Food Preservatives Lecture Notes PDF

Acids Anticaking agents Bases Gases Additives: Buffers systems and Salts Firming Texturizers Chelating Agents...

Acids Anticaking agents Bases Gases Additives: Buffers systems and Salts Firming Texturizers Chelating Agents Clarifying Agents Antioxidants Flour Bleaching Agents Emulsifiers Colorants Gums Fat replacers Flavor Substances Antimicrobial agents Flavor enhancers Sweeteners Stabilizers & Thickeners Redox reactions in Food Redox reactions in Food Hydroxylation and oxidation reactions catalysed by polyphenol oxidase.  Prooxidants 1. Prooxidants that promote formation of lipid hydroperoxides Singlet oxygen 2. Prooxidants that promote formation of free radicals Ionizing radiation Lipoxygenase 3. Prooxidants that promote decomposition of hydroperoxides Transition metals Light and elevated temperatures  CHELATING AGENTS (SEQUESTRANTS)  Chelating Agents Free metal ions in food systems may form insoluble or colored compounds or catalyze the degradation of food components, resulting in precipitation, discoloration, rancidity or loss of nutritional quality. Chelation is the reaction between a metal ion and a complexing agent that produce a stable, nonionized, non toxic complexes which can be eliminated easily Chelating agent is a molecule that can form complexes with a single metal ion Their ability to bind metal ions has contributed significantly to the stabilization of food color, aroma, and texture. The term ‘chelate’ Chelating agents are not antioxidants originates from Greek They arrest oxidation by chain termination or serve as oxygen scavengers word chele (crab claw) Antioxidants synergists since they remove metal ions that catalyze oxidation Chelating Agents Solubility of chelating agents should be considered Citric acid and citrate esters are solubilized by Citric acid and its derivatives , various fats and oils phosphates and salts of EDTA are popular EDTA salts are very effective in emulsion chelating agents systems : salad dressings , mayonnaise , margarine since they can function in the aqueous phase especially at the interface EDTA also show antimicrobial activity pH also affects the formation of strong metal chelates. The non ionized carboxylic acid group is not an efficient donor group but the carboxylate ion Ethylenediaminetetraacetic acid (EDTA) functions effectively Raising the pH enhances chelating efficiency Chelating Agents Trace elements such as iron, cobalt, and copper can act as catalysts for fat or oil oxidation OR, ascorbic acid, vitamin E, thiamine and folic acid are affected by copper and both copper and iron led to the destruction of natural and added vitamin A. Pink discoloration in canned pears, blue-green in shellfish and arthropods, clouding of soft drinks, and chill haze in beer is caused by trace minerals. EDTA usage : Speculation that excessive usage or occurrence in foods could lead to depletion of calcium and other cationic minerals in the body Little dietary concern about these chelator in the amounts permitted or encountered considering the natural concentrations of calcium or other divalent ions Chelating Agents Pink discoloration in canned pears Reddish pigments also form in canned apples and gooseberries Chemical depolymerization of procyanindins (Condensed tannins) into anthocyanins under hot acidic conditions The major pigment in discoloured canned pears is identified as a purple-pink insoluble tin-anthocyanin complex from the effect of reagents for anthocyanins on the spectra of solid and syrup fractions of the product. Blue-green in crab meat Blue discoloration in crabmeat is caused by the reaction of biuret and copper, both found in crab blood, in the presence of ammonia. Chelating Agents Chill Haze occurs when a beer is chilled below approximately 1.6°C (about 35°F) and constituents can aggregate to form relatively large colloidal (gel-like) particles. Free copper catalyzes oxidation of polyphenolic compounds that subsequently interact with proteins to form permanent hazes or turbidity Chelating agents stabilize fermented malt beverages by complexing copper Chelating Agents Polyphosphates and EDTA are used in canned seafood to prevent formation of glassy crystals Seafood contain substantial amount of magnesium that sometimes react with ammonium phosphate during storage of canned seafood to give crystals that may be mistaken as glass contamination Chelating agents could also be used to complex iron, copper and zinc in seafood's to prevent reactions that lead to product discoloration. Tartaric acid and its salts together with antioxidant (for synergistic effect) are added to cheese to prevent color loss and rancidity. Although citric and phosphoric acids act as acidulant in soft drink beverages, they also chelate metals that otherwise could promote oxidation such as terpenes and catalyze discoloration reactions Stabilize fermented malt beverages by complexing copper Free copper catalyzes oxidation of polyphenolic compounds that subsequently interact with proteins to form permanent hazes or turbidity Chelating Agents: Phytic acid Phytic acid (known as inositol hexakisphosphate (IP6), inositol polyphosphate, or phytate when in salt form), a saturated cyclic acid, is the principal storage form of phosphorus in many plant tissues, especially bran and seeds. It can be found in cereals and grains. Phytic acid has a strong binding affinity to important minerals, such as calcium, iron, and zinc, although the binding of calcium with phytic acid is pH-dependent Addition of phytic acid to vegetables prior to blanching can inhibit metal induced discolorations and can remove calcium from pectic substances in cell walls and thereby promote tenderness. Phytic acid inhibits autoxidation and hydrolysis of soybean oil and protects other lipid-containing foods from rancidity. Phytic acid added to foods protects meat, bread, salad and fish and stabilizes natural and artificial colorants. This substance is used to prevent discoloration of riboflavin solutions and fresh vegetables, to increase their nutritional quality and to extend their shelf life. ANTIOXIDANTS  Antioxidants Antioxidants are defined as the compounds that prevent or delay oxidative deterioration in foods. These compounds can prevent undesirable changes in food products such as bad odor, loss of taste and rancidity. *Free radicals are molecules with odd unpaired electrons making them unstable and highly reactive. They are formed as a result of air pollution, radiation, cigarette smoke, sunlight, environmental chemicals, exposure of metals, biological materials (including food), and chemical reactions that take place in our body. Antioxidants An antioxidant agent should: not have toxic effects at the doses used in foods be effective at low concentrations be readily available not lose its effect in heat treatments such as frying. not cause undesirable color or flavor changes in food. have low cost Most commonly used plant extracts are polyphenols and particularly flavonoids presence of carbonyl group at C-4 and a double bond between C-2 and C-3 are important features for high antioxidant activity in flavonoids Classification of Antioxidants Based on mechanisms of action: Primary (Chain – Breakers) This type of antioxidants directly react with free radicals, producing significantly less reactive species or turning off the radical chain reaction. Secondary (Preventive) This type of antioxidants retard the oxidation process by indirect pathways, including metal chelation, decomposition of hydroperoxides to nonradical species, repairing (regenerating) of primary antioxidants by hydrogen or electron donation, deactivation of singlet oxygen or sequestration of triplet oxygen, and absorption of UV radiation. Based on source: Synthetic Natural ACTION MECHANISMS OF ANTIOXIDANTS (1) Quenching known as singlet oxygen scavenging antioxidants reacts with singlet oxygen (1O2) to form intermediate compounds such as endoperoxides and final products which are mainly hydroperoxydienones. The final products are responsible for quenching, in other words, termination of the propagation process that generates free radicals. Examples of antioxidants which exhibit this phenomenon include vitamin E and carotene. Structures of primary oxidation n products of β carotene with reactive oxygen species  ACTION MECHANISMS OF ANTIOXIDANTS (2) Charge transfer There are two ways in which the charge transfer Possible mechanism of butylated hydroxyanisole antioxidants antioxidation mechanism takes place. Firstly, the antioxidation mechanism may occur through hydrogen transfer processes in which the reactive species themselves abstract a proton from the antioxidant, such that the antioxidant will become a highly stable radical which cannot react with any substrate. The second mechanism is by a one electron transfer process where the antioxidant can donate an electron to the reactive species, making itself a highly stable positively charged radical which cannot undergo any reaction with substrates. Examples of antioxidants which undergo charge transfer mechanisms include flavonoids and other phenolic antioxidants.  ACTION MECHANISMS OF ANTIOXIDANTS (3) Bond breaking The alpha-tocopherol is a hydrophobic antioxidant which plays an important role in protecting the cytoplasmic membranes against oxidation reactions caused by lipid radicals. It protects cell membranes by reacting with the lipid radicals, thus terminating the chain propagation reactions due to the reactive species that would otherwise have continued oxidation reactions with the cell membrane Possible mechanistic reaction of -tocopherol antioxidant  Natural Antioxidants: Tocopherol (Vitamin E) Vitamin E is the collective name for a set of eight related tocopherols and Animal fats contain much less vitamin E tocotrienols, which are fat-soluble vitamins with antioxidant properties. than vegetable oils The main component (more than 90% of vitamin E) is always α-tocopherol. Natural Antioxidants: Tocopherol Frequently found in plants but very few in animal tissues Tocopherols are found in vegetable oils Vitamin E supplementation of beef cattle diets is an effective procedure for enhancing the lipid and color stability of meat products α-tocopherol has the highest bioavailability, with the body preferentially absorbing and metabolizing this form Interrupt lipid autoxidation by interfering with either the chain propagation or the initiation processes. By reacting with lipid peroxy radicals, these antioxidants compete with the lipid substrate for the chain-carrying peroxyl radicals to form nonradical products, whereby the antioxidant can be regenerated Natural Antioxidants: Ascorbic Acid (Vitamin C) Ascorbic acid or “vitamin C” is a monosaccharide antioxidant found in both animals and plants. It cannot be synthesized in humans, must be obtained from the diet. Ascorbic acid is used as an oxygen scavenger, especially in foods with headspace, such as canned or bottled products. Approximately 3.5 mg of ascorbic acid should be used in order to retain the oxygen in the 1 cm3 headspace. As ascorbic acid scavenge oxygen from the air or food, it turns into dehydroascorbic acid form. Ascorbic acid is a reducing agent and can reduce and thereby neutralize ROS such as hydrogen peroxide.  Natural Antioxidants: Sulfites and Sulfur Dioxide SO2, Na2SO3 , NaHSO3, KHSO3 Widely used in the fruit and vegetable preservation industry, as an inhibitor of microbial growth and enzymatic and non-enzymatic browning Act as an antioxidant and a reducing agent SO2 can act as an antioxidant by reacting with hydrogen peroxide and by reducing quinones to their phenol form and/or by preventing quinone formation as a result of inhibition of polyphenol oxidase enzymes. Bisulfite forms show antimicrobial properties High pH → active against bacteria but not yeast More effective against Gram negative than Gram positive Not preferred in thiamine (Vit B1 ) containing foods When added to wheat flour dough affects a reversible cleavage of protein disulfide bonds Most effective in acid media and this effect may result from conditions that permit undissociated compounds to penetrate cell wall Sulfurous acid is the most effective form  Natural Antioxidants: Sulfites and Sulfur Dioxide SO2 acts as a solvent during winemaking, allowing grape solid components such as stems, seeds and skins, to be extracted utilized in another three stages of wine making (1) used as an antioxidant during the prefermentation process, in the grapes or must, with the primary goal of avoiding oxidation. However, this phenomenon does not occur by direct elimination of oxygen from edibles, but by binding to the precursors involved in oxidative reactions and compounds resulting from oxidation (2) Used as an antimicrobial agent ; after the fermentation procedures are ended and before the aging or storage phases, it is used to limit microbial development that might affect the wines, (3) shortly before bottling, the wines are stabilized with SO2 to avoid any changes or accidents in the bottles  Sulfite Filters are very popular! High doses of SO2can cause organoleptic changes of the final product and some allergies  Synthetic Antioxidants: Gallates Propyl gallate (PG) is a synthetic derivative of the naturally occurring antioxidant gallic acid The antioxidant activity of gallates, which are more polar compounds than BHA, BHT and TBHQ, is higher in fats with minimum moisture, which is related to the solubility of gallates in two phases PG is suitable for the stabilization of animal fats (e.g. lard and tallow) Gallates are more soluble in emulsions but are less active than BHA and BHT. PG is unstable compound, therefore not suitable for fats used for frying Antioxidant mechanism antioxidant involves its hydrogen- donating ability to neutralize free radicals and its capacity to chelate metal ions. A propyl gallate molecule acts as a very efficient peroxyl radical scavenger, both in aqueous and lipid media. PG causes blue-black complexes with iron and copper residues, therefore it should be used in combination with chelating agents.  Synthetic Antioxidants: BHA Butylated hydroxyanisole C11H16O2 BHA and BHT are hindered phenols in which the phenolic ring contains di-tert-butyl groups, which are extremely effective as primary antioxidants The aromatic ring found in BHA, BHT, and TBHQ is able to stabilize free-radical reactive oxygen species (ROS) by hydrogen donation process and thereby, sequester ROS. BHA is a highly fat-soluble antioxidant that is used extensively in bulk oils as well as oil-in-water emulsions Effective for the protection of lipids containing fatty acids with shorter chains (coconut or palm kernel oils) and in the aroma and color of essential oils Often used in packaging materials where it can migrate into the food Exhibit synergism with BHT and gallates usually blended with other synthetic antioxidants to improve the antioxidative property due to synergistic antioxidation. Known for its ‘carry-through’ property which means that it is also effective as antioxidant in the final heat treated product.  Synthetic Antioxidants: BHT Butylated hydroxytoluene Chemical formula: C15H24O BHA and BHT are hindered phenols in which the phenolic ring contains di-tert-butyl groups, which are extremely effective as primary antioxidants Formerly known as lonol BHT stops this autooxidation reaction by converting peroxy radicals to hydroperoxides. White crystalline solid with properties similar to BHA Appropriate for thermal treatment but is not as stable as BHA Large doses of BHT produce centrilobular necrosis, increased serum transaminase activities, and hemorrhage in the liver. BHT has also been found to increase the mitotic activity of hepatocytes in rats and cats as a promoter for hepatocarcinogenesis  Regulations on BHA-BHT In Europe, the use of BHA is permitted in several foods like bouillons, gravies, dehydrated soups and dehydrated meat, individually or in combination with other antioxidants. The maximum limit is set to 200 mg/kg expressed on the fat content of the product. According to the European Parliament and of the European Council, when combination of gallates, BHA and BHT are used, the individual levels must be reduced proportionally. The FDA limitations for BHA when used alone or in combination with other antioxidants varies as follows: between 2 ppm (in beverages and desserts prepared from dry mixtures) and 1000 ppm (in active dry yeast) for BHA only between 10 ppm (in potato granules) and 200 ppm (in emulsion stabilizers for shortenings) for BHA and BHT in combination Different antioxidants (e.g. BHA and BHT) are present in cosmetic products also. Recent estimates of BHA and BHT daily intakes showed that ingestion of these compounds through an average diet can get close to their acceptable daily intake (ADI). An important aspect is that the additional intake of BHA or BHT through pharmaceuticals could result in exceeding the ADI. Synthetic Antioxidants: Sodium erythorbate ▪ Sodium erythorbate (C6H7NaO6) is a food additive used predominantly in meats, poultry, and soft drinks. ▪ Chemically, it is the sodium salt of erythorbic acid. ▪ When used in processed meat such as hot dogs and beef sticks, it increases the rate at which nitrite reduces to nitric oxide, thus facilitating a faster cure and retaining the pink coloring. ▪ As an antioxidant structurally related to vitamin C, it helps improve flavor stability and prevents the formation of carcinogenic nitrosamines. ▪ The use of erythorbic acid and sodium erythorbate as a food preservative has increased greatly since the FDA banned the use of sulfites as preservatives in foods intended to be eaten fresh (such as ingredients for fresh salads) and as food processors have responded to the fact that some people are allergic to sulfites. ▪ Sodium erythorbate is produced from sugars derived from different sources, such as beets, sugar cane, and corn ANTIMICROBIALS Antimicrobials: Mechanism of Action Effecting genetic system Inhibition of replication and transcription Stopping DNA functions DNA or RNA polymerase is inhibited Inhibition of protein synthesis Attaching to the ribosomes Effect on cell wall/membrane The cell wall in bacteria protects bacteria Mucopeptides, lipopolysaccharides, lipoproteins Antimicrobials could affect the synthesis of one of these constituents Permeability effected Permeability of cell membrane could also be affected by additives Enzyme inhibition Binding to the essential nutrients Antimicrobials: Spices and herbs Essential oils derived from plants (e.g., basil, thyme, oregano, cinnamon, clove, and rosemary) The use of spices and herbs or their extracts is often less effective than the use of their active ingredients Enzymes obtained from animal sources: e.g., lysozyme, lactoferrin Organic acids: e.g., sorbic, propionic, citric acid Already discussed! Naturally occurring polymers: chitosan Biopreservatives: Bacteriocins from microbial sources: nisin, natamycin The use of antibiotics in food is problematic, because the use of the same substances in human and veterinary medicine are not allowed. Only polypeptide antibiotics produced by lactic acid bacteria (LAB) are approved in the EU and other countries (including certain strains of the genera Lactococcus, Lactobacillus), known under the general name bacteriocins. These LAB bacteria have a long and safe tradition in food fermentation, and many potent applications as food preservatives have been established. Bacteriocins are small bacterial peptides that show strong antimicrobial activity against closely related bacteria  Antimicrobials: Bacteriocins Bacteriocins can be used in different ways in foods 1. They can be directly added to foods, inhibiting the growth of both pathogenic and spoilage bacteria; Nisin is the only bacteriocin commercially available. Can be naturally found in certain cheeses as a result of the fermentation process Nisin is a polycyclic antibacterial peptide produced by the bacterium Lactococcus lactis Considered as a Generally Recognized as Safe (GRAS) Nisin is added to milk, cheese, canned foods, mayonnaise, and other foods. Effective against Gram + bacteria. Gram – bacteria are more resistant to nisin because their cell wall is less permeable than gram + 2. To add bacteriocin-producing bacteria to non-fermented foods or use them as starter cultures for the improvement of food safety. Natamycin is produced by fermentation using Streptomyces spp. acting against foodborne molds and yeasts; however, it is inactive against bacteria and viruses 3. To use bacteriocin-producing bacteria as starter cultures to direct the fermentation An increasing problem is resistance to bacteriocins. The emergence of pathogens resistant to bacteriocins can undermine their use as antimicrobial agents. For example, nisin-resistant isolates have been generated from C. botulinum, L. monocytogenes, S. aureus, and Bacillus licheniformis, B. subtilis, and B. cereus.  Antimicrobials: Chitosan Lysozyme Produced commercially from chitin, a by-product A lytic enzyme found in egg obtained from exoskeletons white and milk, and even in of crustaceans and blood arthropods Enzymatic activity: lysozyme Chitosan’s films with acts through peptidoglycan other antimicrobials attached (garlic oil, sorbic acid, and hydrolysis and cell lysis nisin) were used for packaging applications Gram-negative bacteria are a broad antimicrobial spectrum including gram-negative, resistant to lysozyme gram-positive bacteria and fungi. Used in the treatment of some Chitosan interacts with the cytoplasmic membrane’s dairy products and wine anionic polysaccharides and/or interfere the cell protein synthesis, both resulting in cell inhibition by altered permeability and/or compromised protein transport Antimicrobials: Phytoalexins Derived from Greek word, Phyto- ‘plants’; Alexin- ‘to ward off’ Phytoalexins are defined as host-synthesized, low-molecular-weight, broad- spectrum phenolic and antimicrobial compounds whose synthesis from distant precursors is induced in plants in response to microbial infection Phytoalexins are produced by healthy cells adjacent to localized damaged and necrotic cells in response to materials diffusing from the damaged cells. Absent in healthy plants The antimicrobial activity of phytoalexins is often directed against fungi although activity has also been reported toward bacteria Gram-positive bacteria have been found to be more sensitive than Gram- negative bacteria. The chemical structures of phytoalexins produced by plants of a family are usually quite similar; e.g., in most legumes, phytoalexins are isoflavonoids, and in the Solanaceae they are terpenoids Isoflavonoids, characterized by a C6-C3-C6 basic skeleton structure, are among the most important chemical classes of phytoalexins Antimicrobials: Phytoalexins Capsidiol in pepper Allixin in garlic Rishitin in potato Gossypol in cotton Danielone in papaya fruit This compound showed high antifungal activity against Colletotrichum gloesporioides, a pathogenic fungus of papaya Stilbenes are produced in Eucalyptus sideroxylon in case of pathogens attacks. Such compounds can be implied in the hypersensitive response of plants. High levels of polyphenols in some woods can explain their natural preservation against rot Antimicrobials: Essential oils Have antimicrobial, antioxidant, and anti-inflammatory, wound-healing properties Classified as “Generally Recognized as Safe” (GRAS) The antimicrobial or antifungal activity of essential oil might be caused by the properties of terpenes/terpenoids, that—due to their highly lipophilic nature and low molecular weight—are capable of disrupting the cell membrane, causing cell death or inhibiting the sporulation and germination. Gram-negative bacteria are more resistant to EOs than Gram-positive bacteria. Because Gram-negative bacteria possess an outer membrane with the presence of lipopolysaccharide molecules, which provide a hydrophilic surface. The surface acts as a penetration barrier that blocks macromolecules and hydrophobic compounds penetrate into the target cell membrane Antimicrobials: Nitrate and Nitrites NaNO3 , KNO3 : nitrates NaNO2 , KNO2 : nitrites K and Na salts of nitrite and nitrate commonly used in curing of meats The main functions of nitrite in cured meat include the formation of the characteristic reddish-pink color and flavor associated with cured meats in addition to serving as an effective antioxidant and antimicrobial agent alone or in combination with other ingredients Nitrite is well-known to suppress the outgrowth of Clostridium botulinum spores in cured meat products and to completely control botulism pH dependent (optimum value of pH for antimicrobial activity was around 5.5) Nitrate and Nitrites: Cured Color Formation Nitrite – the true curing ingredient – is considered a multifunctional food additive that forms nitric oxide during the curing process. Nitric oxide reaction with myoglobin forms the nitrosylmyoglobin complex, which outline the basis for unique cured meat color. Nitrosylmyoglobin is bright red in color and is an extremely unstable compound. During thermal processing, it is converted to a stable, attractive reddish-pink compound – nitrosohemochrome – because of the denaturation of the protein moiety of the myoglobin pigment. Antimicrobials: Alternatives to Nitrate and Nitrites 120 ppm is the maximum allowed level of nitrite and nitrate salts in sausages Decrease in nitrite/nitrate content to safe levels cannot be fully achieved by heating or during storage. The consumption of nitrite and nitrate salts in cured meat products has been associated with the formation of carcinogenic and mutagenic nitroso compounds, especially N-nitrosamines, which are linked to the development of stomach, liver, esophagus and brain tumors, as well as red blood cells blocking and increasing risk of leukemia in children. Natural alternatives have been studied  Antimicrobials: Epoxides Ethylene oxides Propylene oxides Sterilant to treat certain low-moisture foods and to sterilize aseptic packaging materials  Acids Anticaking agents Bases Gases Additives: Buffers systems and Salts Firming Texturizers Chelating Agents Clarifying Agents Antioxidants Flour Bleaching Agents Emulsifiers Colorants Gums Fat replacers Flavor Substances Antimicrobial agents Flavor enhancers Sweeteners Stabilizers & Thickeners