Effect of Soybean Maturity on Characteristics of Protein and Other Constituents
Yao, Jeng John
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https://hdl.handle.net/2142/70068
Description
Title
Effect of Soybean Maturity on Characteristics of Protein and Other Constituents
Author(s)
Yao, Jeng John
Issue Date
1982
Department of Study
Food Science
Discipline
Food Science
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Agriculture, Food Science and Technology
Abstract
Soybeans from different maturation stages were tested for their chemical composition and storage stability. Maturation was arrested at specified times by spraying paraquat on the plant. The same level of trypsin inhibitor activity was found regardless of maturation. However, the lipoxygenase activity and phytate content were significantly lower in immature beans. Crude oil and protein contents were similar regardless of maturation. The crude oil from immature samples were greener in color and higher in free fatty acid content than that from mature ones. Both yield of isolated soy protein and ratio of 7S to 11S protein in immature soybeans were lower than that from mature. During storage, lipoxygenase activity decreased independently of maturation but free fatty acid content in the crude oil increased at a faster rate in immature beans that that from mature.
Functional properties of isolated soy protein from different stages of maturity were examined. Water imbibing capacity decreased with increasing maturity. Two rheological parameters, i.e., consistency coefficient and flow behavior index of isolated soy protein dispersion varied with maturity; consistency coefficient decreased while flow behavior index increased with increasing maturity. Protein from immature soybeans showed more pseudoplasticity than from mature ones. The pH-solubility profile was similar irrespective of maturation. The 11S protein was more soluble in the acidic pH range than the 7S protein. Oil-in-water emulsion stability of isolated soy protein from mature soybeans was higher than that from the immature due to more 7S fraction in mature soybeans since 7S protein was found to form a more stable emulsion than that formed from 11S protein. This suggests that isolated soy protein from mature soybeans would serve as a better emulsifying agent. Heat-induced soy protein gels became weaker as the soybeans became more mature. This can be attributed to the higher content in the immature soybeans of 11S fraction which gives a stronger gel than 7S fraction in the protein from immature soybeans.
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