Influence of time-temperature cycles on potato starch retrogradation in tuber and starch digestion in vitro

A long storage time (> 7 days) is generally required for starch retrogradation sufficient to resist enyzmatic breakdown. To accelerate retrogradation in tuber to 3 days, two sets of time-temperature cycle processes were studied: cooked potato tubers were stored between (i) -20 degrees C and 4 degrees C, TTC1; and between (ii) 4 degrees C and 65 degrees C, TTC2 for 3 days. Relaxation times measured by LF NMR indicated that freeze-chill cycles led to the redistribution of water pools signifying the creation of starch-rich and starch-depleted (once ice) regions in tuber. Consistent with this, the TTC1 samples had higher retrogradation enthalpies than both TTC2 samples and 3-day chill retrograded samples which were never frozen. TTC-processed tubers subsequently exposed to digestive enzymes in vitro showed 60-67% starch hydrolysis, significantly lower than tubers retrograded for 3-days at 4 degrees C (72%) or freshly cooked tubers (87%). The residual enthalpies of digesta of TTC-processed tubers suggest the formation of slowly digestible starch.