Gelatinisation of starch in mixtures of sugars. II. Application of differential scanning calorimetry

Differential scanning calorimetry was used to investigate the effect of mixtures of glucose and fructose, and five types of honeys on starch gelatinisation. At a 1:1 starch:water ratio, glucose generally increased the enthalpy (ΔHgel) and temperatures (Tonset, Tpeak and Tend) of gelatinisation more than fructose. Upon mixing, ΔHgel of the low-temperature endotherm decreased in comparison to the sole sugars, but was fairly constant (7.7±0.33 J/g dry starch). ΔHgel of the high-temperature endotherm increased with the fructose content. For both endotherms, the gelatinisation temperatures were unchanged (CV≤3%) for the mixtures. With the honeys (moisture, 14.9–18.0%; fructose, 37.2–44.0%; glucose, 28.3–31.9%) added at 1.1–4.4 g per g dry starch, the enthalpy and temperatures of gelatinisation did not vary significantly (CV≤6%). Typical thermograms are presented, and the results are interpreted in the light of the various proposed mechanisms for starch gelatinisation in sugar–water systems, total sugar content and possible sugar–sugar interactions. The thermograms were broader in the presence of the sugars and honeys, and a biphasic character was consistently exhibited. The application of an exponential equation to the gelatinisation temperatures of the starch–honey mixtures revealed an opposing influence of fructose and glucose during gelatinisation. The mechanism of starch gelatinisation may be better understood if techniques could be perfected to quantify breakage and formation of hydrogen bonds in the starch granules, and suggested techniques are discussed.