eng Science and Education Publishing Journal of Food and Nutrition Research 2333-1240 2015-10-30 3 8 550 557 10.12691/jfnr-3-8-10 JFNR20153810 article Pornrat Sinchaipanit pornrat.sin@mahidol.ac.th 1 Mehraj Ahmad 1 Renu Twichatwitayakul 1 Institute of Nutrition (INMU), Mahidol University, Phutthamonthon 4 Rd., Salaya, Nakhon Pathom, Thailand In this study, the kinetics of ascorbic acid degradation and quality changes in guava juice during refrigerated storage at various temperatures were investigated The ascorbic acid degradation in all juice samples during refrigerated storage was fitted in first-order reaction with high regression coefficient (r20.961-0.999). Lowest rate constant (k) was obtained in all juice samples stored at 5°C (3.0-5.8 × 10-2 day-1), followed by 10°C (3.8-7.1 × 10-2 day-1) and 15°C (5.2-9.1 × 10-2 day-1). Accordingly, the half-life (t1/2) values of ascorbic acid were longer when juice samples stored at lower temperature. The estimated activation energy (Ea) of ascorbic degradation was in the range of 0.443-0.544 kcal/mol for 30-100% juice samples. Quality attributes of juice samples stored at various refrigerated temperature for 21 days did not showed any significant difference (p>0.05) in pH (3.80-3.83), acidity (0.25-0.29%), and total soluble solids (12.00-12.20 °Brix). Microbial populations were below the detection limit during the whole storage period. http://pubs.sciepub.com/jfnr/3/8/10/jfnr-3-8-10.pdf kinetics ascorbic acid antioxidant activity