_Applied_  
_sciences_  
Application of Thermal Methods to Analyze the Properties of Coffee Silverskin and Oil Extracted from the Studied Roasting By-Product  
[PERSON] 1,*, [PERSON] 1, [PERSON] 1, [PERSON] 1\({}^{\text{(\textregistered)}}\), [PERSON] 2 and [PERSON] 1  
1 Department of Chemistry, Institute of Food Sciences, Warsaw University of Life Sciences, 166 Nowouvsynowska Street, 02-787 Warsaw, Poland; [PERSON] (R.B. ); [PERSON]W.-W.); [PERSON]ESS] (J.B.); [PERSON].-L.)  
2 Department of Food Engineering and Process Management, Institute of Food Sciences, Warsaw University of Life Sciences, 166 Nowouvsynowska Street, 02-787 Warsaw, Poland; [PERSON]RESS]  
* Correspondence: [PERSON]L_ADDRESS]pl; Tel. : +4822-5937611 check for updates  
Received: 14 November 2020; Accepted: 7 December 2020; Published: 9 December 2020  
[PERSON] Abstract  
The aim of the study was to characterize the thermal properties of coffee silverskin and fat extracted from the material by using differential scanning calorimetry, modulated differential scanning calorimetry and thermogravimetry/derivative thermogravimetry. Additionally, the thermokinetic parameters, oxidative stability and fatty acid composition of the extracted oil were defined. Thermal decomposition of the studied coffee roasting by-product under oxygen occurred in three defined stages. The most significant changes in weight were observed in the region of 200-500 \({}^{\circ}\)C and correspond to polysaccharide decomposition. These results are in agreement with the data obtained from the differential scanning calorimetry curve. On the curve course of silverskin, two main exothermic peaks can be observed with a maximum at 265 and 340 \({}^{\circ}\)C. These exothermic events represent the transitions of hemicellulose and cellulose. Fat extracted from silverskin turned out to be a source of polyunsaturated fatty acids with the recommended n-6 to n-3 ratio reaching the value 4:1. The studied fat was characterized by low oxidative stability. Considering the obtained results, it can be stated that thermal analysis can provide fast and reliable data concerning the composition and properties of coffee silverskin and coffee silverskin oil. thermal analysis; differential scanning calorimetry; thermogravimetry; coffee silverskin; coffee silverskin oil +
Footnote †: journal: Applied  
process, an outer layer of green coffee beans, known as coffee silverskin, is removed [2]. Generally, green coffee beans with attached tegument (silverskin) are exported to consuming countries, where the coffee beans undergo the roasting process [3]. The amount of this waste depends on the type of green beans and on the conditions of processing used, but mostly, coffee silverskin represents about 4.2% (_w/w_) of beans [4]. According to the International Coffee Organization (ICO) statistics [5], total production of coffee by all exporting countries is estimated at 10 million tonnes. Considering the datum presented above, the coffee industry might generated approximately 420 thousand tonnes of the studied by-product. However, this agro-industrial residue currently presents little commercial value and is mostly disposed of as industrial waste. Taking the aforementioned reasons into account, it is imperative to identify the properties and potential applications of coffee silverskin. The reuse of a waste product, such as silverskin, would fit with current trends in circular ecology [6]. In recent years, the problem of development in improving the efficiency of raw material processing has been widely discussed. There is considerably little research conducted on the topic of coffee by-products' properties. Publications mainly deal with antioxidant and prebiotics characteristics [7; 8; 9; 10]. Results show that coffee silverskin can be reused in many industrial fields due to its functional and nutritional properties [11; 12; 13].