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In certain varieties of oranges, an increase in bitterness is currently observed in juices, after extraction, restraining their industrial use. This has been explained by the conversion of the nonbitter precursor, limonoate A-ring lactone, to a bitter compound, limonin, under acidic conditions. The aim of this study was the modelling of limonin consumption in raw and sterilized orange juices by Acinetobacter calcoaceticus isolated from soil. Response Surface Methodology (RSM) was used for modelling bioconversion and optimization reaction conditions, as a function of temperature (23-37 degreesC) and limonin content (8-16 ppm). Initial rate of limonin consumption could be described, both in raw and sterilized orange juices, by concave surfaces with a minimum at 26 and 27 degreesC, respectively. In raw orange juice, after 7 h reaction time, the amount of converted limonin, increased with temperature. Also, the highest conversions (higher than 33%) were achieved at high temperature (higher than 34 degreesC) and low initial limonin content. In sterilized juice, a maximum conversion of about 23% is expected at 31 degreesC, for an initial limonin content of I I mg l(-1). Thus, limonin bioconversion may be carried out directly in raw juice, avoiding juice sterilization. In addition, no significant decrease in reducing sugars was observed. (C) 2002 Elsevier Science B.V. All rights reserved.
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JOURNAL OF MOLECULAR CATALYSIS B-ENZYMATIC. - Vol. 21, n. 40210 (2003), p. 81-88