Influence du pH sur la composition en lipides et en acides gras du rotifère Brachionus plicatilis.

Abstract

L'influence du pH du milieu sur la composition en acides gras de Brachionus plicatilis a ete etudiee en ajustant le pH de cultures semi-continues de rotiferes. Deux groupes ont ete soumis a un pH variant entre 5 et 6, deux autres entre 9 et 10, les deux temoins (pH non modifie) ayant un pH variant de 7 a 8. Les rotiferes ont ete nourris avec un aliment a base de levure de boulangerie et d'huile emulsifiee. Les rotiferes ainsi produits ont ete analyses apres 10 jours de traitement. La teneur en lipides ne varie pas de facon significative. Une nette influence du pH est remarquee sur la composition en acides gras et notamment sur les acides gras longs polyinsatures de la serie n-3 dont les teneurs sont plus importantes a pH acide et surtout basique qu'a pH neutre. Ceci s'effectue au detriment des acides gras de la serie n-7. La difference la plus remarquable concerne l'acide docosahexaenoique (C22:6n-3), maximale a pH basique. La manipulation du pH des cultures peut donc etre une technique permettant d'ameliorer la teneur des rotiferes en acides gras essentiels afin de couvrir les besoins des larves de poissons marins.

The influence of pH of rotifer culture medium on the fatty acid content of rotifers was studied. The pH of rotifer semi-continuous cultures was daily adjusted either at pH 5 to 6, either at pH 9 to 10, while the pH of the untreated control group varied from 7 to 8. Rotifers were fed with a mixture of baker's yeast and emulsified oil. After 10 days, rotifer fatty acid composition of each tank was analysed. Total lipid content did not change between treatments. A clear pH influence was noticed on Long Chain Polyunsaturated n-3 fatty acids content at the expense of the n-7 monounsaturated fatty acids. The acid and mainly basic treatments led to higher levels of n-3 highly unsaturated fatty acids in rotifers than neutral pH. The main difference concerned docosahexaenoic acid (C22:6n-3) with the highest value observed in rotifers cultures at alcaline pH. pH monitoring of the cultures can be a means to improve rotifer quality in their essential fatty acid content and in order to meet requirements of marine fish larvae