Free radical-scavenging activity of nonenzymatically-browned phospholipids produced in the reaction between phosphatidylethanolamine and ribose in hydrophobic media

Maillard reaction products derived from xylose-phosphatidylethanolamine: Potential anti-oxidative substances from hot-pressed flaxseed oil

Hot-pressed flaxseed oil is favored in Northwest China as cooking oil due to its flavor and oxidative stability. The mechanism of enhancing oxidation stability of hot-pressed flaxseed oil by neoformed Maillard reaction products (MRPs) remains mysterious. Maillard model reaction between phosphatidylethanolamine (PE) and reducing sugar of flaxseed, glucose (Glu)/fructose (Fru)/xylose (Xyl), was conducted to investigate the antioxidant characteristics of products. MRPs of PE-Xyl had a superior reactivity and anti-oxidative capabilities, which could improve the oxidative stability of flaxseed oil and inhibited the formation of aldehydes in the accelerated oxidation. Phosphatidylethanolamine-linked pyrrolecarbaldehyde (PLP) was the main antioxidant component in MRPs of Xyl-PE by MS and NMR analysis and verification of antioxidant activity. Furthermore, the results of quantum chemical calculation show that the antioxidant activity center of PLP is the pyrrole group. The findings of this study provide insights into the chemical basis underlying the improved oxidative stability of hot-pressed oils.

Effect of soybean phosphatidylethanolamine-tamarind gum Maillard conjugate on physicochemical stability of water-in-oil emulsions

Lipid oxidation hinders the development of water-in-oil (W/O) emulsions. This work aimed to determine the impact of soybean phosphatidylethanolamine (SP)/tamarind gum (TG) ratios on interface activity and anti-oxidant capacity of Maillard conjugates (MCs) in W/O emulsions. Results showed that grafting degree of MCs reached maximum with SP/TG ratio at 1:1 (43.5 %). Compared with SP and mixtures, interface activity (larger reduction of interfacial tension) and anti-oxidant capacity of MCs, especially with SP/TG = 1:1, were enhanced. The improvement of interface activity was owing to more stable adsorption at the interface caused by the increase of zeta potential and water contact angle as well as faster interface saturation benefited from broader steric network of TG moiety. The higher DPPH scavenging ability and ferric-reducing antioxidant power of MC were attributed to the combined effects of grafting degree, interface activity and molecule behavior of TG moiety. When the MC was added, the emulsion was observed smaller droplet size (1.3 μm), higher zeta potential (-73.5 mV) and lower contents of primary and secondary oxidation products (decreased by 70.9 % and 78.7 %, respectively). Hence, soybean phosphatidylethanolamine-tamarind gum-Maillard conjugate was effective to improve the physicochemical stability of W/O emulsions.

Unraveling the Formation Mechanism of Egg's Unique Flavor via Flavoromics and Lipidomics

Egg products after thermal treatment possess a unique flavor and are favored by consumers. In this study, the key aroma-active compounds of egg yolk products and their formation mechanism during thermal treatment were investigated. The volatile aroma compounds in egg yolks were monitored using an electronic nose, gas chromatography-mass spectrometry (GC-MS) and gas chromatography-olfactometry-mass spectrometry (GC-O-MS), and the lipid molecular species were explored using ultra-high-performance liquid chromatography- mass spectrometry with a Q-Exactive HF-X Orbitrap (UPLC-Q-Exactive HF-X). A total of 68 volatile compounds were identified. Boiled eggs mainly derived their flavor from hexanal, 2-pentyl-furan, 2-butanone, 3-methyl-butanal and heptane. Meanwhile, fried eggs relied mainly on 14 compounds, the most important of which were 2-ethyl-3-methyl-pyrazine, 3-ethyl-2,5-dimethyl-pyrazine, 2-ethyl-3,5-dimethyl-pyrazine, nonanal and 2,3-diethyl-5-methyl-pyrazine, providing a baked and burnt sugar flavor. A total of 201 lipid molecules, belonging to 21 lipid subclasses, were identified in egg yolks, and 13 oxidized lipids were characterized using a molecular network. Phosphoethanolamines (PEs) containing polyunsaturated fatty acids were the primary flavor precursors contributing to the development of egg yolks' flavor, participating in lipid oxidation reactions and the Maillard reaction and regulating the production of aldehydes and pyrazine compounds. This study provides reference and guidance for the development of egg yolk flavor products.

The effect of microwave pre-treatment of rapeseed on the degradation kinetics of lipophilic bioactive compounds of the oil during storage

This study examined the storage stability of tocochromanols and carotenoids in the oils prepared from microwave pre-treated (MV) rapeseeds (2-10 min, 800W) during storage at 20 °C for 12 months. In line with lipophilic antioxidant degradation throughout the storage period, changes in the antioxidant capacity of the oil were monitored. Microwaving significantly affected the concentration of lipophilic antioxidants in the oil. After 10 min of MV pre-treatment the highest content of total tocochromanols (76.64 mg/100g) was achieved, whereas a maximum carotenoid concentration (861.28 μg/100g) was obtained following 6 min seed MV pre-treatment. The degradation kinetics for the tocochromanols and carotenoids followed a zero-order kinetic model. From the kinetic analysis, it was shown that the degradation rate constant (k) of both tocochromanols and carotenoids decreased with longer seed exposure to MV radiation. The kinetics of antioxidant capacity degradation during the storage of oils followed a zero-order reaction. The rate of antioxidant capacity degradation in the control oil was higher (k=9.1 x 10-2 mmol TEAC/l/month) compared with oils prepared from MV pre-treated seeds (k=6.8-8.0 x 10-2 mmol TEAC/l/month).

Impact of phosphatidylethanolamine on the antioxidant activity of α-tocopherol and trolox in bulk oil

The amphiphilic phospholipids dioleoylphosphatidylcholine (DOPC) and dioleoylphosphatidylethanolamine (DOPE), can form reverse micelles in bulk oils, which affects lipid oxidation chemistry. Previous studies showed that reverse micelles formed by DOPC and DOPE shorten the oxidation lag phase of stripped soybean oil. This study examined how these reverse micelles influence the activity of primary antioxidants such as the nonpolar α-tocopherol and the polar trolox in stripped and commercial soybean oils. The results showed that DOPC reverse micelles decreased the activity of 100 μM α-tocopherol or trolox. On the other hand, DOPE increased the antioxidant activity of both α-tocopherol and trolox. The polar trolox exhibited better antioxidant activity than the nonpolar α-tocopherol in the presence of both DOPC and DOPE reverse micelles because trolox partitioned more at the interfaces, which was confirmed by a fluorescence steady state study. Different ratios of DOPE to DOPC were added to oil containing 100 μM α-tocopherol, and antioxidant activity increased with increasing DOPE/DOPC ratio. Addition of DOPE to commercial oil inhibited lipid oxidation, whetrsd DOPC was ineffective. HPLC showed that DOPE regenerated α-tocopherol. This study indicates that the antioxidant activity of tocopherols could be improved by utilizing phosphatidylethanolamine (PE) to engineer the properties of reverse micelles in bulk oil.

Effect of seed roasting on canolol, tocopherol, and phospholipid contents, Maillard type reactions, and oxidative stability of mustard and rapeseed oils

This work was carried out to study the effect of roasting on different compositional parameters and oil oxidative stability of three Brassica species (Brassica juncea (BJ), B. juncea var. oriental (BJO), and Brassica napus (rapeseed, RS)). After 10 min of roasting at 165 °C, canolol contents of BJ, BJO, and RS oil reached 297.8, 171.6, and 808.5 μg/g, and the phospholipid phosphorus contents reached 453.6, 342.6, and 224.2 μg/g oil, respectively. The BJ and BJO seeds showed more prominent browning reactions than RS, due to the presence of higher amounts of reducing sugars, lysine, arginine and the occurrence of Maillard type browning reactions of phospholipids. The UV-visible spectra, fluorescence, and pyrrole content showed the presence of browning reaction products in the roasted seed oils. Roasting increased the oxidative stability of all varieties. Canolol formation could only partially explain such observations. Other roasting effects such as phospholipid extraction and Maillard type browning reaction products were also responsible for the increased stability.

Effect of ultrasound pre-treatment of hemp (Cannabis sativa L.) seed on supercritical CO2 extraction of oil

Ultrasound pre-treatment of intact hemp seeds without any solvent assistance was carried out for 10, 20 and 40 min prior to SCCO2 extraction at 40 °C, 300 bar and 45 kg CO2/kg feed. Sonication time effect on SC-CO2 extraction was investigated by the extraction kinetics. The maximum extraction yield was estimated to be 24.03 (% w/w) after 10 min of ultrasonic pre-treatment. The fatty acid compositions of the oils extracted by SC-CO2 without and with ultrasound pre-treatments was analyzed using gas chromatography. It was shown that the content of linoleic, α-linolenic and oleic acids (the most abundant unsaturated fatty acids) of the hemp seed oils were not affected significantly by the application of ultrasound. UV spectroscopy indices (K232 and K268) and antiradical capacity were used to follow the quality of oils. Significant were the changes in their antiradical capacity due to ultrasound treatment. A comparison with the oil extracted by Soxhlet was also given.

Comparison of ultrasound-assisted extraction with conventional extraction methods of oil and polyphenols from grape (Vitis vinifera L.) seeds

Ultrasound-assisted extraction (US) carried out at 20 KHz, 150 W for 30 min gave grape seed oil yield (14% w/w) similar to Soxhlet extraction (S) for 6 h. No significant differences for the major fatty acids was observed in oils extracted by S and US at 150 W. Instead, K232 and K268 of US- oils resulted lower than S-oil. From grape seeds differently defatted (S and US), polyphenols and their fractions were extracted by maceration for 12 h and by ultrasound-assisted extraction for 15 min. Sonication time was optimized after kinetics study on polyphenols extraction. Grape seed extracts obtained from seeds defatted by ultrasound (US) and then extracted by maceration resulted the highest in polyphenol concentration (105.20mg GAE/g flour) and antioxidant activity (109 Eq αToc/g flour).