Determination of lactate dehydrogenase (LDH) activity in milk by a fluorometric assay

Indigenous L-lactate dehydrogenase (LDH) in milk originates mainly from somatic cells, leucocytes and invading microorganisms. Its activity may be used for detection of mastitis. However, existing methods to measure LDH activity in milk both need pretreatment of the samples and still suffer from methodological problems. The present paper describes a fast, reliable method for determination of LDH activity, suitable for milk samples. The method is based on fluorometric determination of enzyme kinetics when L-lactate is converted to pyruvate. The assay uses raw milk without pretreatment and the method is easily adjustable to large-scale analyses on micro assay plates. Detection is based on (straight line) linear response within 4–7 min of initiation of the reaction. A substrate concentration of 35 mM in the reaction mixture was considered to be optimal for the assay. Intra plate assay precision was approx. 6% (CV) and the inter plate precision approx. 10%. Known inhibitors of LDH activity (oxidative direction), i.e., oxalic acid, oxamate, and pyruvate, were tested in different concentrations in order to verify the specificity of the response. The detailed kinetics of samples analysed indicated that the isoenzyme composition may have differed between milk samples, and that this composition may have been altered in high activity samples.

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Simultaneous Determination of C18 Fatty Acids in Milk by GC-MS

Separations ◽

10.3390/separations8080118 ◽

2021 ◽

Vol 8 (8) ◽

pp. 118

Author(s):

Meiqing Chen ◽

Yangdong Zhang ◽

Fengen Wang ◽

Nan Zheng ◽

Jiaqi Wang

Keyword(s):

Fatty Acids ◽

High Sensitivity ◽

Raw Milk ◽

Uht Milk ◽

Milk Samples ◽

Accuracy And Precision ◽

Different Temperatures ◽

Chromatographic Resolution ◽

Commercial Milk

The determination of C18 fatty acids (FAs) is a key and difficult aspect in FA profiling, and a qualified method with good chromatographic separation and high sensitivity, as well as easy methylation, is required. A GC-MS method was established to simultaneously determine C18 FAs in milk. To simplify the methylation protocol for milk samples, besides a base-catalyzation methylation (50 °C for 20 min), the necessity of an additional acid-catalyzation was also studied using different temperatures (60 °C, 70 °C, 80 °C, and 90 °C) and durations (90 min and 150 min). The results showed that the chromatographic resolution was improved, although three co-eluted peaks existed. The base-catalyzation was sufficient, and an additional acid-catalyzation was not necessary. The proposed method was validated with good sensitivity, linearity, accuracy, and precision, and then applied in determining C18 FAs in 20 raw milk and 30 commercial milk samples. UHT milk presented a different profile of C18 FAs from raw milk and PAS milk samples, which indicated that excessive heating could change the profile. Overall, the proposed method is a high-throughput and competent approach for the determination of C18 FAs in milk, and which presents an improvement in chromatographic resolution and sensitivity, as well as a simplification of methylation.

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Determination of Viable Bacterial Populations in Raw Milk within 20 Minutes by Using a Direct Epifluorescent Filter Technique

Journal of Food Protection ◽

10.4315/0362-028x-60.7.874 ◽

1997 ◽

Vol 60 (7) ◽

pp. 874-876 ◽

Cited By ~ 5

Author(s):

CLAUDE P. CHAMPAGNE ◽

NANCY J. GARDNER ◽

JULIE FONTAINE ◽

JACQUES RICHARD

Keyword(s):

Raw Milk ◽

Plate Count ◽

Bacterial Populations ◽

Filter Technique ◽

Milk Samples ◽

Standard Plate ◽

Plate Counts ◽

Direct Epifluorescent Filter Technique ◽

Triton X

The results from a shortened procedure for the direct epifluorescent filter technique (DEFT) determination of viable bacterial populations in raw milk were compared to standard plate counts. Shortening the prefiltration trypsin-Triton X-100 incubation period from 10 to 3 min enabled the completion of the analysis within 20 min. The short DEFT method results had a correlation coefficient (r) of 0.81 with plate counts. With respect to precision, the average difference between values of duplicate plate count analyses was 0.16 log units; that of the short DEFT was 0.14 log units. The slopes of the regressions equations were less than 1, indicating that a direct correlation is not achieved. Short DEFT values were 0.17 log units higher than those of plate counts on milk samples containing less than 10,000 CFU/ml. For milk samples containing counts over 10,000 CFU/ml, short DEFT values averaged only 0.05 log units above plate count readings. Daily preparation of the stain appears unnecessary since acridine orange solutions stored for up to 2 days at 4°C did not produce results significantly (P > 0.05) different from those obtained with fresh solutions. The short DEFT method has potential for the assessment of the bacteriological quality of raw milk in tanker deliveries.

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Determination of Four Fluoroquinolones in Milk by Liquid Chromatography

Journal of AOAC International ◽

10.1093/jaoac/80.5.982 ◽

1997 ◽

Vol 80 (5) ◽

pp. 982-987 ◽

Cited By ~ 25

Author(s):

José E Roybal ◽

Allen P Pfenning ◽

Sherri B Turnipseed ◽

Calvin C Walker ◽

Jeffrey A Hurlbut

Keyword(s):

Fluorescence Detection ◽

Solid Phase ◽

Raw Milk ◽

Extraction Column ◽

Isocratic Elution ◽

Standard Curve ◽

Milk Samples ◽

Relative Standard ◽

Liquid Chromatographic

Abstract A liquid chromatographic (LC) method with fluorescence detection is presented for the analysis of 4 fluoroquinolones; enrofloxacin (ENRO), ciprofloxacin (CIPRO), sarafloxacin (SARA), and difloxacin (DIFLX) in milk. The procedure consists of extraction of milk with acidified ethanol, isolation and retention on a cation exchange solid-phase extraction column, elution with basic methanol, and LC analysis with fluorescence detection. LC analysis is performed by isocratic elution using an acetonitrile-2% acetic acid (15 + 85) mobile phase and an Inertsil phenyl column with fluorescence detection at excitation and emission wavelengths of 278 and 450 nm, respectively. A target level of 10 ppb for each of the 4 fluoroquinolones has been established for this method. Average recovery from fortified raw milk samples (5-100 ppb each) based on a 5-point standard curve calculation was 70-90%, with relative standard deviations of <15%.

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Physical and microbial qualities of raw milk collected from Bangladesh Agricultural University dairy farm and the surrounding villages

Bangladesh Journal of Veterinary Medicine ◽

10.3329/bjvm.v6i2.2339 ◽

1970 ◽

Vol 6 (2) ◽

pp. 217-221 ◽

Cited By ~ 3

Author(s):

MTG Khan ◽

MA Zinnah ◽

MP Siddique ◽

MHA Rashid ◽

MA Islam ◽

...

Keyword(s):

Microbiological Quality ◽

Dairy Farm ◽

Raw Milk ◽

Viable Count ◽

Physical Parameters ◽

Total Viable Count ◽

Coliform Count ◽

Milk Samples

The present study was undertaken with the aim of investigating the physical parameters (e.g. organoleptic and specific gravity of raw milk) and also to study the microbiological quality of raw milk (total viable count, Coliform count and Staphylococcal count) from different villages and Bangladesh Agricultural University (BAU) Dairy Farm of Mymensingh District of Bangladesh, during the period from July to November 2007. A total number of 100 raw milk samples were collected at morning and evening from BAU dairy farm and surrounding four villages of BAU campus. The organoleptic and bacteriological qualities of each sample were analyzed. The organoleptic examination included taste panel score to assess consumer's acceptance and the bacteriological analysis comprised enumeration of total viable count (TVC), total colifrom count (TCC) and total staphylococcal count (TSC) for the determination of sanitary quality. The organoleptic quality of the milk samples is more or less same except the Churkhai milk samples which had flat taste (in 16% milk sample). The average values of TVC/ml were log 5.920, 5.934, 6.007, 6.075 and 6.127 for BAU Dairy Farm, Boira, Shutiakhali, Churkahai and Paglabazar respectively; coliform count were log 2.501, 2.522, 2.550, 2.620 and 2.619 respectively; staphylococcal count were log 2.832, 2.812, 2.866, 2.931 and 2.988 respectively. So, it may be concluded that the raw milk samples of BAU Dairy Farm were superior to others collected from the selected villages which may be due to maintaining better hygienic condition. Key words: Raw milk, physical and microbial quality Â doi: 10.3329/bjvm.v6i2.2339 Bangl. J. Vet. Med. (2008). 6 (2): 217-221

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Application of a microbial sensor for determination of short-chain fatty acids in raw milk samples

European Food Research and Technology ◽

10.1007/bf01197829 ◽

1992 ◽

Vol 195 (1) ◽

pp. 1-2 ◽

Cited By ~ 8

Author(s):

Hiroyuki Ukeda ◽

Gotthold Wagner ◽

G�nther Weis ◽

Manfred Miller ◽

Henning Klostermeyer ◽

...

Keyword(s):

Fatty Acids ◽

Raw Milk ◽

Short Chain Fatty Acids ◽

Short Chain ◽

Milk Samples ◽

Microbial Sensor ◽

Chain Fatty Acids

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Energy-dispersive spectroscopy for the quantitative determination of the major chemical elements in milk

Research Society and Development ◽

10.33448/rsd-v10i10.18910 ◽

2021 ◽

Vol 10 (10) ◽

pp. e280101018910

Author(s):

Igor Lima de Paula ◽

Isis Rodrigues Toledo Renhe ◽

Rodrigo Stephani ◽

Ítalo Tuler Perrone ◽

Antônio Fernandes de Carvalho ◽

...

Keyword(s):

Quantitative Determination ◽

Chemical Elements ◽

Raw Milk ◽

Energy Dispersive ◽

Mean Values ◽

Milk Samples ◽

Application Potential ◽

Major Chemical ◽

Good Agreement

The present preliminary study aims at the rapid quantitative determination of the major chemical elements in the ashes of raw milk samples, using energy dispersive X-ray fluorescence spectrometry. The precision of the method was satisfactory (variation coefficient ≤ 5%). The mean values (in mmol·kg-1) obtained from the analysis of 32 raw milk samples showed good agreement with data from the Brazilian and international literature: K (26.1 ± 4.6), Ca (33.8 ± 3.7), P (28.4 ± 2.7), Na (21 ± 3.3) and Mg (4.7 ± 0.5). Residual Cl concentration (19.0 ± 3.3 mmol·kg-1) was lower than expected due to incineration losses. The results suggest a good application potential of the method for other dairy products.

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Incidence of Colostrum in Raw Milk

Journal of Food Protection ◽

10.4315/0362-028x-56.7.625 ◽

1993 ◽

Vol 56 (7) ◽

pp. 625-626 ◽

Cited By ~ 5

Author(s):

JERZY ZAWISTOWSKI ◽

RUFINA MACKINNON

Keyword(s):

Immunoglobulin G ◽

Raw Milk ◽

Radial Immunodiffusion ◽

Milk Samples ◽

Bovine Immunoglobulin

A survey was conducted to determine the colostrum content in raw milk from dairies in Manitoba, Canada. Colostrum was indirectly measured by the determination of bovine immunoglobulin G (IgG) using a radial immunodiffusion assay. The results showed that 360 milk samples, which accounted for 89% of the total tested samples, were contaminated with colostrum. Of these, 320 samples had IgG levels in the range of 1.0 to 1.5 mg/ml, while 38 samples had an IgG content in the range of 1.5 to 2.0 mg/ml. Two milk samples contained IgG in excess of 2 mg/ml.

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A survey on the occurrence of aflatoxin M1 in raw milk samples in Bafq and Bahabad, Iran

Journal of Food Safety and Hygiene ◽

10.18502/jfsh.v5i3.5694 ◽

2021 ◽

Author(s):

Vahid Safavizadeh ◽

Mozhgan Mojkar

Keyword(s):

Aspergillus Parasiticus ◽

Raw Milk ◽

National Standard ◽

Aflatoxin M1 ◽

Cow’S Milk ◽

Elisa Method ◽

Cow's Milk ◽

Milk Samples ◽

The City

Aflatoxins are a group of mycotoxins mostly produced by the fungi called Aspergillus flavus, Aspergillus parasiticus, and Aspergillus nomium. Aflatoxin M1 (AFM1) is the major metabolite of aflatoxin B1 and is a hepatotoxic and carcinogenic toxin. The aim of this study was to determine the level of contamination of cow's milk with aflatoxin M1 in Bafq and Bahabad. For this study, samples of raw cow's milk were collected randomly from milk collection centers around the city of Bafq and Bahabad from March to April. The determination of aflatoxin M1 levels was based on the ELISA method. Contamination was observed in 100% of milk samples. According to the results of the study, the rate of contamination with aflatoxin M1 in 43.3% of milk samples was above the acceptable level (50 ng/L) in Iranian national standard. It is concluded that further monitoring of milk production should be carried out in the spring and winter seasons.

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A Vapor Pressure Osmometer for Determination of Added Water in Milk

Journal of Milk and Food Technology ◽

10.4315/0022-2747-38.4.204 ◽

1975 ◽

Vol 38 (4) ◽

pp. 204-207 ◽

Cited By ~ 2

Author(s):

K. PENSIRIPUN ◽

E. C. CAMPBELL ◽

G. H. RICHARDSON

Keyword(s):

Vapor Pressure ◽

Collaborative Study ◽

Raw Milk ◽

Cow Milk ◽

Filter Paper Disc ◽

Milk Samples ◽

Added Water ◽

Sample Chamber ◽

Paper Disc

A vapor pressure osmometer requiring a 5- to 7-microliter sample to saturate a 0.64 cm filter paper disc fixed a digital readout of milliosmolality in 110 sec. A coefficient of variability of 0.70 was obtained on a raw milk sample tested 25 times when an acetone impregnated tissue was used to clean the sample chamber between tests. Two hundred individual cow milk samples from 20 herds averaged 280.0 ± 3.0 milliosmols. Milk samples containing up to 25% added water were evaluated on both the vapor pressure osmometer and a thermistor cryoscope with a resultant correlation coefficient of 0.991. A collaborative study involving eight hospital and industry laboratories was conducted. When the results of two laboratories were discarded, due to instrument maintenance problems, there were no significant differences among the laboratories in their abilities to quantitate added water in milk.

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