Determination Of Lactose In Milk Research Articles

Spectrophotometric Determination of Lactose in Milk with PdCl2

The spectrophotometric method (using PdCl2) for determination of hexoses was applied to samples of milk to determine the lactose content with previous estimation of the conditions for quantitative determination. The method was carried out on milk serum samples, obtained according to four different procedures, in accordance with literature data, to identify the one most suitable to application of the PdCl2 method. The experiments were undertaken on milk serum samples of different pH values, temperatures, and storage times. The possibility of application of the palladometric method was ascertained by statistical treatment of these results using the reference Luff−Schoorl method. The results of the investigations show that the first procedure (using Fehling I) for obtaining milk serum was the most suitable one for applying the PdCl2 spectrophotometric method and that the pH value, temperature, and time of storage did not influence the method and its ability to accurately determine the lactose content. Keywor...

High performance liquid chromatographic analysis of lactose-hydrolysed milk

The application of high performance liquid chromatography to the determination of lactose in milk has been investigated. Both ion-exchange and partition modes were employed, and for unmodified milk, returned equivalent values. However, for milk subjected to the action of β-galactosidases, it has been confirmed that at least one significant transferase disaccharide intermediate is chromatographically unresolved during the former resin-based mode, resulting in an erroneously high lactose estimation. Since such transferase oligosaccharides are adequately separated during partition chromatography on amine-bonded silica, it is recommended that resin-based cation-exchange columns are inappropriate for the estimation of lactose in such lactose-reduced milks.

Enzymic flow injection determination of lactose in milk with on-line dialysis

Milk samples were analysed to determine their lactose content by using flow injection (FI) and incorporating immobilized β-galactosidase and glucose oxidase—mutarotase bioreactors. A dialysis unit was placed after the injection valve to avoid the need for sample pre-treatment. The methodology was based on the chemiluminescence determination of hydrogen peroxide produced by the enzymic reactions, with use of an alkaline reagent containing luminol and hexacyanoferrate(III). Linearity was observed over the concentration range 20–200 mmol l–1 with lactose as standard (r= 0.9995), and 20 milk samples h–1 could be analysed. Comparisons were made with high-performance liquid chromatography and chloramine-T methods. The enzymic FI method afforded a low relative standard deviation (0.49%) and was free from interference. Additionally, the proposed method was simple and did not require precipitation of proteins, or filtration or centrifugation. The enzymic reactors were stable for 6 months when used daily at optimum pH.

Improved spectrophotometric determination of lactose in milk using flow-injection analysis

Milk samples were analysed spectrophotometrically for their lactose content using flow-injection analysis. The methodology is based on the carmine colour that develops (λ Max = 540 nm) when lactose reacts with alkaline methylamine (pH 12.7). Lactose concentrations as low as 0.6 mg ml −1 can be readily detected and up to 40 samples can be analysed per hour. Excellent correlations ( r > 0.999) are obtained when the results are compared with the batch and liquid chromatographic methods for lactose determination. Interference from maltose, if present, should be eliminated by pretreatment with maltase.

Amperometric determination of lactose in human and cow's milk using a flow‐injection system with some immobilized enzyme reactors

AbstractA bioelectrochemical flow‐injection system is proposed for the determination of lactose in milk from humans and cows. The system includes an amperometric flow‐through platinum electrode to measure hydrogen peroxide, which was enzymatically generated by injecting a 10‐μL sample into the packed‐bed reactors of immobilized β‐galactosidase and glucose oxidase that are incorporated in series in the flow line. Because the presence of glucose interfered with the measurement of lactose, a precolumn packed with coimmobilized glucose oxidase and catalase was positioned just before the two immobilized enzyme reactors to remove the glucose from the milk. The peak current was linearly related to the lactose concentration between 0.01 and 2.0 mM. The determinations of lactose in milk could be performed at a rate of 60 samples/h with satisfactory precision (less than 0.8% RSD) and no pretreatment except for the sample dilution.

A simple and rapid colorimetric method for lactose determination in milk

A simple and rapid technique for the estimation of lactose in fluid milk and whey, utilizing trichloroacetic acid (TCA) as a precipitating agent, is outlined. The color development is based on the reaction of picric acid with lactose in the presence of phenol, sodium hydroxide and sodium bisulfate. This method can be completed within 10 min. There is no significant difference ( p ≤ 0·05) between the results obtained by the proposed method and those obtained by the IDF method.

Determination of Lactose by an Enzymatic Method

The general methodology used for the determination of lactose in milk is considered, namely, polarimetry, gravimetry, infrared, colorimetry, gas-liquid chromatography, and high pressure liquid chromatography. The criteria for selecting an ideal analytical method followed by the relevance of most of these criteria in enzymatic methodology are discussed. The principle of the Boehringer-Mannheim method is presented, i.e., lactose is hydrolyzed to glucose and β-galactose in the presence of β-galactosidase and water. β-Galactose is then oxidized by nicotinamide-adenine dinucleotide to galactonic acid in the presence of β-galactose dehydrogenase. The amount of reduced nicotinamide-adenine dinucleotide formed is stoichiometric with the amount of lactose and is measured at 340nm in a spectrophotometer possessing a slit width of ⩽10nm. The results of a recent Association of Official Analytical Chemists collaborative study of the B-M method are presented. From the overall mean of results on all samples, determinations by the enzymatic method averaged .49% lower than by the Association of Official Analytical Chemists gravimetric method. Standard deviations were similar for three sets of blind duplicates, which ranged between 3.67 and 4.55% lactose. F-Values revealed that variations between means obtained by laboratories differed significantly as compared with variations within laboratory means. The method has received Official First Action recognition by Association of Official Analytical Chemists.

Determination of Lactose in Milk: Comparison of Methods

A new enzymatic method based on the spectrophotometric measurement of reduced NAD+ (beta-nicotinamide-adenine dinucleotide) at 340 nm has been evaluated by comparing it with the AOAC copper reduction method. Ten samples of milk containing various levels of lactose were analyzed in duplicate by the enzymatic method, and 5 samples were analyzed by the copper reduction method. Statistical analysis using a factorial design revealed no statistical significance between results obtained by the 2 methods; recoveries were comparable, 97% or greater for all except one sample. There was no relationship between amount of lactose added and percent recovered.

高速液体クロマトグラフィーによる牛乳中の乳糖の定量

高速液体クロマトグラフィーによる牛乳中の乳糖の定量

Study of the high-performance liquid chromatographic separation of reducing sugars, applied to the determination of lactose in milk

The loss of reducing sugars by formation of Schiff bases on amino-bonded silica or on dynamically coated amino-silica columns was investigated at two column temperatures. Depending on the type, age and temperature of the column, these losses were in the range of 0–100%. A dimethylamino-bonded silica column did not cause loss of reducing sugars, but the retention of sugars was too weak to allow separation. The analysis of reducing sugars can be carried out on diol-modified silica with diisopropylethylamine in the eluent to enhance mutarotation. It is also possible to use a cation-exchange resin (Ca 2+) column, equipped with a pre-column packed with a mixed-bed ion-exchanger to remove interfering salts and acids. In combination with an acetate-acetonitrile sample clean-up, this method results in coefficients of variation of less than 1% for the determination of lactose in skim-milk.

A direct enzymatic lactose assay using cellobiose-(lactose-)dehydrogenase from sporotrichum thermophile

Advantage was taken of the high specificity of the cellobiose dehydrogenase (EC 1.1. 99), produced by the fungusSporotrichum (Chrysosporium) thermophile during growth on cellulose, for cellobiose and lactose to devise a direct enzymatic procedure for the determination of lactose in milk and milk products. The assay is based on the colorimetric measurement of the reduction of dichlorophenol indophenol concomitant with the oxidation of lactose to lactobionic acid.

High Performance Liquid Chromatographic Determination of Lactose in Milk

A rapid and simple high performance liquid chromatographic method for the determination of lactose in milk was developed. Samples were diluted with 0.5% perchloric acid and centrifuged, and an aliquot of the supernate was mixed with acetonitrile. Lactose was separated on a 10 micron particle-size silica column with aqueous acetonitrile as the mobile phase. The recovery of lactose from whole, skim, and chocolate milk averaged 99.2, 101.1, and 100.4%, respectively. Coefficients of variation for routinely performed duplicate determinations are between 1.0 and 1.5%.

The determination of lactose in milk: a comparison of gas-liquid chromatography with the Lane & Eynon method

The determination of lactose in milk: a comparison of gas-liquid chromatography with the Lane & Eynon method

An enzymic method for the determination of lactose in milk including human milk.

An enzymic method is described for the determination of lactose in milk. The method is based on the determination of free lactose by its hydrolysis with β-galactosidase, the glucose produced being determined by the hexokinase method. The determination is free from interference by other sugars. The method is more accurate and reliable than other methods currently in use. Further, it is applicable to milk samples available only in small amounts.

Comparison of Japanese Official Lane-Eynon Method for the Determination of Lactose in Milk with Chloramine-T Method

Lane-Eynon volumetric method, the Japanese official method for the determination of iactose in milk, was compared with Chloramine-T method, designated as international standard by IDF, and Munson-Walker gravimetric method.Chloramine-T and Munson-Walker method gave 0.15% and 0.23% higher lactose values respectively than Lane-Eynon method in the case of market milk. The differences in resuits by the three methods were significant at 1% level of probability. The standard deviations of the three methods were 0.057 for Lane-Eynon, 0.058 for Chloramine-T, and 0.043 for Munson-Walker method.

A simple micro colorimetric method for the determination of lactose in milk

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Method for Routine Determination of Lactose in Milk

Summary Recoveries of added lactose in milk samples were significantly high using the polarimetric method of Grimbleby (2). Adjustments were made to the formula used for the calculations when it was found that lactose had a slightly higher than normal specific rotation in the protein-precipitating reagent, and that the serum pH was 0.2 unit lower than that found by Grimbleby. Factors used in correcting for fat and protein precipitate volumes were both increased, the former on theoretical grounds and the latter because of the lower pH, with the result that the recalculated average recovery was not significantly different from 100%. Filtering required 2 to 3 1 2 hr, but it could be shortened to less than 1hr with no loss of accuracy by using a more dilute reagent containing slightly more phosphotungstic acid. Precipitate volumes were determined for 72 composite herd milk samples and, on the basis of these results, a new protein factor was obtained not appreciably different from the adjusted factor calculated for the Grimbleby method. Fat and protein factors were sufficiently similar to be combined. A modified procedure, using the more dilute reagent, and employing a simplified formula for the calculation of lactose, is suggested for routine analysis. Standard deviation between duplicates for the determination was±0.024% lactose. A mercuric chloride preservative could be used without affecting the results.

有機分析 (第27報)

A rapid determination of lactose in milk and powdered milk, and of lactose and sucrose in condensed milk, using 3, 6-dinitrophthalic acid was established. Diluted solution of milk or its products is deproteinized by heating for a short time with basic zinc carbonate and colored by 3, 6-dinitrophthalic acid in the previously established method for reducing sugars. The lactose content is read from the calibration curve. The sucrose in condensed milk is inverted and colored by the same reagent.To deproteinize the solution, the sample is diluted with water to 1% solution for milk, 0.1% solution for powdered milk, and 0.25% solution for condensed milk. Two cc. of this solution is diluted with 3cc. of water, deproteinized with about 150mg. of basic zinc carbonate, and diluted to 20cc., except for condensed milk, which solution is diluted to 100cc. The lactose is determined by developing 2cc. of the diluted solution.For the determination of sucrose in condensed milk, 2cc. of 10% solution is deproteinized with about 300mg. of basic zinc carbonate, hydrolysed with hydrochloric acid, neutralized, and diluted to 2000cc. Two cc. of this solution is developed and total sugar is read from the calibration curve of glucose. Lactose gives the coefficient of 0.785 when it is read on the curve of glucose and sucrose is calculated from the following equation:Sucrose(%)={total sugar(%)-lactose(%)×0.785}×0.95This method of determination is simple and rapid for treating a larger number of sample, and the determined value agrees with the macro methods within the largest deviation of ±3%.

A rapid method for the determination of lactose in milk and cheese

AbstractA colorimetric method is described for the determination of lactose in milk and cheese. It appears to be both speedy and accurate, as is evidenced by the facts that a lactose determination in milk takes about 15 min. to complete, while suitably designed experiments indicate a satisfactory degree of recovery of lactose. As illustrations of the potential uses of the method, figures are given for the lactose content of different types of cheese at different stages of maturity and for milk undergoing the process of souring.

630. The determination of lactose in milk

One of the most important stages governing the accuracy of lactose determinations in milk is the preparation of the protein-free serum. Factors influencing the lactose content of the serum are: (1) the complete precipitation of protein, (2) the formation of lactose-protein complexes, and (3) the degree of hydration of the protein coagulum.Experiments are described which show how these factors are influenced by different clearing agents operating at different pH values. On the basis of the results obtained a reagent containing zinc acetate, phosphotungstic acid and acetic acid is suggested; it reduces to a minimum any errors introduced by the above factors.