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.

Alkaline Phosphatase Survey in Pecorino Siciliano PDO Cheese

“…A variability of ALP values was detected in Pecorino Siciliano cheese samples, particularly those produced with pasteurized milk. Several samples presented ALP values higher than 10 mU/g, a threshold reported by other authors [ 6 , 9 , 10 ]. These values discriminated against cheese produced with raw or pasteurized milk.…”

“…Several studies reported that cheese size impacts the residual activity of ALP and its zonal distribution [ 6 , 7 , 8 , 9 , 10 ]. Additionally, several authors agree that the temperature at which the curd is heated, and the size of the cheese wheel, are the main parameters that influence residual ALP activity in cheese [ 6 , 10 ].…”

“…The above results appear to conflict with those reported in the literature [ 10 ]. However, few papers have analyzed the value of phosphatase on cheeses and, in particular, on traditional cheeses, because this method has only recently been validated [ 6 , 10 , 13 ].…”

“…The overlap of these values suggests that caution should be used when applying alkaline phosphatase as a control tool on raw or pasteurized milk cheeses. According to Clawin-Rädecker et al [ 6 ], further scientific studies are necessary to establish whether there are threshold values capable of discriminating against the type of milk (raw or pasteurized) used for producing PDO Pecorino Siciliano.…”

“…In the past, this proposed method was not considered appropriate for reflecting the heat treatment of cheese milk in some types of cheese [ 5 ]. For cheese, no legal limit has been set, as has been legislated for milk [ 6 ]. Further studies, however, have evidenced that processing conditions, texture, size, and high variability can impact the residual activity of ALP and its zonal distribution in cheese [ 7 , 8 , 9 ].…”