Effect of sausage ingredients and additives on the production of enterocin A and B by Enterococcus faecium CTC492.: Optimization of in vitro production and anti-listerial effect in dry fermented sausages

Enterocin A and B in Enterococcus faecium CTC492 were co-induced by the different factors assayed in this study (r = 0.93) and followed primary metabolic kinetics. Enterocin production was significantly inhibited by sausage ingredients and additives, with the exception of nitrate. The addition of sodium chloride and pepper decreased production 16-fold. The temperature and pH influenced enterocin production, with optima between 25 and 35 degrees C, and from 6.0 to 7.5 of initial pH. The maximum activity was achieved, under favourable growth conditions, with MRS supplemented with sucrose (2%) plus glucose (0.25%) and Tween-80 (1%). MRS concentration, NaCl plus pepper addition, absence of Tween-80 in the growth medium, incubation at 45 degrees C and an initial pH under 5.5 were detrimental to bacteriocin production. Stress conditions did not favour enterocin production. Desadsorption was Tween-dependent. Enterocin A activity in the crude extracts stored at -80 degrees C was better preserved than enterocin B (when tested against their specific indicator strain), but anti-listerial activity remained intact. Applied as anti-listerial additives in dry fermented sausages, enterocins significantly diminished Listeria counts by 1.13 log (P < 0.001), while Enterococcus faecium CTC492 added as starter culture did not significantly reduce Listeria counts (P > 0.1) compared with the standard starter culture (Bac(-)). Enterocins A and B could be considered as extra biopreservative hurdles for listeria prevention in dry fermented sausages.