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A 215 m 3 industrial bubble column reactor for fedbatch production of Baker's yeast was sampled for sugar, to investigate the extent of concentration gradients. The results verify that such gradients exist: the concentration is higher closer to the feeding point. Effects of sugar heterogeneities at different scales were studied by 1) performing a volumetric scale-down of the industrial process in a laboratory stirred tank reactor (STR); 2) performing the same scaled down process in a Scale-Down Reactor (SDR) with repeated short term exposure of the cells to high sugar concentrations. In this reactor about 10% of the Baker's yeast culture was intermittently exposed to high (0.45±1.9 g l A1 ) concentrations of sugar, for periods of 60 seconds. It was found that physiological parameters of glycolysis and respiration were affected by environmental heterogeneities: 1) A biomass yield reduction of about 6±7% was found, with both the production reactor and the SDR, as compared to the homogeneous reactor. The loss of yield is interpreted in terms of a metabolic by-pass via ethanol, where cells are consuming and producing ethanol with different yields. 2) The maximum respiration rate was higher in cells produced in the production unit and in the SDR. 3) The product quality, expressed as gassing power of the yeast in a dough, was increased for sweet and non-sugar doughs in the SDR, and for sweet doughs in the production reactor. Thus, the SDR, when run with de®ned glucose gradients, in some aspects resembles the large reactor. It could be regarded as a tool for scale-down and scale-up studies and may be useful in investigations on the scale-up sensitivity of a process.

Aim: To improve biosurfactant production economics by the utilization of potential low-cost materials. Methods and Results:In an attempt to utilize cost-effective carbon sources in the fermentative production of biosurfactants, various pure and waste frying oils were screened by a standard biosurfactant producing strain. Considering the regional significance, easy availability and the economical advantages, waste frying coconut oil was selected as the substrate for further studies. On isolation of more competent strains that could use waste frying coconut oil efficiently as a carbon source, six bacterial strains were isolated on cetyltrimethyl ammonium bromide-methylene blue agar plate, from a soil sample collected from the premises of a coconut oil mill. Among these, Pseudomonas aeruginosa D was selected as the potential producer of rhamnolipid. Spectrophotometric method, TLC, methylene blue active substance assay, drop collapse technique, surface tension measurement by Du Nouy ring method and emulsifying test confirmed the rhamnolipid producing ability of the selected strain and various process parameters were optimized for the production of maximum amount of biosurfactant. Rhamnolipid components purified and separated by ethyl acetate extraction, preparative silica gel column chromatography, HPLC and TLC were characterized by fast atom bombardment mass spectrometry as a mixture of dirhamnolipids and monorhamnolipids. The rhamnolipid homologues detected were

The fermentative production of rhamnolipid biosurfactant from Pseudomonas aeruginosa MTCC 2297 was carried out by submerged fermentation using various cost-effective waste materials such as orange peelings, carrot peel waste, lime peelings, coconut oil cake, and banana waste. The orange peel was found to be the best substrate generating 9.18 g/l of rhamnolipid biosurfactant with a surface tension reduction up to 31.3 mN/m. The production was growth independent, and optimum conditions were standardized. The emulsifying activity was highest against kerosene (73.3%). Rhamnolipid components were purified and separated by ethyl acetate extraction, preparative silica gel column chromatography, high-performance liquid chromatography and thin-layer chromatography. The major rhamnolipid components were characterized, by fast atom bombardment mass spectrometry, as a mixture of dirhamnolipids and monorhamnolipids.

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