Heat sensitization of Escherichia coli by the natural antimicrobials vanillin and emulsified citral in blended carrot-orange juice

Abstract

Efforts have been focusing on the way to overcome the impact of heating on food quality while achieving the desired shelf life. In this sense, the thermosensitization of E. coli using the natural antimicrobials vanillin (V; 0.8 and 1.0 g/L) or/and emulsified citral (C; 0.012 and 0.025 g/L) was assessed at 58 and 60 °C in blended carrot-orange juice (pH 4.0; 9.0°Brix). All combined treatments exceeded the inactivation achieved by the single thermal treatments in half the time. The inactivation of the binary treatments (V or C + heating) at 58 °C was 3.84-0.62 log-cycles more effective than the control, particularly with vanillin. Ternary treatments (V + C + heating) at 58 °C increased the microbial reduction approximately 30%; however, at 60 °C no further inactivation was observed, suggesting the thermal effect prevailed. This was verified by the higher b Weibullian parameter and the narrower frequency distributions. The selected treatments 1.0 V + 0.012C at 58 and 60 °C were challenged against the pathogenic E. coli O157:H7 and found to be effective. Additionally, the microbiota of the juice was maintained at acceptable levels during storage (4 °C). In conclusion, there was an increase in the heat sensitivity of E. coli due to the natural antimicrobials, particularly vanillin at 58 °C. Therefore, reducing the intensity of the thermal processing will lead to clean label, high-quality juices, while addressing food safety requirements.

Keywords: Citral; Emulsion; Escherichia coli.; Heat sensitization; Mild thermal treatment; Vanillin; Weibull model.