SBK3023Food

Science and Nutrition

GROUP 3BROWNING PREVENTION

WHY SOME FRUITS AND VEGETABLES TURN BROWN WHEN CUT OR BRUISED ????

This is due to browning enzymatic

reaction!!

When fruits or vegetable are peeled or cut, enzymes in the plant tissue, POLYPHENOL OXIDASE are exposed to the air.

In the presence of oxygen, polyphenol oxidase (PPO) enzyme rapidly oxidize phenolic compounds naturally encountered in the fruit tissues to o-quinones.

Then, O-quinone react with protein or amino acids to form melanins.

This compound melanin is responsible for browning of fruits and vegetables.

This reaction is occurs at warm temperatures when the pH of the plant material is between 5.0 and 7.0.

METHOD use to PREVENT browning enzymatic reaction..

Several methods can be applied to avoid enzymatic browning, based on INACTIVATING THE ENZYME (heat) or by REMOVING ESSENTIAL

COMPONENTS (most often oxygen) from the product.

SET A (CHANGE PH)HERE, WE ARE GOING TO USE 3 DIFFERENT PREVENTING AGENT WHICH ARE LEMON JUICE,VINEGAR AND SALT SOLUTION.

ACTIVITY:1)CUT THE LEMON AND SQUEEZE THEM

2)PREPARE THE SALT SOLUTION

3) MEASURE 20 ML OF THE LEMON JUICE, VINEGAR AND

SALT SOLUTION BY USING THE MEASURING CYLINDER.

4)PUT EACH OF THE MEASURED SOLUTION INTO 4

LABELLED BOWL A,B ,C AND D RESPECTIVELY.

5) CUT THE APPLE INTO 4 SLICE.

6)SOAK THE APPLE SLICE INTO THE 3 LABELLED BOWL

RESPECTIVELY TAKING ONE AS A CONTROL FOR 20

MINUTES.

7) TAKE OUT THE APPLE SLICE AND SEE THE TIME

TAKEN FOR IT TO TURN BROWN.

APPLE SLICES BROWNING PREVENTING AGENT

COLOR CHANGE AFTER 1 NIGHT

A LEMON JUICE WHITE B VINEGAR BROWN

( DUE TO DAMAGE)C SALT WATER SLIGHTLY BROWN

D (CONTROL) - DARK BROWN

HOW LEMON JUICE KEEP APPLE FROM BROWNING?

Lemon juice helps keep the apple from browning, because it is full of ascorbic acid (Vitamin C) and it has a low (acidic) pH level.

Low pH level

Polyphenol oxidase works best when the pH level is between 5.0 and 7.0. However, below a pH level of 3.0, the enzyme becomes inactivated. The pH of lemon juice is in the 2.0 range, making it very effective against browning.

Antioxidant

Ascorbic acid (vitamin C) acts as an antioxidant. Oxygen is more likely to react with the ascorbic acid, rather than with the phenolic compounds in the fruit or vegetable. Browning does not proceed until most of the ascorbic acid is used up in the reaction.

HOW VINEGAR WORKS ON APPLE?Like lemon juice, vinegar prevent browning of apple by

lowering the pH of the

Although vinegar can prevent the browning of apple, but too large amount of it will cause damage to the apple.

Why did this happen?As vinegar undergoes the fermentation process, it is a lot stronger when compared with lemon juice. So, it is actually the mildness of acid in lemon juice that is the key to prevent apples from turning brown.

SET 2 (DEHYDRATION)

WE ARE GOING TO USE THE SALT SOLUTION OF 3 DIFFERENT CONCENTRATION.

ACTIVITY:1)PUT THE SALT INTO A MEASURING CYLINDER UP TO 1 ML.THEN PUT 20 ML OF

WATER AND STIR THEM.

2)REPEAT STEP 2 BY REPLACING THE 1 ML LEVEL WITH 3 ML AND 6 ML.

3) PUT THE THREE SOLUTION INTO 3 DIFFERENT LABELLED BOWL.

4)CUT THE APPLE INTO 4 SLICES

5)SOAK THE APPLE SLICE INTO THE 3 LABELLED BOWL RESPECTIVELY TAKING ONE

AS A CONTROL FOR 20 MINUTES.

6) TAKE OUT THE APPLE SLICE AND SEE THE TIME TAKEN FOR IT TO TURN BROWN.

 

HOW SALT WATER PREVENT BROWNING OF

APPLE?The PPO enzyme needs sufficient water to be active. Salt water will lower water activity in the apples by adding water-binding chemicals (sodium chloride). But dehydrating the apple, will only inhibited the enzyme but not destroy it.

APPLE SLICES CONCENTRATION OF SALT WATERIN 20 ml WATER

COLOUR CHANGE AFTER 1 NIGHT

A Salt(up to 1 ml of measuring cylinder)

LIGHT BROWN

B Salt(up to 3 ml of measuring cylinder)

WHITE

C Salt(up to 6 ml of measuring cylinder)

WHITE

D (CONTROL) - DARK BROWN

….THE END