Abundant Existence of Bovine Serum Albumin Non-precipitable Tannins in Red Wines

Abstract

Phenolics in red wines made from three cultivars, Muscat Bailey A (MBA), Merlot (MR), and Cabernet Sauvignon (CS), were separated into four fractions using the bovine serum albumin (BSA) precipitation method in combination with solidphase extraction. An assay for phenolics in all fractions was carried out using the Folin−Ciocalteau (F−C) method. The average recovery of phenolics was 97.4%. Approximately 28% of total phenolics in MR and CS wines were BSA non-precipitable tannins (NP-T). It was also confirmed that approximately 50% of wine phenolics were composed of BSA-precipitable tannins (P-T) and NP-T. Wine made from MBA, the major cultivar for red wine in Japan, had a very low tannin content, and this may be a genetic characteristic of MBA. This is the first report that reveals the abundant existence of NP-T, and the whole aspect of tannins of red wines is shown with a unified quantification method.