A New Phenolic Acid Decarboxylase from the Brown-Rot Fungus Neolentinus lepideus Natively Decarboxylates Biosourced Sinapic Acid into Canolol, a Bioactive Phenolic Compound

Rapeseed meal (RSM) is a cheap, abundant and renewable feedstock, whose biorefinery is a current challenge for the sustainability of the oilseed sector. RSM is rich in sinapic acid (SA), a p-hydroxycinnamic acid that can be decarboxylated into canolol (2,6-dimethoxy-4-vinylphenol), a valuable bioactive compound. Microbial phenolic acid decarboxylases (PADs), mainly described for the non-oxidative decarboxylation of ferulic and p-coumaric acids, remain very poorly documented to date, for SA decarboxylation. The species Neolentinus lepideus has previously been shown to biotransform SA into canolol in vivo, but the enzyme responsible for bioconversion of the acid has never been characterized. In this study, we purified and characterized a new PAD from the canolol-overproducing strain N. lepideus BRFM15. Proteomic analysis highlighted a sole PAD-type protein sequence in the intracellular proteome of the strain. The native enzyme (NlePAD) displayed an unusual outstanding activity for decarboxylating SA (Vmax of 600 U.mg-1, kcat of 6.3 s-1 and kcat/KM of 1.6 s-1.mM-1). We showed that NlePAD (a homodimer of 2 × 22 kDa) is fully active in a pH range of 5.5-7.5 and a temperature range of 30-55 °C, with optima of pH 6-6.5 and 37-45 °C, and is highly stable at 4 °C and pH 6-8. Relative ratios of specific activities on ferulic, sinapic, p-coumaric and caffeic acids, respectively, were 100:24.9:13.4:3.9. The enzyme demonstrated in vitro effectiveness as a biocatalyst for the synthesis of canolol in aqueous medium from commercial SA, with a molar yield of 92%. Then, we developed processes to biotransform naturally-occurring SA from RSM into canolol by combining the complementary potentialities of an Aspergillus niger feruloyl esterase type-A, which is able to release free SA from the raw meal by hydrolyzing its conjugated forms, and NlePAD, in aqueous medium and mild conditions. NlePAD decarboxylation of biobased SA led to an overall yield of 1.6-3.8 mg canolol per gram of initial meal. Besides being the first characterization of a fungal PAD able to decarboxylate SA, this report shows that NlePAD is very promising as new biotechnological tool to generate biobased vinylphenols of industrial interest (especially canolol) as valuable platform chemicals for health, nutrition, cosmetics and green chemistry.

Effects of High-Canolol Phenolic Extracts on Fragrant Rapeseed Oil Quality and Flavor Compounds during Frying

Fragrant rapeseed oil (FRO) is a frying oil widely loved by consumers, but its quality deteriorates with increasing frying time. In this study, the effect of high-canolol phenolic extracts (HCP) on the physicochemical properties and flavor of FRO during frying was investigated. During frying, HCP significantly inhibited the increase in peroxide, acid, p-anisidine, and carbonyl values, as well as total polar compounds and degradation of unsaturated fatty acids. A total of 16 volatile flavor compounds that significantly contributed to the overall flavor of FRO were identified. HCP was effective in reducing the generation of off-flavors (hexanoic acid, nonanoic acid, etc.) and increased the level of pleasant deep-fried flavors (such as (E,E)-2,4-decadienal). Therefore, the application of HCP has a positive effect on protecting the quality and prolonging the usability of FRO.

Optimization of Canolol Production from Canola Meal Using Microwave Digestion as a Pre-Treatment Method

Canola meal, the by-product of canola oil refining, is a rich source of phenolic compounds and protein. The meal, however, is primarily utilized as animal feed but represents an invaluable source of nutraceuticals. Of particular interest are the sinapates, sinapine and sinapic acid, with the decarboxylation of the latter to form canolol. Extracting these phenolics has been carried out using a variety of different methods, although there is an urgent need for environmentally safe and sustainable methods. Microwave-assisted solvent extraction (MAE), as a green extraction method, is receiving considerable interest. Its ease of use makes MAE one of the best methods for studying multiple solvents. The formation of canolol, from sinapine and sinapic acid, is primarily dependent on temperature, which favors the decarboxylation reaction. The application of MAE, using the MultiwaveTM 500 microwave system with green extractants, was undertaken to assess its ability to enhance the yield of sinapates and canolol. This study examined the effects of different pre-treatment temperature-time combinations of 140, 150, 160, and 170 °C for 5, 10, 15, 20, and 30 min on the extraction of canolol and other canola endogenous phenolic compounds. Total phenolic content (TPC), total flavonoid content (TFC), as well as metal ion chelation (MIC) and DPPH radical activity of the different extracts were assessed. The results confirmed that extractability of canolol was optimized with methanol at 151 °C and with ethanol at 170 °C with pre-treatment times of 15.43 min and 19.31 min, respectively. Furthermore, there was a strong positive correlation between TPC and TFC (p < 0.05) and a negative correlation between TFC and DPPH radical activity. Interestingly, no significant correlation was observed between MIC and DPPH. These results confirmed the effectiveness of MAE, using the novel MultiwaveTM 500 microwave instrument, to enhance the yield of canolol. This was accompanied by substantial improvements in the antioxidant activity of the different extracts and further established the efficacy of the current MAE method for isolating important natural phenolic derivatives for utilization by the nutraceutical industry.

Air frying pretreatment and the recovery of lipophilic sinapates from the oil fraction of mustard samples

Roasting of mustard seeds prior to oil extraction is a well-documented unit operation essential to produce canolol and other lipophilic sinapates. This study investigated the effectiveness of air frying as a seed roasting treatment operation for enhancing the recovery of lipophilic sinapates from various mustard samples and fractions/products. Air frying of seeds, powder, cake, bran, and flour from different mustard varieties was carried out at temperature-time combinations of 160, 170, and 180°C for 5, 10, 15, and 20 min, respectively. Oil was extracted using the Soxtec method. Lipophilic sinapates were extracted from the oil using equal volumes of hexane to methanol 70% (v/v) and quantified by high performance liquid chromatography-diode array detection (HPLC-DAD). The total phenolic content (TPC) and antioxidant activity of the oils were also evaluated. The results showed a time-temperature dependency for the recovery of major oil-soluble sinapates in all mustard samples and fractions. The optimum air frying condition 180°C for 15 min produced the maximum yield of canolol as well as other unidentified oil-soluble sinapates (retention time (RT)-7.7, RT-11.50, RT-14.95, and RT-16.24 min). The oil from lower grade yellow mustard seeds (LGYMS) roasted at 180°C for 20 mins specifically had the highest TPC (3402.22 ± 58.79 mg GAE/g oil), while LGYMS oils generally showed better antioxidant activities (2,2-diphenyl-1-picrylhydrazyl (DPPH), ferric ion reducing antioxidant power (FRAP), and inhibition of linoleic acid oxidation) but were lower in metal ion chelating capacity. This information would be beneficial to the oil industry because air frying generated valuable canolol and other antioxidant lipophilic sinapates from mustard varieties and their fractions. PRACTICAL APPLICATION: A major limitation in the application of natural extracts in vegetable oils is the poor lipophilic nature of phenolic compounds. This study employed a new thermal treatment (air frying) in the recovery of canolol and other lipophilic antioxidants. Such treatments can enrich mustard-based ingredients with canolol and other lipophilic antioxidants for domestic and industrial applications.

Rapidoxy® 100: A Solvent-Free Pre-treatment for Production of Canolol

RapidOxy® 100 is an automated instrument originally designed for measuring the oxidative stability of both solid and liquid samples. The compact and portable design of RapidOxy® 100, and its built-in pressurized heating chamber, provides a suitable environment for studying processing conditions. The feasibility of using oxygen or an inert atmosphere provides the ideal environment to study the effect of dry heat pre-treatment on canola antioxidants. The current study used RapidOxy® 100 to examine the impact of pressurized dry heat pre-treatment, under nitrogen, on the ultrasonic extraction of phenolic compounds. The effect of different pre-treatment temperature-time combinations of 120, 140, 160, and 180°C for 2, 5, 10, 15, and 20 min on the subsequent extraction of canola phenolic compounds was examined. The major sinapates identified by HPLC were sinapine, sinapic acid, and canolol. The optimum RapidOxy® condition for the maximum recovery of canolol was 160°C for 10 min. RapidOxy® 100 proved to be a novel and versatile instrument for enhancing the extraction of phenolic compounds.

Understanding of the Role of Pretreatment Methods on Rapeseed Oil from the Perspective of Phenolic Compounds

The thermal pretreatment of oilseed prior to oil extraction could increase the oil yield and improve the oil quality. Phenolic compounds are important antioxidants in rapeseed oil. In this study, we investigated the impact of thermal pretreatment method on the rapeseed oil based on phenolic compound levels. Liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) analysis showed that the phenolic compound contents in the microwave-pretreated oil were higher than those in the oven- and infrared-treated oils. Sinapic acid (SA) and canolol (CA), which are the top two phenolic compounds in rapeseed oil, exerted well 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity with IC₅₀ values of 8.45 and 8.80 μmol/L. The cell experiment uncovered that SA and CA have significant biological activities related to rapeseed oil quality, including increase of antioxidant enzymes superoxide dismutase (SOD), alleviation of reactive oxygen species (ROS), and cytotoxicity of HepG2 cells after the intake of excessive oleic acid. Further investigation indicated that SA and CA reduced cell apoptosis rate through Bax-Bcl-2-caspase-3 and p53-Bax-Bcl-2-caspase-3, respectively. Taken together, our findings suggest that microwave pretreatment is the best method to improve the content of phenolic compounds in rapeseed oil compared with oven and infrared pretreatments.

Preparation of rapeseed oil with superhigh canolol content and superior quality characteristics by steam explosion pretreatment technology

In this study, rapeseed was pretreated by steam explosion pretreatment technology and subsequently pressed to prepare rapeseed oil. GC, UPLC, and HPLC techniques were employed to analyze the quality characteristics of the rapeseed oil, including the canolol content and other quality characteristics. Additionally, the effect of steam explosion pretreatment technology on the canolol content of rapeseed oil was studied and the formation mechanism of canolol elucidated. The results revealed that when the steam explosion pressure reached 1.0 MPa, the canolol content of the tested oil increased from 41.21 to 2,168.69 mg/kg (52.63-fold increase) and that sinapic acid played a significant role in the conversion of canolol. Thus, the sinapine was converted into the intermediate (sinapic acid) by hydrolysis, which in turn was transformed into canolol through decarboxylation. The instantaneous high-energy environment generated by steam explosion pretreatment could intensify the hydrolysis and decarboxylation reactions of sinapine and sinapinic acid, thereby significantly increasing the canolol content of the oil. To prove the superiority of steam explosion pretreatment, we compared it with other pretreatment technologies, including traditional high-temperature roasting and popular microwave pretreatment. The results revealed that rapeseed oil prepared by steam explosion pretreatment displayed the best quality characteristics. This study can be a reference for the preparation process of rapeseed oil with superhigh canolol content and superior quality characteristics using steam explosion pretreatment.

Quality evaluation of rapeseed oil in Chinese traditional stir-frying

Canolol is a potential antioxidation ingredient in rapeseed oil. Rapeseed oil with two levels of canolol (528.9 vs. 250.5 mg/kg) was used for stir-frying different foods (potatoes, tofu, and vegetables). Comprehensive evaluations indicated that the canolol content in high canolol rapeseed oil (HCR) and low canolol rapeseed oil (LCR) after stir-frying were in the range of 187.8-237.7 and 45.6-96.4 mg/kg, respectively. The degradation rate of total phenol was 58.4% and 80.3% in HCR and LCR, respectively. The loss rates of α- and γ-tocopherol were 24.5% and 47.6%, respectively. Phytosterol concentration decreased by 20% and trans-fatty acid was not detected in either rapeseed oil. In addition, the peroxide value, anisidine value, and malondialdehyde content in HCR were lower than those in LCR. The oxidative stability index in HCR was longer, showing lower extent of deterioration. Rapeseed oil with high canolol content displayed good oxidation resistance due to significant positive correlation with oxidation induction time (p < .01).

A Two-Step Bioconversion Process for Canolol Production from Rapeseed Meal Combining an Aspergillus niger Feruloyl Esterase and the Fungus Neolentinus lepideus

Rapeseed meal is a cheap and abundant raw material, particularly rich in phenolic compounds of biotechnological interest. In this study, we developed a two-step bioconversion process of naturally occurring sinapic acid (4-hydroxy-3,5-dimethoxycinnamic acid) from rapeseed meal into canolol by combining the complementary potentialities of two filamentous fungi, the micromycete Aspergillus niger and the basidiomycete Neolentinus lepideus. Canolol could display numerous industrial applications because of its high antioxidant, antimutagenic and anticarcinogenic properties. In the first step of the process, the use of the enzyme feruloyl esterase type-A (named AnFaeA) produced with the recombinant strain A. niger BRFM451 made it possible to release free sinapic acid from the raw meal by hydrolysing the conjugated forms of sinapic acid in the meal (mainly sinapine and glucopyranosyl sinapate). An amount of 39 nkat AnFaeA per gram of raw meal, at 55 °C and pH 5, led to the recovery of 6.6 to 7.4 mg of free sinapic acid per gram raw meal, which corresponded to a global hydrolysis yield of 68 to 76% and a 100% hydrolysis of sinapine. Then, the XAD2 adsorbent (a styrene and divinylbenzene copolymer resin), used at pH 4, enabled the efficient recovery of the released sinapic acid, and its concentration after elution with ethanol. In the second step, 3-day-old submerged cultures of the strain N. lepideus BRFM15 were supplied with the recovered sinapic acid as the substrate of bioconversion into canolol by a non-oxidative decarboxylation pathway. Canolol production reached 1.3 g/L with a molar yield of bioconversion of 80% and a productivity of 100 mg/L day. The same XAD2 resin, when used at pH 7, allowed the recovery and purification of canolol from the culture broth of N. lepideus. The two-step process used mild conditions compatible with green chemistry.

Cold-pressed and hot-pressed rapeseed oil: The effects of roasting and seed moisture on the antioxi- dant activity, canolol, and tocopherol level

BACKGROUND

The paper looks at the levels of canolol, tocopherols and antioxidant activity in cold-pressed and hot-pressed rapeseed oils produced from seeds of various moisture levels (5%, 7.5%, and 10%). The paper also considers the effects of seed roasting on the levels of these compounds.

METHODS

The material used for the tests was rapeseed cv. Adrianna. The quality of the oils obtained is determined using peroxide and acid values. The levels of canolol and tocopherols are analyzed using HPLC. The DPPH radical-scavenging activity method for oil samples and phenolic extract from oils was used.

RESULTS

It has been demonstrated that the oils produced from rapeseeds with a 5% moisture content, and   in particular from cold-pressed oils, were characterized by the lowest peroxide values. Cold-pressed oils produced from rapeseeds with a 5% moisture content were characterized by higher levels of tocopherols and plastochromanol-8. In the case of hot-pressed oils, the highest levels of tocopherols were found in oils pro- duced from seeds with a 7.5% moisture content, and the greatest amount of PC-8 (more than 4 mg/100 g) was found in oils produced from seeds with a 10% moisture content. Hot-pressed oils have been shown to have higher levels of these compounds than cold-pressed oils. Both roasting and hot pressing led to an increase in the amount of canolol in the oils investigated. When analysing the antioxidant activity of the oils and phenolic extracts it was shown that phenolic compounds are responsible for approx. 10% of total antioxidant activity.

CONCLUSIONS

Various levels of biologically active compounds were shown to be present in the rapeseed oil obtained from raw materials of a varying moisture content. The type of pressing process (cold-pressing or hot-pressing) and whether the seeds have undergone roasting has also been shown to affect the resulting oil and the level of native antioxidants it contains.

Anticancer effects of 4-vinyl-2,6-dimethoxyphenol (canolol) against SGC-7901 human gastric carcinoma cells

Gastric cancer remains the fourth most commonly diagnosed cancer and is the second leading cause of cancer-related mortality worldwide. The aim of this study was to investigate the effects of canolol on the proliferation and apoptosis of SGC-7901 human gastric cancer cells and its relevant molecular mechanisms. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was used to observe the effect of canolol on the proliferation of SGC-7901 human gastric adenocarcinoma cells. The results showed that SGC-7901 cells exhibited a marked dose-dependent reduction in the proliferation rate. The survival rate of the cells was 88.86±1.58% at 50 μmol/l, decreasing to 53.73±1.51% at 800 μmol/l (P<0.05). By contrast, canolol had no significant toxicity on the human gastric mucosal epithelial cell line GES-1. The vivid images of cell morphology using an inverted microscope provided confirmation of the MTT assay. Treatment of SGC-7901 cells with canolol resulted in apoptosis demonstrated by flow cytometry. Furthermore, canolol downregulated the mRNA levels of COX-2, but had no significant effect on the mRNA expession of the Bax and Bcl-2 genes. These findings suggest that canolol has potential to be developed as a new natural anti-gastric carcinoma agent.