Shelf life of fresh-cut lamb's lettuce (Valerianella locusta L.) monitored by electronic nose and relationship with chlorophyll a fluorescence and mechanical-acoustic test

The principal aim of this work was to investigate the applicability of electronic nose, as non-destructive technique, in monitoring freshness decay of fresh-cut Valerianella locusta. In addition it was evaluated the possibility to monitor texture changes due to senescence by the mechanical (firmness, dF/dS, area as work required to puncture) and acoustic (dBbreak, dBmax, Nsounds, Nsounds > 50 dB) puncture tests. The sampling was performed for Valerianella samples, packed in air (control) and in three modified atmospheres: nitrogen, CO2/O2/N2 mix and argon, stored at 4 °C up to 13 d. The experimental plan was repeated twice. The Fv/Fm ratio, an index of chlorophyll a fluorescence, showed a negative trend for all the samples, even though with some fluctuations, along the shelf life. Samples packed in air showed the least decay and the highest final Fv/Fm value, while those packed in argon and CO2/O2/N2 mix showed the lowest final Fv/Fm values. Chlorophyll a fluorescence was confirmed to be an useful tool for monitoring the senescence of ready to eat Valerianella. The mechanical-acoustic puncture test was not found to be appropriate to evaluate textural property throughout shelf life. No differences were found between the electronic nose profiles (E-nose) of the two repetitions, except for samples packed in nitrogen. Sensor responses significantly depended on packaging atmosphere. W1C, W5C and W3C sensors showed an overall decreasing trend in response throughout shelf life. The sensors W2S, W1S and W5S showed an increasing trend in response for samples packed in argon and in packages with a mixed gas atmosphere. Principal component analysis was applied to E-nose measurements. The highly significant correlation (P < 0.001) was found between PC-1 and Fv/Fm ratio, demonstrating that the E-nose technique, applied directly on Valerianella bags, could be proposed as a rapid and non-destructive method for monitoring shelf life.