Concentration of feijoa and boysenberry fruit aroma condensates using pervaporation : a thesis presented in partial fulfillment of the requirements for the degree of Master of Food Technology at Massey University

Abstract

This present work aimed to investigate pervaporation for aroma recovery and concentration from fruit aroma condensate collected during evaporation of fruit juices. A 5% ethanol solution, feijoa and boysenberry aroma condensates were concentrated in a pervaporation apparatus fitted with polydimethyl siloxane (PDMS: GFT1060, GFT1070) and poly-ether-block-amide (PEBA, GKSS) membranes, under the following operating conditions: feed temperature of 30°C, feed flow rate of 8.3 x 10 or 1.4 x 10 , and permeate pressures of 100 Pa or 1000 Pa. Feijoa and boysenberry aroma condensates were also concentrated by vacuum distillation. Aroma compounds and their concentrations in the feed, retentate and permeate were identified and determined by gas chromatography (GC) and a mass spectrometer coupled to a GC. The three membranes investigated for pervaporation gave different total fluxes, partial fluxes, mass transfer coefficients, enrichment factors and aroma compositions for feijoa and boysenberry condensate. PEBA membranes proved to have best performance for concentration of feijoa and boysenberry aroma due to high enrichment factors and mass transfer coefficients for the important aroma compounds of both feijoa and boysenberry. Increasing the feed flow rate from 1.1 x 10 to 1.4 x 10 did not affect the total flux, but increased significantly the partial fluxes and enrichment factors of preferentially permeating compounds such as methyl benzoate, ethyl benzoate and linalool. Decreasing permeate pressure significantly increased the total flux, the partial fluxes and enrichment factors for higher boiling aliphatic alcohols. The mass transfer resistances of methyl benzoate, ethyl benzoate and linalool was dominated by the boundary layer effects. The mass transfer resistances of high boiling aliphatic alcohols, hexanol, Z-3-hexenol and E-2-hexenol were strongly influenced by permeate pressure. Compared with vacuum distillation, pervaporation showed better performance for producing concentrated feijoa and boysenberry aromas which were highly enriched in the important flavour compounds for each fruit.