Effects of heat treatment and storage on orange juice composition and HMF formation kinetics

In this study, changing of browning index, color, ascorbic acid, hydroxymethylfurfural (HMF), furfural and total carotenoid content of orange juice which was obtained from Kozan Yerli variety were investigated during processing to juice with different thermal treatments (temperature: 70-90 oC and time: 15-120 s) and storage conditions (180 days, at 4 and 25 oC). According to results of the ascorbic acid degradation kinetics; the half-lifes (t1/2) of thermally processed orange juice at 70, 75, 80, 85 and 90 ° C were 1136.3, 1004.6, 877.4, 796.7 and 666.5 s, respectively. D values for the same temperatures were calculated 3774.7, 3337.1, 2914.7, 2646.6 and 2214 s, respectively. z, Ea and Q10 values of ascorbic acid were also calculated as 86.32 0C, 26.87 kJ/mol, and 1.31; respectively. According to results of HMF formation kinetics data, the doubling time (t2x) of thermally processed orange juice at 70, 75, 80, 85 and 90 ° C were 77.0, 70.7, 60.8, 52.1 and 42.0 s, respectively. D values for the same temperatures were calculated 255.8, 235, 202, 173.1 and 139.6 s, respectively. z, Ea and Q10 values of HMF were also calculated as 75.98 oC, 31.34 kJ/mol, and 1.35; respectively. According to results of furfural formation kinetics data; doubling time (t2x) of thermally processed orange juice at 70, 75, 80, 85 and 90 °C were 74.5, 66.6, 55.9 and 52.1 s, respectively. D values for the same temperatures were calculated 274.12, 247.59, 221.40, 185.69 and 173.13 s, respectively. z, Ea and Q10 values of furfural were also calculated 100.21˚C, 24.98 kJ/mol and 1.26, respectively. The most obvious changes for compounds and qualities of processed orange juice were determined during storage at 25 oC. And also, during storage period according to initial values, browning index values increased between 46.92-145.32%; L*, a*, b*, C* and Hue* values decreased between 0.61-24.40 %, 42.91-175.05 %, 5.3-20.5 %, 3.02-12.44 %, and 3.02-12.44 %; respectively. The effects of different thermal processing conditions on the total carotenoid content of orange juices were found insignificant. During storage period at 4 and 25 °C, the k values were changed between 1.07-2.64 and 1.20-2.81 day-1x10-2, respectively.