preprints.org > biology and life sciences > food science and technology > doi: 10.20944/preprints202411.0358.v1

Preprint Article Version 1 This version is not peer-reviewed

Version 1 : Received: 4 November 2024 / Approved: 5 November 2024 / Online: 5 November 2024 (16:56:41 CET)

Drying is one of the most effective preservation methods for extending the shelf-life of perishable foods. Microbial safety of the final products has not been a concern until outbreaks reported over the past decade in products contaminated with bacterial pathogens, in particular Salmonella. There is now an urgent need to understand the influence of process conditions on the thermal inactivation of pathogens in various drying operations. This study aimed to develop a predictive model for Salmonella inactivation in diced apples during hot air drying and in high-humidity heating in closed environment. Fresh-cut apple cubes (6 mm) were inoculated with a cocktail of Salmonella enterica strains (Enteritidis PT30, Montevideo 488275, and Agona 447967). The samples were placed in a preheated sample treatment box within a convection oven under three conditions: 1) open air drying, the sample box was open in the oven pre-set at 90°C (Drying-90); 2) closed-box heating, the oven was also set at 90°C (Preheating-90); and 3) closed-box heating, the oven was at 70°C (Pre-heating-70). For open-air drying, hot air at the oven temperature was circulated through the samples, facilitating the heating and drying. In closed box heating, the sample box maintained a high-humidity environment, retaining moisture evaporated from the apple samples and allowing heat conduction through the box walls. In each test, air temperature, relative humidity (RH), and sample temperatures were monitored, and Salmonella survival was measured at multiple time points. After 10 minutes of heating, the air RH levels in the closed-box configurations were 66% (Preheating-90) and 74% (Preheating-70), much higher than in the Drying-90 condition (30%). Results indicated that in-box heating achieved a 5-log reduction Salmonella after 8.5 min at 90°C, compared to 28.7 min in open air drying at the same temperature. It took 14 min to achieve 5-log reduction at 70°C in in-box heating. A mathematical model was developed to estimate sample surface RH based on sample temper-ature and ambient absolute humidity, with further adaptation to predict microbial inactivation over time using surface temperature and RH profiles. This model accurately predicted Salmonella inactivation across all treatments (RMSE = 0.92 log CFU/g, R² = 0.86), with thermal death param-eters comparable to literature values from isothermal studies. This study highlights the im-portance of air humidity in enhancing bacterial inactivation during drying and suggests that a preheating step under high-humidity conditions may serve as an effective control measure, en-suring microbial safety before conventional drying. Additionally, this work demonstrates the potential of a nonlinear mathematical model to predict microbial inactivation under complex drying conditions with fluctuating temperature and humidity.

apple drying; Salmonella inactivation; Food drying process; Nonlinear modeling; humidity-controlled preheating; Low-moisture foods; Predictive microbiology

Biology and Life Sciences, Food Science and Technology

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