Annatto (Bixa orellana) and its extracts have been used as a colourant to provide orange/red hues to fat-rich products, and recently it has also demonstrated to possess inhibitory activity against some pathogens. Alheira is a non-ready-to-eat sausage from Northern Portugal, which has shown moderate occurrence and survivability of Staphylococcus aureus during processing. The aim of this study was to model the effect of annatto extract against S. aureus (SA) in alheira during maturation.
Alheira batter was prepared with 0.0%, 0.5%, 1.0% or 1.5% of annatto extract (w/w), and stuffed in pre-washed natural casings, following inoculation with a SA overnight culture to reach ~5 log CFU/g, and hung in a climatic-controlled chamber at 10 ºC for 13 days. Moisture, pH and SA counts were determined every 2-3 days. For every treatment, a dynamic model was adjusted: a log-decay function with tail in differential form as primary model (with parameter D-value), coupled to a secondary model Bigelow equation of D as a function of the varying pH (with parameters logD* at pH 7.0 and zpH).
The models adequately fitted to all survival curves with residuals and root mean square errors between 0.0008-0.0016 and 0.029-0.040, respectively, producing significant parameter estimates. The addition of extract produced logD* slightly higher (1.040 [SE=0.064], 1.040 [SE=0.294] and 1.079 [SE=0.303]) than the control (1.036 [SE=0.142]), whereas zpH tended to be lower with increasing extract doses (2.426 [SE=0.561], 2.144 [SE=0.230], 2.113 [SE=1.033] and 2.005 (SE=0.904)). Therefore, the addition of annatto extracts significantly decreased the time to achieve one log reduction, which in practical terms corresponded to up to 1.04 [SE=0.08] log CFU/g reduction by the end of maturation.
Through a novel dynamic predictive microbiology model, this work characterised S. aureus survival parameters in alheiras; and demonstrated that annatto extract has beneficial effects in controlling this pathogen during maturation.