Sachiko Takagi

Effects of seed roasting temperature and time on the quality characteristics of sesame (Sesamum indicum) oil

The quality characteristics and composition of sesame oils prepared at different roasting temperatures (160–250°C) from sesame seeds using a domestic electric oven were evaluated as compared to an unroasted oil sample: only minor increases (P<0·05) in characteristics, such as peroxide value, carbonyl value, anisidine value and thiobarbituric acid reactive substances, of sesame oils occurred in relation to increasing roasting temperature and time between 160 and 200°C, but colour units of oils increased markedly over a 220°C roasting temperature. Significant decreases (P<0·05) were observed in the amounts of triacylglycerols and phospholipids in the oils prepared using a 250°C roasting temperature. The amounts of γ-tocopherol and sesamin still remained over 80 and 90%, respectively, of the original levels after roasting at 250°C. In the oil prepared using a 250°C roasting temperature, sesamol was detected at 3370 mg per kg oil, but sesamolin was almost depleted after 25 min of roasting. Burning and bitter tastes were found in the oils prepared at roasting temperatures over 220°C. The results suggested that a high-quality product would be obtained by roasting for 25 min at 160 or 180°C, 15 min at 200°C and 5 min at 220°C when compared with the other samples.

Antioxidative effects of sesamol and tocopherols at various concentrations in oils during microwave heating

The effectiveness of sesamol and tocopherols or their mixtures at different concentrations (50 to 800 ppm) on the oxidative stability of tocopherol-stripped oils was studied under microwave heating conditions. Microwave heating accelerated the oxidation of the purified substrate oils. The oxidative deterioration of the oils was significantly (P<0.05) retarded during microwave heating by the addition of sesamol or tocopherols, and also mixtures of these antioxidants. A combination of sesamol and γ-tocopherol was more efficient than that of sesamol and the other tocopherol homologues in inhibiting hydroperoxide formation in the oils. Useful levels of these antioxidants were 400 ppm for tocopherols and 50–400 ppm for sesamol. In general, the residual amount of sesamol in the oils during microwave heating was significantly greater (P<0.05) than that of tocopherols. Very effective combinations of tocopherols and sesamol as antioxidants for the purified oils were 200 or 400 ppm of γ-tocopherol and 50, 200 or 400 ppm of sesamol, respectively. © 1999 Society of Chemical Industry

Microwave heating influences on fatty acid distributions of triacylglycerols and phospholipids in hypocotyl of soybeans(glycine max L.)

Soybeans were exposed to microwave heating for 6, 12 or 20 min at a frequency of 2450 MHz. The hypocotyls were then separated from the other tissues, and the lipid components and the positional distribution of fatty acids in triacylglycerols (TAG) and phospholipids (PL) were investigated. Major lipid components were TAG and PL, while steryl esters (SE), free fatty acids (FFA), and 1,3- and 1,2-diacylglycerols (DAG) were minor ones. Following microwave heating, a significant increase (p<0.05) was observed in FFA and in both forms of DAG (primarily 1,3-DAG). The greatest rate of PL losses (p<0.05) was observed in phosphatidylethanolamine (PE), followed by phosphatidylcholine (PC) and phosphatidylinositol (PI). Significant differences (p<0.05) in fatty acid distributions occurred (with few exceptions) when soybeans were microwaved for 12 min or more. Nevertheless, the principal characteristics for the positional distribution of fatty acids still remained after 20 min of microwave heating.

Molecular species of triacylglycerols in the seed coats of soybeans (glycine max L.) following microwave treatment

Soybeans (glycine max) were exposed to microwaves for 6 or 12 min at a frequency of 2450 MHz. The seed coats were then stripped from the soybeans and roasted in a microwave oven. Molecular species and fatty acid distributions of triacylglycerols (TAG), isolated from total lipids in the seed coats were analysed by a combination of argentation thin-layer chromatography (TLC) and gas chromatography (GC). Based on their different degrees of unsaturation and total chain-length of fatty acid groups, 15 molecular species of TAG were still detectable in the seed coats after the roasting treatment. However, roasting caused a significant decrease (P<0.05), not only in molecular species containing more than four double bonds, but also in the amounts of diene and triene species present in a TAG. These results indicate that microwaves could (P<0.05) affect TAG in the seed coats more signficantly than those in the other structural parts of soybeans.

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  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

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 relation 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.

Roasting influences on molecular species of triacylglycerols in sesame seeds (Sesamum indicum)

Sesame seeds were roasted at different temperatures (180–220 °C) using a domestic electric oven. Molecular species and fatty acid distributions of triacylglycerols (TAGs) isolated from total lipids in the sesame seeds were analysed by a combination of argentation thin-layer chromatography (TLC) and gas–liquid chromatography. A modified argentation TLC procedure, developed to optimise the separation of the complex mixture of total TAGs, provided 11 different groups of TAGs, based on both the degree of unsaturation and the total length of fatty acid groups. Fatty acid methyl ester analysis was performed to determine the composition of each zone. Eleven molecular species of TAGs were still detected in the sesame seeds following roasting treatment. Dilinoleolein (33.7–35.8%), palmitoleolinolein (20.3–22.8%), dioleolinolein (15.0–15.4%) and trilinolein (8.8–10.7%) were the main components during roasting. However, roasting for 10 min at 220 °C caused a significant decrease (P < 0.05) not only in molecular species containing more than four double bonds, but also in the amount of diene and triene species present in TAGs (with a few exceptions). These results suggest that no significant changes in molecular species or fatty acid distribution of TAGs would occur within 25 min of roasting at 180 °C, ensuring that a good-quality product would be attained. © 2000 Society of Chemical Industry