorb UV/visible radiation [45,52]. The barrier ability of anthocyanin-based Intelligent packaging is an important innovation in the field of food films was attributed to the formation of compact inner microstructure packaging. In addition to the function of conventional packaging, it can and the reduction in the exposure of hydrophilic groups of the films also monitor food quality and safety and inform the product status to through strong intermolecular interactions especially hydrogen bonds consumers. The pH-responsive intelligent packaging provides a new between polymers and anthocyanins [42,52]. In addition, the thermal strategy for monitoring food freshness due to its advantages of stability of the films can be analyzed by differential scanning calorim­ simplicity, rapidity and non-destructive food. However, there are still etry (DSC) and thermogravimetric analysis (TGA) methods. The many limitations in the promotion and application of anthocyanin- compact structure of anthocyanin-based films formed by the intermo­ based pH-sensitive smart packaging: (1) The stability of anthocyanins lecular interactions between anthocyanins and polymers was crucial for is poor and the film preparation technology is underdeveloped, which the elevated thermal stability of the films. Notably, the pH sensitivity limit the potential of using intelligent packaging in the market; (2) The is crucial to evaluate the potential of the films for food freshness real food composition is complex, and the good monitoring results ob­ monitoring. The colors of anthocyanin solutions are related to the tained in the laboratory are not in good agreement with those from structures of anthocyanins and can change from red to pink, purple, practical applications; (3) The differences in anthocyanin sources and blue, green and yellow with increased pH values. However, the film matrix lead to great differences in the pH-indicative and physico­ color change of anthocyanin-based films was not always consistent with chemical properties of packaging films; (4) The increased cost of intel­ that of corresponding anthocyanin solutions, which was due to the ligent packaging in the food industry limits its wide application. formation of intermolecular hydrogen bonds between anthocyanins and In view of the above problems, the researches on anthocyanin-based polymers. Moreover, some researchers have observed opposite ef­ pH-sensitive smart packaging in the future can focus on the following fects of anthocyanins on the physicochemical properties of the films, aspects: (1) Improving the detection accuracy and sensitivity of which could be related to the addition content and source of anthocy­ anthocyanin-based pH-sensitive smart packaging, and reduce the anins. Generally, excessive addition of anthocyanins could reduce detection rate of false positive or false negative results; (2) Improving the performance of the films. the stability of anthocyanins and film-forming matrix, as well as the barrier and mechanical properties of the film; (3) Development of 4.4. Advantages and disadvantages inexpensive and promising renewable film-forming materials for intel­ ligent packaging; (4) Establishing the correlation between the color Anthocyanin-based films are highly pH-sensitive and could act as a change of packaging and the freshness of different food, and detecting real-time indicator of food spoilage/freshness. These films are safe, non- food freshness using mobile optical and electronic equipment. toxic and biodegradable, and usually possess excellent antioxidant and Therefore, with the deepening of scientific research and the antimicrobial properties, thus can prevent food deterioration against improvement of relevant technologies, anthocyanin-based food intelli­ oxidation reactions and food-borne microorganisms. However, the gent packaging which helps to monitor food quality and safety will have anthocyanin-based films are prone to light and thermal degradation and a broader market and development prospect. water vapor and oxygen permeation which may lead to food deterio­ ration. Moreover, many composite films often exhibit dissatisfactory 4 L. Zhao et al. Journal of Agriculture and Food Research 9 (2022) 100340 Fig. 3. 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