This collaborative study was conducted to determine the total monomeric anthocyanin concentration by the pH differential method, which is a rapid and simple spectrophotometric method based on the anthocyanin structural transformation that occurs with a change in pH (colored at pH 1.0 and colorless at pH 4.5). Eleven collaborators representing commercial laboratories, academic institutions, and government laboratories participated. Seven Youden pair materials representing fruit juices, beverages, natural colorants, and wines were tested. The repeatability relative standard deviation (RSDr) varied from 1.06 to 4.16%. The reproducibility relative standard deviation (RSDR) ranged from 2.69 to 10.12%. The HorRat values were ≤1.33 for all materials. The Study Director recommends that the method be adopted Official First Action.

No abstract

Frozen blueberries (Vaccinium corymbosum L.) were processed into juice and concentrate, and the changes in anthocyanin pigments and polyphenolics (cinnamates, procyanidins, flavonol glycosides) were monitored. While juice yield was 83%, only 32% of the anthocyanins were recovered in single-strength juice. Flavonol, procyanidin and chlorogenic acid recoveries in juice were 35%, 43%, and 53%, respectively. The proportion of polyphenolics remaining in the press-cake residue ranged from 1% (chlorogenic acid) to 18% (anthocyanins). Pronounced losses of anthocyanins and polyphenolics during milling and depectinization are believed to be due to native polyphenol oxidase. Losses during concentration ranged from 1.5% (anthocyanins) to 20% (procyanidins). Striking changes occurred in the anthocyanin profile with malvidin glycosides being most stable and delphinidin glycosides the least.

Frozen blueberries (Vaccinium corymbosum L. cv. Rubel) were pilot-plant-processed into juice and concentrate: 2 treatments (heat and SO 2 ) and a control. Pressed juice yield ranged from 74 to 83% (w/w), but only 13 to 23% of the anthocyanins and 36 to 39% of the polyphenolics were recovered in the pasteurized juice. A substantial amount of anthocyanins and polyphenolics (> 42% and > 15%, respectively of the starting material) were present in the presscakes. Measurements of total and individual flavonoids showed a great loss after the initial processing steps (thawing, crushing, and depectinization). Overall anthocyanin levels were higher in treated samples after each processing step, but polyphenolic levels remained similar to those in the control.

The polyphenolics of raisins were extracted, separated by HPLC, and characterized by their UV-vis spectra, and their concentrations measured. Color measurements and browning indices were also determined. Samples (n = 20) included sun-dried, dipped, and golden raisins. Comparisons were also made with fresh and frozen Thompson Seedless grapes. Golden raisins (which are treated with SO(2)) had the highest amount of hydroxycinnamic acids and the highest lightness values. In comparison with fresh grapes, percent losses of the two major hydroxycinnamics (caftaric and coutaric acids) in sun-dried, dipped, and golden raisins were on the order of 90%. Flavonols were not influenced by processing as much as hydroxycinnamics, while procyanidins and flavan-3-ols were completely degraded in all raisin samples. Formation of hydroxymethylfurfural and loss of amino acids in sun-dried and dipped raisins are ascribed to Maillard browning reactions.