Abstract
The juice clarification, one of the key steps in juice processing, suffers from haze formation that results from residual phenolic compounds. In this study, laccase was immobilized on metal-chelated magnetic silica nanoparticles and used for continuous juice clarification in a magnetically stabilized fluidized bed (MSFB) assisted by alternating magnetic field. Furthermore, a new combination of laccase catalysis and microfiltration was developed for the juice clarification. Immobilized laccase provided high relative activity within broader ranges of pH and temperature compared to the free enzyme. Magnetic immobilized laccase exhibited the best reaction rate of 12.1 μmol g–1 min–1 for catechol oxidation under the alternating magnetic field of 400 Hz, 60 Gs. No activity loss occurred in immobilized laccase after 20 h continuous operation of juice treatment in MSFB under an alternating magnetic field. Combined with microfiltration after treatment with immobilized laccase, the color of apple juice was decreased by 33.7%, and the light transmittance was enhanced by 20.2%. Furthermore, only 16.3% of phenolic compounds and 15.1% of antioxidant activity was reduced for apple juice after the clarification. By this combination strategy, the apple juice possessed good freeze–thaw and thermal stability.
Highlights
The consumption of fruit juice continuously increases due to the well-known beneficial effects of fruit juice and the consumers’ continued pursuit of health and wellness (Bharate and Bharate, 2014; Kahraman et al, 2017)
These results indicated that the immobilized laccase can be more stable within a wider pH range
It was due to the increased activation energy of immobilized laccase resulted from multipoint chelate interactions that caused laccase to reorganize an optimum conformation for substrate binding at a high temperature (Kara et al, 2005; Sari et al, 2006)
Summary
The consumption of fruit juice continuously increases due to the well-known beneficial effects of fruit juice and the consumers’ continued pursuit of health and wellness (Bharate and Bharate, 2014; Kahraman et al, 2017). Different clarification methods have been applied in the fruit juice industry, such as thermal treatment, absorbents/flocculants, centrifugation, and/or filtration (Lettera et al, 2016; Belgheisi and Kenari, 2019) These strategies can improve the clarity and stability of fruit juice, the formation of haze cannot be avoided due to the presence of reactive phenolic compounds (Lettera et al, 2016). Endo-βmannanase, endo-β-xylanase, β-glucosidase, β-xylosidase, αgalactosidase, and protease have been investigated in terms of juice clarification (Benucci et al, 2019; Suryawanshi et al, 2019) These enzymes cannot catalyze the reaction with polyphenol and remove these phenolic compounds. A continuous operation of juice clarification in MSFB assisted by alternating magnetic field was investigated
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