Ultrasound-accelerated debittering of olive fruits

Abstract

Abstract Effects of ultrasound-accelerated debittering (UAD) at different NaOH concentrations (1.50, 1.75, and 2.00% w/v) and temperatures (25, 30 and 35 °C) on physicochemical and textural properties of olive fruits were investigated and compared with conventional debittering (CD). In UAD, processing time decreased up to 48% in comparison with CD method. During debittering, increasing moisture and decreasing nitrogen and ash contents of the samples were observed. In UAD, reduction rate of phenolic compounds and as a result the speed of debittering process increased in comparison with CD method. UAD was able to reduce textural hardness at a higher rate than CD method. Fatty acid compositions of UAD and CD samples were similar. Both UAD and CD methods similarly caused considerable damages to the structure of olives as observed on micrographs. Overall, UAD method was able to debitter olive fruits at a higher rate without causing any undesirable changes. This can have practical implications in reducing NaOH and water usage for olive processing. Industrial relevance In this research, the efficacy of ultrasound-assisted debittering (UAD) of olive fruit was evaluated. UAD increased the rate of sodium hydroxide penetration into the olive flesh, leading to a higher rate of oleuropein hydrolysis and significant reduction of processing time of up to 48% in comparison with CD method. Therefore, ultrasound-assisted debittering was found to be a suitable and applicable technique in minimizing debittering time of olive fruits and reducing NaOH concentration. It is also possible to reduce the number of wash-cycles required for the completion of debittering resulting in substantial reduction in water usage.