Influence of roasting pretreatment on high-oleic rapeseed oil quality evaluated by analytical and sensory approaches

Roasting treatments affect oil extraction rate, fatty acids, oxidative stability, antioxidant activity, and flavor of walnut oil

Introduction

The quality of pressed walnut oil can be improved by moderate roasting treatment.

Methods

This study compared physicochemical characteristics and antioxidant ability of walnut oils pressed from differently roasted pretreated walnuts, analyzed the correlation among these indicators by using Pearson correlation coefficient and correlation coefficient heatmap, and evaluated the volatile organic compounds (VOCs) of walnut oil under optimal pretreatment roasting conditions using headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS).

Results

Hierarchical cluster analysis (HCA) and principal component analysis (PCA) were able to remarkably distinguish walnut oil produced by different roasting processes. In addition, correlation analysis showed that there was a significant impact among indicators. There were 73 VOCs were identified in the optimum roasted treated walnut oil, consisting of 30 aldehydes, 13 alcohols, 11 ketones, 10 esters, 5 acids, 2 oxygen-containing heterocycles, 1 nitrogen-containing heterocycle and 1 other compound. GC-IMS results showed that aldehydes contributed significantly to the volatile flavor profile of walnut oil, especially (E)-2-heptenal, (E)-2-pentenal and hexenal.

Discussion

The properties of walnut oil based on varying roasting pretreatment of walnut kernels were significantly differentiated. Roasting at 120°C for 20 min is a suitable pretreatment roasting condition for pressing walnut oil. Roasting at 120°C for 20 min is a suitable pretreatment roasting condition for pressing walnut oil.

Comparative characterization of key odorants and aroma profiles of fragrant rapeseed oil under different roasting conditions

Fragrant rapeseed oil (FRO) produced by typical roasting process is popular for its characteristic aroma. Accordingly, key aroma-active compounds were characterized in FRO by the Sensomics approach and then correlated to the crucial roasting parameters revealed by aroma profile analysis and hierarchical cluster analysis. Nineteen key odorants in FRO were identified and quantified, among which dimethyl trisulfide (OAV, odor active value, 323, cabbage-like, sulfury) and 4-isothiocyanato-1-butene (OAV, 88, pungent) were the most important aroma-active compounds in FRO and showed first rising and then decline trends as the increased roasting temperature and time. The oil under high-temperature-short time and low-temperature-long time conditions imparted similar aroma profiles. On the basis of sensory evaluation, roasting at 160, 170, 180, 190, and 200 °C should not exceed 50, 40, 30, 30, and 30 min, respectively to satisfy consumer preference. All findings provide a reference on industrial FRO production in terms of not only aroma but also sustainability.

Comprehensive two-dimensional gas chromatography-time of flight mass spectrometry as a tool for tracking roasting-induced changes in the volatilome of cold-pressed rapeseed oil

The aim of this study was to track changes in the volatilome of cold-pressed oil and press cakes obtained from roasted seeds and to combine it with the profile of non-volatile metabolites in a single study, in order to understand pathways of volatile organic compound (VOC) formation caused by thermal processing. Comprehensive two-dimensional gas chromatography-time of flight mass spectrometry was used for the analysis of VOCs in cold-pressed oils and corresponding press cakes obtained after roasting of seeds at 140 and 180 °C prior to pressing. Contents of primary metabolites (amino acids, saccharides, fatty acids) as well as selected secondary metabolites (glucosinolates, polyphenols) were determined, as many of them serve as precursors to volatile compounds formed especially in thermal reactions. After roasting, the formation of Maillard reaction products increased, which corresponded to the reduction of free amino acids and monosaccharides. Moreover, levels of the products of thermal oxidation of fatty acids, such as aldehydes and ketones, increased with the increasing temperature of roasting, although no significant changes were noted for fatty acids. Among sulphur-containing compounds, contents of the products and intermediates of methionine Strecker degradation increased significantly with the increasing temperature of roasting. Degradation of glucosinolates to nitriles occurred after thermal treatment. The results of this study confirmed that seed roasting before cold pressing has a significant effect on the volatiles, but also indicated roasting-induced changes in non-volatile metabolites of oil and press cake. Such an approach helps to understand metabolic changes occurring during rapeseed processing in cold-pressed oil production.

Phytosterol, Tocopherol and Carotenoid Retention during Commercial Processing of Brassica napus (Canola) Oil

Brassica napus (canola) seed is a rich source of phytosterols, tocopherols and carotenoids, which all have recognized health benefits, although these are reduced or lost during crude oil refinement. Many studies are now outdated, so new research to monitor bioactive retention through current processing techniques is warranted. In this work, canola seed, in-process seed, and oil samples were collected from the major stages of five commercial canola oil processes. Analysis of phytosterols, tocopherols and carotenoids indicated seed pre-treatment enhanced bioactive concentrations in the crude oil. Although the bleaching step in each process eliminated all carotenoids, high concentrations of phytosterols and tocopherols remained in the refined oil across all processes, with losses notably lower than those found in previous reports. Moreover, crude oil samples from a two-stage cold pressing process showed greatly enriched concentrations of tocopherols (+122%), sterols (+140%) and carotenoids (+217%). The results show that modern Australian canola oil processing retains high phytosterol and tocopherol concentrations and warrants further investigation into bioactive enrichment strategies. Given the growing interest in health-enhanced foods, this study provides opportunities for nutrition and health-enhanced oil products and the potential for adding value in the edible oil industry.

Influence of dry air and infrared pre-treatments on oxidative stability, Maillard reaction products and other chemical properties of linseed (Linum usitatissimum L.) oil

In this study, the influence of dry air and infrared pre-treatments on linseed oil (LO) yield, chemical properties, colour, pigment content, total phenolic content (TPC), Maillard reaction products (MRPs), fatty acid composition (FAC), radical scavenging activity (RSA), and oxidative stability index (OSI) were investigated. An increase in dry air and infrared roasting temperature had increased the LO yield, pigment content, a* value, TPC, RSA, OSI, and browning index (BI) while lowered the L* and b* values of LO. Higher OSI (2.24 h), chlorophylls (2.29 mg/kg), carotenoids (3.87 mg/kg), TPC (63.67 mg GAE/100 g), RSA (62.53%), BI (0.330), and MRPs (2.10 mg/kg) were detected in LO by dry air roasting at 180°C for 10 min. Dry air and infrared roasting had slightly affected the FAC of LO. Both dry air and infrared pre-treatments had influenced the LO quality characteristics. However, dry air roasting of linseed at 180°C for 10 min proved more effective in improving oxidative stability, antioxidant activity and other quality characteristics of LO.

SUPPLEMENTARY INFORMATION

The online version of this article at 10.1007/s13197-021-05023-6.

Flavor of rapeseed oil: An overview of odorants, analytical techniques, and impact of treatment

As one of the three major vegetable oils in the world, rapeseed oil is appreciated for its high nutritional value and characteristic flavor. Flavor is an essential attribute, determining rapeseed oil quality and consumer acceptance. The present manuscript provides a systematic literature review of recent advances and knowledge on the flavor of rapeseed oil, which focuses on aroma-active as well as off-flavor compounds, flavor analysis techniques (i.e., extraction, qualitative, quantitative, sensory, and chemometric methods), and effects of treatments (storage, dehulling, roasting, microwave, flavoring with herbs, refining, and oil heating) on flavor from sensory and molecular perspectives. One hundred thirty-seven odorants found in rapeseed oil from literature are listed and possible formation pathways of some key aroma-active compounds are also proposed. Future flavor analysis techniques will evolve toward time-saving, portability, real-time monitoring, and visualization, which aims to obtain a "complete" flavor profile of rapeseed oil. The changes of volatile compounds in rapeseed oil under different treatments are summarized in this view. Studies to elucidate the influence of different treatments on the formation of aroma-active compounds are needed to get a deeper understanding of factors leading to the variations of rapeseed oil flavor.

Physicochemical properties and health risk assessment of polycyclic aromatic hydrocarbons of fragrant rapeseed oils in China

BACKGROUND

Fragrant rapeseed oil is a type of hot-pressed oil in China. In this study, physicochemical properties, oxidative stability index (OSI), tocopherols, sterols, and polycyclic aromatic hydrocarbons (PAHs) in fragrant rapeseed oils were evaluated. Additionally, the cancer risk assessment pertaining to PAHs in fragrant rapeseed oil was investigated.

RESULTS

Acid values (0.64-2.68 mg potassium hydroxide per gram), peroxide values (1.58-4.86 mmol kg^-1 ), and color values (R = 2.6-5.8, Y = 35) of fragrant rapeseed oils were all within codex limits. Tocopherols and sterols ranged from 559.5 to 783.7 mg kg^-1 and 4412.6 to 7859.8 mg kg^-1 respectively. The OSI (110 °C) was between 4.8 and 15.9 h, with an average value of 10.8 h. Mean values of benzo[a]pyrene and PAH4 (chrysene, benz[a]anthracene, benzo[b]fluroranthene, and benzo[a]pyrene) were 2.32 μg kg^-1 and 8.21 μg kg^-1 respectively. The 95% dietary exposure of benzo[a]pyrene equivalent (BaPeq) contents from PAH4 were 0.3474 ng kg^-1 day^-1 , 0.3942 ng kg^-1 day^-1 , 1.8293 ng kg^-1 day^-1 , and 0.4294 ng kg^-1 day^-1 for male children, adolescents, adults, and seniors respectively. For females, these values were 0.3443 ng kg^-1 day^-1 , 0.3228 ng kg^-1 day^-1 , 1.8697 ng kg^-1 day^-1 , and 0.4084 ng kg^-1 day^-1 , respectively. Moreover, incremental lifetime cancer risk values at the cumulative probabilities of 91.3% and 91.6% for male adults and female adults respectively were higher than 1 × 10^-5 .

CONCLUSION

The results imply that the potential risk of cancer with PAHs in fragrant rapeseed oil should be a concern, especially for the health of adults. Fragrant rapeseed oil is still a product subject to contamination by PAHs. Limits for PAH4 of fragrant rapeseed oil should be included in Chinese regulations to improve safety. © 2020 Society of Chemical Industry.

A Novel Method for Generation of a Fingerprint Using Electronic Nose on the Example of Rapeseed Spoilage

The paper presents application of a new three-parameter method for identification of volatile organic compounds (VOCs) and creation of fingerprints based on the impregnation time (t_IM ), cleaning time (t_CL ), and maximum response ([ΔR/R]_max ) of chemically sensing sensors for detecting spoilage of agricultural commodities. The novelty of this method consists in the use of two additional parameters: an impregnation time and a cleaning time for the first time. An Agrinose built of eight metal oxide semiconductors was used for identification of loss in the rapeseed quality during a short period of storage after harvest. Principal component analysis was applied as a method of data analysis to verify the suitability of the new three-parameter method and visualization of groups of different quality of raw materials. Fourier transform infrared spectroscopy spectra for identification of the infrared bands of fungal polysaccharides and gas chromatography-mass spectrometry analysis of the headspace was applied to describe volatile metabolite contents in reference to the electronic nose technique. The investigations and analyses have demonstrated that the new three-parameter method for determination of volatile compounds ([ΔR/R]_max , t_IM , t_CL ) describes the changes in VOCs more efficiently than the single-parameter approach based only on the maximum sensor response ([ΔR/R]_max ). The proposed method for generation of electronic fingerprints clearly discriminated between rapeseed samples infected with field and storage microflora. Three-parameters method can be useful for quality control in food microbiology and safety, as a rapid method of analysis and detection, including electronic nose sensor technology. PRACTICAL APPLICATION: The use of the proposed method for generation of fingerprints requires no interference with the hardware of the electronic nose but necessitates modification of the software only. This facilitates implementation of the three-parameter method in available devices. This kind of methods and devices can be useful for example in storage process with active ventilation.

Effects of heat pretreatment of wet-milled corn germ on the physicochemical properties of oil

Corn germ oil is removed from the milled germ using a conditioning (heating) process, followed by mechanical expelling and/or hexane extraction. In this study, the effect of pretreatment by oven roasting (OR) and microwave (MW) radiation on wet-milled corn germ was investigated. Three OR temperatures (125, 150, and 175 °C) were used with 60 min exposure, and MW pretreatments were established by combining two powers (440 and 800 W) and three pretreatment times (4, 6, and 8 min). The levels of red value, 1,3-diacylglycerol, total diacylglycerol, free fatty acid, and oleic acid increased substantially, while those of triacylglycerol (TAG), linoleic, and linolenic acid decreased significantly following OR. There were no significant differences in TAG compositions following OR and MW treatments. Both heat pretreatments significantly increased the total tocopherol content. δ-Tocopherol showed minimal changes, while β-tocopherol progressively increased after the heat treatments. No significant differences in phytosterols levels were observed among most samples. The MW radiation Proper roasting temperatures or MW radiation times could enrich the content of individual tocopherols and phytosterols, and improve the oxidative stability of oil. The MW radiation tends to be more applicable and sustainable for oil industry to improve the quality of corn germ oil.

Mechanical hulling and thermal pre-treatment effects on rapeseed oil antioxidant capacity and related lipophilic and hydrophilic bioactive compounds

In this study, the effect of rapeseed mechanical hulling and thermal pre-treatment by microwaves (from 2 to 10 min with 2-min intervals, 800 W) and roasting (from 20 to 100 min with 20-min intervals, 165 °C) on the content of phytochemicals in the oil was investigated. Results showed that both pre-treatments applied differentiated the oils in terms of the content of bioactive compounds. In general, oils pressed from hulled and thermally pre-treated seeds contained higher content of tocopherols, PC-8 and phytosterols, while oils pressed from non-hulled and pre-processed seeds had significantly higher concentration of polyphenols. Both microwaving and roasting contributed to an increase of antioxidant capacity of studied oils. The increase of radical scavenging activity of oils was seen mainly in hydrophilic fraction of oil, which was highly positively correlated with the amount of canolol formed during seeds heating.