Lab 1 - browning apple PDF

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Lab 1: The Browning Apple When an apple is cut, the plant tissue is exposed to oxygen and enzymes called polyphenol oxidase react with oxygen to oxidize phenolic compounds (Subhashree, Sunoj, Xue & Bora, 2017). As a result of the oxidation reaction, quinones are formed which react with amino acids to produce melanin which gives the cut apple its' brown-colored pigment (Holderbaum, Kon, Kudo & Guerra, 2010). Ways to decrease the time it takes for the apple to brown includes lowering the pH and oxygen levels, and increasing temperature (Massantini & Mencarelli, 2007). Lowering the pH levels of the apple will affect the enzymatic efficiency of PPO, therefore, reducing the browning of the apple (Massantini & Mencarelli, 2007). Coating the fruit with citric juices such as lemon juice will slow the reaction down (Massantini & Mencarelli, 2007). Lowering oxygen levels by coating the fruit with sugar syrup, honey, or caramel will effectively provide a physical barrier between the exposed cells and the surrounding oxygen (Massantini & Mencarelli, 2007). Reducing the exposure of the fruit will decrease the diffusion of the oxygen through the apple cells (Massantini & Mencarelli, 2007). Submerging the exposed fruit in water also reduces oxygen supply (Massantini & Mencarelli, 2007). Finally, applying heat to the fruit will also reduce the browning of the apple (Massantini & Mencarelli, 2007). High temperatures can cause the PPO enzyme to denature (Massantini & Mencarelli, 2007). The alteration of the structure of the enzyme can reduce its' enzymatic activities (Massantini & Mencarelli, 2007). Decreasing the temperature can also reduce browning of the apple (Massantini & Mencarelli, 2007). Refrigerating the fruit can slow down the oxidation reaction between oxygen and PPO (Massantini & Mencarelli, 2007).

References

Holderbaum, D., Kon, T., Kudo, T., & Guerra, M. (2010). Enzymatic browning, polyphenol oxidase activity, and polyphenols in four apple cultivars: Dynamics during fruit development.45(8), 1150-1154. doi:https://doi.org/10.21273/HORTSCI.45.8.1150

Massantini, R., & Mencarelli, F. (2007). Understanding and Management of browning in fresh whole and lightly processed fruits., 94-100.

Subhashree, S., Sunoj, S., Xue, J., & Bora, G. (2017). Quantification of browning in apples using colour and textural features by image analysis.1(3), 221-226....