The use of analytical techniques for the rapid detection of microbial spoilage and adulteration in milk

  • Nicoletta Nicolaou-Markide

Student thesis: Phd

Abstract

Milk is an important nutritious component of our diet consumed by most humans on adaily basis. Microbiological spoilage affects its safe use and consumption, itsorganoleptic properties and is a major part of its quality control process. EuropeanUnion legislation and the Hazard Analysis and the Critical Control Point (HACCP)system in the dairy industry are therefore in place to maintain both the safety and thequality of milk production in the dairy industry.A main limitation of currently used methods of milk spoilage detection in the dairyindustry is the time-consuming and sometimes laborious turnover of results.Attenuated total reflectance (ATR) and high throughput (HT) Fourier transforminfrared (FTIR) spectroscopy metabolic fingerprinting techniques were investigatedfor their speed and accuracy in the enumeration of viable bacteria in fresh pasteurizedcows' milk. Data analysis was performed using principal component - discriminantfunction analysis (PC-DFA) and partial least squares (PLS) multivariate statisticaltechniques. Accurate viable microbial loads were rapidly obtained after minimalsample preparation, especially when FTIR was combined with PLS, making it apromising technique for routine use by the dairy industry.FTIR and Raman spectroscopies in combination with multivariate techniques werealso explored as rapid detection and enumeration techniques of S. aureus, a commonmilk pathogen, and Lactococcus lactis subsp cremoris, a common lactic acidbacterium (LAB) and potential antagonist of S. aureus, in ultra-heat treatment milk. Inaddition, the potential growth interaction between the two organisms wasinvestigated. FTIR spectroscopy in combination with PLS and kernel PLS (KPLS)appeared to have the greatest potential with good discrimination and enumerationattributes for the two bacterial species even when in co-culture without previousseparation. Furthermore, it was shown that the metabolic effect of L. cremorispredominates when in co-culture with S. aureus in milk but with minimal conversegrowth interaction between the two microorganisms and therefore potentialimplications in the manufacture of dairy products using LAB.The widespread and high consumption of milk make it a target for potential financialgain through adulteration with cheaper products reducing quality, breaking labelingand patent laws and potentially leading to dire health consequences. The timeconsumingand laborious nature of currently used analytical techniques in milkauthentication enabled the study of FTIR spectroscopy and matrix-assisted laserdesorption/ionisation time-of-flight mass spectrometry (MALDI-ToF-MS) as rapidanalytical techniques in quantification of milk adulteration, using binary and tertiaryfresh whole cows', goats' and sheep's milk mixture samples. Chemometric dataanalysis was performed using PLS and KPLS multivariate analyses. Overall, resultsindicated that both techniques have excellent enumeration and detection attributes foruse in milk adulteration with good prospects for potential use in the dairy industry.
Date of Award1 Aug 2011
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorRoyston Goodacre (Supervisor)

Keywords

  • MALDI MS
  • Raman
  • FT-IR
  • spoilage
  • milk
  • adulteration

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