Comparative Study of Structural and Physicochemical Properties of Pigeon Pea (Cajanus cajan L.) Protein Isolates and its Major Protein Fractions

Quantifying the effects of pre-roasting on structural and functional properties of yellow pea proteins

Roasting could modify the protein structure/conformation, contributing to changes in functional properties. Here we investigated the effects of pre-roasting on the extraction efficiency, structural and functional properties of pea protein concentrates and isolates (PPC and PPI) produced from yellow split peas. The shorter roasting times (150 °C, 10 and 20 min) had little effect on protein yields and could increase the solubility of PPC or PPI by ∼ 12% at pH 7 and enhance the solubility of PPI by ∼ 12% (10-min roasting) and ∼ 24% (20-min roasting) at pH 3. However, a longer duration of pre-roasting (150 °C, 30 min) significantly reduced the extraction efficiency of PPC and PPI by ∼ 30% and ∼ 61%, respectively. Meanwhile, pre-roasting had minor effects on SDS-PAGE profiles and the secondary structures of pea proteins but significantly altered tertiary structures by reducing free sulfhydryl groups, increasing disulfide bonds and surface hydrophobicity. As for the emulsifying properties, pre-roasting improved the emulsion ability index (EAI) of PPC and PPI but decreased the emulsion stability index (ESI) of PPC and had no significant effect on PPI. Moreover, PPC and PPI with shorter pre-roasting duration (10 and 20 min) had endothermic peaks and showed a slight decrease in the denaturation temperature (Td) and the onset temperature (To), respectively. Overall, the study demonstrated that controlled pre-roasting at 150 °C for 10 min and 20 min altered protein structures (mainly tertiary structures), improving the solubility and EAI of pea proteins at pH 7, while retaining their thermal properties in comparison to unroasted samples.

Thermal Gelation of Proteins from Cajanus cajan Influenced by pH and Ionic Strength

Cajanus cajan [pigeon pea (PP)] is an important legume crop for subsistence agriculture and its seeds are an alternative plant-based protein source. PP protein isolates (PPI) are able to form heat-induced gels that could be used for food applications. The aim of this work was to study the influence of pH (2.1, 3.9, 6.3, and 8.3) and ionic strength (μ) (0.10 and 0.54) on thermal stability and thermal gelation of PPI obtained by alkaline extraction (pH 8.0) and isoelectric precipitation. Thermal stability of PPI changed with pH variation at low ionic strength (μ = 0.10), decreasing this dependence with the increase of ionic strength (μ = 0.54). At μ = 0.10, gelation capacity of PPI was lower at pH 2.1 and pH 3.9. These gels presented a coarse network, which entails low WHC. At pH 6.3 and pH 8.3, gels showed a solid-like character with a compact and homogeneous matrix, with better WHC. At μ = 0.54, gel formation was favoured at pH 2.1 and pH 3.9. G'20/G'95 ratio values and differential solubility results suggest that hydrogen bonds and electrostatic interactions could play an important role in gel formation at pH 6.3 and pH 8.3.

In vitro gastrointestinal digestion of buckwheat (Fagopyrum esculentum Moench) protein: release and structural characteristics of novel bioactive peptides stimulating gut cholecystokinin secretion

Satiety hormone cholecystokinin (CCK) plays a vital role in appetite inhibition. Its secretion is regulated by dietary components. The search for bioactive compounds that stimulate CCK secretion is currently an active area of research. The objective of this study was to evaluate the ability of buckwheat (Fagopyrum esculentum Moench) protein digest (BPD) to stimulate CCK secretion in vitro and in vivo and clarify the structural characteristics of peptides stimulating CCK secretion. BPD was prepared by an in vitro gastrointestinal digestion model. The relative molecular weight of BPD was <10 000 Da, and peptides with <3000 Da accounted for 70%. BPD was rich in essential amino acids Lys, Leu, and Val but lacked sulfur amino acids Met and Cys. It had a stimulatory effect on CCK secretion in vitro and in vivo. Chromatographic separation was performed to isolate peptide fractions involved in CCK secretion, and five novel CCK-releasing peptides including QFDLDD, PAFKEEHL, SFHFPI, IPPLFP, and RVTVQPDS were successfully identified. A sequence length range of 6-8 and marked hydrophobicity (18-28) were observed among the most CCK-releasing peptides. The present study demonstrated for the first time that BPD could stimulate CCK secretion and clarify the structural characteristics of bioactive peptides having CCK secretagogue activity in BPD.