Alkaline phophatase levels in Finnish hard cheeses and milk products

Show full item record

Title: Alkaline phophatase levels in Finnish hard cheeses and milk products
Author: Ninios, Aliki Ilona
Other contributor: Helsingin yliopisto, Maatalous-metsätieteellinen tiedekunta, Elintarvike- ja ympäristötieteiden laitos
University of Helsinki, Faculty of Agriculture and Forestry, Department of Food and Environmental Sciences
Helsingfors universitet, Agrikultur- och forstvetenskapliga fakulteten, Institutionen för livsmedels- och miljövetenskaper
Publisher: Helsingfors universitet
Date: 2013
Language: eng
Thesis level: master's thesis
Discipline: Livsmedelsteknologi
Food Technology
Abstract: Alkaline phosphatase (ALP) is an endogenous enzyme found in milk, which is inactivated at higher temperatures than vegetative bacteria and is thus used as an indicator of a successful pasteurisation. The ability of ALP to reactivate allows it to be found in milk products that are claimed to be pasteurised. The aim of this Master‘s thesis was to understand the reactivation behaviour of ALP in order to ascertain whether high levels found in milk products are correlated to a normal reactivation property of the enzyme or other possible reasons, such as a failed pasteurisation or contamination. This work also aimed to define the mean ALP activities found in specific commercial milk products and their deviation from the acceptable levels. Another scope was to determine the freeze stability of ALP to define its appropriateness for post-stored analysis. Lastly, the examination of ALP location in milk fat membrane globules was examined to interpret the variation of enzyme activity levels in products of different fat content. The experimental part of the Master‘s thesis was divided into three parts. The first part included the record of ALP activities of different commercial Finnish milk products which are analysed in different groups according to their fat content and product type. The second part concentrated on the heat-treatment of milk samples at different time-temperature relationships and followed the reactivation behaviour of ALP. The total micro-flora was taken into consideration in order to observe any relation between the increased ALP activities and microbial growth. ALP activities were measured by a fluorimetric method, a quick three minute method which has the advantage of being more accurate compared to colourimetric methods. The third part examined the fraction in which ALP activities are found in milk after separation and its freeze stability when stored at -79 ºC. Commercial cheeses showed a high ALP activity in Emmental thermised cheeses and an activity less than 10 mU/g in other cheese types and pasteurised cheeses. In commercial milks, UHT treated and those closer to expiration date, high ALP activities were found, while pasteurised milks had low activities below the higher acceptable levels. The reactivation property of milk samples that were heat-treated in ALP was not related with the microbial growth and was quicker when the milk samples were heat-treated at higher temperatures. After the separation of cream from whole milk samples, ALP activity was found in the skim milk part. In conclusion, ALP activities did not decrease significantly following freeze storage for a few days showing its stable freeze properties.
Subject: alkaline phosphatase
UHT treatment
fluorimetric method

Files in this item

Total number of downloads: Loading...

Files Size Format View
Ninios AI_Master thesis-1.pdf 1.047Mb PDF View/Open

This item appears in the following Collection(s)

Show full item record