The effects of roasting temperatures on the formation of headspace volatile compounds in perilla seed oil

Volatile compounds of perilla seed oils roasted at different temperatures (150–190°C) were analyzed by dynamic headspace gas chromatography-mass spectrometry. The headspace volatiles in roasted perilla seed oils (RPSO) were composed of thermally produced flavors and compounds originating from the raw perilla seeds. The roasting temperatures significantly affected the production of thermal reaction flavors. Oils from parilla seeds roasted below 170°C had relatively high concentrations of aldehydes, whereas pyrazines and furans were the predominant volatiles above 170°C. In all of the RPSO, the contents of both perilla aldehyde and perilla ketone remained almost constant and might be used to discriminate perilla seed oils from other roasted vegetable seed oils.     

Roasting-Related Changes in Oxidative Stability and Antioxidant Capacity of Apricot Kernel Oil

Apricot kernels were roasted for various lengths of time (0–30 min) at 180 °C and changes in the oxidative stability, antioxidant capacity, color, as well as the level of tocopherols and fatty acids of the apricot kernel oil (AKO) were monitored. While the level of tocopherols decreased, the oxidative stability and antioxidant capacity of AKO increased with roasting, probably due to the formation of antioxidative Maillard reaction products (MRPs) during the roasting. Medium roasted samples (15–20 min) were found to be more resistant to oxidative deterioration. The oil from the 30-min roasted sample was more susceptible to oxidation compared to the oil from the 20-min roasted sample in most of the stability tests. Relatively shorter roasting periods (5–10 min) also led to a decrease in oxidative stability in comparison to the unroasted sample. Brownish color and antiradical activity increased with roasting and the highest values were measured in the 30 min roasted sample.     

Effect of Roasting on Flaxseed Oil Quality and Stability

The food industry is interested in the application of roasted flaxseeds because the treatment improves their sensory acceptability. However, it also influences flaxseed oil nutritional quality and stability. The aim of the study was to analyze oxidation changes in situ and in flaxseed oil compounds (fatty acids, phytosterols, tocochromanols) and Maillard reaction products (MRP) after roasting. The effect of the roasting temperature (160–220 °C) and flaxseed cultivars (golden- and brown-seed) was taken into consideration. The results showed that the selection of roasting temperature (<200 °C vs. ≥200 °C) and flaxseed cultivar significantly influenced the nutritional quality and oxidative stability of roasted flaxseed oils. The roasting of flaxseeds did not significantly affect the fatty acid profiles of oil but it influenced the content of the other bioactive compounds. As the roasting temperature increased (≥200 °C), the γ-tocopherol degradation decreased, whereas the content of plastochromanol-8 increased. The total content of phytosterols in the roasted seed samples was higher than in the raw seeds but there was no correlation between the phytosterol content and roasting temperature. The temperature ≥200 °C significantly accelerated in situ oil oxidation during roasting. On the other hand, these conditions favored the MRP formation, which may have slowed down the dynamics of oil oxidation during storage. There was lower oil oxidation in the brown-seed cultivar; in consequence, the tocopherol retention was higher than in the golden-seed cultivars. The results could be useful for the selection of the best cultivars and treatment conditions to decrease unfavorable changes in flaxseed oil nutritional quality and stability.     

Influence of roasting conditions on fatty acids and oxidative changes of Robusta coffee oil

The aim of this study was to determine the influence of roasting conditions, including elevated humidity of air used in the process, on the properties of coffee oil. Beans of Robusta coffee were roasted in a laboratory convective roaster with a possibility of changing the temperature, humidity, and velocity of roasting air. Roasting temperatures from 190 to 216°C, air humidity from 0.07 to 1%, and air velocity of 0.5 and 1 m/s were used. Parameters analyzed in roasted beans were: oil content, fatty acids composition, including trans fatty acids using the GC/FID method and indicators of oxidation level, namely peroxide value and content of conjugated dienes and trienes. Also a thermal profile of oil with the use of the DSC method and finally the bean aroma were evaluated. For maintaining the maximal amount of PUFA, the most favorable roasting conditions were, either, roasting at relatively high temperature and short time, or roasting at low temperatures. Using moderately high temperature resulted in the highest oxidative changes, but on the other hand, the aroma of received beans presented the best sensory properties. For the best nutritional properties, the best roasting conditions were: temperature 210°C and 1% humidity content in roasting air at 1 m/s flow velocity. In such conditions roasted beans obtained a very high quality aroma, and the roasting time was relatively short. Practical applications: This research concerns the quality of oil obtained from roasted coffee beans. The composition of coffee oil changes slightly during roasting, but nevertheless it might be a source of peroxides and trans fatty acids in human diet. In industrial processing coffee oil is extracted from the remains left over from instant coffee production, and it is a popular agent for aromatizing food products. Thus, in this kind of processing, roasting conditions that limit the unfavorable changes of coffee oil should be used.     

Effects of Seed Roasting on Tocopherols,Carotenoids, and Oxidation in Mustard Seed Oil During Heating

Seed roasting is practiced in the mustard oil industry in some areas of the world, and can affect the physicochemical properties of the oil for further applications. This research studied the differences in oxidative stability, tocopherols, and carotenoids during heating at 160 °C between oil extracted from roasted mustard seeds and that from unroasted seeds. The content of free fatty acids, polar compounds (PC), and lutein were not significantly different between the roasted and unroasted seed oils before heating. The fatty acid compositions of both oils were also similar, with high amounts of erucic, linoleic, and oleic acids, moderate amounts of linolenic and eicosenoic acids, and low amounts of palmitic and stearic acids. However, the levels of tocopherols and conjugated dienoic acids (CDA) were higher in the roasted seed oil. Heating increased the content of CDA and PC in both oils, but decreased tocopherols and lutein. The rates of increase in CDA and PC and the degradation rates of tocopherols and lutein during heating were lower in the roasted than in the unroasted seed oil. Overall, the increased thermo-oxidative stability of the mustard oil by roasting the seeds before oil extraction was highly correlated with improved heat stabilities for both tocopherols and lutein.     

The Effects of Infrared Roasting on HCN Content,Chemical Composition and Storage Stability of Flaxseed and Flaxseed Oil

Flaxseeds were roasted at 1150 W/m² radiation intensity with short and medium wave infrared (IR) emitters for specific durations, which provided good visual and sensory quality. The effects of IR roasting on color properties, hydrogen cyanide (HCN) content, tocopherols and fatty acid composition of the flaxseed and flaxseed oil were investigated. Further, flaxseeds were stored for 6 months and free fatty acid content and peroxide values were followed at 1-month intervals to understand the effect of IR treatment on hydrolytic and oxidative stability. HCN content of the flaxseeds was reduced up to 59% with IR roasting. Tocopherol content of the IR roasted flaxseed oil was higher than that of the control. No notable variation was observed in fatty acid composition with regard to IR treatment. Free fatty acid content of IR roasted flaxseeds did not increase during storage, while peroxide value of the seeds significantly increased up to 95 mEq O₂/kg oil.     

Formation of Benzo(a)pyrene in Sesame Seeds During the Roasting Process for Production of Sesame Seed Oil

The main aim of this research was to enhance the understanding of the formation mechanisms of benzo(a)pyrene (BaP) during roasting of sesame seeds (SS). BaP levels in hot‐ and cold‐pressed sesame seed oil (SSO) were evaluated to correlate oil technology and BaP formation. Extracted principal components from SS were roasted either singly or in mixtures at 230 °C for 30 min. BaP was measured by HPLC with fluorescence detection. The results showed that BaP levels in hot‐pressed SSO were significantly higher than those in cold‐pressed SSO (p < 0.05), BaP formation mostly occurred during SS roasting and increased with roasting temperature (between 80 and 280 °C) and time (from 10 to 50 min). Furthermore, the BaP level in the roasted hulled SS (3.64 μg/kg) was higher than it was in roasted whole SS (1.63 μg/kg). The maximum BaP level observed (5.03 μg/kg) was detected in a roasted mixture of SS protein and SSO. The addition of sesame protein to protein‐free SSO promoted the formation of BaP, which suggests that the pyrolysis products of protein and triacylglycerols are probably important precursors in BaP formation.     

Aqueous enzymatic extraction of peanut oil and protein hydrolysates

The aqueous enzymatic process of simultaneously preparing oil and protein hydrolysates from peanut was investigated. The optimum parameters for hydrolysis using Alcalase 2.4L were established by the single-factor and orthogonal test. The optimal processing conditions were as follows: hydrolysis temperature 60 °C, pH 9.5, ratio of material to water 1:5 (w/w), alkaline extraction time 90 min, enzyme amount 1.5% (w/w) and hydrolysis time 5 h. Under these conditions, the free oil and protein hydrolysates yields were 79.32% and 71.38% respectively. In order to improve these yields, As1398 was chosen to hydrolyze the residue and emulsion. The total free oil and protein hydrolysates yields were increased to 91.98% and 88.21% respectively.     

Effect of roasting on oxidative and tocopherol stability of walnut oil during storage in the dark

The effect of roasting on the oxidative stability of oil from walnut (Juglans sinensis Dode) was investigated by observing changes in the characteristics of oils from unroasted and roasted kernels during storage in the dark at 60°C. Walnut kernels were roasted at 160°C for 15 min prior to oil extraction with the solvent, hexane. Roasting of kernels increased the peroxide value (POV) and conjugated dienoic acid (CDA) value of the oil. The rate of increase in the POV was significantly lower in roasted than in the unroasted walnut oil during storage at 60°C (1.90 vs. 1.06 and 4.45 vs. 3.55 meq/kg/day during induction period (IP) and post‐IP, respectively). Roasting of kernels significantly increased the IP of walnut oil from 0.89 to 3.39 days during storage. The total tocopherol content in roasted walnut oil was lower as compared to that in unroasted one (277.77 vs. 314.88 µg/g). However, the rate of degradation of total tocopherol during storage was lower in roasted walnut oil compared to unroasted one (1.18 vs. 2.17%/day), which showed that the tocopherol retention was higher in roasted walnut oil. These results indicate that roasting of kernels increased the oxidative and tocopherol stability of oil during storage in the dark.     

The effect of roasting on the chemical composition and oxidative stability of pumpkin oil

This study is concerned with the effect of the process of roasting of naked pumpkin seeds prior to their pressing on the chemical composition and oxidative stability of the extracted oil. Ground seeds were roasted at temperatures of 90, 110, and 130°C for 30 and 60 min, according to the traditional technology of production of roasted pumpkin oil. Depending on the roasting conditions of the seeds, this treatment resulted in a significant increase of the contents of phospholipids (from 0.005 to 0.463%), total phenolic compounds (from 4.63 to 19.60 mg/kg), and total tocopherols (from 265.79 to 350.98 mg/kg) in oil. Higher contents of these minor components enhanced the oxidative stability of the oil, i.e., increased the induction period (from 4.50 to 12.93 h). However, at the same time, the applied thermal treatment generated an increase in the primary and secondary oxidation products, resulting in higher Totox values that could lower the quality of the oil.     

Effect of roasting oil composition on the stability of roasted high-oleic peanuts

Off-flavor due to lipid degradation is an important factor in the shelf life of peanut products. The use of recently developed peanuts with high-oleic acid/linoleic acid (O/L) ratio has the potential to significantly extend the shelf life of roasted peanuts. To determine the full potential for shelf-life improvement of oil-roasted high-O/L peanuts, a study was conducted to examine the effects of roasting high-O/L peanuts (O/L=30) in high-O/L (O/L=23.2) or conventional (O/L=1.5) peanut oil. Peanuts were roasted at 177°C to Hunter L values of 49±1. Roasted peanuts were stored at 30°C for 20 wk. Samples were taken at regular intervals to determine PV, oxidative stability index (OSI), moisture content, and water activity. The O/L ratio of high-O/L roasted peanuts was 27.9 vs. 13.6 for the conventional oil-roasted peanuts. After 20 wk of storage, PV of conventional oil-roasted peanuts was 10.8 compared to 5.3 for the high-O/L-roasted peanuts. OSI values were 88.5 and 52.4 immediately after roasting for the high-O/L-roasted vs. conventional oil-roasted peanuts. OSI for both decreased, but differences remained similar throughout the storage period. Shelf life of high-O/L peanuts decreased when roasted in conventional O/L-peanut oil vs. high-O/L peanut oil.     

Babassu Oil (Orbynia phalerata), an Artisanal Product: Process Optimization of Seed Roasting on Yield,Phenolic Compounds,and Antioxidant Capacity

Babassu oil has high concentrations of phenolic compounds. When seeds are preheated, these compounds tend to migrate to the oil depending on the degree of roasting applied. This study aims to optimize the roasting conditions of babassu seeds using response surface methodology (RSM) and the desirability functions. A central composite rotational design (CCRD) is employed to investigate the effects of two independent variables, temperature (X₁) and roasting time (X₂) which significantly affected response variables, namely yield (%), total phenolics content (TPC), number of phenolic compounds, oxygen radical absorbance capacity, acid value and peroxide value. The quadratic model is adjusted for most responses. The roasting temperature of 222 °C and the roasting time of 43 min are standardized as ideal conditions. Thus, the oil produced at the optimized conditions shows a yield of 54.47% and TPC of 91.53 mg GAE/100 g. In the control oil sample, the presence of phenolic compounds analyzed by HPLC-DAD is not observed while under optimized conditions, seven phenolic compounds are observed. The model of optimized conditions shows a good correlation between the predicted and experimental values. In general, these results demonstrate the effectiveness of optimum roasting conditions in improving the quality of bioactive compounds in babassu oil. Practical Applications : This work aims to optimize the babassu seeds roasting process to obtain oil with a greater number of phenolic compounds and better antioxidant capacity. As the first study on babassu seeds roasting, it contributes to the generation of important data in relation to the identification and quantification of phenolic compounds in the oil. Finally, the optimum roasting conditions established in this work can be explored commercially in babassu oil extraction.     

Oxidative Stability of Cashew Oils from Raw and Roasted Nuts

Cashew nut oils, extracted from raw and roasted whole cashew nuts, were examined for their fatty acid composition, color change and oxidative stability. Fatty acids were analyzed using gas chromatography, and a spectrophotometric method was used to determine the color changes of the resultant oils. Oxidative stability was determined under accelerated oxidation conditions by employing conjugated diene (CD) and thiobarbituric acid reactive substances (TBARS) assays. The contents of monounsaturated (MUFA), polyunsaturated (PUFA) and saturated (SAFA) fatty acids were 61, 17 and 21%, respectively. Oleic acid was the major MUFA whereas linoleic acid was the main PUFA present in cashew nut oils. Oxidative stability of the oil as determined by CD values after 72 h of storage under Schall oven condition at 60 °C was 1.08 and 0.65 for the raw and high temperature roasted cashew nut, respectively. The TBARS values, expressed as malondialdehyde equivalents decreased with increasing roasting temperature. Thus roasting of whole cashew nuts improved the oxidative stability of the resultant nut oils.     

Antioxidant (Tocopherol and Canolol) Content in Rapeseed Oil Obtained from Roasted Yellow-Seeded <Emphasis Type="Italic">Brassica napus</Emphasis>

In this study, the effect of temperature (140, 160, 180 °C) and roasting time (5, 10, 15 min) on the bioactive compound content (canolol, tocopherol and plastochromanol‐8) of cold‐pressed oil from yellow‐seeded rapeseed lines of different colors was investigated. Roasting increased the peroxide value in the seed oils compared to the oils from the control samples. However, roasting did not affect the acid values of the oils, which were 1.15–1.47 and 1.30–1.40 mg KOH/g, for line PN1 03/1i/14 (yellow seeds) and line PN1 563/1i/14 (brown seeds), respectively. In this study, the seeds of line PN1 03/1i/14 were characterized by different changes in canolol content during roasting than the seeds of PN1 563/1i/14. There was a 90‐fold increase in canolol for the line PN1 03/1i/14 (768.26 µg/g) and a 46‐fold increase for the line PN1 563/1i/14 (576.43 µg/g). Changes in tocopherol and PC‐8 contents were also observed. There was an increase in the contents of γ‐T and PC‐8 in the oils obtained from the seeds roasted at 180 °C for 10 and 15 min. γ‐T content increased by 17–18% after 15 min of roasting, whereas the PC‐8 content increased twofold.     

Characteristics and Composition of Watermelon Seed Oil and Solvent Extraction Parameters Effects

Watermelon seed oil characteristics were evaluated to determine whether this oil could be exploited as an edible oil. Hexane extraction of watermelon seeds produced yields of 50% (w/w) oil. The refractive index, saponification and iodine value were 1.4712 (at 25 °C), 200 mg KOH/g and 156 g I/100 g, respectively. The acid and peroxide values were 2.4 mg KOH/g and 3.24 mequiv/kg, respectively. The induction time of the oil was also 5.14 h at 110 °C, which was measured for the first time. Total unsaturation contents of the oil was 81.6%, with linoleic acid (18:2) being the dominant fatty acid (68.3%). Considering that the watermelon seed oil was highly unsaturated, the relatively high induction time might indicate the presence of natural antioxidants. In addition, the influence of extraction parameters on extraction of oil from watermelon seed with hexane as a solvent was studied at several temperatures (40, 50, and 60 °C), times (1, 2, and 3 h) and solvent/kernel ratios (1:1, 2:1, and 3:1). The oil yield was primarily affected by the solvent/kernel ratio and then time and temperature, respectively. The protein content of the oil-free residue was 47%.     

Antioxidant Activities and Phenolic Compositions of Wheat Germ as Affected by the Roasting Process

Wheat germ is a good source for wheat germ oil, and it is a by‐product with highly concentrated nutrients from the wheat flour‐milling industries. In the present study, raw wheat germ was firstly heat‐treated at 180 °C for 20 min in a fluidized bed dryer, and further roasted at 180 °C for different periods of time. Roasting influence on total phenolic content (TPC), antioxidant activities, and phenolic compositions of wheat germ were evaluated. The roasting process significantly increased the TPC and antioxidant activities including free radical scavenging against DPPH and ABTS radicals, FRAP, and ORAC. In particular, the wheat germ roasted at 180 °C for 20 min showed higher antioxidant activity than those roasted at 180 °C for 5 and 10 min. Three major phenolic acids, namely, ferulic, chlorogenic, and caffeic acid, and four main flavonoids, namely, schaftoside and its isomers or adduct of sinapic acid were identified by HPLC. In general, the content of individual phenolic compounds decreased with prolongation of the roasting time except for ferulic acid. The results suggest that the antioxidant activities of wheat germ can be enhanced by roasting, and the enhancement effect might be partially attributed to the formation of Maillard reaction products (MRP).     

Selective recovery of metals from spent desulfurization catalyst

Valuable metals including V, Mo, Ni, Co, and Al were selectively recovered from spent desulfurization catalyst by means of extractive separation. Prior to selective metal recovery the spent catalyst was roasted at temperatures of 400–800 °C, and BET, SEM, and XRD data showed that roasting the spent catalyst at 550 °C gave birth to the surface and pore structures accounting for good extractibility of the roasted spent catalyst. A sequential scheme consisting of leaching and chelate extraction was developed to recover the metals from the spent catalyst roasted at 550 °C and oxygen space velocity of ca. 1800 hr⁻¹.     

Effects of processing on oxidative stability of sesame oil extracted from intact and dehulled seeds

Oxidative stability of oils extracted from intact and dehulled sesame seeds was determined by monitoring changes in fatty acid composition, iodine value (IV), peroxide value (PV), conjugated diene (CD), para-anisidine value (p-AV), and 2-thiobarbituric acid (TBA) value and by nuclear magnetic resonance spectroscopy after storage under Schaal oven conditions at 65°C for up to 35 d. The oils from coated seeds were more stable, as reflected in PV, CD, p-AV and TBA values, than those extracted from dehulled seeds after roasting at 200°C, steaming at 100°C, roasting at 200°C plus steaming, or microwaving at 2450 MHz, except for TBA values of oil from microwaved seeds. After 35 d of storage at 65°C, the CD, p-AV, and TBA values of extracted oil from dehulled microwaved seeds were 17.72, 10.20, and 1.22, respectively, while those of their coated counterparts were significantly (P<0.05) different at 14.20, 16.47, and 1.26, respectively. Few significant changes were evident in the fatty acid composition of oil obtained from either coated and dehulled seeds subjected to different treatments. Nuclear magnetic resonance analyses found that R_ao (aliphatic to olefinic protons) and R_ad (aliphatic to diallylmethylene protons) ratios increased steadily over the entire storage period, which indicated progressive oxidation of unsaturated fatty acids.     

Comparison of the effects of oven- and microwave-roasting on the physicochemical properties and bioactive compounds of tomato seeds and oils

The tomato processing industry generates a significant amount of a by-product (pomace), which is a mixture of peels and seeds. The purpose of this study was to compare the effects of conventional oven-roasting (at 120°C, 150°C, and 180°C for 25 min) and innovative microwave-roasting (at 240, 388, and 536 W for 3 min) pretreatments on the physicochemical properties, fatty acid profiles, bioactive contents, and aroma profiles of tomato seeds and their hexane-extracted oils. The total flavonoids contents (TFCs) of the seeds decreased from 258.40 to 141.20 mg quercetin equivalent (QE) per kg after roasting. All roasting treatments improved the extractability of both α- and γ-tocopherols. The amounts of total tocopherols in the seeds increased from 917.61 to 1256.25 mg kg^–1 after pretreatment. Luteolin was found to be the most abundant phenolic in seed oils, increasing from 10.68 to 91.72 mg kg^–1, followed by quercetin, ferulic acid, and catechin. Within each roasting technique, the ones treated at 150°C and 338 W yielded the oils with the highest concentrations of aroma compounds, 418 and 92 mg kg^–1, respectively. The detrimental effect of microwave-roasting on these compounds was more pronounced. In conclusion, microwave-roasting at shorter times than conventional roasting produced tomato seed oils with well-preserved bioactive components and few unfavorable changes. Industrial relevance: Conventional oven-roasting has been widely applied to oilseeds to improve oil yield as well as to obtain desirable sensory characteristics of extracted oils for years. However, longer roasting times may also cause detrimental changes in the properties of oils. On the other side, microwave-assisted applications as an emerging technology provide homogenous and well-controlled heat distribution, shorter treatment times, and considerable energy savings for the processing of various foods. Microwave technology has been easily scaled up and is currently employed for sterilization, drying, pasteurization, precooking, and extraction by the food and chemistry industries. Therefore, the present research suggests the use of microwaves for comparatively short roasting times to produce edible oils with enhanced physicochemical attributes and bioactives contents, and well-maintained sensory properties. This promising innovative technology has the potential to be industrialized for a cost-effective seed roasting process.     

Nitrogen bubble refining of sunflower oil in shallow pools

High-temperature steam deodorization of sunflower oil results in the formation of unwanted by-products, such as trans isomers and polymers, and partial destruction of vitamins. There is an urgent need to develop a process that replaces steam with an inert gas such as nitrogen. The use of nitrogen bubble sparging at low temperatures has recently been reported as a technique to strip volatiles from edible oils. In this study, a hypothesis was proposed that nitrogen bubbles sparged at temperatures of 25 to 150°C are able to remove odoriferous, surface-active, or volatile contaminants from shallow pools of sunflower oil. Analysis of the composition of sunflower oil that had been sparged at 3 mbar pressure showed that both the odor and peroxide content of the oil were considerably reduced to values that are commercially acceptable. Odor improvement occurred at temperatures between 100 and 150°C, while the peroxide content reduction was achieved at a temperature of 150°C. There were no significant improvements in the free fatty acid concentration or color.