33B-2 |
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P. N. GAMBHIR, Y. J. Choi, and M. J. McCarthy. Dept. of Food Science & Technology, Univ. of California, Davis, 1 Shields Ave., Davis, CA 95616 Nuclear Magnetic Resonance (NMR) is a versatile technology which has emerged as a powerful analytical technique that probes the physical state of matter and provides both spatial and chemical information. In the food industry NMR applications appear in examining the physical and chemical characteristics of the products related with important quality parameters. In the present study, low field pulsed NMR was used to determine the spin-spin relaxation time (T2) of whole navel and Valencia oranges. Navel oranges were exposed to ~ 5°C and -5°C, and Valencia oranges exposed to ~5°C, -5° C and -17°C. The weight and T2 values were recorded before and after overnight (~20 h) exposure at each temperature. In navel oranges the exposure to 5°C did not change the T2 values compared to those obtained before the exposure but the exposure to -5°C reduced the T2 values by ~ 10%. Whereas, the Valencia oranges did not show any significant reduction in T2 on exposure to 5°C and -5°C, however, exposure to -17°C caused more than 20 % reduction. The small reductions in weights were also observed due to dehydration as a result of exposure at each temperature studied. This suggested that the observed reduction in T2 can not be attributed due to dehydration. The possible cause of reduction in T2 values when exposed to freezing temperature may be due to break down of membranes of juice segments and leakage of juice. The reduction in T2 values of freeze-affected oranges can be potentially used for fast separation and grading of damaged fruits.
Session 33B, Citrus Products: General
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