Genetic improvement of soybean protein meal is a complex process because of negative correlation with oil, yield, and temperature. This review describes the progress in mapping and genomics, identifies knowledge gaps, and highlights the need of integrated approaches.
 Meal protein derived from soybean [Glycine max (L) Merr.] seed is the primary source of protein in poultry and livestock feed. Protein is a key factor that determines the nutritional and economical value of soybean. Genetic improvement of soybean seed protein content is highly desirable, and major quantitative trait loci (QTL) for soybean protein have been detected and repeatedly mapped on chromosomes (Chr.) 20 (LG-I), and 15 (LG-E). However, practical breeding progress is challenging because of seed protein content’s negative genetic correlation with seed yield, other seed components such as oil and sucrose, and interaction with environmental effects such as temperature during seed development. In this review, we discuss rate-limiting factors related to soybean protein content and nutritional quality, and potential control factors regulating seed storage protein. In addition, we describe advances in next-generation sequencing technologies for precise detection of natural variants and their integration with conventional and high-throughput genotyping technologies. A syntenic analysis of QTL on Chr. 15 and 20 was performed. Finally, we discuss comprehensive approaches for integrating protein and amino acid QTL, genome-wide association studies, whole-genome resequencing, and transcriptome data to accelerate identification of genomic hot spots for allele introgression and soybean meal protein improvement.

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Molecular mapping and genomics of soybean seed protein: a review and perspective for the future.

Effects of the size and content of protein aggregates on the rheological and structural properties of soy protein isolate emulsion gels induced by CaSO 4

As a traditional soybean product with good quality and a healthy food with many functional components, tofu is increasingly consumed in people's daily life. Traditional tofu processing consists of numerous steps, including the soaking and grinding of soybean seeds, heating of the soybean slurry, filtering, and addition of coagulants, and others. The properties of soybean seeds, processing scale, soaking and heating conditions, type and concentration of coagulant, and other factors collectively impact the processing steps and the final tofu quality. The generation of whole soybean tofu with more nutritive value comparing with traditional tofu has been successfully reported by several studies. As one of the most important functional component, isoflavones and their presence in tofu are also influenced by the above-mentioned factors, which influence the nutritive value of tofu. Research investigating the influence of tofu processing conditions on the quality and isoflavone profiles of tofu are the subject of this review. Issues that should be further studied to investigate the influence of processing conditions on the quality and nutritive value of tofu are also introduced.

Research progress in tofu processing: From raw materials to processing conditions.

Interactions of protein content and globulin subunit composition of soybean proteins in relation to tofu gel properties.

Profiling and relationship of water-soluble sugar and protein compositions in soybean seeds

The oxidation of unsaturated lipids by lipoxygenases in soybeans causes undesirable flavors in soy foods. Using a traditional and a nontraditional soy food user group, we examined the cultural difference in perceiving the sensory characteristics of soymilk and tofu produced from soybeans with or without lipoxygenases (Lx123). The two groups described the samples using similar terms. The traditional users preferred the control soy milk and lipoxygenase-free tofu while the nontraditional users preferred the lipoxygenase-free soymilk with no preference for tofu. In a separate study, a trained descriptive taste panel compared the odor of soymilk and tofu from control soybeans or those lacking lipoxygenase-1 and lipoxygenase-2 (Lx12) or all three isomers (Lx123). The rancid/grassy odor was rated the lowest in Lx123 products, followed by Lx12 products with the control products given the highest rating. The Lx12 and Lx123 products were also sweeter and less bitter than the controls. Taken together, our results demonstrated that soybeans lacking lipoxygenases can produce soy foods with less undesirable aromas and are therefore likely more acceptable to the consumers.

/pdf/sensory-quality-of-soymilk-and-tofu-from-soybeans-lacking-10hrlji3i2.pdf

Sensory quality of soymilk and tofu from soybeans lacking lipoxygenases.

BACKGROUND

Texture and water holding are important for silken tofu manufacturers and are affected by many factors, including soybean variety and processing conditions. In this study we evaluated these two key quality attributes of silken tofu produced from two soybean varieties – Bunya and Cowrie – using a soak or a dry processing method with glucono-δ-lactone or nigari as coagulant at concentrations of 1.5–5.0 g kg−1.



RESULTS

The soak method produced substantially firmer silken tofu with either coagulant. The optimum coagulant concentration to achieve maximum hardness was 2.5–3.0 g kg−1. At 3.0 g kg−1, Bunya produced silken tofu with firmer texture for each of the coagulant–method combinations and lower water loss, an indicator for water holding capacity, for the soak method. The two varieties differed significantly in the composition of major protein subunits for the seed and soymilk. Bunya had no 11SA4, less 11S and more 7S and therefore a lower 11S/7S ratio.



CONCLUSION

Both variety and processing conditions affect textural properties and water loss of silken tofu. The absence of 11SA4 and subsequent protein subunit compositions are important in determining these two key quality attributes. Variety Bunya produces silken tofu with firmer texture and lower water loss. © 2013 Society of Chemical Industry

Effects of soybean protein composition and processing conditions on silken tofu properties.

Drought is a major factor limiting plant growth causing yield reduction in crops; hence the characterisation of drought tolerance and the development of drought-tolerant crop varieties have been a goal of many crop breeding programs. Using the proteomics approach, we compared the differential protein abundance of drought-tolerant and drought-sensitive soybean leaves subjected to mild or severe drought stress. Proteins were extracted and separated using two-dimensional electrophoresis. Those protein spots with significant and more than 2-fold difference in abundance, 174 in total, were further analysed and 102 proteins were positively identified. Around 38.5% of these proteins were related to energy metabolism and photosynthetic functions, followed by those associated with defence response (36.4%) and protein metabolism (25.2%). Severe drought resulted in a greater number of proteins with differential abundance. Genotypes responded differently to drought stress with the tolerant genotype showing a higher capacity for reactive oxygen species scavenging and maintaining energy supply than the sensitive genotype. The sensitive genotype had a greater number of proteins with significant differential abundance than the tolerant genotypes due to drought. The different patterns in protein abundance induced by drought stress may potentially be utilised to screen and select candidate soybean lines with improved drought tolerance.

https://bioone.org/journals/crop-and-pasture-science/volume-67/issue-5/CP15314/A-comparative-proteomic-study-of-drought-tolerant-and-drought-sensitive/10.1071/CP15314.pdf

Aijun Yang

Papers

Interactions of protein content and globulin subunit composition of soybean proteins in relation to tofu gel properties.

Sensory quality of soymilk and tofu from soybeans lacking lipoxygenases.

Effects of soybean protein composition and processing conditions on silken tofu properties.

A comparative proteomic study of drought-tolerant and drought-sensitive soybean seedlings under drought stress

Rebalance between 7S and 11S globulins in soybean seeds of differing protein content and 11SA4