Enhancement of nisin production by Lactococcus lactis in periodically re‐alkalized cultures

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Abstract
Synthesis of nisin as well as biomass production by Lactococcus lactis subsp. lactis CECT (Colección Española de Cultivos Tipo) 539 on both hydrolysed mussel‐processing waste and whey medium were followed in three fixed volume fed‐batch fermentations, with re‐alkalization cycles. The two cultures on mussel‐processing waste (MPW) were fed with a 240 g/l concentrated glucose and with a concentrated MPW (about 100 g of glucose/l). The culture on whey was fed with a mixture of concentrated whey (48 g of total sugars/l) and a 400 g/l concentrated lactose. The three cultures were mainly characterized with higher nisin titres [49.7, 109.6 and 124.7 bacteriocin activity units (AU)/ml respectively] compared with the batch process on de Man, Rogosa and Sharpe [(1960) J. Appl. Bacteriol. 23, 130–135] medium (49.6 AU/ml), MPW (9.5 AU/ml) and whey (22.5 AU/ml) [1 AU/ml is the amount of antibacterial compound needed to obtain 50% growth inhibition (LD50) compared with control tubes]. In the three fed‐batch cultures a shift from homolactic to mixed‐acid fermentation was observed, and other products (acetic acid, butane‐2,3‐diol or ethanol) in addition to lactic acid were detectable in the medium. However, their contributions to the total antibacterial activity of the post‐incubates (the cell‐free culture supernatant obtained at the end of the fermentation process) of L. lactis CECT 539 against Carnobacterium piscicola CECT 4020 were very low.

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