Abstract
In order to extract antioxidant phenolic compounds from spent grain (SG) two extraction methods were studied: the ultrasound-assisted method (US) and the Ultra-Turrax method (high stirring rate) (UT). Liquid to solid ratios, solvent concentration, time, and temperature/stirring rate were optimized. Spent grain extracts were analyzed for their total phenol content (TPC) (0.62 to 1.76 mg GAE/g SG DW for Ultra-Turrax pretreatment, and 0.57 to 2.11 mg GAE/g SG DW for ultrasound-assisted pretreatment), total flavonoid content (TFC) (0.6 to 1.67 mg QE/g SG DW for UT, and 0.5 to 1.63 mg QE/g SG DW for US), and antioxidant activity was measured using 2,2-diphenyl-2-picrylhydrazyl (DPPH) free radical (25.88% to 79.58% for UT, and 27.49% to 78.30% for UT). TPC was greater at a high stirring rate and high exposure time up to a certain extent for the Ultra-Turrax method, and at a high temperature for the ultrasound-assisted method. P-coumaric acid (20.4 ± 1.72 mg/100 SG DW for UT, and 14.0 ± 1.14 mg/100 SG DW for US) accounted for the majority of the phenolic found compounds, followed by rosmarinic (6.5 ± 0.96 mg/100 SG DW for UT, and 4.0 ± 0.76 mg/100 SG DW for US), chlorogenic (5.4 ± 1.1 mg/100 SG DW for UT, and non-detectable for US), and vanillic acids (3.1 ± 0.8 mg/100 SG DW for UT, and 10.0 ± 1.03 mg/100 SG DW for US) were found in lower quantities. Protocatechuic (0.7 ± 0.05 mg/100 SG DW for UT, and non-detectable for US), 4-hydroxy benzoic (1.1 ± 0.06 mg/100 SG DW for UT, and non-detectable for US), and caffeic acids (0.7 ± 0.03 mg/100 SG DW for UT, and non-detectable for US) were present in very small amounts. Ultrasound-assisted and Ultra-Turrax pretreatments were demonstrated to be efficient methods to recover these value-added compounds.
Highlights
Whisky is one of the most popular alcoholic beverages made from cereals, and generally are all produced in a similar manner [1,2]
Whisky is subject to strict regulations, with many types and classes regarding the fermentation of grains, distillation and aging in wooden barrels [3,6,7]
The composition of spent grain used in this study (%w/w, dry basis) was moisture (5.04 ± 0.42%), ash (3.47 ± 0.02%), protein (18.88 ± 0.37%), lipids (7.11 ± 0.39%), and fibers (22.67 ± 0.42%), which are in agreement with the results obtained for spent grain from malt whisky [13,32]
Summary
Whisky is one of the most popular alcoholic beverages made from cereals, and generally are all produced in a similar manner [1,2]. In Europe, whisky is defined as an alcoholic beverage produced by distillation of malt or cereal wort. There are many types of whisky depending on the country in which it is produced. In European countries, whisky is mainly produced with malt made from barley, water and cereals, such as wheat or rye. The main production countries are Scotland, the USA, Ireland, Canada, and Japan. The top 10 whisky markets by volume are India, the USA, France, Japan, the United Kingdom, Spain, Canada, Brazil, South Africa, and Germany [8,9]
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