1614
Ind. Eng. Chem. Res. 2008, 47, 1614-1619
Application of Supercritical Fluid Extraction to Brewer’s Spent Grain Management M. P. Ferna´ ndez, J. F. Rodriguez, M. T. Garcı´a, A. de Lucas, and I. Gracia* Departamento de Ingenierı´a Quı´mica, Facultad de CC. Quı´micas, UniVersidad de Castilla-La Mancha, AVenida Camilo Jose´ 12, 13071 Ciudad Real, Spain
This work reports a study of the the use of supercritical fluid technology coupled with pretreatment processes for the valorization of brewer’s spent grain (BSG), a beer production residue, to design a global management process producing valuable extracts and raffinate stabilization. The SC-CO2 extraction of BSG was performed at temperatures of 313, 333, and 353 K and at pressures from 10 to 35 MPa using raw and milled BSG. Optimal extraction conditions were selected considering the criterion of maximum yield: 313 K temperature, 35 MPa pressure, and milled BSG. Equilibrium and mass-transfer parameters were determined for use in the development of scale-up procedures. A preliminary economic study was performed to determine that the proposed process is economically feasible. 1. Introduction
Table 1. Applications of BSG as a Function of Moisture Content
Beer production processes generate large volumes of byproducts and wastes such as brewer’s spent grain (BSG), spent hops, and yeast. BSG is the most abundant brewing byproduct, corresponding to about 85% w/w of the total byproducts generated. BSG contains a large proportion of profitable compounds such as proteins, fiber, vitamins, and amino acids. However, its low biological stability resulting from its high moisture content (higher than 75% w/w) makes its potential use difficult because of its rapid deterioration.1-3 Table 1 summarizes the possible applications of BSG as a function of moisture and the cost-effectiveness ratio of each option.4 It can be observed that, as the moisture content decreases, the stability of BSG increases and, therefore, putrefaction is delayed. Dried and stabilized BSG could be used as a raw material for the recovery of both valuable compounds and fiber and protein flours with interest in nutrition or combustion. Environmental and economic reasons justify BSG posttreatment, especially considering that it sometimes constitutes a large-scale residue that is problematic to dispose, it is low in cost, and it is available in large quantities. Several methods have been proposed to remove water from BSG: filtration, cold or hot squeezing, pressing, freeze-drying, and others.5 These processes reduce the moisture content of BSG, but they are not able to recover valuable compounds and they usually result in BSG degradation.6 Optimal residue management would involve drying BSG to a level that assures stabilization, allowing the recovery of highly valuable compounds. The use of organic solvents to recover valuable compounds results in severe food standard restrictions and oxidative degradation reactions in the solvent recovery step.7 The increasing interest in both high-quality products and environmentally friendly technologies indicates that supercritical fluid extraction (SFE) could be a suitable process for obtaining vegetable extracts. In addition, SFE has additional advantages such as flavor preservation, higher mass-transfer rates, and selectivity.8-10 The aim of this work was to study the use of SFE technology coupled with pretreatment processes for the valorization of BSG * To whom correspondence should be addressed. Tel.: +34 926295300/3419. Fax: +34926295318. E-mail:
[email protected].
moisture (% w/w)
application
associated problems
cost effectiveness
80-60
animal feed
low biological stability
medium/low
60-50
animal feed combustion (low heat capacity)
medium biological stability
medium
