Abstract
Extraction temperature, extraction time and liquid (water) to solid ratio were optimized in order to extract antioxidant phenolic compounds from brewers’ spent grain (BSG). The extracts were analysed for their total phenol content (TPC) and antioxidant activity was measured using three different methods: 2,2-diphenyl-2-picrylhydrazyl (DPPH) free radical, 2,2′-azino-bis(3-ethylbenothiazoline-6-sulphonic acid) (ABTS), and reducing power (RP) assays. All the parameters except extraction time promoted different efficiencies for the extraction of antioxidant phenolic compounds. TPC extraction was higher at lower temperatures and lower liquid/solid ratios up to a certain point. In this sense, a decrease in TPC with increasing liquid/solid ratios took place until a 16:1 ratio and a plateau was reached beyond that ratio. The highest DPPH activity was reported for 30–35 °C and 60–90 min extraction and 60–90 min extraction with a 25 mL/g ratio. ABTS values increased as the liquid to solid ratio decreased, being positively correlated with TPC (R = 0.788; p < 0.01). The highest RP was achieved at 30–33 °C extraction temperature and 10–14 mg/mL v/w ratio and at 116–120 min extraction and 16–17 mg/mL ratio. Gallic acid accounted for the majority of the phenolic compounds found, followed by hydroxyphenylacetic acid, epicatechin, and protocatechuic acid. Sinapic, 4-hydroxy benzoic, and syringic acids were also found in lower quantities. Coumaric, vanillic, ferulic, and caffeic acids were present in very small amounts. All the extracts contained phenolics and showed in vitro antioxidant activity, but the extracts obtained by using 30 °C, 121.9 min, and 10 mL/g liquid/solid ratio exhibited the highest content in TPC and antioxidant potential. The aqueous extraction of a potentially bioactive extract from BSG was demonstrated to be an efficient and simple method to recover these value-added compounds.
Highlights
Over the last several years, the global beer industry has experienced an outstanding increase in production and consumption, reaching up to 1.95 billion hectoliters and 357 million hectoliters, respectively [1]
Optimization of the experiment was carried out using Response Surface Methodology (RSM) for the extraction of total phenol content (TPC) and in vitro antioxidant activity (DPPH, reducing power (RP), and ABTS)
The optimized conditions were validated for the maximum total phenol content (TPC) and antioxidant activities (DPPH, RP, and ABTS), based on the values obtained using RSM
Summary
Over the last several years, the global beer industry has experienced an outstanding increase in production and consumption, reaching up to 1.95 billion hectoliters and 357 million hectoliters, respectively [1]. The addition of water to these organic solvents is a common practice, since it creates a more polar medium and may facilitate the extraction of compounds that are soluble in organic solvents and/or water, as phenolics [8]. Those mentioned solvents show some disadvantages, like their toxicity, low biodegradability, high cost, the need for further separation stages, and their environmental hazards [10]. The selection of the extraction parameters, such as temperature, stirring rate, extraction time, sample particle size, pH, and liquid/solid ratio can determinantly affect the recovery of phenols from crop by-product substrates [6]. A systematic approach was used to optimize extraction factors such as temperature, time, and liquid/solid ratio, leading to the maximum extraction of phenols and the highest in vitro antioxidant activity
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