Enumeration Agar, Acid Exposure and Sampling Time Are Relevant Factors Accounting for the High-Pressure Inactivation...

Area of Science:

• Food Science
• Microbiology
• Food Engineering

Background:

• High pressure processing (HPP) is a non-thermal method for inactivating microbes in foods.
• Its application in fruit and vegetable purees requires understanding inactivation dynamics.
• Enumeration methods and pre-treatment conditions can influence perceived microbial reduction.

Purpose of the Study:

• To evaluate the impact of enumeration agar on HPP inactivation of key foodborne pathogens (L. monocytogenes, Salmonella spp., E. coli) in fruit purees.
• To quantify HPP inactivation and sublethal injury in apple puree, considering acid exposure and sampling time.
• To identify factors influencing HPP efficacy in fruit-based products.

Main Methods:

• Comparative analysis of HPP inactivation using different enumeration agars in banana-apple and apple purees.
• Quantification of microbial inactivation and sublethal injury in apple puree after acid exposure (24h) and HPP (300 MPa, 2 min).
• Enumeration of surviving bacteria immediately and 24 hours post-HPP.

Main Results:

• HPP inactivation was higher in apple puree (0.9-4.5 fold) compared to banana-apple puree.
• Selective agars overestimated inactivation compared to nutrient-rich media.
• Acid exposure and delayed sampling (24h) significantly influenced inactivation and sublethal injury, with delayed sampling slightly increasing inactivation.
• E. coli O157:H7 (CECT5947) showed higher piezo-resistance, while L. monocytogenes Scott A was more piezo-sensitive.

Conclusions:

• Enumeration agar choice significantly affects HPP inactivation data interpretation.
• Acid exposure and sampling time are critical variables affecting microbial response to HPP.
• Product-specific validation and careful consideration of all factors are essential for effective HPP treatment design and verification.