Use of self-diffusion spin-echo magnetic resonance for non-destructive measurement of soluble solids content of fruits.

摘要

Non-destructive sorting of ripeness of fruits and vegetables could save the US approximately {dollar}1.4times10sp{lcub}13{rcub}{dollar} BTU of invested energy each year. Sugar content is a good indicator of ripeness for most fruits and vegetables. Self-diffusion of water molecules in sugar solution decreases dramatically as sugar content increases. For purposes of this research, sugar content was assumed to be equivalent to or linearly related to brix content as measured with a refractometer. Self-diffusion spin-echo proton magnetic resonance with a static magnetic field gradient was successfully used to determine brix content of whole fruits and vegetables. New pulse sequences were used to solve two practical problems: (a) effects of sample size and shape which are in turn related to the homogeneity of the {dollar}Bsb1{dollar} and {dollar}Bsb0{dollar} fields, and (b) changes (drift) in magnetic field strength ({dollar}Bsb0{dollar}). A simple calibration equation was used to correct for sample temperature effects and changes in T{dollar}sb2{dollar} caused by variation in composition among fruits and vegetables. A gradient driver and gradient coils were designed and built for the experiments. Major fruits tested included whole sweet cherries, whole plums, whole strawberries, whole blueberries and cylindrical samples cut from apples, oranges, nectarines, pears, bananas, pineapples, potatoes and tomatoes. Values of the correlation coefficient r for linear regression models of predicted % brix (i.e. the brix content estimated by means of the newly developed pulse sequence) versus % brix (refractometer reading) were 0.95 for sweet cherries, 0.87 for apples and bananas, 0.84 for nectarines, 0.62 for blueberries and pears, and 0.59 for potatoes. The predicted brix content estimations by means of the newly developed pulse sequence varied from refractometer measurements by no more than 3% (absolute).