Abstract
Brewer’s spent grain (BSG) was chemically characterized obtaining 52.1% of carbohydrates, 17.8% protein, 5.9% lipids, 13.5% insoluble lignin and 24.3% of water-soluble extractives. This work has been focused on the study of polyphenol extraction of the extractive fraction by water ultrasound-assisted extraction. Selected extraction conditions were 47 °C and 21.7 mL water/gdry-BSG. The effect of solvent polarity on polyphenol extraction was studied by using ethanol aqueous mixtures, from 20% to 100% ethanol. The kinetics of polyphenol extraction have been fitted to the power law and the Weibull models yielding mean values of the root mean square deviation lower than 7.5%. Extracts have been characterized in terms of quantification of individual phenolic compounds by HPLC-DAD and protein and sugar soluble fractions (glucose, xylose, and arabinose). Polyphenol profile has been compared with other hydrolytic techniques, such as acid, basic and enzymatic hydrolysis, showing that ultrasound was not as effective as basic hydrolysis to release the phenolic acids esterified to the cell wall. A further centrifuge ultrafiltration concentration step was able to yield a retentate enriched in the protein fraction while individual phenolic compounds where mainly transferred to the permeate.
Highlights
Brewer’s spent grain is the main by-product produced by breweries, accounting for 20 kg per100 L of beer produced [1]
One of the main objectives of this work was to provide a comprehensive study of total polyphenol content (TPC) extraction kinetics from Brewer’s spent grain (BSG) by using water as solvent, having the advantage of being “the greenest solvent”
The local BSG used in this work showed an important amount of starch, 7.87% w/w (78.7 mg starch/g dry BSG), that can be associated with the source of the BSG
Summary
Brewer’s spent grain is the main by-product produced by breweries, accounting for 20 kg per. 100 L of beer produced [1]. BSG represents up to 30% of the starting malted grain [2]. It is mostly used as animal feed, but its high moisture content results in an increased cost of transportation. The presence of fermentable sugars, reduces its shelf life. BSG presents a great potential to obtain valuable products to be incorporated in the food and pharmaceutical industries. Taking into account that European beer production reached nearly 39.7 billion liters in 2017 [3]. BSG valorization will contribute to reduce the percentage of BSG that is released in landfills yearly
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