Extraction of polyphenolics from apple juice by foam fractionation

This research was undertaken to test the feasibility of using the foam technology to separate polyphenols from fruit juices for use as functional food ingredients. The separation performance, expressed as enrichment ratio, selectivity and percentage recovery, was determined as a function of operating variables, namely air or N2 flow rate, initial feed concentration, bubble size, solution pH and the presence of alcohol to modify the surface tension. Measurements were made of the average bubble size and gas hold-up volume to calculate interfacial area. The bulk phase concentrations of the polyphenolics in the feed and foam fractions were analysed for total phenolic content by Folin assay and phenolic composition by reverse phase HPLC. Enrichment factors of up to 6 were found under optimum conditions of low sugar concentration (6-9 oBrix), low flow rate (0.2-0.6 ml min-1) and acidic pH (3-4). However recoveries were low at around 30% of total phenolics and selectivity was poor. It was concluded that foam fractionation represents a potential low cost technology to recover a proportion of the polyphenolic content in an enriched juice concentrate suitable for use as a functional ingredient