Ethanol and phenylacetylcarbinol production processes of Candida tropicalis TISTR 5306 and Saccharomyces cerevisiae TISTR 5606 in fresh juices from longan fruit of various sizes

Abstract

© 2018 Wiley Periodicals, Inc. Fresh juice from C grade longan (mg/g fresh fruit; total sugars 51.6 ± 0.5, nitrogen 0.021 ± 0.004; gallic acid 0.025 ± 0.001; ellagic acid 0.016 ± 0.001) with addition of 8.52 g ammonium sulfate/l was the optimal medium for cultivation processes of Saccharomyces cerevisiae TISTR 5606 and Candida tropicalis TISTR 5306 capable of producing ethanol and phenylacetylcarbinol (PAC) among five longan grades. S. cerevisiae TISTR 5606 produced ethanol (33.4 ± 3.2 g/L) at a significantly higher level (p ≤ 0.05) than C. tropicalis TISTR 5306 (22.3 ± 1.1 g/L) with similar ethanol yields (Yp/s) between 0.21 and 0.22 g ethanol produced/g sugars consumed. Whole cells of C. tropicalis TISTR 5306 produced a significantly higher (p ≤ 0.05) PAC level (27.2 ± 0.7 mM) than S. cerevisiae TISTR 5606 (3.59 ± 1.33 mM) after 6 hr in an equivalent volume biphasic biotransformation system. Practical applications: Longan is one of the important economic fruit of Thailand with production volume in 2017 reaching one million tons. Less than 10% of these are domestically consumed while more than 90% are exported to several countries whose population frequently consume longan as a nutritious food supplement. This study can help solving overproduction problem of longan fruit by processing C grade fresh longan, which is accounted for 5% of the overall production volume, in the form of juice extract with the relatively high sugars content. Microbial fermentation of this juice and subsequent whole cells biotransformation process result in ethanol and PAC, respectively. Ethanol can be used as an alternative biofuel or important industrial solvent while PAC is a precursor for production of commercial nasal decongestant (ephedrine) or anti-asthmatic compound (pseudoephedrine).