Effects of Sesame Oil Addition to Soybean Oil During Frying on the Lipid Oxidative Stability and Antioxidants Contents of the Fried Products During Storage in the Dark

ABSTRACT: Effects of sesame oil addition to soybean oil during frying on the lipid oxidative stability and antioxidants contents of fried products during storage in the dark were studied. Flour dough pieces (2 cm × 2 cm × 0.1 cm) were fried at 160 °C for 1 min in sesame oil-added soybean oil. Concentrations of sesame oil in the frying oil were 0%, 10%, and 20% by volume. Fried products were put into a glass bottle, and the bottles were tightly sealed and stored at 60 °C in the dark for 18 d. Lipid oxidation of fried products was determined by fatty acid composition changes and conjugated dienoic acid (CDA) and p -anisidine (PA) values. Tocopherols and lignan compounds in the fried products were determined by high-performance liquid chromatography. Relative content of linolenic acid decreased, and CDA and PA values increased during storage of the fried products in the dark. Fatty acid composition change and CDA and PA values during storage were lower in the products fried in sesame oil-added soybean oil than in the products fried in soybean oil without sesame oil. The results clearly showed that addition of roasted sesame oil to soybean oil at 10% and 20% during frying decreased the lipid oxidation of fried products during storage in the dark for 18 d by extension of induction period and decrease in decomposition of oxidized lipids. Fried products contained 134 to 267 ppm tocopherols and 0 to 148 ppm lignans before storage; however, their contents decreased during storage in the dark. Lignan compounds were more stable than tocopherols, and the rate of tocopherols degradation was lower in the products fried in sesame oil-added soybean oil than in the products fried in soybean oil without sesame oil, which could be because of protection of tocopherols from degradation by lignan compounds.     

Stability of tocopherols and lutein in oil extracted from roasted or unroasted mustard seeds during the oil oxidation in the dark

This study compared stabilities of tocopherols and lutein in oil extracted from roasted mustard seeds (RMSO) with those in oil from unroasted seeds (URMSO) during oil oxidation at 60°C in the dark for 12 days. Tocopherols and lutein were determined by high performance liquid chromatography, and the oil oxidation was monitored with conjugated dienoic acid (CDA) content and fatty acid composition by gas chromatography. The rate of CDA increase was lower in RMSO (0.038%/day) than in URMSO (0.047%/day) during 12-day oxidation in the dark, with little change in fatty acid composition in both oils. Tocopherols and lutein were more abundant in RMSO, initially 465.38 and 100.55 μg/g, respectively, than in URMSO, and their stability was higher in RMSO (−4.63 and −5.94%/day of degradation in tocopherols and lutein, respectively) than in URMSO during 12-day oxidation of oil, both of which contributed to higher autoxidative stability of RMSO than URMSO.     

Chemistry and reactions of reactive oxygen species in foods

Reactive oxygen species (ROS) are formed enzymatically, chemically, photochemically, and by irradiation of food. They are also formed by the decomposition and the inter-reactions of ROS. Hydroxy radical is the most reactive ROS, followed by singlet oxygen. Reactions of ROS with food components produce undesirable volatile compounds and carcinogens, destroy essential nutrients, and change the functionalities of proteins, lipids, and carbohydrates. Lipid oxidation by ROS produces low molecular volatile aldehydes, alcohols, and hydrocarbons. ROS causes crosslink or cleavage of proteins and produces low molecular carbonyls from carbohydrates. Vitamins are easily oxidized by ROS, especially singlet oxygen. The singlet oxygen reaction rate was the highest in ss-carotene, followed by tocopherol, riboflavin, vitamin D, and ascorbic acid.     

Effects of catechin and α-tocopherol addition on the autoxidative stability of diacylglycerol oil derived from an olive oil and perilla oil mixture

The effects of tea catechin and α-tocopherol addition (1 mM) on the oxidative stability of oleic and linolenic acid-rich diacylglycerol (DAG) oil derived from an extra virgin olive oil and perilla oil mixture (6:4, w/w) were evaluated. Oil was oxidized at 50°C for 10 days, after which oxidation was evaluated based on headspace oxygen consumption and peroxide values (POV). The polyphenol and tocopherol contents were also monitored. Addition of catechin did not affect the oxygen consumption or POV of DAG oil, whereas α-tocopherol acted as a prooxidant. Addition of antioxidants had no significant (p>0.05) effect on the fatty acid composition of the oil. Degradation of γ-tocopherol during oil oxidation was inhibited by addition of α-tocopherol, and addition of antioxidants inhibited polyphenol degradation. The autoxidative stability of DAG oil can be improved using polar rather than non-polar antioxidants.     

Effects of light and lipids on chlorophyll degradation

Stability of chlorophylls was studied in a system of paraffin oil with added oleic acid or triolein under 1,700 lx and in the dark. Chlorophyll contents were determined using HPLC. Sample oxidation was evaluated using the headspace oxygen content based on GC and the peroxide value. The chlorophyll content decreased with time and was higher and decreased faster under light than in the dark. Singlet oxygen was involved in chlorophyll degradation under light. Chlorophyll degradation was lower and slower in samples with added lipids than in samples without lipids. Protection of chlorophyll from photodegradation was greater using triolein than using oleic acid. Oxidation was slightly higher in samples with added lipids than in samples without lipids, however, there was no significant (p>0.05) difference between samples with added oleic acid or triolein. Decreased chlorophyll degradation under light by lipids is due to competition between lipids and chlorophyll for singlet oxygen.     

Effects of gardenia seed,green tea,and cactus pear in rice batter on the chemical quality of lotus root <Emphasis Type="Italic">bugak</Emphasis> and frying oil

This study investigated the effects of the addition of gardenia seed, green tea, or cactus pear (Opuntia ficus-indica) to rice batter at 10% on the lipid oxidation, pigments, antioxidants, and antioxidant activity of lotus root bugak and frying oil. Lipid oxidation was evaluated based on the conjugated dienoic acid and p-anisidine values. Lipid oxidation and tocopherol degradation were significantly reduced in the gardenia seed-added bugak and frying oil, whereas the cactus pear-added bugak and frying oil showed an increase. The addition of green tea had no significant effects on the lipid oxidation of bugak and frying oil. The in vitro antioxidant activity of lotus root bugak significantly increased with the addition of gardenia seed, green tea, or cactus pear. The results suggested that green tea and gardenia seed could improve the health and food functionality of antioxidation for lotus root bugak, respectively.     

Temperature dependence of the autoxidation and antioxidants of soybean, sunflower, and olive oil

Effects of temperature on the autoxidation and antioxidants changes of soybean, sunflower, and olive oils were studied. The oils were oxidized in the dark at 25, 40, 60, and 80 °C. The oil oxidation was determined by peroxide (POV) and p-anisidine values (PAV). Polyphenols and tocopherols in the oils were also monitored. The oxidation of oils increased with the oxidation time and temperature. Induction period decreased with the oxidation temperature; 87 and 3.6 days at 25 and 60 °C, respectively, for sunflower oil. The activation energies for the autoxidation of soybean, sunflower, and olive oils were 17.6, 19.0, and 12.5 kcal/mol, respectively. Olive oil contained polyphenols at 180.8 ppm, and tocopherols were present at 687, 290, and 104 ppm in soybean, sunflower, and olive oils, respectively. Antioxidants were degraded during the oil autoxidation and the degradation rates increased with the oxidation temperature of oils; for tocopherols, 2.1 × 10⁻³ and 8.9 × 10⁻²%/day at 25 and 60 °C, respectively, in soybean oil.     

Effects of Water Activity on the Lipid Oxidation and Antioxidants of Dried Laver (Porphyra) During Storage in the Dark

Lipid oxidation and antioxidant degradation in dried laver (Porphyra) were determined during storage at water activities (A_w) of 0.11, 0.30, 0.51, 0.75, or 0.89 in the dark at 40 °C for 15 d. Lipid oxidation was evaluated by measuring peroxide value (POV) and conjugated dienoic acid (CDA) contents, and fatty acid composition was analyzed by gas chromatography. Contents of polyphenols, tocopherols, and porphyran were determined by spectrophotometry, HPLC, and gravimetry, respectively. The POV and CDA contents of the dried laver lipids increased during storage as A_w increased from 0.11 to 0.30, 0.51, 0.75, and 0.89, whereas the relative content of eicosapentaenoic acid was decreased; however, the contents of polyphenols, α‐tocopherol, and porphyran in dried laver showed the reverse phenomena. Lipid oxidation and antioxidant degradation in dried laver sharply increased at an A_w of 0.51. Polyphenols, α‐tocopherol, and porphyran contributed to reduction of lipid oxidation in dried laver. The degree of lipid oxidation of dried laver was more dependent on the concentration of α‐tocopherol than that of either polyphenols or porphyran during storage in the dark. The results strongly suggest that the quality of dried laver can be improved by preserving tocopherols as much as possible while decreasing A_w during storage.