The browning of sweet potato occurs due to the oxidation and dehydrogenation of colorless polyphenols present in the plants. The initial reaction is catalyzed by polyphenol oxidase and produces reddish-brown o-quinones. The inhibition of polyphenol oxidase (PPO) and browning by extract gotten from ginger, garlic and white onion in the processing of sweet potato samples were investigated. The physicochemical properties were also evaluated using standard methods of analysis. The sweet potato samples with/without inhibitors were steeped in water for 2 hours at 600C, 700C and 800C to know the solubility of the samples. At 60°C the solubility was more using 10% white onion extract which gave the value of 0.04±0.00 g/g, while 5% ginger extract reduced the solubility to 0.02±0.02 g/g. At 70°C, 10% white onion extract increased the solubility to 0.034±0.000g/g, while at 80°C, both 5% and 10% white onion extract where able to increase the solubility to 0.04±0.00g/g. White onion extract (5%) increased the protein estimation to 12.38±0.39 units/mg, 5% ginger extract was able to increase the polyphenol oxidase level to 19.79±1.80 units/mg. Ginger extract (15%) increased the level of the browning index to 1.10 ± 1.07 units/mg, while 5% onion extract reduced it 0.11 ± 0.01 units/mg (an indication of anti-browning activity). Ginger extract (10%) was effective in increasing the hydration capacity of sweet potato to 2.27±0.00g/g while 5% ginger extract decreased it to 0.46±0.00g/g. The swelling capacity increased to 114.00±0.00g/g using 5% garlic extract and 77.50±0.71g/g using 15% white onion extract. The energy value also increased using 15% ginger extract to 19.25±1.06Kj/g. This study thus, revealed that only 5% onion extract was able to inhibit browning in the processed sweet potato samples.
Key words: Browning, extracts, polyphenol oxidase, samples, sweet potato
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