Effects of Formic or Acetic Acid on the Storage Quality of Mixed Air-Dried Corn Stover and Cabbage Waste, and Microbial Community Analysis

Abstract

A mixture of air-dried corn stover and cabbage waste was ensiled to preserve lignocellulosic biomass for use as biofuel. Furthermore, the effects of different fresh mass fractions (0.3 and 0.6%) of formic or acetic acid on the mixed silage quality were evaluated to guarantee its quality. The application of formic or acetic acid prior to mixing the silage led to higher water-soluble carbohydrate fractions than the negative control, indicating that both acids contributed to preservation of water-soluble carbohydrates during storage for 170 days. The dry matter content was also increased after storage from 90 to 170 days. It was found that the content of neutral and acid detergent fibre, cellulose and holocellulose (the sum of cellulose and hemicellulose) in mixed silage treated with formic or acetic acid was significantly lower than that obtained in the negative control. The pH and the ratio of ammoniacal nitrogen to total nitrogen in mixed silage treated with acetic acid also significantly decreased. Furthermore, the addition of formic or acetic acid significantly weakened the fermentation intensity of lactic acid, depending on the ratio of lactic to acetic acid, as well as the ratio of lactic acid to total organic acids. The number of bacterial species and their relative abundance shifted during silage mixing, wherein microbial communities at phylum level mainly consisted of Proteobacteria and Firmicutes. The dominant bacteria were also observed to shift from Lactobacillus and Enterobacter in presilage biomass to Lactobacillus and Paralactobacillus. Specifically, Enterobacter disappeared after 130 days of storage. In conclusion, the addition of a low dose of acetic acid to fresh mass (0.3%) could effectively improve the fermentation quality and is conducive to the preservation of the organic components.

Keywords: air-dried corn stover; cabbage waste; fermentation quality; formic and acetic acids; microbial community diversity; mixed ensiling.

Fig. 1

Relative abundance of microbial community of pre-ensiled: a) air-dried corn stover and b) cabbage waste at the genus level

Fig. 2

Relative abundance of bacterial community at the phylum level. ADCS=air-dried corn stover, CW=cabbage waste, ME=mixed silage of ADCS and CW without any additives (negative control group), FA=mixed silage with low dose of formic acid (0.3%), FB=mixed silage with high dose of formic acid (0.6%), AA=mixed silage with low dose of acetic acid (0.3%), AB=mixed silage with high dose of acetic acid (0.6%), 1, 2, 3, 4, 5=storage period of 30, 60, 90, 130 and 170 days, respectively

Fig. 3

Relative abundance of bacterial community at the genus level. ADCS=air-dried corn stover, CW=cabbage waste, ME=mixed silage of ADCS and CW without any additives (negative control group), FA=mixed silage with low dose of formic acid (0.3%), FB=mixed silage with high dose of formic acid (0.6%), AA=mixed silage with low dose of acetic acid (0.3%), AB=mixed silage with high dose of acetic acid (0.6%), 1, 2, 3, 4, 5=storage period of 30, 60, 90, 130 and 170 days, respectively

Fig. 4

Relative fraction of lactic acid bacterial (LAB) during 170 days of storage. ADCS=air-dried corn stover, CW=cabbage waste, ME=mixed silage of ADCS and CW without any additives (negative control group), FA=mixed silage with low dose of formic acid (0.3%), FB=mixed silage with high dose of formic acid (0.6%), AA=mixed silage with low dose of acetic acid (0.3%), AB=mixed silage with high dose of acetic acid (0.6%), 1, 2, 3, 4, 5=storage period of 30, 60, 90, 130 and 170 days, respectively