Differential Microbial Composition of Monovarietal and Blended Extra Virgin Olive Oils Determines Oil Quality During Storage

A New Natural Processing System Based on Slight Carbon Dioxide Pressure for Producing Black Table Olives with Low Salt Content

Naturally fermented black table olives are usually processed in brine with low pH and high NaCl content. Because salt is responsible for several cardiovascular problems, methods are needed to decrease the salt (NaCl) content in olive pulp. This study investigated a new natural processing system wherein microorganism growth is inhibited by slight pressure of CO2 (spCO2), in addition to low pH and NaCl, in brine with decreased salt content. The fermentation performed under spCO2 with a low-salt brine with 6% (w v-1) NaCl and 0.5% (w v-1) citric acid, unlike the traditional system, inhibited the growth of bacteria and fungi and decreased the concentration of yeasts. Processing tests with spCO2 in the presence of different salt and citric acid concentrations indicated a slight decrease in yeasts in brines containing 6% (w v-1) NaCl and 0.6% (w v-1) citric acid but not after inoculation of the same brines with Saccharomyces cerevisiae. In contrast, in the presence of 11% (w v-1) NaCl and 0.3% or 0.6% (w v-1) citric acid, the inhibitory effect of brines was greater compared to those with low-salt and it was also confirmed in the same brines inoculated with S. cerevisiae.

Effect of oil-born yeasts on the quality of extra-virgin olive oils of Basilicata region

The olive oil microbiota mainly consists of yeasts, which may positively or negatively affect the physicochemical and sensory features of product. In this study, 17 yeast strains belonging to Candida boidinii, Lachancea fermentati, Nakazawaea molendinolei, N. wickerhamii and Schwanniomyces polymorphus species were collected during olive oil production, identified and tested for the ability to ferment sugars, to grow at low temperatures, for the occurrence of different enzymatic activities, for the tolerance and degradation of phenolic compounds, radical scavenging activities, biofilm formation, survival to simulated gastro-intestinal (GIT) tract. Yeasts were also inoculated in extra virgin olive oils (EVOO; from Leccino and Coratina cultivar) to evaluate their survival and their effect on EVOO quality (changes in analytical indices) during 6-months of storage. Most of strains were able to grow at 15°C, while the ability to ferment different sugars was strain-specific. All strains had β-glucosidase activity, while none exhibited lipolytic activity; peroxidase was widespread among the strains, while protease activity was strain-dependent. Esterase and the ability to hydrolyse oleuropein and form hydroxytyrosol was present only in N. wickerhamii strains. All strains were able to survive in olive mill wastewater, used as a model of phenolic compounds-rich matrix. A potential biofilm formation was observed only in N. wickerhamii, while the ability to scavenge radical and to cope with GIT-associated stresses were strain-dependent. High levels of survival were observed for almost strains (except S. polymorphus), in both Leccino and Coratina samples. Yeasts limited the acidity rise in olive oils, but overtime they contributed to increase the parameters related to oxidative phenomena (i.e. peroxides, K₂₃₂, K₂₇₀), resulting in a declassification of EVOOs. The total phenolic content (TPC) was correlated to the presence of yeasts and, at the end of storage period (6 months) inoculated samples had significantly lower concentrations compared to the control oils. This study confirms that yeasts are able to survive in olive oils and, therefore, the control of their occurrence during extraction process and storage conditions is needed to obtain high-quality products and to maintain the standards of EVOO classification.

Use of Slightly Pressurized Carbon Dioxide to Enhance the Antimicrobial Properties of Brines in Naturally Processed Black Table Olives

Naturally fermented black table olives are processed at low pH in the presence of high sodium chloride concentrations ranging from 8 to 12% (w v⁻¹). Reducing the salt content of brine has become an urgent issue as it is responsible for several health and environmental problems. The study aim was to evaluate slightly pressurized CO₂ (spCO₂) as a third barrier to microbial growth in naturally processed black table olives with low pH and a reduced NaCl concentration. Based on the assessments performed on a pilot plant scale, an spCO₂ of 1 bar completely inhibited the growth of the bacteria and molds in the presence of reduced saline concentrations. Furthermore, the amount of yeast decreased in the brine as a function of the NaCl content. Laboratory tests performed under spCO₂ conditions using a single yeast species from the same habitat confirmed the high sensitivity of some oxidizing yeasts and indicated that the fermenting yeast, Saccharomyces cerevisiae, is the most tolerant species. Overall, in the brine of naturally processed olives with a low pH between 4 and 4.2, the antimicrobial properties observed with the high concentrations of NaCl can be achieved with a lower salt dose of 5% (w v⁻¹) when combined with spCO₂.

Microbiological and Enzymatic Activity Modulates the Bitter Taste Reduction in Decanted Coratina Olive Oil

Coratina monocultivar extra virgin olive oil (EVOO) is known for its level of bitterness, which, if too high, can cause consumer acceptance problems. The aim of this study was to modulate the bitter taste of freshly produced olive oil through endogenous enzymatic activity and microbiota during the decantation phase. The opalescent appearance of the newly produced EVOO was substantially reduced during the first three months of decantation due to the deposition of more than 90% of suspended material, consisting of vegetation water and suspended solid particles. The high content of biophenols and the reduction in water concentration in the oil samples negatively affected the survival of yeasts, which were absent in the oil samples at the end of the third month of decantation. The oleuropeinolytic activity was very intense during the first month of decantation, whereas the reduction in the bitter taste associated with the aglycons was consistent only in the second and third months of decantation. At the end of decantation, the sensory notes of bitterness in the Coratina EVOO were reduced by 33%, lowering the position on the value scale without altering the other qualitative parameters whose values fell within the limits of the commercial EVOO class.

Role of yeasts in the qualitative structuring of extra virgin olive oil

This review sought to describe the role played by some components of the microbiota of extra virgin olive oil (EVOO), particularly yeasts, in structuring the physicochemical and sensorial quality of freshly produced olive oil. Yeasts can survive during the entire storage period of the product. To date, approximately 25 yeast species isolated from oil produced in more than six countries have been identified, eight of which are classified as new species. Some yeast species with probiotic traits improve the health qualities of oil, whereas many others improve the chemical composition and sensory characteristics based on β-glucosidase and esterase enzymes, which are involved in the hydrolysis of the bitter glucoside known as oleuropein. However, some species, which are typically favored by the high water content in the oily matrix, such as lipase-producing yeasts, can worsen the initial chemical characteristics of EVOO oil during storage. Some physical treatments that are compatible with the EVOO production specification affect the biotic component of the oil by reducing the concentration of yeasts. The possibility of minimizing the invasive action on the biotic component of the oil by appropriately selecting the physical treatment for each oil is discussed.

Effects of the Filtration on the Biotic Fraction of Extra Virgin Olive Oil

Filtration is a widely used process in the production of extra virgin olive oil. We studied the influence of filtration performed with cotton filters and cellulose filter press on the biotic components of the oily mass containing probiotic traits in two freshly produced monocultivar extra virgin olive oils. The concentration of bacteria was reduced from 100% to 28%, while that of fungi was reduced from 100% to 44% after filtration, according to the filtration system and the initial contamination of the original monocultivar extra virgin olive oil. Compared with the control, the yeast content in the oil samples filtered with cotton filters was reduced from 37% to 11% depending on the cultivar. In the oil filtered with cellulose filter press, the yeast content reduced from 42% to 16%. The viable yeast that passed through the oily mass during the filtration process with cellulose filter press, unlike all the other samples, were unable to survive in the oil after a month of storage. The possible health benefits of compounds from both the biotic and abiotic fraction of the oil, compared to the control, were significantly low when filtered with the cellulose filter press.

Virgin Olive Oil Quality Is Affected by the Microbiota that Comprise the Biotic Fraction of the Oil

This review summarizes the current knowledge on the effects of oil-borne yeasts on the physicochemical, sensorial, and health-related characteristics of virgin olive oil (VOO) during storage. Bacteria, yeasts, and molds constitute the biotic fraction of freshly produced VOO. During storage, the bacteria and molds often die after a short period, while the yeasts survive and condition the quality of VOO. To date, approximately twenty-four yeast species have been isolated from different types of olive oil and its by-products, and seven of these species have been identified as new species. The activity of some yeasts of the biotic fraction of olive oil improves the sensorial characteristics of VOO. Some yeasts can also worsen the quality of the product by allowing the appearance of defects, oxidation of polar phenols, and triacylglycerol hydrolysis. Some yeast species of VOO show in vitro beneficial health effects, such as probiotic and antioxidant activities.