Rudolf Galensa

Influence of postharvest processing and storage on the content of phenolic acids and flavonoids in foods

The review is based on the evaluation of electronically collated data published between 2002 to June 2006. It is based on 325 references dealing with the following subclasses of phenolic compounds: hydroxycinnamic and hydroxybenzoic acids, chalcones, flavanones, flavones, flavonols, monomeric flavanols and anthocyanins. Only publications dealing directly with the effects of storage and postharvest processing on the phenolic acid and flavonoid contents of foods were considered. The expectation that the structural diversity even within each subgroup, and the number of different procedures and of different parameters would make finding homogenous tendencies unlikely, has, in most instances, been confirmed. By adding a database Excel table combined with a focused and unified evaluation, specific additional information was rendered accessible and concise. It holds true for most of the subclasses in question that the effect of storage and food processing on the polyphenol content is negligible in comparison to the differences between different varieties of plants. Variety dependence must always be considered, for all classes of compounds.

(-)-Catechin in Cocoa and Chocolate: Occurence and Analysis of an Atypical Flavan-3-ol Enantiomer

Cocoa contains high levels of different flavonoids. In the present study, the enantioseparation of catechin and epicatechin in cocoa and cocoa products by chiral capillary electrophoresis (CCE) was performed. A baseline separation of the catechin and epicatechin enantiomers was achieved by using 0.1 mol x L(-1) borate buffer (pH 8.5) with 12 mmol x L(-1) (2-hydroxypropyl)-gamma-cyclodextrin as chiral selector, a fused-silica capillary with 50 cm effective length (75 microm I.D.), +18 kV applied voltage, a temperature of 20 degrees C and direct UV detection at 280 nm. To avoid comigration or coelution of other similar substances, the flavan-3-ols were isolated and purified using polyamide-solid-phase-extraction and LC-MS analysis. As expected, we found (-)-epicatechin and (+)-catechin in unfermented, dried, unroasted cocoa beans. In contrast, roasted cocoa beans and cocoa products additionally contained the atypical flavan-3-ol (-)-catechin. This is generally formed during the manufacturing process by an epimerization which converts (-)-epicatechin to its epimer (-)-catechin. High temperatures during the cocoa bean roasting process and particularly the alkalization of the cocoa powder are the main factors inducing the epimerization reaction. In addition to the analysis of cocoa and cocoa products, peak ratios were calculated for a better differentiation of the cocoa products.

Online coupling of pressurized liquid extraction, solid-phase extraction and high-performance liquid chromatography for automated analysis of proanthocyanidins in malt

A new instrumental setup for automated extraction of solid samples by online coupling of pressurized liquid extraction, automated SPE (solid-phase extraction) and HPLC is presented. From the extraction to the chromatogram no manual sample handling is required. The application to the determination of proanthocyanidins in malt reduces time and manual work to a minimum compared to former manual methods. Twenty samples can be processed within 24 h in respect to eight samples with the manual method. Using the features of the instrumental coupling, an optimized strategy for SPE of proanthocyanidins from natural samples was developed, requiring no evaporation step, using commercial cartridges and delivering concentrated eluates. The recovery of five main malt proanthocyanidins was 97%, with a reproducibility of 5%. This new instrumental coupling is thought to reduce time and costs along with improved results for a broad range of solid sample materials.

Temperature influences epimerization and composition of flavanol monomers, dimers and trimers during cocoa bean roasting.

Cocoa consumption is suggested to promote many health benefits, since cocoa is a rich source of flavanols; but amounts and profiles of flavanols depend strongly on the bean type, origin and manufacturing process. Roasting is known as a crucial step in technical treatment of cocoa, which leads to flavanol losses and modifications, especially the epimerization of (-)-epicatechin to (-)-catechin. This study monitors the influence of cocoa bean roasting on the composition of flavanol monomers to trimers, with special focus on epimerization, which was quantified for procyanidin dimers, and also observed for trimers for the first time. Five dimeric and two trimeric potential epimerization products were detected and the extent of epimerization during cocoa roasting was shown to be a function of temperature. The data also showed remarkable variations in the change of flavanol content. The quantified flavanols decreased about 50% in Java beans and increased about 30% in Ivory Coast beans, despite being roasted under equal conditions.

Chiral separation of six diastereomeric flavanone-7-O-glycosides by capillary electrophoresis and analysis of lemon juice.

The diastereomers of six major flavanone-7-O-glycosides (naringin, prunin, narirutin, hesperidin, neohesperidin and eriocitrin) were completely separated for the first time by chiral capillary electrophoresis (CE) employing various buffers and chiral selectors on the basis of the results achieved in 1998 in our research group by Mellenthin. The following chiral additives to the background electrolyte (BGE) were examined: native cyclodextrins (CDs; alpha-, beta- and gamma-CD), neutral cyclodextrin derivatives (dimethyl-beta-CD, hydroxypropyl-beta-CD, hydroxypropyl-gamma-CD) and charged cyclodextrin derivatives (carboxymethyl-beta-CD, carboxyethyl-beta-CD). The effect of CD type, CD concentration and pH value on chiral recognition will be discussed in the following article. In this work, lemon juice (Citrus limon L.) was also examined by chiral CE. Eriocitrin and hesperidin could be identified as characteristic flavanones and chiral separation of their diastereomers could be achieved according to the developed chiral method by capillary electrophoresis using a 0.2 M borate buffer at pH 10.0 and with 5 mM gamma-CD as chiral selector.

High-performance liquid chromatography of diastereomeric flavanone glycosides in Citrus on a β-cyclodextrin-bonded stationary phase (Cyclobond I)

Abstract The flavavone glycosides prunin, naringin, neohesperidin and narirutin were separated into their diastereomers by high-performance liquid chromatography elution in the reversed-phase mode on a β-cyclodextrin bonded stationary phase (Cyclobond I). Application to the analysis of Citrus extracts showed that immature grapefruit fruits contained almost entirely (2 S )-naringin and (2 S )-prunin, whereas in grapefruit juice both diastereomers of naringin and narirutin were present (about 60% S and 40% R isomers). In bitter-orange juice only (2 S )-neohesperidin was detected and sweet orange juice contained racemic narirutin. Benzoylated flavanone glycosides (naringin, prunin) were also separated on Cylcobond I in the normal-phase mode.

Analysis of flavonoids by high-performance liquid chromatography

Abstract Numerous acetates of flavonoids (flavones, flavonols and flavanone aglycones and glycosides) have been separated and determined on silica gel, using four different liquid systems (benzene-acetone; benzene-acetonitrile; benzene-ethanol; isooctane-ethanol-acetonitrile) at temperatures between 45° and 0°. This method has been applied to the determination of analytically pure substances and fruit and vegetable extracts.

Malonated flavonol glycosides and 3,5-dicaffeoylquinic acid from pears

Abstract 3- O -(6″- O -malonyl)-β-Glucosides of quercetin, kaempferol, isorhamnetin and 3,5-dicaffeoylquinic acid were isolated and identified from leaves of pears. The compounds are also present in the fruits.

The influence of postharvest processing and storage of foodstuffs on the bioavailability of flavonoids and phenolic acids

Postharvest processing and storage not only influence the content and composition of flavonoids and phenolic acids in foodstuffs, thereby altering the amount of potentially bioavailable bioactive compounds, but can also modify their chemical form. Moreover, due to the intensive metabolism during absorption, the metabolites circulating in blood differ from the parent compounds found in food. Thus, it is difficult to predict potential in vivo effects of phenolic compounds merely by their contents in foodstuffs. Their specific bioavailability needs to be determined. This review considers studies regarding the bioavailability of flavonoids and phenolic acids from foodstuffs that meet the following criteria: providing actual concentrations of flavonoids and phenolic acids in blood plasma, body tissues, or urine, comparing differently stored or processed foods (excluding studies that use supplements or pure substances), and considering the high interindividual variability by repeated measurements in the same individuals. Only a few studies meet all of these criteria. In conclusion, processing and storage of food can have either positive or negative effects on the bioavailability of flavonoids and phenolic acids because these treatments may not only change the content, but also the chemical form of these compounds.

Improved chiral stationary phase based on cellulose triacetate supported on non-macroporous silica gel diol for the high-performance liquid chromatographic separation of racemic flavanones and diastereomeric flavanone glycosides

Abstract Microcrystalline cellulose triacetate (MCCTA) and depolymerized MCCTA were dissolved and coated on non-macroporous silica gel diol. The chiral stationary phases obtained were found to be superior to a commercially available column based on cellulose triacetate for the enantiomeric separation of polyhydroxylated flavanones. Diastereomeric flavanone glycosides could also be resolved, together with the aglycones in a mixture. As an example of the analysis of a complex matrix, the separation of naringenin enantiomers in a tomato skin extract is presented.