Aqueous pigment extracts

There are commonly accepted experimental standards for the determination of conductivity and specific resistance in aqueous pigment extracts [18]. The electrical conductivity y is calculated from the electrical conductance its inverse is the specific resistance f=l/-y, derived from the electrical resistance. Additional experimental methods have been developed for the determination of soluble sulfates, chlorides, and nitrates [19]. 

The electrical conductivity (or resistivity) of an aqueous pigment extract is determined from the electrical conductance (or resistance). For standards, see Table 1 ( Resistivity ). Apparatus centrifuge with glass containers, resistance measurement bridge, electrolytic cell. 

The hot extraction method is a variation of this procedure. The aqueous pigment suspension, prepared as above, is refluxed for a certain time, usually 5 minutes, cooled rapidly, and filtered. A known amount of extract is then dried by evaporation and the weight of the residue determined, or the extracted pigment weighed and the dissolved portion determined by calculating the difference. 

In the authors experience, the pigments of a wide variety of plant materials have been stable in the aqueous acetone extract. However, problems have been encountered with pigment degradation for certain potato cultivars with high polyphenol oxidase activity. This problem can be circumvented by putting the aqueous acetone extract (uncapped) in a boiling water bath for 5 min. After heating, the volume of acetone lost by evaporation should be replenished. This enzyme inactivation step has been found unnecessary for most materials. 

It has been reported that protein-free, lipid-pigment extracts from chlorosomes can spontaneously reform chlorosome-like structures in an aqueous solution. ... 

Gas chromatographic analysis of tobacco alkaloids does not require derivation. The general procedures for GC analyses are as follows (1) use the smallest sample applicable for analysis (2) utilize preparations that clean up the sample without loss of alkaloids (3) pre-extract the sample prior to alkaloid extraction with hexane (removes pigments and lipids) (4) extract alkaloids from tobacco with an aqueous acid solution, filter, partition the aqueous acid extract with organic solvent (hexane, methylene chloride, chloroform, etc.) (5) increase pH of the aqueous extract to pH 10 (5N NaOH) and partition the basic solution with chloroform (6) dry the chloroform solution over Na2S04, and (7) concentrate the sample or analyze as is. 

Annato is a yellow oil or aqueous alkaline extract of fruit pulp of Raku or Orleans shrubs or brushwood Bixa orellana). The major pigments of annato are bixin (XVIII) and norbixin, both of which give dicarboxylic acids upon hydrolysis. Oleoresin from paprika is a red, oil extract containing about 50 different pigments. The aqueous extract of saffron (more accurately, from the pistils of the flower Crocus sativus) contains crocin (XVII) as its main constituent. It is used for coloring beverages and bakery products. 

The colorant is prepared by leaching the annatto seeds with an extractant prepared from one or more approved, food-grade materials taken from a hst that includes various solvents, edible vegetable oils and fats, and alkaline aqueous and alcohoHc solutions (46,47). Depending on the use intended, the alkaline extracts are often treated with food-grade acids to precipitate the annatto pigments, which ia turn may or may not be further purified by recrystallization from an approved solvent. Annatto extract is one of the oldest known dyes, used siace antiquity for the coloring of food, textiles, and cosmetics. It has been used ia the United States and Europe for over 100 years as a color additive for butter and cheese (48—50). 

The Betalaines. The main pigment in the concentrated colour beet red is betanin. This is classified as El62 by the EU. The pure pigment is obtained by aqueous extraction of the red table beet. Approximately 80% of the pigment present in beetroot is betanin. 

The acid or alkali number of a pigment is determined by titrating the aqueous extract of 100 g of pigment with a 0.1 N alkali (acid) solution [16]. 

DIN 53202 Bestimmung der Aciditatszahl oder Alkalitatszahl. ISO 787-4-1981 General methods of test for pigments and extenders, Part 4 Determination of acidity or alkalinity of the aqueous extract. 

DIN 53 208 Bestimmung der elektrischen Leitfahigkeit und des spezifischen Widerstandes von waBrigen Pigment-Extrakten. ISO 787-14-1985 General methods of test for pigments, Part 14 Determination of resistivity of aqueous extract. 

Another study employed an ODS column and different mobile phase composition for the measurement of carotenoids in orange juice. Citrus fruits were hand-squeezed and the juice was filtered. Aliquots of 5 ml of juice were extracted with ethyl acetate (3 X 50 ml) containing 0.004 per cent butyl hydroxytoluene (BHT). The organic phase was dried with 50 g of anhydrous sodium sulphate and the aqueous phase was mixed with 50 ml of mehanol and 100 ml of 1 M NaCl, extracted with 75 and 25 ml of ethyl acetate. The ethyl acetate fractions were combined, evaporated to dryness at 40°C and redissolved in the mobile phase. Extracts were analysed in an ODS column (250 X 4.6 mm i.d. particle size 5 jian). The mobile phase consisted of ACN-methanol-l,2-dichloroethane (60 35 5, v/v) containing 0.1 per cent BHT, 0.1 per cent triethylamine and 0.05 M of ammonium acetate. The column was not thermostated and the flow rate was 1 ml/min. Pigments were detected... 

TLC and HPLC have been applied for the separation of the flower pigments of some Delphinium species. Anthocyanins were extracted with 70 per cent aqueous ACN containing... 

A novel pigment has been isolated from the petals of Rosa hybrida with complex chromatographic techniques and the structure was elucidated with spectroscopic methods and high resolution fast-atom bombardement mass spectrometry, lH NMR, and FTIR. Anthocyanins were extracted from 7.9 kg of petals of Rosa hybrida cv. M me Violet with 80 per cent aqueous ACN containing 0.1 per cent TFA. The extract was purified in a Sephadex LH-20 column, and the fraction eluted with 80 per cent ACN was further fractionated in a HP-20 column using water, 15, 20 and 30 per cent ACN as mobile phases. The last fraction was lyophilized and separated by preparative RP-HPLC using an ODS column (50 X 5 cm i.d.). Solvents were 0.5 per cent aqueous TFA (A) and water-methanol... 

Normal-phase HPLC has also found application in the analysis of pigments in marine sediments and water-column particulate matter. Sediments were extracted twice with methanol and twice with dichloromethane. The combined extracts were washed with water, concentrated under vacuum and redissolved in acetone. Nomal-phase separation was performed with gradient elution solvents A and B being hexane-N,N-disopropylethylamine (99.5 0.5, v/v) and hexane-2-propanol (60 40, v/v), respectively. Gradient conditions were 100 per cent A, in 0 min 50 per cent A, in 10 min 0 per cent A in 15 min isocratic, 20 min. Preparative RP-HPLC was carried out in an ODS column (100 X 4.6 mm i.d. particle size 3 jum). Solvent A was methanol-aqueous 0.5 N ammonium acetate (75 25, v/v), solvent B methanol-acetone (20 80, v/v). The gradient was as follows 0 min, 60 per cent A 40 per cent A over 2 min 0 per cent A over 28 min isocratic, 30 min. The same column and mobile phase components were applied for the analytical separation of solutes. The chemical structure and retention time of the major pigments are compiled in Table 2.96. 

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