Study On Pretreatment And Enzymatic Hydrolysis And Saccharification Of Chinese Medicinal Herbal Residues

In recent years,with the rapid development of traditional Chinese medicine industry,the annual output of Chinese medicinal herbal residues(CMHRs)has also increased.CMHRs contain rich resource components such as cellulose,hemicellulose,lignin,and bioactive ingredients.Currently,the processing methods for CMHRs,such as stacking,incineration,and landfilling,not only pollute the environment but also result in the waste of various resource components.Therefore,the high-value utilization of CMHRs to achieve "turning waste into treasure" is an important embodiment of the "improving quality and efficiency,green development" circular economy concept.In this paper,several common and representative types of medicinal residues were selected for in-depth research on their enzymatic hydrolysis and saccharification,and the following conclusions were obtained:(1)Available literature on CMHRs bioconversion highlights pretreatment prior to saccharification with cellulase without considering the presence of starch constituent.Herein,four commonly found CMHRs(Glycyrrhizae Radix et Rhizoma,Radix Astragali,Magnoliae Officinalis Cortex,Scutellariae Radix)were tested for starch content,and it was found that they all contained starch with content ranging from 4.74% to 16.78%.Hydrolysis of raw CMHRs with combined cellulase and amylolytic enzymes yielded increments of 16.85% to26.51% in 48-h glucan conversion compared to cellulase alone.Further study showed 48-h glucan conversion of raw CMHRs outperformed that pretreated by water-ethanol successive extraction,ultrasound and acid,but underperformed alkali-pretreated CMHRs.Although 48-h glucan conversion increased in the range of 7.40% to 24.10% compared to raw CMHRs,alkaline pretreatment demonstrated low glucose recovery and incurred additional cost,making it unfavorable.Saccharification of the four raw CMHRs with combined enzymes seems like a preferred option considering the elimination of high-cost pretreatment step.(2)In the actual biological conversion process,not only a high glucan conversion is required,but also the glucose concentration in the enzymatic hydrolysate should reach a sufficiently high level.Herein,three CMHRs(Isatidis Radix,Sophorae Flavescentis Radix,Ginseng Radix)which contained high starch contents(26.36%-63.29%)were used in batch and fed-batch enzymatic hydrolysis for production of high-concentration glucose.Due to their high starch content,combined cellulase and amylolytic enzymes resulted in more glucose release from the raw CMHRs than either enzyme.Batch enzymatic hydrolysis of10%(w/v)raw CMHRs with low loadings of cellulase(≤10 FPU/g substrate)and amylolytic enzymes(≤5.0 mg/g substrate)offered a high glucan conversion of ≥70%.Addition of PEG6000 and Tween 80 did not have much influence on glucose production.Furthermore,to attain a higher concentration of glucose,fed-batch enzymatic hydrolysis was performed to achieve a total 30%(w/v)solids loading.Glucose concentrations of 125 g/L and 92 g/L were obtained after 48 h hydrolysis of residues of Isatidis Radix(IR)and Sophorae Flavescentis Radix(SFR),respectively,and 83 g/L after 96 h digestion of Ginseng Radix(GR).The high glucose concentration produced from these raw CMHRs suggests that they can serve as ideal substrates for a profitable biorefinery with the obvious advantage of eliminating pretreatment operation compared to commonly investigated agricultural and woody biomass.