ABSTRACT
Different enzymes play a vital role in the development of desired color, texture, avor, nutritive value, and bioactivity of edible vegetable parts, that is, leafs, seeds, stems, roots, owers, and fruits. The activity of enzyme systems including those that affect the quality of edible parts is controlled by natural mechanisms unless the plant is exposed to an unusual stress originating from different factors such as diseases, infection, drought, and wrong agricultural practices. Some of the important natural mechanisms that control enzyme-substrate interaction and enzyme activity are compartmentation, latency, solubility control, and inhibition by endogenous inhibitors (Whitaker 1996). The compartmentation is an effective mechanism that maintains enzymes and their substrates in different organelles or locations in the cell, while latency works by preventing the synthesized proenzyme’s full transformation into a final active form, and solubility control works by regulating release or binding of enzymes and/or their substrates on cell walls, membranes, or organelles. The separation of soluble polyphenol oxidase (PPO) in cytoplasm from its phenolic substrates in vacuoles and presence of the majority of this enzyme in inactive state in some vegetables are classical examples of compartmentation and latency, respectively (Moore and Flurkey 1990; Nicolas et al. 1994). On the other hand, the ionic binding of the majority of pectin methyl esterase (PME) in plant cell walls is an effective control mechanism over this enzyme by solubility control (Simsek and Yemenicioglu 2010).
