Cj. Clark et al., QUANTITATIVE NMR IMAGING OF KIWIFRUIT (ACTINIDIA-DELICIOSA) DURING GROWTH AND RIPENING, Journal of the Science of Food and Agriculture, 78(3), 1998, pp. 349-358
Quantitative H-1 magnetic resonance (MR) imaging was used to determine
relaxation changes (T-1, T-2-CPMG) at regular intervals during growth
and ripening of kiwifruit (Actinidia deliciosa var deliciosa). Tempor
al trends and differences between flesh, locule and core tissue were f
ound for both relaxation parameters. However, no consistent associatio
ns were found between nondestructive measurements and those for indivi
dual free sugars, soluble solids content (SSC) and macronutrients and
micronutrients determined on dissected companion samples. Increases of
200% in total free sugar concentration in flesh and 68% in SSC accomp
anied starch hydrolysis after harvest. Despite the magnitude of these
changes, relaxation times remained unaltered. These observations were
repeated in a second investigation using A arguta fruit and T-1, T-2,
T-2-CPMG and self-diffusion image contrasts. Here, SSC increased 125%
during a compressed 15-day ripening period, while MR parameters like s
elf-diffusion declined only 7-14% from harvest values. T-2-CPMG relaxa
tion was also investigated in aqueous solutions containing individual
organic acids, sugars or pectate and juice from ripening fruit (4.7-15
.5% SSC). Analysis of solutions and juices showed relaxation is indeed
sensitive to increases in sugar composition but relatively insensitiv
e to changes in organic acids and soluble pectin at concentrations nor
mally found in fruit. Results imply that relaxation parameters determi
ned from MR images map not be appreciably influenced by processes that
cause solution composition to vary dramatically, even though these ch
anges are reflected in the relaxation properties of the juice itself.
Possible reasons for this are discussed with regard to the impact of c
ell structure and magnetic field strength on relaxation processes. (C)
1998 Society of Chemical Industry.