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Extraction of Spent Hops Using Organic Solvents

Spent hops obtained from supercritical carbon dioxide hop extraction are a potential, high-nutritive value additive in fodder production and a source of xanthohumol, which has received much attention in recent years as an anticancer and antioxidant agent. In this paper, we present some results of experiments involving the removal of residual hop acids from this waste, because feed stuffs containing such spent hops are not willingly eaten by animals. Spent hops were extracted with different solvents (methanol, ethanol, acetone, and hexane) and under different conditions, namely room and boiling temperatures and ultrasonic extraction. The total content of hop acids in the extracted spent hops was 1,051 μg/g (222 μg of bitter isohumulones and 757 μg of humulones per g). The percentage of acids removed depended on the polarity of the solvents applied. The best results were obtained for ethanol and methanol (more than 80%) and the worst for hexane (30%) for 60-min extractions in boiling solvent. Hexane at room temperature barely extracted hop acids (5% of hop acids removed). Fast isomerization of humulones into isohumulones was observed in overheated water steam at 121°C. The isomerized spent hops resulting from this process contained 581 μg of isohumulones and 103 μg of humulones per g and were extracted with hexane or acetone. The latter was slightly better at extracting hop acids from isomerized spent hops than from unisomerized hops, enabling the removal of 74% of hop acids. The paper also describes the modification of EBC method 7.7 using isooctane in low concentrations instead of diethyl ether for bitter acid analysis of spent hops.