Understanding quantitative relationships between protein and other chemical components in diverse soybean genotypes (lines) grown in different locations and the firmness of tofu can provide scientific insight for selecting soybean suitable for tofu making. Locations showed significant effects on seed components, including total protein, major storage proteins, subunits and polypeptides of the major storage proteins, and calcium, but not magnesium or phytic acid. Results showed that 11S content, but not 11S/7S ratio, was only correlated with filled tofu firmness when analyzed over all locations. A strong and positive correlation between firmness and A3 polypeptide of the 11S protein content was found for both pressed tofu (r = 0.80, p < 0.001) and filled tofu (r = 0.76, p < 0.001) over three locations (overall pooled data) and within most individual locations. The correlation of filled tofu firmness and A3 polypeptide was significant for each of the three individual locations. However, the correlation of pressed tofu firmness and A3 polypeptide content was significant at two of three locations. Mean calcium content was positively correlated with mean pressed and filled tofu firmness over all locations, but calcium was not correlated with pressed tofu firmness at any individual location, and only one location showed a significant correlation of calcium and filled tofu firmness. In addition, pressed tofu firmness was found to be negatively correlated with tofu yield. The findings that A3 polypeptide's strong relationship with tofu firmness within certain locations may be used by the food industry to select proper soybean for manufacturing tofu and to facilitate tofu soybean breeding for tofu making.
Keywords: planting location; soy A3 polypeptide; soy genotype; soy storage protein; tofu firmness.
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