Relative Bioavailability of Riboflavin in Cows' Milk and Fermented Milk using Rat Bioassay

Bioavailability of riboflavin from cows' milk and fermented milk was assessed using riboflavin-depleted rats. The fermented milk was prepared using Lactococcus lactis subsp, lactis, and cremoris and Propionibacterium shermanii as starter cultures. Rats were depleted of riboflavin by feeding a riboflavin-free diet for 30 days. At this stage, hepatic riboflavin and erythrocyte glutathione reductase (EGR) activity decreased significantly (P < 0.05) while the activity coefficient (AC) on FAD addition increased sharply. Depleted rats were repleted for 15 days with 150, 300 or 450 mu g riboflavin from fermented milk, milk and pure vitamin. Total hepatic riboflavin and EGR activity increased significantly (P < 0.05) in all groups. The increase was significantly (P < 0.05) greater in the fermented milk and milk groups than in the pure riboflavin group. Significant positive correlations between total riboflavin intake and hepatic riboflavin (r = 0.97) and EGR activity (r = 0.96) were observed. Relative bioavailability (RBV), relative to pure vitamin, of riboflavin from milk and fermented milk was determined by slope ratio statistics using multiple linear regression with hepatic riboflavin, EGR activity and AC on FAD addition as response criteria. RBV for milk and fermented milk were 144 and 161% with hepatic riboflavin as a response criterion, 135 and 154% with EGR activity as a criterion and 116 and 125% with AC as a criterion. RBVs were significantly greater for milk and fermented milk than for the pure vitamin.