Pectinesterase activity and proximate analyses of sea buckthorn juices

Three varieties of sea buckthorn fruit were harvested and pressed to obtain juices. These were analyzed for pectin methylesterase activity, moisture, nitrogen, oil, pH, total acid, and degrees Brix. Yields of press juice for Hippophae rhamnoides ssp. rhamnoides L. varieties Luchistaya, Prozrachnaya, and ssp. mongolica Rousi cv. Indian Summer were 68%, 69%, and 66% w/w, respectively. Differences in juice composition were found to be in moisture content, degrees Brix, pH, and in total acid with the Luchistaya variety having the highest acid levels and lowest pH. Pectin methylesterase (PME) was present in all sea buckthorn juices with initial activity levels of 6.8 to 14.0 mu equivalents per min per 100 g of juice at pH 8 and 23 degrees C. Activity was pH-dependent with little PME activity at pH 3 to 5 and the highest activity at pH 8. The cream, pellet, and serum layers of centrifuged juices all contained PME. Heat treatment reduced PME activity in the juices by 1 decimal reduction or less.