FROM FOOD WASTE TO FOOD PRESERVATION: PRODUCTION AND APPLICATION OF SAKACIN A

This thesis has been conceived in the frame of a broader project named “NANOSAK- Nanocellulose–sakacin A conjugates for food packaging purposes”, financend by Fondazione Cariplo and developed in collaboration with several divisions of the Department of Food, Environmental and Nutritional Sciences (DeFENS), with the Department of Environmental Science and Policy (ESP) of the Università degli Studi di Milano and together with the Department of Food quality and preservation of the Instituto de Agroquímica y Tecnología de Alimentos (IATA), CSIC (Valencia, Spain). NANOSAK aims at exploring the use of cheese whey and/or their derivatives as cheap substrates for growth of bacterial species that produce two families of molecules: a specific bacteriocin sakacin A, and bacterial cellulose (BC), that will be turned into nanocellulose (BNC) using sustainable procedures. In Italy most of the liquid whey is exported, often after an ultrafiltration (UF) step. The by-product of whey UF, namely permeate, still represents a valuable raw material due to the high content of lactose, minerals and vitamins. This permeate from the dairy industry is a low-cost alternative for industrial production, which can provide high yields of the antimicrobial agent. Both the molecules, sakacin A and bacterial cellulose, expected to be produced by microorganisms through whey utilization can be considered products of high added value. Bacterial cellulose also represents an emerging material with excellent intrinsic properties due to its high crystallinity, tensile strength and water holding capacity (Shoda and Sugano, 2005). On a subsequent step, NANOSAK will also aim at using sustainable procedures for turning BC into nanocellulose, in fact, bacterial cellulose has potential to be turned into bacterial nanocellulose by chemical modification, thus forming an innovative material that finds applications across several industrial sectors, including the use in the food packaging sector. Recently, more attention was given to the development of packaging materials based on bacterial nanocellulose as functional nanofiller in papers and in coatings for plastic matrices. An interesting application is related to the use of cellulose nanocomposites to extend shelf-life and enhance the quality of perishable foods, not only acting as barriers against moisture, water vapor and gasses but also serving as a carrier of active substances, such antimicrobials, in bioactive packaging (Lee et al., 2013). In particular, stand-alone BNC films and coatings incorporating sakacin A will be developed, using food-compatible biopolymers and aqueous chemistry. BNCs/sakacin A conjugates will also be applied to paper by surface sizing. The functional properties of the nanocellulose/sakacin A films and coatings will be assessed, as well as the kinetics of sakacin A release in several food simulants, in order to establish suitable mathematical release models. The results will contribute to increase shelf-life and quality of perishable food. The main significance of NANOSAK is the demonstration that application of industrial biotechnologies will achieve innovative and highly sustainable bioprocesses. The bioeconomic model approach developed by the project would give original opportunities to improve the sustainability of Lombardy economy, in the general food sector, and for what attains food packaging operators. In particular, the focus of this thesis is the optimization of the production of the bacteriocin sakacin A using cheese whey permeate, its food-grade isolation and purification and the development of active packaging solutions based on the antimicrobial activity of this molecules.