Enzymatic removal of off-flavors from apple juice.

Contaminating microorganisms such as Actinomycetes, Alicyclobacillus, and Chlostridium can generate off-flavors in apple juices. Such bacterial metabolites represent, besides phenol types such as guaiacol and 2,6-dibromophenol, a broad range of other chemicals, for example, geosmin, 2-methylisoborneol, or alpha-terpineol. A laccase from Trametes hirsuta was purified, immobilized, and applied for the selective elimination of off-flavor substances in apple juice caused by microbial contamination. The evaluation using GC-MS showed that enzymatic treatment could reduce the amount of guaiacol and 2,6-dibromophenol in apple juice significantly by 99 and 52%, respectively. Upon addition of mediators, the degradation could be increased and the spectrum of substrates extented. Furthermore, commercial apple juices spiked with off-flavors were treated in a continuous-flow reactor and tested by sensory evaluation.