NMR relaxometry study of development of freeze damage in mandarin orange.

Abstract

Freeze damage to citrus fruit is one of the major causes of the loss of marketable fruit for the citrus industry. Because freeze damage occurs inside citrus fruit, detecting freeze damage is very challenging. This study addresses this problem by using NMR relaxometry to monitor changes at the sub-cellular level in mandarin flesh at two freezing temperatures, -4 °C and -20 °C. The T2 relaxation spectra of mandarin flesh segments displayed three relaxation components, each representing a sub-cellular water compartment. Freezing treatment at -4 °C for 240 min significantly decreased the relative magnitude of the slow relaxation component and increased that of the intermediate relaxation components. These changes are signs of water redistribution between sub-cellular compartments and an increase in membrane permeability. Freezing treatment at -20 °C caused more evident changes in the T2 relaxation spectra. Noticeable changes occurred as early as 120 min of freezing. In addition, NMR relaxometry was performed on cold-stored mandarins. Smaller changes were observed in samples stored at 4 °C than frozen samples. The relative magnitudes of relaxation components are sensitive to sub-cellular changes in mandarin flesh due to freeze damage. Thus, freeze damage in mandarin flesh can be tracked by NMR relaxometry. © 2015 Society of Chemical Industry.