Why Salmonella is a Critical Concern Even in Dry Foods – A Scientific Perspective

When it comes to food safety, Salmonella is often associated with raw poultry, eggs, and dairy. However, this resilient pathogen poses a serious threat even in low-moisture foods (LMFs) like tea, spices, chocolate, flour, and powdered dairy products. Unlike many bacteria that perish in dry conditions, Salmonella has evolved to persist for months or even years in LMFs, making it a critical parameter in microbiological risk assessment.

Understanding Salmonella in Low-Moisture Foods

- Salmonella belongs to the family Enterobacteriaceae, typically thriving in intestinal environments. However, it survives desiccation stress (low water activity) and can become pathogenic when rehydrated.

- Due to its low infectious dose (as few as 10–100 cells can cause illness) (FDA, 2021), regulatory bodies enforce zero-tolerance limits in ready-to-eat (RTE) dry foods.

- Salmonella can persist for months in dry conditions and becomes heat-resistant at low water activity, meaning standard pasteurization is often ineffective in dry foods.

Growth and Survival Parameters of Salmonella

Temperature

Favorable Range: 35–43°C (95–109°F) (optimal)

Extreme Limits: Min: 5°C (41°F), Max: 54°C (129°F) (Podolak et al., 2010)

pH Tolerance

Favorable Range: pH 6.5–7.5 (optimal)

Extreme Limits: Survives in pH 4.0–9.5 (álvarez-Ordo?ez et al., 2019)

Water Activity (aw)

Favorable Range: >0.94 for growth

Extreme Limits: Can survive at aw 0.2–0.5 (Beuchat, 2015)

Osmotic Stress Resistance

Favorable Range: Can tolerate high salt and sugar concentrations, aiding survival in dry foods (Mattick et al., 2000)

Detection Methods for Salmonella in Dry Foods

Given its low infectious dose and resilience in dry environments, Salmonella testing in LMFs requires highly sensitive detection methods.

Key Testing Methods

• Traditional Culture Methods: ISO 6579:2017, FDA BAM, and USDA-FSIS methods use pre-enrichment in BPW (Buffered Peptone Water) followed by selective enrichment (RV broth, TT broth) and plating on XLD, HE, or BGA agars.
• Molecular PCR & RT-PCR Methods: Rapid and specific identification via 16S rRNA or invA gene targeting.
• ELISA & Lateral Flow Assays: Common for quick screening but require confirmation. - Whole-Genome Sequencing (WGS): Increasingly used for source tracking and outbreak investigations.

(Salmonella in dry foods often enters a viable but non-culturable (VBNC) state, making detection difficult. Advanced methods like qPCR and WGS help identify these dormant cells)

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Critical Limits and Control Measures by Industry

To mitigate Salmonella risks, industries apply strict critical limits and process interventions:

Tea & Herbal Products

-??????? Critical Limit: Zero tolerance (absence in 25g sample)

-??????? Control Measures,

• Steam sterilization (≥90°C for 5–10 min)
• Irradiation (≥5 kGy) for microbial reduction
• Dry heat treatment (≥100°C)

Spices & Seasonings

-??????? Critical Limit: Absence in 25g (FDA, 2017)

-??????? Control Measures,

• EO (ethylene oxide) treatment for decontamination
• Superheated steam (≥120°C)
• High-pressure processing (HPP)

Chocolate & Cocoa Products

-??????? Critical Limit: Absence in 375g (EU Regulation 2073/2005)

-??????? Control Measures,

• Roasting cocoa beans at ≥130°C
• Post-roast contamination prevention (hygiene & GMPs)

Dairy & Infant Formula (Powdered)

-??????? Critical Limit: Absence in 25g (Codex Alimentarius, 2020)

-??????? Control Measures,

• Spray-drying with inlet temp ≥160°C
• Post-pasteurization GMP & HACCP monitoring

Flour & Bakery Ingredients

-??????? Critical Limit: Absence in 50g sample (FDA, 2018)

-??????? Control Measures:

• Heat-treated flour (≥90°C)
• Hygienic milling & post-processing controls

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As food safety professionals, we must continuously refine risk assessment and mitigation strategies to keep consumers safe.

Citations & References

• Beuchat, L. R. (2015). "Survival mechanisms of Salmonella in dry foods." Food Microbiology.
• álvarez-Ordo?ez et al. (2019). "Acid and pH resistance of foodborne pathogens." Frontiers in Microbiology.
• Podolak, R. et al. (2010). "Thermal resistance of Salmonella in low-water activity foods." Journal of Food Protection.
• Mattick, K. et al. (2000). "Osmotic stress and survival of Salmonella." Applied and Environmental Microbiology.
• ISO 6579:2017, Microbiology of food and animal feeding stuffs – Horizontal method for detection of Salmonella.

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