Microbiological quality of heat processed milks

Finekher, Thamir Melhan (1980) Microbiological quality of heat processed milks. MSc(R) thesis, University of Glasgow.

Abstract

1. The aim of this work was to investigate the quality of pasteurized milk. The work involved a study of the quality of pasteurized milk from retail sources in Ayr and district. One hundred and thirty-two packs of pasteurized milk were purchased over a five month period from six retail sources - four shops and two supermarkets. The milks were processed by six different dairies. The quality of the milk was assessed using total colony count, psychrotrophic count, lipolytic count, proteolytic count. Bacillus cereus count, coliform count, pH, titratable acidity and phosphatase test. It was found that 6.06 per cent of the samples failed the phosphatese test. However, 13.6 per cent failed the standard for coliform bacteria in pasteurized milk in Scotland i.e. absent in 1/1000 ml of milk. 15.9 per cent of the samples showed a higher total colony count than the maximum count for the 'standard' grade of raw milk in Scotland [< 50,000 per m1]. 2. A comparison was made of the microbiological quality of pasteurized milk packaged in glass bottles and single-service containers (SSC) using samples of pasteurized milk-obtained from two commercial dairies. The bacteriological teats referred to above were used. The effect of the fallowing factors on the microbiological quality was investigated. (i) storage at 5°C for 2, 4 and 6 days, (ii) the package i.e. either glass bottles or single-service containers, and (iii) exposure treatment for 3 h to light and temperature conditions simulating the doorstep delivery system. It was concluded from the tests that exposure to simulated doorstep delivery conditions had no significant effect on the microbiological quality during the trials which took place in winter time. The mean microbial counts of pasteurized milk processed in dairy A and packaged in glass bottles were significantly higher than those obtained from pasteurized milk from the same tank packaged in SSC. These differences appeared in some tests made on the day of processing. However, the mean of similar microbial counts of milk processed in dairy B, gave the exact opposite results of those obtained at dairy A. The results showed that there was no significant difference in the microbiological quality of pasteurized milk packaged in SSC in the two dairies. However, a highly significant difference was found in the bacteriological quality of the samples of pasteurized milk packaged in glass bottles between the two dairies. The empty glass bottles were found to be an important source of post-pasteurization contamination. The micro-organisms which were responsible for the contamination were Aeromonas species, Citrobacter freundii, Escherichia coli, Enterobacter aerogenes, Enterobacter cloacae, Enterobacter agglomerans, Pseudomonas species and Serratia liquefaciens. (Abstract shortened by ProQuest.)

• Item Type: Thesis (MSc(R))
• Qualification Level: Masters
• Additional Information: Adviser: R JM Crawford
• Keywords: Food science.
• Colleges/Schools: College of Science and Engineering
• Supervisor's Name: Supervisor, not known
• Date of Award: 1980
• Depositing User: Enlighten Team
• Unique ID: glathesis:1980-72108
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 24 May 2019 15:11
• Last Modified: 03 Aug 2022 12:59
• URI: https://theses.gla.ac.uk/id/eprint/72108