NETHERLANDS – New study from Wageningen University claims to have proven for the first time that processing soy increases the protein’s nutritional quality.

Unilever called the research a ‘very exciting development’ which ‘proves that meat-free alternatives can fulfill our bodies’ protein requirements.

Just as soy remains the most widely used and studied plant-based protein source thanks to its high protein content and quality, relative to other plant-based ingredients, little is known about the effect of processing methods on protein nutritional quality.

During the production of soy-based products, the ingredient generally undergoes several processing methods such as soaking, grinding, and heating to create soy milk, or dehulling and fat extraction to create soybean flour, and then removing soluble carbohydrates from this to create soy protein concentrate.

Processing has been said to influence the amino acid pattern and digestibility of soy protein, leading to different protein quality scores for different soy protein products.

Even some consumers expressed concern that processed soy products found in meat-free alternatives are made less nutritious by these processes.

To gain a better understanding of the effect of processing on the protein quality of soy, Unilever and Wageningen University researchers assessed the indispensable amino acid (IAA) composition and digestibility of varying soy products, to obtain both digestibility indispensable amino acids scores (DIAAS) and protein digestibility corrected amino acid scores (PDCAAS).

DIAAS is the current standard for evaluating protein quality and was developed by the UN’s Food and Agriculture Organization about a decade ago to address certain limitations of the older PDCAAS score.

The major difference between these two protein quality scores, for example, is that the DIAAS relates the amount of ingested protein with the levels present at the end of the small intestine (‘ileal digestibility’). PDCAAS uses the levels of protein remaining in the feces (‘fecal digestibility’).

The researchers, therefore, used both methods to gain insight into the effect of processing on the protein quality of soy.

The results, based on a quantitative review of in-vivo and in-vitro studies, showed soymilk had the highest DIAAS followed by soy protein concentrate, soybean meal, soybean, soy protein isolate, soy flour, soy hulls, soy flakes, and tofu.

For all soy products combined, the mean DIAAS was 84.5 ± 11.4 and the mean PDCAAS was 85.6 ± 18.2. 

This study confirms that the majority of soy products have high protein quality scores and we demonstrated that processing and post-processing conditions can increase or decrease protein quality,” the study’s authors wrote.

They added: “Additional experimental studies are needed to quantify to which extent processing and post-processing impact protein quality of plant-based protein-rich products relevant for human consumption.”

Amelia Jarman, Unilever Future Health & Wellness Science and Technology Director, said the findings of this research put to bed concerns that processed soy-based foods are an inadequate source of protein. She added that Unilever’s food brand, The Vegetarian Butcher, offers plant-based meats that provide a good source of protein and can be used to create delicious and nutritious meals.

Plant-based foods are better for the health of people and the planet, and this research demonstrates that protein quality is not compromised.

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