Evaluating the dynamic effects of complex probiotics as cellulase replacements during fermentation of apple pomace

Apple pomace, an abundant agricultural by-product with low utilization rates, often leads to environmental pollution if not properly managed. This study aimed to enhance the nutritional value of apple pomace by comparing the effects of solid-state fermentation using complex probiotics and cellulase preparation. Additionally, the study investigated the dynamic changes in various components throughout the fermentation process with complex probiotics. The results of single-strain solid-state fermentation tests indicated that Lactiplantibacillus plantarum DPH, Saccharomyces cerevisiae SC9, and Bacillus subtilis C9 were the optimal strains for fermenting the most effective substrate combination, comprising 73 % apple pomace and 20 % millet bran. The strains (complex probiotics) and a cellulase preparation were used for the solid-state fermentation of the apple pomace mixture for nine days, respectively. The contents of acid detergent fiber, neutral detergent fiber, hemicellulose, and insoluble dietary fiber decreased by up to 9.99 %, 9.59 %, 23.21 %, and 14.34 %, respectively. In contrast, the content of soluble dietary fiber significantly increased by up to 29.74 %. Both methods reduced cellulose crystallinity and modified the substrate's surface structure, resulting in a looser arrangement. Fermentation with complex probiotics for three or six days increased the abundance of lactic acid bacteria, which comprised >87 % of the total microbial population. Concurrently, the abundance of detrimental bacteria, such as Salmonella, Acetobacter, Escherichia, and Pantoea, significantly decreased. Furthermore, fermentation with complex probiotics for six or nine days enhanced antioxidant properties, leading to a significant increase in beneficial metabolites, including amino acids, organic acids, gamma-aminobutyric acid, serotonin. In conclusion, complex probiotics can effectively substitute for cellulase preparation in the solid-state fermentation of apple pomace, with a six-day fermentation period yielding optimal results. This study provides valuable insights into enhancing the value of apple pomace in the feed industry and the effective application of agro-industrial by-products.