Quantitative magnetic resonance imaging of satsuma mandarin fruit during growth

Abstract

Whole-fruit proton magnetic resonance (MR) imaging was performed on satsuma mandarin (Citrus unshiu Markovich cv. Miho Wase) during a 15-week period commencing 10 weeks after anthesis and continuing to maturity, and at 6 weeks after anthesis the following season. Images with long repetition times (>1600 ms) and short echo times (20 ms) provided the clearest details of anatomical changes in the peel (flavedo, albedo) and vascular system, while those with similar repetition times but longer echo times (120 ms) were best for viewing juice sac morphology within pulp segments. At 6 weeks after anthesis, images of fruits of slightly different physiological ages highlighted rapid changes in the vascular bundles and albedo tissue at this stage of development. Variation in the relaxation measurements, T1 and T2, was determined from quantitative MR images of the juice sacs in equatorial slices, and images of expressed juice from whole fruit. Seasonal measurements of T1 determined in situ (1760 ms) were significantly greater than those in juice (1413 ms). By contrast, there was no mean seasonal difference between in situ T2 measurements (360 ms) and those for juice (332 ms). No associations between trends in the MR data and total soluble solids, pH, titratable acidity, and sugar and organic acid composition of the juice were established. Cell structure is identified as a hindrance in the use of quantitative MR imaging for probing compositional changes in solution in serial imaging studies.