Flavor-active esters, produced during fermentation, are vital components and important contributors to the aroma of beer. In order to separate trace amounts of esters, their adsorption behavior in the presence of high concentrations of ethanol and their thermodynamic behavior under the influence of temperature needs to be understood. This study reports the influence of temperature on single component adsorption isotherms of four esters (i.e. ethyl acetate, isopentyl acetate, ethyl 4-methylpentanoate, and ethyl hexanoate) on two hydrophobic resins (i.e. Amberlite XAD16N, and Sepabeads SP20SS) and the estimation of heat, entropy, and Gibbs energy of adsorption. Higher heat and entropy of adsorption are obtained for ethyl hexanoate and ethyl 4-methylpentanoate in comparison, due to their higher hydrophobicity, stronger binding, and the exothermic nature of their adsorption. A higher concentration of ethanol (tested from 1 to 30% (v/v)), lowers the activity coefficient of esters in the aqueous phase, and subsequently lowers adsorption and Langmuir affinity parameters. Increase of temperature from 284.15 to 325.15 K shows a reverse influence on maximum adsorption capacity and Langmuir affinity parameters. Langmuir affinity parameters are obtained at various ethanol concentrations and temperatures. The reported parameters and thermodynamic properties in this paper, are essential for designing an industrial scale adsorption step for separation of flavor-active esters under non-isothermal conditions.

For simulating an adsorption/elution step for separation and recovery of flavor-active esters in beer in the presence of ethanol at various temperatures, and validating the predicted breakthrough behavior, equilibrium data on concentration of each ester is required. This work evaluates the application of frontal analysis method (FA) for prediction of breakthrough behavior for adsorption of ethyl acetate, and determination of equilibrium concentrations and binding capacity for competitive adsorption of four major flavor-active esters in beer (i.e. ethyl acetate, isopentyl acetate, ethyl 4-methylpentanoate, and ethyl hexanoate), together with improvement of the obtained results, through fraction collection, and offline analysis, on columns packed with hydrophobic resins, Amberlite XAD16N and Sepabeads SP20SS. Single-component adsorption of ethyl acetate reveals a shorter breakthrough time, and higher slope of breakthrough curve for adsorption on SP20SS, due to smaller particle size, (50–100 µm), and enhanced mass transfer characteristics of this resin. Competitive frontal analysis tests, neatly demonstrate that increase in temperature is not favorable for adsorption but aids the elution step, 63–100% recovery of flavors at 333.15 K in comparison to 40–80% recovery at 298.15 K. Lower binding capacity of esters and shorter adsorption/elution cycle time is achieved at higher ethanol concentration and cyclic operation simulated under non-isothermal condition, exhibit higher accuracy between predicted and experimental breakthrough curves for XAD16N. A cyclic operation is simulated, for a larger scale column, for two scenarios, separation of ethyl acetate and complete separation of all flavor-active esters in the mixture. For more detailed prediction of breakthrough behavior, the influence of other components present in process streams needs to be investigated on competitive adsorption of esters.

Recovery of volatile flavor-active aroma compounds which are key components of processed liquid food streams is of utmost concern to food industry, as these compounds contribute to the quality of the final product. This review paper highlights the recently published research on different techniques that can be applied for recovery of the key flavor components which all aim for minimizing the loss of volatile aromas and (re-) using them in process streams, in order to enhance the flavor profile of the liquid food product. Among the available techniques for flavor recovery in food industry, distillation or stripping, pervaporation, supercritical fluid extraction, and adsorption showed potential for selective recovery of the flavor components from liquid food streams. These techniques can be combined in different stages of the process or applied as an alternative to the other techniques for aroma recovery. Less attention has been paid to supercritical fluid extraction among the available techniques, especially for recovery of aroma components from alcoholic beverages. Since this technology demonstrated high selectivity for flavor recovery in fruit juices and can take profit from applying natural solvents like CO₂, further research on the application of this technology combined with counter-current flow in a multi-stage contactor is recommended to optimize the recovery process. Adsorption also shows potential for flavor recovery that can be combined with thermal processing or applied as an alternative stand-alone technique.

This work aims to propose an optimum resin that can be used in industrial adsorption process for tuning flavor-active components or removal of ethanol for producing an alcohol-free beer. A procedure is reported for selective adsorption of volatile aroma components from water/ethanol mixtures on synthetic hydrophobic resins. High throughput 96-well microtiter-plates batch uptake experimentation is applied for screening resins for adsorption of esters (i.e. isoamyl acetate, and ethyl acetate), higher alcohols (i.e. isoamyl alcohol and isobutyl alcohol), a diketone (diacetyl) and ethanol. The miniaturized batch uptake method is adapted for adsorption of volatile components, and validated with column breakthrough analysis. The results of single-component adsorption tests on Sepabeads SP20-SS are expressed in single-component Langmuir, Freundlich, and Sips isotherm models and multi-component versions of Langmuir and Sips models are applied for expressing multi-component adsorption results obtained on several tested resins. The adsorption parameters are regressed and the selectivity over ethanol is calculated for each tested component and tested resin. Resin scores for four different scenarios of selective adsorption of esters, higher alcohols, diacetyl, and ethanol are obtained. The optimal resin for adsorption of esters is Sepabeads SP20-SS with resin score of 87% and for selective removal of higher alcohols, XAD16N, and XAD4 from Amberlite resin series are proposed with scores of 80 and 74% respectively. For adsorption of diacetyl, XAD16N and XAD4 resins with score of 86% are the optimum choice and Sepabeads SP2MGS and XAD761 resins showed the highest affinity towards ethanol.