In Vitro and Mouse Evaluation of Methods for Protecting Whey Protein and Casein from Ruminal Degradation

A series of in vitro buffer (protein solubility) and rumen fermentation (ammonia production) studies were conducted to evaluate varying formaldehyde (.25, .5, 1, and 3%) and tannic acid (.5, 1, 2, 3, and 6%), and three heating times (1, 2, and 3 h at 104 C) on protection of whey protein concentrate and casein from ruminal degradation. Subsequent trials of mouse growth were conducted to evaluate the effectiveness of protection of treated proteins. Formaldehyde (.25 to 3%) reduced solubility of whey protein and casein to less than 10% of the untreated in pH 6.8 buffer and approximately 30% of the untreated in pH 2.5 buffer plus pepsin. Formaldehyde reduced ammonia production, indicating protection and reduced solubility of whey protein and casein under rumen conditions in vitro. Tannic acid (.5 to 6%) did not greatly reduce protein solubility and ammonia production. Heat treatment reduced protein solubility to less than 10% of the untreated in pH 6.8 buffer and to 50% of the untreated in pH 2.5 buffer and reduced ammonia production to approximately 20% of the untreated. Growth and feed intake of mice were decreased with 1% formaldehyde treated diets (17% protein), indicating overprotection of protein. Growth decreased as tannic acid increased. Mouse growth also decreased as the length of heat treatment increased. Diets with .5% formaldehydecasein depressed gains. Based on these in vitro and mouse-evaluation studies, formaldehyde less than .5% of the dry weight is required to protect whey protein and casein from ruminal degradation and permit solubilization in the lower intestinal tract.