PHYSICOCHEMICAL PARAMETERS TO PREDICT THE MICROBIOLOGICAL AND SENSORY QUALITIES OF FRESH-CUT BABY LETTUCE LEAVES

Baby lettuce leaves have recently been developed for the unwashed fresh-cut and ready-to-eat markets. The aim of this research was to characterize this product by sensory, physicochemical and microbiological analyses performed during storage at 4 and 10°C. Products were analysed at sampling times chosen on the basis of 5 sensory visual quality (VQ) levels. Samples scoring VQ5 and VQ4 were considered acceptable (Ac), whereas the remaining scores were defined as unacceptable (UAc). Each VQ level was then characterized for physicochemical (colour, ammonia, antioxidant activity, electrolytic leakage, phenols, chlorophyll, respiratory activity) and microbiological (total viable count, Pseudomonas spp, Enterobacteriaceae, lactic acid bacteria, yeast and moulds) parameters. UAc samples also proved unsatisfactory from a microbiological point of view (total viable count >=107 CFU/g). Partial Least Square (PLS) regression analysis allowed to identify colour change (?E*) and total chlorophyll (TC) as X-variables to predict the microbial load (TVC) (Y-variable) associated with each sensory VQ level. The model obtained showed R2CV=0.94, RMSECV=0.41 and a relative error of 5.61%. In conclusion, the use of these parameters as quality indicators could be a new strategy for discriminating green leafy vegetables into acceptable or unacceptable products.