1. Titratable Acidities in Fruits Jacob Boroff a, Meredith Gray b, Dr. Faith Wyzgoski c and Dr. Tammy Siciliano c a Pharmaceutical Sciences Class of 2014, b Animal Sciences Class of 2014 and c Science Club Advisors Introduction Total acidity calculations, as they pertain to fruits, are a measure of the level of Hydrogen ions, H +, in fruit cell fluids. Total acidity levels are driven by the concentration of organic acids in the fruit juices. Why are we interested in acidities of fruits? During ripening, some acid content in fruits decrease. Acids in fruits have significant bearing on the pH of fruit juices. Fruit acidity effects taste, color and microbial stability of fruit juices. Same Stage Fruit Preparation A slurry for each red raspberries, black raspberries and blueberries at the same stage of ripening was made by mixing 2 parts desired fruit with 1 part water in a blender. Approximately 45 mL of DI water was added to 5 g fruit slurry and gently mixed. The mixture was allowed to stand for 10 minutes with periodic swirling. The solids were removed by vacuum filtration, leaving the supernatant. Black Raspberry Stage Preparation A slurry for black raspberries at stage 3 and stage 7 of ripening was made by mixing 2 parts desired fruit with 1 part water in a blender. Approximately 42.5 mL of DI water was added to 7.5 g fruit-stage slurry and gently mixed. The mixture was allowed to stand for 10 minutes with periodic swirling. The solids were removed by vacuum filtration, leaving the supernatant. Titration Procedure A 0.101 M sodium hydroxide, NaOH, solution was prepared. Approximately 20 mL of supernatant was placed in a beaker with a pH meter present. NaOH was added to the beaker via a buret with minimal stirring until a pH of 8.2 was achieved. Total acidity calculations were performed as shown in equation 1. Acknowledgements This experiment was conducted using a modified procedure from the University of Wisconsin RIPENING STAGES Stage R0 – green; Stage R1 – blush; Stage R2 – red; Stage R3 – red violet; Stage R4 – violet; Stage R5 – black, torus firmly attached; Stage R6 – black, removed from torus with gentle force Stage R7 – ripe (black) fruit easily removed from torus Analysis of Acidities FruitInitial PHFinal PHmL of.101M NaOH Blueberry3.448.221.42 Blueberry3.487.981.41 Black Raspberry3.208.124.20 Black Raspberry3.418.133.88 Red Raspberry3.478.701.60 Red Raspberry3.318.341.78 Average mL NaOH Blueberry1.42 Black Raspberry4.04 Red Raspberry1.69 Percent Acid in Fruit Samples Ripening StageInitial phFinal pHmL of.101M NaOH Stage 32.688.326.83 Stage 73.488.162.24 Black Raspberry Blueberry Black Raspberry Red Raspberry Conclusions The titratable acidity measures the level of acidity in the sample resulting from tan acidic functional group, The titratable acidity levels in fruits are driven by the concentration of soluble acids found in the fruit. Black raspberries had the highest percent acidity of the three fruits tested. Stage 3 ripening had a much higher percent acidity than stage 7 ripening in black raspberries.