Studies on phenolic content and polyphenol oxidase activity of sugarcane varieties with reference to sugar processing

The phenolic content of sugarcane varieties was analysed during 6, 10 and 12 months age. The total phenolic content (TPC) was found to increase from 10 to 20 mg/100 ml (6 months) to 70–90 mg/100 ml (12 months) and stabilize during peak maturity period. Concentration of phenolics was found to be higher at the top portion of the sugarcane. The raw juice from cane samples were clarified by defecation and 30–40 % removal of TPC was observed. The sugar samples and the intermediate process products collected from sugar factories were analysed for the phenolic content and colour. Dark coloured sugars and intermediate products were found to have higher phenolics. Enzymic browning due to polyphenol oxidase (PPO) activity contributes significantly to colouring of cane juice. The absorbance increased to an extent of 70–80 % during the first 10 min of juice extraction. Colour input to sugar process can be reduced by inhibition of PPO activity of cane juice by chemical inhibitors and heating. Ascorbic acid alone inhibited PPO activity by 35 % and to an extent of 85 % combined with heating. Juice holding time in mills for 10–15 min increases enzymic browning hence; heating the juice instantly on extraction could reduce the colour formation to an extent of 40 %