Influence of thermal treatments on the antioxidant activity of hemp cake polar extracts.

The effect of preheating temperature (X1), preheating time (X2) and the nature of the extracting solvents (X3) on the antioxidant activity of ultrasonic extracts of hemp cake was evaluated using a factorial design with a general linear multiple regression method using the three variables (X1, X2, and X3) and three levels including low (-1), intermediate (0) and high (+ 1). The results indicated that the extracting solvent and the preheating temperature levels were the principal effects influencing the total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activity (DPPH and FRAP). The highest level of preheating temperature (+ 1 = 180 °C) and extracting solvent (+ 1 = Ac80) were the optimal conditions for enhancing the extraction of the total phenolics and providing the highest antioxidant activity in hemp cake extracts. The interaction between temperature (X1), and the type of solvent (X3) significantly (p < 0.05) affected all the dependent variables examined. Supplementary Information: The online version contains supplementary material available at 10.1007/s13197-021-05325-9.

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.

Valorization of Heat-Treated Brewers' Spent Grain Through the Identification of Bioactive Phenolics by UPLC-PDA and Evaluation of Their Antioxidant Activities.

Thermal processing not only disrupts cell membranes and cell walls, but also cleaves covalent bonds releasing low molecular phenolic. This study examined the impact of various heat treatments (100, 140, and 160°C) on the composition of phenolic acids and antioxidant activities in extracts obtained from defatted brewers spent grain (BSG) meal. Heating BSG at 160°C resulted in a 2-fold increase in total phenolic content [TPC, 172.98 ± 7.3 mg Gallic acid equivalent (GAE)/100 g defatted meal] and total flavonoid content [TFC, 16.15 ± 2.22 catechin equivalents (CE)/100 g defatted meal] compared to the untreated BSG extracts. The antioxidant activities of treated BSG extracts, determined by radical scavenging and ferric reducing antioxidant power (FRAP) were significantly (p < 0.5) higher than the corresponding untreated BSG extracts. Eleven phenolic acids were identified and quantified in BSG extracts by Ultra Performance Liquid Chromatography with Photodiode Array (UPLC-PDA). The amounts varied significantly (p < 0.05) depending on the degree of toasting BSG was subjected to. Chlorogenic acid, an ester of caffeic and quinic acid was the predominant phenolic acid present in all fractions. Significant (p < 0.05) increases in TPC, TFC, individual phenolic acids and antioxidant activity were observed in BSG extracts exposed to increasing oven temperatures. These results confirm the ability of heat processing to release bioactive phenolic from their bound forms thereby enhancing the phenolic acids and the digestibility of BSG meal in the intestinal tract.

Antioxidative Polyphenols of Canola Meal Extracted by High Pressure: Impact of Temperature and Solvents.

Canola meal, a by-product of oil pressing, is a rich source of phenolic antioxidants. However, its use in the food and feed sector is still limited by the need for greener, sustainable, and more cost-effective extraction methods. This study used accelerated solvent extraction (ASE) to enhance the extraction efficiency of the phenolic antioxidants. The high selectivity and short extraction time associated with ASE were ideal for obtaining high yields of these antioxidants. The structure-based activity of phenolic compounds may be influenced by the high pressure and temperature of the greener ASE process. The present study evaluated the effect of temperature (140, 160, and 180 °C) and pressure (1,500 psi) on the extraction and yield of phenolic compounds from canola meal as well as the solvent type (ethanol and methanol) and concentration (30%, 40%, 60%, and 70% v/v). Antioxidant activity was determined by 2,2-diphenyl-1-picrylhydrazyl, ferric reducing/antioxidant power assay, and ion-chelating activity. The highest yield of phenolic compounds was obtained with 70% methanol (20.72 ± 1.47 mg SAE/g DM [milligrams of sinapic acid equivalents per gram of dry matter]) and 70% ethanol (24.71 ± 2.77 mg SAE/g DM) at 180 °C temperature. A similar trend was observed for the antioxidant activity of the extracts and their total flavonoid content. The structure-based antioxidant activity of the extracts examined increased with the increase in the percentage of the extracting solvent (P > 0.05). This study established ASE as an efficient green method for extracting phenolic compounds from canola meal, with potential application for the production of natural bioactive compounds from underutilized agricultural by-products. PRACTICAL APPLICATION: ASE is an efficient eco-friendly method for extracting phenolic compounds from agricultural by-products such canola meal. Under the conditions of high pressure and temperature, ASE significantly improved the yields of phenolic compounds, sinapine, sinapic acid, and canolol. Under these conditions, water, as an extractant, was not effective in extracting sianpine. Moreover, it was much less effective than both 70% ethanol and 70% methanol in extracting sinapine or canolol. These phenolic compounds are of great interest as natural antioxidants for enhancing the shelf life of food products. They also represent new sources of neutraceuticals for improving human health.

In situ oxidation of canola meal sinapic acid by horseradish peroxidase (type II) and tyrosinase.

The enzymatic oxidation of sinapic acid catalyzed by horseradish peroxidase (HRP) or tyrosinase was investigated using model systems, which contained the pure compound or canola meal. Spectrophotometric scanning of pure sinapic acid solution in the presence of HRP (0.2 U) or tyrosinase (40.3 U) showed continuous decreases in absorbance at 304 nm over a period of 90 and 60 min, respectively. HPLC analyses of enzymatic end products, obtained by the catalysis with HRP or tyrosinase, indicated the presence of two main compounds (1 and 2). After alkaline hydrolysis of canola meal, sinapic acid that was released from sinapine was also converted to compounds 1 and 2 by HRP or tyrosinase. Enzyme reaction kinetics results indicate that the catalytic efficiency (CE = 0.538), reaction velocity (Vmax  = 5.67 ∆A/h), and Michaelis-Menten constant (Km  = 926.64 µM) of HRP are significantly higher than those of tyrosinase (CE = 0.041, Vmax  = 0.41 ∆A/h, Km  = 173.03 µM) at 50-250 µM pure sinapic acid concentrations. PRACTICAL APPLICATIONS: Canola meal contains a large amount of sinapine, which is the choline ester of sinapic acid, a strong antioxidant compound. However, the oxidation or decarboxylation products of sinapic acid could add value by increasing the level of electron-dense carboxylic and carbonyl compounds. In this study, enzymatic treatment of alkaline-hydrolyzed canola meal with horseradish peroxidase (HRP) and tyrosinase was investigated and shown to be suitable for converting sinapic acid into oxidized compounds. Therefore, the enzymatic treatment is a potential application for value-added processing of canola meal.

Effect of pretreatments and endo-1,4-ß-xylanase hydrolysis of canola meal and mustard bran for production of oligosaccharides.

Alkali/acid-pretreated canola meal and mustard bran were subjected to endo-1,4-ß-xylanase (T. longibrachiatum) hydrolysis for oligosaccharide production. Pretreatments significantly (α = 0.05) increased the relative content of pentose sugars, especially in alkali-pretreated canola meal (∼44 %) and mustard bran (∼72 %). The amounts of pentosan (g/100 g) in acid- and alkali-pretreated canola meal were 7.50 and 8.21 and in corresponding mustard bran were 8.67 and 10.39, respectively. These pretreated substrates produced a pentose content (g/100 g) of 2.10 ± 0.14 (18 h) and 2.95 ± 0.10 (24 h), respectively, during hydrolysis. As per UPLC-MS data, the main oligosaccharides in the hydrolyzates of alkali-pretreated substrates are xylo-glucuronic acid and xylobiose. The release of total phenolics of the hydrolyzates increased until 18 h irrespective of the type of substrate or pretreatment. Hydrolyzates of acid-pretreated substrates indicated more total antioxidant activity than alkali-pretreated substrates, attributed to its high phenolic content. The study suggests the potential of canola meal and mustard bran for the production of oligosaccharides, wherein the use of various combinations of cell-wall-degrading enzymes and its optimization may result in a better yield, with simultaneous production of endogenous phenolics.

Value-added potential of expeller-pressed canola oil refining: characterization of sinapic acid derivatives and tocopherols from byproducts.

Valuable phenolic antioxidants are lost during oil refining, but evaluation of their occurrence in refining byproducts is lacking. Rapeseed and canola oil are both rich sources of sinapic acid derivatives and tocopherols. The retention and loss of sinapic acid derivatives and tocopherols in commercially produced expeller-pressed canola oils subjected to various refining steps and the respective byproducts were investigated. Loss of canolol (3) and tocopherols were observed during bleaching (84.9%) and deodorization (37.6%), respectively. Sinapic acid (2) (42.9 µg/g), sinapine (1) (199 µg/g), and canolol (344 µg/g) were found in the refining byproducts, namely, soap stock, spent bleaching clay, and wash water, for the first time. Tocopherols (3.75 mg/g) and other nonidentified phenolic compounds (2.7 mg sinapic acid equivalent/g) were found in deodistillates, a byproduct of deodorization. DPPH radical scavenging confirmed the antioxidant potential of the byproducts. This study confirms the value-added potential of byproducts of refining as sources of endogenous phenolics.

Endogenous Phenolics in Hulls and Cotyledons of Mustard and Canola: A Comparative Study on Its Sinapates and Antioxidant Capacity.

Endogenous sinapic acid (SA), sinapine (SP), sinapoyl glucose (SG) and canolol (CAN) of canola and mustard seeds are the potent antioxidants in various lipid-containing systems. The study investigated these phenolic antioxidants using different fractions of canola and mustard seeds. Phenolic compounds were extracted from whole seeds and their fractions: hulls and cotyledons, using 70% methanol by the ultrasonication method and quantified using HPLC-DAD. The major phenolics from both hulls and cotyledons extracts were SP, with small amounts of SG, and SA with a significant difference of phenolic contents between the two seed fractions. Cotyledons showed relatively high content of SP, SA, SG and total phenolics in comparison to hulls (p < 0.001). The concentration of SP in different fractions ranged from 1.15 ± 0.07 to 12.20 ± 1.16 mg/g and followed a decreasing trend- canola cotyledons > mustard cotyledons > mustard seeds > canola seeds > mustard hulls > canola hulls. UPLC-tandem Mass Spectrometry confirmed the presence of sinapates and its fragmentation in these extracts. Further, a high degree of correlation (r = 0.93) was noted between DPPH scavenging activity and total phenolic content.