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Session 2: Interaction at the post-harvest stage

Chairman S.K. Majumder
Rapporteur H.S.R. Desikachar

Effects of processing on the nutritional and culinary properties of food grains, with special reference to millets

H.S.R. Desikachar. Central Food Technological Research Institute. Mysore, India

Heat treatment


The outer bran layers, in coarse grains, are fibrous and contain tannins, pigments, and bitter principles. Their removal would considerably enhance their palatability and may even add to nutrition. Appropriate techniques for effecting this have been developed.

For grains with hard endosperm (sorghum, maize, and pearl millet) incipient wet conditioning with 2-3 per cent moisture followed by abrasive milling could remove the outer bran. Polishing should be judicious as over-polishing causes undue depletion of nutrients. The polished or pearled grains could be used as whole grain, semolina, or flour Alternatively, similar wet conditioning, followed by immediate grinding in a plate grinder and sieving, gave a highly nutritious flour. nearly free from bran.

Heat treatment of these grams was found to affect their nutritional, physical, textural, and storage properties. Steam treatment of ragi reduced the stickiness of the cooked mudde or dumpling and contributed grainy texture to it. Heat treatment reduced the hot paste viscosity of millet flours, inactivated the lipase, and increased the shelf-life of whole-meal flours. Drastic heat treatment, however, triggered development of oxidative rancidity. Puffed or popped coarse grains are also highly acceptable products.

Elaboration of amylases during germination was faster in pearl millet and ragi than m sorghum or maize. Amylases degraded the starch, reduced its hot paste viscosity and increased the caloric density of weaning foods based on malted grains. Weaning foods based on malted ragi, millet, sorghum, and maize, and with a legume supplement, have been developed. Other advantages of germination are increase in lysine, hydrolysis of phytin, and release of vitamin C. Varietal differences in respect of amylase activity during malting have been noted.

Semolina from sorghum and maize could replace rice or wheat semolina in idli and dose. Lactic fermentation of gelatinized ragi or other cereal flours has recently been studied.

Some form of processing usually precedes the consumption of all food grains. The processing treatment could be milling to remove bran/husk, heat treatment to cook it and remove raw flavour or taste, puffing, popping, or roasting to introduce crunchy texture and impart desirable aroma, malting, or fermentation to improve nutrition or digestibility, canning for convenience, dehydration for enhancing storage life, and so on. Some forms of processing or over-processing may also adversely affect the nutritional qualities of the food grains.

An enormous amount of work has been carried out and documented with respect to the science and technology of such processing and its effects on the nutritive value. culinary quality, storage life, and utilization potential of food grains, particularly of such major cereals as wheat and rice and the majority of legumes and oilseeds. Generally, optimal processing has been found to be necessary and usually beneficial, although severe or long processing adversely affects nutritive value, storage life and their culinary quality. For instance, while milling is necessary, over-milling or a high degree of extraction reduces yield and nutritive value. Optimal heat treatment improves flavour, texture and nutritive value, but severe heat treatment may destroy vitamins, bind nutrients or even initiate rancidity. The processing should therefore be judicious or optimized to derive the best utilization potential from it.

Such information on coarse grains like sorghum, maize, and other millets is recent and quite meagre. The object of the present paper is to highlight and review some of our recent work on these grains, which happen to be staples consumed by large sections of the population in the relatively drier and semi-arid parts of Asia, Africa, and South America. The processing treatments that will be considered are milling, heat treatments, germination, and fermentation.


The outer bran in coarse grains is fibrous, bitter, astringent, or coloured. Milling of the coarse grains is therefore desirable to confer adequate consumer acceptability to them. The technique and the machinery for the purpose have been standardized. The grains are wetted or moistened with 2-3 per cent moisture, conditioned for 5 to 15 minutes, and the bran removed by an abrasive device used in rice milling (Viraktamath et al. 1971). It is desirable to regulate the milling in such a way that only the outermost bran layers are removed retaining the germ and the nutritive aleurone layers intact. The polished grains could be used as such, or ground to flour or semolina for culinary uses (Desikachar 1975).

Where the grain being processed is soft or small-sized, the moist conditioned grain is ground in a plate grinder mill (chakki. plate or emery grinder) and immediately sieved. The bran, which resists grinding to fine particles, is removed on a 16-20 BS mesh sieve. The flour or semolina obtained is a fairly refined product with minimum bran contamination (Desikachar et al. 1980).

It is obvious that overmilling or very high refining must be avoided, since it removes the aleurone layers and germ rich in protein, vitamins, and minerals. The chemical composition of the fractions at a different stage of polishing sorghum illustrates this point. A 85-90 per cent extraction flour or a 10-15 per cent polished grain retains a high proportion of nutrients with minimum bran contamination (Raghavendra Rao and Desikachar 1964).

Heat treatment

The presence of a dense horny endosperm in sorghum and maize hinders quick or soft cooking of the millet grains. They are therefore used as flour for making roti, chapati, etc. Size-reduction of grain into semolina, or flattening it to a flake, enable quicker cooking (Raghavendra Rao et al. 1979). Sorghum semolina is found to be highly resistant to quick hydration. Cooking, especially in an acid medium, improves digestibility.

The effects of pre-cooking, steaming, roasting, puffing, and so on are generally beneficial. For example, the slimy character of starch in its cooked form is reduced by prior heating of the grain (Desikachar 1974). Cold slurry viscosity is increased and hot paste viscosity reduced by heat treatment (Raghavendra Rao et al. 1981). The storage life of the whole-meal flour/semolina is enhanced by heat treatment, since the lipase is inactivated and hydrolytic rancidity eliminated (Wamajee 1978; CFTRI Report 1976). Severe heat treatment, however, sets off oxidative rancidity.

Popped or flaked millet grains have been made use of for development of different types of weaning foods or of supplementary foods for feeding school and pre-school children (Desikachar et al. 1981). Popping or puffing is especially useful here, because it imparts a highly crunchy texture and desirable flavour. The millet is supplemented with pulses to increase protein quality. Varieties suitable for popping have been identified in sorghum and ragi (Viraktamath et al. 1972; Malleshi and Desikachar 1981a).


Malting of grains, particularly pulses, is a traditional practice in certain parts of India. The benefits of germination are many. Vitamin C is elaborated, phosphorus availability is increased, and lysine and tryptophan are synthesized (Dulby and Tsai 1976). Both starch and protein are partially degraded making for better digestibility (Ram et al. 1979). Some of the flatus factors are also degraded (Rao and Belavady 1978). The elaboration of amylases results in a lower viscosity and thinning down of the starch slurry (Brandtzaeg et al. 1981). There is also an overall improvement in the flavour profile. In view of these multiple benefits. use of germinated grains, to a larger extent, should be advocated. The germination, however, should not be prolonged as otherwise too much root formation and metabolic weight loss of grain may become a problem.

Elaboration of amylases during malting has been taken advantage of in the development of weaning food formulations for babies, wherein a low hot paste viscosity and a high calorie density is desired. One formulation consists of malted ragi and green gram with supplemental vitamins and minerals. The formulation has been widely tested and found to have good consumer acceptance. Its nutritional value has been found to be comparable to that of common proprietary weaning foods. Addition of a small amount of malt flour has been found to bring down the paste viscosity of many weaning foods (Malleshi and Desikachar 1981b).


Fermentation of foods has also been practised for improving the flavour, texture, and palatability of foods. Bacterial or yeast fermentations are more common in India, while fungal fermentation is more widely practised in the Far East. Synthesis of B-complex vitamins, partial digestion of starch and proteins, and release of enzyme are brought about during fermentation (Ready et al. 1980), Increase of vitamin B12 and folic acid, and the synthesis also of a few antibiotics, have been noted, particularly in fungal fermentation used to make "tempeh" and "natto" (Van Veen and Steinkraus 1970). The overall effects of fermentation are highly beneficial. Millet grains can substitute for the rice or wheat component of such fermented foods. Maize or sorghum semolina can replace rice or wheat semolina in making idli (Cheeptongkum 1976). Sorghum. maize or ragi can replace rice in dose formulations (Raghavendra Rao et al. 1979). Sorghum, millet, or maize flour can also replace up to about 20 per cent of the wheat used in making bread (Haridas Rao and Shurpalekar 1976).


Brandtzaeg, B., N.G. Malleshi. U. Svanberg, H.S.R. Desikachar. and O. Mellander. 1981.

"Dietary Bulk as a Limiting Factor for Nutrient Intake - with Special Reference to the Feeding of Pre-school Children. III. Studies on Malted Flour from Ragi, Sorghum and Green Gram." Journal of Tropical Pediatrics. (Accepted.)

CFTRI (Central Food Technological Research Institute). 1976. "Storage Stability of Balahar." A report submitted to the Ministry of Food and Agriculture, Government of India. CFTRI, Mysore.

Cheeptongkum, N. 1976. "Studies on the Substitution of Cereal and Legume Components in Instant Idli Flour Compositions." Thesis for the M.Sc. (Food Technology) degree, University of Mysore. CFTRI, Mysore.

Desikachar, H.S.R. 1972. "Effect of Wet Heat Treatment on the Culinary Qualities of Ragi." Journal of Rood Science and Technology, 9: 149-150.

___. 1975. "Processing Maize, Sorghum and Millets for Food Uses." Journal of Scientific and Industrial Research, 34 23-237.

Desikachar, H.S.R, N.G. Malleshi, C S. Viraktamath, S.N. Raghavendra Rao, S. Sreedhara Murthy, and S. Ananda. 1981 "Weaning Food Formulations Using Puffed and Flaked Cereals " (Unpublished.)

Desikachar, H S.R., R. Shankara, N.G. Malleshi, M.N. Narayana, and S. Anand. 1980. "Milling of Cereal Grains in an Improved Plate Grinder." CFTRI Annual Report. CFTRI, Mysore.

Dulby, A., and C.Y. Tsai. 1976. "Lysine and Tryptophan Increases during Germination of Cereal Grains." Cereal Chemistry, 53: 222-224.

Haridas Rao, P., and S.R. Shurpalekar. 1976 "Use of Milo in Bakery Products." Journal of Food Science and Technology, 13: 293-295

McDivitt, M.E., and S.R Mudambi. 1969. Human Nutrition Principles end applications in India Prentice-Hall, Englewood Hills, N. J.

Malleshi, N.G., and H.S.R Desikachar 1981a. "Varietal Differences in Puffing Quality of Ragi (Eleusine coracana)." Journal of Food Science and Technology, 18: 30-32.

1981b. "Formulation of a Weaning Food with Low Hot Paste Viscosity Based on Malted Ragi (Eleusine coracana) and Green Gram (Phaseolus radiatus) " Journal of Food Science and Technology. (Accepted.)

Raghavendra Rao, S. N., and H.S.R. Desikachar. 1964. "Pearling as a Method of Refining Jowar and Wheat and Its Effect on Their Chemical Composition " Journal of Food Science and Technology, 1: 40-42 Raghavendra Rao, S.N., C.S. Viraktamath, and H.S.R. Desikachar. 1976 "Relative Cooking

Behaviour of Semolina from Maize, Sorghum, Wheat and Rice." Journal of Food Science and Technology, 13: 34-36.

Raghavendra Rao, S.N., N.G. Malleshi, S. Sreedhara Murthy, C.S. Viraktamath, and H.S.R. Desikachar. 1979. "Characteristics of Roti, Dosa and Vermicelli from Maize and Bajra." Journal of Food Science and Technology, 16: 21-24

Raghavendra Rao, S.N., S. Sreedhara Murthy, and H.S.R. Desikachar. 1981. "Effect of Heat Processing on the Paste Viscosity of Cereal Flours." Journal of Food Science and Technology. (Communicated.)

Rao, P.U. and B. Belavady. 1978. "Oliosaccharides in Pulses: Varietal Differences and Effects of Cooking and Germination. " Journal of Agricultural Food Chemistry, 26: 316 319.

Ram, P.C., M L. Lodha, K.N. Srivastava, R.S. Tyagi, Joginder Singh, and S.L. Mehta. 1979. "Improving Nutritive Value of Maize (Zea mays L) By Germination." Journal of Food Science and Technology, 16: 268-260.

Reddy, N.R., D.K. Salunkhe, and R.P. Sharma. 1980. "Flatulence in Rats Following Ingestion of Cooked and Germinated Black and a Fermented Product of Black Gram and Rice Blend " Journal of Food Science, 45: 1161-1164

Van Veen, A.G., and K.H. Steinkraus. 1970. "Nutritive Value and Wholesomeness of Fermented Foods." Journal of Agricultural and Food Chemistry, 18: 576-578.

Viraktamath, C.S., G. Raghavendra, and H.S.R. Desikachar. 1971 "Use of Milling Machinery for Commercial Pearling of Grain Sorghum (Jowar) and Culinary Uses for Pearled Sorghum

Products." Journal of Food Science and Technology, 8 11-13. . 1972. "Varietal Differences in Chemical Composition of Physical Properties and Culinary Qualities of Some Recently Developed Sorghum." Journal of Food Science and Technology, 9: 73-76

Wamajee, D.W. 1978. "Deteriorative Changes during Storage of Whole Maize Flour and Their Control " Thesis for M.Sc. (Food Technology) degree, University of Mysore. CFTRI, Mysore.

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