Determining effect of different pH ranges on the oxygen uptake capacity of gallic acid and designing active package for orange juice

Orange juice is one of the most commonly consumed fruit juices in the market. Orange juice has its unique taste and odor characteristics, and contains high levels of vitamin C which is known to have a positive effect on the immune system. However, it is known that due to the accumulated oxygen in the packages of orange juices, considerable loss of vitamin C might be observed in the first weeks of storage and browning may occur as a result of the oxidation of vitamin C. In this thesis, oxygen absorption capacity of gallic acid, which is frequently found in plant based food sources, was investigated and active packaging by using gallic acid as an oxygen scavenger was designed to prevent ascorbic acid degradation and color loss in orange juice. In this study, 5 ml buffer solutions of gallic acid at different pH values which were pH 2.9, 5.1, 5.8, 7.2, 7.9, 9.2 and 10.4 with Na2CO3 and pH 2.9, 5.7, 7.3, 7.9, 9.1, 11 and 13.8 with NaOH, were prepared. During 28 day experiments, oxygen uptake rates were compared and the oxygen uptake capacity of gallic acid was calculated in terms of mg O2 / g gallic acid unit for different pH values. The highest oxygen uptake capacity was obtained at pH 11 of the GA and NaOH mixture, and it was decided to place the same amount of gallic acid and NaOH powder mixture into the orange juice packages as oxygen scavenger sachets. As a result of experiments, it has been concluded that the oxygen uptake capacity of gallic acid is not related to the strength of the used base, but is directly related to the pH value of the buffer solution. In addition, when the color changes of different buffer solutions at different pH values was examined, similar color changes were observed in the solutions compared to the amount of oxygen retention of gallic acid. According to this result, the color change in the solutions can be regarded as the basic indicator of the oxygen uptake rate of gallic acid in different buffer solutions. The orange juice storage test was carried out for 21 days, in the dark for the first 7 days and in the presence of daylight fluorescent lamps between 7th and 21st days. In these experiments, ascorbic acid content of samples collected from oxygen scavenger including glass bottle, nonscavenger including glass bottles and PET bottles. Then, ascorbic acid contents were determined by HPLC method and evaluation of color changes were performed by DIGI-EYE color measurement device. In the experiments, the sachets were made from Tyvek® 1073B (DuPont ™) material consisting of polyethylene fibers, and 2.2327 g GA, 1.2640 g NaOH and 0.550 g superabsorber were put as scavenger mixture inside the sachets in powder form. Thanks to the utilization of superabsorber, the reaction between gallic acid (weak acid) and NaOH (strong base) was kept into the sachet throughout the experiment. For ascorbic acid analysis of the orange juice storage test, samples were collected in eppendorf tubes on days 0th, 1st, 3rd, 7th, 14th and 21st and were stored at -30 ° C until the end of the experiment. In ascorbic acid determination by HPLC method, the lowest decrease in ascorbic acid occurred in glass bottle containing oxygen scavenger. In color change analyzes CIA L * a * b * values were measured and compared for all bottle types. As a result of the color analysis, the discoloration towards browning were occurred in similar ratio at all bottles.