An evaluation of microbial safety and quality parameters in ready-to-use spinach

Minimally processed packaged vegetables have become increasingly popular in recent years. Concurrently, there is also a desire amongst manufacturers for obtaining longer shelf life on these products while ensuring product quality and safety. Furthermore, the availability of rapid detection methods for the direct and specific detection of microorganisms in these products would also be useful to the industry. This thesis describes investigations on the quality and safety of ready-to-use packaged vegetables in conjunction with the influence of packaging, storage and temperature conditions with development of a rapid and specific detection method for pathogenic microorganisms in RTU vegetables without the requirement of preenrichment. The potential for microbial colonization and biofilm formation on vegetable tissue and packaging film of RTU packaged spinach and tissue textural properties at the cellular level were investigated. Scanning electron microscopy demonstrated microbial attachment and biofilm formation on packaging film material, vegetable tissues and tissue textural changes during storage. The microbiological quality and the growth dynamics of the microorganisms identified on the RTU vegetable products were also evaluated under different time, temperature and packaging conditions. The RTU products were examined for a variety of microbial groups including specific pathogens such as Listeria monocytogenes. Another goal was to develop polymerase chain reaction protocols directly in RTU vegetables without the requirement of a preenrichment step for rapid and specific detection of L. monocytogenes at the genus and species levels. The test system was developed using 5 different strains of L. monocytogenes. Another objective of this study was to probe into the three-dimensional colorimetric facets and chromaticity attributes of RTU spinach, to investigate the effects of time and temperature and packaging conditions on the various colorimteric properties and to assess the effectiveness of colorimetry as a potential quality-control tool for industrial applications and in spoilage and shelf life predictions. The Electronic Nose and its pattern recognition systems were analysed and evaluated for determination of aromatic properties of RTU packaged spinach and as quality control tools useful for the industry. The microperforated system was found to be most effective for aromatic quality preservation of the packaged spinach products under both refrigerated storage and temperature abuse situations.