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The heat process is a safe method of food preservation. The use of mathematical modeling for heat transfer by finite elements analysis (FEA) makes it possible to determine the cold spot of conventional and non conventional packages, evaluate their thermal history, microbial and enzyme inactivation and nutrients retention for an optimum process design. Several works use simplifications during mathematical modeling, such as adiabatic headspace, considering the thermal resistance of package negligible. The impact of these simplifications is rarely evaluated. The aim of the present work was to evaluate the effect of these simplifications on sterilization value (Fp) for a conductive food. Two commercial glass bottles (G1 and G2) were selected for the assays. FEA model was built using the bottles' real geometries. Three methodologies were evaluated, considering (i) the four components of the system, i.e., product, glass wall, headspace and metal cap, and uniform heating (PGHM); (ii) adiabatic headspace, i.e., a model considering product and glass wall, with its upper side adiabatic (PG); and (iii) only product, with adiabatic upper side (P). A tomato concentrate industrial pasteurizator profile was used as boundary condition. The Fp was determined by using two values of thermal coefficient (z), 5.5ºC and 12.5ºC, representing a possible range of contaminant’s z-value. The cold spot of the two packages was located at 32% (G1) and 46% (G2) of the product height. For the same process, the differences of Fp for the two packages ranged between 62 and 320%. Comparing the Fp by PGHM and PG models, differences were observed between 4 and 13%. These differences were over 45% when comparing PGHM with P models, even with similar thermal history. The results indicated the importance of the previous evaluation of the impact of each simplification on the accuracy of the model. Due to exponential relationship between temperature and reactions during the heat process, the need for Fp evaluation instead of thermal history in conductive food was confirmed.

Thermal process, specially the in‐package process, is one of the safest and most frequently used methods for food preservation. Mathematical models for heat transfer have been widely used as a powerful tool in safety and high‐quality food process design. The convective heat transfer coefficient (h) is essential for heat flux calculation in model boundary conditions, and its determination must be done by the actual heat transfer system. The present study has determined the h‐values for two commercial bottles (G1 and G2) in two water immersion systems, one for heating and one for cooling. It was calculated by an inverse heat transfer problem, using computational fluid dynamics. Two methodologies for h determination were compared, using either a conductive material or a convective material inside the packages. The methodology that uses a conductive material showed simpler and faster computational simulation, but presented a limitation related with the Biot number of the process. Results indicated a limitation in the most used methodology for h determination, and suggest that the convective material methodology can be an alternative for this analysis. For the same systems, the hheating value for G1 was almost 50% higher than for G2, and hcooling values for G1 were almost 70% higher than for G2. Differences obtained between bottles highlight the need to determine h for the exact heat transfer system. Moreover, these results indicate that there is a potential for process optimization only by varying its package format, as it can influence the heat flux for the packaging. PRACTICAL APPLICATIONS The results obtained from this study highlight the influence of geometry on the convective heat transfer coefficient among bottles and immersion water systems. It also confirms the possibility of optimizing the thermal process through package format changes, allowing the obtainment of safer products with better sensorial and nutritional characteristics at a lower cost and energy expenditure. However, further studies are needed to better understand the package geometry in thermal processes. On the other hand, it contributes for thermal processes studies as it stands out the importance of determining this property for the actual system studied, besides showing its limitations for determination based on a conductive product widely utilized in the literature.

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