Modeling of combined effects of citral, linalool and β-pinene used against Saccharomyces cerevisiae in citrus-based beverages subjected to a mild heat treatment

The aim of this work was to evaluate the antimicrobial activity of three terpenes (citral, linalool and β-pinene), in combination with a mild heat treatment (55 °C, 15 min). The study has been carried out on an orange based soft drink inoculated using a wild strain of Saccharomyces cerevisiae. The results, expressed as growth/no-growth data, were analyzed with the logistic regression. A model comprising only of significant individual parameters (p ≤ 0.05) and describing the relationships between terpene concentrations and the probability of having stable beverages was obtained. When citral and β-pinene were combined, the citral concentration required to achieve a 50% probability of having stable bottles (P = 0.5) dropped from 100.9 µL/L in the absence of β-pinene to 49.3 µL/L in the presence of 20 µL/L of β-pinene. The mixture of citral and linalool was less effective, in fact, the same probability (P = 0.5) was obtained combining 60 µL/L of linalool with 35.1 µL/L of citral. The addition of 20 µL/L of linalool and β-pinene reinforced citral bioactivity and the concentration of citral needed to reach P = 0.5 fell from 100.9 µL/L in the presence of citral alone to 42.0 µL/L. The presence of both linalool and β-pinene at a concentration of 40 or 60 µL/L in the absence of citral led to a lower spoilage probability (P = 0.58 and P = 0.93, respectively). It can be concluded that the antimicrobial potential of the three terpenes alone can be strengthened combining appropriate concentrations of each of them. This study confirmed also the potentiating effect of a mild temperature treatment on the antimicrobial efficacy of the molecules. Neither the thermal treatment alone nor the presence of the terpenes at their maximum concentrations (without thermal treatment) were able to guarantee the microbial stability of the beverages.