Synergism of microorganisms and enzymes in solid-state fermentation of animal feed. A review

Solid-state fermentation (SSF) has been researched and applied in the food industry for a long time and constitutes a feed material processing technique. An important objective of SSF is the production of enzymes, organic acids and other metabolites of economic importance. It was indicated that the utilization value of some substrates was increased by post-fermentation by probiotics (Chu et al., 2017; Chuang et al., 2019). Recently, SSF has been employed to enhance nutrient bioavailability, inhibit gut pathogenic bacteria and reduce anti-nutritional factors content in plant protein sources, resulting in improved nutrient digestibility, thereby improving performance and gut health of domestic animals (Olukomaiya et al., 2019). In the fermentation process, the utilization efficiency of microorganisms on the macromolecular material in feed can be improved by using enzymatic co-fermentation. For example, the monosaccharide produced by cellulase hydrolysis of crude fibre can provide energy for probiotics to synthesize microbe protein (Ghosh et al., 2019). Simultaneously, cofermentation can also overcome the challenge of less enzyme production by microbial fermentation alone, and improve feed quality. This advantage is of great significance for the development and application of feed sources (Bartkiene et al., 2018; Wang et al., 2019). So, the main purpose of this review is to summarize the SSF method in which enzyme and microbe are used simultaneously in feed processing and to evaluate their simultaneous effect on feed SSF. Moreover, the basis for the follow-up of the rational use of enzyme in feed SSF is provided. ABSTRACT. Fermentation and enzymolysis are commonly used biological treatment methods to treat forage, especially unconventional one. Both these treatments can improve the nutritional value of the forage, reduce the content of anti-nutritional factors and ameliorate the digestibility of feed. Microbial-enzymatic synergism treatment constitutes an organic combination of fermentation and enzymolysis, which can strengthen the processing of forage and achieve a superior feeding effect. In this review, the objectives of microbial-enzymatic synergism treatment are summarized, including decomposing macromolecular nutrients, decreasing anti-nutritional factors and increasing specific target products. The substrates, microbes and enzymes used in microbe-enzyme synergy are also summarized. Furthermore, the similarities and differences between one-step and two-step technological processes of synergy are presented and the current evaluation system of microbial-enzymatic synergism treatment is reviewed. Existing problems and future development directions of microbial-enzymatic synergism treatment are also discussed. Received: 5 January 2021 Revised: 7 February 2021 Accepted: 8 February 2021