A commercial ~-galactosidase isolated from Kluyveromyces lactis (Maxilact® L2000) was used for the synthesis of galacto-oligosaccharides (GOS) from lactose by trangalatosylation reaction in a stirred-tank reactor. In the experimental range examined (220-400 mg/ml lactose with 2.9-8.7 D/ml enzyme), the results showed the amount of GOS formed depended on lactose concentration. A laboratory scale ultrafiltration membrane reactor was used in a continuous process. Transmembrane pressure played an important role on the flux and productivity due to the impact of concentration polarisation. A probiotic ~-galactosidase, extracted from truncated Bifidobacterium bifidum DSM20215, was used for GOS synthesis in a stirred-tank reactor. The truncated enzyme showed high efficiency in GOS synthesis and gave a high yield (400/0) regardless of initial lactose concentration used (50-150 mg/mllactose). The GOS synthesised by both enzymes were fractionated and analysed for their structures and fermentation properties. The comparison of product structures of GOS synthesised by Maxilact® L2000 in batch and continuous processes showed similarities (1 ~6Galp) but differed from the structures found in the truncated probiotic GOS (1 ~3Galp) and a commercial GOS product (1 ~4Galp). The results from batch culture fermentations showed that all GOS samples increased the number of bifidobacteria and promoted the production of short-chain fatty acids. A model proposed in the literature was applied to estimate kinetic parameters for both enzymes. The model gave a sastisfactory preliminary analysis from which it predicted lactose and GOS concentrations very well. However, improvements are needed to obtain better fits for glucose and galactose concentrations and better sensitivity for the determination of inhibition rate constants.

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A range of novel and commercially available guar gums and novel potato fibre samples were investigated to see if their fermentation characteristics would make them new potential prebiotic candidates. Samples were examined using in vitro. pH controlled, 24h hatch culture fementations inoculated with human faeces. Fermentation of the guar gum samples mainly stimulated the growth of Bifidobacterium spp. and Bacteroides spp., producing considerable amounts of acetate, propionate and large amounts of gas. A direct relationship between molecular weight (MW) and fermentability was not found but instead two possible optimum molecular weight ranges - MW >500,000 Da and those with much lower MW (-34,000 Da)were suggested. Potato fibre samples produced by pectinase treatment and hemicellulase treatment gave the highest increases in bifidobacteria and lactobacilli, producing considerable amounts of acetate and propionate. Three guar gum samples and One potato fibre sample were investigated further using a three-stage human gut model. The MW of guar gum and its combination were found to affects its fermentibility, bacterial and SCFA profiles, with those containing low MW fractions (34,500 Da) giving higher increases in bifidobacteria and lactobacilli than those containing high MW fractions. Potato fibre treated with pectinase treatment 2 was found to significantly increase bifidobacteria in vessel I (VI) and vessel 2 (V2) and lactobacilli by over 1 log10 in all three vessels. Propionate was also increased significantly in all three vessels. Overall, guar gum and potato fibre derivatives have been shown to exhibit positive fermentation characteristics and prebiotic properties by increasing the beneficial bacteria such as bifidobacteria and lactobacilli and the production of SCFA. This in combination with other health promoting properties and desirable properties to food manufactures make their future use as functional food ingredients encouraging. Further investigation of these samples in human volunteer studies is required to confirm the prebiotic effect and to study potential beneficial properties