title: Optimization of processing conditions to improve antioxidant activities of apple juice and whey based novel beverage fermented by kefir grains.
abstract: A central composite design (CCD) was used to evaluate the effects of fermentation temperature (20-30 ºC) and kefir grains amount (2-8%w/v) on total phenolic content and antioxidant activities of apple juice and whey based novel beverage fermented by kefir grains. The response surface methodology (RSM) showed that the significant second-order polynomial regression equation with high R(2) (>0.86) was successfully fitted for all response as function of independent variable. The overall optimum region was found to be at the combined level of 7.56%w/v kefir grains and temperature of 24.82 ºC with the highest value for total phenolic content (TPC) and antioxidant activities. At this optimum point TPC, 1, 1-Diphenyl-2-picrylhydrazyl radical scavenging, metal chelating effect, reducing power, inhibition of linoleic acid autoxidation and inhibition of ascorbate autoxidation were 165.02 mgGA/l, 0.38 ml/1 ml, 0.757 (absorbance at 700 nm), 46.12 %, 65.33 % and 21 %, respectively. No significant difference (p < 0.05) was found between actual values and predicated values.
authors.affiliation: Department of Food Science and Technology, School of Agriculture, Shiraz University, Shiraz, Islamic Republic of Iran.
authors.forename: Nayereh
authors.initials: N
authors.lastname: Sabokbar
authors.affiliation: Department of Food Science, Engineering and Technology, Faculty of Agricultural Engineering and Technology, Campus of Agriculture and Natural Resources, University of Tehran, Karaj, Islamic Republic of Iran.
authors.forename: Faramarz
authors.initials: F
authors.lastname: Khodaiyan
authors.affiliation: Department of Food Science and Technology and Seafood Processing Research Group, School of Agriculture, Shiraz University, Shiraz, Islamic Republic of Iran.
authors.forename: Marzieh
authors.initials: M
authors.lastname: Moosavi-Nasab
keywords: Antioxidant activities; Apple juice; Fermentation; Kefir; Total phenolic content; Whey