Desorption isotherms, net isosteric heat and the effect of temperature and water activity on the antioxidant activity of two varieties of onion (Allium cepa L)

• Published in: International journal of food science & technology 2014-02, Vol.49 (2), p.444-452
• Main Authors: Bouba, Armand A., Njintang, Nicolas Y., Nkouam, Gilles Bernard, Mang, Yannick Dimitry, El-Sayed Mehanni, Abul-Hamd, Scher, Joël, Montet, Didier, Mbofung, Carl Moses
• Format: Article
• Language: English
• Subjects: Allium cepa L; antioxidant activity; Antioxidants; Desorption; isosteric; Isotherms; Life Sciences; Mathematical analysis; Mathematical models; Moisture content; Onions; Temperature; Water activity
• ISSN: 0950-5423; 1365-2621
• DOI: 10.1111/ijfs.12321

Summary The standard static gravimetric method was used to determine moisture desorption isotherms (MDIs) of two onion varieties (Goudami and Galmi Violet) at 30 °C, 45 °C and 60 °C in the water activity ranging from 0.055 to 0.83. The combined effects of temperature and water activity on the antioxidant activities of the onion varieties were also studied. GAB, Oswin, Smith and BET equations were tested to fit the experimental data. The net isosteric heat of sorption was calculated. Equilibrium moisture content (EMC), total phenolic content (TPC) and antiradical activity were also measured. The isotherm and the EMC vary significantly with the onion variety and drying temperature, irrespective of water activity (aw). Desorption isotherms were best described by the GAB model. The maximum net isosteric heats for Galmi Violet (32.58 kJ mol−1) were greater than those of Goudami (23.50 kJ mol−1) at each EMC. The TPC and antiradical activity of the Galmi Violet were significantly (P ≤ 0.05) higher than that of the Goudami at all investigated temperatures and water activities.