Formation of biogenic amines in well fermented grass silages

Biogenic amine formation was studied in silages made from perennial ryegrass. In 1991 two batches of grass from the same sward of the ID-DLO permanent pasture were wilted to either 250 or 450 g dry matter (DM)/kg, and ensiled in eight l-litre laboratory silos for each treatment (Expt A). To induce differences in fermentation pattern, the grass was ensiled without additive (CON) or treated with formic acid (5 ml/kg; FA), cell wall degrading enzymes (2.1 ml/kg; ENZ), molasses (50 g/kg; MOL), or inoculated with Lactobacillus plantarum (10(7) colony forming units (CFU)/g; LP), a combination of Lactobacillus plantarum and Streptococcus faecium (10(5) CFU/g; LPSF), or Enterobacter sakazakii (6 x 10(6) CFU/g; EB). One silo for each treatment was opened after 1, 2, 4 and 7 days for pH determination and duplicate silos were opened after 10 and 90 days for pH determination and analysis of fermentation products. Two similar experiments (B and C) were performed using the CON, FA and LP treatments. Total amine content of the grass was low (0.1-0.2 g/kg DM). The well preserved silages in each experiment contained considerable amounts of amines, ranging from 0.1 g/kg DM in the wilted LP and FA silages to 7.4 g/kg DM in a low DM CON silage. Tyramine, cadaverine, putrescine and histamine were, in descending order, the principal biogenic amines formed, representing together 90 (S.E. 9)% of the total biogenic amine content of the silages. Formation of amines occurred mainly during the first 10 days of fermentation, and was highest in silages with a slow acidification rate. Ensiling at high DM content, with formic acid or inoculation with large numbers of lactic acid bacteria significantly (P < 0.01) reduced the amount of amines in the silage. Total and individual amine contents of the silages were significantly correlated with concentrations of ammonia and acetic acid. It was concluded that the formation of biogenic amines in grass silage is related to protein degradation, and that amine formation can be reduced by restriction of fermentation in the silage, or by achieving rapid acidification during the first phase of ensiling.