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.

Proteolytic characterization of a novel enzymatic extract from Bromelia serra leaves.

Bromelia serra leaves collected from Corrientes, Argentina, were assessed to analyze and characterize the proteolytic system and to evaluate its potential use as an industrial catalyst. The specific activity of the enzymatic extract (EE), which was prepared using acetone as a precipitating agent of the crude extract (CE), increased 2-3 folds with different substrates (hemoglobin, azocasein and casein). The proteins present in the EE have isoelectric points between 4.55-8.15 and they were significant inhibited by pepstatin A (50%) and E-64 (15%). Proteolytic activity in EE presented high activity in acidic pH (2.7-4), and low activity in neutral alkaline pH (6-11.75). The EE optimum activity was reached at 60ºC, and referring to the thermal stability, it retained over 97% of the proteolytic activity after incubation at a temperature range of 37‒60 ºC for 60 min. The effect of reducing agents and ionic strength were also measured, and it showed that the EE had its maximum activity with 5mM of cysteine, and it was inactivated with 2.5 M of NaCl. The chromatography procedures presented two purified enzymes of 21 and 54 KDa with proteolytic activity. The characteristics of the EE suggest that it is a potential candidate as an industrial catalyst.

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

Pigeon pea protein isolates (PPI) are an option to obtain a high yield of good quality proteins and represent a great potential for the food industry. In this work, physicochemical and structural properties of albumin (ALB), globulin (GLB), and PPI obtained at different pHs (8, 9, 10, and 11) were studied to deepen the knowledge of these proteins for future application. GLB presented protein aggregates and polypeptides characteristics of 7S vicilin subunits while ALB presented polypeptides with low molecular masses. GLB showed a more compact and less flexible structure than ALB fraction due to the distinct conformational characteristics found in DSC, fluorescence spectroscopy, Ho. These structural characteristics conferred GLB greater conformational stability (∆GH2O) than ALB fraction. The latter presented a higher proportion of ß-strand in aggregated structures. PPI11 showed the highest protein recovery, but the least So with more presence of protein aggregates with the least proportion of ß-strands in aggregated structures. A higher percentage of protein unfolding and exposure of hydrophobic residues to solvent was observed as the extraction pH of the isolates increased. Enthalpy change of transition decreased, and the maximum emission wavelength shifted to red in fluorescence spectroscopy. However, PPI11 showed only a slight increase in Ho (10%) with respect to PPI8. The variation in pH for protein extraction constitutes a simple, rapid, and low-cost method to obtain PPI with physicochemical and structural properties that will determine its functional properties and their use as food ingredients.

High-intensity ultrasound-assisted extraction of phenolic compounds from cowpea pods and its encapsulation in hydrogels.

Currently and according to the growing worldwide interest in the revaluation of agricultural by-products, the use of legumes waste presents great potential to obtain bioactive compounds. In this context, an extract rich in phenolic compounds was obtained from Vigna unguiculata (cowpea) pods by optimizing the high-intensity ultrasound conditions (10 min and 36% of amplitude) using response surface methodology. Then, the extract was encapsulated in Ca(II)-alginate beads with the addition of arabic or guar gums or cowpea isolated proteins. A complete morphological study by image analysis and microstructural evaluation by SAXS has been carried out. Results showed that beads containing alginate and alginate-guar gum have the highest loading efficiency of total phenolic compounds (47 ± 5%) and antioxidant activity (44 ± 3%). However, the coupled effect of the cowpea extract and the isolated proteins (at it higher concentration) increased the antioxidant capacity of the beads due to the contribution of the phenolic compounds and the amino acids with anti-radical activity, reaching a value of 67 ± 3 % of inhibition of ABTS.+. Finally, the microstructural analyses revealed that cowpea pod extract increased the interconnectivity of the rods due to the presence of trivalent cations, conferring versatility, and larger coordination to the network. Also, it was observed that the addition of cowpea proteins produced more interconnected bigger and fewer compacts rods than beads containing only alginate, increasing 12 and 49 % the interconnection and the size, respectively, and decreasing 10 % their compactness. This research demonstrated the use of cowpea sub-products as a source of bioactive compounds that further modulate the microstructure of the hydrogel network, and the outstanding potential for being incorporated in techno-functional foods by using Ca(II)-alginate as a carrier.