Extraction and characterization of polysaccharides and phenolic compounds from spent coffee grounds and their incorporation into edible films/coatings for food applications (2016)

Coffee has been one of the most popular beverages around the world since ancient times. It is made from a mixture of hot water and coffee powder being consumed for its refreshing and stimulating properties. However, along its production process many wastes are generated. Spent coffee ground is the major waste produced during the soluble coffee preparation. This residue is rich in polysaccharides and polyphenols, making its use interesting as raw material for the production of edible films and coatings for foods. Nowadays, food packaging industries explore edible coatings to replace the synthetic liners, in order to protect the environment and offer consumers a product of high quality, while reducing synthetic chemical preservatives. Therefore, this project aims at the extraction of polysaccharides and phenolic compounds from spent coffee grounds and their incorporation into edible films and coatings for further application on goldenberry fruit (Physalis peruviana) in order to increase its shelf-life. The thesis work is based on a sequence of tasks, starting by the characterization of two coffee residues (i.e. spent coffee grounds (SCG) and coffee silverskin (CS)) in order to have a detailed knowledge of their chemical composition and functional properties and then, choosing the residue with the highest polysaccharide content and antioxidant activity. After having selected SGC as the residue of interest, two different techniques were tested to extract polysaccharides from SCG, including an alkali pretreatment and autohydrolysis, being the later used to extract the phenolic compounds. The polysaccharides and phenolic compounds were characterized in terms of their physicochemical and functional properties, including antioxidant and antimicrobial activities. The extracted phenolic compounds were encapsulated in maltodextrin and gum arabic matrices using freeze-drying and spray-drying processes and then, the encapsulation efficiency was evaluated. On the other hand, different concentrations of the polysaccharides extracted were incorporated in carboxymethyl cellulose (CMC)-based films and their effect on the films properties were evaluated. Finally, the influence of three coatings on physicochemical and microbiological properties and gas exchange rate of goldenberry (Physalis peruviana) was determined at different temperatures and relative humidities (RH) of storage. The tested coatings were: coating A (CMC-based coating), coating B (CMC-based coating with a selected polysaccharide concentration in the previous step) and coating C (CMC-based coating with the selected polysaccharide concentration and phenolic compounds encapsulated). Results showed that SCG residues are sugar-rich lignocellulosic materials, composed by high levels of insoluble and soluble dietary fibers with interesting functional properties. The methods and conditions used to extract polysaccharides and phenolic compounds from SCG showed to be efficient (39% and 29% (w/w) of recovered polysaccharides by alkali pretreatment and autohydrolysis, respectively, and 41.36 mg/g SCG of phenolic compounds). The most relevant sugar recovered from both methods was galactose, followed by arabinose, mannose and glucose, while chlorogenic acid and flavonoids content were among the recovered phenolic compounds with high antioxidant activity. The results also indicated that the extracted polysaccharides presented good thermal stability. Additionally, these polysaccharides showed high antioxidant activity and antimicrobial against P. violacea and C. cladosporioides, making them attractive bioactive compounds. Although freeze-drying and spray-drying showed to be appropriated techniques for encapsulation of phenolic compounds, in this case, the use of maltodextrin as wall material and freeze-drying as encapsulation method showed the best encapsulation efficiency. In general, the addition of polysaccharide from SCG in CMC-based films improved and/or maintained the physicochemical properties of the edible films when comparing with CMC-based films without polysaccharides from SCG, reducing the water solubility of the films and acting as a light barrier. The results showed lower gas transfer rates (O2, CO2 and ethylene) for the coated fruits in comparison with the uncoated fruits when using a storage temperature of 20 °C and a RH of 65%. Physicochemical properties of goldenberries with or without coatings present significant changes regarding weight loss and the microbiological contamination, being both reduced, in particular when the coating B was applied. In conclusion, polysaccharides and polyphenols extracted from SCG can be used as raw materials in the production of edible films/coatings for application on goldenberries turning these coatings into a promising way to replace synthetic packaging materials.