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Biomedical subjects

D H Kleyn

Publications and source records attributed to D H Kleyn.

12 recordsLinked to original sources
PubMed1985

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 beta-galactose in the presence of beta-galactosidase and water. beta-Galactose is then oxidized by nicotinamide-adenine dinucleotide to galactonic acid in the presence of beta-galactose dehydrogenase. The amount of reduced nicotinamide-adenine dinucleotide formed is stoichiometric with the amount of lactose and is measured at 340 nm in a spectrophotometer possessing a slit width of less than or equal to 10 nm. 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.

Animals↗
PubMed1983

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.

Animals↗
PubMed1978

Rapid screening method for alkaline phosphatase activity in cheese: collaborative study.

The method developed for developed for determining alkaline phosphatase activity in cheese, in which phenolphthalein monophosphate is used as the substrate, was collaboratively studied. A 7.5% butanol extract of cheese is reacted with phenolphthalein monophosphate; phenolphthalein is released and yields a red solution that is compared visually with a standard (s) prepared from the same extract. Seven collaborators analyzed 8 samples of cheese, in duplicate, by the screening method and Scharer I method. Of the 208 observations returned, only 4 were incorrect. The alkaline phosphatase method has been adopted as official first action.

Alkaline Phosphatase↗
PubMed1977

Rapid determination of alkaline phosphatase reactivation.

A study was conducted to determine the feasibility of using the qualitative screening method specifying phenolphthalein monophosphate for differentiating reactivated and residual alkaline phosphatase activity. The relative increase in activity of the enzyme in the presence of MgCl2 serves to distinguish reactivated and residual alkaline phosphatase activity. Ten samples each of pasteurized (172 degrees F for 24 sec), sterilized (about 300 degrees F for a minimum of 2 sec) half-and-half and heavy cream were analyzed. Most samples yielded negative results initially but demonstrated activity after incubation 1 hr at 34 degrees C. The average values in terms of + marks, for the half and half and heavy cream in samples without MgCl2 were less than 1 and 2.4, respectively; for samples treated with MgCl2, the values were 2.18 and 4.6, respectively, indicating reactivated phosphatase activity. In samples containing various levels of raw milk, the activity observed in the diluted, Mg2+-containing samples was less than in the undiluted samples containing no Mg, indicating residual phosphatase activity.

Alkaline Phosphatase↗
PubMed1977

Rapid determination of alkaline phosphatase activity in cheese.

A visual screening method specifying phenolphthalein monophosphate as the substrate was applied to cheese by analyzing the extract obtained with 7.5% butanol. In the extraction step, all of the alcohol was added at one time, and the mixture was filtered after mixing. Analysis of 10 samples of various types of cheese resulted in data identical to that obtained by the Scharer rapid method. Quantitative data obtained by dialysis of the butanol filtrate and spectrophotometric measurement of the phenolphthalein compared favorably (r = 0.96) with data obtained by the Scharer spectrophotometric method on 13 samples of cheese.

Alkaline Phosphatase↗
PubMed1976

Qualitative and quantitative changes in carbohydrates during the manufacture of yogurt.

The average lactose content of yogurt mix was 8.50% and decreased during fermentation to 5.75%. The initial galactose content of the mix was a trace but increased to 1.20% during fermentation. Glucose content remained a trace throughout fermentation. Several brands of commercial yogurt were purchased from local supermarkets and analyzed for carbohydrate content. Lactose ranged from 3.31 to 4.74%, galactose varied from 1.48 to 2.50%, and glucose was only a trace in all samples. Several samples of buttermilk also exhibited the near absence of glucose.

Carbohydrates↗
PubMed1976

Influence of viable yogurt microflora on digestion of lactose by the rat.

Laboratory rats were fed experimental diets including yogurt, pasteurized yogurt, and simulated yogurt with sucrose or lactose for 7 days followed by a single experimental meal of yogurt, pasteurized yogurt, or simulated yogurt. Assays of blood galactose demonstrated that animals fed natural yogurt containing the viable culture microflora were able to absorb galactose more efficiently. Intestinal lactase activity of yogurt-fed animals was greater than in animals fed other experimental diets including pasteurized yogurt. Gastrointestinal survival of culture organisms was demonstrated in vivo up to 3 h after feeding, and thus, the viable cells resulted in more efficient hydrolysis which favored lactose digestion in natural yogurt.

Animals↗
PubMedDate not supplied

Determination of fat in raw and processed milks by the Gerber method: collaborative study.

The Gerber method is used worldwide as a simple and rapid method for determining fat in raw and processed milks. However, the volume of the test portion used in the method has not been internationally agreed upon. A collaborative study was conducted to evaluate performance of the Gerber method using either a weighed test portion (11.13 g) or by a 10.77 mL test portion delivered by pipet. For each method, laboratories received 10 test samples: 5 raw and 5 pasteurized homogenized milks, 2 of which were blind duplicate pairs. Eleven and 10 laboratories participated in the evaluation of aliquot addition by weight and pipet, respectively. Mojonnier ether extraction (Method 989.05) was used as the reference method. Interlaboratory study statistics were similar between methods of test portion addition and between raw and processed materials; therefore, summary interlaboratory study statistics were pooled. The fat content of milk samples ranged from 0.96 to 5.48%. Absolute reproducibility and repeatability were not affected by fat level, and pooled statistical performance (invalid and outlier data removed) was (g fat/100 g milk) s(r) = 0.026, s(R) = 0.047, r = 0.074, and R = 0.132. Relative standard deviations increased with decreasing fat content, and were summarized by fat level: 1-2% fat milk, mean = 1.437, RSD(r) = 1.809%, RSD(R) = 3.271%; 2-6% fat milk, mean = 4.156, RSD(r) = 0.626%, RSD(R) = 1.131%. Compared with ether extraction, test results by the Gerber method were slightly lower (0.02% fat) using a weighed test portion and significantly lower (0.06% fat) using a 10.77 mL volume addition by pipet. A trend toward underestimating fat content at lower fat concentrations (1-2% fat) was observed with the weighed test portion but not when a pipet was used. The Associate Referee recommends that the Gerber method using a weighed test portion be adopted as First Action with applicability limited to whole milk.

Animals↗
PubMedDate not supplied

Determination of fat in raw milk: comparison of mojonnier (ether extraction) and Gerber method.

Results are compared for the approved Gerber method that specifies a TC 11.07 mL pipet and 2 modifications that specify a TC 10.77 mL pipet or a weighed 11.125 g sample of milk rather than a pipetted sample. All results were also compared with results obtained with the Mojonnier method for determining the fat content of raw milk. The standard deviation is somewhat lower for the Mojonnier method than for any of the Gerber methods; among the Gerber methods, the standard deviations were lower for the TC 10.77 mL and 11.125 g modifications. It is recommended that one of these modifications replace the current specified TC 11.07 mL pipet method.

Animals↗
PubMedDate not supplied

Enzymatic-ultraviolet method for measuring lactose in milk: collaborative study.

Collaborators in 8 dairy and food industry laboratories performed one lactose determination on each of 8 unknown samples of milk, lowfat milk, or skim milk, as 3 pairs of blind duplicates. Two known samples were provided to gain experience prior to analysis of the unknown samples. All of the above samples were also analyzed for lactose content by the official AOAC gravimetric method (16.507) by a commercial laboratory. From the overall mean of results on all samples, determinations by the enzymatic method averaged 0.49% lower than by the AOAC method. This difference was significant by the t-test (P = 0.05), which indicated a lack of agreement between the compared methods in determining lactose content. Standard deviations were similar for the 3 sets of blind duplicates which ranged between 3.67 and 4.55% lactose content. F-values revealed that variations between means obtained by laboratories differed significantly as compared with variations within laboratory means. The method has been adopted official first action.

Animals↗