Food Preservatives Lecture 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 ACIDS  Serve a dual purpose, as acidulants and as preservatives: ✓ Participation in buffering systems ✓ Chemical leavening agents Acids ✓ Antimicrobial agents ✓ Chelating agents ✓ Preventing enzymatic browning ✓ Setting the pectin gels ✓ Defoaming agents and emulsifiers ✓ Coagulation of milk proteins in cheese production ✓ Produce a sour or tart taste The organic acids, e.g. citric, malic, acetic, are generally used for their taste while inorganic acids such as hydrochloric, sulfuric and nitric, are used in very small amounts to reduce pH. An exception is lactic acid, which is used to reduce the pH of bottled vegetables because it reduces the pH while having a particularly mild acid taste. Acids: Flavor Enhancers How do acids taste ? Sour, bitterness and astringency Sourness is evoked by the hydronium ion (H₃O⁺) of acidic compounds Weak acids have a stronger sour taste than strong acids at the same pH: Because weak acids exist primarily in the undissociated state. As hydronium ions are neutralized in the mouth, more undissociated acid (HA) molecules ionize to replace the hydronium ions lost from equilibrium. The newly released hydronium ions are then neutralized until no acid remains: At pH 3.5, lactic acid has more intense sour taste than citric acid because where 70% of LA is undissociated at this pH, only 30% of CA is undissociated Acids can also modify the taste sensations of other flavor compounds and mask undesirable aftertastes. Ex: in fruit drinks formulated with low-caloric sweeteners, acids mask the aftertaste of the sweetener and impart the tartness that is characteristic of the natural juice pH and aw on the growth of bacteria Interacting effects of pH and water activity on growth of bacteria FDA Good Manufacturing Practice Regulations governing processing requirements and classifcation of foods Acids: Microbial Inhibition Which one shows antimicrobial activity? Weak acids or Strong acids In a liquid solution, a weak acid can be present in its undissociated form (WAH). Only weak acids in their undissociated form (WAH) are able to diffuse through the plasma membrane into the cytoplasm. Therefore, when the pH < pKa, the weak-acid molecules diffuse through the plasma membrane and, because of the near neutral pH of the cytoplasm, the undissociated acids (WAH) are forced to dissociate into charged ions (WA- and H+). The charged ions (WA- and H+) are not able to diffuse back through the plasma membrane and accumulate in the cytoplasm, resulting in acidification of the cytoplasm.  The most commonly used food acids are acetic acid, citric acid, phosphoric acid, and tartaric acid Acids: Hydrochloric acid (HCl) Citric Acid (C6H8O7) Acetic acid (C2H4O2) Sulfuric acid (H2S04) Succinic acid (C4H6O4) Malic acid (C4H6O5) Fumaric acid (C4H4O4) Tartaric acid (C4H6O6) Lactic acid (C3H6O3) Adipic acid (C6H10O4) Phosphoric acid (H3PO4) : the most widely used acid food acidulant since the strongest and the least expensive one and the one giving the lowest pH Acids: Hydrochloric acid & Sulfuric acid Strong acids Increase acidity and provide hydrolysis of large molecules such as proteins Although concentrated forms are highly corrosive, they do not cause any adverse health effects since they are added in the form of a dilute solution Industrially synthesized from salt Strong acids gives a less acidic taste unlike weak acids Summary for Mode of Action of pH Strong acids, which lower the external pH but do not themselves permeate through the cell membrane. These acids may exert their influence by the denaturing effect of low pH on enzymes present on the cell surface. Weak acids, which are lipophilic and permeate through the membrane. The primary effect of such acids is to lower cytoplasmic pH, and the undissociated acid may have specific effects on metabolism, which amplify the effects of the weak acid. Acid potentiated ions, such as carbonate, sulfate, and nitrate, which are more potent inhibitors at low pH.  Acetic Acid Main component of vinegar and found naturally in unprocessed figs along with citric acid Commercially produced with bacterial fermentation involving grain and apples pH reduction and microbial growth control finds application within the food industry mainly as a flavouring agent (in the form of sodium diacetate), in confectionaries Used in vinegar, salad dressings, mayonnaise, ketchup, sweet and sour pickles and many sauces, meat curing, and canned vegetables In mayonnaise production, Salmonella's resistance to heat is reduced by adding acetic acid are effective in destroying salmonellae and staphylococci. Pure (100%) acetic acid is called glacial acetic acid because it freezes to an icelike solid at 16.6oC. Pure form does not have common use in the food industry.  The most widely used organic acid: accounts for more than 60% of all acidulants consumed Naturally present in animal and plant tissues especially in citrus fruits Acids: Citric Acid Commercially produced with corn fermentation by fungal microbes known as Aspergillus niger→ citric acid, oxalic acid, carbon dioxide High solubility in water Appealing effects on flavor: providing sharp tastes to foods; Enhances acidic flavor in carbonated beverages Strong metal chelation properties: acting as an antioxidant (especially in fatty foods). It can be used as an additive to protect the fresh color of meat cuts during storage. Antioxidant synergist in lipids: serving as a preservative agent for foods such as meat In seafood processing, citric acid inactivates enzymes and promotes the action of antioxidants, pH control: Used in jams, marmalades Fermentation in wine production  a natural organic acid found in many plants especially grapes, and bananas produced synthetically using maleic anhydride, and can also be obtained Acids: Tartaric Acid naturally by extraction from wine products. use as an acidulant, pH control agent, preservative, emulsifier, chelating agent, flavor enhancer and modifier, stabilizer, anti-caking agent, and firming agent Strong sour taste As an acidulant and flavoring agent, tartaric acid is known to enhance the flavors of the fruits of which it is a natural derivative. Tartaric acid is commonly used to enhance grape flavors and to enhance flavors associated with raspberry, oranges, lemon, and gooseberry. DATEM (diacetyl tartaric acid ester of mono- and diglycerides) is an emulsifier primarily used in baking to strengthen the gluten network in dough. Tartaric acid acts as a chelating agent and is used in the production of canned fruit products. The acidic monopotassium salt of tartaric acid (cream of tartar) is used in baking powder and leavening systems. Because it has limited solubility at lower temperatures, cream of tartar does not react with bicarbonate until the baking temperatures are reached; maximum volume development is obtained Acids: Phosphoric Acid Phosphoric acid is a substance that does not exist in nature but rather is produced from mineral sources Phosphoric acid has uses in food and beverage processing as a pH adjuster, flavor ingredient, and processing agent in dairy products Food-grade phosphoric acid (additive E338) is used to acidify foods and beverages such as various colas and jams, providing a tangy or sour taste. the use of phosphoric acid as an acidifying agent in dairy products dry curd cottage cheese to facilitate curd formation in cottage cheese and “reach a pH of between 4.5 and 4.7”  Acids: Benzoic Acid (Benzoates) Has been widely used as an antimicrobial agent in pickles, ciders, carbonated beverages, salad dressings Naturally in cranberries, prunes, cinnamon and cloves Undissociated acid is the form with antimicrobial activity Optimum activity in the pH range of 2.5-4.0 Sodium and potassium benzoates (salts of benzoic acids) are most commonly used since they are more readily dispersible in aqueous foods than the acid form Most active against molds, yeast and bacteria Inhibits toxic forms of Aspergillus species Heat + Benzoic Acid: Synergistic effect towards molds and fungi Benzene formation created concern since benzene is a recognized carcinogen Acids: Parabens Parabens are alkyl esters of p-hydroxybenzoic acid. The alkyl groups may be methyl, ethyl, propyl, butyl, or heptyl Extensively used in non food products such as cosmetics and antiperspirants Parabens are colorless, tasteless, and odorless (except the methyl paraben) Esterification reassure that they remain unionized to pH values 8.5. Differ from benzoic acid in that they have antimicrobial activity in both acid and alkaline pH regions. Little effect on flavor, Effective inhibitors of molds, yeasts and relatively ineffective against bacteria especially gram negative bacteria Antimicrobial activity increases and their solubility decreases with increases in the length of the alkly chain Shorter chain members are used because of their solubility characteristics Parabens are used as microbial preservatives in baked goods , soft drinks olives, pickles , jams and jellies  Acids: Sorbic Acid Sorbic acid are widely used to inhibit mold and yeast in a variety of foods including cheese, baked products , fruit juices, wine and pickles Found nature mostly in berries of the mountain ash Since sorbic acid is chemically a fatty substance from labeling perspective its use contributes to the trans fat content of a food Carboxylic group is very active It contributes little flavor at the concentrations employed Activity increases as the pH decreases indicating that undissociated form is more inhibitory than the dissociated form Potassium sorbate is the most common Lipid solubility is 3 times more than water solubility Only unsaturated organic acid permitted in foods Some m/o’s utilize it as a lipid source Can not be used in bread since it inhibits yeast There is growing interest to use it to replace at least some of the nitrite in cured meat product  Propionic Acid Occurs naturally in Swiss cheese: Gives Swiss cheese its characteristic flavor and holes by CO2 production Commercially produced with bacterial fermentation Shows antimicrobial activity against molds and a few bacteria. Used as an antifungal and antibacterial gents in agricultural and livestock operations. In the bakery field where it not only inhibits molds but also effective against the roppy bread organism Bacillus mesentericus Preservative in animal feeds Limitations to the value of organic acids as microbial inhibitors in foods They are usually ineffective when initial levels of microorganisms are high. Many microorganisms use organic acids as metabolizable carbon sources. There is inherent variability in the resistance of individual strains. The degree of resistance may also depend on the conditions. Acids: Chemical Leavening Agents Leavening agents also known as raising agents are composed of compounds that react to release gas in a dough or batter under appropriate conditions of moisture and temperature. Most are based on a combination of acid (usually a low molecular weight organic acid) and a salt of bicarbonate (HCO3−). After they act, these compounds leave behind a chemical salt. Chemical leavens are used in quick breads and cakes, as well as cookies and numerous other applications where a long biological fermentation is impractical or undesirable. Carbondioxide is the only gas generated. It is derived from a carbonate/bicarbonate salt and acid mixture. During baking, this gas release, along with the expansion of entrapped air and moisture vapor, imparts a characteristic porous, cellular structure to finished goods. Leavening acids are often not easily recognized as acids in the usual sense, yet they must provide hydrogen ions to release carbon dioxide. Chemical Leavening Agents: Baking Powder Are baking powders acid or base? ▪ Baking powder is a dry chemical leavening agent, a mixture of a carbonate or bicarbonate and a weak acid, and is used for increasing the volume and lightening the texture of baked goods. ▪ The most common salt is sodium bicarbonate (NaHCO3). However, ammonium carbonate (NH4)2CO3 , ammonium bicarbonate (NH4)HCO3 are sometimes used in cookies. Do not require a leavening acid for functionality ▪ Baking powder works by releasing carbon dioxide gas into a batter or dough through an acid-base reaction, causing bubbles in the wet mixture to expand and thus leavening the mixture. It is used instead of yeast for end-products where fermentation flavors would be undesirable or where the batter lacks the elastic structure to hold gas bubbles for more than a few minutes, or to speed the production. ▪ Because carbon dioxide is released at a faster rate through the acid-base reaction than through fermentation, breads made by chemical leavening are called quick breads. Quick breads are not made with yeast. They don’t need time to rise. ▪ Most commercially available baking powders are made up of sodium bicarbonate (also known as baking soda or bicarbonate of soda) and one or more acid salts. Typical formulations (by weight) call for 30% sodium bicarbonate, 5-12% monocalcium phosphate (MCP) or Sodium Acid Pyrophosphate (SAPP), and 21-26% Sodium Aluminum Sulfate (SAS). ▪ The last two ingredients are leaving acids. Another typical acid in such formulations is cream of tartar, a derivative of tartaric acid. Acids as Chemical Leavening Agents in Baking Powder Acids combine with the sodium bicarbonate and water to produce the gaseous carbon dioxide. The use of two acidic components is the basis of the term "double acting”. The acid in a baking powder can be either fast-acting or slow-acting A fast-acting acid reacts in a wet mixture with baking soda at room temperature, and a slow-acting acid will not react until heated in an oven. Baking powders that contain both fast- and slow-acting acids are double acting; those that contain only one acid are single acting. By providing a second rise in the oven, double-acting baking powders increase the reliability of baked goods by making the time passed between mixing and baking less critical, and this is the type most widely available to consumers today. Double-acting baking powders work in two phases; once when cold, and once when hot Baking powders also include components to improve their consistency and stability. The most important additive is cornstarch, although potato starch may also be used. The inert starch serves several functions in baking powder. Primarily it is used to absorb moisture, and thus prolong shelf life by keeping the powder's additional alkaline and acidic components dry so as not to react with each other prematurely. A dry powder also flows and mixes more easily. Biological Leavening Agents Saccharomyces cerevisiae (baker’s yeast) produce carbon dioxide in: Bread Beer (unpasteurized—live yeast) Kefir Sourdough starter (Lactic acid bacteria) BASES Bases Preservation with pH control Carbon dioxide evolution (as chemical leavening agents) Enhancement of color and flavor Sanitation Solubilization of proteins Chemical peeling Bases: Alkali treatment Enhancement of color and flavor Ripe olives are treated with 0.25%-2% NaOH to remove the bitter taste and develop a darker color. Green olives are not treated to avoid the loss of green color Pretzels are dipped into a solution of 1.25% NaOH at 87-88 oC before baking to enhance proteins and starch interactions so that the surface becomes smooth and develops a deep brown color NaOH treatment used to prepare tortilla dough destroys disulfide bonds that are base labile and improves the flavor Increase in pH results in higher rates of browning, polymerization of flavonoids: less bitter, less acid and bitter chocolate flavor, darker color and slightly improved solubility. Bases: Alkali treatment Delignification Refers to the removal of lignin and part of hemicellulose by NaOH, lime, or ammonia water to increase cellulose accessibility and isolation. Cellulose: Most abundant polymeric raw material Used as bulking agent, stabilizer, thickener, and anticaking agent Found in a matrix together with hemicellulose and lignin Delignification is a must to extract cellulose! Bases: Alkali treatment Sanitation - Clean-in-place (CIP) Wash cycle using an alkaline solution is a standard clean- in-place (CIP) process Whole milk contains abundant nutrient elements; however, they easily attach to the internal surfaces of pipes and tanks, providing an excellent environment for bacterial growth and cause contamination. In the milk industry, a NaOH solution (aka caustic soda) (usually 1.5% - 2.5%) is used to remove butterfat and protein deposits Bases: Alkali treatment Solubilization of proteins Most proteins are highly soluble at alkaline pH 8–9. Soy proteins are solubilized through alkali processing. However, concerns have been expressed about alkaline-induced racemization of amino acids and losses of other nutrients. Chemical Peeling : Peeling of fruits and vegetables Hot solutions 60-82 oC of sodium hydroxide (about 3%) effect peel removal with substantial reductions in plant wastewater as compared with other conventional peeling techniques. Differential solubilization of cell and tissue constituents (pectic substances in the middle lamella are particularly soluble) provides the basis for caustic peeling processes. Bases: Alkaline salts Food systems sometimes require adjustment to higher pH values to achieve more stable or more desirable characteristics Instant milk-gel puddings Pre-gelatinized starch + Cold milk Emulsifying salts such as tetrasodium pyrophosphate and disodium phosphate in the presence of calcium ions in milk cause milk protein to gel with pre-gelatinized starch Emulsifying salts could also be used to neutralize excess acid in the production of such foods as cultured butter Reduction in acidity improves churning efficiency and retards the development of oxidative flavors. Use of alkaline agents in excessive amounts lead to soapy or neutralizer flavors especially when substantial quantities of fatty acids are present. Addition of emulsifying salts to evaporated milk prevents separation of butterfat and aqueous phases Bases: Alkaline salts In melting cheeses: Alkaline salts, aka emulsifying salts, such as disodium phosphate, trisodium phosphate, and trisodium citrate are used in the preparation of processed cheese to increase the pH and to effect protein (casein) dispersion During heating, emulsifying salts detach calcium ions from casein micelles and replace them with sodium ions. This ionic exchange converts the insoluble calcium to a more soluble form with more water binding capacity and enhanced emulsifying property Used extensively in processed cheeses and imitation cheeses to promote a uniform , smooth , texture Bases: Alkaline salts = (Emulsifying salts) = (Melting salts) When cheese is melted without any additive, fat separates from protein and the result is terrible. The secret of 'processing' cheese is in keeping the fat in the protein matrix. Heating, however, decreases the ability of the cheese proteins to keep the fat globules in the dispersed state, which means that the emulsifying capability of the proteins has been reduced. Melting salts restore it by binding (sequestering) calcium which is present in the caseins. Melting salts with very strong calcium-binding ability (affinity for calcium) lead to the production of hard processed cheeses which contain fat in the form of very small globules. It has to be emphasized that the melting salts are not emulsifiers but they restore the emulsifying ability of the milk proteins very efficiently.  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 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 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 For instance, 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, grey bean in canned maize, 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 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 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), discovered in 1903, 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. Chestnuts contain 47 mg of phytic acid for 100g. Buckwheat contains 10 mg /g phytic acid. 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 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 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  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