Separation of Polyphenols in Hop Bract Part Discharged from Beer Breweries and Their Separability Evaluation Using Solubility Parameters

Food wastes discharged from beer breweries are mainly composed of malt and hop. The nutritional value of malt is quite high and, consequently, it is recycled as feed for domestic animals; however, the nutritional value of hop as feed is not so high. A new utilization method for hop waste is therefore required. In the previous paper, it has been found that. Procyanidin, a polymer composed of catechins, was abundantly contained in hop bract part and hop itself. This research deals with the extraction of total polyphenols, catechins, and procyanidin-B2 from hop bract part using some pure solvents and aqueous solutions under the various extraction conditions. In this experiment, water, methanol, ethanol, 1-propanol, acetone and their aqueous solutions were used as solvent for polyphenol extraction. The magnitude of extracted amount of polyphenols from hop bract part were water > methanol > acetone > ethanol > 1-propanol. In the case of aqueous solutions (methanol-water, ethanol-water, acetone-water systems), it is round that there is the optimal concentration for polyphenol extraction. The amount of extracted polyphenols at the concentration of 40 vol% (about 0.2 mol%) for methanol-water system shows the maximum value. Similar tendencies at 50 vol% for ethanol-water system and at 40 vol%, for acetone-water system are obtained. In order to evaluate the separabiliy of polyphenols containing in hop bract part, Hildebrand's solubility parameter (delta(H)) and Hansen's solubility parameters (delta(d), delta(p), delta(h)) for the polyphenols and solvents were calculated by the method of Fedors and van Klevelen. When solubility parameter difference between solvent and solute is smaller, the amount of extracted polyphenols shows higher values. Furthermore, the 3-dimensional plots and the triangular diagrams of Hansen's three parameters give similar tendency on the separability of polyphenols with Hildebrand's parameter, and it was found that their diagrams could be applied to the prediction of optimum concentration for the polyphenol extraction. This research shows that Hansen's solubility parameters could be used for choosing good solvent and solvent mixture for separation of polyphenols from hop bract part.