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Gewählte Doctoral Thesis:

Doctoral Thesis - Institut für Lebensmittelwissenschaften, BOKU-Universität für Bodenkultur, pp 84. UB BOKU obvsg

Data Source: ZID Abstracts
Cheese spoilage is frequently caused by undesirable microbial fermentation during ripening. Late-blowing, a particularly severe quality defect of hard and semi-hard cheese, is a result of metabolic activities of cheese-damaging clostridia. It is well-known that the resulting sensory defects lead to practically unmarketable cheeses. However, the quantification of clostridial spore contamination as an indicator of milk quality remains a major challenge for quality assurance in hard cheese production. This thesis discusses the relevance of clostridia in milk and cheese as well as advantages and drawbacks of existing methods for clostridial analysis. Currently, only most probable number (MPN) – methods can meet the required method sensitivity. However, the variability and manual workload of MPN procedures complicate the comparability of results and the agreement on a critical threshold value for clostridia in milk. We investigated the impact of method variability on quantitative results by assessing four routine media and MPN methods for the detection of clostridia in milk. The use of different procedures yielded significantly different results and all four methods showed a severe lack of selectivity. Based on these findings, we developed and evaluated a new MPN-approach for the enumeration of butyric acid producing clostridia in milk. The new method provides for a reliable quantification of clostridial spores in milk over a wide concentration range. By using an optimised growth medium, we improved the selectivity towards clostridia and significantly reduced the analysis time. Furthermore, the new method design enabled semi-automation and reduced the uncertainty of test results. A fast and precise enumeration of clostridial spores in milk is an important prerequisite for a selective routine monitoring in hard cheese production. The implementation of the new method can contribute to the avoidance of spoilage and an early detection of microbial causes for late-blowing.

Betreuer: Domig Konrad
1. Berater: Kneifel Wolfgang
2. Berater:

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