The paper comes at a time of “huge interest” in finding new prebiotics from agrofood industrial waste.
The researchers from the Universities of Reading and Roehampton in the UK and the Ciudad Universitaria in Spain looked at the in vitro effect of Okara on human faecal microbiota in a 48-hour, pH-controlled simulated gut model.
They compared ‘native’ Okara and Okara treated with the food-grade enzyme Ultraflo and High Pressure Processing (HHP) – which can up soluble dietary fibre (SDF) contents by nearly 60% – with commonly used prebiotic fructo-oligosaccharides.
They found both Okara forms showed potential prebiotic effects but the model using the treated Okara showed higher levels of short-chain fatty acids (SCFA) plus lactic acid and better growth of 'good bacteria' including bifidobacteria after four and 48 hours and lactobacilli after four hours of fermentation.
It also showed a greater ability to curb potentially harmful bacterial groups such as clostridia and Bacteroides.
At four hours, lactic acid for native Okara was 2.45 fold higher than the control fructo-oligosaccharides.
“Differences found between fructo-oligosaccharides and Okara substrates could be attributed to the great complexity of Okara’s cell wall, which would need longer times to be fermented than other easily digested molecules, thus allowing an extended potential prebiotic effect," the researchers wrote in the British Journal of Nutrition.
“These results support an in vitro potential prebiotic effect of Okara.”
Finding value in waste
Common prebiotics used by the food industry include soluble dietary fibre, inulin-derived fructans like fructo-oligosaccharides and galacto-oligosaccharides.
Yet the researchers said there was now “great interest” in finding novel prebiotics from waste biomass or by-products from food industry.
Such sources include polydextrose, lactosucrose, malto-oligosaccharides, gluco-oligosaccharides, xylo-oligosaccharides and soyabean oligosaccharides.
“One of these promising potential prebiotics is Okara, an abundant and inexpensive by-product obtained after extraction of the soluble fraction from soybean seed for tofu or soy milk production, and its re-valorisation would be economically valuable,” they wrote.
They said Okara was an insoluble by-product with a more complete nutritional profile than prebiotics current on the market like health claim- backed inulin or fructo-oligosaccharides and galacto-oligosaccharides since beside its dietary fibre content Okara also contained protein, oil and minerals.
Okara has a high total dietary fibre content of around 55% made up of about 51% insoluble dietary fibre and 4.5% soluble dietary fibre.
Research has pointed to Okara a potential weight loss aid because of this fibre content and its impact on lipid metabolism.
Source: British Journal of Nutrition
Published online ahead of print, doi:10.1017/S0007114516002816
“In vitro fermentability and prebiotic potential of soyabean Okara by human faecal microbiota”
Author: E. Pérez-López, D. Cela, A. Costabile, I. Mateos-Aparicio and P. Rupérez