Seminar - Tyrosinase from Food Waste: Extraction, Characterization and Food Application

Polyphenol oxidases (PPOs) are copper-containing enzymes, such as tyrosinase, laccase, and catechol oxidase, that catalyze the oxidation of mono- and di-phenolic compounds into reactive o-quinones. The quinones quickly undergo non-enzymatic polymerization to form melanin pigments or cause protein cross linking by reacting with amine and thiol groups. While enzymatic browning is usually undesirable in fresh produce (e.g., button mushrooms, apples, pears, and avocados), PPOs have significant potential for other food applications, including gel formation, biosensing, edible film production, and emulsion stabilization. Agricultural waste streams (e.g., mushroom stumps, apple and pear pomace, and avocado seeds) are typically discarded during food processing, but may serve as cost-effective and sustainable sources of PPOs for industrial use. The aim of this study is to extract and characterize PPOs from selected by-products and evaluate their potential in food processing applications.

In the first study, we explore the recovery and application of tyrosinase from white button mushroom (Agaricus bisporus) stumps, an underutilized agricultural byproduct. The crude extract displayed optimal enzyme activity at pH 7.5 and 45 °C and contained a 43 kDa protein identified as tyrosinase. Partial purification via ammonium sulfate precipitation (50–70% saturation) enhanced tyrosinase activity, with the 50% fraction achieving 4.4-fold purification. The crude tyrosinase extract also contained proteases, which hindered protein crosslinking. However, the use of partially purified fractions and protease inhibitors (EDTA and PMSF) reduced proteolysis and allowed the demonstration of tyrosinase-mediated casein polymerization by SDS-PAGE. This is the first study to demonstrate the extraction and functionality of tyrosinase from mushroom waste as a potential sustainable, low-cost source for protein modification.

In the second study, we investigated the extraction and characterization of acid-adapted polyphenol oxidases (PPOs) from fruit by-products, including Hass avocado seeds (Persea americana), cider and pomace from Anjou and Bartlett pears (Pyrus communis L.), and cider and pomace from Red Delicious and McIntosh apples (Malus domestica). PPOs from Anjou and Bartlett pear pomace exhibited the most acid-adapted activity profiles, with optimal activity at 20 °C and pH ranges of 4.0–5.0 and 5.0–8.0, respectively. Protein bands at ~44 kDa and ~25.6 kDa were observed, corresponding to known PPO isoforms in pear. Both pear pomace extracts were capable of oxidizing L-DOPA and EGCG, with Anjou PPO displaying higher catalytic efficiency toward EGCG, whereas Bartlett PPO showed a preference for L-DOPA. However, oxidation rates for other phenolic substrates (gallic acid, caffeic acid, tannic acid, and ferulic acid) were negligible. These findings highlight pear pomace as a promising, underutilized source of acid-stable PPOs with potential applications in acidic food systems such as beverages and fermented dairy products.

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