Biosensors Based on Phenol Oxidases (Laccase, Tyrosinase, and Their Mixture) for Estimating the Total Phenolic Index in Food-Related Samples

Abstract

Plant phenolic compounds demonstrate bioactive properties in vitro and/or in vivo, which creates demand for their precise determination in life sciences and industry. Measuring the concentration of individual phenolic compounds is a complex task, since approximately 9000 plant phenolic substances have been identified so far. The determination of the total phenolic content (TPC) is less laborious and is used for the qualimetric evaluation of complex multicomponent samples in routine analyses. Biosensors based on phenol oxidases (POs) have been proposed as alternative analytical devices for detecting phenolic compounds; however, their effectiveness in the analysis of food and vegetal matrices has not been addressed in detail. This review describes catalytic properties of laccase and tyrosinase and reports on the enzymatic and bienzymatic sensors based on laccase and tyrosinase for estimating the total phenolic index (TPI) in food-related samples (FRSs). The review presents the classification of biosensors, POs immobilization, the functions of nanomaterials, the biosensing catalytic cycle, interference, validation, and some other aspects related to TPI assessment. Nanomaterials are involved in the processes of immobilization, electron transfer, signal formation, and amplification, and they improve the performance of PO-based biosensors. Possible strategies for reducing interference in PO-based biosensors are discussed, namely the removal of ascorbic acid and the use of highly purified enzymes.

Keywords: bienzymatic biosensor; enzymatic biosensor; food analysis; food control; food quality; laccase; polyphenol oxidase; total phenolic content; total phenolic index; tyrosinase.

Figure 1

Some types of biological (pharmacological) activities of plant phenolic compounds [2,3,5,6,7,8,9,10].

Figure 2

Schematic representation of the laccase catalytic site: His, histidine ligand; Cys, cysteine ligand; L, other ligand (a). Laccase catalyzed reactions (b) [80,81,82].

Scheme 1

Phenolic substrate oxidation pathway catalyzed by laccase: enzymatic oxidation (1), non-enzymatic oxidation (2), and polymerization (3). Adapted from [82,84,85].

Figure 3

Schematic representation of the tyrosinase catalytic site and tyrosinase catalyzed reactions [87,88].

Scheme 2

Phenolic substrate oxidation pathway catalyzed by tyrosinase: ortho-monooxygenation (1), oxidation (2), and polymerization (3). Adapted from [76,86,87].

Figure 4

Common enzyme immobilization techniques.

Figure 5

Functions of nanomaterials in PO-based biosensors.

Figure 6

Schematic representation of catalytic cycles implemented in PO-based biosensors: independent of a mediator (above) and dependent of a mediator (below).

Figure 7

Operating pH ranges of PO-based biosensors.