Effects of Silica Hydrogel on Degumming of Fragrant Rapeseed Oil.

Hot-pressed rapeseed oils with pleasant flavor, i.e., fragrant rapeseed oils, are favored by consumers, especially people from the southwest provinces of China. Although degumming is an important section in producing edible rapeseed oils, conventional degumming techniques are generally suffered from disadvantages such as moisture control, and large losses of micronutrients and flavors. In the present paper, hot-pressed rapeseed oils were treated with silica hydrogel to remove their gums, and changes in phospholipids, acid values, peroxide values, tocopherols, total phenols, and flavor compounds were analyzed to compare the silica hydrogel-degumming with conventional methods. The optimized conditions were suggested to be carried out at 45°C for 15 min, and the silica hydrogel dosage was 1.10%. More than 97.00% of phospholipids were removed after the degumming, and more than 85.00% of micronutrients, were retained in the treated oils. The degumming efficiency was therefore significantly higher than those operated by conventional acid degumming and soft degumming techniques. It was found that the dosage of the silica hydrogel significantly affected the removal rate of phospholipids compared with degumming time and temperature. There were nearly typical volatile compounds found in the rapeseed oils, while most of them kept almost stable after the silica hydrogel-degumming. In this regard, silica hydrogel adsorption exhibited little effect on volatile compounds, making it more suitable for the production of fragrant rapeseed oils.

A comparative study on flavor trapping techniques from the viewpoint of odorants of hot-pressed rapeseed oil.

Rapeseed oil, as one of the three major vegetable oils in the world, its matrix effect makes the decoding flavor a challenge. Solid-phase microextraction (SPME), SPME-Arrow, headspace stir bar sorptive extraction (HSSE), direct thermal desorption (DTD), and solvent-assisted flavor evaporation (SAFE) were compared based on the odorants in hot-pressed rapeseed oil. Besides, methodological validation for 31 aroma standards was conducted to compare reliability and robustness of these approaches. DTD showed the largest proportion of acids, while the other techniques extracted a majority of nitriles. The highest number of odorants was detected by SAFE (31), followed by HSSE (30), SPME-Arrow (30), SPME (24), and DTD (14). SPME-Arrow showed the best performance in linearity, recovery, and reproducibility followed by SPME, HSSE, DTD, and SAFE. Results reveal the advantages and limitations of diverse methodologies and provide valuable insights for the selection of extraction methods in an oil matrix and flavor decoding.

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.

Comparative analysis of aroma compounds in French fries and palm oil at three crucial stages by GC/MS-olfactometry, odor activity values, and aroma recombination.

BACKGROUND: Flavor is a key element affecting the popularity of French fries (FFs). When oil is heated, the changes in oil quality can affect the flavor of the food directly. RESULTS: The flavor of FFs showed three crucial stages: the break-in (3.0% to 6.8% of total polar compounds (TPC)), optimum (7.0% to 19% of TPC), and degrading (above 19.5% of TPC) stages. To distinguish the key aroma compounds in the three stages, the FFs, prepared in palm oil (PO) at TPC of 3.0% (FF3), 7.5% (FF8), 19.5% (FF20), and their relevant oils (PO3, PO8, PO20), were selected for molecular sensory science analysis. The results indicated that the concentration of (E, E)-2,4-decadienal linked with the deep-fried odor was low in FF3, which led to a lower sensory score in the FF3 sample. The FF8 sample had a high (E, E)-2,4-decadienal content and received a high sensory score. The FF20 sample possessed high hexanoic acid, heptanoic acid (sweaty odor), benzaldehyde (stale odor), octanoic acid (sweaty odor), (E)-2-undecenal (fatty odor), and trans-4,5-epoxy-(E)-2-decenal (metallic odor) content, thus leading to FFs having an undesirable flavor and PO20 showed high hexanoic acid and heptanoic acid content, contributing to a lower sensory score in PO20. CONCLUSION: The FFs' flavor became undesirable when TPC was above 19.5% due to significant influences of some off-flavor compounds. It is therefore essential to prevent the generation of rancid substances to prolong the optimum stage during frying. © 2021 Society of Chemical Industry.

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.

A chemometrics approach comparing characteristics and free radical scavenging capacity of flax (Linum usitatissimum L.) oils obtained from seeds and cakes with different extraction methods.

BACKGROUND: Flax oil, a nutritive vegetable oil, is a rich natural source of the essential C18:3 α-linolenic acid and trace nutrients (tocopherol, phytosterol, polyphenol, flavonoid, etc.). In most small- and medium-sized facilities, the oil content in pressed cake is as high as 10%, which is not fully extracted and utilized. These cannot be neglected since they account for a considerable proportion. Characteristics and free radical scavenging capacity of flax (Linum usitatissimum L.) oil obtained from seeds and cakes with different extraction methods - cold-pressing, hot-pressing (120 and 160 °C) and solvent extraction (oil extracted with solvent from flaxseed, cold-pressed cake, and hot-pressed cake) - were evaluated and analyzed using chemometrics methods. RESULTS: The composition of C18:3 α-linolenic acid of flax oil was not affected by the extraction methods in this work. Flax oils extracted with solvent from pressed cakes had lower content of bioactive minor components (tocopherols and phytosterols) compared with pressed and solvent-extracted seed oils. The former also showed poorer oxidative stability and free radical scavenging capacity (polar fraction) when compared with the latter. Flax oils could be distinguished with principal component analysis and hierarchical cluster analysis. Tocopherols and phytosterols exhibited significant contributions to the antioxidant capacity of flax oils via correlation analysis and multiple linear regression analysis. CONCLUSION: Tocopherols and phytosterols were appropriate and potent indicators for evaluating the antioxidant capacity of flax oil. Results have important implications for the industrial production and nutritional value of flax oil, especially for flax oils from the cakes after pressing. © 2021 Society of Chemical Industry.

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.

Assessment of contamination source and quality control approach for polycyclic aromatic hydrocarbons in wood-pressed rapeseed oil.

Contamination sources of polycyclic aromatic hydrocarbons (PAHs) in the raw material, oil production and storage processes of wood-pressed rapeseed oil were investigated in this study. The results showed that benzo[a]pyrene (BaP) and PAH4 (sum of BaP, benzo[a]fluoranthene, benzo[b]fluoranthene and chrysene) were unevenly distributed in the kernel (0.56-0.98 and 2.84-8.64 µg/kg, respectively) and hull (1.53-3.17 and 13.49-22.31 µg/kg, respectively) of the rapeseed raw materials. The contents of BaP and PAH4 continuously increased during the process of wood-pressed rapeseed oil, ranging from 2.21 to 10.93 and 9.36 to 40.03 µg/kg, thus demonstrating that a wide range of pollution sources of PAHs existed for the test wood-pressed rapeseed oils. The initial temperature and time of roasting should be controlled at <210°C and <60 min, due to the generation of PAHs in rapeseed by over-roasting. In addition, contact tools and substance such as lubricating oil (from the mill), heat-transfer oil (from roasting machine), rubber gaskets and straws should be properly screened. The BaP and PAH4 of rapeseed placed in the roasting area increased from 0.5 to 2.24 and from 2.08 to 9.03 µg/kg, respectively. Therefore, roasting fume control and treatment systems are necessary and the roasting section should be strictly isolated from the other stages. Storage can slightly lower the PAHs amounts in the rapeseed oil, which made the contents of BaP and PAH4 decrease from 27.00 to 24.70 and from 138.63 to 117.58 µg/kg, respectively. Quality control measures of PAHs in wood-pressed rapeseed oil were proposed and implemented, and the final oil products' BaP and PAH4 were kept below 2 and 10 µg/kg, respectively, which meets the European Commission Regulation No. 835/2011.