Protein content correlates with starch morphology, composition and physicochemical properties in field peas

Protein and starch are two major components in field peas. In this study, we investigated the starch morphologies, compositions, and thermal properties between high protein peas (approximately 30%) and other market types of field peas (yellow, green, maple, and marrowfat peas, with approximately 23% protein contents). For the shape and size, high protein peas had the compound starch granules that could be easily fragmented into small irregular and polygonal granules, whereas other pea types had oval or kidney-like starch granules with high percentage of large granule sizes. High protein peas had significantly lower starch contents (27.2%-34.2%) than other pea types (45.5%-47.4%). However, the amylose content (74.6%-89.2%) in high protein peas were significantly higher that of other pea types (50.1%-54.1%). Our differential scanning calorimeter (DSC) data showed that the onset temperature (To), peak temperature (Tp), and conclusion temperature (Tc) of starch gelatinization in high protein peas were significantly higher than those of other pea types, whereas the enthalpy change (ΔH) of high protein peas was significantly lower than those of other pea types. The unique properties of high protein peas characterized in this study provided useful information to further improve pea quality.