Chemical conversions of free phytosterols during the bleaching of corn oil.

Phytosterols have health benefits; however, they are partially removed during the bleaching of corn oil. We evaluated the chemical conversion of free phytosterols (FPs) during bleaching. FP degradation accelerated with increased time and temperature, following a first-order kinetic model. In the n-heptane system, air and activated clay promoted the chemical conversion of the FPs. Sterenes formation was analysed under different conditions using a zero-order kinetic model. The apparent activation energies revealed sterene formation decreasing in the following order: campesta-3,5-diene ≈ stigmasta-3,5,22-triene > stigmasta-3,5-diene. Isomers of the above were not detected, indicating that these sterenes were the only primary products of FPs. The desorption test indicated that the FP loss from corn oil was not only due to FPs being adsorbed the activated clay, but also FPs adsorbed at acidic activated sites being degraded. This study presents a vital scientific foundation for retaining FPs to develop healthier and more nutritious oils.

NMR Analysis of Lipid Oxidation in Flaxseed Oil-in-Water Emulsions.

The formation of linolenic (Ln) and linoleic (L) acyl oxidation products during storage of flaxseed oil (FO)-in-water emulsions was monitored using proton nuclear magnetic resonance (1H NMR) spectroscopy, as well as chemical analytical methods and gas chromatography. Emulsions containing 10% FO and 1% Tween 60 were prepared by homogenization and then stored at 37 °C in the dark for 21 days under accelerated oxidation conditions (500 µmol ferrous sulfate). The induction time of the emulsions, after which rapid lipid oxidation was first observed, was 5-7 days, as shown by increases in peroxide values and hydroperoxide concentrations determined by NMR spectroscopy. Analysis of the hexanal and propanal concentrations during storage by HS-SPME-GC indicated that the oxidation of Ln and L acyls in the emulsions occurred simultaneously. The oxidation products originating from the Ln and L acyls were monitored using 1H NMR spectroscopy throughout the oxidation process. These results also showed that the Ln and L acyls oxidized simultaneously, and isomers of hydroperoxy-cyclic hydroperoxides (HCPs), Z,E-conjugated dienic hydroperoxides (ZECDHPs), and E,E-conjugated dienic hydroperoxides (EECDHPs) were the major primary oxidation products. Aldehydes were observed after 7 days, which was taken to be the start of the propagation stage, with the formation of a significant amount of oxygenated α, ß-unsaturated aldehydes (OαßUAs). Based on the concentrations of hydroperoxides originating from the Ln and L acyls, our results suggested that the loss rate of L acyls was parallel to that of Ln acyls. This result was consistent with Ln acyls adopting a tighter packing at the oil-water interface in the emulsions than L acyls. This hypothesis was supported by the NMR relaxation time data. A good correlation between the isomer concentrations of ZECDHPs and HCPs in Ln acyls and between ZECDHPs and EECDHPs in L acyls was shown, with the mole ratios between them being 1.2 and 1.1, respectively. Droplet size and microstructure analyses showed that droplet aggregation occurred from 11 days onwards, which was attributed to polar oxidation products located at the oil droplet surfaces promoting coalescence. Zeta-potential measurements indicated that the droplets became more negative during storage, which was attributed to the accumulation of anionic reaction products at the droplet surfaces.

Thermal degradation of stigmasterol under the deodorisation temperature exposure alone and in edible corn oil.

Phytosterols are commonly found in vegetable oils and possess health benefits for humans. While investigating the chemical conversion of stigmasterol at deodorisation temperatures, gas chromatography-mass spectrometry (GC-MS) and ultra-high performance liquid chromatography coupled to high-resolution mass spectrometry (UHPLC-HRMS) experiments led to the identification of 5-ethyl-6-methyl-3-heptene-2-one, 3-hydoxy-steroid, 3-ketostigmasterol, and 3,7-diketostigmasterol as by-products. The identification of these compounds assisted in the interpretation of the stigmasterol oligomers characterised by high-pressure size exclusion chromatography (HPSEC). A similar analysis was conducted in stripped corn oil at the deodorisation temperatures. As such, 5-ethyl-6-methyl-3-heptene-2-one, 3-hydoxy-steroid, 3-ketostigmasterol and 3,7-diketostigmasterol were also detected in stripped corn oil, while the contents of 3-hydoxy-steroid and 5-ethyl-6-methyl-3-heptene-2-one were higher than those of 3-ketostigmasterol, as revealed by quantum chemical simulations. In addition, stripped corn oil exhibited the characteristic of preventing stigmasterol degradation below 200 °C, whereas it enhanced the chemical conversion (such as esterification and degradation) of stigmasterol at higher temperatures.

Comparative Study on Functional Components, Physicochemical Properties and Antioxidant Activity of Amaranthus Caudatus L. Oils Obtained by Different Solvents Extraction.

Functional compositions, physicochemical properties and antioxidant activities of Amaranthus caudatus L. oils (ACO) obtained by different solvents were comparatively investigated. All the resulted ACO were enrich in 75% unsaturated fatty acid and in squalene of about 4 g/100 g. Different solvents showed varying in oil extraction, where acetone results a highest yield of 6.80 g/100 g. ACO extracted by ethanol showed a highest tocopherol (1351.26 mg/kg), polyphenols (211.28 mg/kg) and squalene (42519.13 mg/kg). However, phytosterols in ACO extracted by hexane (27571.20 mg/kg) was higher than that by acetone (19789.91 mg/kg), ethanol (22015.73 mg/kg) and petroleum ether (24763.30 mg/kg). Furthermore, antioxidant activity of ACO was also measured by DPPH, ABTS and FRAP assay. According to principal component and correlation analysis, squalene was correlated with the DPPH scavenging ability, but phytosterols and tocopherols was correlated with the ABTS and ferric reducing ability of the oils, respectively. This study provides a promising excellent source of functional oil for food industries.

Effect of unsaturation of free fatty acids and phytosterols on the formation of esterified phytosterols during deodorization of corn oil.

BACKGROUND: Phytosterols are partly removed during oil refining, and the magnitude of phytosterols loss largely depends on the refining conditions applied and the molecular conformation. The aim of this research was to study the effect of deodorization conditions and molecular unsaturation on the esterification of phytosterols during deodorization of corn oil. RESULTS: In the chemical model, free fatty acids (FFAs) were the major provider of acyl groups during the formation of phytosteryl fatty acid esters (PEs) under deodorization conditions. Among the main parameters of the deodorization, temperature played a role in the formation of PEs with a time-dependent manner. In comparison, saturated palmitic acid had a higher capability of esterifying free phytosterols (FPs) to PEs than unsaturated oleic acid and linoleic acid. Moreover, the influence of FFA unsaturation on the degradation of FPs depended on temperature. Besides, the formation of stigmasteryl ester had a competitive advantage over that of sitosteryl ester by quantum chemistry simulation. CONCLUSION: For laboratory-scale deodorization of corn oil, saturated fatty acids and deodorization process with steam as stripping gas could obviously esterify FPs to PEs. FPs were abundantly enriched in distillate during the deodorization process with nitrogen as stripping gas, whereas FPs and PEs were distilled simultaneously during the deodorization process with steam. © 2020 Society of Chemical Industry.

Molecular reaction mechanism for elimination of zearalenone during simulated alkali neutralization process of corn oil.

Zearalenone (ZEN) is one of the most widely distributed harmful mycotoxins produced by Fusarium species, especially deposited in corn oil. In this study, we systematically tracked the changes of ZEN in the refining of corn oil, and especially during neutralization process. An alkali neutralization process could remove certain amounts of ZEN that was much more than that of others refining steps. In a mimicking condition, ZEN contents decreased continuously and significantly with increasing neutralization temperature. However, when returned to neutral, recoverable ZEN decreased with increasing temperature, which confirmed more degradation of ZEN at high temperature. HPLC-Q/TOF MS and NMR evidence showed that non-reversible hydrolyzate followed decarboxylation was observed in a high-temperature alkali neutralization condition. The results may serve as the scientific basis for the elimination of zearalenone in refined vegetable oils, and provide clues to understanding the oil-safety aspects of elimination of zearalenone.