Nuclear magnetic resonance water relaxation time changes in bananas during ripening: a new mechanism

BACKGROUND: Nuclear magnetic resonance studies of banana fragments during ripening show an increase on the water transverse relaxation time (T-2) and a decrease in water self-diffusion coefficient (D). As T-2 and D are normally directly correlated, we studied these two properties in intact bananas during ripening, in an attempt to rule out the effect of injury on the apparent discrepancies in the behavior of T-2 and D. RESULTS: The results show that injury in bananas causes a decrease in T-2 of the water in vacuoles (T-2vac). They also show that T-2vac increased and D decreased during ripening, ruling out the injury effect. To explain the apparent discrepancies, we propose a new hypothesis for the increase in T-2 values, based on the reduction of Fe3+ ions to Fe2+ by galacturonic acid, produced by the hydrolysis of pectin and a decrease in internal oxygen concentration during ripening. CONCLUSION: As injury alters T-2 values it is necessary to use intact bananas to study relaxation times during ripening. The novel interpretation for the increase in T-2vac based on reduction of Fe+3 and O-2 concentration is an alternative mechanism to that based on the hydrolysis of starch in amyloplasts. (C) 2010 Society of Chemical Industry