| dc.description.abstract | The thesis entitled “Studies on the Amino Acid Composition and Nutritive Value of Some Indian Foodstuffs” presents the following pieces of research work carried out by the candidate:
Standardisation of the microbiological methods of assay of the ten essential amino acids;
Estimation of the essential amino acids in different varieties of some Indian cereals;
Correlation of the essential amino acid composition of the cereals with their nutritive value as found by animal experiments;
Standardisation of the microbiological assay methods for some non-essential amino acids and studies on the nutritive value of some milk products which are widely consumed in India (viz.) curds, khoa, channa and kheer.
An introduction to the development of knowledge concerning the chemistry and nutritive role of the amino acids with the necessary background information on the subject of the analytical methods for the determination of amino acids in foods has been provided to enable an appreciation of the work presented in the thesis. The need for further investigation of the amino acid composition of Indian foodstuffs as a means of assessing the nutritive value of their proteins and the element of varietal difference as a factor in determining the nutritive value of foodstuffs have been brought out. Earlier work on the development of microbiological methods for the assay of amino acids in food proteins has been reviewed.
The aims of the investigations carried out and scope of the present work are presented in brief.
A total of eighteen samples consisting of six varieties of rice, six of jowar, three of ragi, two of bajra and one of wheat has been analysed for the essential amino acids. Detailed description of the samples and analytical figures for moisture, ash and total nitrogen of the samples are given.
The standardisation of the methods used in the assay and data for the reliability of the values obtained as tested by the following criteria are presented in detail: reproducibility of assay values; agreement with values of other workers; recovery of added amino acid; agreement of values obtained from different levels of hydrolysate and avoidance of ‘drift’ in the assays. The following ten essential amino acids were analysed with the test organisms noted against them:
Amino acids assayed – Organism employed
Tryptophan, leucine, isoleucine, valine – Lactobacillus arabinosus 17-6
Lysine, methionine, phenylalanine, histidine – Leuconostoc mesenteroides P-60
Threonine and arginine – Streptococcus faecalis R.
A small lag section was observed in the standard curves for threonine and the possible causes like imbalance in the arginine-threonine ratio in the basal medium are discussed. An improvement in the basal medium for the assay of threonine has been effected to get a higher acid production.
Data on the essential amino acid content of cereals indicate that some cereal proteins like those of bajra are superior to good quality animal proteins like egg in their tryptophan content, and the proteins of jowar contain ample amounts of leucine. The reliability of the methods was checked by the analysis for some standard proteins like casein and egg for lysine and methionine. The total proteins from two samples of rice and bajra were isolated and analysed for lysine and methionine and compared with the values obtained for the whole foodstuffs and the divergence in values from the two procedures suggests the adoption of the amino acid analysis of the whole foodstuff to gain a true picture of the amino acid content of food proteins. An incidental observation on the loss of lysine in some cereal flours on storage records an overall decline of 20 per cent of the original amount in the course of ten months. Varietal difference appears to exert a profound influence on the amino acid composition of the cereal proteins and this has been discussed.
On the basis of the hypothesis of Block and Mitchell on the correlation of the nutritive value of proteins with their essential amino acid composition, the data obtained in the present experiments have been correlated to the nutritive value of the cereal proteins. The limiting essential amino acid in the case of all the cereal samples was found to be lysine and in one sample of ragi, it was found to be phenylalanine. Data for the biological value calculated on the basis of the amino acid figures were lower compared to the values found by balance sheet method while data for the protein efficiency ratio on the basis of the amino acid figures were higher compared to the values found by growth method and these have been discussed.
The relevant literature on the growth of the subject on the assay and nutritional importance of the so-called non-essential amino acids has been covered and the assay of the following non-essential amino acids using the organisms noted against them has been successfully carried out:
Amino acids assayed – Organism employed
Cystine, tyrosine, serine, aspartic acid and proline – Leuconostoc mesenteroides P-60
Glutamic acid – Streptococcus faecalis R.
A simultaneous examination of the degree of hydrolysis and the extent of the liberation of cystine during acid hydrolysis of some proteins was made and it was found that 2–3 hour hydrolysis using 2.6 N hydrochloric acid gave the optimum results. No glutamine was found necessary to be added to the basal medium to avoid the lag section in the standard curves for glutamic acid. The assay of glycine and alanine using Leuconostoc mesenteroides P-60 and Leuconostoc citrovorus was attempted but was not successful.
Paucity of information on the nutritive value of some indigenous milk products like khoa, dahi, channa and kheer and the need for such investigation have been emphasised. Planning of the present work on the nutritive value of indigenous milk products in the light of the earlier work on the subject has been dealt with.
The nutritive value of the various milk products listed above and boiled milk which is the form in which milk is ordinarily consumed in India have been investigated under the following heads:
(a) Analysis for fat, protein, minerals, moisture etc., and the vitamins thiamine, riboflavin, nicotinic acid, ascorbic acid and vitamin A.
(b) Growth of rats when fed milk or milk products derived from an equivalent quantity of milk as the sole diet.
(c) Survival rate and fertility studies on rats.
(d) Supplementary value to a poor rice diet.
The results indicate that there is a varying degree of lowering in nutritive value in the case of channa and khoa on the basis of the various studies but milk always ranks first in the list.
The preparation of the indigenous dairy products is described. | |
