The study of heat stress in tomato fruits by NMR microimaging

The ripening of the tomato fruit was delayed for several days (average 5 da ys) by a 1-day heat treatment at 42 degrees C, Ethylene production increase d during the first 3 h, but, after 6 h inhibition was almost total in tomat o fruit incubated at 42 degrees C. However, recovery of ethylene production was rapid if fruits were returned to a temperature of 25 degrees C after h eating. In NMR microimaging, three imaging pulse sequences with different r epetition and echo times at 42 degrees C were used to obtain the proton den sity (TR = 6000 ms, TE = 15 ms), the T-1 weighted image (TR = 1000 ms, TE = 15 ms) and the T-2-weighted image (TR = 6000 ms, TE = 120 ms). After 12 h heating, the water in locular tissues began to show shorter T-1 and T-2 val ues, Though the tomatos were returned to 25 degrees C and preserved one mor e day, the water having a shorter T-2 value in locular tissues, did not cha nge. These results show that tomato fruit do not fully recover from heating even after one day, although ethylene production is recovered almost immed iately, For this reason, we suggest that some denaturation event inside the tomato, which goes on after the end of heating, is the cause of the delay in tomato ripening. (C) 1999 Elsevier Science Inc.