|Authors: ||M.J.M. Paillart, J.M.B.M. van der Vossen, E. Lommen, E. Levin, E.C. Otma, J.C.M.A. Snels, E.J. Woltering|
|Keywords: ||fresh-cut, lettuce, overall visual quality, Leuconostoc, acetic acid, lactic acid|
The shelf-life of fresh-cut lettuce packed in a modified atmosphere (MA) is determined by its "overall visual quality" (OVQ), being a measure of its general appearance based on colour and shape criteria.
In addition to the OVQ, the development of off-flavour and acid off-smell reduces consumer acceptance of such products.
Concomitant with these changes in organoleptic properties, there is a rapidly developing microbial population inside the MA package (MAP), dominated by lactic acid bacteria.
We studied the bacterial population dynamics of active MAP fresh-cut lettuce as well as the effect of metabolites produced by the bacteria (lactic acid and acetic acid) on lettuce quality aspects.
Within 3 days of packaging, the oxygen concentration in the package was reduced to near zero, and this resulted in the selective advantage of lactic acid bacteria, in particular Leuconostoc and Lactococcus species. Leuconostoc, when cultivated on lettuce-enriched artificial medium, was found to produce both acetic and lactic acids.
Low concentrations of acetic and lactic acids were found in MAP lettuce after 5 days of storage at 7°C. Freshly prepared fresh-cut product treated with comparably small amounts of acetic and lactic acids showed severe quality loss.
This was reflected by rapid browning, yellowing and loss of texture.
The experiments demonstrate that, under anaerobic conditions, organic acids are produced by lactic acid bacteria, affecting both off-flavour production and sensorial quality in fresh-cut lettuce.
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