Bilberry extract - Organic acids A unit of NIST-3291 consists of five packets, each containing approximately 1 g of bilberry extract. Certified mass fraction values for organic acids (dry-mass basis) Citric acid ......................................... 22.9 ± 2.5 mg/g Quinic acid ....................................... 12.2 ± 2.2 mg/g Malic acid ........................................... 5.9 ± 1.7 mg/g Indicative values for organic acids and anions