The use of alkaline phosphatase and possible alternative testing to verify pasteurisation of raw milk, colostrum, dairy and colostrum-based products

Abstract

Pasteurisation of raw milk, colostrum, dairy or colostrum-based products must be achieved using at least 72°C for 15 s, at least 63°C for 30 min or any equivalent combination, such that the alkaline phosphatase (ALP) test immediately after such treatment gives a negative result. For cows' milk, a negative result is when the measured activity is ≤ 350 milliunits of enzyme activity per litre (mU/L) using the ISO standard 11816-1. The use and limitations of an ALP test and possible alternative methods for verifying pasteurisation of those products from other animal species (in particular sheep and goats) were evaluated. The current limitations of ALP testing of bovine products also apply. ALP activity in raw ovine milk appears to be about three times higher and in caprine milk about five times lower than in bovine milk and is highly variable between breeds. It is influenced by season, lactation stage and fat content. Assuming a similar pathogen inactivation rate to cows' milk and based on the available data, there is 95-99% probability (extremely likely) that pasteurised goat milk and pasteurised sheep milk would have an ALP activity below a limit of 300 and 500 mU/L, respectively. The main alternative methods currently used are temperature monitoring using data loggers (which cannot detect other process failures such as cracked or leaking plates) and the enumeration of Enterobacteriaceae (which is not suitable for pasteurisation verification but is relevant for hygiene monitoring). The inactivation of certain enzymes other than ALP may be more suitable for the verification of pasteurisation but requires further study. Secondary products of heat treatment are not suitable as pasteurisation markers due to the high temperatures needed for their production. More research is needed to facilitate a definitive conclusion on the applicability of changes in native whey proteins as pasteurisation markers.

Keywords: alkaline phosphatase; colostrum; goat; indicators; milk; pasteurisation; sheep.

Figure 1

Schematic presentation of a pasteurisation unit

Figure 2

D‐values of the inactivation of Alkaline Phosphatase (ALP) activity in cows’, sheep, goat and equine milk as derived from various studies


1. LOR = Lorenzen et al. (2010); VAM = Vamvakaki et al. (2006); DUM = Dumitraşcu et al. (2014); WIL = Wilińska et al. (2007); and MAR = Marchand et al. (2009). A regression line for each species has been added.

Figure 3

Testing of alkaline phosphatase (ALP) activity in pasteurised milk of non‐bovine origin as provided by four different countries in comparison to bovine ALP data (a) and zoomed in for better visualisation without clipping the data (b)


1. The dashed line represents the legal limit for bovine milk of 350 mU/L.

Figure 4

Comparison of ALP activity and Enterobacteriaceae levels in goats’ milk samples

Figure D.1

Overview of mean ALP values from studies included in the assessment (Table 5)