Screening phytochimique, potentiel antioxydant de l’huile et aptitude technologique de la farine du gland de trois espèces de Quercus
Makhlouf, Fatima Zohra
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Oak acorns (Quercus) are among the underutilized vegetable resources in the agri-food sector. Few studies are present in literature on acorn fruit, which is a handicap for the valorization of these fruits which unfortunately remain under-exploited. These studies show that the acorn fruit has interesting nutritional and functional properties. The present study aims at investigating the biochemical composition and the technological aptitude of two acorn products ""oil"" and ""flour"" in order to valorize this neglected natural resource. Firstly, a detailed study of the physicochemical properties and chemical composition of oil extracted from three Quercus (Q. ilex, Q. coccifera and Q. suber) species was carried out. Antioxidant proprieties and oxidative stability of extracted oil were also evaluated. Then, a technological aptitude study of Quercus flours for the elaboration of a functional biscuit was performed. The study of physicochemical characteristics showed a similarity between acorn oil and olive oil. GPC analysis of Quercus oil revealed a predominance of unsaturated fatty acids (oleic acid), and a particular sterol composition, which differs from those of most conventional edible oils. The volatile fraction analysis, reported for the first time, indicated that acorn oils were found to contain specific and variable range volatiles compound profiles. Twenty phenolic compounds were detected by LC / MS analysis; all of them were hydrolysable tannins derivatives. Studied oils had significant amounts of phenolic compounds, tocopherols and carotenoids, which give them a strong antioxidant capacity, which was revealed by the two tests ABTS and DPPH. Monitoring the oxidation state of the Quercus oil during 180 days (6 months) of storage showed slight variations in the measured oxidation markers. The chemical characteristics of acorn flour obtained from three different Quercus species were compared. Q. coccifera L. flour, which were the most antioxidant, was used for preparing biscuits at two levels of substitution Q30 and Q60. Acorn-added biscuits showed significantly higher content of phenolics, higher antioxidant activity and oxidative stability (induction time) than control biscuits. The acorn-based biscuits also showed technological (volume, friability,...) and organoleptic properties (odor, color, taste, ..) better than the control biscuits.