Acidity and alkalinity are measured using the pH scale, where a value of 7.0 is considered neutral. Anything below 7.0 is acidic, and anything above 7.0 is alkaline. Prune juice measures as mildly acidic when initially consumed, but its ultimate effect on the body’s chemistry is considered alkaline-forming. The question of whether prune juice is acidic or alkaline requires a two-part answer depending on whether the measurement is taken in a laboratory or after the juice has been processed by the body.
The Measured pH of Prune Juice
When tested outside of the body, prune juice consistently registers on the acidic side of the pH scale, typically falling between 3.9 and 4.4. This places it in a category similar to other naturally acidic fruit juices, such as orange or apple juice. This initial acidity is attributable to naturally occurring organic acids within the prunes. The primary contributors to this low pH are phenolic acids, specifically neochlorogenic and chlorogenic acids. This laboratory pH value measures the liquid itself and does not reflect its biological effect once consumed and metabolized.
Metabolic Impact and PRAL Score
The true answer to the acid or alkaline question lies in the body’s metabolic response, assessed using the Potential Renal Acid Load (PRAL) score. The PRAL score estimates the amount of acid or alkali a food generates after digestion and metabolism. A positive PRAL score indicates an acid-forming food, while a negative score signifies an alkaline-forming food. Prune juice consistently has a negative PRAL score, typically around -5.09 mEq per 100 grams, classifying it as alkaline-forming.
This alkaline-forming effect relates to the “ash” or residue left after the food’s components are broken down. While blood pH is tightly regulated, the PRAL score reflects the load placed on the kidneys to manage acid excretion. The metabolic process burns off the organic acids that caused the initial low pH, leaving behind the alkalizing mineral content to influence the PRAL calculation.
Components Driving the Alkaline Effect
The negative PRAL score is primarily driven by the high concentration of specific alkalizing minerals found in prune juice. The most significant of these are potassium and magnesium, which are present in large amounts. These minerals are considered base precursors because they do not form acid during metabolism.
When prune juice is metabolized, the organic acids like chlorogenic acid and neochlorogenic acid are broken down into carbon dioxide and water, effectively neutralizing their acidic properties. The remaining potassium and magnesium ions then serve as buffers in the body. These mineral compounds contribute to the alkaline ash measured by the PRAL calculation, confirming the juice’s classification as an alkaline-producing food.