Identification of a thermophilic protease‐producing strain and its application in solid‐state fermentation of soybean meal

Abstract

BACKGROUND: Thermophiles can thrive at 50-80 °C and produce some enzymes with special promise for biocatalysis. A thermophilic protease-producing strain YYC4 was isolated from Yunyan cigarette and employed in solid-state fermentation (SSF) of unsterilized soybean meal (SBM). RESULTS:The isolate was identified as Bacillus licheniformis based on appearance of colonies, microscopic observation and 16S rDNA sequencing. After SSF, soluble and crude protein contents in SBM increased from 49.24 to 185.73 g kg −1 and from 404.18 to 479.46 g kg −1 , respectively, under the fermentation conditions of 10 7 cfu g −1 inoculation of strain YYC4, 1:1.8 (g mL −1 ) SBM to distilled water, 1.2 g kg −1 magnesium sulphate addition, 55 °C and 48 h. During fermentation, pH of the medium increased from 6.30 to 9.09 and protease activity especially neutral protease increased significantly from 13.5 to 181.31 U g −1 . Meanwhile, trypsin inhibitor (TI) activity was decreased from 8.19 to 3.19 mg g −1 . The safety of fermented SBM (FSBM) was verified by acute toxicity animal experiment. Analysis of microbial community in FSBM showed that Bacillus licheniformis YYC4 as a dominant strain inhibited most of the other microorganisms pre-existing in the materials during fermentation.CONCLUSION: Increments of soluble and crude protein by 277.19% and 18.63% and decrement of harmful TI by 61.05% in SBM were achieved using thermophilic SSF by Bacillus licheniformis YYC4, providing a basis for the application of thermophiles in fermentation industry in an environmentally friendly and energy-saving way.

Effect of Bacillus subtilis and Lactobacillus plantarum on solid‐state fermentation of soybean meal

“…However, MC fermented with both L. plantarum and B. subtilis had a higher final pH value than those with single bacterium starter. It was previously reported that the ammonification and mineralization of organic nitrogen via microbial activity promoted the increase in pH value 2 . Therefore, MC with the highest protease activity had a higher pH value than the other treatments.…”

“…Thus, the high yield of FAA was probably produced by protease, which was secreted by increasing the amount of bacterium. The application of a protease‐producing strain in FSBM could increase the FAA content 2 . It was concluded that microbes in MC could produce more protease, leading to the increase in the relative content of FAA 24,25 .…”

“…However, studies have shown that the existence of antinutritional factors has a negative impact on the feed conversion ratio 1 . The high contents of crude fiber and phytic acid lead to low efficiency of utilization of soybean meal (SBM) 2,3 …”

“…Solid fermentation is a reliable method of feed production, which could efficiently eliminate harmful elements under low cost and mild reaction conditions 4 . In the fermentation process, the macromolecular protein could transform to a low molecular protein and release free amino acid (FAA) 2,4 . Meanwhile, the crude fiber and phytic acid could be degraded to nutritious compounds.…”

Characterization of redox and salinity-tolerant alkaline protease from Bacillus halotolerans strain DS5

“…During the last few years, many extreme enzymes have been studied, including thermophilic ( Dai et al, 2022 ), psychrophilic ( Santiago et al, 2016 ), acidophilic ( Parashar and Satyanarayana, 2018 ), alkalophilic ( Ito et al, 1998 ), halophilic ( Mokashe et al, 2018 ), radiophilic, and barophilic enzymes ( Raddadi et al, 2015 ), but the number of extreme enzymes is currently insufficient to meet growing industrial demands ( Mesbah, 2022 ). Halophilic microorganisms have natural advantages in protease production, and many new extreme enzymes can be developed.…”