... softening is caused by the cellulase acting on the cell walls, or pectin binding layer changing. In unripe fruit, pectin is bound to cellulose in the cell walls. This type of pectin is insoluble and the liquid within the cell remains fluid. The fluid asserts pressure on the cell walls making the fruit seem hard because of the cell walls rigidity. Enzymes are large globular molecules of which the vast majority are made of protein. All globular proteins have a tertiary structure, which is maintained by hydrogen bonds, ionic bonds and sometimes disulphide bonds, which are links between different parts of the polypeptide chain. Enzymes have catalytic properties; in other words, they alter the rate of reaction without themselves undergoing a permanent change. Most chemical reactions require an initial input of energy, called activation energy, to enable them to occur. Enzymes reduce the need for activation energy and so allow ...

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