PhD: Non-digestible oligosaccharides with prebiotic characteristics as new components in functional foods

Ruzica Jovanovic-Malinovska
Department for Food Technology and Biotechnology, Faculty of Technology and Metallurgy, Ss. Cyril and Methodius University, Skopje, Macedonia
December, 2012


Production and application of non-digestible oligosaccharides with prebiotic characteristics were the main subjects of research in this doctoral thesis. In addition, the consumer acceptance of prebiotics as part of functional foods in Macedonia was assessed.

Detailed data on oligosaccharide type and content present in a wide range of fruits (32) and vegetables (41) grown and commonly consumed in the R. Macedonia were attained. White onion and scallion were found to have relatively high fractions of fructo-oligosaccharides (FOS) and rafinose-family oligosaccharides (RFO), while Jerusalem artichoke, chicory root and garlic distinguished themselves by the highest fructan levels. Most fruits contained low amount of oligosaccharides; the highest content of FOS was found in nectarine. Cluster analysis showed that blueberry, raspberry, watermelon and nectarine from the fruits, and garlic, spring garlic, leek, white onion and scallion from the vegetables formed statistically significant clusters reach in oligosaccharides, thus pointing them as potential sources for commercial extractions of prebiotics.

In the next step, ultrasound assisted extraction was used as a simpler and more effective alternative to conventional extraction method of individual fractions of FOS and RFO from fruits and vegetables which proved to have the highest OS content. Experimental design was performed to determine the optimal conditions for ultrasound extraction (extraction time of 10 min, temperature of 40°C and 60% ethanol concentration). Ultrasonication not only reduced the extraction time for 83.5% compared with the conventional extraction, it also increased the extracted oligosaccharide content. The highest increase (4.4-fold) of the totally extracted oligosaccharides was observed in Jerusalem artichoke (7.17±0.348 g/100g FW) compared with conventional extraction (1.62±0.094 g/100g FW).

The synthesis of galacto-oligosaccharides (GOS) by β-galactosidase immobilized in both polyvinyl alcohol (PVA) lenses and sol-gel TMOS carriers was studied and compared with the performance of the free enzyme. PVA-immobilized β-galactosidase retained 95% of the initial activity after seven repeated uses and retained 51% of the initial activity after 3-month storage. Lactose conversion occurred at a higher rate in the PVA immobilized β-galactosidase, compared to the immobilized β-galactosidase in sol-gel. Continuous production of GOS from either lactose or whey, with PVA-immobilized β-galactosidase, was performed in a packed-bed reactor. A maximal GOS yield of 30% of the 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/Lh. 3-OS and 4-OS were the major types of GOS formed. Conversion of whey in a continuous mode resulted in a GOS production of 15% of the total sugars and formation of 45% 3-OS, 40% 4-OS and 15% 5-OS.

The oligosaccharides were applied for the development of new functional products, a fresh and a processed one. Inulin was incorporated into the fresh quince with vacuum infusion for development of a new functional product that can be consumed as dried quince snack, or as a part of dried energy bar, or muesli formulation. Ultrasonication pre-treatment led to the significant increase in its elasticity and to lower color changes and browning index when compared to the non-treated dried quince. Furthermore, new baked products fortified with oligosaccharides, such as cookies and muffins, were developed. The oligosaccharides used were GOS produced by enzymatic catalysis in this research. The cookies and muffins had good texture and colour characteristics and they were very well accepted by the sensory panel.

A survey based on a web-questionnaire distributed to Macedonian consumers showed their perception, attitude and behavior toward functional foods and prebiotic products. The consumers are willing to buy prebiotic products, although their perception of this kind of products is not clear. They are aware of the effect of healthy nutrition on the human health. Yet, the consumers should be further educated to better understand the exact benefits of functional foods.