Study On Mechanism Of Recalcitrance To Celluase And Utilization Technology Of Potato Pulp

Potato pulp is a low-efficiently utilized solid waste mainly produced from the starch extraction step of potato starch manufacturing industry and potato flour industry with considerable quantities more than 5 million tons per year.It primarily contains water and starch,as well as cell-wall polysaccharides which mainly comprise cellulose,hemicellulose and pectin.Compared with other agricultural waste resources such as corn stalk,wheat straw and rice straw,the existing utilization technology can not match the development of China's potato processing industry,leading to low conversion efficiency of potato pulp.The lack of theoretical research on the effect of composition and structure of potato pulp on the adsorption of cellulase to substrate limits the development of technologies related to pretreatment of substrate,optimization of enzymatic hydrolysis and innovation of new conversion methods.This paper focuses on the characteristic substrate information which benefits hydrolysis procedure most,and analyze the inhibition effect of other non-cellulosic components on the effective adsorption of enzymes on substrates.The results will not only greatly contribute to saccharification utilization of lignocelluloses from root and tuber crops,but also help to solve environmental pollution problems and facilitate the development of related industries.The main results are summarized below:?1?Cellulose with purity more than 80%?m/m?was extracted from potato pulp by a combined alkali and sodium sulfite treatment.Its physicochemical properties were characterized and compared with cellulose from corn stalk.The results showed that with the removal of non-cellulosic components,the enzymatic hydrolysis efficiency of the samples increased significantly.The enzymatic hydrolysis efficiency of cellulose from potato pulp was enhanced by 29.33%and 18.94%respectively compared with de-starched potato pulp and alkali treated potato pulp at 48 h.Compared with corn stover cellulose,the enzymatic hydrolysis efficiency of cellulose from potato pulp increased slightly at 48 h,but it was more efficient in the initial stage of enzymatic hydrolysis,and degraded more than 50%?m/m?of substrate after8 h of treatment which was improved by 25.90%than that of corn stalk cellulose.Maximum adsorption capacity(W_max)and equilibrium constant?K?were obtained by fitting the adsorption data with the Langmuir adsorption isotherm,suggesting that cellulose from potato pulp had the highest cellulase adsorption efficiency.Cellulose from potato pulp had more loosened and porous structure,lower crystallinity index and larger specific surface area?SSA?compared with cellulose from corn stalk and other pretreated samples,which was the main reason why potato pulp cellulose had better cellulase adsorption capacity and higher enzymatic efficiency.?2?Pectinase was used to hydrolyze pectin components contained in potato pulp to enhance the enzymatic hydrolysis efficiency of the substrate.The enzymatic hydrolysis efficiencies at12 h and 48 h were increased by 30.68%and 23.35%respectively for samples treated with 5.0U/g pectinase.Studies on the physicochemical properties of samples treated with different amounts of pectinase showed that pectinase treatment could make the substrate exhibit a more obvious layered distribution structure,significantly improve the porosity and specific surface area?SSA?of the substrate,and thus enhanced the accessibility of substrate to enzyme.SSA and enzyme adsorption of samples treated by 5.0 U/g pectinase was improved by 47.16%and21.15%respectively.Microscale themophoresis,confocal laser raman microscopy and other leading analytical methods were applied to study the mechanism of inhibition effect of pectin on the enzymatic hydrolysis of cellulose in potato pulp.The results showed that the pectin dissolved in the system had no significant inhibition and adsorption effect on cellulase.However,the insoluble pectin had a certain adsorption effect on cellulase,and the pectin attached to the cellulose surface acted as a physical barrier to prevent cellulase adsorption behavior to substrate.By treated with a lower amount of pectinase,insoluble pectin in the system and pectin attached to substrate could be efficiently hydrolyzed,alleviating the competitive adsorption and physical barrier effect.With the help of push off and peeled off force caused by the enrichment of cellulase on cellulose segments,the sporadically distributed pectin could fall off the substrate,thereby achieving high enzymatic hydrolysis efficiency.?3?Based on the fact that potato pulp cellulose is easy to be hydrolyzed and removal of pectin can significantly enhance the hydrolysis efficiency,cellulase,pectinase and combined use of them were used to prepare soluble dietary fiber?SDF?.The results showed that potato pulp SDF was efficiently prepared by pectinase-assisted cellulase treatment.Under the lower pectinase dosage?2.5 U/g?,the yield of SDF could reach 41.56%?m/m?,which was enhanced by more than 28%compared with SDF prepared by single cellulase treatment.The addition of pectinase could also significantly reduce the viscosity of the filtrate,helping to improve the efficiency of filtration and operation.Physicochemical and functional properties of different potato pulp SDF samples and commercially available SDF products showed that the main components of potato pulp SDF were?-glucan and hydrolysates from pectin,which were characterized with good solubility.Compared with commercially available SDF,potato pulp SDF had a larger molecular weight,system viscosity and better functional properties.Among three potato pulp SDF samples,SDF prepared by combined enzyme treatment had the best free radical scavenging ability,with glucose dialysis retardation ability,amylase inhibitory effect,and sodium cholate binding capacity slightly lower than those of SDF prepared by single cellulase treatment,and pancreatic lipase inhibitory activity slightly lower than pectinase treated SDF.These resluts were mainly due to the differences in viscosity and group exposure caused by different compositions of the samples and the degree of enzymatic hydrolysis.?4?The effects of enzymatic treatment and physical treatment on the structural damage of the insoluble residues from SDF preparation procedure were studied,and their application in adsorption of Pb²⁺and Cr⁶⁺was also evaluated.The results showed that the particle size of the residues from enzymatic treatment and mechanical crushing treatment was significantly lower than original potato pulp,with more loosened and porous structure,and significantly improvement in SSA.High-speed shearing treatment could better break the residual hemicellulose and lignin components with stronger toughness than high-pressure homogenization treatment,which is more conducive to further damage of the target product structure and particle size reduction.The median particle size of samples from high-speed shearing treatment was 58.4?m,which was 58.9%lower than original samples,and the specific surface area reached 8.14 m²/g,which was 229.55%higher than raw potato pulp.Optimization of adsorption conditions showed that the prepared adsorbent had the strongest adsorption capacity for Pb²⁺at pH 5.5 and 30?,and has the strongest adsorption capacity for Cr⁶⁺at pH4.5 and 30?.This was mainly due to the competitive adsorption capacity of H⁺ions and the hydrate formation of two different metal ions under different pH conditions.The Langmuir isotherm adsorption model could fit the adsorption behavior of Pb²⁺and Cr⁶⁺well,and the calculated maximum adsorption capacity reached 14.69 mg/g and 8.28 mg/g,respectively.Focused on the specific adsorption of cellulase which was the first and decisive step of cellulose hydrolysis,this paper analyzed the enzymatic utilization characteristics of cellulose from potato pulp,and clarified the inhibition effect of pectin on the cellulase adsorption to substrate.Based on the theoretical findings mentioned above,utilization strategies for the preparation of SDF by efficient hydrolysis of potato pulp,together with the preparation of heavy metal adsorbents from insoluble residues were developed.This technology will not only realize the highly efficient utilization of potato pulp,but also greatly contribute to the development of enzymatic utilization of biomass from root and tuber crops.