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 (T2) 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 T2 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 T2 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.


CONCLUSIONS
As injury alters T2 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 O2 concentration is an alternative mechanism to that based on the hydrolysis of starch in amyloplasts.
Ribeiro
Fayene Zeferino
FZ
Embrapa Instrumentação Agropecuária, CEP 13560-970 São Carlos, São Paulo, Brazil.
Marconcini
Lucinéia Vizzotto
LV
de Toledo
Ingrid Bertoni
IB
de Vasconcellos Azeredo
Rodrigo Bagueira
RB
Barbosa
Lucio Leonel
LL
Colnago
Luiz Alberto
LA
D002412:Cations / Q000378:metabolism*; D005290:Ferric Compounds / Q000378:metabolism; D005296:Ferrous Compounds / Q000378:metabolism; D005511:Food Handling; D005638:Fruit / Q000502:physiology*; D006603:Hexuronic Acids / Q000378:metabolism*; D006868:Hydrolysis; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D028521:Musa / Q000502:physiology*; D010100:Oxygen / Q000502:physiology*; D010368:Pectins / Q000378:metabolism*; D014617:Vacuoles / Q000502:physiology; D014867:Water / Q000502:physiology*
D002412:Cations; D005290:Ferric Compounds; D005296:Ferrous Compounds; D006603:Hexuronic Acids; D014867:Water; C007819:galacturonic acid; D010368:Pectins; D010100:Oxygen