Influence of protein extraction and texturization on odor-active compounds of pea proteins.

BACKGROUND: The use of plant proteins as food ingredients might be limited due to the presence of foreign or 'off' flavors, which may evolve during extraction and subsequent processing. In this study, the influence of dry (TVP) and wet (WTP) texturization on characteristic volatile compounds of two different pea protein isolates was assessed using gas chromatography-mass spectrometry-olfactometry (GC-MS-O) after direct immersion stir bar sorptive extraction (DI-SBSE). RESULTS: Twenty-four odor-active compounds were found, with a prevalence of carbonyls from fat oxidation. Nine of these compounds which are also known as major (off-) flavor contributors in peas were distinctively impacted in all texturates: hexanal, nonanal, 2-undecanone, (E)-2-octenal, (E, Z)-3,5-octadiene-2-one, (E, E)-2,4-decadienal, 2-pentyl-furan, 2-pentyl-pyridine, and γ-nonalactone. For example, hexanal, a characteristic green odorant, was reduced by up to sixfold by wet texturization, from 3.29 ± 1.05% (Pea Protein I) to 0.52 ± 0.02% (Pea WTP I). Furthermore, (E,Z)-3,5-Octadiene-2-one and (E,E)-2,4-decadienal were decreased by 1.5- and 1.8-fold when Pea Protein I and Pea TVP I were compared. CONCLUSION: An overall reduction in fat oxidation products and of green and fatty odor-active compounds was observed. The results represent a first insight into the process-related modulation of pea protein (off-) flavors to broaden the applicability of pea proteins as food ingredients.

Effect of alkaline extraction pH on structure properties, solubility, and beany flavor of yellow pea protein isolate.

In the current study, the impact of alkaline extraction pH (8.5, 9.0, and 9.5) on chemical composition, molecular structure, solubility and aromatic profile of PPI was investigated by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), the quantification of free sulfhydryl group and disulfide bond contents, size exclusion chromatography with multi-angle static light scattering and refractive index (SEC-MALS-RI), circular dichroism (CD) spectroscopy, and headspace solid phase micro extraction gas chromatography-mass spectroscopy (HS-SPME-GC-MS). We found that protein recovery yield increased from 49.20% to 57.56% as the alkaline extraction pH increased from 8.5 to 9.5. However, increasing the extraction pH promoted the formation of protein aggregates which decreased the percent protein solubility although there was no influence on protein secondary structure. PPI extracted at pH 9.0 possessed the lowest beany flavor as revealed by the selected six beany flavor markers including alcohols, aldehydes, ketones and pyrazine. The lowest lipoxygenase activity at pH 9.0 may contribute to the least beany flavor in PPI. Therefore, pH 9.0 was found to be the optimal condition for preparing premium PPI in terms of yield, functionality, and aromatic profile using alkaline extraction-isoelectric precipitation process. The findings could have fundamental implications for the preparation and utilization of pea proteins in food applications.

Molecularization of Bitter Off-Taste Compounds in Pea-Protein Isolates (Pisum sativum L.).

Activity-guided fractionations, combined with taste dilution analyses (TDA), were performed to locate the key compounds contributing to the bitter off-taste of pea-protein isolates (Pisum sativum L.). Purification of the compounds perceived with the highest sensory impact, followed by 1D/2D-NMR, (LC-)MS/MS, LC-TOF-MS, and MSE experiments, led to the identification of 14 lipids and lipid oxidation products, namely, 9,10,13-trihydroxyoctadec-12-enoic acid, 9,12,13-trihydroxyoctadec-10-enoic acid, 9,10,11-trihydroxyoctadec-12-enoic, 11,12,13-trihydroxyoctadec-9-enoic acid, (10E,12E)-9-hydroxyoctadeca-10,12-dienoic acid, (9Z,11E)-13-hydroxyoctadeca-9,11-dienoic acid, (9E,11E)-13-hydroxyoctadeca-9,11-dienoic acid, 1-linoleoyl glycerol, α-linolenic acid, 2-hydroxypalmitic acid, 2-hydroxyoleic acid, linoleic acid, (9Z,11E)-13-oxooctadeca-9,11-dienoic acid, and octacosa-6,9,19,22-tetraen. Herein, we present the isolation, structure determination, and sensory activity of these molecules. Depending on their structure, the isolated compounds showed human bitter recognition thresholds between 0.06 and 0.99 mmol/L in water.

Preparation and characterization of pea protein isolate-pullulan blend electrospun nanofiber films.

The objective of this work was to fabricate and characterize food-grade pea protein isolate (PPI) and carbohydrate polymer pullulan (PUL) nanofiber films by using green electrospinning technology. The effect of the blend ratios on the PPI/PUL solution properties (e.g. viscosity, surface tension and electrical conductivity) and morphology of the resulting electrospun nanofibers was investigated. The presence of PUL in the blends resulted in decreased apparent viscosity (P < 0.05), stable surface tension (42.09-46.26 mN/m) (P < 0.05) and lower conductivity of the solutions (P < 0.05), which were due to a better chain entanglement and decrease in the polyelectrolyte protein character, respectively, both factors were needed for uniform nanofiber (around 203 nm) formation. Rheological evaluation indicated a pseudoplastic behavior for all formulations. The Fourier transform infrared spectral changes and XRD patterns indicated that the protein and polysaccharide were well tangled in nanofibers. The results of the differential scanning calorimetry (DSC) indicate that thermal stability of the electrospun nanofiber films were improved in comparison to pure PUL. Finally, in order to expand the application range of the electrospun nanofiber films in future, thermal crosslinking method was conducted and water contact angles (WCAs) of the thermal treated nanofiber films exhibited better hydrophobic properties compared to the un-crosslinking samples.

Development and evaluation of antibacterial electrospun pea protein isolate-polyvinyl alcohol nanocomposite mats incorporated with cinnamaldehyde.

Electrospun film is developed from an electrically charged ultrafine jet of a polymer solution or melt as a matrix of thin/nano fibers struck on to a target surface. The objective of this work was to obtain homogeneous nanofibers from pea protein isolate (PPI) in polyvinyl alcohol (PVA) by hybrid electrospinning as well as incorporating cinnamaldehyde (CA) into the matrix to obtain an antibacterial mat. The effect of processing conditions, pH, polymer and CA concentrations on formulation properties and nanofiber morphology were investigated and the mats were visualized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). Rheological evaluation indicated a pseudoplastic behavior for all formulations. Alkaline pH formulation led to a decreasing apparent viscosity and an increasing electrical conductivity resulting in the formation of more homogeneous fibers. The 50:50 mass percentage ratio of PPI/PVA solutions produced homogeneous nanofibers with the average fiber diameter of 485 ±â€¯85 nm. FTIR spectroscopy confirmed uniform dispersion of PPI and PVA. The minimum concentration of CA to inhibit both Gram negative and Gram positive bacteria was 1%. The average diameter of nanofibers decreased from 257 ±â€¯51 nm to 219 ±â€¯31 nm by increasing CA content from 0.25 to 1.5%.