The valorization of agro-industrial wastes represents a huge advantage for the transformation industry and the environment. Particularly, biomasses like spent coffee grounds are largely produced worldwide by coffee-based industries and do not require any pre-treatment for their use as raw material for extraction processes. Indeed, exhaust coffee grounds are usually collected in separated containers, either in coffee shops either in vending machines and are already in powder form. Several authors, analyzing chemical composition of spent coffee grounds, demonstrated their potential use as natural source of antioxidants, which are molecules that can find several applications in food, pharmaceutical and cosmetic industries. In the first chapter of this work, a brief introduction on the biorefinery concept and proposed reuses of spent coffee grounds, based on literature data, were exposed, focusing the attention on the main valuable step of a potential biorefinery based on coffee: the recovery of high added-value compounds from exhaust coffee by green and innovative techniques and methods finalized to preserve their bioactivity. The antioxidant activity of spent coffee grounds can be traced back to polyphenols, like chlorogenic acid and its isomers, its derivatives, and melanoidins. The antioxidant activity and type of antioxidants that are recoverable from exhaust coffee powder, as well as its chemical composition, are functions of the type of raw material (e.g. Coffea arabica, Coffea canephora), but also the brewing process used for beverage preparation. In this thesis, spent coffee grounds collected by common vending machines, were subjected to a preliminary characterization, whose results were reported in chapter 2, and to a study on different extraction techniques (solid-liquid extraction, high- pressure and temperature-assisted extraction, microwave-assisted extraction and continuous pressurized ultrasound-assisted extraction), solvents, and operating conditions. Indeed, one of the main aims of this research project was to perform the antioxidant recovery from SCG by using green solvents as water-ethanol solutions and to improve the extraction yields by working on the other process variables. A study on the recovery of antioxidants by microwave-assisted extraction was carried out in chapter 3, evaluating process optimization, extraction kinetics and the potential use of the extract for cosmetic purposes. For the study, both response surface modeling and kinetic studies were employed as tools for process optimization and the extracts were evaluated in terms of total polyphenol yield, total flavonoid yield and antiradical power. Chapter 5 deals with the utilization of high pressure and temperature-assisted extraction for antioxidant recovery from spent coffee grounds, while continuous pressurized ultrasound-assisted extraction results were reported in chapter 6. Since antioxidants are subjected to loss of activity when exposed to heat, light, and oxygen, novel and green post-processing (freeze-drying and supercritical antisolvent extraction) and microencapsulation techniques were used for antioxidant activity preservation, and to enhance product features. Thus, spray drying was employed to micro-encapsulate spent coffee grounds extracts using both inulin and maltodextrins as wall materials suitable for food application purposes. Encapsulation was optimized (chapter 4) by investigating process parameters like coating agent composition, inlet temperature, feed flow rate, using response surface methodology. In addition, different preservation techniques, finalized to prevent loss of activity and improve extract bioavailability were evaluated in chapter 5, where also a novel technique, supercritical fluid-assisted liposome formation (SuperLip), was tested for the encapsulation of the produced extracts in liposomes.
|Titolo della tesi:||Spent coffee grounds valorization by green and innovative extraction technologies: process optimization and product stabilization for industrial purposes|
|Data di discussione:||30-apr-2019|
|Appare nelle tipologie:||Tesi di dottorato|