Enzymatic Browning Control Methods

It is crucial to grasp the two primary forms of reactions responsible for browning: enzymatic phenol oxidation and nonenzymatic browning. Enzymatic browning, especially, presents a significant challenge in many food systems due to its adverse effect on the visual appeal of fruits and vegetables. Nevertheless, with a thorough comprehension of these reactions, it becomes possible to devise effective methods to control this undesirable phenomenon.

Enzymatic browning can be succinctly described as the initial enzymatic oxidation of natural phenols into slightly colored quinones, which act as precursors to pigments through subsequent enzymatically catalyzed or nonenzymatic reactions. For example, cutting the surfaces of fruits and vegetables triggers enzymatic browning as a result of reactions involving o-quinones. These nonenzymatically catalyzed oxidations lead to the polymerization of the oxidation products, further accelerating the browning process.

The essence of enzymatic browning lies in the activity of polyphenol oxidases (PPOs), which play a crucial role in catalyzing the oxidation of phenols in the presence of oxygen. These enzymes are abundant in various fruits and vegetables, rendering them susceptible to enzymatic browning upon damage or exposure to air.

To counter enzymatic browning, several strategies can be employed. One common approach involves using inhibitors that target PPOs, thereby hindering the enzymatic oxidation of phenols. Moreover, adjusting the pH, temperature, and oxygen levels of the environment can also help regulate enzymatic browning reactions in fruits.

In conclusion, enzymatic browning reactions in fruits represent a complex process influenced by enzymatic phenol oxidation and nonenzymatic browning. By comprehending the intricacies of these reactions, food scientists can develop effective strategies to mitigate the adverse effects of enzymatic browning, ensuring the visual appeal and quality of fruits and vegetables are maintained.
Enzymatic Browning Control Methods

Processing of Raisins

Processing of Raisins
Raisins are produced from grapes by sun during and artificial drying. In sun drying, the grapes are picked as bunches and placed in a single layer on wooden trays between the rows of grapes vines. The trays are tilted to face the sun. After they are partially dried, the grape bunches are turned and allowed to dry to the point where no juice can be pressed out. The trays are then stacked, and the air drying is continued in the shade until moisture content of about 17% reached. After drying, the raisins are placed in sweat boxes to equilibrate, or to even out, the moisture that is present, and then they are packed in retail size containers or in larger containers to be sold to the bakery trade.

In artificial drying, grapes are first dipped n 0.25 – 1 % lye (sodium hydroxide) solution at 200 – 212 degree F for 2 – 5 sec to remove a natural wax that impedes drying and to check or crack the skin of the grape to facilitate drying, They are then washed, placed on trays, and treated with sulfur dioxide to prevent enzymatic and nonenzymatic browning during drying. Hence instead of having the dark brown color of raisins that normally be expected, the raisins will be of a light yellow color when dried. Raisins are dried at temperatures not exceeding 165 degree F and at a low relative humidity. After the moisture content has been lowered to about 16 – 18%, the raisins are packaged in containers of various sizes to be sold at retail or for use by the food industry.
Processing of Raisins