Abstract: The experiment was to study the strain and the best process of solid-state fermentation of citrus peel residue for protein feed. Using citrus peel residue as raw material, strains were isolated by sodium carboxymethyl cellulose and pectin medium, and the cellulase activity and pectinase activity of the strains were determined, and identified by morphological observation and molecular biology techniques. The results showed that a high cellulase-producing and pectinase-producing strains of Aspergillus niger HCR was screened and identified, with the filter paperase (FPase) , carboxymethyl cellulase (CMCase) and pectinase activities reached 6.548 9 IU/mL, 20.915 2 IU/mL and 12 223.50 U/mL, respectively. Applying three strains of Aspergillus niger HCR, Aspergillus oryzae MQ and Cyberlindnera Jadini 1769 and using the crude protein content of citrus peel pomace fermentation product as the evaluation indexes, the optimal combination of citrus peel pomace fermentation strains and inoculation ratio were screened by a one-way experiment. The results showed that the optimal solid-state fermentation conditions were as follows: the ratio of fermentation substrate citrus peel pomace to bran was 8∶2, the ratio of Aspergillus niger HCR : Aspergillus oryzae MQ : Cyberlindnera jadinii 1769 inoculated at the ratio of 3∶3∶2, the amount of inoculum was 10%, the content of urea was 1.5%, the water content was 60%, and the time of fermentation was 6 d at 30 ℃. Under the conditions, the crude protein of the fermentation product was 33.67%, and 72.75%, higher than those before optimization. It provides a basis for the solid-state fermentation of citrus peel waste to produce protein feed.

Key words: citrus peel, solid-state fermentation, protein feed, cellulase, pectinase