Effects of Quillaja Saponin on Physicochemical Properties of Oil Bodies Recovered from Peony (Paeonia ostii) Seed Aqueous Extract at Different pH.

Peony seeds, an important oil resource, have been attracting much attention because of α-linolenic acid. Oil bodies (OBs), naturally pre-emulsified oils, have great potential applications in the food industry. This study investigated the effects of extraction pH and Quillaja saponin (QS) on the physicochemical properties of peony oil body (POB) emulsions. POBs were extracted from raw peony milk at pH 4.0, 5.0, 6.0, and 7.0 (named pH 4.0-, 5.0-, 6.0-, and 7.0-POBs). All POBs contained extrinsic proteins and oleosins. The extrinsic proteins of pH 4.0- and pH 5.0-POB were 23 kDa and 38 kDa glycoproteins, the unknown proteins were 48 kDa and 60 kDa, while the 48 kDa and 38 kDa proteins were completely removed under the extraction condition of pH 6.0 and 7.0. The percentage of extrinsic proteins gradually decreased from 78.4% at pH 4.0-POB to 33.88% at pH 7.0-POB, while oleosin contents increased. The particle size and zeta potential of the POB emulsions decreased, whereas the oxidative stability, storage stability, and pI increased with the increasing extraction pH. QS (0.05~0.3%) increased the negative charges of all the POB emulsions, and 0.1% QS significantly improved the dispersion, storage, and the oxidative stability of the POB emulsions. This study provides guidance for selecting the proper conditions for the aqueous extraction of POBs and improving the stability of OB emulsions.

Effect of Heat Treatment on the Digestive Characteristics of Different Soybean Oil Body Emulsions.

Soybean oil body (SOB) emulsions were prepared using OBs extracted at pH 11.0 and pH 7.0. The pH 11.0-SOB comprised oleosins, whereas pH 7.0-SOB comprised extrinsic proteins and oleosins. All SOB emulsions were heated at 60-100 °C for 15 min. Heating may lead to the release of extrinsic proteins from the surface of pH 7.0-SOB due to heat-induced denaturation. The total proportion of α-helix and ß-sheets gradually decreased from 77 (unheated) to 36.2% (100 °C). During stomach digestion, the extrinsic protein hydrolysis of heated pH 7.0-SOB emulsions was fast between 60 and 80 °C, and it then slowed between 90 and 100 °C; heating inhibited the oleosin hydrolysis of pH 7.0- and 11.0-SOBs. Heat treatment promoted aggregation and coalescence, and it resulted in increased particle sizes for all emulsions. Larger aggregates were found in heated pH 7.0-SOB emulsions, and larger oil droplets were found in heated pH 11.0-SOB emulsions. After intestinal digestion, the droplets of all SOB emulsions gradually dispersed, and particle sizes decreased. Different heating temperatures had lesser effects on particle sizes and microstructures. Lipolysis was affected by the extraction pH and heating. For pH 11.0-SOB emulsions, the FFA release tendency was greatly affected by the heating temperature, and heating to 80 °C resulted in the highest FFA release (74%). However, all pH 7.0-SOB emulsions had similar total FFA releases. In addition, the droplet charges of heated pH 7.0-SOB emulsions were lower than those of unheated pH 7.0-SOB emulsions in both the intestine and stomach phases; however, the charge changes in different pH 11.0-SOB emulsions showed the opposite tendency. This study will offer guidance regarding the application of SOB emulsions in food.

Digestive characteristics of oil body extracted from soybean aqueous extract at different pHs.

Soybean oil bodies (SOBs), a natural source of pre-emulsified oil, have important potential applications in food industry. In this study, SOBs were extracted from raw soybean milk at pH 5.0, 7.0, 8.0, 9.0 and 11.0. The pH 5.0-, 7.0- and 8.0-SOB contained extrinsic proteins (mainly 7S, 11S and γ-conglycinin) and oleosins (24 kDa, 18 kDa and 16 kDa), and pH 9.0-, 11.0-SOB only had oleosins. Extrinsic protein contents decreased from 83.9% at pH 5.0-SOB to 58.2% at pH 8.0-SOB, zeta potentials increased gradually from -21.7 mV to -14.67 mV and particle sizes decreased from 924 nm to 359 nm with increasing extraction pHs. In stomach digestion, oleosins of pH 5.0-, 7.0-, 8.0-SOB were hydrolyzed more rapidly than extrinsic proteins. All 24 kDa oleosins were hydrolyzed during 5 min, and 18 kDa oleosins were completely hydrolyzed at 30 min for all SOBs. Oleosins were hydrolyzed and produced <15 kDa pepsin-resistant peptides. In addition, some 7S and 11S of pH 5.0-, 7.0-, 8.0-SOB resisted pepsin hydrolysis. For all SOB emulsions, zeta potentials decreased and the droplets sizes increased significantly (P < 0.05) with the extension of gastric digestive time. The oil droplets of all SOB emulsions aggregated, and the coalescence of oil droplets more easily occurred in pH 9.0- and 11.0-SOB emulsions. During the intestinal phase, zeta potentials and diameters of the droplets decreased gradually, and the droplets of SOB emulsions dispersed according to the CLSM. FFA release rates of pH 5.0-, 7.0-, 8.0-SOB emulsions increased rapidly and then increased slowly, however, the release tendency of pH 9.0-, 11.0-SOB emulsions were opposite. Total FFA releases of pH 5.0-, 7.0-, 8.0-, 9.0-, 11.0-SOB emulsions were respectively 52.5%, 70.5%, 59%, 48.8%, 43.3% at 180 min. Therefore, the digestive behaviors of SOB emulsions extracted at different pHs were different. This study will provide guidance for SOB products.

Effects of soybean oil on rheological characteristics of dough under high hydrostatic pressure.

In order to improve the stability of dough with soybean oil, this article explored the effect of soybean oil addition on the rheological characteristics of dough under high hydrostatic pressure. The results showed that, compared with the dough without soybean oil, the ß-sheet, disulfide bonds content, and gauche-gauche-gauche in the dough increased by 4.23%, 0.85 µmol/g, and 4.16%, respectively when the dough was added with 6% soybean oil, which improved the degree of cross-linking polymerization of gluten protein and the stability of gluten network. Meanwhile, the dough had the highest elastic modulus and the lowest maximum creep compliance (6.85 × 10-4 Pa-1 ), indicating that 6% soybean oil significantly increased the elasticity and hardness of the dough. The results of short-range ordered structure and paste properties showed that with the addition of soybean oil, the ordered structure and paste viscosity decreased with the increase of soybean oil.

Selective Extraction and Antioxidant Properties of Thiol-Containing Peptides in Soy Glycinine Hydrolysates.

A highly selective procedure to extract thiol-containing peptides (TCPs) from complicated soy glycinin hydrolysates (SGHs) was described. This procedure included the reduction of disulfide bonds by 1,4-dithiothreitol (DTT) and enrichment of TCPs through Thiopropyl-Sephrose 6B covalent chromatography. TCPs were confirmed using a strategy based on mass shift after differential alkylation of sulfhydryl groups with iodoacetamide and N-ethylmaleimide by matrix-assisted laser desorption ionization mass spectrometry (MALDI-TOF-MS). The antioxidant activities of TCPs were evaluated using chemical assays. DTT reduction increased the concentration of sulfhydryl groups from 1.8 µmol/g to 113.8 µmol/g. The efficiency of the extraction was improved by optimizing the loading of sample, extraction and desorption time and the content of desorption reagent. Both of the adsorption and desorption process were found to fit a pseudo-second order model. MALDI-TOF-MS showed that 36 of the 45 extracted peptides were TCPs. The EC50 of TCPs for DPPH, hydroxyl radical, and superoxide anion radical was 0.1, 1.49 and 0.084 mg/mL, respectively. The reducing power of TCPs (0.2 mg/mL) was of 0.375. These results suggest that the combination of DTT reduction and Thiopropyl-Sepharose 6B covalent chromatograph was a successful pathway to extract TCPs from SGHs and the TCPs could be used as potential antioxidants.

Heavy metal complexation of thiol-containing peptides from soy glycinin hydrolysates.

Many thiol-containing molecules show heavy metal complexation ability and are used as antidotes. In this study, the potential function associated with thiol-containing peptides (TCPs) from soy protein hydrolysates as natural detoxicants for heavy metals is reported. TCPs enriched by Thiopropyl-Sepharose 6B covalent chromatography had different molecular weight distributions as well as different numbers of proton dissociable groups, depending on the proteases and degree of hydrolysis. The major contribution of sulfhydryl groups was confirmed by the largest pH decrease between 8.0 and 8.5 of the pH titration curves. The complexation of TCPs with heavy metals was evaluated by stability constants (ßn) of TCP-metal complexes whose stoichiometry was found to be 1:1 (ML) and 1:2 (ML2). TCPs from degree of hydrolysis of 25% hydrolysates gave high affinities towards Hg2+, Cd2+, and Pb2+ (giving similar or even bigger lgß values than that of glutathione). A significantly positive correlation was found between the logarithm of stability constants for ML2 (lgß2) and the sulfhydryl group content. Molecular weight distribution of TCPs affected the complexation with Pb2+ notably more than Hg2+ and Cd2+. These results suggest that soy TCPs have the potential to be used in the formulation of functional foods to counteract heavy metal accumulation in humans.