Soy remains the most used and studied source of vegetable protein thanks to its high protein content and its quality compared to other plant-based ingredients.
But when producing soy products, the ingredient usually undergoes several processing methods such as soaking, grinding and heating to create soy milk, or shelling and fat extraction to create soy flour, then remove the soluble carbs from it to create soy. protein concentrate.
Thus, although soy is well known for its high protein quality, little is known about the effect of processing methods on the nutritional quality of protein. Processing can influence the amino acid structure and digestibility of soy protein, leading to different protein quality scores for different soy protein products. Additionally, consumers have expressed concern that processed soy products found in meatless alternatives are rendered less nutritious by these processes.
To better understand the effect of processing on soy protein quality, researchers from Unilever and Wageningen University evaluated the essential amino acid (IAA) composition and digestibility of various soy products. , to obtain both Digestibility Essential Amino Acid Scores (DIAAS) and Protein Digestibility Corrected Amino Acid Scores (PDCAAS).
The DIAAS is the current standard for assessing protein quality and was developed by the Food and Agriculture Organization of the United Nations about a decade ago to address some limitations of the old PDCAAS score.
The main difference between these two protein quality scores, for example, is that the DIAAS relates the amount of protein ingested to the levels present at the end of the small intestine (“ileal digestibility”). The PDCAAS uses the protein levels remaining in the faeces (“faecal digestibility”).
However, because data on amino acid digestibility at the ileal level are limited, the use of faecal digestibility remains a widely accepted method for assessing protein quality and comparing protein quality between sources. The researchers therefore used both methods to better understand the effect of processing on the protein quality of soybeans.
The importance of post-processing
The results, based on a quantitative review of in vivoand in vitrostudies, have shown different protein quality scores between soy product groups. Soy milk had the highest DIAAS, followed by soy protein concentrate, soy flour, soy, soy protein isolate, soy flour, soy hulls, soy flakes soy and tofu. For all soy products combined, the mean DIAAS was 84.5 ± 11.4 and the mean PDCAAS was 85.6 ± 18.2.
Additionally, researchers observed wide variations in protein quality scores within soy product groups, indicating that differences and variations in protein quality scores can also be attributed to various forms of post-processing (such as additional heat treatment or humidity conditions). For example, the numbers show that the majority of studies on soy have resulted in DIAAS and PDCAAS values above 75, which classifies them as high-quality proteins. However, for some product groups, values below 75 were found, especially for post-processed soy products such as post-processed soy, soy protein meal and soy protein isolate.
After excluding post-processed data points, for all soy products combined, the mean DIAAS was 86.0 ± 10.8 and the mean PDCAAS was 92.4 ± 11.9.
“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,”wrote the study authors. They added: “Further experimental studies are needed to quantify the extent to which processing and post-processing impact the protein quality of plant protein-rich products relevant to human consumption.”
Unilever called the research a “very exciting development” that “proves that meatless alternatives can meet our body’s protein needs.”
Amelia Jarman, Director of Science and Technology, Unilever Future Health & Wellness, said: “The results of this research have put to rest concerns that processed soy foods are an inadequate source of protein. Our Unilever 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 healthier for people and the planet, and this research demonstrates that protein quality is not compromised.
Protein quality of soybeans and the effect of processing: a quantitative review