Monitoring the Microbial Load of Ready-to-Eat Rocket Salad During the Shelf-Life by NIRS

Ready-to-eat (RTE) salads have gained popularity among consumers seeking healthy and freshly prepared foods. Rocket salad, rich in biologically active compounds like glucosinolates, is favored for its health benefits. However, its high metabolic rate limits shelf life and poses a safety problem. The shelf-life of RTE rocket salad packed under modified atmospheres was evaluated using Near-Infrared Spectroscopy (NIRS) to predict microbial load. Freshly cut rocket salad was packed in air (A) and in two modified atmospheres (B = 30% O2, 70% N2; C = 10% CO2, 5% O2, 85% N2) in BOPP bags. Samples were examined at t = 0 and during 13 days of refrigerated shelf-life. Headspace composition was analyzed by checking CO2 and O2 concentrations. The microbial load was monitored by plate counts of: i) yeasts and moulds; ii) aerobic bacteria; iii) E. coli and coliforms; iv) Enterobacteriaceae; v) Staphylococcus spp.; vi) Listeria spp. Reflectance NIR spectra (900–1600 nm) were collected with a portable NIR probe. Regressions between microbiological and spectral data were computed by partial least square (PLS) regression. The monitoring of the headspace composition evidenced changes due to the physiological respiratory activity of plant tissue. The C atmosphere confirmed the ability to control the aerobic microbial growth. PLS regression models predicted the microbial load of non-pathogenic bacteria with R2 higher than 0.76 and low errors in cross-validation. These preliminary results suggested the suitability of NIRS as sustainable technique also in microbiological field, reducing cost and time of analysis.