MECHANICAL AND MICROSTRUCTURAL PROPERTIES OF PECTIN STARCH FILMS

Films were made from blends of high methoxy pectin and high amylose st arch gelatinized in a microwave oven in the presence and absence of gl ycerol at times ranging from 10 to 105 s. Three thermodynamic transiti ons were observed when storage modulus, loss modulus, and loss tangent were plotted against temperature. All three transitions gave minima w hen the transition temperature was plotted against time of gelatinizat ion. Overall, there were only modest changes in these moduli over the range of gelatinization times studied, with little difference between films made with the starch gelatinized in either the presence or absen ce of glycerol. Starch granules were found to disappear at gelatinizat ion times between 20 and 30 s, although much smaller starch particles seemed to recur at gelatinization times of 75 s and above. The minima found in the transition temperature and modulus plots were believed to result from a minimum in the amount of intermolecular interactions be tween the starch molecules. (C) 1995 John Wiley & Sons, Inc.