Quantitative nmr imaging of kiwifruit ( actinidia deliciosa ) during growth and ripening

Quantitative 1 H 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 ). Temporal trends and differences between flesh, locule and core tissue were found for both relaxation parameters. However, no consistent associations were found between non‐destructive measurements and those for individual 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 accompanied 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 self‐diffusion declined only 7–14% from harvest values. T 2 ‐CPMG relaxation 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 insensitive to changes in organic acids and soluble pectin at concentrations normally found in fruit. Results imply that relaxation parameters determined from MR images may not be appreciably influenced by processes that cause solution composition to vary dramatically, even though these changes are reflected in the relaxation properties of the juice itself. Possible reasons for this are discussed with regard to the impact of cell structure and magnetic field strength on relaxation processes. © 1998 Society of Chemical Industry.