LECTURE 6 CHEMICAL PRESERVATION OF FOODS
PRESERVATIVES • are substances which, under certain conditions, either delay the growth of microorganisms without necessarily destroying them or prevent deterioration of quality during manufacture and distribution. • Can be naturally occurring or synthetic substance that is added to products such as foods, pharmaceuticals, paints, biological samples, wood, etc. to prevent decomposition by microbial growth or by undesirable chemical changes.
Preservatives………… • these substances are added in very low quantities (up to 0.2%) which do not alter the organoleptic and physico- chemical properties of the foods at or only very little. • This method is usually based on the combined or synergistic activity of several additives, intrinsic product parameters and extrinsic factors
• Food preservatives, spices, and flavouring agents have been added to foods for thousands of years. These compounds which are added to foods are termed as food additives • Chemical food preservatives are applied to foods as direct additives during processing, or develop by themselves during processes such as fermentation.
FOOD ADDITIVES • Substance or mixture of substance, other than a basic foodstuff which is present in food as result of any aspect of production, processing, storage or packaging. • This definition does not include any chemicals that are contaminants pesticides, colour additives or new animal drugs.
Guidelines for use of food additives 1. Additives should be used only vto maintain the nutritional quality of food, vto improve appearance of food 2. An additive is not justified vif it reduces the nutritive value of a food, vif it disguise faulty quality or processing and handling that is not allowed, vif it deceive the customer or if the desired effect can be obtained by other manufacturing practices that are economically and technologically satisfactory.
3. The smallest amount of additive should be used that will produce the desired effect under good manufacturing practices. 4. The additive used must conform to a standard purity. 5. Additives should be subjected to adequate toxicological evaluation and should be kept under observation for possible deleterious effects 6. The approval of an additive should be limited to specific foods for specific purposes under specific conditions. Sorbet acid for example is an approved food additive, but its use in meat was denied because its presence could mask spoilage produced by microorganisms.
Chemical Preservatives • The purpose of using a chemical agent as a preservative is to retard food spoilage caused by microorganisms the WHO has estimated that 20% of the world’s food is lost by this type of spoilage. • Partial prevention of this spoilage can be achieved through the use of refrigeration, drying, freezing and fermentation. • The use of chemical additives or preservatives will prolong the shelf life of the food even further
Chemical Preservatives • Chemical preservatives vInterfere with the cell membranes of microorganisms, vtheir enzyme activity or then genetic mechanisms. • Preservatives may also serve vas antioxidants, vas stabilizers, vfirming agents vas moisture retainers. • Chemicals that function to preserve the food are generally added after the food has been processed and before it is packaged.
Chemical Preservatives • Certain preservatives have been used either accidentally or intentionally for centuries, and include sodium chloride (common salt), sugar, acids, alcohols and components of smoke. • In addition to preservation, these compounds contribute to the quality and identity of the products, and are applied through processing procedures such as salting, curing, fermentation and smoking.
Chemical Preservatives • Different chemical preservatives are used, which involves 1. Traditional chemical food preservatives v Sugar v Salt 2. Acidulants v Benzoic acid v Sorbic acid v Lactic acid 3. Gaseous chemical food preservatives/ leavening agents v Sulphur dioxide and sulphites v Carbondioxide
Chemical Preservatives 4. Antioxidants v Butylated Hydroxy Anisole (BHA) v Butylated Hydroxy Toluence (BHT) v Propyl Gallate v Natural/Synthetic Tocophelos (Vitamin E) v Ascorbic Acid (vitamin C) and v Lecithin. 5. Colour additives 6. Flavour additives 7. Sweeteners 8. Emulsifiers
Table Sugar and salt • Sugar is used in making jellies and cured hams. • Salt is used in brines or is directly applied to the food. • Their effect is to increase osmotic pressure at a level which will prevent microorganism development. • The cell growth of the micro organisms is inhibited or the organism itself may be completely destroyed. • Salt also cause dehydration by drawing out and tying up water from the tissue of the food. • Salt added to food also ionizes, yielding the chlorine ion, which is harmful to micro organisms and interferes with the action of proteolytic enzymes. The more salt used the greater the protection afforded by the food.
Table Sugar and salt • Sugar preserving action is determined by the ration between the total sugar quantity in the finished product and the total sugar concentration in the liquid phase. The concentrations of 60% in the finished product assures food preservation • The food preserved with sugar, the water activity cannot reduced below 0.845; this value is sufficient for bacteria and neosmophile yeast inhibition, other technique should be employed to prevent mould growth
Benzoic acid • Benzoic acid in the form of its sodium salt, constitutes one of the most common chemical food preservative. • Sodium benzoate is a common preservative in acid or acidified foods such as fruit juices, syrups, jams and jellies, sauerkraut, pickles, preserves, fruit cocktails, etc. • Yeasts are inhibited by benzoate to a greater extent than are moulds and bacteria.
Sorbic acid • Sorbic acid and its salts are practically tasteless and odourless in foods, when used at reasonable levels (< 0.3 %) and their antimicrobial activity is generally adequate. • It is considered non toxic and is metabolised; among other common food preservatives the WHO has set the highest acceptable daily intake (25 mg/kg body weight) for sorbic acid. • Sorbates are used for mould and yeast inhibition in a variety of foods including fruits and vegetables, fruit juices, pickles, sauerkraut, syrups, jellies, jams, preserves, high moisture dehydrated fruits, etc.
Sorbic acid • Potassium sorbate, a white, fluffy powder, is very soluble in water (over 50%) and when added to acid foods it is hydrolysed to the acid form. • Sodium and calcium sorbates also have preservative activities but their application is limited compared to that for the potassium salt, which is employed because of its stability, general ease of preparation and water solubility.
Lactic acid • This acid is the main product of many food fermentations; it is formed by microbial degradation of sugars in products such as sauerkraut and pickles. • The acid produced in such fermentations decreases the pH to levels unfavourable for growth of spoilage organisms such as putrefactive anaerobes and butyric-acid-producing bacteria. • Yeasts and moulds that can grow at such pH levels can be controlled by the inclusion of other preservatives such as sorbate and benzoate.
Sulphur dioxide and sulphites • SO2 and sulphites may be added to such foods as dived fruits, fruit pulp and juices, and molasses. • They conserve colour, act as antioxidants and control microbial growth. • Sulphur dioxide and its various sulphites dissolve in water, and at low pH levels yield sulphurous acid, bisulphite and sulphite ions. • The various sulphite salts contain 50-68% active sulphur dioxide. A pH dependent equilibrium is formed in water and the proportion of SO2 ions increases with decreasing pH values. At pH values less than 4.0 the antimicrobial activity reaches its maximum
Sulphur dioxide and sulphites • In the past cut fruits and vegetables in salads bars were sprayed or dipped in a solution of sulphites. • Sulphur inhibits enzymatic browning and keeps plant tissue fresh longer. But this practice has been banned by the FDA because there were over 100 reported cases of adverse reactions including death. • Approximately 5-11% of asthmatics are sensitive to sulphates and experience symptoms such as headaches, nausea, abdominal pains and dizziness.
Carbon dioxide • Carbon dioxide is used as a solid (dry ice) in many countries as a means of low- temperature storage and transportation of food products. • Beside keeping the temperature low, as it sublimes, the gaseous CO2 inhibits growth of psychrotrophic micro-organisms and prevents spoilage of the food (fruits and vegetables, etc.) • Carbon dioxide is used as a direct additive in the storage of fruits and vegetables
Carbon dioxide • In the controlled/ modified environment storage of fruit and vegetables, the correct combination of O2 and CO2 delays respiration and ripening as well as retarding mould and yeast growth. • The final result is an extended storage of the products for transportation and for consumption during the off-season. • The amount of CO2 (5-10%) is determined by factors such as nature of product, variety, climate and extent of storage.
Nitrates and Nitrites • Have been used as preservatives for meats for centuries especially in hams, bacon, bologna hotdogs and sausages. • Their use produces a cured meat flavour and helps stabilize the pink colour. • Nitrites prevent the growth Clostridium botulinum, micro organisms that secrete a deadly toxin these micro organisms grow in anaerobic condition readily found in the interior of ham or in meat that has been vacuum package. • However, it has been found that nitrite has the ability to react with amino acids (found in proteins of meat) to form nitrosamines. These compounds have been reported to include livers cancers in animals.
Antioxidants • Antioxidants are beneficial in preventing rancidity in fats and foods containing fats. • Fats exposed to light, moisture, heat or heavy metal ions become activated and oxidize (reach with available oxygen) to peroxides. • The most used antioxidants are Butylated Hydroxy Anisole (BHA), Butylated Hydroxy Toluence (BHT), Propyl Gallate, Natural/Synthetic Tocophelos (Vitamin E) Ascorbic Acid (vitamin C) and Lecithin. • BHA + BHT are frequency used in variety of products because they are relatively stable to heat and maintain their effect in cooked products.
Colour Additives • The acceptance of food products is determined largely by its appearance, consumers become accustomed to standardized colours in familiar foods and base their purchasing habits/decisions or past experiences. • In order to improve the colour of foods colorants are added to carbonated beverages, frozen desserts some dairy and baked products.
Flavour additives • Natural food flavours are rarely used because the methods required to obtain the necessary amounts are expensive. In addition may are not uniform in flavour quality or chemical composition and main availability is dependent on the season. • Suppose that a manufactures wanted to produce bananas ice-cream, it will take 5 tons of bananas to extract ½ litre of banana oil. • Hence if the demand for flavourings agents in our food supply is to be met, artificial flavourings become a necessity. • The flavouring agents commonly used are Esters C pentylacetate responsible for banana flavour, aldehyde like benzylaldehyde with cherry flavour.
Sweeteners • Are added to many foods to enhance taste they can be classified as nutritive or non nutritive. • Nutritive sweeteners contain calories because they are metabolized by the body to produce energy • Examples of nutritive sweetener include sucrose, glucose (dextrose, fructose and invert sugar. High fructose corn syrup) • High fructose corn syrup are produced from corn syrups, that have been treated with an enzyme, glucose isomerase’s. This enzyme converts the corn syrup to a product containing 42% fructose 50% glucose.
Sweeteners • Further fractionation of the 42% HFCS result into second generation that contains 90% fructose. Because fructose is sweeter either sucrose or glucose, the use of HFCS in food products permits a smaller amount of sugar to be added especially in the manufacture of soft drinkers • Non nutritive sweeteners, such as saccharin do not provide calories because they are not metabolized. Aspartame is classified as a non nutritive sweeter even though it is metabolized to two amino acids (phenylalamine and aspartic acid) because the level of aspartame used is extremely small only of aspartame is weeded to produce a sweetness that is equivalent to sucrose.
Emulsifiers • Emulsifiers allows molecule that are mutually antagonistic (water and oil) to mix together. They also improve the texture, volume and body of baked goods by maintaining an even distribution of ingredients. • One of the most used emulsifiers is lecithin found naturally in milk, eggs and soybeans.
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