Optimization of Extraction Conditions to Improve Phenolic Content and In Vitro Antioxidant Activity in Craft Brewers’ Spent Grain Using Response Surface Methodology (RSM)

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.

Spent Grain from Malt Whisky: Assessment of the Phenolic Compounds

“…In comparison, for ultrasound-assisted pre-treatment, the phenolic compound extraction rate varied from 0.57 to 2.11 mg GAE/g SG DW. Those results are in agreement with other studies [ 33 , 34 , 35 , 36 , 37 , 38 ]. Multiple regression analysis was used to analyze the experimental data, and thus a quadratic polynomial equation of the response surfaces was obtained as follows (*** p < 0.001; ** p < 0.01; * p < 0.05): TPC Ultra-Turrax = 1.40 + 0.22 * X 1 *** − 0.05 * X 2 − 0.20 * X 3 *** + 0.22 * X 4 *** − 0.01 * X 1 X 2 + 0.05 * X 1 X 3 − 0.01 * X 1 X 4 + 0.03 * X 2 X 3 − 0.04 * X 2 X 4 − 0.004 * X 3 X 4 + 0.004 * X 1 2 + 0.05 * X 2 2 − 0.24 * X 3 2 ** − 0.08 * X 4 2 …”

“…Protocatechuic acid, p-hydroxybenzoic acid, and caffeic acid for Ultra-Turrax pre-treatment were found in lower quantities. Hydroxycinnamic acids, ferulic acid, coumaric acid, sinapic acid, and caffeic acid were the main phenolic compounds identified in spent grain [ 33 , 34 , 35 , 37 , 38 ]. The differences between the methodologies applied for the two extraction methods: UT is based on high-stringing rates of 10,000 to 30,000 rpm at ambient temperature in a relatively short time of 30–90 s, while US is based on the sonication of samples in an ultrasound bath at temperatures between 30 and 70 °C at an interval of 10–30 min.…”

Revalorization of Coffee Husk: Modeling and Optimizing the Green Sustainable Extraction of Phenolic Compounds

“…Generally, a high extraction temperature is associated with an increase in the solubility of phenolic compounds from the matrix [ 36 ]. A decrease in the S/L ratio enhances the extraction of phenolic compounds from plant matrices by reducing the saturation effects due to the concentration of phenolic compounds [ 37 ]. The TF ranged from 5.52–10.10 mg g −1 ( Table 1 ).…”

Phytochemical characterization and effects on cell proliferation of Pinus nigra Arn. bark

“…Being the most suitable solvent for recovering polyphenols from Pinus bark, ethanol, recognized as safe for human consumption, [24] could also fulfill requirements of toxicity in terms of an environment-friendly and economically viable perspective. [27] The observed differences between the extracts from Mokra gora and Tara may be explained by the black pine genetic variability. A high degree of genotypic variability observed in P. nigra subspecies is reflected in the biochemical variability of this plant.…”