Effect of Infrared Heating on the Formation of Sesamol and Quality of Defatted Flours from Sesamum indicum L.

ABSTRACT:  Infrared (IR) heating offers several advantages over conventional heating in terms of heat transfer efficiency, compactness of equipment, and quality of the products. Roasting of sesame seeds degrades the lignan sesamolin to sesamol, which increases the oxidative stability of sesame oil synergistically with tocopherols. IR (near infrared, 1.1 to 1.3 μm, 6 kW power) roasting conditions were optimized for the conversion of sesamolin to sesamol. The resultant oil was evaluated for sesamol and tocopherol content as well as oxidative stability. The defatted flours were evaluated for their nutritional content and functionality. IR roasting of sesame seeds at 200 °C for 30 min increased the efficiency of conversion of sesamolin to sesamol (51% to 82%) compared to conventional heating. The γ-tocopherol content decreased by 17% and 25% in oils treated at 200 and 220 °C for 30 min, respectively. There were no significant differences in the tocopherol content and oxidative stability of the oil. Methionine and cysteine content of the flours remained unchanged due to roasting. The functional properties of defatted flours obtained from either IR roasted or conventionally roasted sesame seeds remained the same.
Practical Applications: Sesame oil is stable to oxidation compared to other vegetable oils. This stability can be attributed to the presence of tocopherols and the formation of sesamol, the thermal degradation product of sesamolin—a lignan present in sesame. Roasting of sesame seeds before oil extraction increases sesamol content which is a more potent antioxidant than the parent molecule. The conversion efficiency of sesamolin to sesamol is increased by 31% by infrared roasting of seeds compared to electric drum roasting. This can be used industrially to obtain roasted oil with greater oxidative stability.     

Influence of sn‐1,3‐lipase‐catalysed interesterification on the oxidative stability of soybean oil‐based structured lipids

The oxidative stability of structured lipids (SLs) synthesised by specific sn‐1,3‐lipase catalysed interesterification of soybean oil (SBO) with caprylic acid (CA) in a stirred batch reactor was studied. SLs contained considerable amounts of tocopherol (TOH) isomers, although they lost almost 25% of endogenous TOHs during production. The effects of the addition of different TOH homologues (α, β, γ, δ), ascorbyl palmitate (AP, 200 ppm), lecithin (Le, 1000 ppm), butylated hydroxytoluene (BHT, 100 ppm) and butylated hydroxyanisole (BHA, 100 ppm) on the oxidative stability of SLs were investigated. Induction time (IT) of SBO, determined by the Rancimat method, decreased from 8.4 to 5.8 h at 110 °C after the modification. On the other hand, purified SLs and purified SBO had the same IT due to the tocopherol reduction during silica purification. No significant difference was observed between IT of SLs and SLs plus different α‐tocopherol concentrations (50, 100, 150, 200, 300, 500 and 1000 ppm) (P > 0.05). However, the addition of Le and/or AP significantly improved oxidative stability of purified SLs and SBO. The ternary blend containing δ‐TOH, AP and Le had higher IT than ternary blends of α‐TOH, β‐TOH or γ‐TOH. Furthermore, ternary blend containing BHA, AP and Le had higher IT than ternary blends of BHT, AP and Le. In addition, there was an increase in peroxide value (PV), conjugated diene (CD) content and p‐anisidine value (AV) during oxidation of oils at 60 °C. Antioxidant mixtures of α‐TOH (50 ppm) and δ‐TOH (500 ppm) with AP and Le decreased PV, CD and AV effectively. Copyright © 2006 Society of Chemical Industry     

Effects of microwave energy on the relative stability of vitamin E in animal fats

The relative stabilities of individual tocopherols during microwave heating were evaluated in purified animal fats. Each tocopherol (α, β, γ and δ) was added to the purified beef tallow and lard at 0.25 μmol g^?1 fat immediately before use. During microwave heating the highest rate of loss was shown by α-tocopherol, followed by γ-, β- and δ-tocopherols. This order did not depend on the types of fats present. The indices such as peroxide value, carbonyl value and anisidine value for assessing quality of fats showed a significant difference (P < 0.05) in the final stage (12–20 min) of heating. It is therefore necessary that particular attention be paid to the loss of vitamin E when cooking pork or beef in a microwave oven.     

Microwave Heating Effects on Relative Stabilities of Tocopherols in Oils

The relative stabilities of individual tocopherols during microwave heating were investigated in fatty acid esters and tocopherol-stripped vegetable oils. The rate of tocopherol loss during heating was less from the highly unsaturated ethyl esters or vegetable oils than from ethyl laurate or olive oil. However, changes in chemical properties of the substrates depended on degree of unsaturation of esters and oils. The stability of tocopherols during microwave heating was δ > β > γ > α, and the order did not change with differences in the type of ethyl esters of fatty acids or oils.     

Optimization of Hull‐Less Pumpkin Seed Roasting Conditions Using Response Surface Methodology

Abstract: Response surface methodology (RSM) was applied to optimize hull‐less pumpkin seed roasting conditions before seed pressing to maximize the biochemical composition and antioxidant capacity of the virgin pumpkin oils obtained using a hydraulic press. Hull‐less pumpkin seeds were roasted for various lengths of time (30 to 70 min) at various roasting temperatures (90 to 130 °C), resulting in 9 different oil samples, while the responses were phospholipids content, total phenols content, α‐ and γ‐tocopherols, and antioxidative activity [by 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) free‐radical assay]. Mathematical models have shown that roasting conditions influenced all dependent variables at P < 0.05. The higher roasting temperatures had a significant effect (P < 0.05) on phospholipids, phenols, and α‐tocopherols contents, while longer roasting time had a significant effect (P < 0.05) on γ‐tocopherol content and antioxidant capacity, among the samples prepared under different roasting conditions. The optimum conditions for roasting the hull‐less pumpkin seeds were 120 °C for duration of 49 min, which resulted in these oil concentrations: phospholipids 0.29%, total phenols 23.06 mg/kg, α‐tocopherol 5.74 mg/100 g, γ‐tocopherol 24.41 mg/100 g, and an antioxidative activity (EC₅₀) of 27.18 mg oil/mg DPPH. Practical Application: A well‐defined roasting process is very important for the food industry to be able to produce pumpkin seed oil with desirable nutritive and chemical characteristics of this unique salad oil, which changes during the roasting. This study contributes to the knowledge of a product design process for the roasting conditions of naked pumpkin seeds based on results that have demonstrated that an increase in roasting temperature significantly increased the biochemical values and antioxidant properties of the obtained virgin oils.     

Impact of Roasting on the Chemical Composition and Oxidative Stability of Perilla Oil

Abstract: The impact of roasting was observed with regard to certain changes in the chemical components and oxidative stability of oil expelled from the roasted perilla seeds. The roasting times were established differently at each roasting temperature of 180, 200, and 220 °C. Trans fatty acids in perilla oil were detected, and the level detected increased as the roasting time increased. Moreover, the roasting of perilla seed led to an increase of 4 tocopherols, α‐, β‐, γ‐, and δ‐tocopherol, as well as phosphorus in the oil. The oxidative stability of the oils obtained after roasting increased during 60 d of storage at 60 °C. The rate of decrease of tocopherol in the oil from unroasted perilla seed was faster than that of the tocopherol in the oils from roasted perilla seeds during storage. Practical Application: The results reported in present research provide useful information that the producers of perilla oil could apply for their processing.     

Loss of tocopherols and formation of degradation compounds at frying temperatures in oils differing in degree of unsaturation and natural antioxidant content

Samples of oils of different degrees of unsaturation, namely palm olein, olive oil, high‐linoleic sunflower oil, high‐oleic sunflower oil, rapeseed oil and soybean oil, were heated at 180 °C for 2, 4, 6, 8 and 10 h in the presence or absence of their natural antioxidants. Also, tocopherol‐stripped oils were supplemented with α‐tocopherol (500 mg kg^?1), δ‐tocopherol (500 mg kg^?1) or a mixture of α‐, β‐, γ‐ and δ‐tocopherols (250 mg kg^?1 each) and heated under the same conditions. Losses of tocopherols and formation of polymeric triacylglycerols were followed. Total polar compounds were also evaluated after 10 h of heating. Results demonstrated that tocopherols were lost very rapidly, in the expected order, with α‐tocopherol being the least stable. Polymeric and polar compound formation during heating was inhibited to a variable extent, being more dependent on the natural content and type of tocopherols than on the degree of unsaturation of the oil. For example, polymeric and polar compound contents in soybean oil were significantly lower than those found in high‐linoleic sunflower oil. However, the expected influence of the degree of unsaturation was evident when oils were unprotected or possessed identical initial antioxidant contents. Finally, levels of degradation compounds after 10 h of heating were not dependent on the remaining content of antioxidants. © 2002 Society of Chemical Industry     

Variations in the phytosterol and tocopherol compositions and the oxidative stability in seed oils from four safflower (Carthamus tinctorius L) varieties grown in north‐eastern Morocco

Phytosterol and tocopherol contents and oxidative stability were evaluated from seeds oils of four safflower (Carthamus tinctorius L) varieties originating from Spain (Rancho), India (Sharda) and Morocco (Cartamar and Cartafri), which were cultivated at the experimental station in Oujda (a semi‐arid region of eastern Morocco). Total phytosterols ranged from 3640 to 4140 mg kg^?1. GC analysis allowed the identification of nine compounds, of which β‐sitosterol was the major component. Total tocopherols ranged from 461.56 to 499.68 mg kg^?1. HPLC analysis allowed the identification of three compounds, α‐tocopherol (99.45%–98.84%), β‐tocopherol (0.94%–0.5%) and γ‐tocopherol (0.21%–0.01%). Oxidative stability study showed that Sharda had the lowest induction period of 2.3 h compared with 7.18, 7 and 6.67 h for Cartafri, Rancho and Cartamar, respectively. Likewise, we established a positive correlation between the oxidative stability and γ‐tocopherol; however, this difference was not significant.     

Microwave Energy Effects on Quality of Some Seed Oils

Effects of microwave heating were investigated on chemical properties of seed oils in relation to tocopherol contents. For assessing quality of oils (linseed, soybean, corn, olive, and palm) during microwave treatments, peroxide, thiobarbituric acid, carbonyl and anisidine values were determined. As the amount of polyunsaturated fatty acids in oils increased the index for the chemical properties increased. After 8-10 min heating the amount of tocopherols decreased substantially in linseed, olive and palm oils, whereas that in corn and soybean oils was still ca. 90%. Thus, the reduction in tocopherols in oils is not necessarily in agreement with chemical properties of the oils.     

Enhancing oxidative stability of frying oils by low-frequency radio wave treatment

Radio wave treatment (approximately 50 kHz frequency) on the oxidative stability was evaluated in corn oil at 180 °C and chicken frying oil for 150 cycles. Radio wave treatment decreased moisture content and critical micelle concentration of lecithin in corn oil. Moisture content in frying oil remained higher when radio wave was treated for the first 30 frying cycles. Radio wave treatment prevented lipid oxidation significantly in corn oil heated at 180 °C when moisture was not added (P < 0.05). p-Anisidine value and total polar material in chicken frying oils treated with radio waves were significantly lower than those of frying oils without radio wave treatment (P < 0.05). Radio wave treatment enhanced the stability of tocopherols in corn oil heated at 180 °C in the absence of moisture, while the reverse result was observed with moisture addition. Overall, radio wave treatment can be a useful tool to enhance the oxidative stability of frying oils by modifying their moisture content and tocopherol stability.     

Chemical Properties and Oxidative Stability of Perilla Oils Obtained From Roasted Perilla Seeds As Affected by Extraction Methods

Abstract: The chemical properties and oxidative stability of perilla oils obtained from roasted perilla seeds as affected by extraction methods (supercritical carbon dioxide [SC‐CO₂], mechanical press, and solvent extraction) were studied. The SC‐CO₂ extraction at 420 bar and 50 °C and hexane extraction showed significantly higher oil yield than mechanical press extraction (P < 0.05). The fatty acid compositions in the oils were virtually identical regardless of the extraction methods. The contents of tocopherol, sterol, policosanol, and phosphorus in the perilla oils greatly varied with the extraction methods. The SC‐CO₂‐extracted perilla oils contained significantly higher contents of tocopherols, sterols, and policosanols than the mechanical press‐extracted and hexane‐extracted oils (P < 0.05). The SC‐CO₂‐extracted oil showed the greatly lower oxidative stability than press‐extracted and hexane‐extracted oils during the storage in the oven under dark at 60 °C. However, the photooxidative stabilities of the oils were not considerably different with extraction methods.     

Enhancing Antioxidant Activity of Sesamol at Frying Temperature by Addition of Additives through Reducing Volatility*

Additives were evaluated to investigate their effects on volatility of sesamol at frying temperature with the hypothesis that the interaction between an additive and sesamol would reduce sesamol volatility. Twenty‐two additive : sesamol combinations were examined by thermogravimetric analysis (TGA) under nitrogen in neat form and in soybean oil. The results indicate that these additives could bind to or interact with sesamol and consequently reduced its volatility. ¹H NMR study provided evidence for hydrogen bonding between sesamol and a hydroxyl group, an amino group, and ether groups. Subsequent heating tests were conducted to investigate the effect of the reduced volatility of sesamol on antioxidant activity in soybean oil at 180 °C. Oxidation of soybean oil was monitored with gel permeation chromatography for formation of polymerized triacylglycerols and with ¹H NMR for loss of olefinic and bisallylic protons. Sesamol retained in soybean oil during the heating process was determined by high‐performance liquid chromatography. A strong correlation between the retained sesamol and the antioxidant activity was observed. The mixture of 830 ppm sesamol and mono‐/diglycerides, polysorbate 20 or l ‐carnosine showed much improved antioxidant activity compared to sesamol itself and slightly better antioxidant activity than 200 ppm tert‐butylhydroquinone. It is believed that this method can also be used for many other antioxidants for which volatility is a problem.     

Cholesterol Oxidation in Egg Yolk Powder During Storage and Heating as Affected by Dietary Oils and Tocopherol

The effects of feeding flax, sunflower, palm and fish oils, with and without tocopherols, to laying hens was investigated on oxidative stability of cholesterol in egg yolk powders. Storage of spray-dried egg yolk powders at room temperature resulted in loss (p <0.05) of tocopherols. The initial levels of spray-dried yolk cholesterol oxides were 7–10 ppm and increased (p <0.05) with storage. The cholesterol oxide contents in the egg yolk powders were: fish > flax > sunflower > palm. Heating egg yolk powder increased (p <0.05) the amounts of total cholesterol oxides. Diets with tocopherol supplementation resulted in a decrease (p <0.05) of cholesterol oxides during storage and heating.     

Vitamin E and Oxidative Stability of Soya Bean Oil Prepared with Beans at Various Moisture Contents Roasted in a Microwave Oven

Whole soya beans ( Glycine max ) at various moistures (96, 382 and 519 g kg⁻¹) were roasted by exposure to microwaves at a frequency of 2450 MHz and the effects on the tocopherols of soya beans were studied in rela-tion to chemical changes in the oils. The amounts of α-, β-, γ- and δ-tocopherols in the soya beans before microwave treatments ranged from 62 to 187, 43 to 89, 673 to 757 and 542 to 593 mg kg⁻¹ oil, respectively. Increasing moisture contents by soaking prevented, not only the reduction of tocopherols but also, the oxidative deterioration of soya bean oils during microwave roasting. The amounts of tocopherols still remained >80% of the original level in soaked soya bean oils after 20 min of roasting, and microwave roasting after soaking caused no significant differences ( P> 0·05, with few exceptions) in the chemical changes of the oils in comparison with those before soaking. These results implied that microwave roasting after soaking would be effective in making full-fat soya flour with high vitamin E without a burnt odour and browning from raw beans.     

Synergism of phosphatidylcholine on the antioxidant properties of α‐tocopherol in corn oils under different relative humidity

The effects of phosphatidylcholine on the antioxidant properties of α‐tocopherol (84 ppm) were determined in stripped corn oil with various moisture contents at 60 °C. The degree of oxidation in the oils was determined by analysing headspace oxygen content and conjugated dienoic acids (CDA). Generally, phosphatidylcholine acted as an antioxidant in stripped corn oils, whereas it accelerated the rate of lipid oxidation in nonstripped corn oils. As the relative humidity and moisture content increased, the antioxidant properties of phosphatidylcholine increased significantly (P < 0.05). Strong synergistic antioxidant effects were observed in samples containing both phosphatidylcholine and α‐tocopherol compared to samples with only phosphatidylcholine or α‐tocopherol. Oils containing phosphatidylcholine or α‐tocopherol under different moisture contents had different oxidative stabilities.     

Microwave roasting effects on the composition of tocopherols and acyl lipids within each structural part and section of a soya bean

Whole soya beans (Glycine max) were exposed to microwave roasting for 6, 12 or 20 min at a frequency of 2450 MHz. The seed coat, axis and sections of cotyledons separated from the three cultivars were analysed not only by high‐performance liquid chromatography for tocopherols but also by gas chromatography for fatty acids before and after microwave roasting. The tocopherols were predominantly detected in the axis, followed by the cotyledons and the seed coat, and the distribution patterns of tocopherol homologues for Mikawajima differed significantly (P < 0.05) from those for Okuhara or Tsurunoko. As many as 40% of the individual tocopherols originally present in the coat were lost at 12 min of roasting, whereas they were still retained to the extent of >80% in the cotyledons and the axis after 20 min of roasting. Significant decreases (P < 0.05) were observed not only in the amounts of triacylglycerols and phospholipids but also in the percentages of polyunsaturated fatty acids in the coat compared with those of the cotyledons or the axis. These results imply that microwave energy effected more significant differences (P < 0.05) in the distribution of tocopherols and acyl lipids in the coat than those of the cotyledons or the axis. © 1999 Society of Chemical Industry     

Effects of α-, γ-, and δ-Tocopherols on Oxidative Stability of Soybean Oil

The effectts of 0, 100, 250, 500 and 1000 ppm of α-, γ-, or δ-tocopherol on oxidative stability of purified soybean oil in the dark at 55°C were studied. We measured peroxide value and headspace oxygen consumption in the samples. Purified soybean oil was prepared by liquid column chromatography. Tocopherols acted as antioxidants or prooxidants depending on their concentration. Optimum concentrations of α -, γ -, and δ– tocopherols to increase oxidative stability was 100, 250 and 500 ppm, respectively. The tocopherols had significant prooxidant effect (P < 0.05) at higher concentrations above this.     

Additive antioxidant capacity of vitamin C and tocopherols in combination

Vitamin C (ascorbic acid) and vitamin E (tocopherols) are water-soluble and fat-soluble essential nutrients, respectively, present ubiquitously in cellular membranes and plasma through dietary intake of fruits and vegetables. These vitamins act as antioxidants by virtue of their free hydroxyl groups. To quantitatively assess the vitamin C-tocopherol interaction in generating total antioxidant capacity, various binary mixtures of vitamin C and tocopherols (α, β, δ, and γ) were titrated with ABTS radicals. In this assay, the antioxidant capacity of tocopherols increased as follows: β-tocopherol<α-tocopherol<δ-tocopherol<γ-tocopherol. As the total concentration of mixed antioxidants vitamin C and tocopherols increased, the total antioxidant capacity increased linearly. The sum of the individual antioxidant capacities of vitamin C and tocopherol in the assay was very close to the total antioxidant capacity of the corresponding combination of two compounds. Using this assay system, and in the concentration ranges applied, vitamin C and tocopherols in combination displayed additive interaction.     

Influence of fruit ripening process on the natural antioxidant content of Hojiblanca virgin olive oils

The effect of fruit ripeness on the antioxidant content of `Hojiblanca' virgin olive oils was studied. Seasonal changes were monitored at bi-weekly intervals for three consecutive crop years. Phenolic content, tocopherol composition, bitterness index, carotenoid and chlorophyllic pigments and oxidative stability were analysed. In general, the antioxidants and the related parameters decreased as olive fruit ripened. The phenolics and bitterness, closely related parameters, did not present significant differences among years. Although in general, the tocopherols decreased during olive ripening γ-tocopherol increased. Differences between crop years were found only for total tocopherols and α-tocopherol, which showed higher content in low rainfall year oils. The pigment content decreased during ripening, chlorophyll changing faster. For low rainfall years, the level of pigments was higher, reaching significant differences between yields. Significant differences among years were found for oil oxidative stability; higher values were obtained for drought years. A highly significant prediction model for oxidative stability has been obtained.     

The relationship of antioxidant components and antioxidant activity of sesame seed oil

Although sesame seed oil contains high levels of unsaturated fatty acids and even a small amount of free fatty acids in its unrefined flavored form, it shows markedly greater stability than other dietary vegetable oils. The good stability of sesame seed oil against autoxidation has been ascribed not only to its inherent lignans and tocopherols but also to browning reaction products generated when sesame seeds are roasted. Also, there is a strong synergistic effect among these components. The lignans in sesame seed oil can be categorized into two types, i.e. inherent lignans (sesamin, sesamolin) and lignans mainly formed during the oil production process (sesamol, sesamolinol, etc.). The most abundant tocopherol in sesame seed oil is γ‐tocopherol. This article reviews the antioxidant activities of lignans and tocopherols as well as the browning reaction and its products in sesame seed and/or its oil. It is concluded that the composition and structure of browning reaction products and their impacts on sesame ingredients need to be further studied to better explain the remaining mysteries of sesame oil. © 2014 Society of Chemical Industry