Hydroxypropylation product of amaranth starch showing high freeze-thaw stability

Hydroxypropylation is frequently used to inhibit starch retrogradation during the low-temperature storage shelf-life, thereby stabilizing the texture and water-holding capacity of starchy foods. Amaranth starch (AMS) shows exceptional small granular size (about 0.5-2 μm), however, the property of its hydroxypropylation products was less explored. In this study, AMS and waxy corn starch (WCS) was subjected to hydroxypropylation modifications under various conditions (45-55 °C, pH 10.6-12.0, and sodium sulfate (Na₂SO₄) concentration 10% ∼ 20%). The degree of substitution (DS) and the physicochemical properties of the two hydroxypropylated starch products were compared. Results indicated that the DS for hydroxypropylated AMS (HP-AMS) were generally 7% ∼ 218% higher than hydroxypropylated WCS (HP-WCS) under the same modification conditions. In comparison with HP-WCS, HP-AMS after pasting in overall showed lower transparency and viscosity, but demonstrated exceptional freeze-thaw stability even at the lower DS. The low freeze-thaw syneresis of AMS and HP-AMS may be related to their amylopectin fine structures, possessing the short-and-rich external branching chains and the less abundant intra-cluster branching chains. The outcomes of the study may contribute to the broader application of AMS in improving the quality of starchy foods against the low-temperature storage. In the study, freeze-thaw performance was primarily evaluated by syneresis, and the proposed structure-function relationship was interpreted in conjunction with amylopectin fine structure analysis.