Abstract Dextransucrase is an important class of extracellular enzymes with great industrial importance. Dextransucrase synthesizes the high molecular weight glucose polymer dextran by transferring D-glucosyl moieties to a growing glucan chain. Keeping in view the potential of dextransucrase, bench scale production of Acetobacter tropicalis cells with high dextransucrase activity was carried out in laboratory fermenter at 7 l scale. The growth of A. tropicalis has been affected by the supply of oxygen during the fermentation. Therefore, the optimum combination of aeration rate and agitation speed for dextransucrase production from A. tropicalis was found to be 0.5 vvm and 450 rpm. The volumetric oxygen transfer coefficient, KLa values were found to affect the growth of A. tropicalis and production of dextransucrase. In the present study, the growth and dextransucrase production increased with increase in KLa upto an optimum limit and then started decreasing with increase in KLa. Maximum biomass (1.41 mg/ml) and maximum dextransucrase activity (15.8 U/ml) was obtained at KLa value of 0.28 min-1. The maximum dextransucrase activity obtained in laboratory fermenter was 15.8 U/ml which was greater than the enzyme level obtained at shake flask level (11.6 U/ml).
Keywords: dextransucrase; Acetobacter tropicalis; dextran; fermentation; agitation; aeration; dissolved oxygen; dissolved oxygen concentration (CL); volumetric oxygen transfer coefficient (KLa)

Abstract Statistical experimental designs were carried out for enhancing the ethanol production from cashew apple juice after obtaining the biochemical analysis of cashew apple juice. The biochemical analysis of the cashew apple juice was as follows: 79.2 % moisture, 12.5 % total sugars, 4.9 % reducing sugars, 0.16 % protein, 0.2 % fat, 1.91 % tannin and 1.13 % ascorbic acid. Cashew apple juice can be preserved at -18oC for several months. The Plackett - Burman design was used initially to screen seven nutritional parameters which are critical and important for growth of Saccharomyces cerevisiae as well as enhancing ethanol production. Among them three parameters were found to have a significant effect on ethanol production and these three elements were further optimized using central composite design (CCD) by response surface methodology. The optimal values of three variables obtained for maximum production of ethanol was (g/l): ammonium chloride 0.45, magnesium sulfate 0.08 and dipotassium phosphate 0.21 and the predicted ethanol production was 61.34 g/l. With the predicted optimal values, experiments conducted in the laboratory yielded an ethanol production of 59.80 g/l equal to 93.62% of its theoretical yield. Statistical experimental designs such as Plackett-Burman design and CCD are critical and important for rapid screening and determining significant nutritional parameters and then optimizing them for enhancing the ethanol production.
Keywords: Saccharomyces cerevisiae; cashew apple juice; ethanol; response surface methodology; Plackett-Burman design; central composite design