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-ß-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 (5-15min) were examined using response surface methodology (RSM). Ethanol concentration of 63% v/v, temperature of 40°C and extraction time of 10min 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±0.348g/100gFW, compared to 1.62±0.094g/100gFW with conventional method.

Galacto-oligosaccharides synthesis from lactose and whey by ß-galactosidase immobilized in PVA.

The synthesis of galacto-oligosaccharides (GOS) by ß-galactosidase immobilized in both polyvinyl alcohol (PVA) lenses and sol-gel carriers was studied and compared with the performance of the free enzyme. PVA-immobilized ß-galactosidase retained 95 % of the initial activity after seven repeated uses and retained 51 % of the initial activity after 3 months of storage, while sol-gel-immobilized ß-galactosidase only retained 39 % of the initial activity under storage. Lactose conversion takes place at a higher rate in the PVA-immobilized ß-galactosidase, while the lowest rate of lactose conversion was noticed with immobilized ß-galactosidase in sol-gel. Continuous production of GOS from either lactose or whey, with PVA-immobilized ß-galactosidase, was performed in a packed-bed reactor. A maximum GOS production of 30 % of total sugars was attained for a 40-% lactose feed solution with a feed rate of 10.8 ml/h, at pH 4.5 and 40 °C, corresponding to a productivity of 117 g/l h. The maximum GOS productivity of 344 g/l h was obtained at a flow rate of 28.7 ml/h. 3-OS and 4-OS were the major types of GOS formed. Conversion of whey in continuous mode resulted in GOS production of 15 % of total sugars and formation of 45 % 3-OS, 40 % 4-OS, and 15 % 5-OS.