Evaluation of low field (5.40-MHz) proton magnetic resonance measurements of DW and T2 as methods of nondestructive quality evaluation of apples

Abstract

A 5.40-MHz NMR system was used for measuring the self-diffusion coefficient of water (DW) and the spin-spin relaxation constant (T2) in apple (Malus xdomestica Borkh.) tissue. The pulsed field gradient spin echo (PFGSE) technique was used to measure DW, and the Carr-Purcell-Meiboom-Gill (CPMG) technique was used to measure T2· T2 and DW values were compared for apples with differing amounts of soluble solids concentration (SSC) and with and without internal defects, such as bruising, watercore, and internal browning. 'Granny Smith', 'Golden Delicious', and 'Delicious' apples were tested. In 'Golden Delicious', DW highly correlated with apple tissue SSC (P < 0.002, r2 = 0.68). This indicates that DW could potentially be used for sorting 'Golden Delicious' apples based on SSC, but the coefficient of determination needs to be improved before it would be commercially viable. There were no measurable differences in DW among healthy apple tissue and tissue affected by either watercore or internal browning. T2 values showed no relationship between healthy apple tissue and bruised tissue in 'Golden Delicious' and 'Granny Smith'. However, in 'Delicious' tissue, T2 values were statistically different between healthy and bruised tissue (P<0.02). Further comparisons in 'Delicious' between watercore and healthy apple tissue showed no differences. But, there were statistical differences found between T2 in healthy apple tissue and tissue with internal browning (P < 0.01). These results indicate that T2 could potentially be used for separating 'Delicious' apples with internal browning or with bruising from healthy apples. Titratable acids and pH were correlated for 'Golden Delicious' (P < 0.08). This correlation is significant because one may be able to noninvasively measure pH in 'Golden Delicious' apples using NMR, which could then be correlated to titratable adds.