Polyphenol oxidase (PPO) in wheat (Triticum aestivum): a systematic review on bioactivity, inheritance, functionality and their effects on end products

Polyphenol oxidases (PPOs) are enzymes found in several plant species, including wheat (Triticum aestivum L.), that contribute to the undesirable brown discoloration of many food products. Wheat serves as a fascinating system for studying PPO function due to its complex genome and economic significance. Over the past two decades, wheat PPOs have received considerable attention due to their well-established role in causing brown discoloration and their suspected involvement in various adverse reactions to wheat-based end products such as bread, chapati, pasta and noodles. Wheat PPOs have been extensively studied over two centuries, with a focus on the PPO activity assay and their role in causing brown discoloration of wheat-based products like pasta, chapati, bread and noodles. This scientific review provides a quick overview of wheat PPOs, emphasising the mechanism, activity assay and characteristics that are pertinent to its function in brown discolouration of wheat-based end products. It covers descriptions of PPOs’ biological roles, the structures and interactions of PPO gene families and the presence of similar forms of PPOs that may alter nutritional characteristics and the end-product quality of wheat. Thus, it provides a basic overview of the PPOs system and impact on wheat end products.