Application of central composite design and response surface methodology to the fermentation of olive juice by Lactobacillus plantarum and Debaryomyces hansenii

The objectives of this study were to investigate the effects of NaCl, calcium acetate and calcium lactate in concentrations corresponding to ionic strengths equivalent to 2–10%, w/v salt brines as well as the 50% replacement of NaCl contained in the above mixture by KCl. A central composite design and response surface methodology were used to optimize the maximum specific growth rate of Lactobacillus plantarum ATCC 8014 and Debaryomyces hansenii 2114. The fermentation was carried out in olive juice obtained from Kalamon black olives at 30 °C with initial pH 5.0. Mathematical models describing the combined effects of these factors on the maximum specific growth rate of L. plantarum or D. hansenii were established. Both strains in single cultures showed higher maximum specific growth rate in olive juice supplemented with NaCl/KCl, Ca-acetate and Ca-lactate. But in mixed culture fermentations of olive juice supplemented with NaCl, Ca-acetate and Ca-lactate, higher specific growth rates were obtained. Under the optimum growth conditions determined for the single culture fermentations, i.e. 378.4 mM NaCl, 34.1 mM Ca-acetate and 39.9 mM Ca-lactate, mixed culture fermentation was undertaken by varying the time of inoculation of the yeast strain. When D. hansenii was inoculated 48 h before L. plantarum the maximum specific growth rate of L. plantarum was increased to 0.247 per hour, which was significantly higher compared to L. plantarum alone (0.211 per hour). In mixed culture fermentation of olive juice supplemented with the mixture of NaCl/KCl under similar conditions as above, a maximum specific growth rate of L. plantarum of 0.218 per hour was determined. The optimum conditions determined for mixed culture fermentation are useful in fermentation of black olives Kalamon variety under lower salt content.