HPLC Determination of Lactulose in Heat Treated Milk

Lactulose (4-O-β-d-galactopyranosyl-d-fructose), formed from lactose (4-O-β-d-galactopyranosyl-d-glucose) by the Lobry de Bruyn–Alberda van Ekenstein rearrangement during severe heat treatments, is considered a useful indicator of heat-induced modifications in milk. Its chromatographic determination in milk is particularly troublesome due to the concomitant presence of a lactose amount two orders of magnitude larger than the lactulose amount and to a similar retention time of the two compounds. In this work, four HPLC methods have been compared with the aim to develop a more accurate analytical procedure to determine lactulose in milk, together with lactose. The developed method is based on a Carrez precipitation followed by a HPLC separation on two in-series amino-based columns, using CH₃CN:H₂O 75:25 (v:v) as the mobile phase at 1 ml/min flow rate and a refractive index as the detector. The linearity test for the quantitation of lactulose has been carried out over the range 0.060–1.006 mg/ml, the limit of detection, is 0.013 mg/ml (256 ng injected) and the limit of quantitation is 0.028 mg/ml (556 ng injected). The proposed method, simple, cheap and time-saving, allows an accurate lactulose–lactose separation, with conventional HPLC equipment.     

乳糖异构生产乳果糖的条件优化

首先对乳糖异构生产乳果糖的异构剂进行筛选,选出最佳异构剂为亚磷酸氢二钠,然后对异构条件进行优化,得出乳糖异构生产乳果糖最佳条件为:异构剂加量为2.0%,反应时间为3 h,反应温度为110℃,乳糖浓度为70%,在上述最佳条件下得到异构混合液中乳果糖含量为56.84%。     

应用高效液相色谱快速测定奶粉中的乳糖,蔗糖,葡萄糖

讨论了应用高效液相色谱（ＨＰＬＣ）对奶粉及调制奶粉中的乳糖,蔗糖,葡萄糖的一种快速测定方法。样品经简单的前处理后由Ｃａｒｂｏｈｙｄｒａｔｅ Ａｎａｌｙｓｉｓ柱分离,流动相为乙腈／水,示差折光检测,奶粉中乳糖,蔗糖,葡萄糖完全分离并定量测定。方法简便,快速,结果令人满意。     

Multivariate Classification of UHT Milk as to the Presence of Lactose Using Benchtop and Portable NIR Spectrometers

Lactose hydrolyzed milk was developed in the 1970s to serve individuals with lactose intolerance. This demand for lactose-free products by lactose-intolerant consumers has created a market segment for this food whose quality control has to be guaranteed. In order to assess milk samples for lactose content, this work proposes an analytical methodology to classify regular and lactose-free ultra high temperature (UHT) milks using multivariate classification methods and NIR spectra obtained in FT-NIR and ultra-compact NIR spectrometers, aiming at field analysis. For this, 71 samples were purchased; 41 were lactose-free UHT milk and 30 regular UHT milk. Diffuse transflectance spectra were obtained by FT-NIR (833 to 2500 nm, 4 cm^?1 of resolution and mean of 16 scans), and by ultra-compact NIR (908 to 1676 nm, with 12.5 nm of resolution and mean of 50 scans). The classification models were obtained by PLS-DA and LDA techniques with robust variables selection by SPA and GA, evaluating different spectral pre-processing (MSC, SNV, and derivatives). The three models developed (PLS-DA, GA-LDA, and SPA-LDA) with benchtop equipment spectra correctly classified all samples with sensitivity and specificity of 100%. For the portable equipment spectra, PLS-DA and GA-LDA models obtained sensitivity and specificity of 100%. The SPA-LDA model, however, presented sensitivity and specificity of 80 and 100%, respectively. These results indicate that methodologies using NIR equipment, especially the ultra-compact NIR, with multivariate classification techniques are feasible in discrimination between regular and lactose-free milk in the field, thus enabling a quick and precise analysis.     

Determination of Lactose and Lactose Hydrolysis in Milk Using Cerium(IV)

Lactose and lactose hydrolysis in milk were determined using a novel method involving a measurement of the time for 0.39M Cerium(IV) [Ce(IV)] in 0.5M nitric acid to be reduced to Cerium(III) [Ce(III)] after an initial precipitation of milk protein and fat. The time for the absotbance at 445 nm to decrease to 0.4 could be directly correlated with standard curves to determine either the amount of lactose or the degree of lactose hydrolysis. This Ce(IV) oxidation method was rapid (15 min) and exhibited good agreement with infrared methods of determining lactose and enzymatic methods of determining percentage lactose hydrolysis. Recoveries of lactose found using the Ce(IV) oxidation method from a number of milk samples containing different amounts of fat were comparable to recoveries using the infrared method of lactose determination.     

低乳糖牛奶褐变抑制剂的筛选

利用正交实验方法,以5-HMF的含量为指标,对低乳糖牛奶褐变抑制剂A、B、C、D进行优化配比的研究.直观分析、因素指标分析的结果表明:A、B、C和D四种褐变抑制剂,对低乳糖牛奶褐变抑制效应依次为:C＞B＞D＞A.四种褐变抑制剂的最优化组合为A0.01%、B 0.02%、C 0.02%、D 0.02%.该组合的褐变抑制剂使低乳糖牛奶产品中的5-HMF的含量降到0.63μg/mL,抑制率达到59.5%.     

Fractionation of Nonfat Dry Milk Powder into Protein and Lactose Products

Five processes were used to fractionate low heat NDM into a number of products including crude casein, three types of lactalbumin, crude lactose, United States Pharmacopeia-grade lactose, and a partially deproteinated whey product. Regular lactalbumin and crude lactose were produced by process 1 with a total recovery of 91% of starting NDM solids including those obtained from the casein fraction. Process 2 led to the production of both high and low ash lactalbumin and crude lactose, but the total solids recovery was about 10% lower than process 1 due to extra material handling. Both Processes 3 and 4 allowed for the crystallization of crude lactose from condensed whey containing the full protein complement. Process 4 was similar to process 3 except provision was made to return the mother liquor from the United States pharmacopeia lactose preparation back to the starting casein whey; this increased the solids recovery from 91 to 96%. The fifth process was used to purify the crude lactose of processes 1 to 4 for the preparation of United States Pharmacopeia grade lactose.     

低乳糖芒果风味发酵乳制作工艺研究

以生牛乳、芒果泥为原料,通过试验对低乳糖芒果风味发酵乳产品配方及乳化稳定剂的复配方案进行了研究。结果表明:低乳糖芒果风味发酵乳最优配方为白砂糖8.0%、乳清蛋白粉1.0%、芒果泥5.0%、芒果香精0.04%、乳糖酶0.025%;产品最佳稳定剂为羟丙基二淀粉磷酸酯0.4%、明胶0.15%、琼脂0.1%。在该配方及稳定体组合条件下,可获得口感优良,风味合适,货架期质量稳定的低乳糖芒果风味发酵乳。     

Production and Characterization of an Enzymatic Hydrolysate of Skim Milk Lactose and Proteins

Enzymatic hydrolysis of skim milk lactose and proteins was investigated in a batch reactor; the final aim is to produce a predigested dietary product. The use of yeast β-galactosidase, a vegetable protease, a fungal protease, and a bacterial protease was investigated. Sequential and simultaneous lactose and protein hydrolysis were studied in order to diminish incubation times. In the lactose hydrolysis, 90% conversion was obtained after 4 hr using reconstituted spray-dried skim milk, and after 3 hr using fluid pasteurized skim milk. In the simultaneous hydrolysis, 82% lactose hydrolysis and a substantial peptide hydrolysis with 80% of material smaller than 5,000 molecular weight (and high in small peptides) was obtained after 5 hr. This was adequate for the preparation of a specialized dietary product to be used in enteral hyperfeeding.     

Comparison of High Performance Liquid Chromatography and Enzymatic Method for the Measurement of Lactose in Milk

A high performance liquid chromatographic (HPLC) procedure was compared with an enzymatic method for the measurement of lactose in milk. A new rapid HPLC sample preparation technique was used for precipitating milk proteins with 2-propanol. Results indicated that lactose detected in milk (expressed as percentage) was consistently lower with the enzymatic method than the HPLC procedure. Mean difference between the two methods was 0.15% with a range of 0.04 to 0.51. Coefficient of variability for the HPLC and enzymatic methods were 1.02 and 2.75, respectively. Recovery of added lactose in milk by HPLC was 100.3% for whole milk, 97.1% for low fat milk, and 99.5% for skim milk.     

低乳糖牛奶水解率的快速测定方法研究

本文以Willstarter Schudel的醛糖测定方法为依据,从乳糖水解反应的本质出发,提出并建立了一套快速测定低乳糖牛奶水解率的新方法。实验测定结果表明,该方法具有使用方便和操作简单以及快捷准确等特点。     

Alpha-Tomatine Purification and Quantification in Tomatoes by HPLC

A high-performance liquid chromatographic procedure was developed for purification and quantification of α-tomatine from tomatoes. A crude preparation of glycoalkaloids from tomato fruits was fractionated on a column of Nucleosil NH₂ (10 μm), and eluted with a mixture of tetrahydrofuran/acetonitrile/0.02 M KH₂PO₄ (50/30/20, v/v/v). The column effluent was monitored at 205 run. Total analysis of α-tomatine was completed in < 10 min. It was present at highest concentrations in fruit at the mature-green stage but its level decreased rapidly as fruit approached full maturity. The technique should be useful for analysis of α-tomatine in biological samples.     

Application and improvement of aflatoxin analysis in foods using a multifunctional column and HPLC

In an earlier report, we developed a rapid, sensitive and clean method consisting of non-chloroform extraction, clean-up on a commercial multifunctional cartridge column and HPLC with fluorescence detection for the analyses of aflatoxins. In this report, we applied this method to analyze aflatoxins in nuts, giant corn, cereals, spice and black teas. The method was effective for macadamia nuts, walnuts, hazelnuts, brazil nuts, giant corn, rice, wheat and buckwheat, and the recoveries of aflatoxins B1, B2, G1 and G2 spiked in them at the level of 10 ng/g were 85-106%. However, in the chromatograms of spices and black tea, many background peaks were observed. Therefore, we added a purification step with an affinity column to the clean-up of these samples with the multifunctional cartridge column. After the additional purification, most of the background peaks were gone. The recoveries of aflatoxins B1, B2 and G1 spiked at the level of 10 ng/g were 71-112% except for the case of B2 in white pepper (48%). The recoveries of G2 were 49-95%.     

High Performance Liquid Chromatographic Determination of Lactose, Glucose, and Galactose in Lactose-Reduced Milk

A simple, rapid high performance liquid chromatographic (HPLC) method was developed to simultaneously determine lactose, glucose, and galactose in lactose-reduced milk. The sugars were separated on a Bio-Rad HPX-87C fixed ion resin column in the Ca⁺⁺ form, using water as the mobile phase and a flow rate of 0.6 ml/min. The column was heated to 80°C, and the sugars were detected using refractive index. Lactose-reduced milk was analyzed for lactose and its hydrolysis products. Milk samples were rapidly prepared for injection by precipitating protein and fat with acetonitrile. Retention times for lactose, glucose, and galactose were 9.3, 10.8, and 12.3 min, respectively. Transgalactosylation products were estimated to be at least 7.8%.     

HPLC测定乳制品中的甲醛含量

针对奶糖及奶制品的甲醛残留问题,建立了一种灵敏、快速和有效的HPLC-UV检测乳制品中甲醛的方法。牛奶和奶粉样品中甲醛经三氯乙酸(TCA)提取,奶糖另添加乙酸锌和亚铁氰化钾进行辅助沉淀,用1mg/mL2,4-二硝基苯肼(DNPH),在60℃条件下衍生30min后,用HPLC-UV分离测定,外标法定量。该方法对3种奶制品平均加标回收率在95%以上,日内精密度和日间精密度在5%以下,甲醛含量在0.03～4.00μg/mL范围内呈良好的线性关系,检出限和定量限分别为0.03μg/mL和0.10μg/mL,对常见醛类和醇类有较好的抗干扰性。该方法具有操作简单,准确性高,稳定性好,抗干扰性强的特点,是一种测定乳制品中甲醛的有效分析技术。     

奶粉中雌二醇的高效液相色谱法检测

建立高效液相色谱法检测奶粉中雌二醇的方法。优化实验条件,采用紫外检测器,检测波长为230 nm。方法对奶粉中雌二醇的检出限为5 ng/g。在低、中、高3个加标水平下,奶粉中雌二醇的回收率在81.0%～91.9%的范围内,相对标准偏差在3.71%～4.74%范围内(n=4)。该法可有效监控奶粉中雌二醇的残留量。     

高效液相色谱法测定牛奶中林可霉素的残留量

研究建立牛奶中林可霉素残留量的高效液相色谱测定方法。样品用水相提取,离心分离,经C18固相萃取柱净化,在210nm波长下用二极管矩阵检测器检测。色谱柱为Agilent ZORBOX SBC18柱(4.6×250mm,5μm),以0.05mol/L硼砂溶液(用磷酸调节pH6.0)-甲醇(55:45,V/V)为流动相,流速1.0ml/min。林可霉素浓度在1.0～10.0μg/g范围内与峰面积呈良好的线性关系,平均回收率为82.9%～93.1%,变异系数为1.45%～4.58%,最低检测限为0.5μg/ml。本方法简便、快速、准确。     

鲜牛乳中乳杆菌的检测及脂肪酶、蛋白酶测定方法的研究

对鲜牛乳中乳杆菌、脂肪酶及蛋白酶的检测方法进行了初步研究 ,并以改良MRS培养基检测了 4个鲜牛乳样品中的乳杆菌数目 ,以改进的脂肪酶活力分析法测定了 4个样品的脂肪酶活力及蛋白酶活力 ,取得了较满意的结果