Application of Candida boidinii and Candida norvegica to improve the quality and safety of Nocellara del Belice table olives processed through Castelvetrano-style technology.

Abstract

Table olives are daily consumed in Mediterranean countries and their production constitutes an economically important activity in this area. The methods mostly applied to process table olives in the major producing countries are Spanish- and Greek-style. However, in Sicily region, green olives are also consistently (31,000 tons/year) processed according to Castelvetrano-style consisting of a treatment with soda and salt addition, followed by storage in coldrooms (5-6 °C). Low temperatures are insufficient to limit the growth of undesired microorganisms (annual product losses of 10-15%). To this purpose, yeasts were isolated from brine samples during the last five olive campaigns in order to characterise phenotypically and genotipically interesting strains to be used to stabilise the fermentation process. Nineteen strains belonging to the species Candida boidinii, Candida norvegica and Debaromyces hansenii were further technologically screened. C. boidinii LC1 and C. norvegica OC10 showed the best results in terms of low temperature growth, pH and NaCl resistance were inoculated in experimental productions of Castelvetrano-style table olives. The process was monitored for physicochemical and microbiological parameters. At the end of the process (180 d), pH was around 5.0 and NaCl content was 8 % (w/v). The olives processed with the selected strains retained colour and pulp hardness was higher than that registered for the olives of the control trial. The dominance of inoculated strains (> 96 % over microbial community), strongly reduced the levels of potential spoilage and/or pathogen microorganisms. Sensory analysis showed an increase in colour, sweetness and crispness attributes for the olives of the trials inoculated with LC1 and OC10. Further studies are being prepared to validate the use of LC1 and OC10 strains under non-refrigerated conditions to increase the production sustainability.