Effects of type and concentration of polyols on the molecular structure of corn starch kneaded with pullulanase in a Farinograph

For investigating the effects of type and concentration of polyols on the molecular structure of starch, corn starch (50 g, d.b.) were kneaded in a Farinograph at 60 °C for 3 h with 15 ml polyol solutions (10–100% for glycerol, 10–50% for erythritol, xylitol and sorbitol, and with water as control) and with or without pullulanase (32 NPUN/g starch). The molecular weight and chain length distributions of kneaded starch were determined by high-performance size-exclusion chromatography (HPSEC). Results showed the average molecular weight and chain length of amylose of the kneaded starch obviously decreased. Starch kneaded with water had lower extent of degradation than that of starch kneaded with polyol solutions. For starch kneaded with the same polyol, the degradation extent of starch decreased with the increasing concentration of polyol solution, but no apparent trend was found for starch kneaded with different polyol solutions at the same concentration. In addition, kneading without pullulanase leads to starch degradation to a similar magnitude as when the starch was kneaded with the enzyme. Results of this study imply that the mechanical force is the main factor on the degradation of starch kneads with pullulanase and different polyol solutions in a Farinograph. Furthermore, starches knead with different polyol solutions have distinct extent of degradation. For the same type of polyol uses, the extent of degradation depends on the polyol concentration.