Effect of atmospheric pin-to-plate cold plasma on oat protein: Structural, chemical, and foaming characteristics

The impact of novel pin-to-plate atmospheric cold plasma was investigated with input voltage (170 V, 230 V) and exposure time (15 & 30 min) on oat protein by studying structural (FTIR, circular dichroism (CD), UV-vis, Fluorescence), morphological (particle size analysis, SEM, turbidity), chemical (pH, redox potential (ORP), ζ potential, carbonyl, sulfhydryl, surface hydrophobicity), and foaming characteristics. The plasma treatment reduced the pH while increasing the ORP of the dispersions. These ionic environment changes affected the ζ potential and particle size leading to the formation of larger aggregates (170-15; 230-15) and distorted smaller ones (170-30; 230-30) as confirmed by SEM. The FTIR spectra showed reduced intensity at specific amide bands (1600-1700 cm^-1) and also an increase in carbonyl stretching (1743 cm^-1) representing oxidative carbonylation (increase in carbonyl content). Thus, the partial exposure of hydrophobic amino acids increases surface hydrophobicity. The altered secondary structure (rise in α-helix, decrement in β-sheets and turns), and tertiary structures were observed in circular dichroism (CD) and UV absorbance and fluorescence characteristics of proteins respectively. Furthermore, the increase in free sulfhydryl content and disulfide content was highly affected by the plasma treatments due to observed protein unfolding and aggregations. Besides, the increased solubility and reduced surface tension contributed to the improved foaming characteristics. Thus, plasma processing influences protein structure affecting their characteristics and other functionalities.

Effect of food matrix and fermentation on angiotensin-converting enzyme inhibitory activity and β-glucan release after in vitro digestion in oat-based products

The aim of this study was to determine the effects of fermentation and food matrix on the ACE inhibitory activities of the peptides obtained after in vitro gastrointestinal digestion, protein profiles (SDS-PAGE) and β-glucan amounts of oat products. Furthermore, the physicochemical and microbiological properties of fermented oat drinks and oat yogurt-like product obtained from oat fermentation were evaluated. Oat grains were mixed with a certain ratio of water 1:3 w/v (oat:water, yogurt consistency) and 1:5 w/v (oat:water, drink consistency), and this mixture was fermented with yogurt culture and probiotic Lactobacillus plantarum and fermented drinks and yogurt were produced. The results indicated that the fermented oat drink and the oat yogurt-like product had L. plantarum viability over 10⁷ cfu/g. After the in vitro gastrointestinal digestion of the samples, the hydrolysis levels ranged from 57.70 % to 82.06 %.The hydrolysis level of the samples with fermented-drink consistency was significantly higher than the samples with yogurt consistency (p < 0.05).The SDS-PAGE profiles of the non-digested samples showed that the bands had molecular weights of 12-15 kDa and around 35 kDa. Bands whose molecular weights were around 35 kDA disappeared after gastric digestion. ACE inhibitory activities of the fractions composed of molecular weights of 2 kDa and 2-5 kDa obtained after in vitro gastrointestinal digestion of the oat samples were in the range of 46.93-65.91 %. The effect of fermentation on the ACE inhibitory activities of the peptide mixture with molecular weights between 2 and 5 kDa was not statistically significant, however, fermentation caused an increase in the ACE inhibitory activities of the peptide mixture with a molecular weight<2 kDa (p < 0.05). The β-glucan amounts of fermented and non-fermented oat products were in the range of 0.57-1.28 %. The β-glucan amounts detected after gastric digestion decreased considerably and β-glucan could not be detected in the supernatant after gastrointestinal digestion. This indicated that β-glucan did not solubilize in the supernatant (bioaccessible) and remained in the pellet. In conclusion, fermentation is a valuable process for releasing peptides with moderately high ACE inhibitory effects from the parent oat proteins.