Effect of different clarifying agents on the physico-chemical and microbial properties of grape juice concentrate

Grape juice concentrate is the local product of grape growing regions in Iran and is mainly extracted from the rotten grape of the late days of the year. In order to study the effects of clarifying agents on the quality of prepared grape juice concentrate, an experiment was conducted using the complete randomized factorial experimental design. The first factor was types of clarifying agents in 6 levels including syrup soil, bentonit, silicasol, gelatin bentonit, gelatin-silicasol, gelatin-bentonit-silicasol and the second factor was the amount of clarifying agents in 3 levels and 3 replicates. Statistical analysis of the results showed that the increase of the amount of syrup soil decreases the level of acidity of grape juice concentrate and increases its pH. But the addition of other filter-aid like bentonit, silicasol and gelatin didn’t have any significant effect on the level of acidity and pH. Using bentonit and silicasol comparison with syrup soil increase of transparency and decrease of turbidity significantly. The addition of gelatin to bentonit and silicasol in comparison to bentonit and silicasol alone decreased turbidity and increased transparency of samples significantly. Treatment of gelatin-bentonit-silicasol has the highest amount of transparency (89.467%). The lowest amount of turbidity (8.483%) was considered as the brightest and clearest treatment among all of samples. The resulting grape juice concentrate had no adverse changes of pH, acidity, protein, sugar, ash, brix, total solid as the most important quality indices. Finally, 2%gelatin-4%bentonit-7%silicasol treatment was chosen as effective treatment for clarification of grape juice concentrate.