Biomass measurement is one of the most critical measurements in biotechnological processes. The technologies developed for the measurement of biomass in situ have developed over the years. Because it has been over 10 years since the last review concentrating on practical issues concerning biomass measurements, it is time to evaluate recent developments in the Weld. This review concentrates on the applications of dielectric spectroscopy, optical density, infrared spectroscopy, and Xuorescence for in situ measurement of biomass. The advantages oVered by these methods and an economic way of estimating biomass concentration, the software sensors, are considered.

Two on-line probes for biomass measurement in bioreactor cultivations were evaluated. One probe is based on near infrared (NIR) light absorption and the other on dielectric spectroscopy. The probes were used to monitor biomass production in cultivations of several different microorganisms. Differences in NIR probe response compared to off-line measurement methods revealed that the most significant factor affecting the response was cell shape. The NIR light absorption method is more developed and reliable for on-line in situ biomass estimation than dielectric spectroscopy. The NIR light absorption method is, however, of no significant use, when the cultivation medium is not clear, and especially in processes using adsorbents or solid matrix for the microorganism to grow on. The possibilities offered by dielectric spectroscopy are impressive, but the on-line probe technology needs to be

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A novel immunoaffinity separation material, cross-linked antibody crystals (CLAC), was developed by crystallization and cross-linking of a recombinant antibody Fab fragment ENA5His capable of enantiospecific separation of a chiral drug, finrozole. Crystallization conditions of the antibody fragment were screened by hanging drop vapor diffusion experiments. The small-scale vapor diffusion crystallization was easily scaled up to 10-mL batch crystallization with a 70% yield. Also, the low affinity mutant of ENA5His having one single amino acid mutation crystallized at the same conditions. Simple glutaraldehyde cross-linking of the crystals yielded CLAC, which were insoluble in water, 5-100% methanol, and 2% DMSO in PBS buffer. Batch experiments showed that the CLAC material was functional as it specifically bound the desired enantiomer from the drug racemate.

Ten heterofermentative lactic acid bacteria were compared in their ability to produce D-mannitol from D-fructose in a resting state. The best strain, Leuconostoc mesenteroides ATCC-9135, was examined in high cell density membrane cell-recycle cultures. High volumetric mannitol productivity (26.2 g l(-1) h(-1)) and mannitol yield (97 mol%) were achieved. Using the same initial biomass, a stable high-level production of mannitol was maintained for 14 successive bioconversion batches. Applying response surface methodology, the temperature and pH were studied with respect to specific mannitol productivity and yield. Moreover, increasing the initial fructose concentration from 100 to 120 and 140 g l(-1) resulted in decreased productivities due to both substrate and end-product inhibition of the key enzyme, mannitol dehydrogenase (MDH). Nitrogen gas flushing of the bioconversion media was unnecessary, since it did not change the essential process parameters.