Roles of microbes and lipolytic enzymes in changing the fatty acid profile, α-tocopherol and β-carotene of whole-crop oat silages during ensiling and after exposure to air

The aim of present study is to clarify the roles of microbes, lipase and lipoxygenase in changes of fatty acids (FA) profile, α-tocopherol and β-carotene of whole-crop oat silages treated without (Control) or with Lactobacillus plantarum (LP) and propionic acid additive (PA) during ensiling and aerobic exposure. Whole-crop oat was harvested from the 8 fields (1000 m2 per field) and mixed as a pile which was then separated into 12 piles in the laboratory. The 12 piles (630 g per pile) were randomly ensiled with above additive treatments. Four piles per additive treatment were separately filled into 4 experimental silos (polyvinyl chloride bottle, 1 L), immediately. After ensiling for 65 d at room temperature, a part of silages (200 g) was sampled and the others (420 g) were exposed to air for 4 d. The increase of palmitic acid, reduction of linoleic acid and α-linolenic acid, and β-carotene loss occurred in the control silage because of bio-hydrogenation of lactic acid bacteria, lipase responsible for degrading lipid into FA, and lipoxygenase in charge of degrading β-carotene, linoleic acid and α-linolenic acid after ensiling. Compared with the control silage, an increase in linoleic acid content was found in LP-treated silage because LP increased the activity of lipase; Moreover, higher activity of lipoxygenase resulted in big losses of α-linolenic acid and β-carotene in LP-treated silage. In PA-treated silage, effects of lipase and lipoxygenase on changing the contents of linoleic acid and α-linolenic acid were not found, and slight loss of β-carotene was observed. During aerobic exposure for 4 d, multiplication of aerobic bacteria and yeasts resulted in most of FA and β-carotene loss and increased α-tocopherol content in all treatments. Compared with the control and LP-treated silages, PA relieved loss of β-carotene and reductions of linoleic acid and α-linolenic acid, because PA restrained the multiplication of aerobic bacteria and yeasts. In conclusion, lipase had a contribution in increasing contents of palmitic acid and linoleic acid during ensiling, and microbes played a potential role in increasing α-tocopherol content before aerobic deterioration in the present study.