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

Abstract

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.

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

“…The number of yeasts in the brine with spCO 2 decreased to 33% of that of the control at the 6th month and to 10% of that of the control in subsequent months of incubation (Table 1). The results are in agreement with findings from other pilot studies investigating the use of spCO 2 to enhance brine antimicrobial activity, in which the total number of yeasts was below the detection limit of the method during the first months of incubation of the olives in brine [15]. The slow increase in the number of total yeasts recorded after the third month of incubation in brine subjected to spCO 2 is attributable to the differing resistance of microbial cells to adverse conditions through the use of baroprotective compounds [26].…”

“…In a previous study, we performed the first investigation of the antimicrobial activity of brine treated with slightly pressurized CO 2 (spCO 2 ). This study provides a theoretical basis for increasing the antimicrobial activity of brine with low-salt content in naturally fermented black table olives [15]. The CO 2 dissolved in the brine decreases the pH and simultaneously penetrates microbial cells and exerts growth inhibitory effects [16].…”

“…On the basis of the chromogenic characteristics of the colonies, the presence of pseudohyphae, and the cell shapes and sizes, the yeasts were divided into homogeneous chromogenic groups. From each homogeneous chromogenic yeast group, ten isolates of the most frequently observed yeasts were chosen at random and identified at the species level by sequencing of the D1/D2 region (approximately 600 bp) of the large (26S) ribosomal subunit gene, as previously reported [15].…”

“…The low salt concentration was chosen in accordance with the IOC, which recommends storage with a minimum content of 6% (w v −1 ) NaCl in the brines of olives previously processed in the natural style [25]. The highest concentration of NaCl of 11% (w v −1 ) was chosen, because it is one of the most frequently used salt concentrations in black table olive processing, while the yeast S. cerevisiae was chosen considering the results of previous studies [15]. Each 5 L PET demijohn bottle was filled with 2.6 kg of olives and 2.4 L of brine.…”

“…SpCO 2 less than one megapascal (10 bar) may be a promising means of controlling microbial growth. Tests performed on a pilot plant scale have shown that spCO 2 completely inhibits the growth of bacteria and fungi in brine with a decreased saline concentration [15]. However, beyond these pilot studies, spCO 2 has never been used in black table olives naturally processed with a decreased salt content.…”