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The microalga Phaeodactylum tricornutum was grown in a concentric tube airlift photobioreactor. A maximum specific growth rate of 0.023 h−1 was obtained using a superficial gas velocity around 0.055 m/s. Lower or higher gas flow rates limited the culture performance. To establish if the observed limitation was due to CO2 or to the photosynthetically active irradiance, characteristic times for mixing, mass transfer and CO2 consumption, and the photon flux absorbed by the culture were analyzed. The CO2‐gradients in the culture were shown to be responsible for the limitation during the exponential growth phase, and both CO2 and light irradiance were limiting in the linear growth phase. The decrease in specific growth rate relative to the maximum was found to be related to the specific gas‐liquid interfacial area, the length scale of the microeddies and the shear rate. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 60: 317–325, 1998.

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Colored potatoes (Solanum tuberosum L.) provide a natural source of phytochemicals that help reduce the risk of diseases. However, there is a lack of information on the degree of variation of the antioxidant activity and polyphenolic contents of these native potatoes. Thus, the antioxidant activity (AA) and total phenolic content (TPC) of native Chilean potatoes were determined. Twelve potato landrace clones collected from established cultivations on Chiloe Island and Valdivia were selected. Total phenolic content and AA were compared with two commercial varieties, Shepody and Desirée. Total phenolic content was determined by the Folin-Ciocalteu method, and β-carotene bleaching was used to compare AA. The TPC varied in the peeled potato samples from 191 to 1864 mg 100 g -1 DM meanwhile these parameters varied from 345 to 2852 mg 100 g -1 DM in unpeeled samples. Antioxidant activity was higher in unpeeled potatoes, and was the highest in the unpeeled NG-6 or 'Bruja' native potato. The commercial var. Shepody showed pro-oxidant activity and had a relatively lower TPC. Results also indicated a higher concentration of total phenolics in the periderm of the colored native Chilean potatoes.