Interaction and protection of antimicrobial compounds with carbohydrate-based colloidal systems for improved food safety

The food processing industry has focused on using conventional methods for food preservation. However, the recurring incidence of food borne illnesses and outbreaks due to pathogenic or spoilage organisms have called for creation of novel intervention strategies. In recent years, antimicrobial compounds from natural sources are gaining significant importance in improving food safety and security. However, antimicrobials suffer from extensive degradation when applied to complex food systems due to several specific or non-specific interactions. There is an urgent need for the protection of such antimicrobials to prolong their activity in foods. One strategy of achieving the goal is by the combination with a delivery vehicle. In this work, we explored the interaction between novel carbohydrate biomaterial and model antimicrobial compounds. In addition, we studied the protection of such antimicrobials using carbohydrate based colloidal systems. In the first part, we examine the interactions between nisin and carbohydrate based materials in non-emulsion (aqueous) and emulsion systems. Phytoglycogen octenyl succinate (PG-OS), a dendrimer-like amphiphilic material was used as the model carbohydrate nanoparticle and nisin was used as the model antimicrobial peptide. Equilibrium dialysis experiments showed that PG-OS with different degree of substitution (DS) interacts with nisin in a Langmuir monolayer adsorption pattern in both non-emulsion and emulsion systems. The monolayer adsorption capacity (Qm) increased in non-emulsion system and was significantly higher in the emulsion system. At the equivalent concentration of PG-OS (5.0 mg/mL), and nisin (200 µg/mL), adsorbed nisin concentration in aqueous and emulsion systems were 22 and 157 µg/mL, respectively. The study demonstrated that DS of PG-OS can be used to control nisin adsorption in the non-emulsion system. In addition, the distribution of PG-OS at the droplet interface affects nisin adsorption in the emulsion system. In the second part of the thesis, we studied the protection of nisin as model antimicrobial using starch octenyl succinate or starch-OS based oil-in-water emulsion system against Listeria monocytogenes. Cantaloupe juice was used as the model food system because of its significant protease concentration, which depletes nisin activity. Nisin was combined with starch-OS stabilized emulsion at 500 µg/mL initial concentration and compared with nisin solution in cantaloupe juice model. The study demonstrated that protease in cantaloupe juice was the key factor behind nisin depletion. Antimicrobial efficacy tests revealed that starch-OS stabilized emulsion can prolong nisin activity till 6 days of interaction with cantaloupe juice. In addition, equilibrium dialysis experiments demonstrated that nisin adsorption to the colloidal system was responsible for prolonged antibacterial activity. In the last part, the protection of nisin and thymol combined with starch-OS emulsion against a model Gram-positive bacteria (Listeria monocytogenes) and a model Gram-negative bacteria (Salmonella Typhimurium) in cantaloupe juice is reported. Thymol, being a volatile essential oil component suffers from extensive loss from foods due to evaporation, therefore it needs to be protected using a delivery vehicle. In general, combinations of nisin and thymol formulations demonstrated minor collaborative effects with regards to bacterial inhibition. Delivery system combined antimicrobials demonstrated effect till 7 days of incubation with cantaloupe juice. Out of all formulations, nisin and thymol combination with emulsion demonstrated the best antibacterial efficacy for a prolonged period of time. After 7 days of incubation, it showed 2.53 and 2.80 log10 CFU/mL difference against Listeria monocytogenes and Salmonella Typhimurium, respectively. Overall, this research was an attempt to understand the interaction and extend the effect of antimicrobial molecules combined with carbohydrate materials as colloidal systems