Enhanced Solid State Fermentation For Laccase Production Through NaOH Pretreatment Rice Straw

Solid state fermentation(SSF)is an attractively economic strategy for laccase production,yet its efficiency is low.Pretreatment of solid substrate might be a desirable breakpoint to solve this problem.In this study,alkaline pretreatment using Na OH as an active reagent was involved to prepare solid substrate from rice straw.In order to clarify the mechanism of pretreatment,the fermentability of solid substrate was evaluated.Mycelia growth and distribution,laccase production and distribution,water content and nutrient utilization were investigated.The main results were stated as follows:(1)The pretreated rice straw exhibited prominent fermentability.After pretreatment,the cellulose content,in vitro enzymatic digestibility,and cellulose accessibility increased to 66.78%,66.78%,and 375.29 mg/g,respectively.The water retention values of solid substrates were observably higher than that of the CK,which increased from 101.73% to 339.17%.(2)Pretreatment destroyed the rigid structure of solid substrate.The pretreated solid substrates were reduced,whitened from dark yellow and twined after drying.Notably,the surface became visually rough and porous.After pretreatment,the intact structure of tissue was diminished.And the basic structure,air gap,epidermis and vascular bundle were seriously damaged.(3)The solid substrates with different pretreatment conditions all gave higher laccase production than the CK.The maximum laccase production of2912.34 U/g was obtained from the pretreated rice straw(1 h)with diameter less than 0.085 cm,which was 7.72 times higher than that of the control with the similar size.(4)Mycelium could grow into the inner and intertwine with the pretreated solid substrate,indicating that F.trogii penetrated into the inner space to get more nutrients.In addition,sufficient balance analysis between nutrition accessibility and structure support of solid substrate must be conducted before SSF with various process requirements.In conclusion,alkaline pretreatment provided desirable solid substrates with higher enzymatic digestibility and optimal water retention value,which further facilitated the homogeneity of mycelium growth,laccase distribution and nutrition utilization during SSF.