Optimization of Preparation Process of Protein Feed by Solid Fermentation of Wild Broussonetia papyrifera Leaves with Different Treatment Methods

To reduce tannin content in Broussonetia papyrifera leaves, steam explosion and ball milling were used to pretreat Broussonetia papyrifera leaves, and response surface methodology was used to determine the best technology for preparing protein feed by solid fermentation of Broussonetia papyrifera leaves with complex bacteria of Bacillus subtilis, lactic acid bacteria and Saccharomyces cerevisiae. Results showed that, the optimum process conditions were as follows: Steam explosion pressure 1.4 MPa, maintaining pressure time 90 s. The ball milling time was 20 min. The fermentation time was 4 d, water content was 60.07%, fermentation temperature was 32.50 ℃, and the ratio of Saccharomyces cerevisiae:lactic acid bacteria:Bacillus subtilis was 1:1:1. The tannin content of Broussonetia papyrifera leaves after fermentation, steam explosion fermentation and ball milling decreased by 36.2%, 39.5% and 60.5% respectively. The crude protein content increased by 23.59%, 10.28% and 7.84% respectively. Crude ash content increased by 16.7%, 31.80% and 24.23% respectively. The crude fiber content decreased by 15.33%, 12.32% and 7.85% respectively. The calcium content of Broussonetia papyrifera leaves was 2.70%, which had no obvious change after fermentation. But the calcium content increased by 23.33% and 22.22% respectively after steam explosion and ball milling (P<0.05) by fermentation. Pretreatment and fermentation had little effect on phosphorus and crude fat content, with phosphorus content being 0.3% and crude fat content being 2.4%. The enzyme activities of raw material fermentation, steam explosion fermentation and ball milling fermentation were as high as 41.43, 44.77 and 65.10 U. The tannin reduction effect of ball milling fermentation is far superior to steam explosion fermentation and raw material fermentation, and the protein increase effect of raw material fermentation is the best.