VIBRATIONAL SPECTROSCOPY FOR THE EVALUATION OF MOLECULAR PERTURBATIONS INDUCED IN FRUIT LIPIDS BY COLD-STORAGE

Vibrational spectroscopy (Raman, FT-IR-ATR) has been applied for the f irst time to the study of the mechanism of chilling stress and the mon itoring of the best operative conditions for cold storage of fruit. In particular, this work deals with some results of the application of v ibrational spectroscopy to the molecular characterization of lipidic e xtracts of fruits (apples and pears, pulp and peel) stored at low temp eratures. The results have been obtained in a cooperative interdiscipl inary research project performing experiments on fruits for one year c ycles under different storage conditions of temperature (0-degrees-C, 8-degrees-C) and atmosphere (normal, controlled). The Raman spectra, u seful for the evaluation of the transition temperature and the coopera tive effect in the fruit membrane lipids, were masked by the strong re sonance spectrum of carotenoids. The lipid unsaturation, the natural r esponse to cold storage, was evaluated in the FT-IR-ATR spectra and ex pressed as the ''total'' unsaturation degree R = I3012 cm-1/2858 cm-1. The results on pulp and peel lipids have shown that the R value. high er in the pulps than in the peels, is dependent on the storage tempera ture and time. The increase in R is correlated with the higher fruit r esistance to the chilling stress. Furthermore, the FT-IR spectra of th e outer part of the fruits stored at 8-degrees-C show modifications of the carbonylic band at 1738 cm-1 (esteric group) such as the appearan ce of two other bands at 1715 and 1700 cm-1 increasing in intensity wi th storage time. These new components can be considered as molecular m arkers of the onset of a hydrolysis reaction and also of a partial per oxidation of the acylic unsaturated chains.