Submitted to: Carbohydrate Polymers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/23/2007
Publication Date: 9/20/2007
Citation: Stevenson, D.G., Jane, J., Inglett, G.E. 2007. 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. Carbohydrate Polymers. 70(2):149-159. Interpretive Summary: Soybean variety that exhibit at maturity seeds with normal, low-linolenic or low-saturate fatty acid oil composition had starch isolated from seeds 20 days prior to harvest to determine if starch structure influences oil composition. Low-linolenic acid and low-saturate soybean varieties had significantly lower absolute amylose content than the normal soybean variety. Low-saturate soybean variety had a higher percentage of amylopectin molecules with branch-chains that had between 6 to 12 glucose molecules compared with the low-linolenic and normal soybean varieties. This study showed that starch structure of developing soybean seeds may influence soybean oil fatty acid composition, thereby influencing the potential industrial uses of globally the most economically important vegetable oil.
Technical Abstract: Soybean variety exhibiting at maturity, normal (NM), low-linolenic (LL) or low-saturate (LS) fatty acid seed oil composition had starch structure and functional properties studied from seeds collected 20 days prior to harvest. Soybean starch had small granules (0.4-4.5 micrometers 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 equipped with multi-angle laser-light scattering and refractive index, ranged from 5.91 x 108 g/mol for LL to 8.92 x 108 g/mol for NM, but no significant differences observed. Amylopectin branch chain-length distribution, measured by HPAEC equipped with amyloglucosidase post-column and pulsed amperometric detector, showed soybeans had short average chain-length (DP 19.9-21.9) and LS soybeans had significantly higher 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 degrees C-51.8 degrees C) and peak viscosity (79-100 RVU) both low. High variability in starch characteristics were observed among field replicates, with more differences likely to be observed once variation sources are understood. Further research would be worthwhile to establish if amylose content or amylopectin fine structure of developing soybean seeds influences fatty acid oil composition at maturity.