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Enzymatic Browning Inhibition of Banana [Musa (AAA Group) 'Gros Michel'] by Pineapple Juice
Abstract:
The effectiveness of pineapple juice in enzymatic browning inhibition was evaluated on the cut surface of banana slices. After storage of banana slices at 15ºC for three days, unheated and heated pineapple juice showed more browning inhibitory effect than 8 mm ascorbic acid and were as effective as 4 mm sodium metabisulfite. Poluphenol oxidase (PPO) from banana pulp was extracted and partially purified by precipitation with 80 percent ammonium sulfate followed by conventional column chromatography on Sephacryl S-200 HR and Fast Protein Liquid Chromatography (FPLC) on a Mono Q column. A 6.63 fold purification was achieved with 9.62 percent recovery. The partially purified enzyme exhibited at least three isoenzymes on polyacrylamide gel electrophoresis (PAGE). The partially purified PPO from gel filtration had optimum pH for activity at 7.0 and it was stable at the same pH. The enzyme was relatively stable at high temperature; only 48 percent of initial activity lost after heating at 70ºC for 30 minutes. The enzyme was completely inhibited by 2 mm sodium metabisulfite, 2 mm L-cysteine, 4 mm ascorbic acid, and 100 mm 4-hexylresorcinol. The Km and Vmax of banana PPO for dopamine were 2.08 mm and 66.67 unit/ml, respectively. A lineweaver-Burk plot showed that pineapple juice was a noncompetitive inhibitor of banana PPO. Fractionation of unheated and heated pineapple juice by reversed-phase C18 cartridge revealed that directly eluted (DE) fraction inhibited banana PPO activity about 100 percent when compared with that treated with Milli Q water. DE fraction showed more inhibitory effect than 8 mm ascorbic acid in enzymatic browning inhibition of banana puree during storage at 5ºC for 24 hours. Further identification of DE fraction by fractionation with ion exchange chromatography and confirmation using model systems indicated that organic acids play an important role in enzymatic browning of the beverage as the same extent as 8 mm ascorbic acid.