Impact of Partial Gelatinization on Structure, Physicochemical and Enzymatic Digestion Properties of Rice Starch Used for Rice Noodle-Making

Currently, information remains limited regarding how controlled gelatinization alters structure and functional properties of rice starch intended for rice noodle-making. The objective of this research is to understand the effect of partial gelatinization on structural and physicochemical attributes of rice starch from an elite variety Zhenguiai specifically for rice noodle production and their relations to digestion properties. Starch samples partially gelatinized at 60-76 °C were analyzed for crystalline fraction, amylose content (AC), swelling power, gelatinization properties and <i>in vitro</i> enzymatic digestibility, and compared with native starch. The results demonstrated substantial variations in relative crystallinity (RC), AC, swelling power, gelatinization transition temperatures and gelatinization enthalpy (Δ<i>H</i>). As the partial gelatinization temperature increased, the proportion of rapidly digestible starch (RDS) rose, whereas the contents of slowly digestible starch (SDS) and resistant starch (RS) declined. Correlation analyses between starch digestibility and other properties indicated that RDS was significantly positively correlated with both the onset (r = 0.936, <i>p</i> < 0.05) and peak (r = 0.895, <i>p</i> < 0.05) gelatinization temperatures but negatively correlated with RC (r = -0.954, <i>p</i> < 0.01), AC (r = -0.888, <i>p</i> < 0.05), and Δ<i>H</i> (r = -0.992, <i>p</i> < 0.01). Furthermore, RS demonstrated positive correlations with AC (r = 0.872, <i>p</i> < 0.05) and Δ<i>H</i> (r = 0.974, <i>p</i> < 0.01) while showing negative correlation with gelatinization onset temperature (r = -0.971, <i>p</i> < 0.01). Additionally, SDS exhibited a significant positive correlation with RC (r = 0.838, <i>p</i> < 0.05). These findings identify potential applications of partial gelatinization in guiding the development of modified starches with optimized physicochemical and digestibility properties, such as maintaining high levels of AC and RS, for the production of premium rice noodles.