Prediction of oxidative stability in bulk oils using dielectric constant changes

Reduction of toxic aldehydes in heated flaxseed oil using sesame and perilla protein enzymatic hydrolysates

Reducing ability of sesame meal protein enzymatic hydrolysates (SMH) and perilla protein enzymatic hydrolysates (PMH) on the content of toxic aldehydes including acetaldehyde, formaldehyde, 2-hydroxylhexenal (HHE), and 2-hydroxyl nonenal (HNE), were evaluated in heated flaxseed oil at concentrations ranging from 0.01 to 1.0 g. Adding SMH and PMH decreased the formation of secondary oxidation products and toxic aldehydes during heating. In particular, HHE and HNE were not detected, even at 0.01 g of protein concentration. Free radical scavenging activities in heated flaxseed oil significantly increased when 1.0 g of SMH and PMH were added (p < 0.05). Some volatiles including 2-ethylpyridine, pyrazines, and trimethylamine were formed or increased substantially in flaxseed oils with higher concentrations of SMH and PMH. In general, SMH showed higher antioxidative activity and reducing ability on the toxic aldehydes than PMH. Plant protein enzymatic hydrolysate could control the formation of toxic aldehydes during oxidation of ω-3 edible oil.

Evaluation of oxidative stability of rice oil from brown rice flour under thermal oxidation and light irradiation

Effects of autoxidation and light irradiation on the oxidative stability were evaluated in rice oil from two brown rice flours including 'Baromi2' and 'Samkwang'. 'Baromi2' is a newly developed variety for rice flour production while 'Samkwang' is a typical rice variety as a control. Degree of oxidation and volatile profiles were evaluated in rice oil stored at 60 °C or under fluorescent light at 25 °C. The oil yields of 'Baromi2' and 'Samkang' were 2.63 and 1.78%, respectively whereas rice oil from 'Baromi2' had lower degree of unsaturation than 'Samkang'. Rice oil from 'Samkwang' possessed higher volatile compounds and more oxidized products during autoxidation whereas rice oil from 'Baromi2' had more oxidation products under light irradiation. Hexanal and 2-heptenal were major headspace volatile from heated rice oil while 2-heptenal and 1-octene-3-ol were main volatiles from light irradiated rice oil, which implies the involvement of singlet oxygen in rice oil during photooxidation.

Antioxidant properties of lipid concomitants in edible oils: A review

Edible oils are indispensable for human life, providing energy and necessary fatty acids. Nevertheless, they are vulnerable to oxidation via a number of different mechanisms. Essential nutrients deteriorate as well as toxic substances are produced when edible oils are oxidized; thus, they should be retarded wherever possible. Lipid concomitants have a strong antioxidant capacity and are a large class of biologically active chemical substances in edible oils. They have shown remarkable antioxidant properties and were documented to improve the quality of edible oils in varied ways. An overview of the antioxidant properties of the polar, non-polar, and amphiphilic lipid concomitants present in edible oils is provided in this review. Interactions among various lipid concomitants and the probable mechanisms are also elucidated. This review may provide a theoretical basis and practical reference for food industry practitioners and researchers to understand the underlying cause of variations in the quality of edible oils.

Understanding the variations in dielectric properties of mustard (Brassica nigra L.) and argemone (Argemone mexicana) oil blends at different temperatures

Mustard oil is the most commonly adulterated edible oil, invariably with argemone oil. This study was aimed to develop a parallel plate capacitive sensor for measurement of dielectric properties of pure mustard oil, pure argemone oil and their blends (25, 50 and 75%) at five levels of varying temperature (10 to 50 °C). The effect of blend ratio and temperature on the selected dielectric properties of oil-capacitance (C), dielectric loss tangent (tanδ), dielectric constant ( ε ' ), dielectric loss factor ( ε ″ ) and electrical conductivity (σ) were investigated. It was observed that composition of the individual oils in terms of moisture and fatty acids influenced the physical and dielectric properties. The sensor was used to relate the dielectric properties of oil samples with blend ratio and temperature by means of statistically significant (p < 0.05) and robust (R 2 > 0.8) multiple linear regression model. The effect of temperature on C and ε ' was negative, while it was otherwise for tanδ, ε ″ and σ. Increase in argemone oil content in the blends, increased the dielectric measures due to the associated changes in the physical and chemical properties. The capacitive sensor could distinctly identify mustard oil, argemone oil and its blends on the basis of dielectric properties.

Microwave resonator can help to predict oxidative stability in C18-based vegetable oils

Effects of moisture content, degree of oxidation, degree of unsaturation of fatty acid compositions in C18-based edible oils were determined by a microwave resonator in the range of 0-4.4 GHz. Moisture content and degree of oxidation in corn oil made difference in signal intensity at 1.7-1.9 GHz and 1.0-1.2 GHz, respectively without uniform trend in signal intensity. Degree of unsaturation of C18-based edible oils including corn, sesame, soybean, olive, perilla, and flaxseed oils provided difference in 3.0-3.1 GHz with a dependent manner of degree of unsaturation. Average of signal intensity (ASI) in 3.0-3.1 GHz had high correlation (R² > 0.93) to the degree of unsaturation in edible oils. Oils with high oleic acid had relatively low ASI while those with high linolenic acid had high ASI value. Oxidative stability of C18-based edible oils can be categorized successfully without fatty acid analysis using a microwave resonator.

Development of methods for determining free fatty acid contents in red colored oils

Buah merah oil and red palm oil are red colored and unrefined edible oils. Because of this color characteristic, measuring acid value by titration method can be uncertain and subjective, so more accurate and objective methods are needed. Gas chromatography-flame ionization detector (GC-FID) and high-performance liquid chromatography-evaporative light scattering detector (HPLC-ELSD) methods were developed to determine acid value in 3 buah merah oils and 1 red palm oil by measuring free fatty acid contents. The acid value was high in the order of titration > GC-FID > HPLC-ELSD in all samples. GC-FID method showed accurate and reliable results, whereas HPLC-ELSD showed rough data partly due to the non-linear standard curve and high limit of detection. Difference in acid value between titration method and GC-FID might be due to unrefined components that reacted with KOH titration solution. GC-FID can be used measuring free fatty acid contents in red colored oils.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-021-00964-2.

Influence of lipid nanoparticle physical state on β-carotene stability kinetics under different environmental conditions

Carotenoids are lipophilic compounds that provide important health-related benefits for human body functions. However, they have low water solubility and chemical stability, hence their incorporation in aqueous-based foods requires the use of emulsion-based lipid carriers. This work aimed at elucidating whether their inclusion in emulsion-based Solid Lipid Nanoparticles (SLNs) can provide a protective effect against β-carotene degradation under different environmental conditions in comparison to liquid lipid nanoemulsions. Glyceryl Stearate (GS) was mixed with Medium Chain Trygliceride (MCT) oil to formulate SLNs. SLNs presented a significantly enhanced β-carotene retention and a slower β-carotene degradation kinetics at increasing storage temperature, acidic conditions and light exposure. In fact, SLNs formulated with 5% GS in the lipid phase and stored at 4 °C and pH 7 retained almost 70% of the initially encapsulated β-carotene after 55 days of storage, while it was completely degraded when it was encapsulated in liquid nanoemulsions. Moreover, it was observed that the solid lipid type affects the protective effect that SLNs may confer to the encapsulated lipophilic bioactives. Saturated long chain triglycerides, such as hydrogenated palm oil (HPO) presented slower and lower β-carotene degradation kinetics in comparison to solid lipids composed of MCT, such as Coconut Oil (CNUT) or MCT + 5% of GS in the lipid phase. This work evidences that the incorporation of lipophilic bioactive compounds, such as β-carotene, into SLNs slows down their degradation kinetics which might be attributed to a reduced diffusion of the oxidative species due to the lipid crystalline structure.

Dielectric properties of Mexican sauces for microwave-assisted pasteurization process

The dielectric properties and specifically the complex relative permittivity of foods are key elements for the design of pasteurization processes with high frequency electromagnetic waves. Mexican sauces are recognized worldwide for their flavor and nutritional properties. In this work, the complex permittivity of four of the most representative sauces of Mexican cuisine (chipotle chili, habanero chili, red and green sauce) is presented. The permittivity was measured with the open coaxial probe method at temperatures of 25, 40, 55, 70, 85 °C and in the frequency range of 500 MHz to 6 GHz. Additionally, moisture content, specific heat, viscosity, water activity, density and electrical conductivity are reported, these last three at 25 °C. Dielectric properties were affected by the sauce formulation. The loss factor of each sauce sample at any temperature presents significant changes in relation to the frequency. At 915 and 2,450 MHz, d ε ' ' d T > 0 , which would cause a thermal runaway effect or the uncontrolled rise in temperature in the sauces during the microwave pasteurization. At 5,800 MHz, d ε ' ' d T < 0 , which would give better control for microwave heating than at 915 and 2,450 MHz. At 915 MHz, the loss factor of all sauces is higher than at 2,450 and 5,800 MHz, therefore, more rapid heating can be produced. Moreover, at 915 MHz, microwaves exhibit higher penetration depth than at 2,450 and 5,800 MHz; therefore, at 915 MHz, the greatest uniform microwave dielectric heating would be achieved. Thus, 915 MHz is the frequency recommended for the studied sauces pasteurization. PRACTICAL APPLICATION: This work provides the dielectric properties of Mexican sauces at different temperatures and their penetration depths in the microwave range, which are key information for further microwave-assisted pasteurization process and for getting safer sauces for consumers. Moreover, this research supplies suggestions about what frequency for ISM (Industrial, Scientific and Medical) applications is the best for microwave-assisted pasteurization according to the penetration depth of the electromagnetic wave in the sauces and microwave dielectric heating speed of the sauces.

Utilization of novel and rapid techniques for characterization of neem Azadirachta indica seed oil and palm oil blends

The authentication of neem oil and its blending with inexpensive vegetable oil, such as, palm oil is a common practice in the neem oil industry. This study was conducted to investigate the neem kernel (Azadirachta indica) oil (NKO) by blending with palm oil and characterize it by studying its effect on the physicochemical properties, dielectric properties and fatty acid profiles of the blend. Blending significantly influenced the color, dielectric, structural and antimicrobial properties of the virgin oil. The NKO was rich in oleic (44.97%), stearic (21.27%), palmitic (16.88%) and linoleic acids (14.08%). The addition of palm oil into NKO significantly influenced the fatty acids profile , which was further confirmed by the FTIR spectra and the dielectric data. Overall, determination of moisture content, palmitic and stearic acid content, color parameter "a" and dielectric measurements were found to be fastest and precise way to detect the NKO and PO blends.

Evaluation of the effects of aldehydes on association colloid properties and oxidative stability in bulk oils

The effects of amphiphilic aldehydes, including propanal, hexanal, and nonanal, on the critical micelle concentration (CMC) of phospholipids, moisture content, and oxidative stability in soybean oil were evaluated. The selected aldehydes are typical secondary oxidation products from unsaturated fatty acids. Moisture content increased as aldehydes were added to soybean oil during thermal oxidation at a storage temperature of 50 or 100 °C. The CMC of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) increased as propanal and hexanal were added, whereas nonanal decreased the CMC of DOPC, which implies that aldehydes participate in forming association colloids in bulk oils. The addition of aldehydes increased the rates of lipid oxidation significantly in both 50 and 100 °C treatments (p < 0.05), with the effect being more evident in oils treated at 50 °C than at 100 °C. Therefore, aldehydes formed from lipid oxidation affected the association colloidal structures and oxidative stability in a bulk oil matrix.

Effectiveness of the rapid test of polar compounds in frying oils as a function of environmental and compositional variables under restaurant conditions

Effect of fried food, oil type, moisture, fatty acid and molecular distribution on the effectiveness of rapid test of Total Polar Compounds (TPC) in frying oil based on dielectric constant was explored. Effects of all factors were compared and found to be significant (P < 0.05). Throughout the life cycle of frying oil, its rapid results were correlated well with those of conventional chromatography (Y = 0.7625X + 3.681, R² = 0.8734). But the discrepancy was found within selected TPC ranges of 0%-10% and 20%-30%. According to the definition of TPC, three potential reasons for the high TPC values of fresh oils were discussed. For the deteriorated oils, the triglyceride dimers, mono-unsaturated and di-unsaturated fatty acids were found to be the main compositional factors by stepwise multivariate regression analysis. Pieces of advice about the operation guideline, internal control indices, calibration, reference oil, sensor, and detection range were proposed for instrument users and producers.

Understanding water activity change in oil with temperature

Our recent studies and several publications suggest that the low water activity (a_w) of oil in thermal processing might be a major contributing factor towards the increased thermal resistance of bacteria in oils. In this study, we developed a reliable method to measure the water activity of oil by measuring the equilibrium relative humidity in a small headspace. Using this method, water activity of peanut oil was found to decrease exponentially with increasing temperature. A model derived from excess Gibbs free energy was fitted to the observations with an R² = 99.6% and RMSE = 0.01 (a_w). Our results suggest that the sharply reduced water activity of oil resulting from a rise in temperature could cause desiccation of bacteria. This is a possible explanation for the protective effect of oil in thermal processing.

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A method is presented for the measurement of water activity of oil at temperatures up to 85 °C.

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The water activity of peanut oil is found to decrease exponentially as the temperature increases.

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A model is derived to predict the water activity of oil as a function of temperature.

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Desiccation may happen to bacteria in oil during thermal processing, which explains the protective effect of oil.

Determination of the Oxidative Stability of Camellia Oils Using a Chemometrics Tool Based on 1H NMR Spectra and α-Tocopherol Content

This study, for the first time, predicts oxidative stability in camellia oils by partial least squares (PLS) built with proton nuclear magnetic resonance (¹H NMR) and α-tocopherol content. The prediction models were established by the PLS method. Outlier detection, latent variables optimization, data pretreatment, and important variables selection were applied for models optimization. All the developed models exhibited good performance as indicated by R² > 0.895 and root mean square error of estimation and root mean square error of prediction less than 0.322 and 0.307. For verification of the contribution of ¹H NMR spectra and α-tocopherol for prediction performance, a PLS model with fatty acids composition instead of ¹H NMR spectra and one with only ¹H NMR spectra as input variables were developed, respectively. The results showed that the model based on ¹H NMR data was more accurate and precise than that based on fatty acid composition data. And the performance of the models was significantly degraded without α-tocopherol as input variables.