Oxidation of corn oil during frying of soy-flour-added flour dough

ABSTRACT:  Oxidation of corn oil during frying of soy–flour-added dough was studied. Flour dough containing soy flour at 0%, 10%, 20%, and 30% was fried in corn oil at 180 °C for 2.5 min, and a total of 60 fryings were performed every 30 min. The oxidation of oil was determined by contents of free fatty acids (FFA), conjugated dienoic acids (CDA), polar compounds, and p -anisidine values (PAV). Tocopherols and phospholipids (PLs) in the oil were determined by HPLC. Tocopherols were present in corn oil at 1000 ppm before frying and increased after the first frying of dough containing soy flour due to tocopherol transfer from soy–flour-added dough to the oil during frying. However, as the oil repeated frying, tocopherol contents decreased and its degradation rate was higher in the oil that fried soy–flour-added dough than in the oil that fried the dough without soy flour. PL was not detected in corn oil before and after frying. As the oil repeated frying, FFA, CDA, and polar compounds contents, and PAV of frying oil increased due to the oil oxidation. The values were higher in the oil which fried soy–flour-added dough than in the oil fried the dough without soy flour, indicating the acceleration of oil oxidation by soy flour added to dough. Increase in the oil oxidation by soy flour added to the dough was highly correlated with fast decomposition of tocopherol in the oil.     

Volatile compounds and oxidative stability of Pinus halepensis Mill. seed oil under heating conditions

Heating conditions of Pinus halepensis seed oil were monitored to evaluate the effect of thermo‐oxidation processes on the bioactive compounds contained in the samples. The following parameters were monitored: ultra violet absorption at 232 and 270 nm, fatty acid composition, oxidative stability, antiradical activity and aromatic profiles. Under thermo‐oxidation process, trans fatty acids (TFA) increased and conjugated linoleic acid isomers appeared. The antiradical activity significantly decreased from 73.3% to 52.5% after 120 min of heating. Oxidative stability decreased (r = ?0.70). The volatile profile was heavily influenced by heating with the formation of new volatile compounds, such as the two isomers (E,Z)‐2,4‐decadienal and (E,E)‐2,4‐decadienal. α‐pinene, and the main terpene compound was very vulnerable to heating conditions. Despite its peculiar pleasant aroma and nutritional value, the P. halepensis seed oil should not be used for cooking. Indeed, under frying conditions, its antioxidant properties and oxidative stability are lost and potential toxic compounds, such as TFA and unsaturated aldehydes, are formed.     

Effect of flavonoids on the oxidative stability of corn oil during deep frying

To study the effect of flavonoids on the stability of frying oil, refined corn oil was analysed periodically for its peroxide value (PV), p‐anisidine value (p‐AV) and iodine value (IV) after its use for deep‐frying of French fries at 180 °C for varying periods of time, namely 30, 60 and 90 min. PV and p‐AV values increased with respect to time while a decrease in IV was observed with increase in time (P < 0.001). Deep‐frying of French fries in corn oil was then carried out in the presence of flavonoids, viz. pelargonidin, cyanidin, quercetin, myrecetin and gallic acid as antioxidants. All antioxidants effectively reduced the oxidation rate in the oil, as detected by decrease in PVs and p‐AVs and relatively low reduction rate in IVs (P < 0.001). The order of antioxidative activity was gallic acid > quercetin > myrecetin > cyanidin > pelargonidin.     

Use crude olive leaf juice as a natural antioxidant for the stability of sunflower oil during heating

Olive leaves (Kronakii cultivar) were obtained from the annual pruning of olive trees and pressed to obtain a crude juice. Aliquots from the concentrated crude olive leaf juice, representing 400, 800, 1600 and 2400 ppm as polyphenols, were added to sunflower oil. Samples of sunflower oil mixed with olive leaf juice were heated intermittently at 180 ± 5 °C for 5 h day^?1 and the heating process was repeated for five consecutive days. A control experiment was performed where butylated hydroxyl toluene (BHT) at 200 ppm was added to sunflower oil prior to intermittent heating in order to compare the antioxidant efficiency between the natural polyphenolics of olive leaf juice and synthetic antioxidant BHT. Some physical and chemical constants for the unheated and heated sunflower oil were determined. The data indicate that the addition of olive leaf juice to sunflower oil heated at 180 °C induced remarkable antioxidant activity and at 800 ppm level was superior to that of BHT in increasing sunflower oil stability.     

鼠尾草酸对煎炸条件下玉米油品质裂变的影响

采用玉米油为原料,模拟煎炸条件,研究鼠尾草酸对油脂的抗氧化作用。实验采用可见分光光度法研究鼠尾草酸的抗氧化活性,模拟高温煎炸条件研究玉米油的品质变化。结果表明:当鼠尾草酸添加量为0.5 mg/mL时,抗氧化活性最优。通过测定高温煎炸条件下玉米油酸价、过氧化值、丙二醛值,反式脂肪酸含量等表明,随着加热温度的升高,或者煎炸时间增加,各项指标上升,氧化速度加快,鼠尾草酸的加入能有效减缓油脂品质裂变。     

不同储存条件下核桃油的氧化稳定性研究

为了研究合适的核桃油储存方式,以温度、光照、氧气、水分四个因素为自变量,酸价、过氧化值为指标研究氧化规律。Rancimat法和60℃烘箱加速氧化法预测货架期,以常温储存核桃油为对照组,比较两种方法的可靠性。结果表明:效果最好为冷藏组,储存超过60 d,最短为敞口组和摇晃组,不足14 d,添加0. 1%～0.3%水分组,21 d开始酸败,避光组储存期为49 d。Rancimat法预测货架期为212 d,烘箱加速法预测为48～80 d。常温储存49 d酸败,烘箱加速法预测货架期更可靠。建议核桃油低温储存,同时可避光存放,尽量选用与空气接触面积小的储油容器,并减少油的重复使用。     

磷脂含量对煎炸油烟点、耐寒性、氧化稳定性 和煎炸稳定性的影响

通过添加大豆卵磷脂,使大豆油、菜籽油和棕榈油中磷脂含量分别为本底值、10、20、30、40、50 mg/kg,测定不同磷脂含量的3种煎炸油的烟点、耐寒性、氧化诱导时间,同时检测3种煎炸油在170℃下煎炸不同食材过程中的感官品质、酸价、过氧化值和极性组分含量的变化,以评价其煎炸稳定性。结果表明:随着磷脂含量的增加,大豆油、菜籽油、棕榈油烟点呈下降趋势,其中棕榈油烟点下降受磷脂影响最大;耐寒性随着磷脂含量增加整体呈下降趋势;氧化诱导时间随磷脂含量的增加呈波动变化趋势;在本试验范围内,磷脂含量对煎炸油煎炸稳定性影响的规律尚不明显。     

储存条件对玉米胚及粕和毛油中呕吐毒素含量的影响

将不同水分含量(5.03%、9.07%、11.82%、17.97%)的玉米胚在25℃、相对湿度45%条件下储存30 d,将9.07%水分含量的玉米胚在25℃,不同相对湿度(75%、85%、95%)条件下储存30d,取不同储存时间的玉米胚样品检测其水分、粗脂肪及呕吐毒素(DON)含量,并检测玉米胚提取油脂后所得玉米粕和毛油中DON含量,分析储存条件对玉米胚及粕和毛油中DON含量的影响。结果表明:储存期间,低水分含量(5.03%和9.07%)玉米胚霉变较轻,粗脂肪含量变化较小;高水分含量(11.82%和17.97%)玉米胚霉变程度逐渐加深,粗脂肪含量分别下降1.21、2.74个百分点;不同水分含量玉米胚DON含量为160.9~489.5μg/kg,其粕中DON含量为200.2~340.6μg/kg;相对湿度为75%时,玉米胚品质无明显变化;相对湿度为85%和95%时,玉米胚品质劣变显著,其粗脂肪含量分别降低1.93、3.87个百分点,玉米胚DON含量148.3~484.7μg/kg,其粕中DON含量270.6~439.6μg/kg;不同储存条件下得到玉米油中均未检出DON;玉米胚及粕中DON含量均低于国标1 000μg/kg的限量。     

元宝枫籽油在不同储藏条件下的氧化稳定性及货架期预测

以元宝枫籽油为原料,过氧化值 (POV)、酸值 (AV) 及TBA值为氧化稳定性指标,研究温度、光照、空气、包装瓶材质和包装瓶颜色对元宝枫籽油氧化稳定性的影响,进一步建立氧化动力学模型,预测元宝枫籽油的货架期。结果表明：元宝枫籽油在低温、避光、无氧、不锈钢或陶瓷材质、蓝色或绿色玻璃瓶等储藏条件下,POV、AV、TBA值均增长缓慢,氧化稳定性好;元宝枫籽油的氧化过程遵循零级反应动力学方程,经验证POV模型预测值与实测值较为接近;元宝枫籽油在20、25 ℃密封避光储藏条件下的货架期预测值分别为516、335 d。     

Effect of black tea, garlic and onion on corn oil stability and fatty acid composition under accelerated oxidation

Fresh black tea, garlic bulbs and onion skin were macerated in refined corn oil to evaluate their antioxidant properties and the effect of heat on oil stability and fatty acid composition in accelerated oxidation experiments at 55 ° and 140 °C. At the lowest temperature control and onion treatments showed an induction time of 3 days with maximum peroxide values of 62 and 45 meq kg^?1, respectively. Addition of black tea and garlic increased oil stability with peroxide values of 5 meq kg^?1, without appreciable changes in the fatty acid composition. Heating at 140 °C for 48 h produced an accelerated deterioration of corn oil in all treatments. A reduction of polyunsaturated fatty acids of about 40% was observed, with high concentrations of non‐eluted materials which contained thermo‐oxidized substances. It was found that natural extract of black tea and garlic were effective to preserve corn oil under accelerated oxidation at 55 °C which simulates oil behaviour during storage, but cannot reduce the rate of oxidation at frying temperatures.     

Studies of reaction variables for lipase-catalyzed production of alpha-linolenic acid enriched structured lipid and oxidative stability with antioxidants

Alpha-linolenic acid (ALA) enriched structured lipid (SL) was produced by lipase-catalyzed interesterification from perilla oil (PO) and corn oil (CO). The effects of different reaction conditions (substrate molar ratio [PO/CO 1:1 to 1:3], reaction time [0 to 24 h], and reaction temperature [55 to 65 °C]) were studied. Lipozyme RM IM from Rhizomucor miehei was used as biocatalyst. We obtained 32.39% of ALA in SL obtained under the optimized conditions (molar ratio-1:1 [PO:CO], temperature-60 °C, reaction time-15 h). In SL, the major triacylglycerol (TAG) species (linolenoyl-linolenoyl-linolenoyl glycerol [LnLnLn], linolenoyl-linolenoyl-linoleoyl glycerol [LnLnL]) mainly from PO and linoleoyl-linoleoyl-oleoyl glycerol (LLO), linoleoyl-oleoyl-oleoyl glycerol (LOO), palmitoyl-linoleoyl-oleoyl glycerol (PLO) from CO decreased while linolenoyl-linolenoyl-oleoyl glycerol (LnLnO) (18.41%), trilinolein (LLL) (9.06%), LLO (16.66%), palmitoyl-linoleoyl-linoleoyl glycerol (PLL) (9.69%) were increased compared to that of physical blend. Total tocopherol content (28.01 mg/100 g), saponification value (SV) (192.2), and iodine value (IV) (161.9) were obtained. Furthermore, oxidative stability of the SL was also investigated by addition of 3 different antioxidants (each 200 ppm of rosemary extract [SL-ROS], BHT [SL-BHT], catechin [SL-CAT]) was added into SL and stored in 60 °C oven for 30 d. 2-Thiobabituric acid-reactive substances (TBARS) value was 0.16 mg/kg in SL-CAT and 0.18 mg/kg in SL-ROS as compared with 0.22 mg/kg in control (SL) after oxidation. The lowest peroxide value (POV, 200.9 meq/kg) and longest induction time (29.88 h) was also observed in SL-CAT.     

Composition and radical‐scavenging activity of Thymus glabrescens Willd. (Lamiaceae) essential oil

BACKGROUND: Knowledge about the chemical and therapeutic properties of Thymus glabrescens Willd. (Lamiaceae) is scarce and inconsistent. Therefore the main objectives of this study were to determine the yield and chemical composition of essential oils from wild‐growing T. glabrescens populations, to assess their radical scavenging activity and to correlate the results with published data in order to deduce which components are responsible for the activity. RESULTS: The plant material yielded between 4.0 and 8.0 mL kg^?1 of essential oil. All samples contained considerable but variable concentrations of thymol (22.3–55.1%), depending on the source. Radical‐scavenging activities of the oils were estimated by 1,1‐diphenyl‐2‐picrylhydrazyl free radical (DPPH) assay against butylated hydroxytoluene (BHT) and thymol as positive controls. The observed activities (IC₅₀ values ranged from 94 to 230 µg mL^?1) were strongly influenced by thymol concentration, as verified by rapid screening for DPPH radical‐scavenging activity on thin layer chromatography (TLC) plates and regression analysis. CONCLUSION: These results represent the first report on the free radical‐scavenging activity of T. glabrescens essential oil and one of the first comprehensive reports on its composition. Thymus glabrescens could be used in the food industry for seasoning purposes or for preserving processed foods from oxidative degradation. Copyright © 2008 Society of Chemical Industry     

基于1 H NMR分析不同储存条件下大豆油的氧化稳定性

为探讨大豆油在不同包装材料以及有无抗氧化剂条件下的氧化稳定性,基于1H NMR分别对大豆油自动氧化过程中的一级氧化产物和二级氧化产物峰信号进行量化分析。以墨绿磨砂瓶、白色磨砂瓶、透明玻璃瓶包装的大豆油以及透明玻璃瓶包装的含TBHQ的大豆油作为试验对象,将4组油样置于充足日光灯光照的40 ℃烘箱中进行恒温氧化,定期取样进行1H NMR分析。结果表明：采用1H NMR可有效鉴别出大豆油中5种氧化产物,分别为一级氧化产物Z,E型和E,E型共轭烯烃类氢过氧化物,以及二级氧化产物正构醛、E,E-共轭二烯醛和E-共轭烯醛;利用1H NMR可有效监控氧化产物含量,经单因素ANOVA统计分析,抗氧化剂TBHQ（0.05 g/kg）对大豆油储存初期（70 d内）的一级氧化过程有显著的延缓作用（p＜0.05）,墨绿磨砂瓶包装（避光）对大豆油的二级氧化过程有显著的延缓作用（p＜0.05）。     

Physicochemical characterisation and oxidative stability of refined hoki oil,unrefined hoki oil and unrefined tuna oil

Physicochemical characterisation and oxidative stability of refined hoki oil, unrefined hoki oil and unrefined tuna oil were carried out in the present study. Tuna oil contains a higher percentage of polyunsaturated fatty acids (42.57%) than the hoki oils (28.79–30.13%), which have higher percentages of monounsaturated fatty acids (45.02–47.16%). All oils showed a good ratio of n‐3 to n‐6 fatty acid (7.01–8.10). Cholesterol contents in the unrefined hoki (5149.40 μg g^?1) and tuna (2045.48 μg g^?1) oils were higher than the refined hoki oil (1411.27 μg g^?1). Tuna has a higher concentration of natural α‐tocopherol (752.49 μg g^?1) but lower concentration of vitamin A (110.99 μg g^?1) than unrefined hoki oil (151.44 μg g^?1 and 997.60 μg g^?1, respectively). Higher percentages of unsaponifiable matter were found in the hoki oils (4.90–7.24%) compared with the tuna oil (0.56%). The hoki oils appear more yellow than the tuna oil, which is darker by comparison. Moisture, p‐anisidine value and free fatty acid contents in the hoki oils were lower than the tuna oil. Other indicators of oxidative stability showed that the hoki oils were more stable than the tuna oil.     

Short‐term in vivo digestibility assessment of a highly oxidized and polymerized sunflower oil

The aim of this study was to test the in vivo digestibility of a highly polymerized sunflower oil. The true digestibility of both the unheated oil and of an oil heated at frying temperature (180 °C) for 50 h in the presence of air was determined by using a 4 h in vivo test after applying the oil by an oesophageal probe to Wistar rats followed by high‐performance exclusion chromatography analysis of the luminal remaining fat. The true digestibility coefficient of the heated oil did not change significantly with respect to the unheated oil, although it tended to decrease (p < 0.1; 38%). The true digestibility of polymers, dimers, and total oligomers was 30%, 59%, and 38% respectively, whereas those of the unheated oil was much higher (95%, 90%, and 91% respectively). True digestibility did not change for the triacylglycerol monomers. The plasma concentration of triacylglycerol tended to decrease (9.7%; p > 0.05) in the rats receiving the heated oil, suggesting some delay in the absorption mechanism. Data show that thermoxidized compounds from abused oil are poorly but actively hydrolysed and absorbed in vivo. Copyright © 2003 Society of Chemical Industry     

纺丝油剂中脂肪酸酯类平滑剂的抗氧化及热稳定性

为优化油剂的抗氧化和热稳定性,运用烘箱加速氧化法模拟实际纤维生产过程中油酯使用的热温环境,通过酸值、过氧化值、热重差示扫描量热法分析等多种测试手段,对添加了5种酚类抗氧剂的季戊四醇油酸酯的抗氧化性进行研究。结果表明：抗氧剂的加入可改善脂肪酸酯类化合物的热稳定性,减少热分解发烟量,有效提高纺丝油剂的抗氧化性能;抗氧剂的添加可显著抑制油酯受热后的酸值和过氧化值的升高,且抗氧化剂A的效果最好。通过热重差示扫描量热法分析表明：抗氧剂A在油酯中的添加量为0.4%∽1.0%时作用效果最佳,其热重曲线中质量损失50%的分解温度提高13.23℃,氧化诱导温度提高了39 ℃。     

不同贮藏条件下水酶法牡丹籽油的 氧化稳定性与货架期预测

旨在为水酶法牡丹籽油的品质控制提供理论依据,探究不同贮藏条件下水酶法牡丹籽油的氧化稳定性,并对其货架期进行预测。采用Schaal烘箱模拟加速氧化法,探究了抗氧化剂、包装材料、温度对牡丹籽油过氧化值的影响,并进行了氧化动力学分析,采用Arrhenius方程进行拟合,建立了水酶法牡丹籽油货架期预测模型。结果表明：不同抗氧化剂的抗氧化效果排序为0.01%柠檬酸+0.01%TBHQ＞0.02%TBHQ＞0.02%柠檬酸>0.2%γ-谷维素;包装材料的抗氧化效果排序为棕色PET瓶＞棕色玻璃瓶＞透明PET瓶＞透明玻璃瓶;随着温度升高,牡丹籽油的过氧化值明显增加;建立的货架期预测模型预测牡丹籽油在10、20、30 ℃下的货架期分别为117、77、51 d,其实测货架期分别为134、90、60 d。综上,使用抗氧化剂、避光、低温均能有效延缓水酶法牡丹籽油的氧化进程,建立的水酶法牡丹籽油货架期预测模型准确率良好。     

Oxidative stability of camelina oil in salad dressings,mayonnaises and during frying

Oxidative stability of omega‐3 rich camelina oil in food products and during frying was evaluated and compared with sunflower oil. Camelina oil‐based salad dressings were of similar oxidative stability to those prepared with sunflower oil, as indicated by predominantly insignificant (P > 0.05) differences in peroxide values (PV), ρ‐anisidine values (AV), total oxidation values (TOTOX), conjugated diene levels (CD) and conjugated triene levels (CT). However, thiobarbituric acid reactive substances (TBARS) were significantly higher (P < 0.05) for camelina oil and salad dressings throughout storage. Camelina and sunflower oils, alone and in salad dressings or mayonnaises, were acceptable to a sensory analysis panel with slightly lower scores for camelina oil. PV, AV and TOTOX values were similar for camelina and sunflower oil during deep frying but while PVs remained low (<10 meq kg^?1), AV and TOTOX values increased quickly. TBARS values were significantly higher in deep‐frying camelina oil and ‘fishy’ odours were observed.     

以葛根粉酶解物为壁材的粉末油脂理化性质及稳定性研究

对以葛根粉酶解物为壁材的粉末油脂进行了感官评价和理化性质测定.结果表明:产品粉体洁白,有葛根粉的清香,颗粒细,流动性较好；产品水分为2.72％,包埋率达89.42％,溶解度为95.60％；复水乳液平均粒径为239.3 nm.扫描电镜结果显示,产品颗粒为表面光滑、内部空心的完整球形,其囊壁致密且有一定厚度,无裂纹和孔隙.差示扫描量热及热重分析结果表明,产品热熔解温度高,常温下处于稳定的玻璃态,具有良好的热稳定性.Schaal加速氧化试验结果表明,产品的氧化稳定性较好,在室温下的货架寿命可达16个月.     

Storage stability of cod liver oil organogels formed with beeswax and carnauba wax

In this study, organogels of cod liver oil (CLO) with beeswax (BW) and carnauba wax (CW) were prepared, and compared with a commercial margarine (CM). Oil binding capacities (OBC) of BW organogels were over 99%, while CW had a maximum OBC value of 91.28%. Crystal formation time of BW was shorter. Although the highest solid fat content (SFC) was in the 10% CW containing sample (8.69%), it was 28.99% in the CM sample at 20 °C. The peak melting temperature of CM was 43.70 °C, and BW organogel at 3% addition had the closest values (45.42 °C). Firmness and stickiness values of the organogels were lower than that of CM sample. No significant change in the texture parameters during storage was detected, indicating good stability. There was no hurdle against oxidation by organogelation during storage. This study has shown that CLO organogels can be suitable spreadable products.