SBK3023 Food Science and NutritionGROUP 3 BROWNING PREVENTION
WHY SOME FRUITS AND VEGETABLES TURN BROWN WHEN CUT OR BRUISED ????
This is due tobrowning 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.
BLANCHING(SHORT HEAT TREATMENT)
BY CHANGING THE pH
METHOD APPLIED BY OUR GROUPDEHYDRATION
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 4LABELLED BOWL A,B ,C AND D RESPECTIVELY. 5) CUT THE APPLE INTO 4 SLICE.
6)SOAK THE APPLE SLICE INTO THE 3 LABELLED BOWLRESPECTIVELY TAKING ONE AS A CONTROL FOR 20 MINUTES. 7) TAKE OUT THE APPLE SLICE AND SEE THE TIME TAKEN FOR IT TO TURN BROWN.
BROWNING PREVENTING AGENTLEMON JUICE VINEGAR SALT WATER -
COLOR CHANGE AFTER 1 NIGHTWHITE BROWN ( DUE TO DAMAGE) SLIGHTLY BROWN DARK BROWN
A B C D (CONTROL)
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.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.
Low pH levelPolyphenol 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.
HOW VINEGAR WORKS ON APPLE?Like lemon juice, vinegar prevent browning of apple by lowering the pH of theAlthough 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 DIFFERENTCONCENTRATION.
ACTIVITY:1)PUT THE SALT INTO A MEASURING CYLINDER UP TO 1 ML.THEN PUT 20 ML OFWATER 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 SLICES5)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
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 WATER COLOUR CHANGE IN 20 ml WATER AFTER 1 NIGHT A Salt(up to 1 ml of measuring LIGHT BROWN cylinder) B Salt(up to 3 ml of measuring WHITE cylinder) C Salt(up to 6 ml of measuring WHITE cylinder)D (CONTROL) DARK BROWN