Development of enzyme based chromogenic strips for detection of selected adulterants in milk
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Date
2022-09
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College of Veterinary Science, Assam Agricultural University, Khanapara Campus
Abstract
The present investigation was carried out to develop an enzyme based chromogenic
strip for detection of selected adulterant in milk. The experiment was carried out in the
Department of Livestock Products Technology, All India Coordinated Research Project on
Post Harvest Engineering and Technology and Department of Veterinary Biochemistry,
College of Veterinary Science, Assam Agricultural University, Khanapara, Guwahati-
781022.
An enzyme based chromogenic test strip using Whatman filter paper grade 602 and
Whatman filter paper No. 1 was developed for the detection of glucose, starch and urea in
milk using glucose oxidase, amyloglucosidase and urease enzyme in the presence of
potassium iodide for starch and glucose and phenol red for urea as an indicator. The activity
of the test strip was validated in both raw and processed milk spiked with the respective
adulterants.
All the enzyme based test strips were able to detect 2mg/ml of glucose, starch and
urea with definite ring formation within a specified time period.
The response time for the detection of glucose, starch and urea in milk was noted at
31.22±0.014 and 30.00±0.05, 128.3±0.88 and 129±0.57 & 99 ±0.57 and 109.67 ±0.88 sec,
respectively in Whatman filter paper grade 602 and Whatman filter paper No. 1 at a pH of
4.5, 4.5 and 8.0 and a chromogenic substrate concentration of 40, 50 and 1 mg/ml.
The optical density of glucose, starch and urea was found to be almost linear. As the
concentration of the substrate increase the optical density value tends to increase
proportionately.
The test strip was tested for true positive and true negative results. The limit of
detection for glucose, starch and urea were found to be 1.0, 2.0 and 0.8 mg/ml, with response
time of 1, 4 and 3 min, respectively.
To see the effect of different processing condition on the ability to degrade glucose,
starch and urea in milk, all the test strips showed positive response except in household
boiling condition wherein the response was delayed by a few min.
The enzyme based test strip were 100 percent specific for detection of glucose, starch
and urea as presence of similar types of compounds did not interfere with the positivity rate
of the strips which was verified with help of confusion matrix.
The shelf life of enzyme based chromogenic glucose, starch and urea test strips were
found to be 40 and 30, 34 and 30 & 42 and 34 d, respectively for Whatman filter paper grade
602 and Whatman filter paper No. 1, respectively when stored under refrigerated storage
(7±1oC) and ambient storage (29-32oC) condition in airtight glass containers.