Optimization of wheat flour enzymatic hydrolysis for lactobacillus rhamnosus submerged fermentation

Abstract

Cereals and by-products of its processing are known to be applied for lactic acid bacteria fermentation. Wheat grains containing starch, protein and a lot of growth factors seem to be the rich nutrient media for some types of microbes. On the other hand, the niglible number of lactobacilli can produce amylases and proteinases (for native gluten decomposition), so at least the partial hydrolysis of substances mentioned is needed. The complex processing of wheat flour with amylases and proteases was shown to increase the nutritional value of media obtained and the significant count of Lactobacillus of different species can be reached. In the industrial scale the rational consumption of raw materials is of interest. Therefore the central composite design was applied for optimization of enzyme:substrate ratio and substrate solid:solvent ratio for nutrient medium production and Lactobacillus rhamnosus fermentation. The whole-wheat flour was used as the only source of nutrient substances. Hydrolysis was carried out at two stage (amylases treatment followed by proteases treatment), and the solid residue was not separated before fermentation. The response surface equation obtained was statistical significant according to F-test. The optimal conditions determined were 2% of enzyme to substrate (wheat protein) ratio and 1:5 flour to water ratio. The final lactobacilli count predicated according the model at optimal pre-processing conditions was 9.14 log (CFU/ml) whereas the experimental data was some greater (9.3 log (CFU/ml). The bacterial growth and the rate of acidification in standard MRS medium and wheat hydrolysate medium were the same. Namely, the specific growth rate was about 0.40 L/h, the final lactobacilli count was about bout 9.3 log (CFU/ml) and the final pH of fermentation was about 4.0. So the wheat hydrolysate medium obtained contained all the substances needed for Lactobacillus fermentation compared with the rich MRS nutrient medium, composed of casein peptone, meat extract and yeast hydrolysate.