Effects of cellulolytic lactic acid bacteria on the lignocellulose degradation, sugar profile and lactic acid fermentation of high-moisture alfalfa ensiled in low-temperature seasons

Abstract

The objective of this study was to investigate the effects of cellulolytic lactic acid bacteria on the lignocellulose degradation, sugar profile and lactic acid fermentation of high-moisture alfalfa during anaerobic bioprocessing in low-temperature seasons. Last cut and low dry matter (DM) alfalfa was ensiled with five additives, commercial cellulase (EN), a combination of Lactobacillus plantarum and commercial cellulase (LPEN), a combination of engineered Lactococcus lactis strains (HT2) containing cellulase gene, Enterococcus faecium Y83 (EF83), or Enterococcus faecalis JF85 (EF85), and without additives, as the control, with four replicates each. After anaerobic preservation in a silo from late fall through winter (3 to 20 °C) for 140 days, the ensiled alfalfa was sampled and analysed. Compared with the control, EF85 increased the relative contents of neutral detergent fibre (NDF), acid detergent fibre (ADF), and cellulose and decreased contents of water-soluble carbohydrates (WSCs) and lactic acid, and the conversion of WSCs into lactic acid. Consequently, lactic acid fermentation was decreased in EF85. Compared with the control, supplementation with EN, EF83, HT2, and LPEN decreased contents of NDF, ADF, cellulose, and hemicellulose and increased the contents of WSCs, disaccharide, xylose, and arabinose; interestingly, compared with EN, supplementation with EF83, HT2 and LPEN increased the lactic acid content and the ratio of lactic acid to acetic acid as indicated by strong homo-lactic acid fermentation. Furthermore, HT2 increased the lactic acid concentration to a maximum of 72.2 g/kg DM and had a higher conversion of WSCs into lactic acid than EF83 (36.3%) and LPEN (17.9%), indicating that HT2 had a greater ability to ferment lignocellulose of alfalfa into lactic acid. Therefore, HT2 could enhance the lactic acid production of alfalfa during ensiling in low-temperature seasons.