abnormal fermentations in table-olive processing: microbial origin and sensory evaluation

The process of transformation of table olives is the result of complex biochemical reactions that are determined by the interactions of the indigenous microflora of the olives together with a variety of contaminating microrganisms from different sources (fiber-glass fermenters, PVC tanks, pipelines, pumps and water) with the compositional characteristics of the fruit. One of the most important aspects of improving the quality of table olives is the use of selected microorganisms to drive the fermentation. These can supplant the indigenous microflora and, in particular, the complementary microflora that are responsible for spoilage of canned olives. In this context, from a technological point of view, a well-characterised collection of microrganisms (lactic acid bacteria, yeasts) that is possibly isolated from the matrix to be processed (the olive fruit) will provide the basis for the development of starter culture systems. These cultures can be fully compatible with the typical products and guarantee high quality standards. Inoculation of the brine with such selected starter cultures will reduce the probability of spoilage and help to achieve an improved and more predictable fermentation process. Control of the fermentation processes can thus occur through chemical, chemico-physical and microbiological approaches, and since 2008 (COI/OT/MO/Doc. No 1. Method for the sensory analysis of table olives), also through organoleptic evaluation. This last has established the necessary criteria and procedures for sensory analysis of the negative, gustatory and kinaesthetic sensations of table olives that can also be attributed to abnormal proliferation of microrganisms. It also sets out the systematics for commercial classification, through the assessment of the median of the defect predominantly perceived.