Multi-strain Fermentation Of Extruded Apple Pomace To Produce Microbial Protein Feed

The microbial protein feed is rich in nutrition,good palatability,which could effectively solve the problem of competing for food between human and livestock,and relieve the pressure of animal husbandry.In order to achieve the goal of efficiently converting apple pomace to produce microbial protein feed,the extrusion conditions of apple pomace were optimized by response surface methodology in primarily,extruded apple pomace was obtained under the optimal extrusion conditions.The strain screening experiment and medium optimization experiment were carried out successively for the extruded apple pomace.Effects of fermentation conditions on the fermentation of extruded apple pomace were studied by single factor experiment,and the quality of the best fermentation products was analyzed.The main research contents and results are as follows:1.In order to optimize the extrusion process conditions of apple pomace,the material moisture content,screw speed and sleeve temperature were used as test factors.Combined with single factor and response surface experiments,the optimal extrusion process parameters were obtained as follows:material moisture content 25%,screw speed 163 rpm and sleeve temperature 111?.Under these conditions,the soluble dietary fiber content of extruded apple pomace was 8.64%.The particle size distribution and scanning electron microscopy(SEM)analysis showed that the particle size of extruded apple pomace was more uniform and the structure was more porous compared with the apple pomace,to improve the microbial fermentation capacity.2.The true protein content of fermented products was used as the main indictor,while crude protein content,cellulase activity and effective viable content were used as secondary indictors.Five strains were screened out from 12 tested strains that could produce microbial protein feed,including Aspergillus niger 3.324(Asn),Candida utilis1314(Cau),Geotrichum candidum 1315(Gec),Lactic acid bacteria(Lac)and Bacillus subtilis A308(Bas1).The best mixture of Asn+Cau+Gec+Lac was determined by 15combinations of 5 dominant strains.Based on the orthogonal test L₁₆(2⁴),the true protein content of fermentation product obtained by the mixed strains according to the ratio of1:1:1:1 was the highest.3.The culture medium for the production of microbial protein feed by fermentation extruded apple pomace was optimized by combining Plackett-Burman test,steepest climb test and Box-Behnken test.The true protein content of the fermentation product was regarded as the main indictor,effective viable count and crude protein content were used as secondary indictors.Bran amount,glucose amount,packing quantity and water to material ratio as the main influencing factors selected from the 8 factors were determined by Plackett-Burman test.The steepest climb test determined the intermediate level of Box-Behnken test was bran amount 16%,glucose amount 8%,packing quantity 10 g and water to material ratio 1.5.The results showed that the optimal fermentation medium conditions were as follows:bran 16.31%,glucose 8.08%,packing quantity 9.97 g,water to material ratio 1.56.Under these conditions,the content of true protein,effective viable count and crude protein in fermentation products were 10.42%,9.29 Log10CFU/g and18.73%,respectively.4.By comparing the true protein content,effective viable count and crude protein content of the fermentation products obtained by one-time inoculation and two-time inoculation,it was found that the fermentation effect of two-time inoculation was better than that of one-time inoculation.So two-time inoculation was selected,that was after 24h of Asn fermentation,three other mixed bacteria were added.Through single factor experiment,the optimal fermentation conditions were obtained as follows:fermentation temperature 30?,fermentation time 96 h,inoculum size 10%.Under these conditions,the true protein content of the fermentation product was 11.11%.It could be seen from the dynamic change monitoring process of fermentation products that the true protein and crude protein content of fermentation products increased rapidly after Cau and Gec were added.The amino acids content of fermentation products was significantly higher than that of apple pomace and extruded apple pomace,and most of amino acids in fermentation products were higher than that of soybean meal and fish meal,which met the FAO standards,indicating that fermentation products could be used as a good source of protein for animal feed.By SPME-GC/MS method,the volatile components in fermented products were abundant,which improved the palatability.It was beneficial to the substitution of microbial protein feed for traditional animal feed.