Abstract
As the traditional homemade chungkookjang is replaced by standardized chungkookjang fermented by inoculating Bacillus spp., it is desirable to maintain the anti-diabetic efficacy of the most potent traditional varieties. Preliminary in vitro research suggested that anti-diabetic efficacy can be achieved by using B. lichemiformis as a starter and fermenting for 48 h. Experimental type 2 diabetic male rats induced by partial pancreatectomy and high fat diets were administered either control diet, 10% cooked soybeans, 10% traditional chungkookjang with potent anti-diabetic efficacy, or standardized chungkookjang fermented with B. lichemiformis for 48 h. Rats were fed their respective diets for 8 weeks after surgery. Cooked soybeans as well as both chungkookjangs partially restored fasting serum glucose concentrations, but only the chungkoojangs increased fasting insulin levels. That trend was also seen in the glucose-stimulated insulin secretion during hyperglycemic clamp and was explained by the greater β-cell mass and BrdU incorporation indicating increased proliferation of β-cells. The euglycemic hyperinsulinemic clamp indicated that all soy products improved insulin sensitivity. Phosphorylation of Akt and AMPK in the liver increased in an ascending order of the control, cooked soybeans, traditional chungkookjang and standardized chungkookjang while PEPCK expression was lowered in a descending order of the control, cooked soybeans, traditional chungkookjang and standardized chungkookjang. These results indicate that standardized chungkookjang is most effective for improving hepatic insulin signaling. In conclusion, chungkookjang fermented with B. lichemiformis retains the anti-diabetic properties of the most efficacious traditional chungkookjang and it may be even more effective for improving insulin function than traditionally prepared chungkookjang.