Modeling the inactivation of Lactobacillus brevis DSM 6235 and retaining the viability of brewing pitching yeast submitted to acid and chlorine washing

Abstract

This study aimed to model the inactivation of Lactobacillus brevis DSM 6235 while retaining the viability of yeasts during washing brewer's yeast with phosphoric acid and chlorine dioxide. The independent variables in the acid washing were pH (1-3) and temperature (1-9 °C), whereas in the washing with chlorine dioxide, concentration (10-90 mg/L) and temperature (5-25 °C) were assessed. The predictive models obtained for the four response variables γ_LA, γ_Cl (decimal reduction of L. brevis DSM 6235), V_f/V0_LA, and V_f/V0_Cl (brewer's yeast viability ratio) were found to have R² > 0.80 and values of F_calc > F_reference. Then, the models were considered predictive and statistically significant (p < 0.10). Our results indicated that phosphoric acid and chlorine dioxide washing resulted in up to 7 and 6.4 (log CFU/mL) decimal reductions of L. brevis DSM 6235, respectively. On the other hand, the viability of the brewer's yeast ranged from 22.3 to 99.4%. L. brevis DSM 6235 inactivation was significantly influenced by parameters pH(Q) and T°C(Q) when phosphoric acid was applied, and by parameters mg/L(L), mg/L(Q), T°C(Q), and mg/L × T°C when ClO₂ was applied. The validation of the models resulted in bias (γ_LA, 0.93/V_f/V_0LA, 0.99 - γ_Cl, 1.0/V_f/V_0Cl, 0.99) and accuracy values (γ_LA, 1.12/Vf/V_0LA, 1.01 - γ_Cl, 1.08/V_f/V_0Cl, 1.03). The results of this study indicate that it might be possible to decontaminate brewer's yeast through acid and chlorine dioxide washing while keeping its viability. This procedure will result in the reduction of costs and the lower generation of brewer's waste.

Keywords: Beer; Decontamination; Food spoilage; Predictive microbiology; Wort.