Content and mean polymerization degree of procyanidins in extracts obtained from clear and cloudy apple juices

Bioanalytical characterization of apple juice from 88 grafted and nongrafted apple varieties grown in Upper Austria

The compositional characteristics of untreated pure juice prepared from 88 apple varieties grown in the region of Eferding/Upper Austria were determined. Many of the analyzed varieties are noncommercial, old varieties not present in the market. The aim of the study was to quantitate the mineral, phosphate, trace elements, and polyphenolic content in order to identify varieties that are of particular interest for a wider distribution. Great variations among the investigated varieties could be found. This holds especially true for the total polyphenolic content (TPC) ranging from 103.2 to 2,275.6 mg/L. A clear dependence of the antioxidant capacity on the TPC levels was detected. Bioinformatics was employed to find specific interrelationships, such as Mg²⁺/Mn²⁺ and PO₄³⁻/K⁺, between the analyzed bio- and phytochemical parameters. Furthermore, special attention was drawn on putative effects of grafting on the phytochemical composition of apple varieties. By grafting 27 different apple varieties on two trees grown close to each other, it could be shown that the apple fruits remain their characteristic phytochemical composition. Finally, apple juice prepared from selected varieties was further characterized by additional biochemical analysis including cytotoxicity, epidermal growth factor receptor (EGFR) inhibition, and α-amylase activity tests. Cytotoxicity and inhibition of EGFR activation were found to be dependent on the TPC, while α-amylase activity was reduced by the apple juices independent of the presence of polyphenolic substances. Taken together selected apple varieties investigated within this study might serve as preferable sources for the development of apple-based food with a strong focus on health beneficial effects.

Profiling of phenolic compounds from different apple varieties using comprehensive two-dimensional liquid chromatography

An innovative analytical approach based on the use of comprehensive two-dimensional liquid chromatography (LC×LC) is applied to obtain the profiling of phenolic compounds in different apple varieties. The method combines the use of hydrophilic interaction liquid chromatography in the first dimension and a reversed phase separation in the second dimension, as well as the use of diode array and mass spectrometry detection. Using this methodology is possible to obtain in less than 50 min the complete profiling of phenolic compounds in a complex food matrix such as apple. In fact, different flavan-3-ols including procyanidin oligomers with degree of polymerization up to 8, as well as several dihydrochalcones, flavonols and a phenolic acid are separated and tentatively identified in these samples in a single run. Besides, the total phenols and total procyanidins amounts were determined using two in vitro assays. Reinette apples presented the highest content on total phenols (6.46 mg galic acid equiv./g dry matter) whereas Granny Smith apples were the richest on total procyanidins (0.73 mg epicatechin equiv./g dry matter). This work shows the great potential of LC×LC for phenolic compounds profiling in complex food samples.

Characterization and quantitation of low and high molecular weight phenolic compounds in apple seeds

The phenolic constituents of seeds of 12 different apple cultivars were fractionated by sequential extraction with aqueous acetone (30:70, v/v) and ethyl acetate after hexane extraction of the lipids. Low molecular weight phenolic compounds were individually quantitated by RP-HPLC-DAD. The contents of extractable and nonextractable procyanidins were determined by applying RP-HPLC following thiolysis and n-butanol/HCl hydrolysis, respectively. As expected, the results revealed marked differences of the ethyl acetate extracts, aqueous acetone extracts, and insoluble residues with regard to contents and mean degrees of polymerization of procyanidins. Total phenolic contents in the defatted apple seed residues ranged between 18.4 and 99.8 mg/g. Phloridzin was the most abundant phenolic compound, representing 79-92% of monomeric polyphenols. Yields of phenolic compounds significantly differed among the cultivars under study, with seeds of cider apples generally being richer in phloridzin and catechins than seeds of dessert apple cultivars. This is the first study presenting comprehensive data on the contents of phenolic compounds in apple seeds comprising extractable and nonextractable procyanidins. Furthermore, the present work points out a strategy for the sustainable and complete exploitation of apple seeds as valuable agro-industrial byproducts, in particular as a rich source of phloridzin and antioxidant flavanols.

Phenolics and antioxidant properties of fruit pulp and cell wall fractions of postharvest banana (Musa acuminata Juss.) cultivars

Banana fruits are important foods, but there have been very few studies evaluating the phenolics associated with their cell walls. In the present study, (+) catechin, gallocatechin, and (-) epicatechin, as well as condensed tannins, were detected in the soluble extract of the fruit pulp; neither soluble anthocyanidins nor anthocyanins were present. In the soluble cell wall fraction, two hydroxycinnamic acid derivatives were predominant, whereas in the insoluble cell wall fraction, the anthocyanidin delphinidin, which is reported in banana cell walls for the first time, was predominant. Cell wall fractions showed remarkable antioxidant capacity, especially after acid and enzymatic hydrolysis, which was correlated with the total phenolic content released after the hydrolysis of the water-insoluble polymer, but not for the posthydrolysis water-soluble polymer. The acid hydrolysis released various monosaccharides, whereas enzymatic hydrolysis released one peak of oligosaccharides. These results indicate that banana cell walls could be a suitable source of natural antioxidants and that they could be bioaccessible in the human gut.

Influence of apple polyphenols on inflammatory gene expression

Apples (Malus spp., Rosaceae) and products thereof contain high amounts of polyphenols which show diverse biological activities and may contribute to beneficial health effects, like protecting the intestine against inflammation initiated by chronic inflammatory bowel diseases (IBD). IBD are characterized by an excessive release of several proinflammatory cytokines and chemokines by different cell types which results consequently in an increased inflammatory response. In the present study we investigated the preventive effectiveness of polyphenolic juice extracts and single major constituents on inflammatory gene expression in immunorelevant human cell lines (DLD-1, T84, MonoMac6, Jurkat) induced with specific stimuli. Besides the influence on proinflammatory gene expression, the effect on NF-kappaB-, IP-10-, IL-8-promoter-, STAT1-dependent signal transduction, and the relative protein levels of multiple released cytokines and chemokines were studied. DNA microarray analysis of several genes known to be strongly regulated during gastrointestinal inflammation, combined with quantitative real-time PCR (qRT-PCR) revealed that the apple juice extract AE04 (100-200 microg/mL) significantly inhibited the expression of NF-kappaB regulated proinflammatory genes (TNF-alpha, IL-1beta, CXCL9, CXCL10), inflammatory relevant enzymes (COX-2, CYP3A4), and transcription factors (STAT1, IRF1) in LPS/IFN-gamma stimulated MonoMac6 cells without significant effects on the expression of house-keeping genes. A screening of some major compounds of AE04 revealed that the flavan-3-ol dimer procyanidin B(2 )is mainly responsible for the anti-inflammatory activity of AE04. Furthermore, the dihydrochalcone aglycone phloretin and the dimeric flavan-3-ol procyanidin B(1 )significantly inhibited proinflammatory gene expression and repressed NF-kappaB-, IP-10-, IL-8-promoter-, and STAT1-dependent signal transduction in a dose-dependent manner. The influence on proinflammatory gene expression by the applied polyphenols thereby strongly correlated with the increased protein levels investigated by human cytokine array studies. In summary, we evaluated selected compounds responsible for the anti-inflammatory activity of AE04. In particular, procyanidin B(1), procyanidin B(2), and phloretin revealed anti-inflammatory activities in vitro and therefore may serve as transcription-based inhibitors of proinflammatory gene expression.

Impact of apple polyphenols on GSTT2 gene expression, subsequent protection of DNA and modulation of proliferation using LT97 human colon adenoma cells

Apple extract (AE) enhances expression of glutathione S-transferases (e.g., GSTT2) in human colon cells (LT97). Therefore, aim of the present study was to identify functional consequences of GSTT2 induction by AE and to determine the relation of AE effects to isolated compounds. Polyphenol composition of AE was analyzed. LT97 cells were treated with AE or synthetic polyphenol mixture (SPM) under conditions that induced GSTT2, and challenged with GSTT2-2 substrate cumene hydroperoxide (CumOOH) to determine DNA damage using comet assay. Modulation of GSTT2 expression (real-time PCR) was reassessed, and the influence on cell proliferation and pro-oxidative potential of AE and SPM were assessed to understand additional mechanisms. Induction of GSTT2 by AE was accompanied by protection of LT97 cells from CumOOH-induced genotoxicity. Although SPM was unable to reflect AE-specific bioactivity related to GSTT2 modulation and anti-genotoxicity, inhibition of LT97 cell proliferation by SPM was comparable. Storage of AE caused changes in phenolic composition along with loss of activity regarding GSTT2 induction and amplified growth inhibition. At the applied concentrations, no H(2)O(2) formation was detectable with any of the substances. AE can protect against oxidatively induced DNA damage. Nevertheless, chemopreventive effects of AE strongly depend on the specific composition, which is modified by storage.

Prevention of colon carcinogenesis by apple juice in vivo: impact of juice constituents and obesity

It is estimated that 75-85% of all chronic diseases are linked to lifestyle-related and environmental factors. The development of colon cancer is positively associated with obesity and inversely associated with the intake of dietary fibre, fruit and vegetable. Apple juice is the most widely consumed fruit beverage in Germany. It contains a specific spectrum of polyphenols and other components that may reduce the risk of colon cancer. Epidemiologic studies suggest an inverse correlation between apple consumption and colon cancer risk, although the mechanisms for these observations are not clear. The present review summarizes the preventive potential of apple juices and different apple constituents on biomarkers related to colon carcinogenesis with special focus on the in vivo evidence and the cancer promoting condition of obesity. However, under the cancer promoting condition of obesity, apple juice did not show cancer-preventive bioactivity. In our experiments a cancer-preventive bioactivity of apple juice is lacking in rats under the cancer-promoting condition of obesity. To further investigate, whether this lack of efficacy observed in obese rats might be representative for obese individuals human intervention studies on high risk groups such as obese or diabetic individuals are of interest and will be conducted.

Tannins: current knowledge of food sources, intake, bioavailability and biological effects

Tannins are a unique group of phenolic metabolites with molecular weights between 500 and 30 000 Da, which are widely distributed in almost all plant foods and beverages. Proanthocyanidins and hydrolysable tannins are the two major groups of these bioactive compounds, but complex tannins containing structural elements of both groups and specific tannins in marine brown algae have also been described. Most literature data on food tannins refer only to oligomeric compounds that are extracted with aqueous-organic solvents, but a significant number of non-extractable tannins are usually not mentioned in the literature. The biological effects of tannins usually depend on their grade of polymerisation and solubility. Highly polymerised tannins exhibit low bioaccessibility in the small intestine and low fermentability by colonic microflora. This review summarises a new approach to analysis of extractable and non-extractable tannins, major food sources, and effects of storage and processing on tannin content and bioavailability. Biological properties such as antioxidant, antimicrobial and antiviral effects are also described. In addition, the role of tannins in diabetes mellitus has been discussed.

High contents of nonextractable polyphenols in fruits suggest that polyphenol contents of plant foods have been underestimated

The content of polyphenols in fruits reported in the literature normally refers to extractable polyphenols (EPP) analyzed in aqueous-organic extracts. However, significant amounts of bioactive compounds that are usually not considered in nutritional studies remain in the residue from extraction as nonextractable polyphenols (NEPP). The main objective of this work was to analyze both EPP and NEPP (hydrolyzable polyphenols and proanthocyanidins). EPP were analyzed in methanol/acetone/water extracts, and NEPP were determined in acidic hydrolysates of extraction residue from apple, peach, and nectarine using HPLC-MS and spectrophotometry. Results showed that the NEPP content (112-126 mg/100 g of fresh fruit) was higher than the EPP content (18.8-28 mg/100 g of fresh fruit). Further analyses of NEPP in other fruits and plant foods consumed in diets are needed to compile a complete database of use for nutritional and biological studies.

Developmental, genetic and environmental factors affect the expression of flavonoid genes, enzymes and metabolites in strawberry fruits

The influence of internal (genetic and developmental) and external (environmental) factors on levels of flavonoid gene transcripts, enzyme activity and metabolites was studied in fruit of six cultivated strawberry (Fragaria x ananassa Duch.) genotypes grown at two Italian locations. Gene expression and enzyme activity showed development- and genotype-associated patterns, revealing gene coordination. Analysis clarified the regulation mechanism of the hydroxylation status of the B-ring of the major flavonoid pools and pointed out examples of genotype-specific post-transcriptional regulation mechanisms and key steps of pathway regulation in strawberry fruits. Metabolite profiles were strongly affected by development and genotype. Flavan-3-ols, their proanthocyanidin (PA) derivatives and anthocyanins were the most abundant metabolites. Flavonol levels and PA-associated traits (epicatechin/catechin ratio and mean degree of polymerization) showed significant environmental effects. Multivariate and correlation analyses determined the relationships among genes, enzymes and metabolites. The combined molecular and biochemical information elucidated more in depth the role of genetic and environmental factors on flavonoid metabolism during strawberry fruit development, highlighting the major impact of developmental processes, and revealing genotype-dependent differences and environmental effects on PA-related traits.