Proton spin–spin relaxation time of peel and flesh of navel orange varieties exposed to freezing temperature

Proton spin–spin relaxation times ( T 2 ) of peel (albedo and flavedo) and juice sacs (flesh segments) of navel oranges were measured at 10 MHz using a Bruker Minispec PC 110 NMR spectrometer. The oranges were subjected to chilling (5 °C) and freezing (−7 °C) temperatures for 20 h and warmed to room temperature before peeling for T 2 measurements. The exposure to chilling or freezing temperature did not affect the T 2 values of peel, but freezing caused an appreciable decrease (∼15%) in the T 2 values of flesh segments of the varieties of navel oranges studied. When the peel was exposed to −20 °C, the T 2 showed a drastic reduction suggesting that the peel did not freeze at −7 °C. The possible cause of reduction in the T 2 values when exposed to freezing temperature may be damage to the juice sac membrane and leakage of juice out of the sac. The difference in the T 2 values between juice sacs of freeze‐affected and normal oranges can potentially be used for detection of freeze‐damaged fruits. Copyright © 2005 Society of Chemical Industry