Thermal Destruction of 5-Methyltetrahydrofolic Acid in Buffer and Model Food Systems

Thermal kinetic data (rate constants, k, and activation energies, Ea) for 5-Methyltetrahydrofolic acid (5-CH₃-H₄PteGlu) were determined in citrate buffers (pH 3-6) and in model food systems between 100° and 140°C. As pH increased from 3.0 to 6.0, the rate constants decreased as the temperature increased from 100° to 130°C, the rate constants increased. Ea values were 19.0, 17.0, 19.7 and 19.8 kcal/mole at pH 3, 4, 5 and 6, respectively. In the model food systems, the Ea values (kcal/mole) were 7.85 in apple juice and 10.6 in tomato juice. When dissolved oxygen content was reduced to 5.3 ppm, the stability of the 5-CH₃H₄PteGlu was increased substantially.     

Thermal Stability of Vitamin B6 Compounds in Liquid Model Food Systems

The degradation of pyridoxine (PN), pyridoxal (PL), and pyridoxamine (PM) during thermal processing was evaluated in casein-based liquid model food systems. Limited evaluation of various potentially reactive ingredients suggested that vitamin B6 stability is not strongly a function of food system composition. Rapid interconversion of PL and PM was observed. Kinetic analysis of B6 vitamer degradation revealed approximately 2.5- to 3.5-fold greater stability of PN than the other nonphosphorylated vitamers, with activation energies of 27.3, 23.7, and 20.8 kcal/mol for the loss of total vitamin B6 after initial fortification with PN, PM, and PL, respectively. Limited studies with pyridoxal 5′-phosphate indicated that it is approximately 1.5- to 2-fold less stable than PL.     

Thermal Destruction of Pteroylglutamic Acid in Buffer and Model Food Systems

First order rate constants (k) and activation energies (Ea) of pteroylglutamic acid (PteGlu) were determined between 100 and 140°C in citrate buffer (pH 3–6) and model food systems. The rate constants (hr^-1) in citrate buffer ranged from 0.145–2.36 at pH 3; 0.074–0.840 at pH 4.0; 0.021–0.207 at pH 5.0, and 0.015–0.133 at pH 6.0. Corresponding Ea values were 22.6, 19.5, 17.8, and 16.8 kcal/mole at pH 3, 4,5, and 6, respectively. In an apple juice model (pH 3.4), the rate constants ranged from 0.063–0.822 and in tomato juice model (pH 4.3), from 0.056–0.723. Ea values in apple juice an tomato juice were 20.0 and 19.7 kcal/mole, respectively.     

Verification of 5-Methyltetrahydrofolic Acid in Nutritional Products

A simple method for the verification of supplemental (6R,S)-5-methyl-5,6,7,8-tetrahydrofolic acid, “5-MTHF,” in nutritional products is described. Nutritional product samples are prepared for the liquid chromatographic/fluorescence detection (LC/FLD) determination of 5-MTHF by buffer dilution, 10-min centrifugation, and syringe filtration. Method performance has been defined by assessments of 5-MTHF linearity (r ² averaged 0.9999 ± 0.0001, and all relative calibration errors averaged ≤0.6%, for ten consecutive six-point standard curves), intermediate precision (rsd = 1.1%, n = 9, for three products fortified at ～1.73 μmol/kg = ～795 μg/kg, tested on each of 3 days), accuracy (spike recovery average = 92.8 ± 1.0%, n = 9, for nutritional products spiked with 5-MTHF at ～1.73 μmol/kg, or ～795 μg/kg), and selectivity (absence of interference from reagent blanks, and from four compounds structurally related to 5-MTHF). The 5-MTHF recovery, as % of unheated controls, from a simulated heat treatment (20 min at 120 °C) averaged 99.1 ± 0.6%, n = 4. The limits of 5-MTHF detection (S/N = 3) and quantification (S/N = 10) were experimentally determined to be 10 μg/kg (～0.020 μmol/kg) and 30 μg/kg (～0.060 μmol/kg), respectively (<10× the expected fortification rate). The method provides a simple and inexpensive means for verifying proper fortification, and for assessing the stability to processing and storage conditions, of free 5-MTHF in nutritional products. A finding of interest is the indication that liquid nutritional products may comprise a stable matrix for 5-MTHF fortification.     

Stability of Sorbic Acid in Model Food Systems of Reduced Water Activity: Sugar Solutions

The behavior of sorbic acid in model systems comprised of concentrated sugar solutions (water activity 0.94) at pH 3.5 and 4.5 was studied. Sorbic acid degraded appreciably as a function of time and temperature during storage and its destruction could be described by first-order kinetics. The rate constants of sorbic acid destruction were found to be related to composition of the sugar model system. Non-enzymatic browning reactions which occur in systems containing lysine greatly influenced the kinetics of sorbic acid destruction.     

叶酸脂质体制备工艺优化及其稳定性研究

以叶酸为载药,卵磷脂和胆固醇为膜材,采用薄膜水化- 超声法制备叶酸脂质体;通过单因素考察制备工艺对包封率的影响以及正交设计法进行制备工艺优化。得出最佳制备工艺为卵磷脂与胆固醇比5:1(m/m)、叶酸质量浓度1.4mg/mL、制备温度60℃、水相pH8.0。制备的叶酸脂质体包封率可达到30.36%,平均粒度为335.4nm。将脂质体在4℃下密闭放置15d,以脂质体的粒径变化为指标考察其稳定性。结果表明,脂质体悬液粒径无明显变化,主要集中在300～400nm,脂质体悬液稳定性良好。     

高效液相色谱法测定食品中的叶酸

在食品样品中加入体积分数 60 %高氯酸溶液去蛋白 ,过滤后进样检测叶酸。流动相选用pH 3 .5 ,体积分数 12 %的乙腈 ,浓度 5 0mmol/L的KH2 PO4溶液。流速为 1mL/min ,经ODSC 18柱分离 (柱温为 40℃ ) ,用质量分数 0 .5 %的过二硫酸钾溶液作柱后衍生剂 ,流速为 0 .3mL/min ,柱后反应温度为 60℃ ,经荧光检测器 (Ex :3 65nm ,Em :45 0nm)检测定量。实验结果表明 ,在 0 0 1～3 2 μg/mL的浓度范围内 ,线性良好 ,相关系数为 0 .9999;最低检出浓度为 0 .0 1μg/mL ;方法回收率为 98.1% ;变异系数为 2 3 %。     

高效液相色谱荧光-衍生法测定保健食品中叶酸方法的研究

目的建立保健食品中叶酸的高效液相色谱荧光-衍生检测方法。方法采用0.5%氨水提取,高锰酸钾氧化叶酸衍生生成喋呤-6-羧酸强荧光物质,通过ODS C185μm反相色谱柱分离,荧光检测器检测,Ex=290nm,Em=440 nm,流动相为0.05 mol/L乙酸钠 甲醇=65 35,流速1.0 ml/min。结果方法线性范围为0.05~2.0μg/ml,方法检出限为0.04μg/ml,加标回收率为84.8%~103%,RSD<5.5%。结论实验方法灵敏度高,操作简便,数据可靠,适合于保健食品中叶酸含量的测定。     

Thermal Degradation Kinetics of Pyridoxine Hydrochloride in Dehydrated Model Food Systems

The thermal degradation kinetics of pyridoxine hydrochloride were examined using a dehydrated model food system designed to simulate a ready-to-eat breakfast cereal. This study was carried out to provide information useful in estimating the thermal losses of pyridoxine hydrochloride in the processing of breakfast cereals and other low moisture dehydrated food systems. Portions of the model system which were fortified with pyridoxine hydrochloride were toasted in a conduction oven at 155°, 170°, 185°, and 200°C for a minimum of six heating times at each temperature. Pyridoxine (PN) content was determined in the heat treated model systems by high performance liquid chromatography (HPLC). For each heat treatment, the loss of pyridoxine could be described by a first order kinetics model. The first order rate constants for 155°, 170°, 185°, and 200°C were 1.74 × 10^?2 min^?1, 5.22 × 10^?2 min^?1, 16.88 × 10^?2 min^?1, and 48.95 × 10^?2 min^?1, respectively. The calculated Arrhenius activation energy was 29.8 Kcal/mol. In comparing the HPLC method to the standard microbiological assay, the HPLC assay gave lower PN values for the toasted model system. To explain this discrepancy, HPLC fractions were collected and analyzed by the microbiological assay. No significant vitamin B₆ activity was found in any fraction other than that containing the PN peak. It is possible that the milder extraction procedure used in the HPLC assay is less capable of recovering forms of PN which may become bound during the toasting process. These potentially bound forms may or may not be biologically available.     

超高效液相色谱- 质谱联用测定食品中叶酸含量

建立食品中叶酸含量的超高效液相色谱质谱联用测定方法。样品提取后以Acquity UPLC BEH C18柱(2.1mm×50mm,1.7μm)为色谱柱分离,以电喷雾电离串联质谱在正离子选择反应监测模式下进行测定。以乙腈-0.1%甲酸溶液(5:95,V/V)为流动相、流速0.25mL/min、色谱柱温度40℃、进样量2μL,母离子m/z 442.3、定量子离子m/z 295.1、定性子离子m/z 176.0,碰撞能量为14eV。对空白试样进行3个添加水平4个重复的添加结果表明：回收率80.7%～89.7%,相对标准偏差2.90%～3.85%。该方法检出限1ng/mL,线性范围0.001～1.000μg/mL。该方法具有样品预处理简单、检测周期短、灵敏度较高等优点。     

利用高效液相色谱仪初步研究叶酸的稳定性

本文利用高效液相色谱仪初步研究了叶酸的稳定性。结果表明叶酸对热、中性偏碱、还原剂、蔗糖等较稳定,对酸、氧化剂等不稳定。     

Stability of Lycopene Emulsions in Food Systems

ABSTRACT The chemical stability of lycopene and the physical stability of lycopene emulsions diluted in 3 different food systems (skimmed milk, orange juice, and water as control) were studied. In these investigations, 3 different emulsifiers were used. It was found that lycopene stability strongly depends on the food system. In orange juice, lycopene is particularly stable. The emulsifiers used have only little influence on the stability of lycopene. Emulsions with α-tocopherol as an additional antioxidant showed a good lycopene stability in all food systems. Coalescence of oil droplets was not observed in any of the food systems investigated. Keywords: lycopene, stability, food systems     

酵母菌发酵制备叶酸功能食品的研究

从筛选出的一株酵母菌为发酵菌株,研究其高产叶酸的发酵条件和加工合理性。对所含叶酸及氨基酸等进行了检测,制成叶酸功能食品。     

固相萃取-离子对液相色谱法测定保健品中的叶酸

建立了一种快速、准确、灵敏的固相萃取- 离子对反相高效液相色谱测定保健品中叶酸的方法。用Chromabond-SB 萃取小柱富集保健品中的叶酸,以四丁基溴化铵为离子对试剂,优化了色谱条件。采用 Lu-Na C18色谱柱(250mm × 4.6mm,5μm),SPD-6AV 紫外可见吸收检测器,流动相为0.05mol/L KH2PO4-0.01mol/L 四丁基溴化铵- 乙腈(88:2:10,V/V),用磷酸调节 pH5.5,流速 1.0ml/min,检测波长284nm。结果表明：叶酸在0.06～2.40μg/ml 浓度范围内,峰面积和浓度呈良好的线性关系,相关系数为0.9996,最小检出限为0.008μg/ml,加标回收率为 95.14%～102.87%。     

微生物法快速测定食品中叶酸含量范围

本实验旨在提出一种使用鼠李糖乳杆菌(Lactobacillus casei)ATCC 7469快速估算食品中叶酸含量范围的测定方法。利用鼠李糖乳杆菌生长过程中对叶酸需求的特异性,使用一次性离心管代替玻璃试管作为培养该菌的容器,将整个培养体系从10 mL缩小到1 mL,将培养时间从24 h缩短为8~12 h。在对得到的吸光度数据简单换算后,得到待测样品叶酸含量范围,并进行方法学考察,与国标法GB 5009.211-2014进行对比,判断其是否具有可行性。结果表明,本实验室条件下,该方法的检出限范围为0.4~0.8 μg/100 g,线性范围为0.01~0.08 ng,回收率范围为82.1%~108.0%。本方法检出限范围可估算出叶酸含量下限范围,线性区间范围可估算出叶酸含量上限范围。相对于国标方法需要2~3 d时间测定,本方法只需1 d时间即可得到叶酸含量范围,其步骤简洁且节约试剂材料。     

固液混装罐头食品的传热规律

<正> 一 前言 罐头食品的加热曲线有两种类型;简单型加热曲线和转折型加热曲线(Ball,1957;8tumbo,1973)。简单型加热曲线是由初始曲线部分和一条半对数直线组成,转折型加热曲线则是由初始曲线部分和一条以上的半对数直线组成。一般认为传导加热食品和对流加热食品呈现简单型加热曲线,传导和对流混合加热食品呈现转折型加热曲线,呈现转折型加热曲线的固液混装食品常常是由于在加热过程中食品中淀粉或其它增稠剂析出,汤汁粘度增     

食品加工业中菠萝蛋白酶的热稳定性

运用动力学的方法研究了菠萝蛋白酶的热稳定性，发现某些多羟基、多羟基化合物能明星延长菠萝蛋白酶在较高温度下的半寿期。这些物质无毒无害，能安全有效的提高食品加工业中菠萝蛋白酶的贮藏期和使用期。     

Thermal Destruction of Immunoglobulin A, Lactoferrin, Thiamin and Folic Acid in Human Milk

Kinetic parameters for thermal destruction of immunoglobulin A (IgA), lactoferrin, thiamin and folic acid in human milk were determined. Degradation proceeded following first order reaction kinetics. The times for 90% degradation (D value) at 60°C were, in seconds, 4.9 × 10⁴ (68°C C 78°C) for IgA; 2.4 × 10³ (58°C 70°C) for lactoferrin; 7.7 × 10⁵ (95°C C 110°C) for thiamin and 1.9 × 10⁴ (62°C C 78°C) for folic acid based on inactivation data at four constant temperatures between the range indicated. Z values (temperature change to alter degradation rate by a factor of 10) were 5.5°C, 4.7°C, 28.4°C, and 6.4°C for IgA, lactoferrin, thiamin and folic acid, respectively.     

叶酸及其应用

本文对叶酸的化学结构、理化特性、来源、吸收、需要量等作了介绍,同时对叶酸的提取工艺与检测方法作了详细说明、并展望叶酸的应用前景。     

Free Amino Acid Stability in Reducing Sugar Systems

Solutions of free amino acids were sterilized in different carbohydrate mixtures, at different pH values, and both browning and free amino acid content monitored at different storage temperatures. Results showed the expected behavior of a Maillard process, (e.g., increasing reaction rate with increases in pH, temperature and reducing sugar content). However, only three (tryptophan, histidine and lysine) of the amino acids tested (nine essential + taurine) were notably affected, even under stringent conditions (50°C storage, glucose containing solution at pH 7.5). Thus many free amino acids could probably be added to most food matrices without Maillard reactions affecting overall protein quality.