Novel optimization strategy for tannase production through a modified solid-state fermentation system

Changzheng Wu,Feng Zhang,Lijun Li,Zhedong Jiang,Anfeng Xiao,Hui Ni

doi:10.1186/s13068-018-1093-0

Abstract

BackgroundHigh amounts of insoluble substrates exist in the traditional solid-state fermentation (SSF) system. The presence of these substrates complicates the determination of microbial biomass. Thus, enzyme activity is used as the sole index for the optimization of the traditional SSF system, and the relationship between microbial growth and enzyme synthesis is always ignored. This study was conducted to address this deficiency. All soluble nutrients from tea stalk were extracted using water. The aqueous extract was then mixed with polyurethane sponge to establish a modified SSF system, which was then used to conduct tannase production. With this system, biomass, enzyme activity, and enzyme productivity could be measured rationally and accurately. Thus, the association between biomass and enzyme activity could be easily identified, and the shortcomings of traditional SSF could be addressed.ResultsDifferent carbon and nitrogen sources exerted different effects on microbial growth and enzyme production. Single-factor experiments showed that glucose and yeast extract greatly improved microbial biomass accumulation and that tannin and (NH4)2SO4 efficiently promoted enzyme productivity. Then, these four factors were optimized through response surface methodology. Tannase activity reached 19.22 U/gds when the added amounts of tannin, glucose, (NH4)2SO4, and yeast extract were 7.49, 8.11, 9.26, and 2.25%, respectively. Tannase activity under the optimized process conditions was 6.36 times higher than that under the initial process conditions. The optimized parameters were directly applied to the traditional tea stalk SSF system. Tannase activity reached 245 U/gds, which is 2.9 times higher than our previously reported value.ConclusionsIn this study, a modified SSF system was established to address the shortcomings of the traditional SSF system. Analysis revealed that enzymatic activity and microbial biomass are closely related, and different carbon and nitrogen sources have different effects on microbial growth and enzyme production. The maximal tannase activity was obtained under the optimal combination of nutrient sources that enhances cell growth and tannase accumulation. Moreover, tannase production through the traditional tea stalk SSF was markedly improved when the optimized parameters were applied. This work provides an innovative approach to bioproduction research through SSF.

Highlights

High amounts of insoluble substrates exist in the traditional solid-state fermentation (SSF) system
In SSF, tannase activity is expressed in terms of extracellular protein levels, whereas in submerged liquid fermentation (SLF), tannase activity is expressed in terms of intracellular activity [16, 19]
scanning electron microscopy (SEM) analysis of the internal structures of Polyurethane sponge (PUS) and morphological characteristics of microorganisms The PUS used in this experiment had a density of 40 kg/ m3, open-hole diameter of 300–500 μm, and specific surface area of 380.6 m2/g

Summary

Introduction

High amounts of insoluble substrates exist in the traditional solid-state fermentation (SSF) system. The presence of these substrates complicates the determination of microbial biomass. The aqueous extract was mixed with polyurethane sponge to establish a modified SSF system, which was used to conduct tannase production. With this system, biomass, enzyme activity, and enzyme productivity could be measured rationally and accurately. SSF is the preferred method for tannase production because of its lower cost, lower water consumption, easier operation, and higher enzyme activity than SLF [16,17,18]. In SSF, tannase activity is expressed in terms of extracellular protein levels, whereas in SLF, tannase activity is expressed in terms of intracellular activity [16, 19]

Methods

Results

Discussion

Conclusion