| Abstract [eng] |
Plant by-products contain biologically active compounds – fibers, proteins, which have beneficial properties, but are often used inefficiently. In order to increase the added value of such biomasses, functionalization can be applied. Functionalization can be performed by high-frequency (850 kHz) sonication at low temperatures (<50 ºC), as well as dry separation and solid-phase fermentation. The aim of this work was to investigate biological properties of plant press cakes (raspberry and coconut), apply functionalization to increase nutritional value of the products and use them in the production of antimicrobial hydrated gels (nutraceuticals). In this work, it was determined that applying dry separation on raspberry press cake, it is possible to obtain fractions (<0.315 mm and 0.5–1 mm) with higher content of elagic acid and antioxidant activity (comparing with raw material without fractionation). In addition, raspberry pulp showed antimicrobial activity against antibiotic resistant pathogens: Escherichia coli, Salmonella typhimurium, Staphylococcus aureus, Bacillus cereus, Pseudomonas aeruginosa. Sonification of coconut press cake with high frequency ultrasound (850 kHz) showed that the highest amount and concentration of soluble proteins were released by high frequency sonication (850 kHz, intensity 2 W/cm2) for 10 min at pH 9. Sonicated coconut press cake was tested for LAB (lactic acid bacteria) fermentation and proved its suitability as a culture medium for the cultivation of L. paracasei bacteria with antimicrobial properties. After fermentation, it was determined, that the count of bacteria was 9.097 log CFU/ml. Modification of native starch was additionally tested by applying sonification to give it new functional properties. High-frequency sonication of the suspensions significantly reduces the viscosity of the suspensions and have had a positive effect on its texture. Studies on the antibacterial activity of tea tree, peppermint and grapefruit essential oils have shown that tea tree essential oil had the best antibacterial activity against pathogenic bacteria. The essential oils of tea tree and peppermint immobilized on OSA-starch and coated with entero-soluble material were the most suitable for the production of hydrogels (nutraceuticals). Agar gels with raspberry press cake (20 %) in combination with sorbitol and maltitol were chosen for the structuring of hydrogels (single-layer and three-layer). During the digestibility test of agar gels with immobilized essential oils in vitro, it was observed that most phenolic compounds were released in gastric medium (pH 2) from agar gels with tea essential oil and in an intestinal medium (pH 7.5) from gels with peppermint essential oil (single layer agar gels). Functionalized starch was used as an alternative to agar in gel preparation. Evaluating hydrogels with a new stabilizer (modified starch) it was found, that the most phenolic compounds were released from gels with immobilized tea tree essential oil. |
