Development of nano-encapsulation systems for the food antifungal natamycin: Formulation, characterization and post-processing

Food spoilage has become in the last decades one of the biggest challenges faced by the food industry, with a significant amount of products thrown away at every step of the supply chain. Microbial contamination is listed as one of the major causes of food spoilage and can be at a large extent prevented by application of antimicrobial compounds. Recent trends on the market such as an increasing demand of consumers for natural preservatives and their application in reduced quantities, coupled with the difficulty for industrials to get new antimicrobials approved by health authorities, lead the food industry to a process of reformulation and improvement of functionality and efficiency of already approved ingredients. Natamycin, a naturally-occurring food preservative widely used for the protection of food surfaces, is one of the most popular antifungal agents currently used. This molecule presents several advantages linked to its natural origin, long history of safe use, efficiency at low concentrations and limited modification of food products when applied. Current formulations of the preservative offer however limited specificity or tunability towards applications and little possibilities of controlled/triggered release. This compound also presents a relatively poor aqueous solubility detrimental for its antifungal action and is very sensitive to early-stage degradation by environmental factors such as extreme pH, oxidation and UV exposure.
The main goal of this PhD thesis was to determine if the incorporation of this molecule within nano-encapsulation systems could provide benefits for availability, tunability and degradation issues. As a first step, formulation, optimization and characterization of two model nano-encapsulation systems (biodegradable polymeric nanospheres and nano-liposomes) were performed and compared in terms of relative benefit for the encapsulation, delivery, antifungal performance and stability of the antimicrobial. Post-processing of the most promising nano-encapsulation systems in order to obtain commercial products was further evaluated by purification/concentration (tangential flow filtration) or by transformation into redispersible dry products by lyophilization.
Nano-liposomes were found overall superior to polymeric nanospheres for the encapsulation and delivery of our molecule and offer higher possible levels of tunability in terms of release rates and antifungal performance. Lyophilization in presence of carbohydrates turned out to be a valuable method for the preparation of dried products with enhanced long-term stability of the antifungal, compared to concentrates prepared by tangential flow filtration, a tedious process that impacted negatively the stability of the preservative.