Enhancement of the Knowledge on Fungal Communities in Directly Brined Aloreña de Málaga Green Olive Fermentations by Metabarcoding Analysis

Abstract

Nowadays, our knowledge of the fungal biodiversity in fermented vegetables is limited although these microorganisms could have a great influence on the quality and safety of this kind of food. This work uses a metagenetic approach to obtain basic knowledge of the fungal community ecology during the course of fermentation of natural Aloreña de Málaga table olives, from reception of raw material to edible fruits. For this purpose, samples of brines and fruits were collected from two industries in Guadalhorce Valley (Málaga, Spain) at different moments of fermentation (0, 7, 30 and 120 days). The physicochemical and microbial counts performed during fermentation showed the typical evolution of this type of processes, mainly dominated by yeasts in apparent absence of Enterobacteriaceae and Lactobacillaceae. High-throughput barcoded pyrosequencing analysis of ITS1-5.8S-ITS2 region showed a low biodiversity of the fungal community, with the presence at 97% identity of 29 different fungal genera included in 105 operational taxonomic units (OTUs). The most important genera in the raw material at the moment of reception in the industry were Penicillium, Cladosporium, Malassezia, and Candida, whilst after 4 months of fermentation in brines Zygotorulaspora and Pichia were predominant, whereas in fruits were Candida, Penicillium, Debaryomyces and Saccharomyces. The fungal genera Penicillium, Pichia, and Zygotorulaspora were shared among the three types of substrates during all the course of fermentation, representing the core fungal population for this table olive specialty. A phylogenetic analysis of the ITS sequences allowed a more accurate assignment of diverse OTUs to Pichia manshurica, Candida parapsilosis/C. tropicalis, Candida diddensiae, and Citeromyces nyonensis clades. This study highlights the existence of a complex fungal consortium in olive fermentations including phytopathogenic, saprofitic, spoilage and fermentative genera. Insights into the ecology, identification and quantification of fungi species in olive fermentation will facilitate the design of new strategies to improve the quality and safety of this fermented vegetable.

Deciphering Microbial Community Dynamics and Biochemical Changes During Nyons Black Olive Natural Fermentations

“…Interestingly, both acids were strongly and positively correlated with the dominant yeast species, W. anomalus and C. nyonsensis , and bacterial species, C. diazotrophica , when pH drops in brine. C. nyonsensis was first isolated from Nyons table olives ( Casaregola et al, 2013 ) and since then has been identified in other olive fermentations ( Arroyo-López et al, 2016 ) while W. anomalus is frequently identified in olive fermentations ( Coton et al, 2006 ; Heperkan, 2013 ). OTUs related to C. diazotrophica dominated the fermentation early on, from 21 days, and remained among the most abundant bacterial species to the end of fermentation.…”

Microbial Diversity of Fermented Greek Table Olives of Halkidiki and Konservolia Varieties from Different Regions as Revealed by Metagenomic Analysis

“…Regarding table olive fermentations, culture-independent techniques have been extensively applied in the investigation of the microbial ecology of green olives, belonging mainly to Italian and Spanish varieties, fermented naturally or using the Spanish method [13][14][15][16][17][18]. Furthermore, these studies are usually performed with brines, not taking into consideration the study of the microbial population adhered to olive surface, which is finally the food intake by consumers [19]. However, information about the microbial diversity of natural black and Spanish-style green olive fermentations for Greek table olive varieties is scarce.…”

Technologies and Trends to Improve Table Olive Quality and Safety

“…Therefore, their involvement is particularly important in natural olives, when fruits are not lye treated and phenolic compounds partly inhibit LAB development (Arroyo-López et al, 2012b ). Moreover, the presence of the various yeasts species was observed to vary even during the whole fermentation time (their number increased during the fermentation), because of and depending on their abilities to adapt to the evolution of the physico-chemical conditions of olives and brines (Pereira et al, 2015 ; Arroyo-López et al, 2016 ).…”