Enhancing the quality of corn straw feeds through low-temperature fermentation with synthetic microbial community

Solid-state fermentation (SSF) using synthetic microbial communities (SMC) offers a promising approach to converting straw into nutritionally enriched feed. However, the low-temperature environment is one of the major limiting factors that determines the quantity of SSF, particularly in the alpine region. Here, we developed and optimized a low-temperature (10°C) SSF strategy using a synthetic microbial community (SMC-1) composed of cold-tolerant Saccharomyces cerevisiae W6-Evo20, Lactobacillus lactis LAB1, and Bacillus subtilis JY3242 (ratio 3:1:3) to produce high-quality straw feed. The optimal fermentation conditions were determined as follows: 15.43% inoculation amount, 20.34 days of fermentation time, and 2.5% ammonium sulfate addition. Compared with unfermented straw, the fermented feed with the synthetic microbial community SMC-1 at 10°C exhibited remarkable improvements: the crude protein (CP) content and acid-soluble protein increased by 1.91-fold and 1.94-fold, respectively. Electron microscopy and Fourier Transform Infrared Spectroscopy (FTIR) analyses confirmed significant disruption of the straw's cellulose structure, accompanied by a 37.01% reduction in acid detergent fiber (ADF) content. Additionally, the lactic acid content increased by 2-fold, while the oxalic acid content decreased by 83.66%. The DPPH free radical scavenging rate surged by approximately 4-fold to 54.11%, and the total antioxidant capacity rose by 0.97-fold to 41.31 mmol/100 g. Notably, low-temperature fermentation (10°C) imparted a more intense aroma to the feed compared with normal-temperature fermentation (30°C). Gas chromatography-mass spectrometry (GC-MS) analysis identified 20 aroma components with significant differences, among which phenylethyl alcohol (16.38 μg/g) dominated, contributing a rose-like fragrance. Furthermore, mycotoxin levels were significantly reduced in low-temperature fermented feeds. Additionally, fermentation with SMC-1 speeds up the breakdown of CP and ADF, improving the digestibility of corn straw (CS) as fermented feed.