Impact of pre-growth and storage conditions on the survival of Listeria monocytogenes in acidic baby fruit purees: Implications for food safety and consumer practices

Abstract

Listeria monocytogenes is a foodborne pathogen responsible for listeriosis, a serious disease with high mortality rates, particularly affecting vulnerable populations. Its resilience to environmental stresses, such as pH and cold temperatures, makes it a critical public health concern. Baby fruit purees are high acidic food products that are often the first foods to be introduced as variety in babies' diet. In the case of partial consumption of fruit purees, consumer practices may influence exposure of infants to L. monocytogenes in the event of accidental contamination. The purpose of the study was to investigate the survival of L. monocytogenes in fruit purees under various storage conditions and previous growth conditions, simulating consumer practices. L. monocytogenes 10403S grown at 10 °C (fridge), 25 °C (ambient) or 37 °C (control) at pH 5.5 or 7.2, was inoculated in fruit puree and stored at 10 °C, 25 °C, and 37 °C. Decimal reduction times obtained from fitting inactivation data to the log-linear model, were significantly influenced by storage temperature, showing a protective effect of refrigerated temperature, with extended survival times (mean D_10°C = 10.8 ± 0.34 h at 10 °C). Growth conditions, assimilated to conditions preceding accidental contamination, also influenced L. monocytogenes survival; cells pre-cultured at acidic pH 5.5 before inoculation in fruit puree, exhibited increased resistance, particularly at growth temperatures above 25 °C. This study confirms the role of acid pre-adaptation in enhancing L. monocytogenes survival under acidic stress. These findings highlight the importance of understanding stress adaptation for developing more accurate predictive microbial risk models to communicate appropriately with consumers.

Keywords: Acid resistance; Adaptation response; Bacterial behaviour; Exposure assessment.