Coffee Silver Skin: Chemical Characterization with Special Consideration of Dietary Fiber and Heat-Induced Contaminants

Abstract

Coffee silver skin is produced in large amounts as a by-product during the coffee roasting process. In this study, coffee silver skin of the species Coffea arabica L. and Coffea canephora Pierre ex A. Froehner as well as silver skin pellets produced in the coffee industry were characterized with respect to both nutritional value and potential heat-induced contaminants. Enzymatic-gravimetric/chromatographic determination of the dietary fiber content showed values ranging from 59 to 67 g/100 g with a comparably high portion of soluble fiber, whereas low molecular weight soluble fiber was not detected. Compositional and methylation analysis indicated the presence of cellulose and xylans in the insoluble dietary fiber fraction, whereas pectic polysaccharides dominate the soluble dietary fiber fraction. The protein content as determined by the Kjeldahl method was in the range of 18 to 22 g/100 g, and all essential amino acids were present in coffee silver skin; whereas fat contents were low, high ash contents were determined. Elemental analysis by inductively coupled plasma mass spectrometry (ICP-MS) showed the presence of macroelements in large amounts, whereas toxic mineral elements were only detected in trace amounts or being absent. Acrylamide was quantified with levels of 24–161 µg/kg. Although 5-hydroxymethylfurfural was detected, its concentration was below the limit of determination. Furfuryl alcohol was not detected.

Coffee By-Products as Sustainable Novel Foods: Report of the 2nd International Electronic Conference on Foods—“Future Foods and Food Technologies for a Sustainable World”

“…So both are very close. Applications include distilling and different forms of beverages, syrups and purees [ 6 ].…”

“…The silver skin emerges in masses during roasting [ 6 ]. Historically it had been used as animal feed in Germany, but it can be used for bakery products or as protein bars.…”

“…Although 5-hydroxymethylfurfural was detected, its concentration was below the limit of determination. Furfuryl alcohol was not detected [ 6 ].…”

“…Chemical composition of coffee silverskin from Coffea arabica and Coffea canephora as well as coffee silverskin pellets based on dry material (reprinted with permission from Gottstein et al[6]). …”

Interest of Coffee Melanoidins as Sustainable Healthier Food Ingredients

“…Prior to the consumption of melanoidin isolates from coffee by-products, these products need to be approved for their commercialisation. To the best of our knowledge, melanoidins are generally considered safe ( 40 , 48 , 49 ) and there are no studies showing the potential toxicity of these molecules.…”