电子自旋共振波谱法评价花生油氧化稳定性的可行性研究

为探究花生油加速氧化过程中的自由基链式反应,利用电子自旋共振波谱法（ESR）研究花生油的加速氧化过程,结果发现加速氧化过程中产生大量的烷基自由基（R·）以及少量的烷氧基（RO·）和过氧化自由基（ROO·）。对ESR法与Rancimat法（经典油脂氧化稳定性测定方法）进行比较研究,分别利用这两种方法测定添加不同抗氧化剂花生油的氧化稳定性,发现ESR法的滞后时间（Lagtime）和Rancimat法的诱导时间（IP）结果一致,即加入0.02%TBHQ和0.01%柠檬酸（CA）的花生油中自由基生成量最少,滞后时间最长,且诱导时间最长。此外,滞后时间与诱导时间之间具有良好的线性关系,回归方程为[Lagtime]=79.724[IP]-165.630（R2=0.9688）。综上所述,ESR法可预测Rancimat法的结果,也可作为一种评价花生油氧化稳定性的方法。      

An assessment of the antioxidant potential of coriander extracts in ghee when stored at high temperature and during deep fat frying

A coriander extract was evaluated for its potential to increase oxidative stability of ghee. Antioxidant activity using β‐carotene–linoleic acid model system and radical scavenging activity by 2‐diphenyl‐1‐picrylhydrazyl hydrate free (DPPH) was higher in steam distilled extract compared to its oleoresin counterpart. Steam distilled extract and oleoresin were significantly effective in retarding the deterioration of ghee relative to control, as observed in peroxide value, conjugated dienes, thiobarbituric acid (TBA) value and oxidative stability index at the end of 21 days of storage. However, these were less effective than butylated hydroxyanisole (BHA). During deep fat frying, steam distilled extracts showed higher antioxidant activity compared to oleoresin and BHA.     

滇牡丹籽油的脂肪酸组成及不同天然抗氧化剂对其货架期的影响

采用气相色谱法测定了滇牡丹籽油中的主要脂肪酸组成及含量,通过Rancimat法测定了滇牡丹籽油的氧化稳定性,并分析比较了不同天然抗氧化剂对滇牡丹籽油的抗氧化效果,进而推测出滇牡丹籽油在常温20℃下的货架期。结果表明:滇牡丹籽油的主要脂肪酸组成为油酸0.46%、亚油酸15.48%、亚麻酸74.09%、棕榈酸6.62%、硬脂酸1.37%,其中不饱和脂肪酸含量高达90.03%;天然抗氧化剂的抗氧化效果为原花青素滇牡丹籽黄酮二氢杨梅素V_EV_C茶多酚β-胡萝卜素,添加0.04%原花青素时,常温20℃下滇牡丹籽油的货架期为179.83 d。     

Changes in phenolic compounds and Rancimat stability of olive oils from varieties of olives at different stages of ripeness

BACKGROUND: Recently, diets rich in natural foods and food‐derived components, such as phenolic compounds, have received a great deal of attention because they are perceived as ‘safe’ and ‘non‐medicinal’. In fact, some are known to function as chemopreventive agents against oxidative damage, cerebrovascular disease, and aging. RESULTS: Phenolic compounds, natural antioxidants present in virgin olive oil, play an important role in oil quality by contributing significantly to protecting oil stability against oxidation. In addition, polyphenols are the main contributors to olive oil bitterness, astringency and pungency. The data were fit by linear regression, giving Rancimat stability (h) = 0.18× Total polyphenols (mg L^?1) in the virgin olive oil. CONCLUSIONS: The practice of harvesting ripe olives as soon as possible to produce oils of high phenolic contents and thus high oxidative stability implies bitter and piquant oils, this being admissible for oils of some varieties but detrimental to others appreciated in the market for being more fruity and sweeter. Copyright © 2010 Society of Chemical Industry     

Rancimat法测定3种坚果油脂氧化稳定性的条件研究

研究了温度、气流速度以及样品质量等参数对Rancimat法测定坚果油脂氧化稳定指数(OSI)的影响,以核桃、杏仁、扁桃油脂为试材,通过Rancimat油脂氧化仪测定3种坚果油脂的诱导时间,在单因素实验的基础上,通过Box-Behnken响应面实验,建立回归方程,进行方差分析,得到了优化测定条件.结果表明:温度对3种油的氧化稳定指数测定结果均有极显著影响(p<0.01),气流速度及样品质量对其影响均不显著(p>0.05),温度、气流速度及样品质量等因素间交互作用不显著(p>0.05);由回归方程得到Rancimat法测定核桃油OSI的最佳条件为:温度120℃、气流速度18.14L/h、样品质量3.00g;测定扁桃油的最佳条件为:温度120℃、气流速度13.48L/h、样品质量3.93g;而杏仁油测定的最佳条件为:温度120℃;气流速度12.18L/h;样品质量4.20g.通过优化温度、气流速度和样品质量等条件,可以保证结果稳定、可信的前提下,缩短分析测定时间.     

The Effect of Operational Parameters of the Rancimat Method on the Determination of the Oxidative Stability Measures and Shelf-Life Prediction of Soybean Oil

Operational parameters of the Rancimat method, including oil sample size, airflow rate, and temperature, were evaluated to determine their effects on the oxidative stability index (OSI), temperature coefficient, Q ₁₀ number, and shelf-life prediction for soybean oil. Operational parameters of the Rancimat method had statistically significant effects (P < 0.05) on the OSI. Whenever the oil sample size and airflow rate at a given temperature were such that the air-saturated condition could be established, the OSIs showed no statistically significant differences. As temperature increased, OSIs decreased, while their average coefficient of variation (CV) increased. In general, the conditions where the sample was saturated with air and had a relatively lower CV were an oil sample size of 6 g at all temperatures and airflow rates, then 3-g oil sample size at low temperatures (100 and 110 °C) and low airflow rates (10 and 15 L h⁻¹). The temperature coefficient and Q ₁₀ number were found to be independent of the oil sample size and airflow rate, and their mean values for soybean oil were calculated to be −3.12 × 10⁻² °C⁻¹ and 2.05, respectively. Oil sample size and airflow rate showed a significant effect on shelf-life prediction for soybean oil. Therefore, choosing the right levels of these operational parameters in the Rancimat method may produce the least possible difference between predictions from long-term storage studies and the OSI test.     

Investigation of the effect of detergent–dispersant additives on the oxidation stability of biodiesel,diesel fuel and their blends

Basic materials of biodiesels and molecular structure of different biodiesels were discussed with special focus on their oxidation stability and post-additization. Commercial biodiesels produced from rapeseed oil and used cooking oil were blended to diesel fuel in 5%, 7%, and 10% mass fraction. The samples were stored at ambient temperature for one year to simulate the effects of strategic storage and/or long stock turnover rate. Following the one year storage period the samples were treated with BHT antioxidant and/or succinic type detergent–dispersant additives in 300 mg kg⁻¹, 600 mg kg⁻¹ and 900 mg kg⁻¹ concentrations. BHT was applied as antioxidant additive, while the detergent–dispersant additives were either newly developed additives (polyisobutylene succinic anhydride derivatives containing fatty acid methyl ester in their molecular structure) or commercial ones. Structure of the developed additives and their mechanism is described in detail. Rancimat and Seta TOST devices were applied to evaluate the effect of the additives on the oxidation stability of the samples. It was found that the decrease of oxidation stability during storage can be partially compensated with post-additization by suitable detergent–dispersant additives. Oxidation of biodiesels during Rancimat measurement was investigated with infrared spectroscopy. The results showed that during the thermal oxidation fatty acid methyl esters decompose to carbonyl, carboxyl and hydroxyl compounds, while cis-trans isomerization also occurs.     

Chemo‐enzymatic synthesis and evaluation of novel structured phenolic lipids as potential lipophilic antioxidants

Chemo‐enzymatic synthesis of structured triacylglycerol bearing ferulic acid as a phenolic acid at sn‐1/3 position is described in the present work. Four compounds of varying chain lengths, namely 3‐(4‐hydroxy‐3‐methoxy‐phenyl)‐acrylic acid‐2,3‐bis‐hexanoyloxy‐propyl ester, 3‐(4‐hydroxy‐3‐methoxy‐phenyl)‐acrylic acid‐2,3‐bis‐octanoyloxy‐propyl ester, 3‐(4‐hydroxy‐3‐methoxy‐phenyl)‐acrylic acid‐2,3‐bis‐dodecanoyloxy‐propyl ester, and 3‐(4‐hydroxy‐3‐methoxy‐phenyl)‐acrylic acid‐2,3‐bis‐9‐octadecenoyloxy‐propyl ester were synthesized, and their structures were confirmed by IR, NMR, and MS. Antioxidant activity of the structured phenolic lipids were evaluated using three different in vitro antioxidant assays such as 2, 2‐diphenyl‐1‐picrylhydrazyl free radical (DPPH^•) scavenging, antioxidant potency in lipid matrix using rancimat, and by the rate of inhibition of autoxidation of linoleic acid in micelles. Ferulic acid and dodecylgallate were used as reference antioxidant compounds. DPPH^• assay did not show any improvement in the antioxidant activity of ferulic acid with lipophilic modification. However, the antioxidant potency of the structured phenolic lipids measured by rancimat method as well as by the rate of inhibition of autoxidation of linoleic acid in micelle showed improvement in antioxidant activity compared to ferulic acid. This is probably due to better solubility of the synthesized phenolic lipids in a hydrophobic medium and appropriate anchorage in Tween 20 micelle. The observed activities of the structured phenolic lipids are comparable to dodecyl gallate in rancimat assay, but superior to dodecyl gallate in Tween 20 micellar system.     

Reevaluation of bioactivity and antioxidant activity of <Emphasis Type="Italic">Myrtus communis</Emphasis> extract before and after encapsulation in liposomes

The antioxidant and antimicrobial activity of Myrtus communis extract was determined before and after its encapsulation in liposomes of different composition. Evaluation of the sunflower oil oxidation by the Rancimat stability test and malondialdehyde formation by HPLC were used to measure the antioxidant action in comparison with common commercial antioxidants, such as butylated hydroxytoluene and α-tocopherol. The thermal-oxidative decomposition of the samples, the modification of the main transition temperature for the lipid mixture and the splitting of the calorimetric peak in the presence of the antioxidants were studied by differential scanning calorimetry. The size and the surface charge of liposomes were also studied. The extract showed antioxidant and antimicrobial activity. Αt concentrations up to 160 ppm, the extract showed superior activity than α-tocopherol. When the extract was encapsulated in liposomes, its antioxidant as well as its antimicrobial activity proved to be superior from that of itself in pure form.