Variation in physicochemical and microbiological characteristics of date palm sap (Phoenix dactylifera) during the tapping period in oasian ecosystem of Southern Tunisia

Palm sap tapped from three varieties of date palm Phoenix dactylifera was analyzed during two tapping periods: winter and springtime. These samples were collected once-a-week during 14 weeks for each tapping period. Total soluble solids decreased during tapping period; however no significant variation was noted for pH and titrable acidity. The microbial count indicated that after an initial higher presence during 10 weeks, counts of aerobic mesophilic bacteria and yeasts decreased starting from the 11th week. The sugar composition was determined: Sucrose was the only sugar detected in winter (18%). In springtime, in addition to sucrose, small amounts of glucose (1.00-2.47%) and fructose (1.04-1.79%) were detected. Sap harvested in springtime contains more sugars and lower acidity than the one harvested in winter. During the spontaneous fermentation of sap, pH and total soluble solids decreased from 6.80 and 13% in the first day to 3.40 and 6% respectively at the end of fermentation.