Accelerated Proteolysis of Soy Proteins During Fermentation of Thua-Nao Inoculated With Bacillus Subtilis

Abstract

Thua-nao is a traditional Thai-fermented soy product. It was prepared by the conventional method and also with starter inoculation. Inoculated soybean exhibited a higher rate of fermentation than did the natural fermentation as indicated by greater rate of pH increase, higher extent of proteolysis, ammonia-nitrogen content and nitrogen solubility. Sodium dodecyl sulfatepolyacrylamide gel electrophoresis patterns indicated the extensive degradation of soy proteins during fermentation. Activity staining of Thua-nao extract suggested that proteolysis of soybean was mediated by various proteinases. Active proteinases with estimated molecular weight (MW) of 29,000, 27,000 and 19,000 Da were present during natural fermentation of soybeans. However, proteinases with MW of 40,000 and 29,000 Da were predominant in inoculated soybeans and like the activity bands observed with spent culture broth of Bacillus subtilis BIOTEC 7123. The results suggested that proteinases released by the dominant species in the inoculum, especially B. subtilis , play an important role in proteolysis of soy proteins during fermentation. Inoculation with B. subtilis resulted in an increased proteolysis, which is useful for subsequent reactions leading to development of Thua-nao characteristics.

Optimising fermentation of soymilk with probiotic bacteria

“…lactis Bb12 was performed at 42°C. Both fermentations were conducted until reaching pH 4.6, which is the proximate isoelectrical point of soy proteins (Vissesanguan et al 2005;Božanić 2006). The samples were cooled and stored for 28 days in a refrigerator at the temperature of 4°C.…”

Fatty acid profiles of fermented soybean prepared by Bacillus subtilis and Rhizopus oligosporus

“…Due to the protein-rich nature of soy, proteolysis is typically considered as a key process of soybean fermentation, which has been studied by many researchers (Omafuvbe et al 2000;Visessanguan et al 2005;Hu et al 2010). In contrast, lipolysis has not gained much attention, although the soybean substrate is composed of around 20% of fat.…”

Characterization of Bacillus species exhibiting strong proteolytic activity isolated from Thua Nao

“…It is evident that these proteaseproducing bacteria can be used as a pure starter culture, thereby improving the manufacturing process and nutritive quality of the fermented soybean products. For example, the use of Bacillus pure starter culture accelerated protein hydrolysis, and hence increased the amount of dialyzable proteins in Kinema (KIERS et al, 2000) and Thua Nao (VISESSANGUAN et al, 2005).…”

“…Such proteolysis could enhance the nutritional value of the fermented products. Screening and isolation of protease-producing bacteria from these fermented products are therefore of great interest and are subject to comprehensive study by many scientists (CHANTAWANNAKUL et al, 2002;VISESSANGUAN et al, 2005;DAJANTA et al, 2009). It is evident that these proteaseproducing bacteria can be used as a pure starter culture, thereby improving the manufacturing process and nutritive quality of the fermented soybean products.…”

“…Soy protein degradation contributes to distinct characteristics of these fermented soybeans including texture, appearance, fl avour, and aroma. As a result, these Bacillus strains are hot topics for many scientists studying these fermented soybeans by screening for their proteolytic activity (CHANTAWANNAKUL et al, 2002;VISESSANGUAN et al, 2005;DAJANTA et al, 2009). It is also expected that those Bacillus isolates exhibiting a strong proteolytic activity could be used as inoculum, and this thus helps improving the manufacturing process and products.…”