University of California

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Organic acids produced by lactic acid bacteria (Leuconostoc sp.) are related to sensorial quality decrease in modified atmosphere packed fresh-cut iceberg lettuce

Paillart, M.J.M. (Wageningen UR - Food & Biobased Research);Van der Vossen, J.M.B.M. (TNO); Woltering E.J. (Wageningen UR - Food & Biobased Research)

The shelf life of fresh-cut lettuce packed in modified atmosphere (MA) packaging is generally determined by its “overall visual quality (OVQ)” being a measure of its general appearance based on colour and shape criteria. Additionally to OVQ, development of off-flavour and acid off-smell limits the consumer’s acceptance of such products. Concomitant with these changes in organoleptic properties, there is a rapidly developing microbial population inside MAP, dominated by lactic acid bacteria species. Few studies have investigated the possible interactions between the growth of this specific bacteria population and the sensorial quality decay of fresh-cut lettuce. We studied the bacterial population dynamics of active MA packed fresh-cut lettuce and studied the effect of bacteria-produced metabolites (lactic acid and acetic acid) on lettuce quality aspects. Within 3 days of packaging, the oxygen concentration in the package was near zero and this greatly stimulated the development of lactic acid bacteria, in particular Leuconostoc and Lactococcus species. Leuconostoc, when cultivated on lettuce-enriched medium, was found to produce both acetic and lactic acids. Low concentrations, of acetic and lactic acids were determined in MA packed lettuce after 5 days of storage at 7 degrees C. Fresh-cut lettuce treated with comparable low amounts of acetic and lactic acid showed strong quality decay. This was reflected in rapid discoloration and increases in tissue electrolyte leakage (indication cell damage). The experiments show that organic acids produced by lactic acid bacteria under anaerobic conditions affect both off-flavour production and sensorial quality decay in fresh-cut lettuce.

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