Milk. Determination of urea content. Enzymatic method using difference in pH (Reference method)

10.3403/03134552u ◽

2015 ◽

Keyword(s):

Reference Method ◽

Enzymatic Method ◽

Urea Content

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Evaluation of flow injection analysis for determination of urea in sheep's and cow's milk

Acta Veterinaria Hungarica ◽

10.1556/avet.50.2002.3.2 ◽

2002 ◽

Vol 50 (3) ◽

pp. 263-271 ◽

Cited By ~ 7

Author(s):

Martina Baumgartner ◽

Martina Flöck ◽

Petra Winter ◽

Keyword(s):

Bovine Milk ◽

Reference Method ◽

Measurement Procedure ◽

Ammonium Ions ◽

Routine Diagnostics ◽

Urea Content ◽

Teflon Membrane ◽

Accuracy And Precision ◽

Spectral Photometry

Difficulties in measuring the urea content in sheep's milk often occur with spectral photometry due to the high protein and fat concentrations of the milk. In this study an enzymatic flow procedure (QuickChem 8000 Ion Analyser, Lachat Instruments, Milwaukee, USA) to determine the urea content in ovine and bovine milk was evaluated. Urea content is determined by the Berthelot reaction after splitting it enzymatically with urease. The free ammonia diffuses through a teflon membrane into a stream of reagent solutions. Detection takes place by means of a reaction between the ammonium ions with hypochlorite and salicylate producing a green colour, which is measured spectrometrically in a flow meter at 660 nm. By using a diffusion cell chemical deproteinisation of milk is not necessary and capacity is high. The assessed procedure exhibited high accuracy and precision and reached a sample capacity of 55 samples an hour. Storage of the milk samples for several days as well as chemical preservation with bronopol had no effect on the measurement procedure. Due to the complexity of the apparatus and the costs associated therewith, the device proves less suitable for routine diagnostics but rather serves as a reference method for the measurement of urea concentration in milk.

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Determination of Degree of Retrogradation of Cooked Rice by near Infrared Reflectance Spectroscopy

Journal of Near Infrared Spectroscopy ◽

10.1255/jnirs.223 ◽

1998 ◽

Vol 6 (A) ◽

pp. A355-A359 ◽

Cited By ~ 4

Author(s):

Seung-Yong Cho ◽

Sung-Gil Choi ◽

Chul Rhee

Keyword(s):

Moisture Content ◽

Standard Error ◽

Near Infrared ◽

Reference Method ◽

Reflectance Spectroscopy ◽

Multiple Correlation Coefficient ◽

Enzymatic Method ◽

Near Infrared Reflectance ◽

Cooked Rice

Near infrared (NIR) reflectance spectroscopy was used to determine the degree of retrogradation of cooked rice. Cooked rice samples were stored at 4°C for 120 hours, and the degree of retrogradation was measured every six hours during the storage time. Enzymatic method, using glucoamylase, was used as reference method for the determination of the degree of retrogradation. Spectral differences, due to retrogradation of cooked rice, were observed at 1434, 1700, 1928, 2100, 2284 and 2320 nm. 32 samples were used for calibration set and 16 samples were used for validation set. High correlations were achieved between degree of retrogradation determined by enzymatic method and by NIR with multiple correlation coefficient of 0.9753 and a standard error of calibration of 3.64%. Comparable results were obtained with 3.91% of standard error of prediction, when the calibration equation was applied to an independent group of samples. The moisture content of samples tested significantly affected the determination of degree of retrogradation by NIR. The critical moisture content for the determination of degree of retrogradation by NIR was found to be ca. 5% (W.B.). The results suggested that NIR spectroscopy might be used as a potential method for determining both the degree of retrogradation and gelatinization of cooked rice.

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