The role of immobilized rennet on carbon cloth in flavor development during ripening of Gouda cheese.

Rennet-free Gouda (RFG) cheese was prepared to investigate the influence of rennet on the non-volatile and volatile profiles of cheese and was characterized by HPLC and GC/MS analyses. Chymosin, a major protease in rennet, was immobilized onto oxidized and chemically modified carbon cloth. The chymosin immobilization efficiency was 60.4%, and the milk-clotting activity used as an index of the stability of the immobilized chymosin decreased by around 20% in 2 weeks. However, the activity was maintained at 70-80% from 2 weeks to 32 weeks and was more stable than that of chymosin solution alone. Non-volatile (organic acids) and volatile profiles of the RFG cheese and rennet-containing normal Gouda cheese were not significantly different during ripening with a few exceptions. Therefore, it can be concluded that cheese flavor is developed by lactic acid fermentation, irrespective of the presence of rennet.

Immobilization of a mediator onto carbon cloth electrode and employment of the modified electrode to an electroenzymatic bioreactor.

5,5'-Dithiobis(2-nitrobenzoic acid) (DTNB) was selected as an electron transfer mediator and was covalently immobilized onto high porosity carbon cloth to employ as a working electrode in an electrochemical NAD(+)-regeneration process, which was coupled to an enzymatic reaction. The voltammetric behavior of DTNB attached to carbon cloth resembled that of DTNB in buffered aqueous solution, and the electrocatalytic anodic current grew continuously upon addition of NADH at different concentrations, indicating that DTNB is immobilized to carbon cloth effectively and the immobilized DTNB is active as a soluble one. The bioelectrocatalytic NAD+ regeneration was coupled to the conversion of L-glutamate into alpha-ketoglutarate by L-glutamate dehydrogenase within the same microreactor. The conversion at 3 mM monosodium glutamate was very rapid, up to 12 h, to result in 90%, and then slow up to 24 h, showing 94%, followed by slight decrease. Low conversion was shown when substrate concentration exceeding 4 mM was tested, suggesting that L-glutamate dehydrogenase is inhibited by alpha-ketoglutarate. However, our electrochemical NAD+ regeneration procedure looks advantageous over the enzymatic procedure using NADH oxidase, from the viewpoint of reaction time to completion.

Preservation of kombucha tea-effect of temperature on tea components and free radical scavenging properties.

Kombucha tea is sugared black tea fermented with a consortium of acetic acid bacteria and yeasts (tea fungus) for 14 days. The tea tastes slightly sweet and acidic. The formation of tea fungal biofilms during storage is a big problem when kombucha tea is being stored and commercialized. Various thermal treatments have been tried for long-term storage of kombucha tea. The present study revealed the influence of heat on the biochemical constituents and the free radical scavenging properties of kombucha tea. Heat treatment at 60, 65, and 68 degrees C for 1 min controlled biofilm formation in kombucha tea without changing its clarity, taste, and flavor. However, tea polyphenols and black tea quality parameters showed varying stability during the storage period. A decrease in free radical scavenging properties was also found during the storage period. Because the biological activities of kombucha tea depended on the biochemical constituents, it was concluded that heat treatment was not a suitable method for kombucha tea preservation.

Liquid-phase separation of reactive dye by wood-rotting fungus: a biotechnological approach.

The live and pretreated mycelial pellets/biomass of Trametes versicolor was used for the biosorption of a textile dye, reactive blue MR (RBMR) from aqueous solution. The parameters that affect the biosorption of RBMR, such as contact time, concentration of dye and pH, on the extent of RBMR adsorption were investigated. To develop an effective and accurate design model for removal of dye, adsorption kinetics and equilibrium data are essential basic requirements. Lagergren first-order, second-order and Bangham's model were used to fit the experimental data. Results of the kinetic studies showed that the second order kinetic model fitted well for the present experimental data. The Langmuir, Freundlich and Temkin adsorption models were used for the mathematical description of the biosorption equilibrium. The biosorption equilibrium data obeyed well for Langmuir isotherm and the maximum adsorption capacities were found to be 49.8, 51.6, 47.4 and 46.7 mg/g for live, autoclaved, acid- and alkali-pretreated biomass. The dye uptake capacity order of the fungal biomass was found as autoclaved > live > acid-treated > alkali-pretreated. The Freundlich and Temkin models were also able to describe the biosorption equilibrium on RBMR on live and pretreated fungal biomass. Acidic pH was favorable for the adsorption of dye. Studies on pH effect and desorption show that chemisorption seems to play a major role in the adsorption process. On comparison with fixed bed adsorption, batch mode adsorption was more efficient in adsorption of RBMR.

Construction of an electro-enzymatic bioreactor for the production of (R)-mandelate from benzoylformate.

Coupling both the electrocatalytic recycling of NADH and the enzymatic reduction of the substrate was used to produce (R)-mandelate from benzoylformate using benzoylformate reductase (BFR). The reduction of benzoylformate by BFR in combination with FAD-mediated electrolysis (at -0.5 V vs. Ag/AgCl) was complete in about 18 h and gave 47.5 mM (R)-mandelate from 50 mM substrate, while the process involving MV2+-mediated procedure (at -0.7 V vs. Ag/AgCl) produced 40 mM (R)-mandelate after 30 h. The overpotential for the NAD+ reduction could be decreased by about 0.2 V by substituting a toxic viologen derivative, MV2+, with a natural electron carrier, FAD. MV2+, however, decreased the productivity as BFR lost about 50% of its initial activity after 6 d in its presence.