The Research Of Protein Feed Production By Solid State Fermentation With Citrus Dregs And Its Enzymatic Properties

Citrus is one of the most important fruits in the world,and it has the characteristics of having wide planting area and large output.Citrus has been planted in more than 140 countries and regions around the world,and its annual output has exceeded 100 million tons.Citrus are principally consumed by humans as fresh fruit or processed juice and can,which will produce a large amount of by-products: citrus dregs,which accounting for about 50% of citrus weight.At present,most citrus dregs residues in China can only be treated as waste.This is an enormous waste of resources,and untreated dregs can easily contaminate soil and water bodies,affecting the ecology balance.Therefore,the problem of citrus dregs has gradually become a major obstacle to the development of citrus industry,which makes it imperative to find a green and efficient processing road.There are studies found that citrus dregs contain many nutrients and they are highly biodegradable.Combined with microbial fermentation engineering,they can be used as substrate to produce single-cell protein feeds for animals,and it has advantages of high production speed,high yield,rich nutrition,low-demand facilities and convenient production.This method can not only reduce food pressure,but also reduce environmental pressure and truly achieve green and sustainable development.Four strains of Aspergillus oryzae,Trichoderma koningii,Candida tropicalis,and Trichoderma asperelloides were used in this study.At first,four kinds of strains were activated and cultured respectively,and then liquid fermentation was carried out according to the experimentally designed strain proportions.By studying the impact of different strain ratios of fermentation on protein products(crude protein and soluble protein)and enzyme production characteristics(acid protease,pectinase,and cellulase),it was determined that the optimal strain ratio for fermentative production of protein feed was: Aspergillus oryzae: Trichoderma asperelloides: Trichoderma koningii: Candida tropicalis=1:1:1:2.Then,applying the optimal ratio of strain for solid fermentation,and with citrus dregs and wheat bran as the substrate.Through a single-factor test to examine the influence of the moisture content,urea dosage,temperature,inoculation quantity and fermentation time on the crude protein,soluble protein and acidic protease in products of fermentation,it was finally determined that the optimum fermentation conditions were: moisture content 70%,urea dosage 4%,fermentation temperature 30 °C,inoculation quantity 15%,and fermentation time 6 d.Finally,single-factor test was conducted to determine the optimum fermentation conditions for the degradation of pectin and cellulose which will increase the difficulty of microbial degradation,and the production of enzymes.And in order to further reveal the differences of the degradation of the pectin and cellulose and related enzymatic properties between mixed bacterias fermentation(under optimal conditions)and single-bacterial fermentation,a comparative analysis was processed.The results showed that the maximum activities of pectinase and cellulase produced by single strain were 204.26 U/g and 29.86 U/g,respectively;and the maximum degradation rates of pectin and cellulose were 37.64% and 31.89%,respectively.While the activities of pectinase and cellulase reached the maximum at the 6th day of mixed bacteria fermentation were 242.78 U/g and 35.02 U/g respectively,corresponding to the degradation rate of pectin and cellulose were 50.96% and 43.65%,severally.Therefore,it is believed that the mixed bacteria fermentation not only has better enzyme production capacity,but also is more conducive to degrade pectin and cellulose.