Water-soluble fraction of pea protein isolate is critical for the functionality of protein-glucose conjugates obtained via wet-heating Maillard reaction.

Wet-heating Maillard reaction (MR) has been applied to improve the function of proteins by conjugating with soluble carbohydrates. However, the impact of soluble solutes particularly in plant protein on the degree of MR and the properties of the corresponding conjugates has yet to be discussed. In this study, high-intensity ultrasound (HIUS) was utilized to pretreat commercial pea protein isolate in order to improve its solubility. Two different fractions including soluble fraction (SUPPI) and whole solution (UPPI) of HIUS treated PPI were conjugated with glucose (G) to prepare SUPPI-G and UPPI-G, respectively, over a course of 24 h wet-heating at 80 °C. Conjugation was confirmed by the degree of glycation, SDS-PAGE, FTIR, and intrinsic fluorescence analysis. Color change and glucose content analysis showed that the degree of MR was greater when using SUPPI rather than UPPI. The solubility of SUPPI-G was further improved by 24 h of MR while it remained unchanged for UPPI-G. The emulsifying activity index and foaming capability of SUPPI-G were similar to those of UPPI-G. Interfacial properties determined by dynamic adsorption and dilatational rheology at both oil-water and air-water interface suggested that insoluble fraction of UPPI is essential to make stable emulsions and foams. In conclusion, the proportion of soluble protein in PPI is critical to its wet-heating MR based conjugation with glucose and the solubility of the conjugates.

Structural, functional properties, and volatile profile of hemp protein isolate as affected by extraction method: Alkaline extraction-isoelectric precipitation vs salt extraction.

The utilization of industrial hemp in food is gaining popularity. This study aimed to comprehensively investigate the impact of alkaline extraction-isoelectric precipitation (AE-IEP) and salt extraction (SE) dialysis on structural, functional properties and the volatile profile of hemp protein isolate (HPI). A higher protein content (97.21%) in SE extracted HPI (SE-HPI) was obtained than the AE-IEP extracted HPI (93.37%). In particular, protein subunit composition, structural properties were strongly influenced by the extraction methods. For example, SE-HPI exhibited a larger percentage of albumin (46.53%) and a lower amount of ß-sheet (52.65%) than its counterpart (albumin 20.92%, ß-sheet 54.46%). Consequently, SE-HPI showed the higher solubility, emulsion activity, and thermal stability. Interestingly, the volatile profile of the proteins showed that SE-HPI exhibited a lower number (21) of volatile compounds when compared to its counterpart (25). This study highlights the importance of establishing the relationships between extraction methods and functional attributes of HPI.

Heterologous expression of an agarase gene in Bacillus subtilis, and characterization of the agarase.

A ß-agarase was identified from Pseudoalteromonas sp. Q30F and heterologously expressed in Bacillus subtilis WB800n. The ß-agarase, Aga862 encoded by aga862 gene in an open reading frame of 1338 bp is 445 amino acids in length, and has a calculated molecular mass of 50.1 kDa and an estimated isoelectric point of 4.81. Protein sequence analysis showed that Aga862 belongs to family 16 of glycoside hydrolases (GH16) and carbohydrate-binding module family 13 (CBM13). The agarase was expressed in B. subtilis WB800n and purified by precipitation, anion exchange and gel filtration for a specific activity of 4.6 U/mg, a 27.8-fold improvement over the activity of the crude enzyme. Aga862 exhibited optimal activity at 45 °C and pH 6.5, and showed excellent pH stability with retention of over 80% relative activities after preincubation for the pH range of 3.0-10.0 at 4 °C for 3 h. The agarase exhibited a Km value of 14.15 mg/mL toward agarose and a Vmax of 256.41 U/mg. The mass spectrometry analysis revealed that the end products of agar degradation were neoagarotetraose and neoagarohexaose. Recombinant Aga862 has great potential for the manufacture of agaro-oligosaccharides for the non-pathogenic nature and safety of the B. subtilis WB800n.