Electrophoresis to determine the molecular weight distribution in soluble proteins from various foods and their rumen-resistant residues in cattle

Electrophoresis was used to visually identify and determine the molecular w eight (MW) distribution of rumen-degradable and rumen-resistant or escape p eptides in soluble proteins from 12 agricultural and distillers' food raw m aterials (RM) and their residues (RU) following 18 h of in sacco rumen incu bation (dg(18)) in cattle. Soluble proteins were extracted by using water, salt, acid and alkali in succession to represent albumins, globulins, gluta lin I and glutalin 2 respectively. RM and RU differed substantially in the MW range, number and intensity of bands for various soluble proteins. The b ands were mostly below the MW range of 66 kDa. Low-MW (< 25 kDa) peptides w ere greater in number than high-MW (> 25 kDa) peptides in almost all solubl e proteins from RM. Individual peptides behaved differently during rumen in cubation. Their resistance to or escape from rumen degradation varied with the class of food, type of soluble protein and their MW range. On average, low-MW albumins in agricultural foods were more resistant to rumen degradat ion (0.41 RM vs 0.12 RU; 29%) than their high-MW counterparts (0.12 RM vs 0 .02 RU; 21%). In contrast, high-MW glutalin I was more resistant (0.03 RM v s 0.22 RU) than low-MW glutalin 1 (0.09 RM vs 0.26 RU) in most agricultural foods. Globulins contained the least and glutalins the most resistant pept ides in distillers' foods. While this study reveals an association between dg(18) and protein type, structure and size, we do not recommend the immedi ate use of electrophoresis for routine food evaluation unless more studies are undertaken. It may, however, be suitable for further characterisation o f the degradation of specific, selected peptides by specific micro-organism s. (C) 2001 Society of Chemical Industry.