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(i)                 Aspartame: It is a low caloric sweetener used in soft drinks. It is a dipeptide (two amino acids) made lip or the amino acids phenylalanine (obtained by fermentation) and aspartic acid. It is 150 times sweeter than sucrose (the common sugar) (Fig. 15.1).

Fig. 15.1 Chemical structure of aspartame.

(i)                 Thumatin: It is a protein extracted from the berries of the plant, Thaumatococcus danielli. It is the sweetest compound known and is 3000 times sweeter than sucrose. (Saccharin, that is obtained chemically, is 300 times sweeter than sucrose)

Diagnosis of Food Contamination

Major food contaminating microbes are identified by DNA or RNA probe technology or by ELISA (Enzyme Linked Immunosorbent Assay) technique using commercially available monoclonal antibodies or probes for the contaminating microbes.

Single Cell Protein

Explosive population growth is a major problem of the world, particularly for the developing countries. Conventional agricultural practices are unable to supply sufficient food, particularly the proteins, despite increasing productivity. Through new agricultural practices high protein cereals have been developed. The use of processed microbial biomass, which are usually single-celled or filamentous in structure as the source of protein, is called single cell protein (SCP). The biomass is called single cell protein as it is rich in protein (more than 50% of the dry weight). The interest in SCP was generated to compensate for the protein deficiency, particularly in the developing countries.

People have recognized the nutritional value of mushrooms, yeast, many bacteria and algae from the time immemorial, e.g., people from the Lake Chad in Africa and the Lake Texcoco in Mexico have been harvesting the naturally growing blue-green alga, Spirulina, and using it as food after drying in the sun. During the last three decades, interest is growing in using microbes for food production, particularly for feeding animals, poultry and in aquaculture for the farming of shrimps, prawns, fish, etc., which in turn would improve the human nutrition.

SCP are easier to store and they can replace the traditional protein supplements, like fishmeal and soya meal. They are used as the protein supplement and to improve flavour of food for human consumption. Processing to degrade the nucleic acids of microorganism for SCP is required because metabolism of DNA and RNA yields uric acid, which causes stones in kidney. The quality as well as the quantity of the proteins are the major goals of SCP production. In addition to proteins, microbes also contain carbohydrates, fats, vitamins and minerals. Many companies throughout the world have been involved in the production of SCP, and many products are commercially available, e.g., ‘Sunova’ capsule containing Spirulina is manufactured by Dabur Company in India.

Microorganisms produce proteins more efficiently within a short time period than the farm animals, e.g., the doubling time for the bacteria and yeast is about 20-120 min, whereas, for a young cattle is 1-2 months. Moreover, microbes can be more easily genetically modified for a desirable amino acid composition in comparison to the plants and animals. Microorganisms have relatively high protein content and the nutritional value of protein is also good. Microorganisms can be grown in large amounts in relatively small fermentation bioreactors, particularly through continuous cultures, all the year round, where growth is independent of the climate. Many of the microorganisms can be cultivated on a wide range of low value raw materials or waste materials, particularly low value water, which would also help to reduce the pollution.

A unique aspect of SCP technology is the problem of safety, nutritional value and acceptability of the product. The raw material used for the production of SCP is the main safety hazard, e.g., presence of carcinogenic hydrocarbons, heavy metals and other contaminants as well as the toxin production by certain fungi. Sanitation and quality control procedures must be maintained to avoid the contamination by pathogenic or toxicogenic microorganisms. Toxicological testing of the final product must be thoroughly performed. In addition, the odour, taste and texture of the product are also equally important.

First industrial production of SCP, Candida utilis, occurred during World War I by Germany and it was used in soups and sausages. A variety of substrates, like inorganic carbon (e.g. CO2), industrial effluents (e.g., confectionary effluents, whey, molasses) and low cost organic materials (e.g., cellulosic wastes, like straw, starch hydrolysate) are used for SCP production.

The microorganism used for SCP production must be non-pathogenic, should have good nutritional value, should be easily and cheaply produced on large scale, toxin-free, fast growing and easy to separate from the medium. Some of the important microorganisms used for SCP production are:

(i)                 Algae: Most commonly used algae are Chlorella (a unicellular green algae), Scenedesmus (a colonial green alga) and Spirulina (a filamentous blue-green alga) which are photosynthetic and are generally grown in open tanks or ponds. They utilize CO2, sunlight and a few inorganic nutrients for their growth. Algal SCP has about 60% crude protein with good amino acid composition. They are suitable for protein-rich feed supplement for domestic animals. Chlorella and Scenedesmus (Fig. 15.3) have long been used as food in Japan, while, Spirulina in Africa and Mexico. Chiarella is commercially produced in Japan to be used in yoghurts, ice-cream and breads, while Spirulina maxima in Mexico is used as animal feed. Spirulina is harvested by filtration method. The major disadvantages of algae as SCP are the risk of contamination and costly recovery methods, especially for unicellular algae, green algal cellulosic cell walls that are not digested by, human beings etc. The CFTRI (Central Food Technology and Research Institute) in Mysore produces Spirulina tablets of 1 gm weight to be used as food and feed (Fig. 15.2).

Spiruiina filaments

Spirulina tablets

Fig. 15.2 Spirulina grown in artificial tanks and sun-drying of harvested Spirulina , Spirulina filaments as seen under the microscope and Spirulina tablets.

ChIarella sp.

A single ChIarella cell

Scenedesmus sp.

Fig. 15.3 Animal feed, Chlorella and Scenedesmus.

(ii) Fungi: Some fungi used as SCP are unicellular (yeasts), whereas, others are filamentous in structure.

(a)   Yeasts: Members of Saccharomyces cerevisiae (Baker’s yeast), Candida utilis, (Torula yeast) and Kluyveromyces fragilis are widely used as SCP. They have 55-60% protein with good amino acid balance and also rich in vitamin-B. They are used both for human food and animal feed supplementation. During their production, the risk of bacterial contamination is low and they are harvested by centrifugation.

Saccharomyces cerevisiae is grown on molasses and is used commercially for the fermentation of dough in bakeries, and, thus, eaten indirectly as the component of food. Candida utilis is also used commercially in U.K., USA, Russia, Europe in soups and sausages and grown on various substrates, like confectionary effluents, ethanol and sulphite liquor.

Kluyveromyces fragilis is basically grown on whey and is used commercially in France. The yeast secretes lactase enzyme, which helps in the digestion of the milk sugar lactose into glucose and galactose.

Yeasts have advantages of larger size (easier to harvest), lower nucleic acid content, high
lysine and ability to grow at low pH.

(b) Filamentous Fungi: The commonly used filamentous fungi as SCP are:

Fusarium graminearum, Chaetomium,etc. which are grown on starch hydrolysate and cellulosic wastes, respectively (Fig. 15.4). They are usually grown as submerged cultures and have protein content of 50-55%. Harvesting of these fungi is rather easy, generally by filtration method. The main problem associated with these fungi are their slower growth, and contamination by yeast.

Fig.15.4 Cells of Saccharomyces cerevisiae

Mushrooms are the fruiting bodies of certain large fungi belonging to the group Basidiomycetes and are rich in proteins, vitamins and other nutrients.

Moreover, they are devoid of starch and are suitable for diabetic individuals. Agaricus bisporus is the common white button mushroom and accounts for over 70% of total mushroom production. It (filaments) grown on moistened paddy or wheat straw compost in wooden trays. After white cottony mycelial filaments) growth, the compost bed is covered with a 1-2 cm thick layer of soil and sand. The mushrooms (fruiting bodies) are harvested atthe button stage (Fig. 15.5).

Fig. 15.5 Agaricus bisporus.

Lentinula edodes is the second most cultivated mushroom variety in the world and over 90% of its production occurs in Japan.

Some of the other species of .edible mushroom are Pleurotus and Volvariella.

(i)        Bacteria: A large number of bacterial species have been evaluated for SCP production using wide variety of substrates. They have very high growth rates and are used at commercial level, e.g. Methylophilus methylotrophus grows on methanol. They have over 80% protein. The risk of contamination by pathogenic bacteria is high during cultivation, moreover, their recovery is also problematic. They are recovered by flocculation and floatation combined with centrifugation. Bacteria have high nucleic acid content relative to yeast and fungi.

Sun-drying of SCP is cheap but it reduces its quality. Heat treatments are used during the final stages of harvesting to inactivate heat-sensitive organisms and to reduce RNA content. The biomass may be further processed or even the protein may be isolated and purified from the biomass. SCP can be stored and shipped over long distances.

SCP processes are mostly capita] and energy intensive, most processes must be conducted under sterile conditions in expensive equipments. The future of SCP would depend upon the reduction or production costs and improvement of quality. However, the main limitations for SCP products for human use are sociological and their major role will be in animal feed supplements.



  1. Describe the role of’ various microorganisms and enzymes in food and alcoholic beverages industries.


Discuss the use of various microorganisms in dairy industry.


Discuss the role of various microorganisms in the production of alcoholic beverages.

Briefly outline the steps in the production of following, discussing the role of various micro organisms and enzymes:

  i.  Leavened bread

ii. Yoghurt

iii. Cheese

 iv. Beer

 v. Wine

 vi. Distilled alcoholic beverages

vii. Vinegar

2. Define single cell protein. Briefly describe the production of various SCPs.

3. Write short notes on:

i. Rennet in cheese production

ii. Cloudiness of fruit juices and wines

 iii.  Use of daily industry

iv.  Mushrooms

 v. Fermented foods and beverages

 vi. Single cell protein

4. Discuss the role of the following enzymes in food industry:

i. Protease

ii. Amylases