Thanks in advance for your help. The effect of sugar type and pH on the browning

Question

Thanks in advance for your help.

The effect of sugar type and pH on the browning of sugar cookies, through the Mallard reaction, was investigated using several different types of sugars. The table below gives the color optical density (related to degree of browning, a higher color optical density indicates greater browning) for extracts from the cookies. Discuss the relationship between sugar structure and degree of browning of the cookies. Predict whether the cookies made with glucose would have a higher degree of browning if the pH of the dough was 7.2 compared to a dough with a pH of 5.4. Discuss why.

Explanation / Answer

1. In the case of maillard reaction the amine group containing compound (nucleophile) reacts with the carbonyl carbon (nucleophilic center), which promotes a brown color to the compound. So glucose which has a free carbonyl carbon reacts to a greater extent with the amine group containing compound as compared to xylitol and sucrose which do not have such free carbonyl carbon centers ( xylitol has alchoholic group and sucrose froms a glycosidic linkage with the monomers).

2. With increasing ph the nucleophilicity of the amino group increases so as we increase the ph of the dough the degree of browing should incease as there would be more reaction between the carbonyl group and the amino group. Therefore, between ph 7.2 & 5.4, the dough with ph 7.2 would have a higher degree of browning.

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