Effect of Ultrasound on the Activity of Mushroom (Agaricus bisporous) Polyphenol Oxidase and Observation of Structural Changes Using Time-resolved Fluorescence

Konstantina Tsikrika,David H Bremner,M Adília Lemos,Boon-Seang Chu,Graham Hungerford

doi:10.1007/s11947-022-02777-5

Konstantina Tsikrika, David H Bremner + Show 3 more

Open Access

https://doi.org/10.1007/s11947-022-02777-5

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Abstract

Polyphenol oxidase (PPO) is an enzyme associated with the browning process that can occur from mechanical injury and postharvest storage. Thus, its inactivation to inhibit this process is of great interest to the food industry. Recently a nonthermal technology, high frequency ultrasound (100–1 MHz), has found usage in this aspect. In this work, the application of high-frequency (378 kHz, 583 kHz, 1144 kHz, and 1175 kHz) and low frequency (20 kHz) treatment on a PPO extract (from mushrooms) by monitoring the residual enzymatic activity is described. A control thermal treatment at 40 °C was also performed for comparison purposes. High-frequency inactivation data fitted well using the Weibull model, whereas those obtained upon low frequency followed first-order kinetics. The inactivation rate constant obtained ranged from 0.0054 (20 kHz) to 0.028 min−1 (at 583 kHz). To elucidate changes in the enzyme structure time-resolved spectroscopy of a commercial PPO enzyme model was employed. Results indicated that ultrasound-induced structural changes in PPO, in keeping with the activity behaviour upon sonication.

Highlights

Polyphenol oxidase (PPO; EC 1.14.18.1) is a copper-containing enzyme commonly found in fresh fruit and vegetables, where it is associated with a postharvest browning process (Cheng et al, 2013)
High- and low-frequency ultrasound treatments caused a statistically significant (p < 0.05) decrease in mushroom PPO residual activity, while no PPO reactivation was observed after treatment
Complete PPO inactivation was achieved after the application of high-frequency ultrasound at 378 and 578 kHz at a power level of 48 W

Summary

Introduction

Polyphenol oxidase (PPO; EC 1.14.18.1) is a copper-containing enzyme commonly found in fresh fruit and vegetables, where it is associated with a postharvest browning process (Cheng et al, 2013). It results from mechanical injury, storage, or processing procedures (Fortea et al, 2009). The demand for fresh-like fruit and vegetable products is continually rising, promoting the use of novel nonthermal food technologies for PPO inactivation in foods, namely ultrasound (US), high-pressure processing, and pulsed electric fields (Silva & Sulaiman, 2018; Shinwari & Rao, 2021). Ultrasound technology, in particular, has been investigated as a green milder food processing technique, entailing energy and water saving with reduced carbon and water footprint and relatively low chemical and physical hazards, to provide a full or partial alternative to conventional heat treatment (Chemat et al, 2011, 2017)

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