Examining the effect of freezing on starch gelatinization during heating at high rates using online in situ hot-stage video-microscopy and differential scanning calorimetry

Abstract

Despite its importance, little attention has been paid to the effect of freezing on starch gelatinization during subsequent heating. In an effort to address this problem, the effects of freezing and water accessibility in starch gelatinization during heating were analyzed in situ using hot-stage polarized-light video-microscopy. Native starch granules immersed in water, carrageenan gel or sucrose solution were heated at 15 °C/min or frozen for 48 h and heated at 15 °C/min. Energy changes were measured using differential scanning calorimetry. Surface morphology was examined using scanning electron microscopy and atomic force microscopy. The results showed that freezing delayed the gelatinization degree and that the addition of carrageenan delayed the gelatinization process. That process was further delayed when sucrose was added. The enthalpy of gelatinization decreased accordingly (ΔHstarch−water−sucrose > ΔHstarch−water−carrageenan > ΔHstarch−water). The temperature range over which the degree of gelatinization differed between frozen and unfrozen samples was diminished when accessibility to water was reduced.