Comparison of Structural Characteristics and Physicochemical Properties of Legume Starches from Four Minor Species

In this work, starches were extracted from four species of minor legume widely planted in China: cowpea, lentil, pea, and red kidney bean by wet milling, and their structural characteristics and physicochemical properties were analyzed and compared. The infrared spectra of all the samples presented the typical structural characteristics of starch. The starch granules had complete kidney-like or oval shape with a smooth surface. The average hydrodynamic radii of the four starches were in the following decreasing order of cowpea starch > pea starch > lentils starch > red kidney bean starch. The crystal type of pea starch was C_C-type, while the crystal type of cowpea starch, lentils starch and red kidney bean starch was C_A-type. The relative crystallinity of these starches was significantly different, ranging between 27.6% and 38.5%. The gelatinization characteristics varied greatly among them, all of which had high gelatinization temperature (75.3-82.8 ℃), being difficult to gelatinize. Cowpea starch was not prone to retrogradation with the lowest amylose content (26.3%), and the thermal stability of cowpea paste was best. Red kidney bean starch had the highest amylose content (31.5%) and retrogradation value, which was most prone to retrogradation. In conclusion, the four legume starches had similar granular morphology and all exhibited a C-type crystal structure, and they were similar in their retrogradation characteristics but distinct in their molecular structure and gelatinization characteristics.