Preparation Of Protein Feed By Solid-state Fermentation Of Kitchen Waste And Its Application In The Feeding Of Hermetia Illucens(L.)

Kitchen Waste?KW?is an organic waste produced in the process of people's consumptions,which mainly includes rice,flour,vegetables,oil,bone and other food residues.And it consists of starch,cellulose,protein,lipids,inorganic salts and so on.At present,the main treatment ways of KW are composting,fermentation,landfill and incineration.Composting and fermentation hydrogen production method have some problems,such as long duration,low efficiency,and low utilization of resources.While both direct landfill and incineration method will cause secondary pollution of the environment.Therefore,finding a feasible KW treatment way to realize the resource utilization of organic wastes can not only effectively solve the problem of food waste and environmental pollution,but also provide a new idea for the development of circular economy in China.In this paper,KW was used as raw material to prepare protein feed by solid-state fermentation using microorganisms separated from natural fermentation KW.The feed was used to feed the Hermetia illucens?L.?larvae.The nutritional composition and antioxidant activity of the recovered larvae were analyzed.The main research contents and results are as follow:?1?The moisture content of KW raw material was 62.06%,and the dry matter composition was 22.72%crude protein,29.52%total sugar,11.36%reducing sugar,14.88%crude fat,4.08%crude fiber,7.32%starch,6.80%ash.It can be used as fermentation medium of microorganisms,that was rich in nutritions.22 strains were isolated and purified from natural fermention of KW,including 15 strains of bacteria,4strains of yeast and 3 strains of mould.Bacteria,yeasts and mould were named as KWBA-1 to KWBA-15,KWSA-1 to KWSA-4 and KWMO-1 to KWMO-3respectively.Based on 16S rDNA/ITS gene sequence analysis and phylogenetic analysis,the results showed that the bacteria were identified as a strain of Xanthomonas sacchari,a strain of Bacillus amyloliquefaciens,a strain of Lysinibacillus meyeri,a strain of Bacillus licheniformis,two strains of Eenterobacter xiangfangensis,two strains of Bacillus coagulans,three strains of Bacillus subtilis,four strains of Bacillus cereus,a strain of Candidal intermedia,three strains of Saccharomyces cerevisiae,a strain of Schizophyllum commune,a strain of Talaromyces marneffei,and a strain of Penicillium cinnamopurpureum.?2?Referring to the Catalogue of Varieties of Feed Additives,it was found that the isolated strains could be used in feed production as Bacillus amyloliquefaciens,Bacillus licheniformis,Bacillus coagulans,Bacillus subtilis,and Saccharomyces cerevisiae.Through single and mixed strains fermentation of those strains respectively,with the sensory quality,total protein and soluble protein content increasing rate as the evaluation index,the excellent strain combinations for KW fermentation were identified as KWBA-8,KWBA-12 and KWSA-2,among which KWBA-8 was Bacillus subtilis,KWBA-12 was Bacillus coagulans,KWSA-2 was Saccharhara cerevisiae.?3?Single factor and response surface methodology were used to optimize the process parameters of KW solid-state fermentation for the preparation of protein feed.The results showed that the fermented product had liquor flavor,soft shape and brown color,when the ratio of KW to soybean meal was 3:1?w/w?,the ratio of KWBA-8,KWBA-12 and KWSA-2 was 1:1:1?v/v/v?,the inoculation volume was 1.5%,the moisture content was 65.60%,and the fermentation time was 44.5 h.The total protein content of fermentation products increased 21.64%,the soluble protein content increased 406.18%,compared with unfermented raw materials.The contents of essential amino acids?EAA?and total amino acids?TAA?were 11.65%and 36.52%,which were 22.63%and 21.72%higher than those of unfermented raw materials.The protein component with molecular weight less than 1000 Da was 87.81%,which was23.01%higher than those of unfermented raw materials.GC-MS analysis showed that the content of alcohols in volatile components increased 403.56%,while sulfur and terpenes with foul odor were not detected.?5?The Hermetia illucens?L.?larvae were fed with fermented protein feed and the larvae fed with unfermented raw materials were used as control.The results showed that the single larvae of 6,7,8 and 9-day-old Hermetia illucens?L.?fed with fermented feed respectively increased 20.72%,26.56%,30.32%and 36.37%,compared with the control group.The total weight of single larvae increased 46.61%and the duration shortened 7.75%,compared with the control group.The feed utilization rate,transformation rate and larval survival rate respectively increased 46.59%,56.21%and3.06%,compared with the control group.The total protein content?47.44%?of larvae increased 10.48%,compared with the control group,and the contents of essential amino acids?19.38%?and total amino acids?46.41%?respectively increased 53.09%and30.21%.EAA/NEAA and EAA/TAA of larvae were higher than those of WHO/FAO ideal protein pattern.The essential amino acid index was more than 0.90.The protein of Hermetia illucens?L.?larvae had certain antioxidant activity.The IC₅₀ of protein scavenging DPPH and hydroxyl free radicals in the larvae fed with fermented feed was1.51 and 1.07 times as much as that of the control group,and its total reducing power was 1.53 times as that of the control group.That is to say,the protein of larvae fed with fermented feed had stronger antioxidant activity.