Anthocyanins acid hydrolysis

Just as with anthocyanin analysis, the advent of HPLC/mass spectrometer coupling made it possible to avoid acid hydrolysis for flavonoid identification. Maata... 

Either Basic Protocol 1 or the Alternate Protocol should first be conducted in analyzing an unknown sample. Because of its ease and simplicity, sample preparation of anthocyanins and their HPLC separation on silica Cl8 columns (see Basic Protocol 1) is usually the preferred choice, unless the presence of acylated anthocyanins is anticipated, in which case the protocol described for acylated anthocyanins is used (see Alternate Protocol). If the anthocyanin profile is inconsistent with previously published chromatograms, or if there are extraneous unidentified peaks, then simplification is recommended (see Basic Protocol 3). Acid hydrolysis will simplify the chroma-... 

Figure FI. 3.4 shows HPLC chromatograms for anthocyanidins generated from acid hydrolysis of concord grape and strawberry juices. Extraneous peaks may be present because of incomplete hydrolysis, and degradation and polymerization of the labile aglycons even more of a problem. For acylated anthocyanins, higher yields of anthocyanidins will be achieved if the sample is first saponified (see Basic Protocol 3) and then subjected to acid hydrolysis (see Basic Protocol 2).

The colors of the anthocyanins at acid pH values correspond to those of the oxonium salts. In slightly alkaline solutions (pH 8 to 10), highly colored ionized anhydro bases are formed. At pH 12, these hydrolyze rapidly to fully ionized chalcones (Figure 6-27). Leuco bases are the reduced form of the anthocyanins. They are usually without much color but are widely distributed in fruits and vegetables. Under the influence of oxygen and acid hydrolysis, they may develop the characteristic color of the car-... 

Acid hydrolysis compounds 105 Aminoacetophenone in wines 149 Anthocyanin derivatives 200 Anthocyanidins 164 Aroma compounds in grape 97,103,107... 

Hydrolysis of anthocyanins to yield anthocyanidins might be another important step during analysis. Hydrolysis is either accomplished by acidic hydrolysis of crude or purified extracts or by one-step extraction/hydrolysis protocols. 

The main problem of submission of anthocyanins to UVA IS spectroscopy is the diversity of possible structures with different absorption properties and the lack of reliable calibration procedures. Hydrolysis of anthocyanins to anthocyanidins prior to measurement reduces possible UVA IS absorption variations in both, X max and e, to few well described structures. Yet another advantage of hydrolysis is that most anthocyanidins but only few anthocyanins are commercially available as reference standards for method calibration. The main disadvantages of acidic hydrolysis are that, oligomeric proanthocyanidins present in the sample are also hydrolyzed to anthocyanidins yielding possibly over-estimation of the original monomeric anthocyanin content. 

Flavonoids are the major water-soluble pigments in plants and are contained within the cell sap of plant tissues. The term flavonoids is derived from flavus (yellow) and refers to a diverse group of water-soluble pigments. Of all the flavonoids, the anthocyanins have the greatest importance from the standpoint of practical TLC. The anthocyanins are responsible for the variety of colors associated with autumnal (fall) foliage and with the variety of colors (mainly reds, scarlet, blues) associated with flowers and fruits. The anthocyanins yield anthocy-anids and various sugars upon acid hydrolysis. During the TLC of anthocyanins, it is the anthocyanids that are detected. 

Anditti and Dunn (1969), and Harbome (1984). Following acid hydrolysis, the anthocyanins yield anthocyanidins and sugar residues. Detailed descriptions of anthocyanidins are presented in Anditti and Dunn (1969) and in Harborne (1984). 

The first step in anthocyanin characterization is the identification of the anthocyani-din moiety (aglycon) and the sugar(s). This can be accomplished by acid hydrolysis... 

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