Volumetric mass transfer coefficient (k L a) is an important parameter in bioreactors handling viscous fermentations such as xanthan gum production, as it affects the reactor performance and productivity. Published literatures showed that adding an organic phase such as hydrocarbons or vegetable oil could increase the k L a. The present study opted for palm oil as the organic phase as it is plentiful in Malaysia. Experiments were carried out to study the effect of viscosity, gas holdup, and k L a on the xanthan solution with different palm oil fractions by varying the agitation rate and aeration rate in a 5 L bench-top bioreactor fitted with twin Rushton turbines. Results showed that 10% (v/v) of palm oil raised the k L a of xanthan solution by 1.5 to 3 folds with the highest k L a value of 84.44 h−1. It was also found that palm oil increased the gas holdup and viscosity of the xanthan solution. The k L a values obtained as a function of power input, superficial gas velocity, and palm oil fraction were validated by two different empirical equations. Similarly, the gas holdup obtained as a function of power input and superficial gas velocity was validated by another empirical equation. All correlations were found to fit well with higher determination coefficients.

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Tacca leontopetaloides is a new plant source of starch and has high potential to produce film of thermoplastic. In this study, thermoplastic starch (TPS) derived from T.leontopetaloides was developed with glycerol as plasticizer through casting method at temperature range from 85 °C to 90 °C and enhanced with sulphur vulcanization method. It was found that the addition of 5%, 10%, 15%, 20% and 25% (v/v) of glycerol into T.leontopetaloides starch had affected the mechanical properties, surface morphology, and water absorption of the thermoplastic films. In the mechanical properties study, the TPS films have the highest tensile strength (47.96 MPa) at 5% glycerol content in the formulation. Conversely, the TPS films have increasing value of elongation at break (EAB) with increasing glycerol concentration with the higher EAB obtained at 25% glycerol content (52.90%). The morphology of thermoplastic film was examined by using Scanning Electron Microscopy (SEM). As glycerol content increased, thermoplastic films showed smoother surface, homogenous and good distribution. In water absorption test, TPS films showed lower affinity to water absorption at lower glycerol content. The weight of the TPS films increased ranging from 80.3% to 107.4% after 12 hour of immersion in water. It can be concluded that, glycerol significantly affected the properties of TPS film within the range of glycerol concentration studied.

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