Essential oils and hydrolates: designing a winning strategy for successful applications in the food industry

The growing demand for clean label products has driven the search for natural alternatives to synthetic preservatives. Essential oils (EOs) and hydrolates, used as biopreservatives, have emerged as promising solutions for ensuring food safety and extending product shelf life. In fact, these biopreservatives exert activity against microbial cells by modifying the expression of genes that encode for different cellular functions, including destabilising cytoplasmic membranes, interfering with quorum sensing, and virulence factors. However, the lack of standardised research protocols and the inherent variability of these natural substances may compromise industrial applications, particularly in terms of consistency and effectiveness across different food products, which can lead to unpredictable results in food preservation and safety. Furthermore, the concentrations required to obtain antimicrobial activity are a key challenge for technological transfer because they can affect both product acceptability and cost when higher concentrations lead to undesirable flavours or tastes in food products. This presentation aims to propose a procedure for the successful application of EOs and hydrolates in the food industry, based on several studies carried out by the authors in different food areas. Starting from the selection of aromatic plants, the steps of projects aimed at substituting food preservatives are described. The authors provide hints for solving problems that are crucial for the success of the project, such as the evaluation of the sensory threshold, the toxicological issues, the regulatory aspects, the mechanisms of action, and the dose reduction, also considering the risk associated with sub-MIC doses. Moreover, the authors propose applications where hydrolates, usually considered by-products of steam distillation, can provide the added value of water-soluble bioactive compounds with minimal sensory impact. To investigate microbial reactions to treatments with biopreservatives, experiments carried out in gnocchi formulations are taken as a case study to describe the evaluation of the stress response in Bacillus cereus and Bacillus subtilis treated with Thymus vulgaris and Origanum vulgare subsp. hirtum EOs. In this study, many genes were downregulated at 6 h, indicating that the stressful condition extended the lag phase. However, the gene spo0A was upregulated from 6 h, suggesting an attempt to restore cellular communication and repair membrane damage. All in all, the two EOs mostly affected quorum sensing and cell membrane integrity, with variations in the genes involved.