Protein Quality of Stored Dry Skim Milk With Standard and Lysine-Limiting Diets

Abstract

Changes in protein quality of dry skim milk stored under conditions where moisture uptake was not a factor were monitored by feeding trials with rats. After 1 yr of storage at 25 or 37C, no effects on nitrogen digestibility, protein efficiency ratio, or net protein ratio measured by standard procedures were attributable to storage time or temperature. However, when the skim milk samples were incorporated into diets limiting in lysine to study the effect of storage conditions on lysine bioavailability, relative nutritive value decreased by 8% in the sample stored 12 mo at 25C and by 8, 9, and 8% in samples stored for 3, 6, and 12 mo at 37C. Chemically available lysine determined by 2,4,6-trinitrobenzenesulfonic acid reagent showed similar small decreases in samples stored at 37C.