Production of flavor compounds from apple pomace

Abstract

The production process of flavor compounds from apple pomace was developed by a combination of fermentation and membrane technology in this study. Flavor compounds of apple pomace were extracted with 4 volumes of water containing L-ascorbic acid under agitation for an hour. After centrifugation, the extract was subjected to Ultrafiltration and reverse osmosis (RO) membranes to concentrate the flavor compounds. The filtrate contained n-butanol, 2-methyl butanol, n-hexanol, and ethyl-2-methyl butyrate which were the general apple flavor compounds. These flavor compounds were concentrated in the RO membrane, but the membrane permeation flux decreased by the viscosity increase due to saccharides. The apple flavor compounds were concentrated to about 6.5-fold at that point. The yeast strains, D5-2, K5-1, and E-1 were isolated from the fruits in order to decompose the saccharides of the extract and improve the concentration of the flavor compounds. Bench plant experiments were performed with the use of strain D5-2 which, of the three strains selected, fermented a much larger amount of n-hexanol due to the decomposition of saccharides in the extract. A seed culture of 20 l was added to an extract of 200 l and incubated at 20°C for 2 days in a jar fermenter. After removing yeast cells by filtration, the filtrate was concentrated with the RO membrane. Compared with the RO filtrate without saccharide fermentation, it contained 28-fold concentration of 2-methyl butanol, 18-fold of n-hexanol, and 7-fold of ethyl-2-methyl butyrate. The flavor obtained with fermentation and membrane technology was almost equal to the flavor of an apple. Membrane technology and fermentation can be combined to produce concentrated apple flavor compounds from apple pomace.