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Studies on antioxidant properties of kinnow-peel and pomace

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2013
Bhatia, Surekha
Punjab Agricultural University
Studies on antioxidant properties of kinnow-peel and pomace

Phenols and flavonoids were quantified in relation to their antioxidant potential in kinnow peel and pomace. The effect of heat treatments on phenolics and their antioxidant potential was also ascertained. The kinnow peel and pomace were sun dried and analysed for free-, bound phenols / flavonoids and their antioxidant capacities. In both peel and pomace, phenol content was found to be more than the flavonoid content. Phenol and flavonoid in free form were higher than its respective bound form. Free phenolics had higher amount of antioxidant capacities in terms of reducing power, hydroxyl- and 1,1- diphenyl-2-picrylhydrazyl (DPPH) radical scavenging capacity whereas bound phenolics had higher Fe2+ chelation activity and trolox equivalent antioxidant capacity (TEAC). Content of phenolics and their antioxidant activities were more in pomace than peel. Treatment of peel and pomace in oven at 120°C for 30 to 120 minutes and in microwave at 250 W for 1to5 minutes resulted in increase in total phenolic content. In peel and pomace, content of free phenols, free flavonoids increased and bound phenols decreased gradually with increase in time of treatment. However, bound flavonoids enhanced within first 30 minutes of oven and 1 minute of microwave treatment and then declined. In both peel and pomace, the antioxidant activities viz. hydroxyl radical scavenging capacity, reducing power and TEAC increased with the oven treatment for 120 minutes and microwave treatment for 5 minutes. However Fe2+ chelation activity increased in peel and decreased in pomace with increase in heating time in both treatments. In peel DPPH radical scavenging activity increased with oven and decreased with microwave treatment whereas, in pomace, this activity decreased with both treatments. Maximum change in the phenolic content and their activities were observed after 30 mins. of oven and after 1 min. of microwave treatment. Our results indicated that kinnow peel and pomace were rich in phenolic acids which contributed to their antioxidant activity and can be used as nutraceuticals. Appropriate heat treatment could be used to liberate and activate the bound phenolic compounds and to enhance the antioxidant activity of kinnow peel and pomace.

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