Graduate Thesis Or Dissertation
 

Factors influencing enzymatic browning of ripening bananas

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  • Activity of polyphenol oxidase, concentration of 3, 4- dihydroxyphenylethylamine (dopamine), and concentration of ascorbic acid in the pulp of bananas as they ripened were measured and relationships between these factors and both the extent of browning and the susceptibility to discoloration of the fruit during a 30-minute holding period were studied. Moisture and protein content were determined also. Bananas from three lots were analyzed as purchased and after either two or four days of additional ripening. Initial browning of the filtrates of bananas and the increase in browning upon standing were greater as the fruit ripened. Protein content also increased with ripening. Moisture content of bananas increased significantly in those bananas held for four additional days. The specific activity of polyphenol oxidase (units of activity/mg protein) in bananas decreased with ripening, but when the activity was calculated on a basis of dry weight of banana no significant change was observed. Both the dopamine and ascorbic acid contents decreased in individual bananas with ripening. Decrease in the concentration of dopamine was the variable with the highest correlation to the increase in browning in ripening bananas. Both the increase in browning and the decrease in dopamine in ripening bananas were associated with a decrease in ascorbic acid content. Thus, the concentration of dopamine as influenced in part by concentration of ascorbic acid appears to be the limiting factor in the browning of bananas. The specific activity of polyphenol oxidase did not appear to be a limiting factor in the browning of bananas. Dopamine was located histochemically in the vacuoles of the latex vessels and in a few isolated parenchyma cells of banana. Polyphenol oxidase appeared to occur throughout the pulp.
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