Madhusweta Das

Surface active properties of the culture filtrates of a Micrococcus species grown on n-alkanes and sugars

The surface active properties of the culture filtrates (from shake flash fermentation for 140 h at 37 ± 1°C) of a species of Micrococcus are described in terms of surface tension, emulsification and foamability using carbon sources, such as n-dodecane, n-tetradecane, n-hexadecane and n-octadecane as the different n-alkanes, and sucrose, fructose, glucose and mannose as the different sugars. The surface tension for the culture filtrate was lowest with dodecane (45·2 mN m−1) followed by tetradecane (49·1 mN m−1), hexadecane (50·8 mN m−1) and octadecane (58·3 mN m−1) among the n-alkanes; for the sugars, sucrose had the lowest value (51·4 mN m−1) followed by fructose (52·8 mN m−1), mannose (57·3 mN m−1) and glucose (57·5 mN m−1). All the n-alkane systems showed 70–80% emulsification of a test mixture composed of equal volumes of kerosene and the respective culture filtrate. But only 84 and 50% of the formed emulsions with tetradecane and dodecane, respectively, remained stable during 48 h of ageing. Although the culture filtrate of fructose showed the highest initial emulsification of 62% among the sugars, almost no decay of the formed emulsion (41%) was observed with that of sucrose. Foamability noted with a single nozzle spurger was appreciable with the sucrose and fructose systems, but negligible with the n-alkane systems.

Characterization of de-emulsification capabilities of a Micrococcus species.

Effect of post harvest washing as well as cell concentration on de-emulsification characteristics of an isolated Micrococcus species has been tested with Tween 60 Span 60 stabilised oil in water (o/w) and L-92 pluronic surfactant stabilised water in oil (w/o) model emulsions (kerosene water). The cells used were 140 h old and grown under submerged conditions at 37 degrees C in a medium containing n-tetradecane (4% v/v) as the carbon source. The harvested bacterial cells when in an unwashed condition (at a cell concentration of 2 mg/ml of emulsion) were found to de-emulsify the o/w system at a much faster rate than the w/o system exhibiting half-life values for the respective system as 10.2 and 127.7 h. Post harvest washing of the cells with any lipid solubilising solvent (n-pentane, n-hexane, kerosene, chloroform-methanol-water (CMW)) yielded a decrease in their de-emulsification power for w/o emulsion. But the decay of o/w emulsion became faster with n-pentane- and kerosene-washed cells as evident from their corresponding half-life values of 3.3 and 4.6 h. Compared to the w/o system, an increase in the concentration of kerosene-washed cell had a direct effect on de-emulsification for the o/w system. For cell concentrations of 2, 3 and 4 mg/ml of the emulsion, the half-life values for the w/o system were 364.8, 442.0 and 454.9 h, respectively. For 2 and 4 mg/ml cell contents, the half-life values for the o/w system were 4.6 and 1.0 h. The decay of both the emulsions was very slow or even incomplete for cell concentrations less than 2 mg/ml. De-emulsifying capacity of the n-tetradecane grown Micrococcus species towards o/w model emulsion improved considerably after washing the cells with n-pentane and kerosene, and use of kerosene-washed cells (4 mg/ml) reduced the half-life to 1 h.

Thermophysical Properties of Sugarcane, Palmyra Palm, and Date-palm Granular Jaggery

Effect of moisture content on thermo-physical properties of sugarcane, palmyra palm, and date-palm granular jaggery were investigated. Thermal conductivity and diffusivity were determined by line-heat-source transient heat-transfer methodology, while specific heat was calculated from additional data on bulk density of the samples. Thermal conductivity, diffusivity, specific heat, and bulk density was found to vary from 0.08 to 0.39 W m−1 K−1, 0.10 to 0.13 × 10−6 m2 s−1, 1.19 to 2.97 kJ kg−1 K−1, and 510 to 1310 kg m−3, respectively, for a moisture range of 2.0–14.3 (%d.b.); all at an average temperature of 30°C. All these properties except—thermal diffusivity—followed an increasing trend; with the increase in moisture content, each showed a high correlation coefficients. The variation of thermal diffusivity was found to be insignificant.

Moisture Sorption Isotherms of Sugarcane, Palmyra and Date-Palm Jaggery

The moisture sorption isotherms (MSI) of jaggery obtained from sugarcane, palmyra and date-palm juice were determined by the static method using saturated salt solutions at four temperatures of 25, 35, 45 and 55°C. Among the three MSI models tested with the experimental data for these high sugar foods, GAB model was found to be the best fit followed by Halsey model and Iglesias and Chirife model. The effect of temperature on sorption behaviour was more pronounced than the nature of jaggery. The monolayer moisture contents of sugarcane jaggery was the highest (3.83-13.68%db), followed by palmyra palm jaggery (3.44-5.86% db) and date palm jaggery (2.87- 3.86% db). The net isosteric heat of sorption of three jaggery samples, estimated from the Clausius- Clapeyron equation, decreased exponentially from 3.73 to 2.94 kJ mol-1 (sugarcane); 5.85 to 2.67 kJ mol-1 (palmyra palm) and 3.86 to 2.67 kJ mol-1 (date palm) with the increase in moisture content from 5 to 40%(db).