a b s t r a c t Keywords:Brewer's spent grain Microwave-assisted extraction Polyphenols Antioxidant activity Kilning temperature HPLC-DAD/ESI-MS/MS analysis The antioxidant activity and phenolic composition of brewer's spent grain (BSG) extracts obtained by microwave-assisted extraction from two malt types (light and dark malts) were investigated. The total phenolic content (TPC) and antioxidant activity among the light BSG extracts (pilsen, melano, melano 80 and carared) were significantly different (p b 0.05) compared to dark extracts (chocolate and black types), with the pilsen BSG showing higher TPC (20 ± 1 mg GAE /g dry BSG). In addition, the antioxidant activity assessed by 2,2-diphenyl-1-picrylhydrazyl, 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) and deoxyribose assays decreased as a result of increasing kilning temperatures in the following order: pilsen N melano N melano 80 N carared N chocolate N black. HPLC-DAD/ESI-MS/MS analysis indicated the presence of phenolic acids, such as ferulic, p-coumaric and syringic acids, as well as several isomeric ferulate dehydrodimers and one dehydrotrimer. Chocolate and black extracts, obtained from malts submitted to the highest kilning temperatures, showed the lowest levels of ferulic and p-coumaric acids. These results suggested that BSG extracts from pilsen malt might be used as an inexpensive and good natural source of antioxidants with potential interest for the food, pharmaceutical and/or cosmetic industries after purification.

In recent years, there has been a growing interest in phenolic compounds and their presumed role in the prevention of various degenerative diseases, such as cancer and cardiovascular diseases. Xanthohumol, a prenylated chalcone from hops and beer, is among the phenolic compounds which have received the most attention in recent years. This compound has a range of interesting biological properties that may have therapeutic utility. Based on the health-promoting properties of xanthohumol, the production of a beer enriched in this substance would be of huge interest to the brewing industry, for the benefits this could bring to consumer's health. This paper reviews recent and important data with respect to the health benefits or biological activities of xanthohumol and beer. In addition, an overview of the chemistry and biotechnological aspects of xanthohumol is presented.

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