Application of ultrasound for enhanced extraction of prebiotic oligosaccharides from selected fruits and vegetables

Ultrasound assisted extraction (UAE) was used to extract oligosaccharides from selected fruits (blueberry, nectarine, raspberry, watermelon) and vegetables (garlic, Jerusalem artichoke, leek, scallion, spring garlic and white onion). The individual fractions of the oligosaccharides were analyzed: 1-kestose (GF2), nystose (GF3) and 1F-β-fructofuranosylnystose (GF4) from the fructo-oligosaccharides (FOS), and raffinose and stachyose from the raffinose family oligosaccharides (RFO). Extraction parameters including solvent concentration (35–85% v/v), extraction temperature (25–50 °C) and sonication time (5–15 min) were examined using response surface methodology (RSM). Ethanol concentration of 63% v/v, temperature of 40 °C and extraction time of 10 min gave maximal concentration of the extracted oligosaccharides. The experimental values under optimal conditions were consistent with the predicted values. UAE increased the concentration of extracted oligosaccharides in all fruits and vegetables from 2 to 4-fold compared to conventional extraction. The highest increase of total oligosaccharides extracted by UAE was detected in Jerusalem artichoke, 7.17 ± 0.348 g/100 g FW, compared to 1.62 ± 0.094 g/100 g FW with conventional method.