NMR-IMAGING STUDIES ON FUNGICIDE MOTION INTO CITRUS FRUIT RIND FOLLOWING HOT WATER IMMERSION

Abstract

As a non destructive analysis method, Nuclear Magnetic Resonance Imaging (MRI) may provide helpful information on water movement and physiological effects of transpiration in senescing tissues. In the past decade, the use of MRI has provided a better understanding of some physiological disorders in horticultural product (e.g., internal breakdown) and on quality changes during storage. Here we report on MRI techniques used to study the movement of water into the rind (flavedo and albedo) following fruit immersion in hot water containing imazalil (IMZ). Pummelo hybrid (Citrus paradisi × Citrus grandis 'Oroblanco') was used to study in a completely non-invasive mode the water-IMZ motion and permeation within unwounded or wounded rind following immersion at 25 or 50°C for 2 min. Fruit was harvested in the experimental orchard, graded, rinsed in distilled water and wounded (3×3 mm; O, depth) in the equatorial area. The 2 min treatment was performed 30 min after wounding by immersing the fruit in the mixture at 25 or 50°C. Then, 'Oroblanco' fruit were gently surface wiped with a paper towel, marked (position reference for analysis) and immediately subjected to MRI. Twenty-four hours after immersion, measurements were repeated on the same fruit placed in the identical position based upon the position reference. Comparing resolved spatial information concerning the distribution of free-water, a clear and fast motion of the IMZ mixture into wounded rind occurred only with immersion at 50°C, and permeation in the neighbouring parenchyma cells took place within the subsequent 24h. In wounded fruit immersed at 25°C changes of free-water inside the wounds were insignificant and in unwounded fruit, no differences were found between the two immersion temperatures. From the results of MRI and the residue data it is likely that the fungicide in the albedo is acquired mainly at the time of treatment, while during storage permeation from the flavedo seems to be negligible, independently from the immersion temperature.