Influence of tannins on the protein nutritional quality of food grains

Abstract

Shinjefd, Reading RG2 @TTannins are widely present in higher plants, and their presence in some food grains may significantly impair the nutritional quality. Thus for example, in coloured-flowered varieties of field beans (Vicia fuba L.) the seeds are rich in condensed tannins and their inclusion in the diet of single-stomached animals has been reported to depress the apparent digestibility of the protein (cf. MartinTanguy et af. 1977; Ronnenkamp, 1977). Similarly in sorghum grain (Sorghum vulgare Pers.) the protein quality in some genotypes is severely limited by the high level of tannins in the testa, and different varieties exhibit wide differences in digestibility that reflect corresponding differences in tannin content.The presence of tannins complicates the interpretation of amino acid analysis and other compositional information in terms of nutritional quality. We need to take the digestibility of the amino acids into account in our tests, and there are several microbiological assay methods that are very promising for this purpose and are potentially of great value to the plant breeder in guiding the selection of improved food grains. Compared with animal feeding tests they are quick and precise, and much more economical of test materials. Of these methods, the Streptococcus zymogenes assays for available methionine and for relative nutritional value (RNV) have been extensively tested with a variety of high-protein feedstuffs and with rice ( 0 7 y Z U sutiva L.), sorghum, barley and field beans (Ford & Hewitt, 1979a,b,c). Table I shows the results of amino acid digestibility tests with chicks on ten sorghum varieties of graded tannin content, and for comparison the results of microbiological tests and values for dye-binding lysine. The chick assay values for 'average amino acid digestibility' were negatively correlated (7-0.82 ; P < o . o I ) with tannin content, as were the microbiological assay values for available methionine (~-0 . 9 5 ; P < O . O O I ) and for RNV (~-0 . 9 7 ; P<o.ooI). By contrast, the total methionine content varied little between varieties. The same was true for the dye-binding lysine values, which for these samples were clearly a fair measure of the total lysine present. They gave no indication of the differences in lysine digestibility that were found in chick tests.In similar tests on field beans we compared seed of twenty-two varieties, eleven white-flowered and eleven coloured-flowered. We assayed them with Strep. zymogenes for total and available methionine and RNV, and also for dye-binding lysine and tannin content.As a group, the white-flowered varieties were richer in available methionine than the coloured (P<o.oo I ) , though the differences were much less pronounced than those between high-and low-tannin sorghums. Mean values for the two groups were (g/kg protein; + s n ) 6 . 8 o t o . 4 6 and 6 . 2 7 + 0 . 5 1 . Mean RNV ratings also were available at https://www.cambridge.org/core/terms. https://doi

Effect of processing on the protein nutritional value of Canavalia gladiata seeds

“…Since the limiting amino acids are also highly susceptible to heat, a lower BV can result. The presence of tannins in other legumes have been reported as a cause of low digestibility and BV [40,41]. The digestibility values reported for many other cooked legumes [42] are comparable with those of processed sword beans in our study and as reported previously.…”

Cumin seed meal with enzyme and polyethylene glycol as an alternative to wheat bran in broiler diets

“…Adding PEG to high tannin diets, to which the tannins bind more strongly than to proteins and other macromolecules, spares dietary nutrients so that they are digested and absorbed more effectively. Thus PEG might significantly reduce the adverse effects of tannins on the performance of animals and enhance their FI and FCRs 36–38, 42–45…”

Effects of Storage on Protein Nutritional Quality of Grain Legumes

“…The lowest values for apparent and true crude protein di- Amino acid score Uncorrected 60 74 84 81 73 82 59 Corrected 46 57 69 59 62 68 49 Lys-Met-Cys score Uncorrected 97 100 100 100 100 100 100 Corrected 81 89 88 82 99 100 89 Lys-Met-Cys-Trp score Uncorrected 92 100 100 100 100 100 100 Corrected 77 86 86 79 97 100 85 Lys-Met-Cys-Trp-Thr score Uncorrected 95 100 100 100 100 100 100 Corrected 79 85 92 83 98 100 86 a Corrected for true digestibility of crude protein. Lys = lysine, Met= methionine, Cys = cystine, Trp = tryptophan, Thr=threonine (Table 2) were obtained for black beans, likely reflecting higher tannin or higher residual concentrations of antinutritional factors (Hewitt and Ford, 1982;Sotelo and Hernandez, 1980). The changes in true protein digestibilities and in RNPR over the three years of storage (Table 3) were considered of little practical significance.…”