Abstract
Abstract Advances Polyphenol Oxidase (PPO) from Sorghum bicolor (white and yellow varieties) grains were investigated for optimum processing condition. The partially purified enzyme was obtained from two varieties of Sorghum bicolor by step-wise separation through ion-exchange and size-exclusion chromatography. The final purification gave a yield of 7.33 % and 12.3 % for PPO from white and yellow sorghum respectively. The PPO has Vmax and Km of 2.66 U.mL−1 and 19.72 mM for white sorghum, 1.33 U.mL−1 and 12.92 mM for yellow sorghum. The optimal pH of PPO activity was found at pH 4 and pH 7 for white and pH 4 and pH 8 for yellow sorghum. The pKa 7.4 and 8.7 were obtained for PPO from white sorghum, and pKa 5.4, 7.4 and 8.5 for yellow sorghum. The PPO residual activity were above 70 % at 5 hours of incubation within the neutral pH ranges for white sorghum, while those of yellow sorghum were below 40 %. The optimum temperature of 40 ºC and 30 ºC for white and yellow sorghum PPO respectively. The average value of enthalpy (ΔH), entropy (ΔS) and Gibbs free energy (ΔG) obtained at 20 min of incubation and temperature 50 – 80 °C were respectively 49.03 kJ.mol−1, - 129.52 J.mol−1.K−1, and 92.81 kJ.mol−1 for white sorghum PPO, and 90.1 kJ.mol−1, - 9.29 J.mol−1.K−1, and 93.37 kJ.mol−1 for yellow sorghum PPO. Zn2+, Fe2+ and ascorbic acid inhibited PPO while Cu2+, Na+ and K+ activated the enzyme. The results suggest the processing parameters for controlling PPO in potential industrial application of white and yellow sorghum grains.
Highlights
Sorghum (Sorghum bicolor (L.) Moench) is indigenous to Africa and is a member of the grass family Poaceae and has high morphological variations (Deu and Hamon 1994; Hariprasanna and Patil 2015)
Nigeria is the third largest world producer after the United States and India (FAOSTAT 2011), accounting for about 71 % of the total sorghum production in West Africa which could be of different varieties, with two best known species which are Sorghum vulgare and Sorghum bicolor (L.) Moench (Ogbonna 2011)
The results showed that the rate of polyphenol oxidase activity in white sorghum was better than that of yellow sorghum
Summary
Sorghum (Sorghum bicolor (L.) Moench) is indigenous to Africa and is a member of the grass family Poaceae and has high morphological variations (Deu and Hamon 1994; Hariprasanna and Patil 2015). Effect of pH on polyphenol oxidase activity was determined by incubating 0.1 mL of purified PPO with 0.9 mL of 20 mM catechol prepared in each buffer pH range 2.0 – 9.0 using 20 mM Glycine/HCl (pH 2.0 – 3.0), 20 mM sodium acetate buffer (pH 4.0 – 5.0), 20 mM phosphate buffer (pH 6.0 – 7.0) and 20 mM Tris/HCl buffer (pH 8.0 – 9.0) at room temperature.
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