Search

We examined the effects of lactic acid fermentation of soymilk on the lipid profile and lipid metabolism-related gene expression in rat liver. Male Sprague-Dawley rats aged 7 weeks were fed a control diet (AIN-93), soymilk diet, or fermented soymilk diet for 1 week or 5 weeks. The hepatic triglyceride and cholesterol contents in the soymilk (SM) group and the fermented soymilk (FSM) group were significantly lower than those in the control group after 5 weeks, but these changes had not become apparent until after 1 week. The fatty acid synthesis-related genes were more markedly down-regulated after 1 week than after 5 weeks, whereas the cytochrome p450 family 7 subfamily a polypeptide 1 (CYP7al) gene related to cholesterol catabolism was more markedly up-regulated after 5 weeks than after 1 week. This up-regulation was higher in the FSM group than in the SM group. It is assumed that the bioactive components produced by lactic acid fermentation induced the up-regulation of CYP7a1.

Polyamines, putrescine, spermidine and spermine, are important constituents of all mammalian cells and are essentially involved in a variety of regulatory step during normal and malignant cell proliferation. Okara and soymilk fermented with Lactobacillus were combined to form soy yogurt, which is rich in polyamine content. We investigated the effect of soy yogurt on polyamine levels in intestines and blood of rats. The ingestion of soy yogurt induced the increase of mucosal polyamine level in small intestine. Although the polyamine level in cecum was increased by the ingestion of soy yogurt, the polyamine levels in large intestine and blood were not increased. It was found that the ingestion of polyamine-rich soy yogurt could affect the polyamine level in only small intestinal mucosa. The large intestine seems to regulate the polyamine level to prevent own cells from hyperproliferation. It was assumed that blood kept polyamine level constant in spite of the level changes in intestines.

Soymilk-like white opaque liquid was prepared from whole soybean seeds without imbibition by the nama-shibori method. The solid content of the resulting liquid (non-imbibed soymilk) increased with an increase in blender revolutions and milling time, becoming almost equivalent to that of standard soymilk (imbibed soymilk) after milling at 12,000 rpm or more for 8 min. The precipitate obtained from the non-imbibed soymilk was lower than that from imbibed soymilk after milling for 4 min; however, it was higher after milling for 8 min. The non-imbibed soymilk showed bimodal particle size distribution, differing from imbibed soymilk prepared by milling at 12,000 rpm or less, which showed a unimodal distribution. The findings suggest that non-imbibed soymilk is of slightly lower quality than imbibed soymilk prepared from imbibed soybean seeds, but overall the differences were considered minimal.

We examined the effects of lactic acid fermented soymilk, in which part of the soymilk was replaced with okara (soy yogurt), on plasma and hepatic lipid profiles in rats fed a cholesterol-free diet. Additionally, we investigated the effects of soy yogurt on hepatic gene expression in rats using DNA microarray analysis. Male Sprague-Dawley rats aged 5 weeks (n=5/group) were fed a control diet (AIN-93) or a test diet in which 20% of the diet was replaced by soy yogurt for 7 weeks. Soy yogurt consumption did not affect body weight or adipose tissue weight as compared with control diet. In the soy yogurt group, the liver weight and hepatic triglyceride content were significantly lower than the control group, and the level of plasma cholesterol was also lower. Furthermore, DNA microarray analysis indicated that soy yogurt ingestion down-regulated the expression of the SREBP-1 gene and enzymes related to lipogenesis in the rat liver, while expression of beta-oxidation-related genes was up-regulated. These results suggest that soy yogurt is beneficial in preventing hepatic lipid accumulation in rats.

Soymilk was prepared by non-heated squeezing and then heated at various temperatures. For one-step heating, the precipitate produced by heating soymilk increased for heating at 70 and 80°C and was much less at 90°C or higher temperatures, showing that the dispersion stability of soymilk was dependent on the heating temperature. In the case of two-step heating (combinations of 115°C and a lower temperature), soymilk heated at 115°C in the first step and 70 or 80°C in the second step resulted in increased precipitation. Changes in protein surface hydrophobicity were considered to be related to the precipitate formation of soymilk heated at the two different temperatures, indicating the significance of heat denaturation and aggregate formation of proteins on the dispersion stability of soymilk.