Apples contain several organic acids which are responsible for the fruit’s acidity.
Malic and citric acids are the principal determinants of apple fruit acidity. Tartaric acid, lactic acid, and succinic acid are in lower concentrations.
Vibrant cannot infer the effect size of how eating apples within 48 hours of urine sample collection may influence the specific markers (i.e., 20%, 50% etc.) as organic acid content of apples depends upon the apple variety, harvest time, and amount consumed.
For more information on organic acid content of apples, see the article Determination of Predominant Organic Acid Components in Malus Species: Correlation with Apple Domestication https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6316603/pdf/metabolites-08-00074.pdf
