Protein Tests offer rapid and reliable way to monitor biological contamination on surfaces
To be hygienic, worktops, cookware, utensils and other equipment in contact with food must be free of invisible residue that food leaves behind which could provide opportunities for microbial growth.
This kit indicates the hygiene level after cleaning by detecting residuals of protein which can be left behind after inadequate cleaning. The kit does not directly indicate microbial activity.
Principle of the test
The test is based on the principle of the Buiret reaction where under alkaline conditions the copper ions (Cu2+) form a complex with the peptide bonds of proteins and becomes reduced to copper Cu+. Bicinchoninic acid (BCA) under alkaline
conditions is a highly sensitive, stable and specific reagent for Cu+ forming a purple complex. The chromogen formed can be assessed visually aswith the Pro-tect devices or assayed with a Spectrophotometer (Absorbance at 562nm).
The reaction is time-dependent i.e the colour develops with time and therefore it is important to record colour change after 10 min and disregard any colour change after this set time. If a yes/no (clean/dirty) rather than a semi-quantitative (how dirty?) answer is required then timing can be stopped as soon as any colour change is observed. Even for a semi-quantitative assay, there is no need to continue timing when the surface is
obviously very dirty and the colour changes to dark purple (level 4) before 10 min.
The reaction is also temperature-dependent and therefore it is important to allow the devices to equilibrate to ambient room temperature (15 - 25°C) if they have been stored at a different temperature.
Other reducing agents giving a positive result with Protect
This test also detects other substances capable of reducing the copper (Cu++ to Cu+) such as reducing sugars (glucose) and uric acid. Other strong reducing materials such as ascorbic acid (present in some fruit juices) or tannin (present in tea) may also
give a positive result with Clean-Trace™ (see data for different product residues giving a positive result with Pro-tect® – CID050).
Protein concentration corresponding to colour level with Pro-tect
Protein* amount (μg/100μl)
0 - 30
50 - 80
100 - 300
Smith, P.K; Krohn, R.I.; Hermanson, G.T.; Mallia, A.K.; Gartner, F.H.; Provenzano, M.D.; Fujimoto, E.K., Goeke, N.M.; Olson, Klenk, D.C. "Measurement of Protein using Bicinchoninic acid". Anal. Biochem. (1985) 150, 76-85.
Stoscheck, C.M. "Quantitation of proteins" In: Guide to Protein Purification (Ed. Deutscher, M.P.) Methods in Enzymology (1990) 182, 50 - 68.