Consumption of an acid protease derived from Aspergillus oryzae causes bifidogenic effect in rats

A marked elevation in the abundance of Bifidobacterium was found in the cecum of rats that were fed a high-fat diet supplemented with an Amano protease preparation (derived from Aspergillus oryzae). The protease preparation contains several digestive enzymes, including acid protease (AcP), alkaline protease, and amylase. We hypothesized that the elevation in the abundance of Bifidobacterium by Amano protease preparation is associated with the digestive enzymes involved in the protease preparation. To test this hypothesis, this study was conducted to investigate if such bifidogenic effect is because of the AcP. Rats were fed a high-fat diet containing purified AcP obtained from the Amano protease preparation for 2 weeks. The numbers of Bifidobacterium in the cecum and feces of rats were markedly elevated by the dietary supplementation of 1 g/kg Amano protease. Bifidobacterium numbers were unaffected by supplementation with purified AcP (0.096 g/kg) at the level equivalent to the AcP amount found in the 1-g/kg Amano protease diet. Bifidobacterium numbers in the cecum and feces, and lactate levels in the cecum were significantly (P<.05) elevated when rats were fed a diet containing 0.384 g/kg AcP (4-fold higher amount of AcP than that used in the 1-g/kg Amano protease diet). Thus, the bifidogenic effect of 1 g/kg Amano protease diet could not be explained by the AcP. However, intriguingly, supplemental AcP was found to cause a significant bifidogenic effect at the dose that is 4-fold higher than that used in the 1-g/kg Amano protease diet.