The aim of this work was to characterize the essential oil (EO) of Eryngium foetidum (EfEO) and assess its activity toward Listeria monocytogenes in broth and during thermal inactivation of the pathogen in pineapple juice. In this respect, EfEO was chemically characterized, and its antilisteria potential in broth as a function of pH, cell load, and EfEO concentration was assessed through a central composite design. Furthermore, the inactivation kinetics of L. monocytogenes in the juice were assessed by combining EfEO and low pasteurization temperatures. A total of 81 compounds were identified from EfEO. The reduction of pH and cell load increased EO activity. The use of only 15 ppm of EfEO during pasteurization of pineapple juice at 60°C reduced the time required for a 4-log reduction in L. monocytogenes CFU/ml by 74.9% (i.e., from 8.5 to 2.1 min) compared with treatment without EfEO. It could be concluded that EfEO activity toward L. monocytogenes increases with the reduction of pH and that it can be used at sublethal concentrations in combination with low temperatures in pineapple juice pasteurization. This study demonstrates that EO-assisted pasteurization is a promising strategy for the reduction of thermal impact during juice production. EfEO is easily available and compatible with many juices and is thus promising for industrial application.

Background: Spices are widely consumed in Cameroon, but there is no data available concerning their mycotoxin contamination. A cross-sectional study was conducted from February to June 2017 to assess the occurrence of Ochratoxin A (OTA) in black pepper, white pepper and clove sold in three main markets of Yaoundé (the capital of Cameroon), and the health risk that can be associated taking into account consumers' practices during and after purchase.

Past research on the association of natural antimicrobials and low temperatures for fruit juices pasteurization has not targeted acid-adapted strains which are yet the most relevant strains in these products. We found that previously acid-adapted Escherichia coli ATCC 25922 cells exhibited an increase of their resistance to thermal inactivation at 55 8C for 5 min both in the presence and absence of carvacrol (30 mL/L). The inactivation of E. coli was more intense in pineapple (pH 3.25) and orange (pH 3.61) juice, than in watermelon juice (pH 5.4). Supplementation of juices with carvacrol decreased the survival of both acid-adapted and non-adapted bacterial cells. Our results suggest that the supplementation of fruit juices with natural antimicrobials, such as carvacrol, may contribute to counteract the mild thermal tolerance developed by acid-adapted bacteria. Given the different properties of fruit juices, such combined treatments need to be developed specifically for each fruit product. Practical applicationsSupplementation of fruit juices with natural antimicrobials has been described to increase the efficiency of microbial mild thermal inactivation treatments. However, its effect on the thermal resistance of acid-adapted cells has not previously been addressed. We observed that acid adaptation enhances mild thermal tolerance. Our results suggest that natural antimicrobials can effectively counteract the mild thermal tolerance of acid-adapted cells. The combination of mild temperature treatments and natural antimicrobials is a firm alternative to conventional pasteurization to ensure the safety of fruit juices without affecting their nutritional properties. Moreover, this combined strategy does not require expensive novel technologies or high energy consumption.

Mild thermal treatment in combination with natural antimicrobials has been described as an alternative to conventional pasteurization to ensure fruit juices safety. However, to the best of our knowledge, no study has been undertaken to evaluate what could be its effect on their color and nutritional value. This study therefore aimed at assessing how a low thermal pasteurization in combination with carvacrol could affect these parameters, with orange, pineapple, and watermelon juices as selected fruit juices. The experimental design used had levels ranging from 50 to 90°C, 0 to 60 μl/L, and 0 to 40 min for temperature, concentration of carvacrol supplemented, and treatment length, respectively. The only supplementation of fruit juices with carvacrol did not affect their color. In comparison with high thermal pasteurization (>70°C), a combined treatment at mild temperatures (50–70°C) better preserved their color, antioxidant capacity (AOC), and vitamin C content, and increased their total phenolic content (TPC). Globally, carvacrol supplementation had a positive impact on the TPC of thermally treated juices and increased the AOC of treated watermelon juice, which was the lowest of the three fruit juices. Mild heat treatment in combination with natural antimicrobials like carvacrol is therefore an alternative to limit the negative effects of conventional pasteurization on fruit juices quality.

Aims: This study aimed at assessing the relationship between the initial antimicrobial activity of carvacrol and its effect at sub-lethal concentration when used for low thermal treatment of fruit juices.

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The strengthening effect of a mild temperature treatment on the antimicrobial efficacy of essential oils has been widely reported, often leading to an underestimation or a misinterpretation of the product’s microbial status. In the present study, both a traditional culture-based method and Flow Cytometry (FCM) were applied to monitor the individual or combined effect of Origanum vulgare essential oil (OEO) and mild heat treatment on the culturability and viability of Escherichia coli in a conventional culture medium and in a fruit juice challenge test. The results obtained in the culture medium showed bacterial inactivation with an increasing treatment temperature (55 °C, 60 °C, 65 °C), highlighting an overestimation of the dead population using the culture-based method; in fact, when the FCM method was applied, the prevalence of injured bacterial cells in a viable but non-culturable (VBNC) state was observed. When commercial fruit juice with a pH of 3.8 and buffered at pH 7.0 was inoculated with E. coli ATCC 25922, a bactericidal action of OEO and a higher efficiency of the mild heat at 65 °C for 5′ combined with OEO were found. Overall, the combination of mild heat and OEO treatment represents a promising antimicrobial alternative to improve the safety of fruit juice.