Characterization of extracellular enzymes from Aspergillus niger for debittering citrus juice

To characterize mechanisms of the debittering citrus juice of extracellular enzymes from Aspergillus niger and to investigate fermentation dynamics of the enzyme activities in relation to the debittering, both solid-state fermentation and submerged fermentation were used to prepare the extracellular enzyme of A. niger, the resulting enzymes were submitted to treat Guanxi pomelo juice, followed by sensory evaluation of the bitter taste and high performance liquid chromatography (HPLC) analyses of the naringin and limonin. The results showed the enzymatic treatment significantly decreased the bitter taste and the content of naringin and limonin. During the solid-state fermentation, the cultures of 12 days showed the best debittering activities, which removed 92.5% of the naringin and 27.7% of the limonin in the juice; whereas the submerged fermentation showed the best debittering effect after 10 days, which generated an enzyme liquid that removed 95.5% of the naringin and 30.8% of the limonin. The results indicated A. niger was able to produce extracellular enzymes that significantly decrease the concentration of naringin and limonin, which resulted in the elimination of the bitter taste of citrus juice, indicating the existence of naringinase and limonin debittering enzyme in the extracellular enzymes. Thus, this study provides a new approach to debitter citrus juice.