Structures and physicochemical properties of starch from immature seeds of soybean varieties (Glycine max (L.) Merr.) exhibiting normal, low-linolenic or low-saturated fatty acid oil profiles at maturity

Soybean varieties bred for normal (NM), low-linolenic (LL) or low-saturate (LS) fatty acid composition were collected 20 d prior to harvest. Seed starch structure and functional properties were studied. Soybean starch had small granules (0.5–4.5 μm diameter), and CB-type crystallinity. LL and LS soybean starch had significantly lower absolute amylose than NM soybean. Weight-average amylopectin molecular weight, measured by HPSEC, ranged from 5.91 × 108 g/mol for LL to 8.92 × 108 g/mol for NM. Soybean amylopectin had short average branch chain-length (DP 19.9–21.9) and LS amylopectin had significantly larger percentage of DP 6–12 than LL and NM soybeans. No significant differences among soybean varieties were observed for starch thermal and pasting properties, with onset gelatinization temperature (51.0–51.8 °C) and peak viscosity (79–100 RVU, 8% starch suspension). Further research is needed to understand if amylose content or amylopectin fine structure in developing soybean seeds relates to fatty acid composition of soybean oil at maturity.