Factors Affecting the Protein Quality of Yogurt and Acidophilus Milk

Abstract

The apparent protein digestibility in vivo, the protein digestibility in vitro, the net protein ratio, and computed protein efficiency ratio were used to assess the protein quality of yogurt and acidophilus milk as affected by heat treatment, direct acidification, addition of culture, or fermentation. Rats fed diets containing either heated mix or yogurt tended to eat more and gain more weight than rats fed diets containing either unheated mix or the acidified yogurt. Feed efficiency was also significantly higher for rats fed heated mix and yogurt. The apparent protein digestibility in vivo was significantly higher in yogurt diet than in the unheated yogurt mix diet. The net protein ratio of the yogurt diet was significantly higher than that of either the unheated mix or the acidified yogurt but not significantly different from the heated mix. The computed protein efficiency ratio values were also increased with both heating and fermentation. The direct acidified yogurt had a significantly lower net protein ratio and lower computed protein efficiency ratio than the fermented yogurt. Rats fed either sweet acidophilus (unfermented) or acidophilus milk exhibited a significantly higher protein digestibility than rats fed heated milk, indicating that the lactic culture may have a direct effect on protein digestibility. Despite their increased protein digestibilities, the acidophilus products did not display any significant increase in net protein ratio or computed protein efficiency ratio. © 1988, American Dairy Science Association. All rights reserved.