Rapid methods to assess fungal contamination in tomato products
thesisposted on 10.04.2018, 14:03 by Maria F.H. Pacheco Ferreira
Some new, rapid methods were used in this study for tomato products as alternatives to the traditional Howard mould count. This method proved to be a fastidious but subjective method and therefore inaccurate for use in tomato quality control and/or for legislative purposes. The Apizym system was used to assess fungal presence in tomatoes, tomato juice and crushed tomato, where different patterns of extracellular enzymes were obtained for the different mould species. Growth medium was also found to have an effect. This suggested the possibility of using this method to assess fungal presence in tomato products and tentatively identify them using their enzymic profile. Use of this method may not only apply to assessing raw material quality, but also as a possible monitoring test for assessing heat treatment adequacy or post process contamination. ATP photometry was found to be suitable for assessing mould contamination in tomato juice, but erroneous results were obtained with crushed tomato. This may be related to various difficulties associated with the separation of microbial ATP from the food material, or with its extraction from the fungal hyphae, in some mould species. The Direct Epifluorescent Filter Technique (DEFT) despite slightly overestimating the total viable count, possibly due to the effect of heat treatment on acridine orange staining characteristics, proved useful because of its rapidity in detecting fungal presence in tomato juice. Therefore, it could be used to assess quality during tomato juice production or to predict the shelf-life of the product. Impedance microbiology was used to detect mould presence in tomato juice. In this study it proved very useful in assessing tomato juice sterility using the relationship between impedance detection time and contamination levels. lt also had the advantage of enabling rapid rejection of tomato juice contaminated with mould. This involved the use of a calibration curve based on the above relationship for which a cut-off point corresponding to the minimum detection time was determined.
British Council. Portugal, Junta Nacional de Investigação Científica e Tecnológica (JNICT).
- Aeronautical, Automotive, Chemical and Materials Engineering
- Chemical Engineering