Development of a Glucose Biosensor for Rapid Assessment of Strawberry Quality: Relationship between Biosensor Response and Fruit Composition

Sugars are intimately related to the taste of strawberry fruit and therefore to quality. A disposable prototype glucose biosensor was constructed using glucose. oxidase (GOx) immobilized onto Meldolas Blue mediated screen printed electrodes, to determine glucose content in diluted strawberry juices. Several experimental variables that affect biosensor performance, such as applied potential, GOx loading, and pH of the buffer/electrolyte solution were optimized by means of a 2 3 central composite design. Optimum applied potential, pH, and enzyme loading were +300 mV (versus Ag/AgCl), 7.2, and 20 U, respectively. Although the linear range (0-10 mM) was not significantly affected by the optimization process, the signal given by the biosensor was increased by as much as 3-fold as compared to preliminary experiments, and the reproducibility of the measurements was improved. Unlike total soluble solids (TSS), and as hypothesized, the constructed GOx biosensor was able to discriminate and rank eight different strawberry cultivars on the basis of their glucose content when compared to known concentrations measured by standard HPLC. A detailed study of the possible interferences (viz. total phenolics, antioxidant capacity, and organic acids) found in strawberry samples that could affect biosensor performance was also performed to further understand the relationship between biosensor response and sample composition. Under the imposed experimental conditions the constructed biosensor acted interference-free.