Submitted to: Starch/Starke
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/7/2006
Publication Date: 10/1/2006
Citation: Stevenson, D.G., Doorenbos, R.K., Jane, J., Inglett, G.E. 2006. Structures and functional properties of starch from seeds of three soybean (Glycine mas (l.) merr.) varieties. Starch/Starke. 58(10):509-519. Interpretive Summary: High-protein, lipoxygenase-free and low-linolenic acid soybeans varieties grown in northwest Iowa had their starch characterized at 20 days prior to harvest. Soybeans had 10-12% starch (dry basis) at 20 days prior to harvest, and starch had very small granules, very low amylose content and very short amylopectin branch-chains, which are all conducive for rapid degradation by starch-degrading amylases. Low-linolenic acid soybeans had higher amylose content than high-protein and lipoxygenase-free soybeans, which suggest that soybeans with higher amylose content of their starch during development may have lower levels of the undesirable, unstable linolenic acid. This study assists soybean industry in producing superior quality oil and assists the starch industry in further understanding how modifications to starch structure affect functional properties.
Technical Abstract: Structures and functional properties of starch from high-protein, lipoxygenase-free and low-linolenic acid soybean variety seeds collected 20 days prior to harvest were investigated. Soybean starches exhibit CB-type X-ray diffraction patterns, and granule diameters were very small (0.7 to 4 micrometers). Soybeans, 20 days prior to harvest had 10.9-11.7% starch (dry basis). Apparent amylose content was low (19-22%) and absolute amylose content was very low (11.8-16.2%). Amylopectin weight-average molecular weight ranged from 5.1 to 11.3 x 108. Amylopectin average branch chain-length, determined by anion-exchange chromatography with amyloglucosidase post-column and pulsed amperometric detector, was very short relative to other starches (20.4-20.9). Onset gelatinization temperature ranged from 52-54 deg C, and delta H was 12-13 J/g. Paste viscosity was low relative to other starches, especially peak (81-93 RVU) and final (93-106 RVU) viscosity. Significant differences among soybean varieties were observed for amylose content with low-linolenic acid soybean starch apparent amylose content significantly higher than high-protein soybean starch, and absolute amylose content significantly higher than lipoxygenase-free soybean starch. Based on our results, soybeans with higher amylose content of starch during development may have less undesirable linolenic acid and oil unsaturation. Field replicates for each soybean variety exhibited high variation in starch characteristics, with further differences in starch structures and functional properties likely to be determined once variation is minimized.