Evaluation and Quantification of Heat Treatments Applied to Food Preserves

Abstract

The quantitative study of heat treatments for sterilisation uses the Bigelow model to calculate the sterilising value (F). Calculation of F requires the previous determination of parameters D (decimal reduction time at experimental temperature) and Z (thermal-death time parameter), obtained from the thermal-death kinetics. Herein we compare two different methods, namely the Bigelow model and a predictive-type statistical method, to calculate the sterilisation effect against Bacillus coagulans spores when heat was applied to runner bean preserves (variety: Helda). Samples were subjected to various autoclave treatments at working temperatures (T _ai) of 105, 107, 110, and 115°C for periods from 3 to 35 min. The microorganism used was B. coagulans. Sterilisation achieved by these autoclave treatments was determined by using the equation based on the Bigelow model (n _probe = F ^z _Ti/D _Ti) where n is the fractional concentration of colony-forming units (or some quality factor), F ^z _Ti is F at temperature T _i, and D _Ti is D at temperature T _i. The Bigelow model can be used to obtain Z (thermal-death time parameter), which is needed to calculate the traditional sterilisation factor F, but not to determine the reduction factor n for the heat treatments, particularly when microbial indicators with low decimal reduction times (D) are studied. The thermokinetic parameters for B. coagulans in runner bean solution resulted to be Z = 10.64°C and D ₁₂₁ = 0.0264 min (Af = 1.04). Treatment at 115°C for 20 min resulted in the most efficient sterilisation effect for B. coagulans.