Chemicals For Controling Microorganisms

you read about the various types of microorganisms that are
important in the food industry. In this unit, we shall tell you how the spoilage
of food can be prevented or delayed which are caused due to these
microorganisms or some other chemical reactions. This unit highlights the
various classes of chemical preservatives that have been approved for the use in food and their use.

Chemicals For Controling Microorganisms

The various aspects to be considered for the selection of
chemical additives (food additives), their mode of action and the adverse
reactions resulting due to the consumption of the additives is also elaborated in
this unit. The unit also deals with the developed additives, namely acids,
alcohol and bacteriocins.

Uses Of Various Food Additives And Chemical Preservatives

For centuries, man has recognized the effects of food additives and has used
whatever was available-marigold for colour, wood ashes for leavening, the
lining of calf stomachs for cheese making etc. today, thousands of compounds
are used as food additives, whose chemical identity and structure are known. 
The use of food additives is imperative in the complex and integrated society
in which we live. 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 and packing with which many
additives are involved.
Additives permit the variety of foods that we deem desirable and which
certainly are objectively important in maintaining important nutrition.
Vitamins and minerals are important in maintaining good nutrition. Many of
these chemical additives can be manufactured so that foods can be “fortified”
or “enriched”.
There is then the need for the use of food additives to maintain the nutritional
quality of food, to enhance the stability with resulting reduction in waste, to
make food more attractive and to provide efficient aids in processing, packing
and transport. 
The amount of food additives used should be kept to a minimum
and it should conform to a standard of purity and be safe. Over 3000 different
chemical compounds are used as food additives. They are categorized into
different groups which will be discussed below. 
According to WHO a food additive is defined as a substance or mixture of
substances other than the basic foodstuff, which is present in food as a result of
any aspect of production, processing, storage and packaging. The term does
not include chance contaminants- thus the former refers to intentional food
additive while latter is incidental un-intentional food additive. 
Intentional food additives could be nutritive, freshness maintenance, sensory
and processing aids; preservatives, antioxidants, emulsifiers, stabilizers,
maturing agents, colours, special sweeteners, nutrient supplements, flavouring
compounds and natural flavouring materials.

Types of Additives

• Acidity regulators, used to alter and control the acidity or alkalinity levels
for different desired effects, which can include preservation, added/altered
tartness, colour retention and to assist raising agents. 
• Acids, used to control to what degree other substances function and/or to
impart a sharp taste. Assists in the release of carbon dioxide in raising
agents and can have a preservative effect.
• Anti-caking agents, used to ensure the free flow in products such as dried
milks, icing sugar and table salt. 
• Anti-foaming agents, used to reduce or prevent foaming (frothing) on
boiling and to reduce scum forming. 
• Antioxidants, used to protect food against deterioration caused by exposure
to air (oxidation), such as fat rancidity, flavour deterioration or colour
• Bleaching agents, used to artificially whiten flour. 
• Buffers, see acidity regulators. 
• Bulking agents, used to increase volume without significantly adding to
the energy levels of the food. Normally used in diet foods but can also be
used to pad out expensive ingredients. Not usually digested and acts as a
source of dietary fibre (roughage). 
• Carriers and carrier solvents, used to modify a food additive (by
dissolving, diluting or dispersing etc.), without changing its function, to
enable easier use or handling. 
• Emulsifiers, used to aid in the formation and maintenance of the dispersion
of two or more substances which would normally separate and not
normally mix, such as oil and water. Milk, mayonnaise and salad dressings
are typical oil in water emulsions, butter and margarine water in oil
• Emulsifying salts, used to disperse protein so reducing the stringiness in
cooked cheese. 
• Firming agents, used to make or retain firmness or crispness in fruit and
vegetables and to strengthen gels. 
• Flour improvers, used to enhance the elastic properties and aid the
development of dough. Also accelerates the effect of bleaching agents. 
• Foaming agents, used to provide a uniform dispersion of gas in a food. 
• Gelling agents, used to form a jelly so providing texture to a product. 
• Glazing agents, used to produce a protective coating or to impart a
polish/sheen on the surface of a food such as confectionery or citrus fruit. 
• Humectants, used to retain moisture in foods by absorbing water from the
air to prevent drying out. 
• Modified starch, used for various functions including adding texture,
adding bulk, stabilizing and as a thickener. 
• Packaging gases, used to replace air in the packaging of foodstuffs
susceptible to oxidation but not necessarily shown on food labels
• Preservatives, used to extend the shelf-life of products by preventing the
growth of microorganisms which could otherwise cause food decay and, in
some cases, food poisoning. 
• Propellants, a gas or volatile liquid used to expel foodstuffs from aerosols. 
• Raising agents, used to increase the volume of doughs and batters by
promoting gas release (aeration). 
• Releasing agents, used to prevent foodstuffs sticking to machinery, molds,
packaging etc. but not necessarily shown on food labels even though some
may remain in the food. 
• Sequestrants, used to combine with trace metals in the environment to
render them inactive. 
• Stabilizers, used to maintain the physical state of a food and to stabilize,
retain or intensify the existing colour of a food, particularly emulsions, and
therefore often used with emulsifiers. 
• Sweeteners, there are two different types of sweeteners:
1. Intense sweeteners − these have a sweetness many times that of sugar
and are therefore used at very low levels. They are used in products
such as diet foods, soft drinks and table top sweeteners; 
2. Bulk sweeteners − these have a similar sweetness to sugar and are
used at comparable levels. Unlike intense sweeteners they also provide
bulk (although their main function is to provide sweetness). They are
used in products such as sugar-free confectionery and foods for
• Thickeners, used to increase viscosity, modify texture and impart stability

Role of Food Additives

Food additives help to enhance the consumer acceptability, help in maintaining
or improving the nutritional quality, enhance stability or keeping quality by
acting as antimicrobial agents with the resulting reduction in waste and
prevention of chemical and biological deterioration, make food more attractive
and provide sufficient aids in the food products for improving texture, colour
and flavour, check spoilage by inactivating microorganisms and maintain
safety of foods, facilitate preparation and help to improve palatability of the
It helps to enhance the shelf life of food or food products. It has been estimated
that we consume about 5 kilograms of food additives as preservatives, colours,
bleaches, flavours, emulsifiers and stabilizers every year in the food we eat. 
This not only results in extra work for our body to remove them, but frequently
trigger asthma attacks; rashes; respiratory disturbances; hyperactivity in
children, and in some people, an abnormal sensitivity to prescribed
medications, particularly aspirin. Below are some common additives found in
refined foods, and well-worth avoiding by those susceptible to their effects.
Acceptable daily intake for various preservatives


Preservatives are substances which are capable of inhibiting, retarding or
arresting the process of fermentation, acidification or other decomposition of
food or of masking any of the evidence of putrefaction but it does not include
salt, sugar, vinegar, glycerol, alcohol, spices, essential oils etc. 
Sulphur dioxide
(including sulphites) and benzoic acid (including benzoates) are among the
principle preservatives used in the food processing industry. The permitted
quanitity of sulphur dioxide and benzoic acid is given in the following tables.
Food additives and their usage concentrations

Classes of preservatives

Common salt, sugar, dextrose, spices, vinegar or acetic acid, honey 
Benzoic acid and its salts, sulphur dioxide and the salts of sulphurous
acid, nitrites and nitrates, sorbic acid and its salts, propionic acid and its
salts, lactic acid and its salts.
Sulphur dioxide 
Sulphur dioxide and its derivatives have been extensively used in foods
as a food preservative. It acts both as an antioxidant and reducing agent
and prevents enzymatic and non-enzymatic reactions, leading to
microbial stability. The common used forms are sulphur dioxide gas
and sodium, potassium and calcium salts of sulphite, bisulphite or
It is like a biocidal and biostatic agent and is more
active against bacteria than molds and yeasts.
Sulphite or metabisulphite sprays or dip with or without added citric
acid provides effective control of enzymic browning in pre-peeled and
pre-sliced potatoes, carrots, mushroom and apples

Sodium benzoate

It was the first chemical preservative permitted in foods by the FDA,
and it continues in wide use today in a large number of foods.
Benzoates have greatest activity at low pH. As used in acidic foods,
benzoates act essentially as a mold and yeast inhibitor.
In foods such as fruit juices, benzoates may impart disagreeable tastes
at the maximum level of 0.1 per cent. The taste has been described as
being ‘peppery ‘or burning.
Permitted quantity of benzoic acid in food
Quantity of sulphur dioxide permitted in food


Sour or acidic taste of a food is attributed to the acidic components present in
the food. Many processed foods and beverages, however, need the addition of
acids to impart characteristic taste and flavour to the final food product. The
intensity of sourness and ability to reduce pH vary among the organic group of
acidulants in the decreasing order as follows:
Fumaric > tartaric > malic > acetic > citric > lactic > gluconic acid 
Commonly used acidulants include acetic, adipic, citric, fumaric, lactic, malic,
phosphoric and tartaric acids. Citric acid is the most versatile and widely used
food acidulant.

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