Gan Eng Seng School Presents Apple Browning Project The effect of different PH levels on apple browning. AIM To determine the pH range that is most effective in slowing down the enzymatic browning of apples HYPOTHESIS • pH level affects the rate of action of polyphenol oxidase enzymes. The lower the pH of the solution the apples are soaked in, the lower the rate of enzymatic browning of the apples. INTRODUCTION Apples have a group of enzymes called polyphenol oxidases. When apples are cut, polyphenol oxidase catalyses the reaction between polyphenols, which are naturally present in apple tissues, and oxygen. This oxidation reaction leads to the formation of black-brown complexes called melanin, causing browning of apples MATERIALS •Measuring cylinders •Beakers • Red apples •Stirring Rod • Lime (pH 2.38) •Tea spoon • Lemon (pH 2.49) •Electronic balance • Distilled water (pH 7) •Knife • Common salt (sodium •Chopping Board chloride) (pH 7) •white paper •Marker METHOD • 100ml of fresh lime juice, lemon juice, salt solution and distilled water were prepared. • The apples were cut longitudinally into 5cm by 5cm slices. • The exposed surface of the slices of apple were immersed into the different solutions prepared. • Apple slices were removed from the solutions after 5 minutes. Figure • The treated apple slices were placed on a piece showing a 5 of white paper cm x 5 cm • The apple slices were labeled with the name of the solution it was dipped in accordingly. apple slice • Photographs of the apples were taken at 1 hour intervals for a total of 5 hours to show the colour changes in the apples DISCUSSION Lime Lime Lime DISCUSSION As seen from the results, lime juice is able to preserve the fresh-cut colour of the apple best, followed by lemon juice, salt solution and lastly distilled water. Though salt solution and distilled water have a pH value of 7, salt solution is able to retain the colour better. Salt (sodium chloride) is a water binding chemical which removes water molecules from the cells. This causes dehydration of the apple. Since water is an important factor for enzymatic browning of apples, salt solution has an anti-browning effect. DISCUSSION • Effect Of Acids 1.Lemon and lime juice contains ascorbic acid (vitamin C) and citric acid. 2.Ascorbic acid also acts as an anti-oxidant. 3.These acids react with oxygen before the oxygen reacts with the polyphenol oxidase, thus, giving an anti-browning effect. DISCUSSION • Effect of pH 1. Polyphenol oxidase (PPO), which is responsible for the enzymatic browning of apples, works best when the pH level is between 5.0 and 7.0. 2.By bringing the pH level to less than 3, PPO will be denatured. 3.The pH of lime and lemon juice is in the range of 2.0 and 2.5, making them very effective against enzymatic browning. CONCLUSION We conclude that the more acidic the solution in which apples are soaked in, the slower the rate of enzymatic browning of the apples. From our results, lime juice is the most effective in preserving the fresh-cut colour of apples.