Anthocyanins concentration

Considerable studies have been done on the effects of the most important chemical and physical factors involved in the degradation of anthocyanins (temperature, light, pH, SO2, metal, sugar, and oxygen) in model systems and food extracts. In addition, anthocyanin concentrations, its chemical structures, and media compositions are fundamental factors influencing stability. 

Singha, S. et al., Anthocyanin distribution in delicious apples and the relationship between anthocyanin concentration and chromaticity values, J. Am. Soc. Hort. Sci., 116, 497, 1991. 

Uphoff, W., Identification of European orchids by determination of the anthocyanin concentration during development of the blossoms, Experientia, 38, 778, 1982. 

The influence of the stems, also studied in model solutions, is summarized in Table XIII (49). Stem extract and stems themselves are added to a solution of anthocyanins the anthocyanin concentration is the same in all cases. The stems decrease the anthocyanin levels and color intensity which is not observed with stem extract alone. These pieces exert their effects through absorption rather than through chemical reactions of one of their constituents. 

Table XVI shows two experiments which compared the same wine stored under different conditions (46). In both cases, the wine richer in anthocyanins is also that which is less colored. The mediation of tannins is not enough to explain the differences in color these can only be explained by a different structuring of the anthocyanin molecules. More specifically, the anthocyanin molecules will be reduced to colorless flavenes (14) during fermentation, which is a reductive process. The reoxidation occurs more rapidly in wooden casks which allow better oxygen penetration than metal storage tanks or large capacity casks. However, the flavenes themselves are relatively instable and can be irreversibly hydrolyzed into dihydrochalcones (16). This explains the lack of relationship between anthocyanin concentration and color, independent, of course, of the eventual appearance of free sulfur dioxide.

Ehlenfeldt, M.K. and Prior, R.L. Oxygen radical absorbance capacity (ORAC) and phenolic and anthocyanin concentrations in fruit and leaf tissues of highbush blueberry, J. Agric. Food Chem., 49, 2222-2227, 2001. 

Glycosyl-Glucose (G-G) analysis. The skin extracts and juices were assayed for total G-G (3 mL of skin extracts, and 10 mL of juices taken for analysis) and anthocyanin concentration (1 mL taken for analysis) using procedures set out in Hand Qtal (17),... 

Brettanomyces can endure SO2 treatment in barrels (45). The yeast survives treatment in areas of limited SO2 contact around bung holes, in the oak, and in the yeast sediment (lees). Work by Swaffield Scott (61) showed yeast and bacteria could penetrate the porous cellular structure of oak barrels and establish active permanent sub-surface mixed cultures even after cleaning. Variations in wine composition (pH, anthocyanin concentration, nutrient content, and temperature) can affect SO2 treatment in wine (60,62). 

Major limitations in many of the in vitro studies to date have been (1) the use of aglycones, when there is no evidence that the aglycone is absorbed and presented to the tissues, and (2) the use of concentrations well above those observed in plasma. Few studies to date have attempted to measure anthocyanin concentrations in different tissues. Research with anthocyanins has been slowed due to the lack of pure standard compounds, particularly of the anthocyanins and the availability of isoto-pically labeled anthocyanins, labeled so that the label is stable at different pH. Understanding any potential relationships to disease prevention has been limited because of the lack of availability of any database on the food content of anthocyanins. These data are being acquired in the U.S., allowing for estimation of daily intakes of anthocyanins from food intake data and for studying relationships to disease outcome in epidemiology studies. 

The increase in anthocyanins concentration results in an increase in absorbance at Xmax, greater than expected according to the Beer-Lambert law. It is probably connected with anthocyanins self-association. 

After a progressive decline in anthocyanin concentration, the presence of a broad unresolved peak is typically observed from aged wine when analyzed by reversed-phase HPLC (23) or gel permeation chromatography (7). Historically this hump was considered to be composed primarily of pigmented polymers, although until recently (16) evidence for this was based upon chromatographic evidence. 

Figure 1. Change in total anthocyanin concentration due to radiation dose and storage time. Bars represent the 95% confidence limit for each point which represent the mean of two wine sources and three repetitions.

The first step in this investigation was to isolate the pigment from strawberry juice by the method described by Sondheimer and Kertesz (11). This method involved the saturation of the juice with salt and extraction with 1-butanol, then concentration of the butanol extract under vacuum and in a nitrogen atmosphere. The anthocyanin concentrate was then taken up with hydrochloric acid in anhydrous methanol, precipitated with ether, dissolved in 0.01% hydrochloric acid, and saturated with picric acid. The anthocyanin picrate crystallized out of this solution upon storage at 0° C. as lustrous reddish bronze prisms which were further purified by recrystallization. 

The changes in anthocyanin concentration were followed by a modification of the method of Sondheimer and Kertesz (9)> which is based on the measurement of absorbance (optical density) at 500 mp of solutions of the anthocyanin at pH 3.4 and 2.0. The anthocyanin concentration is proportional to the absorbance difference. Figure 1 shows the spectra of solutions of anthocyanin pigment of the same concentration at different pH values. 

The effect of carbon dioxide on anthocyanins, and on some enzymes related to anthocyanin biosynthesis, was investigated in the arils of pomegranates stored under 10 or 20% CO2 for 6 weeks [161]. The total anthocyanin concentration of the arils increased during storage both in air and in air + 10% CO2. However, after 6 weeks, the anthocyanin concentration of pomegranates stored in air + 20% CO2 was lower than the initial concentration. Anthocyanin concentration was well correlated with the activity of phenylalanine ammonia lyase (PAL), but not with glucosyltransferase activity. 

It is possible to determine the free anthocyanin concentration (Al) after fractionation. The wine is adsorbed on a PVPP column, also known as Polyclar AT. After rinsing with water, elution with a dilute alcohol solution releases the free anthocyanins (Hrazdina, 1970), while the Ac and tannins remain adsorbed on the PVPP. After evaporation, the eluate is brought up to the initial volume and assayed using sulfur dioxide to obtain the Al concentration. 

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