DETERMINING STORED PERIOD OF LAMB'S LETTUCE USING VIS/NIR REFLECTANCE SPECTROSCOPY

Lamb’s lettuce (Valerianella locusta L.) delivered at the vegetable auctions is not always fresh. The product could have been stored for a certain period of time depending on the season. The prior stored samples cannot be distinguished visually from fresh material but their shelf life potential is reduced compared to that of the latter. Batches with limited shelf life potential lead to losses in distribution and lower consumption quality. The aim of this work was to develop a methodology that could estimate the time that lamb’s lettuce has been in storage. Lamb’s lettuce samples grown at an experimental garden were stored at 4°C and ca. 92% relative humidity (RH). Visible/near infrared (VIS/NIR) spectra were obtained at harvest and at least once a week during storage on different samples. Lamb’s lettuce samples were taken at harvest and after 11 days of storage. Glucose, fructose, chlorophyll a, chlorophyll b and total carotenoid content were measured to find an explanation for observed changes in spectral data. VIS/NIR reflectance spectra were linked to the time in storage using partial least squares regression (PLS). The resulting PLS-model was able to estimate the stored period of lamb’s lettuce (RMSEC=2.2 days; R²=0.92). To validate the model an external test set of a different batch of lamb’s lettuce was used (RMSEP=3.4 days). Glucose and fructose content decreased during storage. A reduction of chlorophyll a and b was observed after 11 days in cool storage while total carotenoid content remained stable.