The dish became complete with the presence of fruit that can complement the nutritional needs of the body. Fruit lovers are of course very familiar with color change on some fruit after peeled and stored within a certain period. Why the flesh of the fruit may change to brownish color?
Discoloration of the flesh of the fruit is caused by the presence of enzymatic changes on the fruit. The enzyme is a type of protein that can accelerate the process of reaction. Enzymes that play a role in this process is the enzyme polyphenol oxidase (PPO) can oxidize compounds phenolic group. In this case, PPO triggered a reaction in the fruit component so that changes the observed components through the color change. PPO is found on the island of all plants (gnetophyta covered) (George and Christoffersen, 2016).
One fruit that often changes color to Brown is avocado. Avocados contain katekol (phenolic compounds) which with the help of the enzyme PPO can undergo oxidation reactions when exposed to oxygen, forming a reddish brown coloured Quinones. Further highly reactive Quinones experience nonenzimatik reactions (occurring without the help of the enzyme) form of melanin polymer (Busch, 1999; Compound Interest, 2014; Zhou dkk, 2015). Melanin is the pigment that gives color to brown to black that is also found in hair, skin, and iris of the eye.
Brown color on the flesh of the fruit resulting in the fruit looks less fresh. One effort that can be done is to inhibit the responsible component changes the color of the flesh of the fruit, namely enzymes PPO. Conventionally, the addition of lemon on the fruit a lot done to inhibit discoloration. Lemon's ability to inhibit fruit caused by vitamin C or Ascorbic acid which can reduce Quinones became dihidroksi polyphenols so not forming melanin. However, this process only inhibits the formation of melanin, continuous oxidation reactions take place can result in a buildup of melanin forming next Quinones (Compound Interest, 2014; Jang, 2011).
Â
Reference:
- Bush, J.M. 1999. Browning enzymatic reactions in potatoes: a simple assay for a polyphenols oxidase catalysed reaction. Biochemical Education 27:171-173.
- Compound Interest. 2014. The chemistry of an avocado. http://www.compoundchem.com/2014/08/03/why-do-avocados-turn-brown-the-chemistry-of-avocados/
- George, H.L., Christoffersen, R.E. 2016. Differential latency toward (-)-epicatechin and catechol mediated ny avocado mesocarp polyphenols oxidase (PPO). Postharvest Biology and Technology 112:31 – 38.
- Jang, J-H., Moon, K-D. 2011. Inhibition of polyphenols oxidase and peroxidase activities on fresh-cut apple by simultaneous treatment of ultrasound and ascorbic acid. Food Chemistry 124:444-449.
- Zhou, d., Li, l., Wu, y., Fan, j., j. Ouyang, 2015. Salicylic acid inhibits browning offresh enzymatic reactions-cut Chinese chestnut (Castanea mollissima) by competitively inhibiting polyphenols oxidase. Food Chemistry 171:19-25.