Biochemistry and Human Nutrition

Module 4. Human nutrition

Lesson 33
SAFETY ASPECTS OF FOOD ADDITIVES, TOXIC ELEMENTS, RADIONUCLIDE IN MILK AND MILK PRODUCTS

33.1 Introduction

Though we have made rapid strides in the modern technology, maintaining and providing safe food still remains a global problem. Contamination of food remains a major risk and serves as source of disease and death in many of the developing countries. The food contaminants may generally be classified into two groups viz. chemical and biological. The reporting system for the food borne disease is not well organized and most of the problems are of biological in nature.

33.2 What are Food Additives?

A food additive is defined as a substance or mixture of substances other than a base foodstuff, which is present in a food as a result of any aspect of production, processing, storage or packing. This definition includes both intentional and unintentional additives. The unintentional additives, which are not added to achieve an effect in the food but which may accidentally enter into foods as a result of their use in agricultural production, raising animals, food processing or packing, are not additives in the technical sense of the term, but they are ‘food contaminants’.

An expert committee on Food Additives made up of representatives of FAO and WHO has defined food additives as non-nutritive substances added intentionally to food, generally in small quantities to improve its appearance, flavour, texture or storage properties. This definition excludes substances added primarily for their nutritive value, such as vitamins and minerals.

33.3 Need for Food Additives

• Additives have provided protection against food spoilage during storage, transportation, distribution or processing. Also, with the present degree of urbanization it would be impossible to maintain food distribution without the processing and packing with which many additives are involved.
• Many foods, particularly those with high moisture contents, do not keep well. All foods are subject to microbial attack. Fats or oily foods become rancid, particularly when exposed to humid air. The conservation of the quality of foods against agents causing such deterioration of foods requires the addition of preservatives.
• Additives are also used to color foods, add flavor, impact firmness and retard or hasten chemical reactions in food to enhance stability with resulting reduction in waste. Over 3000 different chemical compounds are used as food additives. They are categorized into different groups. A few types of additives are indicated below.

33.3.1 Antioxidants

• An antioxidant is a substance added to fats and fat containing substance to retard oxidation and thereby prolong their wholesomeness, palatability and sometimes keeping quality (time). Antioxidants function by interrupting the free radical chain mechanism involved in lipid oxidation. They are effective in small concentrations (0.01-0.02%)
• It should not contribute an objectionable odor, flavor or color to the fat or to the food in which it is present. It should be effective in low concentrations and be fat soluble.
• Also, it should not have harmful physiological effect.e.g. BHA (Butylated hydroxyl anisole), BHT (Butylated hydroxyl toluene), PG (propyl gallate) and TBHQ (Tertiary butyl hydroquinone) which are all phenolic substances.
• Naturally occurring substances that act as antioxidants are the tocopherols, but they are rarely used as they are more expensive than synthetic ones.

33.3.2 Chelating agents

• Chelating agents or sequestrates are compounds that form complexes with metal ions. Many metals exist in food in a naturally chelated form, such as, Mg in chlorophylls, Fe in ferreitin and hemoglobin and Cu, Zn and Mn in enzymes.
• When metallic ions are released due to hydrolytic or other degradative reactions, they are free to participate in reactions that lead to discoloration, oxidative rancidity, turbidity and flavor changes in foods.
• Addition of chelating agents results in the complexing of these metal ions and thereby the stabilization of foods.
• Chelating agents are not antioxidants; they serve as scavengers of metals which catalyze oxidation. They however, are antioxidant synergists.e.g. Citric acid and its derivatives, phosphates and salts of ethylene diamine tetra acetic acid (EDTA).

33.3.3 Colouring agents

• These include color stabilizers, color fixatives, color retention agents, etc. They consist of synthetic colors, synthesized colors that also occur naturally and other colours from natural sources.
• Colors add nothing to the nutritive value of foods, without certain colors most consumers will not take some foods. Thus, colors are frequently added to restore the natural ones lost in food processing or to give the preparations the natural color we expect.
• Originally, many color additives were natural pigments or dyes. E.g. spinach juice or grams, marigold flower, and cochineal (a natural red pigment obtained by extraction from the female insect Coccus cacti were used to obtain green, yellow and red color respectively.
• But synthetic colors generally excel in coloring power, color uniformity, color stability and cost. Furthermore, in many cases, natural coloring materials do not exist for a desired hue. Therefore, now synthetic ones are preferred.
• Carbonated beverages, gelatin dessert, candies and bakery goods are some foods that are colored with coaltar dyes. As a number of coaltar compounds have been shown to be potent carcinogens the use of coaltar dyes as food additives is restricted.
• A number of natural food colours extracted from seeds, flowers, insects and foods are also used as food additives. One of the best known and most widespread red pigment is bixin, derived from the seed coat of Bixa orellana, the lipstick plant of South American origin. Bixin is not considered to be carcinogenic. The major use of this plant on a worldwide basis is for the annatto dye, a yellow to red coloring material extracted from the orange-red pulp of the seeds. Ammato has been used as coloring matter in butter, cheese, margarine and other foods. Another yellow color, a carotene derived from carrot, is used in margarine. Saffron has both flavoring and coloring properties and has been used for coloring foods.

33.3.4 Curing agents

• These are added to preserve (cure) meats, give them desirable color and flavor, discourage growth of microorganisms and prevent toxin formation.
• Sodium nitrate has been used for centuries as a preservative and color stabilizer in meat and fish products. The nitrite, when added to meat, gets converted to nitric oxide which combines with myoglobin to form nitric oxide myoglobin (nitrosylmyoglobin) which is a heat stable pigment. Nitrite curing inhibits the growth of Clostridium and Streptococcus and also lowers the temperature required to kill Clostridium botulinum.
• It has been discovered that cooking nitrite cured meat products results in the formation of small amounts of N-nitrosamines, which are potent carcinogens. The nitrosamines are formed by the reaction of secondary and tertiary amines, through the following type of reaction.

Addition of ascorbates and isoascorbates reduce the formation of toxin during curing.

33.3.5 Flavors and flavor enhancers

• Flavouring additives are the ingredients both naturally occurring and added, which give the characteristic flavor to almost all the foods in our diet. Flavor enhancers are not flavors themselves but they amplify the flavors of other substances through a synergetic effect. Flavor and flavor enhancers constitute the largest class of food additives. There are about 2,100 approved natural and synthetic flavors of which more than 1,600 are synthetic ones.
• Natural flavor substances, such as spices, herbs, roots, essences and essential oils have been used in the past as flavor additives. The flavors of such materials are not uniform. They vary with the season and area of production. In addition, it would take about a ton of many spices to produce 1g of the flavor substances and in some cases even less than that. Natural food flavors are thus being replaced by synthetic flavor materials.
• The agents responsible for flavor are esters, aldehydes, ketones, alcohols and ethers. Typical of the synthetic flavor additives are amyl acetate for banana, methyl antheanilate for grapes, ethyl butyrate for pineapple etc. Generally, most synthetic flavors are mixtures of a no of different substances e.g. one imitation cherry flavor contains 15 different esters, alcohols and aldehydes.
• One of the best known, most widely used and somewhat controversial flavors enhancer is monosodium glutamate (MSG), the sodium salt of the naturally occurring amino acid glutamic acid. It is largely added to meat and soup to produce enhanced flavor. MSG enhances the desirable flavor while minimizing the undesirable ones, like the sharpeners of raw onions, vegetables etc. the 5’-nucleosides are a group of substances obtained by the enzyme hydrolysis of ribonucleic acid having the same flavor enhancing properties as MSG, but are more powerful. Both of these substances appear to affect all the four kinds of taste buds in the mouth.

33.3.6 Preservatives

• A Preservative is defined as any substance which is capable of inhibiting, retarding or arresting the growth of micro organisms, or any deterioration of food due to micro-organisms, or of making the effect evidence of any such deterioration.
• Chemical preservatives interfere with cell membrane of micro-organisms, their enzymes or their genetic mechanisms. The compounds used as preservatives include natural preservatives such as sugar, salt, acids, etc., as well as synthetic preservatives. Chemical preservatives are generally added after the foods are processed.

33.3.7 Artificial sweetness

• Some synthetic or naturally occurring compounds are used as artificial sweetners, which are used as a substitute for sugar.
• Most commonly used artificial sweetners are aspartame, saccharine (both synthetic), steroids (naturally occurring).
• Ministry of Health and Family Welfare has issued a notification for use of artificial sweetners. (Table 33.1)

Table 33.1 Notification issued by Ministry of Health and Family Welfare on 25th June, 2004

33.4 Food Toxins

Foods contain not only the nutrient we need but also a large number of chemicals some of which are toxic.

• Plants synthesize toxic chemicals apparently as a primary defense against attacks by bacteria fungi, insects and other animal predators.
• Some toxic chemicals may enter the food supply by fortuitous natural mechanisms. These may be of microbial origin and environmental pollutants (including heavy metals)
• Chemicals sprayed on plants in the form of pesticides may be present in foods of plant origin and may be transmitted through food grains to animals.
• There are also substances added to foods for functional purposes such as preservatives, antioxidants and calorie reducing agents.
• Natural toxicants in some common foods and their actions are given below. (Table 33.2)

Table 33.2 Natural toxicants in some common foods

33.5 Radionuclide

• A radionuclide (radioactive nuclide) is a nuclide with an unbalanced and unstable nucleus.
• A nuclide is an atom with a defined atomic number and a defined neutron number. In any nuclide, the number of neutrons determines whether the nucleus is radioactive. For the nucleus to be stable, the number of neutrons should in most cases be a little higher than the number of protons. If the number of neutrons is out of balance, the nucleus has excess energy and sooner or later will discharge the energy by decay processes, that is, by emitting rays or subatomic particles. A nuclide with such an unbalanced nucleus is unstable and is called a radioactive nuclide, or radionuclide.
• Radionuclides are often referred to by chemists and biologists as radioactive isotopes or radioisotopes, and play an important part in the technologies that provide us with food, water, and good health. Radionuclides may occur naturally, but they can also be artificially produced.
• Nuclear weapons tests have released large quantities of plutonium, 90Sr, and 137Cs throughout the Northern Hemisphere, with maximum levels found around 40°N to 50°N latitude .
• In Switzerland, particular attention has been paid to the highly radiotoxic 90Sr since the beginning of the nuclear era . As milk and dairy products constitute an important part of the diet of the Swiss population, it was recognized that 90Sr, an alkaline earth cation, follows the same metabolic pathways as calcium, and represents the main contributor to the internal dose by fission products. There was a large increase in 90Sr activity in milk samples during the 1960s, corresponding to nuclear testing in the atmosphere. The 90Sr activity profile in milk teeth matches that of milk, illustrating that 90 Sr present in the environment has been transferred to the food. After the Chernobyl accident, it was observed that the 90Sr activity of milk and dairy products in Switzerland doubled from 0.1 to 0.2 Bq/l during the first months after the accident.
• Discharge routes for radioactive waste from a nuclear site can be liquid, gaseous, and solid. The aquatic pathway covers potential contamination of oceans, rivers, and lakes due to liquid discharges. The terrestrial pathway deals with potential contamination of land predominately due to gaseous discharges to the atmosphere.
• For terrestrial radiological monitoring programs, cow’s milk is often the predominant sample taken because it is readily available, consumed by a large number of people, consumed by children in relatively large quantities, and is a good indicator of radionuclides present in the environment. In the U.S., the Environmental Protection Agency (EPA) runs the Environmental Radiation Ambient Monitoring System program, which covers air, drinking water, precipitation, and milk . Under Euratom Treaty, the European Union (EU) recommends that member states analyze 137 Cs and 90 Sr in milk from large milk processing sites .
• The maximum average value is the mean concentration at the farm or dairy with the highest individual result. For most foods, the maximum concentration can be selected for a dose assessment, as there is the possibility of storage of that food following harvesting, which could coincide with a peak level of activity in the food. Milk is generally not stored for long periods, so maximum averages may be used on the basis that the farm or milk production site where the highest value is found can supply milk to a consumer who consumes it in large quantities (a “high-rate” consumer). 14 C is a naturally occurring radionuclide, so some will be present in all milk samples. The U.K. uses a carbon content of 7% in milk, a background activity value of 250 Bq 14C/kg total carbon, and a subsequent background level of 18 Bq/l 14C for milk samples .