Beneficial Effects of Dietary Tempeh Prepared with Rhizopus stolonifer on Liver Function in Rats Fed with a High-Fat Diet.

The regional standard for tempeh established by the Codex Alimentarius defines the use of Rhizopus oligosporus, R. oryzae, and/or R. stolonifer as soybean tempeh starters. However, comparative studies on the functions of tempeh prepared with these Rhizopus species are scarce. In the present study, we examined the effects of dietary tempeh prepared with these three Rhizopus species using rats fed with a high-fat diet. Compared to the control diet, consumption of tempeh prepared with R. stolonifer significantly suppressed serum levels of aspartate transaminase, total bilirubin, and ammonium (indices of liver function). However, less or no suppression was observed with tempeh prepared with R. oligosporus or R. oryzae. Serum levels of triglyceride, total cholesterol, HDL cholesterol, and glucose were unaffected. Liver levels of free cholesterol, a parameter relating to liver injury, were significantly decreased by the three types of the tempeh examined; however, there was no difference in the free cholesterol levels among the tempeh groups. We conclude that the ingestion of tempeh prepared with R. stolonifer might have beneficial effects pertaining to the liver function in rats fed with high-fat diets.

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.