Mix-and-read method for assessment of milk pasteurization using a smartphone or a common digital camera

• Published in: Analytical and bioanalytical chemistry Vol. 412; no. 23; pp. 5663 - 5669
• Main Authors: Sevastou, Areti, Tragoulias, Sotirios S., Kalogianni, Despina P., Christopoulos, Theodore K.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.09.2020; Springer; Springer Nature B.V
• Subjects: Adequacy; Alkaline phosphatase; Alkaline Phosphatase - metabolism; Analytical Chemistry; Animals; Assessments; Biochemistry; Calibration; Cameras; Cattle; Characterization and Evaluation of Materials; Chemiluminescence; Chemistry; Chemistry and Materials Science; Coefficient of variation; Colorimetry; Cost analysis; Cow's milk; Dairy industry; Detectors; Digital cameras; Digital imaging; Electronic cameras; Food Science; Image acquisition; Laboratory Medicine; Methods; Milk; Milk - chemistry; Milk - enzymology; Monitoring/Environmental Analysis; Pasteurization; Phenolphthalein; Phosphatases; Photography - instrumentation; Photomultiplier tubes; Pretreatment; Research Paper; Sheep; Smart phones; Smartphone; Smartphones; Alkaline phosphatase; Chemiluminescence; Smartphone; Digital camera; Pasteurization; Milk
• ISSN: 1618-2642; 1618-2650
• DOI: 10.1007/s00216-020-02786-3

Alkaline phosphatase (ALP) is the most widely used marker of the adequacy of milk pasteurization since it is inactivated at temperatures slightly higher than those required for elimination of pathogens. The cutoff level is 350 mU/L. The approved colorimetric, fluorometric, and chemiluminometric methods require specialized readers with photomultipliers as detectors, and the samples are usually analyzed one-by-one. We developed a low-cost mix-and-read method that exploited a smartphone or a common digital camera as detectors for the chemiluminometric determination of ALP in milk. As samples, we used pasteurized cow and sheep milk spiked with ALP, as well as mixtures of pasteurized and raw (non-pasteurized) milk. Chemiluminescence images acquired by the smartphone or the digital camera were analyzed by the ImageJ software. The limits of detection (LODs), for images captured by the smartphone, were 4.4 mU/L and 11.1 mU/L for cow milk and sheep milk, respectively, while with the digital camera, the respective LODs were 6.2 mU/L and 6.7 mU/L, respectively. The coefficients of variation (CVs) at the cutoff level of 350 mU/L were 8% and 8.5% for the cow and sheep milk, respectively. For images by the digital camera, the CVs were 5.8% and 5% for cow and sheep milk, respectively. The performance of the method is similar to methods that use a microtiter plate and a luminometer for chemiluminescence measurements. Sample pretreatment is not necessary. The microtiter well format combined with detection by a smartphone enables the analysis of multiple samples simultaneously. It is anticipated that the method will prove useful for the rapid assessment of milk pasteurization efficiency in dairy industries, especially in remote areas where expensive instruments are not available. Graphical abstract