Soy protein – more than meets the eye

QUALITY MATTERS AS MUCH AS QUANTITY IN ENSURING CANADIAN GROWERS KEEP A COMPETITIVE EDGE

the future of soybeans has never been brighter. More and more, the general population of North America is recognizing the health benefits of products made from this inexpensive, high-quality protein source. Consumption of soy beverages, tofu, and other soy foods is also increasing due to the growing number of Asian immigrants in the US and Canada.

In addition, an overwhelming global demand for functional foods (those with added health benefits) has created an almost insatiable parallel demand from the food industry for novel ingredients. One of these ingredients is protein gels – gels that can be made from soy. “Soy proteins have the potential to provide the food industry with a rich selection of ingredients,” says Dr. Vaino Poysa, a soybean research scientist at Agriculture and Agri-food Canada in Harrow, Ontario. “They can provide impressive functional traits, nutritional qualities and
health-promoting bioactivities.”

quality versus quantity
It’s not only soy protein quantity that matters in the quest to capture these opportunities for Canadian growers. “The quality of the protein in the seed is very important in influencing soybean quality in the manufacture of food products,” says Poysa. “If we can develop new soy cultivars with proteins optimized for specific end-uses, the quantity of protein in the seed could be reduced modestly from around 45 percent to between 40 and 42 percent.”

In other words, if research and breeding can concentrate both on protein quality and quantity, there is the potential to boost yields for soy growers (given the negative correlation between yield and protein content) while ensuring strong market demand for Canadian soybeans – where end-users are highly satisfied with the specific improved protein qualities  they need.

high quality tofu and soy beverages
With regard to tofu, Poysa and his colleagues have investigated whether certain cultivar lines (possessing or lacking certain protein subunits) could be used to make a similar quality of tofu using fewer soybeans. The first step in this research involved developing lines with unique subunit combinations using conventional breeding approaches. In conjunction with food science researchers at the AAFC Centre in Guelph and the University of Guelph, Poysa’s team then discovered there is one subunit in particular (A3 glycinin) that plays the major role in contributing to tofu firmness. “Our research shows that tofu-makers should require less soy to make a product of similar quality at the same protein level by using lines that have high levels of this subunit and are lacking specific other subunits,” says Poysa. 

On the soy beverage front, Poysa discovered that beverages prepared from soybeans that lack glycinin protein  (or lack specific subunits of glycinin) possess a smaller particle size distribution compared to soybean lines containing glycinin. “That means using these lines should improve solubility and stability of soy protein in soymilk,” he says, “enhancing shelf-life and reducing sedimentation.”

moving beyond the obvious
Direct products such as soy beverages and tofu aside, soybeans in Canada are also commonly added to enriched white bread to improve its protein quality. “Soy and wheat gluten proteins are complementary in terms of amino acid content,” says Poysa. “While soy proteins contain only small amounts of the sulphur-containing amino acids we need for good health, they are found in relatively high amounts in wheat gluten.” Conversely, soy proteins are rich in lysine, a critical amino acid found in low amounts in gluten.

Furthermore, the addition of soy to baked goods during the past few years has gone beyond simple protein enrichment. “Companies want to add it nowadays because of its health benefits,” says Poysa.

However, adding soy to bread is not a simple matter. “Studies have demonstrated some negative effects when commodity soy protein is
added to bread formulations,” Poysa notes. “It causes a significant decrease in loaf volume, weakening of dough strength, lower quality crumbs and a strong flavour.”

If the quality of the protein is tweaked, Poysa wanted to know, can these problems be averted? To investigate the interactions between wheat gluten and soy proteins during bread-making, Poysa and his colleagues set about testing many different sources of soy protein isolates – and they’ve found some exciting results.

“Our data strongly suggests that soybean lines rich in two particular subunits and low in one other could have significant potential for gluten substitution in bread-making,” Poysa says. “These lines could improve the protein content and quality, while not adversely affecting baking quality.”

Much more research is required to confirm these results in other lines with these protein subunit profiles and it will be several years before any soy cultivars with improved protein quality are ready for commercial release, says Vaino, but he considers the future promising for soy growers and soy consumers alike. •