Studies were conducted with used frying oils in a flat membrane batch cell using five different types of polymeric membranes to decrease the soluble degradation products. During membrane processing, triglycerides permeated preferentially compared to the majority of the polar compounds including oxidation products, polymers, and color compounds. Two of the composite membranes, NTGS-AX and NTGS-2200, selectively rejected polar compounds and oxidation products to the extent of 25-48% and 24-44%, respectively. The reduction in Lovibond color values (5R+Y) was in the range of 83-93%. The viscosity of the used frying oil was reduced to the extent of 22%. The composite membranes were effective in reducing the soluble impurities, as well as insoluble particulates, without causing any undesirable changes to the oil. The membrane process appears to improve the life of used frying oils and does not have the disadvantages associated with the active filtration systems, however, for commercial application the permeate flux needs to be improved considerably.
Application of microwave and infrared radiation was explored for thermal processing of honey and its effect on the physico-chemical characteristics as well as the microbiological quality of honey were studied. Microwave heating provided a rapid means of achieving the desired level of yeast reduction with reduced thermal damage. Though different combinations of heating duration and microwave power intensity achieved the commercially acceptable level of yeast reduction in honey, heating for a shorter duration (15 s) at higher power intensity (16 W/g) was desirable in terms of lower hydroxymethylfurfural (HMF) value (3.8 mg/kg) and higher diastase activity (12.0). Infrared heating was not as rapid as microwave heating but achieved the desired results in a relatively shorter period (3-4 min) offering advantages over the conventional method.
The application of aqueous two-phase extraction for the downstream processing of lipase has been exploited. The influence of system parameters such as phase forming salts, molecular weight of the phase forming polymer, system pH, tie line length, and phase volume ratio on the partitioning behavior of lipase was evaluated. The aqueous two-phase system consisting of PEG6000 and disodium phosphate (Na 2 HPO 4 ) resulted in one-sided partitioning of lipase with partition coefficient 0.11, activity recovery 116%, and purification factor of 2.25. Further, the purity of lipase was increased to 3.59-fold using multi-stage extractions.
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