Develop and characterize thermally reversible transparent gels from pea protein isolate and study the gel formation mechanisms

Gels with thermo-reversibility and transparency like gelatin have been applied in various products in food and pharmaceutical industry. The replacement of gelatin by ingredients of plant origin has attracted attentions owing to the emerging markets of vegan, Halal and Kosher products. This work reports a thermo-reversible protein gel prepared with pea protein isolate extracted using ammonium sulfate precipitation method. The protein concentration and pH were discovered to be critical, and within a window of pH 2.4–4.2 and protein concentration of 10–15%, thermo-reversible gels were obtained, many of which possessing good mechanical properties with compressive stress up to 6.32 ± 1.40 kPa. Dynamic rheological measurement disclosed the thermo-reversibility of the gel being stable upon repeated heating and cooling process from 80 °C to 4 °C. Lower pH favored the formation of transparent gels with fine-stranded network as observed by scanning electron microscopy (SEM), whereas with the increase of pH up to 4.2, the gel gradually became opaque when the gel network changed to particulate aggregates while gel thermo-reversibility retained. Hydrogen bonds were shown to be dominant in forming the gel network structure during the cooling process while hydrophobic interactions and disulfide bonds were not significantly involved. The pea protein gel has the characteristics of being transparent and thermo-reversible with good mechanical property, which has provided opportunities of replacing gelatin in food applications such as fruits, beverage and fermented food products with mild acidic pH environment.