The effect of water on “antiplasticization” and plasticization of green and roasted coffee was studied by texturalanalysis, sorption isotherms, differential scanning calorimetry (DSC), and nuclear magnetic resonance (NMR). From BETmonolayer value to aw = 0.61 and 0.75 for green and roasted coffee, respectively, the solid matrix hydration occurred and waterinduced hardening. Very short NMR T2 values and the concomitant absence of any DSC endothermic peak assignable to waterfreezing were observed at these aw values. When solid matrix hydration was completed, water started to act as a plasticizing agent, thecompressive modulus started to decrease, and NMR revealed the appearance of a new proton pool with increased mobility.According to DSC, only when the plasticizing effect became important did water present enough mobility to freeze. Above thismoisture value (aw = 0.78 and 0.86 for green and roasted coffee, respectively), water determined a decrease of bean hardness and afurther decrease of the elastic modulus.[...]
The role of water state and mobility on the antiplasticization of green and roasted coffee beans
SACCHETTI, Giampiero;PITTIA, Paola
2011-01-01
Abstract
The effect of water on “antiplasticization” and plasticization of green and roasted coffee was studied by texturalanalysis, sorption isotherms, differential scanning calorimetry (DSC), and nuclear magnetic resonance (NMR). From BETmonolayer value to aw = 0.61 and 0.75 for green and roasted coffee, respectively, the solid matrix hydration occurred and waterinduced hardening. Very short NMR T2 values and the concomitant absence of any DSC endothermic peak assignable to waterfreezing were observed at these aw values. When solid matrix hydration was completed, water started to act as a plasticizing agent, thecompressive modulus started to decrease, and NMR revealed the appearance of a new proton pool with increased mobility.According to DSC, only when the plasticizing effect became important did water present enough mobility to freeze. Above thismoisture value (aw = 0.78 and 0.86 for green and roasted coffee, respectively), water determined a decrease of bean hardness and afurther decrease of the elastic modulus.[...]I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
