Sustainable formulations composed of biosurfactants and phytochemicals with potential application in fresh-cut food industry

The demand for minimally processed fruits and vegetables is increasing every year as consumers become aware of the health benefits associated with the consumption of fresh, unprocessed produce. Washing and disinfection steps are critical for ensuring the safety of these products, which are susceptible to microbial contamination and lack any thermal treatment. The most used sanitizers are chlorine-based, yet concerns have been raised regarding their efficacy and safety, due to the formation of toxic disinfection by-products. Thus, with the aim of proposing innovative green and safe alternatives, we have formulated and thoroughly characterized mixtures composed of two natural phytochemicals, either 1,2-O,O'-diacetyllycorine (DAL) or ungeremine (UN), and the biosurfactant rhamnolipids (Rha). We performed an investigation into the ecotoxicological properties of DAL and UN, the results of which are encouraging with regard to their utilisation in washing formulations. The combination of UN and Rha has been shown to enhance the solubility of UN and the micellization of Rha, due to electrostatic interactions between the positively charged UN molecules and the negatively charged Rha molecules. In contrast, DAL exhibited minimal interaction with Rha. Notably neither DAL nor UN modify the surface properties of the biosurfactant necessary for ensuring optimal wetting of food surfaces. As a proof of concept, the washing process of minimally processed fruits and vegetables was closely mimicked using lettuce leaves: we showed that the UN + Rha formulation is highly effective against several food-related pathogens and is more effective than the control hypochlorite solution against the normal microbial load present on lettuce leave; furthermore it does not affect leaf appearance for up to eight days. Our results highlight the importance of a comprehensive physico-chemical characterisation of both isolated components and complete mixtures to facilitate the rational design of sustainable formulations for use in food processing. Moreover, this study indicates that formulations based on biocompounds have the potential to be proposed as effective green washing formulations for the fresh-cut food industry.