COOKING INFLUENCE ON COLOR ATTRIBUTES, TOTAL PHENOLIC CONTENT, PHENOLIC PROFILE (LC-UV-MS) AND POLYPHENOL OXIDASE ACTIVITY IN NEW HYBRIDS OF YAM (DIOSCOREA ALATA)

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English. Yam is a major staple food which provides both energy and bioactive compounds. In the French West Indies, over the past ten years, yam production declined by 70%, which was partly due to a fungal disease leaf anthracnose. New hybrids resistant to anthracnose were created but some of them have quality flaws. Some hybrids are susceptible to browning when cut [1]. We showed recently that this susceptibility is positively correlated to total phenolic and catechin contents and negatively correlated to procyanidins with high degree of polymerization. Moreover, an extra change in color is observed after cooking. Darkening appearing after cooking is highly undesirable in potatoes [2] but has not been previously reported in yams. We determined the influence of boiling on color attributes, total phenolic content, phenolic profile (LC-UV-MS) and polyphenol oxidase activity in three varieties of yam contrasted for their susceptibility to browning. The new hybrids “INRA15”, highly susceptible to browning, and « Caribinra » with low susceptibility to this defect, were compared to “Kabusah”, which exhibited moderate susceptibility. Boiling during 22 min led to darkening in all varieties. It also induced an average 42 % decrease in the total phenolic, flavanols and total procyanidins contents of the pulp without any significant modification in the structure of procyanidins. The decrease in the contents of phenolics compounds after cooking could be due either to oxidation or to leakage in the boiling water. Polyphenol oxidase activity was the highest in « INRA15 » and was inhibited only after 11 min in boiling water when the temperature of the core of the pulp attained 60 °C. The leakage of flavanols in water was on average of 2 % and was linked to compounds with a low degree of polymerization. Cooling at ambient temperature during one hour induced no significant change in color attributes or total phenolic content. For the first time, the phenolic profile of flavanols and the polyphenol oxidase activity in the pulp of yam were determined sequentially throughout cooking. The phenolic profile of flavanols in boiling water had not yet been examined. Cooking darkening in yam occurs during boiling and not during cooling, unlike what was reported in potatoes [2]. Further studies are needed to determine how to prevent cooking darkening in yam. [1] Rinaldo D. Sotin H., Pétro D., Le-Bail G. & Guyot S., LWT – Food Science and Technology, 162, 113410, https://doi.org/10.1016/j.lwt.2022.113410, 2022.[2] Wang-Prusky G. & Nowak J., American Journal of Potato Research, 81, 7-16, 2004.