Safety is found in steamy apple slices
Food safety is no longer simply a sensible standard for dried fruit processors. It is a firm federal fixture. Under the FDA’s Food Safety Modernization Act Final Rule for Preventive Controls, manufacturers must prove that their processes can consistently control harmful pathogens. For dried apple producers, that challenge has sparked fresh interest in practical processing steps that improve safety without sacrificing the crisp character consumers expect.
Researchers from Michigan State’s Department of Biosystems & Ag Engineering explored one promising possibility by testing whether a brief burst of steam before drying could strengthen Salmonella control while safeguarding product quality.
The work, delivered by Narindra Randriamiarintsoa, Ian Hildebrandt, Michael James and Bradley Marks, built on previous studies showing that humidity can help reduce Salmonella during apple drying. Earlier laboratory studies suggested increased humidity improved pathogen inactivation in tightly controlled systems. Even so, evidence demonstrating whether this approach could succeed under commercially relevant drying conditions has remained limited.
The Michigan State team set out to bridge that gap with testing designed to reflect real production practices.
Their goal was straightforward but significant. The researchers evaluated the effectiveness of steam pre-treatment on Salmonella inactivation during a two-stage apple drying process using an impingement oven (a type of convection oven that uses jets of hot air to penetrate the cold air around food). Beyond improving microbial safety, they also wanted to determine whether steam treatment could preserve the appearance and texture that define high-quality dried apple slices.
The process paired precision with practicality. Apple slices either received a two-minute steam pre-treatment at a dew point of 158º F or remained under dry conditions at a 75.2º dew point before drying. The samples were then dried at temperatures of 176º, 230º or 284º for one to two hours with airflow maintained at 20% fan speed. This combination allowed the team to evaluate how steam, heat and humidity worked together throughout the drying process.
The findings painted a persuasive picture. Steam pre-treatment significantly improved the overall lethality against Salmonella during drying, demonstrating that a relatively simple processing step can strengthen food safety performance. The researchers also developed a model describing Salmonella inactivation as a function of product temperature and process humidity. That model provides valuable insight into how processors can better predict and validate microbial reductions during production.
Importantly, better safety did not come at the cost of better quality. Steam-treated apple slices displayed significantly lower browning than untreated samples, creating a more appealing finished product. Both the steamed and non-steamed apples also showed lower browning index values than comparable commercial products. Texture testing revealed no significant differences in hardness between treated and untreated samples. The result was a balanced blend of stronger safety and stable sensory quality.
For dried apple processors, these results offer promise. Steam pre-treatment could become an effective preventive control that supports FSMA requirements while maintaining product appeal. Rather than relying solely on higher temperatures or longer drying times, processors may be able to harness humidity as an additional hurdle against harmful pathogens.
Their research team’s continuing work focuses on developing user-friendly food safety validation tools to help dried fruit processors demonstrate regulatory compliance with confidence. By pairing scientific rigor with industry ready solutions, they are delivers meaningful momentum toward the safer processing of consistently satisfying slices.
by Enrico Villamaino
