Uso della fluorescenza della clorofilla a per valutare la qualità della lattuga da IV gamma conservata in atmosfera controllata

The leafy vegetables used for minimally processed products have a limited shelf life usually 5- 6 days. The quality of the vegetables is generally represented by antioxidant compounds, vitamins and leaf pigments that all together contribute to the aesthetical and nutritional quality. During storage the quality declines and atmosphere modification inside packaging such as oxygen reduction and carbon dioxide increase can be used for slowing down the degenerative processes. The aim of this work was to monitor the chlorophyll a fluorescence parameters during storage and evaluate if this non destructive system might be used for monitoring the quality of product during postharvest stage. Among the chemical compound the ascorbic acid has been determined. Lettuce baby leaf (Lactuca sativa L.) was harvested and processed following the industry procedures. Lettuce was packed and stored at 4 °C with air or with a modified atmosphere packaging (MAP). The oxygen concentration in MAP was lowered to 13-14%. During storage the ascorbic acid rapidly declined during storage in the control and MAP bags. The reduction was stronger in lettuce stored in MAP. At beginning of experiment the ascorbic acid was 12 mg/ 100 g p.f., after 3 days the higher values was found in normal atmosphere 2 mg/100 g p.f. while in MAP stored lettuce the ascorbic acid was very low almost 0. The chlorophyll a fluorescence progressively decreased with storage time and in MAP the reduction was faster showing lower values of all parameters measured. The Fv/Fm ratio declined until to reach 0.64 at 4 °C and 0.68 at 8 °C in MAP, while in control leaves the values at both storage temperatures were 0.83-0.84 and did not statistically decrease during storage. The Fo increased during storage and higher values were observed in lettuce stored in MAP. The Fm values declined in MAP at both storage temperatures after 6 days. The JIP test performed on the intermediate points of induction curves showed that the energy absorbed per cross section (ABS/CS) and the dissipation energy per cross section (DIo/CS) increased in MAP stored leaves. On the contrary, the electron flux per cross section, the density of active reaction centres per cross section (RC/CSm) and the performance index (PI) drastically decreased in MAP. The PI after 6 days strongly declined in leaves stored under MAP, reaching values close to 0. In conclusion, data obtained suggest that lettuce stored under MAP was more stressed than in normal atmosphere.