The document discusses enzymatic activity in foods. It defines enzymes as proteins that act as biological catalysts, speeding up reactions in living organisms. It describes how enzymes are made of amino acids linked into specific shapes that determine their functions. The document then discusses several theories of enzymatic action and factors that can affect enzymatic activity, such as temperature, pH, and substrate concentration. It also categorizes the six main types of enzymes and provides examples of how enzymes like polyphenol oxidase and peroxidase cause browning in fruits and vegetables. The document concludes with an overview of how to assay enzymatic activity, using polyphenol oxidase activity and catechol as a specific example.