Pitaya (Hylocereus spp.) stems are a promising yet underutilized source of bioactive components, such as polysaccharides and sterols, which are of significant agricultural importance. However, their recalcitrant structures, including indigestible cellulose frameworks, acicular calcium oxalate crystals, and hydrophobic waxy cuticles, render them unsuitable for direct application as animal feed. Large-scale discarding of pitaya stems poses considerable environmental hazards if not properly disposed of, while existing extraction technologies for their bioactive components struggle with issues such as high pollution loads or difficulties in scale-up. Consequently, the development of efficient resource utilization strategies is imperative. This study adopts synthetic microbiome construction technology for the solid-state fermentation of pitaya stems, aiming to enhance their nutritional value for feed applications. This study utilized a synthetic microbial consortium consisting of Saccharomyces cerevisiae, Bacillus subtilis, Lactobacillus casei, and Aspergillus niger. After optimizing the fermentation conditions using response surface methodology (RSM), with the optimal parameters determined as 34 °C, 12 days of fermentation, and 55% moisture content, the nutritional quality of pitaya stems was substantially improved. Specifically, the protein content increased from 7.32 to 14.16%, the cellulose content decreased from 18.63 to 11.14%, and the total amino acid content was enhanced by 56.77%. Meanwhile, the dry matter digestibility and true protein digestibility of the fermented product reached 55.96% and 67.88%, respectively. During the fermentation process, the microbial community exhibited a phasic succession pattern: the early stage was dominated by Bacillus and Aspergillus, while the later stage became dominated by Lactobacillus and Saccharomyces. Metabolomic analysis further demonstrated a significant upregulation of metabolic pathways related to amino acid biosynthesis and energy metabolism. This study confirms microbial fermentation effectively degrades recalcitrant components in pitaya stems, enriches nutrients, and enhances substrate digestibility and bioavailability. Specifically, it establishes a sustainable approach to convert low-value pitaya stems into high-quality, nutritionally balanced ruminant feed. Facilitating resource utilization of this by-product, the approach yields significant economic and environmental benefits. These findings provide critical insights for high-efficiency fermented feed development and empirical support for advancing sustainable agriculture via waste recycling and resource optimization.
Chen et al. (Sun,) studied this question.