An amperometric biosensor developed for detection of limonin levels in kinnow mandarin juices
The bitterness in kinnow mandarins (also in certain other citrus juices) has been ascribed to limonin that is gradually formed during processing of the juice, which lowers the consumer’s acceptability. Thus, detection of limonin at various stages of processing is crucial for the employment of suitable debittering interventions. Owing to the lack of rapid, reliable and economical method for determining limonin levels during the juice production process, an attempt has been made to develop an amperometric microbial biosensor using a mutant (lim+) of a strain Pseudomonas putida G7, that could selectively utilize limonin as a carbon source in the presence of other sugars in kinnow mandarin juice. Analytical determination was based on the respiratory activity of this stable, lim+ auxotrophic mutant in the presence of the analyte, limonin. The temperature of 30°C, pH 6.5 and the mid-log phase cells at concentrations of 106 CFU/ml were the most optimal operating conditions. A consistent correlation between limonin concentrations of 20, 25, 30 ppm (i.e. an optimal substrate–to-cell mass concentration) and the dissolved oxygen (DO) was established. Response times of approximately 20 min for the steady-state method and 12 min for the initial slope method were recorded. The calibration curve for limonin was linear in the 15–50 ppm range of limonin. The performance of the biosensor was reproducible and remained unaffected following intermittent storage and reuse for at least 1 month. Overall, this study suggests the possible application of the developed biosensor for monitoring the limonin content in citrus juices during processing.
KeywordsLimonin Amperometric biosensor Pseudomonas putida G7 Debitterring
This work was supported to M.G. by Department of Science and Technology, under the SERC Fast Track Scheme for young scientists.
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