Yellow pea aqueous fractionation increases the specific volume fraction and viscosity of its dispersions

Abstract

Some studies have shown that mild fractionation may result in similar or even better functional properties, than those of highly purified ingredients. This study aimed to relate the level of aqueous purification to the composition, solubility and viscosity of yellow pea fractions. A seldomly used method of cryo-planing combined with Cryo-SEM revealed the presence of protein bodies and starch granules in the seeds and flour, with sizes of ~3 μm and ~20 μm, respectively. Fractions with protein purities ranging from 40 to 85% (w/w) were obtained from the flour and characterized. These fractions were also compared to commerially available yellow pea protein isolate. The fractions that were only exposed to a solubilisation step contained high quantities of carbohydrates (23.6% w/w), which were mostly present as oligosaccharides. Subsequent fractionation steps increased the protein content and changed the ratio between the different pea proteins to some extent. We found that more fractionation steps reduced the solubility of the fractions. The most purified fraction contained 17% (w/w) insoluble protein aggregates with radii ≥ 100 nm. This fraction showed a substantial thickening capacity, with a viscosity of up to 103 mPa s at a concentration of 23% (w/w). The impurities (i.e. sugars, starch granules) present in the fractions only had a small effect on viscosity. Based on the protein specific volume fraction and particle size analysis, it was concluded that yellow pea protein can form aggregates with a rarefied structure responsible for its thickening capacity.