Interference by formaldehyde in the 2-thiobarbituric acid test for rancidity

The 2-thiobarbituric acid (TBA) test is often used to detect oxidative rancidity, although certain limitations of the technique have been described. This study was of formaldehyde (FA) interference in the TBA test in model systems involving various concentrations of malonaldehyde (MA), FA and TBA. At a TBA concentration of 20 μmol ml^?1 it was found that FA could give rise to turbidity or precipitation. However, as the amount of MA in the reaction mixture increased (10 to 400 times higher than the upper limit of the standard curve), higher FA concentrations were required. Turbidity or precipitation resulted in fluctuating readings, and centrifugation or filtration lowered the readings (532 nm) to below those obtained when no FA was present. The ratio of TBA to MA must be ?1000 for full colour development, and hence lack of colour may be due to the TBA acting as a limiting factor in the reaction. The presence of a peak at 323 nm and/or turbidity or precipitate confirmed of the reaction between FA and TBA. FA competed with MA for TBA thereby lowering the effective TBA:MA ratio. Other TBA-reacting substances (TBARS) present in the medium may augment this effect.     

The Thiobarbituric Acid (TBA) Reaction in Foods: A Review

The wide diffusion of 2-thiobarbituric acid (TBA) in the scientific literature is due to the TBA assay, or TBA test, which has been employed in the determination of autoxidative alterations of fats and oils. Two processes occur in autoxidation, generally: the free radical and the photo-oxidation mechanisms. The better studied is the free radical mechanism. The hydroperoxiepidioxides and bicycloendoperoxides are malonaldehyde (MDA) precursors. The absorption spectrum obtained with oxidized fatty foods is like the spectrum obtained when TBA and MDA react. However, during the secondary phase of the autoxidation process other aldehydes (alkanals, 2-alkenals, dienals) are formed which react with TBA, and they are responsible for off-flavors. Three kinds of pigments (yellow, orange, red adducts) are involved. Also, aromatic aldehydes, which constitute the flavor profile of diverse fruits and essential oils, form with TBA the characteristic arylidene-2-TBA acids. Other substances, such as ketones, ketosteroids, acids, esters, sugars, imides and amides, amino acids, oxidized proteins, pyridines, pyrimidines, and vitamins can react with TBA; they are named TBARS (substances that react with TBA), and form principally in meats and meat derivatives. Several organic or bio-organic acids, as shikimic and sorbic acids, react photometrically with TBA if a Malaprade reaction takes place before. A structural study of the red adduct TBA-MDA has been carried out.     

A critical examination of some experimental variables in the 2-thiobarbituric acid (TBA) test for lipid oxidation in meat products

By comparison of various procedures for the determination of TBARS (2-thiobarbituric-acid-reactive substances) in non-cured meat samples, it was found that a direct extraction procedure with trichloroacetic acid gave significantly higher reaction yields than a rapid Kjeltec steam distillation procedure (50 ml distillate in 2.5 min). When optimizing the distillation procedure with regard to distillation principle (heating by thermal conductivity or steam injection) and rate, the reaction yield was more affected by changes in distillation principle than by changes in distillation rate. Simple distillation (conduction heating) yielded significantly higher TBA values than steam distillation at the same distillation rate. The reproducibility of the distillation procedure was found to be about 5–10 times poorer than of the extraction procedure and, because of the high reaction yields and robustness of the extraction procedure, the use of the extraction procedure is recommended with food matrices such as non-cured meat samples with less than 14–18% fat and no artificial colorants.     

A novel miniaturised electrophoretic method for determining formaldehyde and acetaldehyde in food using 2-thiobarbituric acid derivatisation

A novel miniaturised capillary electrophoresis with electrochemical detection (mini-CE-ED) method has been developed for fast determination of formaldehyde (FA) and acetaldehyde (AA) in several food products without preconcentration. Because FA and AA usually exist as uncharged molecules with zero electrophoretic mobility, plus the fact that these two compounds lack of chromophore for sensitive ultraviolet (UV) detection, effective and sensitive determination of FA and AA in real samples is often a challenging task. In this work, an electroactive compound 2-thiobarbituric acid (TBA) was selected as the ideal derivatisation reagent to facilitate the electrochemical determination of FA and AA. Under the optimum conditions, FA-TBA and AA-TBA adducts can be well separated by mini-CE-ED with low detection limit of 9.10 × 10⁻⁹ g/mL (13.2 fg) for FA (S/N = 3). The proposed method should find a wide range of analytical applications in food products as an alternative to conventional and microchip CE approaches.     

A review of the methodology of the 2-thiobarbituric acid test

The 2-thiobarbituric acid (TBA) test for the measurement of lipid oxidation was discovered over 40 years ago. Since then it has been widely used for the measurement of the oxidative state of biological and food materials. Despite copious literature references and its widespread usage there are still uncertainties over the exact chemistry of the reaction and its applicability. This review attempts to draw together the relevant publications and discuss the merits of the TBA test, particularly in the analysis of foods.     

啤酒老化的预测——TBA值测定方法的探讨

对由Grigsby和Palamand提出并用于预测啤酒老化的TBA(硫代巴比妥酸 )值测定方法进行了进一步的探讨和改良 ,确定了TBA值的测定条件为 :测定吸收波长为 5 3 0nm ;TBA溶液为含质量分数为 0 2 8%TBA的体积分数为 60 %的乙酸溶液 ;反应温度 60℃ ,反应时间 60min ;空白样中添加体积分数为 60 %的乙酸溶液。同时对TBA值与醛类物质及其他羰基化合物的相关性进行了初步研究。     

三种TBA方法用于测定腌腊肉制品脂肪氧化程度适用性的研究

本文研究了亚硝酸钠和蔗糖对TBA试验的影响,比较了这两种物质对三种不同的TBA方法(蒸馏法、酸萃取法和样品直接反应法)用于腌腊肉制品脂肪氧化程度测定的适用性。研究发现,亚硝酸钠在酸性或加热条件下与丙二醛反应,导致吸光值降低;此外,TBA在常温下就可以和亚硝酸钠反应生成不可逆产物,利用此反应能够消除亚硝酸钠对吸光值的影响。蔗糖对TBA反应的影响与溶液pH值有关,当反应液的pH值小于2时,蔗糖与TBA反应生成的黄色物质(吸收峰450nm)就会叠加到532nm的吸收峰上,导致吸光值偏高;当反应液的pH值大于2时,蔗糖不会对吸光值产生影响。在三种不同的TBA试验方法中,样品直接反应法受亚硝酸钠和蔗糖的影响不显著(P>0.05)。蒸馏法和酸萃取法试验中TBA值都会随亚硝酸钠含量的增加而降低,随蔗糖含量的增加而升高。     

Evaluation of three 2-thiobarbituric acid methods for the measurement of lipid oxidation in various meats and meat products

The aim of this work was to study the influence of different conditions on the 2-thiobarbituric acid (TBA) number, determined by the extraction and distillation method, as a measure of lipid oxidation in various meats and meat products. Different extracting agents (trichloroacetic acid and perchloric acid), different reaction times (20, 30, 40, 50 and 60 min) and the effect of sulfanilamide additions were evaluated. Significant differences with respect to reaction times were found. The best results were generally obtained with 40 min at 80 ± 2 °C. Different values were found between samples with and without the addition of sulfanilamide.     

Effect of processing methods on product characteristics,lipid, fatty acid composition and oxidative stability of smoke-dried beef

Smoke-dried beef was pre-processed with water or by pressure cooking, weight losses were 50 and 54% respectively, with the rate of drying faster in the latter. There was a greater loss of total lipid and triglycerides in pressure cooked samples but the reverse was true for the phospholipids. The proportions of saturated and monoenoic fatty acids were slightly higher in the water cooked products although total unsaturation was slightly lower, the values being 37 and 39%, respectively. The fatty acid composition of the phospholipids was similar for both treatments except that the levels of polyenoic fatty acids were 16.4 and 14.43%, respectively in water and pressure cooked samples. Of the polyenes C20:4 accounted for about 75% of the fatty acids in the water cooked samples, compared with 40% with pressure cooking. After 60 weeks of storage at room temperature, pressure cooked samples were found to be more stable oxidatively: malonaldehyde was the principal oxidative by-product in both treatments.     

A modified distillation method for the detection of fat oxidation in foods

A rapid distillation procedure for the estimation of fat oxidation in food using the 2-thiobarbituric acid test has been developed. The apparatus generates steam rapidly and allows high sample throughput while minimizing cleaning of glassware. Using the standard compound, tetramethoxypropane (TMP), and a number of food samples spiked with standard, the recovery of malondialdehyde was determined and suitable operating conditions selected. Levels of TMP equivalent to TBA numbers between 1 and 10 were used. Recovery of standard increased from 25.3% at 20 ml to 81.6% at 120 ml, and recoveries at different TBA numbers were similar. After consideration of various factors, 50 ml was chosen as the distillate volume and was collected in about 4 min. With food samples, the recovery varied depending on the composition of the food and, in order to determine TBA number, it was necessary to calculate recoveries from each type of sample. In the reaction of distillate with thiobarbituric acid, colour development was found to be extremely temperature sensitive, and careful temperature control of the heating bath was required.     

Urinary 2-ethyl-3-oxohexanoic acid as major metabolite of orally administered 2-ethylhexanoic acid in human

Human metabolism of 2-ethylhexanoic acid (2-EHA), which is a known metabolite of important phthalates, was investigated using 2-EHA-contaminated food. The results of our studies reveal that the major catabolic pathway of 2-EHA in human is beta-oxidation. The dominant final urinary metabolite was identified and quantified as 3-oxo-2-ethylhexanoic acid (3-oxo-2-EHA), but only after immediate methylation of the extract from urine and prior to GC-MS analysis. Former studies without the precaution of immediate methylation had found 4-heptanone as the major metabolite, which is obviously an artifact arising from the decarboxylation of 3-oxo-2-EHA.     

Development of an improved two-alternative choice (2AC) sensory test protocol based on the application of the asymmetric dominance effect

The goal of this study was to demonstrate that participants in a 2AC test can be induced to select the no-difference alternative by modifying the design of test ballots. Four different protocols (2AFC, 2AC, and two modified versions of 2AC) were evaluated; the two modified versions consisted of one where the judges were told that samples were the same and another where an “I do not know” alternative was included. Aqueous sucrose solutions were employed to evaluate the discriminative efficiency of the tests. Both 2AC modified versions effectively increased (p ? 0.05) the proportion of judges choosing the “no-difference” option. The discriminative efficiency of the “I do not know” 2AC version was about three times higher than that of the other three protocols. This study demonstrated that it is possible to modify the proportion of judges choosing the no-difference option through ballot design, and that free-choice protocols may show much higher discriminative power than forced-choice tests when the no-difference alternative is properly used.     

乳酸菌抗氧化活性及检测方法

通过对30株乳酸菌清除DPPH自由基和抗亚油酸过氧化能力的实验,筛选出了抗氧化活性较强的乳酸菌L3和L4。从得到的两株乳酸菌分别制备无细胞提取物(菌数为1010mL-),利用6种方法对这两株乳酸菌无细胞提取物的抗氧化性能进行了检测分析,发现L31和L4可螯合Fe2+,分别为54.3×10-和41.3×10-,清除超氧自由基分别为14.9%和87.0%,清除羟自由基分别为83.5%和45.7%,并具有还原66活性。进一步研究发现乳酸菌L4SOD活性为(73.70±1.77)U/mg,但这2株乳酸菌均未检测到GSH-Px活性。     

纺织品中甲醛释放机理的研究

阐述纺织品中甲醛的释放曲线图及机理，对试验方法GB/TS912。1和GB/T291.2进行对比试验，确定测试条件对测试结果的影响程度，提出将甲醛的危害性降到最低限度的方法。     

The recovery of added malondialdehyde from rancid chicken by the distillation method for thiobarbituric acid-reactive substances

Roasted chilled chicken muscle which had been chopped and stored at 5°C was spiked with 1,1,3,3-tetra-ethoxypropane and steam distilled at 20–25 ml of distillate per min. Malondialdehyde concentration in the distillate decreased exponentially with distillate volume, producing 88% recovery in 10 min, more than double than in a previously published method with a similar rate of sample throughput.     

Some comments on the usefulness of 2-thiobarbituric acid (TBA) test for the evaluation of rancidity in frozen fish

Rancidity of frozen fish (Baltic cod and herring, mackerel, horse mackerel and hake) was determined by means of TBA value, organoleptical scoring and peroxide value. The correlation between the rancid odour sensory assessment and TBA test results proved insignificant (r = 0.53). Model experiment was undertaken in which promine D with addition of papain was incubated at 50°C over 44 h. It was shown that as accumulation of protein hydrolysis products proceeded the increase of TBA value has taken place without development of rancid odour and with peroxide content below sensibility of sulphocyanide method. With regard to fish, therefore, it seems that the TBA test applied by means of techniques in which the reaction with TBA proceeds in the presence of interfering substances should be treated as a ?freshness test”? rather than a strictly rancidity one.     

乳酸菌冷冻干燥保护剂的筛选及加速储存稳定性试验

通过正交试验设计,确定适合嗜热链球菌最佳冻干保护剂配方为脱脂乳粉12%,海藻糖1%,甘油3%,谷氨酸钠1%(均为质量分数)。通过加速储存实验,同批冻干样品在不同温度(30,42,60℃)条件下储存,分别采样,测定活菌数,建立储存稳定性方程,由方程外推出得到4℃降解速率常数为1.656×10-4。     

关轭亚油酸调节血脂的试验研究

采用预防型大鼠脂质代谢紊乱模型法,以人体摄入量(2.6g/kg@bw)的10、20、30倍,作为低、中、高剂量组.采用SPF级Wistar大鼠经口灌胃,与模型对照组比较体重差异,比较胆固醇变化情况,比较甘油三酯变化情况,比较高密度脂蛋白胆固醇变化情况.结果表明大鼠体重明显低于模型对照组,差异有显著性;胆固醇含量下降幅度分别为45.0%、16.2%、8.0%;甘油三酯含量下降幅度分别为32.2%、21.0%、3.4%;高剂量组对高密度脂蛋白胆固醇有升高作用.从而说明共轭亚油酸有明显的调节血脂作用.     

7种特种油脂的脂肪酸组成及抗氧化性能

采用气相色谱法对7种特种油脂的脂肪酸组成进行分析,并对烘箱法加速氧化前后7种特种油脂的过氧化值(POV)和TBA值进行测定。结果表明:7种特种油脂的不饱和脂肪酸含量均显著高于饱和脂肪酸含量;黄秋葵籽油棕榈酸含量最高,为26.86%,木瓜籽油油酸含量最高,为36.80%,哈密瓜籽油亚油酸含量最高,为62.31%,牡丹籽油α-亚麻酸含量最高,为39.21%;加速氧化条件下,牡丹籽油和黄秋葵籽油的POV上升较慢,品质稳定性较好,而核桃油、小麦胚芽油、玉米胚芽油和木瓜籽油的POV上升速度较快,品质容易下降;加速氧化条件下,黄秋葵籽油、哈密瓜籽油、玉米胚芽油等的TBA值相对较低且稳定,而核桃油的TBA值最高且随温度升高增加较快。     

过氧乙酸快速检测试纸条研制与应用

分别用定性滤纸、定量滤纸、微孔滤膜为试纸条载体制作了过氧乙酸快速检测试纸条,并制成标准比色卡对过氧乙酸消毒液进行含量检测。结果显示,微孔滤膜为最适宜制作过氧乙酸快速检测试纸的材质,最适烘干温度为55℃,最适烘干时间为15min,最适保存条件为4℃下密封贮藏保存21d。利用微孔滤膜制作的检测试纸条能够在30s内对消毒液中的过氧乙酸浓度进行检测,最低检出限为质量百分比0.1%。