Polyphenol and glycoalkaloid contents in potato cultivars grown in Luxembourg

Comparative metabolite and genome analysis of tuber-bearing potato species

The cultivated potato Solanum tuberosum is unrivalled among crop plants for its wild relatives, which potentially represent an important source of genetic diversity to improve the nutritional value of potato varieties and understand metabolism regulation. The main aim of this research was to profile human health-related metabolites in a number of clones from 13 Solanum species. Results from HPLC-DAD and LC-ESI-MS analyses highlighted a high interspecific variability in the level of metabolites analysed. Ascorbic acid was confirmed to be the most abundant antioxidant in potato and chlorogenic acid the primary polyphenol. Generally, metabolite-based hierarchical clustering (HCL) and correlation networks did not group clones of identical species in the same cluster. This might be due to various factors, including the outcrossing nature of potato species, gene expression level and metabolic profiling techniques. Access to the genome sequence of S. tuberosum and S. commersonii allowed comparison of the genes involved in ascorbic acid, aromatic amino acid, phenylpropanoid and glycoalkaloid biosynthesis and helped interpret their respective pathways.

Chlorogenic acid, anthocyanin and flavan-3-ol biosynthesis in flesh and skin of Andean potato tubers (Solanum tuberosum subsp. andigena)

Natural variation of Andean potato was used to study the biosynthesis of phenolic compounds. Levels of phenolic compounds and corresponding structural gene transcripts were examined in flesh and skin of tubers. Phenolic acids, mainly chlorogenic acid (CGA), represent the major compounds, followed by anthocyanins and flavan-3-ols. High-anthocyanin varieties have high levels of CGA. Both metabolite and transcript levels were higher in skin than in flesh and showed a good correspondence. Two hydroxycinnamoyl-CoA transferases (HCT/HQT) have been involved in CGA production, of which HCT reflects CGA levels. Catechin was found in pigmented tissues whereas epicatechin was restricted to tuber skin. Transcripts of leucoanthocyanidin reductase (LCR), which generates catechin, could not be detected. Anthocyanidin reductase (ANR) transcripts, the enzyme responsible for epicatechin production, showed similar levels among samples. These data suggest that the biosynthesis of flavan-3-ols in potato tuber would require ANR but not LCR and that an epimerization process is involved.

Health-beneficial properties of potato and compounds of interest

Potatoes have shown promising health-promoting properties in human cell culture, experimental animal and human clinical studies, including antioxidant, hypocholesterolemic, anti-inflammatory, antiobesity, anticancer and antidiabetic effects. Compounds present such as phenolics, fiber, starch and proteins as well as compounds considered antinutritional such as glycoalkaloids, lectins and proteinase inhibitors are believed to contribute to the health benefits of potatoes. However, epidemiological studies exploring the role of potatoes in human health have been inconclusive. Some studies support a protective effect of potato consumption in weight management and diabetes, while other studies demonstrate no effect and a few suggest a negative effect. As there are many biological activities attributed to the compounds present in potato, some of which could be beneficial or detrimental depending on specific circumstances, a long-term study investigating the association between potato consumption and diabetes, obesity, cardiovascular disease and cancer while controlling for fat intake is needed. © 2016 Society of Chemical Industry.

A review of Occurrence of Glycoalkaloids in Potato and potato products

There has been increasing consumption of potato products such as French fries and crisps in most countries as a result of lifestyle change in both developed and developing countries. Due to their generally pleasurable taste and texture, they are appreciated by a high number of consumers across the world, with the younger members of the population mostly those in the urban areas having a higher preference. The hard economic situations have also driven many people to their consumption as they are affordable. Moreover, these products are convenient for the younger generation who do not prepare their own food. However, there have been food safety concerns that have been linked in the past to glycoalkaloids in the raw potatoes that are used for processing. Potatoes are known to accumulate glycoalkaloids (GAs) during growth and postharvest storage. Some potato varieties have been shown to have high glycoalkaloids. These toxicants have been found to bioaccumulate in the body especially if daily consumption of foods containing the glycoalkaloids are consumed. Glycoalkaloids lead to intestinal discomfort, vomiting, fever, diarrhea and neurological problems and can lead to human or animal deaths in cases of acute toxicity. Transportation, handling, poor storage and exposure to sunlight during marketing of potatoes exposes consumers to potential risk of glycoalkaloids due to injury and greening which lead to increased levels of glycoalkaloids. Glycoalkaloids are quite stable and therefore, freeze-drying, boiling, dehydration or microwaving have got limited effect and thus persist through the processing conditions into the final products with the levels being proportional to the concentrations in the raw materials used. This current review focuses on the occurrence of glycoalkakloids in potato and potato products that are commonly consumed.

Bioactivity of Polyphenols: Preventive and Adjuvant Strategies toward Reducing Inflammatory Bowel Diseases-Promises, Perspectives, and Pitfalls

Inflammatory bowel diseases (IBDs) are characterized by autoimmune and inflammation-related complications of the large intestine (ulcerative colitis) and additional parts of the digestive tract (Crohn's disease). Complications include pain, diarrhoea, chronic inflammation, and cancer. IBD prevalence has increased during the past decades, especially in Westernized countries, being as high as 1%. As prognosis is poor and medication often ineffective or causing side effects, additional preventive/adjuvant strategies are sought. A possible approach is via diets rich in protective constituents. Polyphenols, the most abundant phytochemicals, have been associated with anti-inflammatory, antioxidant, immunomodulatory, and apoptotic properties. Locally reducing oxidative stress, they can further act on cellular targets, altering gene expression related to inflammation, including NF-κB, Nrf-2, Jak/STAT, and MAPKs, suppressing downstream cytokine formation (e.g., IL-8, IL-1β, and TNF-α), and boosting the bodies' own antioxidant status (HO-1, SOD, and GPx). Moreover, they may promote, as prebiotics, healthy microbiota (e.g., Bifidobacteria, Akkermansia), short-chain fatty acid formation, and reduced gut permeability/improved tight junction stability. However, potential adverse effects such as acting as prooxidants, or perturbations of efflux transporters and phase I/II metabolizing enzymes, with increased uptake of undesired xenobiotics, should also be considered. In this review, we summarize current knowledge around preventive and arbitrary actions of polyphenols targeting IBD.

Phenolic Compounds in the Potato and Its Byproducts: An Overview

The potato (Solanum tuberosum L.) is a tuber that is largely used for food and is a source of different bioactive compounds such as starch, dietary fiber, amino acids, minerals, vitamins, and phenolic compounds. Phenolic compounds are synthetized by the potato plant as a protection response from bacteria, fungi, viruses, and insects. Several works showed that these potato compounds exhibited health-promoting effects in humans. However, the use of the potato in the food industry submits this vegetable to different processes that can alter the phenolic content. Moreover, many of these compounds with high bioactivity are located in the potato's skin, and so are eliminated as waste. In this review the most recent articles dealing with phenolic compounds in the potato and potato byproducts, along with the effects of harvesting, post-harvest, and technological processes, have been reviewed. Briefly, the phenolic composition, main extraction, and determination methods have been described. In addition, the "alternative" food uses and healthy properties of potato phenolic compounds have been addressed.

Levels of potential bioactive compounds including carotenoids, vitamin C and phenolic compounds, and expression of their cognate biosynthetic genes vary significantly in different varieties of potato (Solanum tuberosum L.) grown under uniform cultural conditions

BACKGROUND

In addition to their high carbohydrate content, potatoes are also an important dietary source of vitamin C and bioactive secondary metabolites, including phenolic compounds and carotenoids, which have been suggested to play a role in human health. The expression of genes encoding key enzymes involved in the synthesis of these compounds was assessed by reverse transcription-quantitative polymerase chain reaction and compared to the accumulation of the corresponding product in seven potato varieties showing contrasting levels of metabolite accumulation.

RESULTS

Strong positive correlations were found between phenolic content in the flesh of tubers and transcript levels of phenylalanine ammonia lyase (PAL) and chalcone synthase (CHS) genes. The expression of PAL and CHS was also related to that of AN1, a transcription factor involved in the synthesis of anthocyanins, suggesting that these genes are regulated in a coordinated manner. No clear relationship was found between transcript levels of phytoene synthase (PSY) or L-galactono-1,4-lactone dehydrogenase (GLDH) genes and total carotenoid or vitamin C accumulation, respectively.

CONCLUSION

Data indicate that levels of total phenolic and flavonoid compounds in potato are controlled primarily by PAL and CHS gene expression. Transcript levels of PSY and GLDH did not control accumulation of carotenoids or vitamin C.

Dependence among total polyphenols content, total antioxidant capacity and heavy metals content in potatoes

Polyphenols belong to the most significant compounds with antioxidant effects in potatoes. Their content depends on several factors. The most important factor is the variety of potatoes and the conditions of their growing such as temperature, rainfall, altitude, agronomic and chemical characteristics of the soil. We have compared two potato cultivars in the study which have been grown in the Slovak localities Dolné Obdokovce and Vrbová nad Váhom (cv. Agria) and Nitra, Radošina and Vrbová nad Váhom (cv. Impala). In lyophilized samples of potatoes total polyphenols content in ethanolic extracts using Folin-Ciocalteu agens and in methanolic extracts total antioxidant capacity using DPPH were spectrophotometrically determined. The average total polyphenols content in the potato variety Impala was 604.26 ±120.70 mg.kg-1 dry matter (DM) and 529.37 ±59.35 mg.kg-1 DM in the variety Agria. The average value of total antioxidant capacity, expressed in % inhibition, was 8.44 ±1.68% in the potato variety Impala and 8.09 ±1.14% in Agria. The results obtained were evaluated by One-way analysis of variance ANOVA (LSD-test), using Statistical Analysis Software Statgraphics. Mutual correlations among the total polyphenols content, total antioxidant capacity and heavy metals concent (Pb, Ni, Cd - determined using atomic absorption spectrometry (AAS) method: Cd, Pb: GF-AAS and Ni F-AAS) were evaluated using the correlation and regression analysis (Microsoft Excel). Statistically significant interdependence (p <0.05) was only confirmed between the Cd content and total antioxidant capacity in both cultivars, or between the Ni content and total antioxidant capacity in the variety Impala.

Carotenoid and polyphenol bioaccessibility and cellular uptake from plum and cabbage varieties

Plum and cabbage are rich in carotenoids and polyphenols. However, their bioactivity depends on their release and intestinal uptake. Four varieties of Brassicaceae (Duchy, Scots Kale, Kale, Kalorama) and Prunus (Cherry Plum, Plum 620, Ersinger, Italian Plum) were studied; bioaccessibility following in vitro digestion, cellular uptake (Caco-2 vs. co-culture cell model: Caco-2:HT-29-MTX (90:10%) and colonic fermentation were determined for carotenoids/polyphenols; the influence of certain kitchen preparations was likewise studied. Carotenoids were non-significantly influenced by the latter, while for polyphenols, boiling and steaming significantly reduced total phenolics (p<0.05). Carotenoid bioaccessibility did not differ significantly between Prunus vs. Brassicaceae varieties, but xanthophyll was higher than carotene bioaccessibility (p<0.01). Polyphenol bioaccessibility was low (<10%), possibly compromised by the cream containing test meal. Total carotenoid cellular uptake varied between varieties (0.3-4.1%), being higher for carotenes (4.1%) than for xanthophylls (1.6%, p<0.01), and were higher for the co-culture cell model compared to Caco-2 cells (p<0.01). Total carotenoid recovery in the colonic fraction varied from 4% to 25%. Lower bioaccessibility of carotenes thus appeared to be somewhat counterbalanced by higher cellular uptake. The potential positive role of the mucus layer for cellular uptake and the fate of the colonic digesta deserve further attention in the future.

In Vitro Bioaccessibility and Bioavailability of Iron from Potatoes with Varying Vitamin C, Carotenoid, and Phenolic Concentrations

The bioaccessibility and bioavailability of iron from 12 Andean potato clones were estimated using an in vitro gastrointestinal digestion procedure and the Caco-2 cell line as a model of human intestine, with ferritin formation as a marker of iron absorption. We first showed that 63.7% (for the genotype CIP_311422.016) to 79.0% (for the genotype CIP_311575.003) of the iron is released from the potato tuber matrix during in vitro gastrointestinal digestion and is therefore available at the intestinal level. On average, 32 and 24.5% of the hydrophilic bioactive components, vitamin C and chlorogenic acid, respectively, were also bioaccessible from boiled tubers. Intestinal absorption of intrinsic iron from potato tubers could not be detected using our in vitro Caco-2 cell model. When an extrinsic source of iron (20 μM FeCl3 and 1 mM ascorbic acid) was added to the digestion mixture, iron absorption varied from 1.8 to 8% for the genotypes CIP_311422.016 and CIP_311624.021, respectively, as compared to the reference control. Principal component analysis revealed negative relationships between bioavailable iron values and phenolic concentrations, whereas vitamin C concentrations were positively associated with the ferritin values. Further controlled intervention trials would be needed to conclusively assess the bioavailability of intrinsic iron from potato tubers.

Optimisation and validation of ultra-high performance liquid chromatographic-tandem mass spectrometry method for qualitative and quantitative analysis of potato steroidal alkaloids

An ultra-high performance liquid chromatographic-tandem mass spectrometry (UHPLC-MS/MS) method for quantification of potato steroidal alkaloids, namely α-solanine, α-chaconine, solanidine and demissidine was developed and validated. Three different column chemistries, i.e. ethylene bridged hybrid (BEH) C18, hydrophilic lipophilic interaction and amide columns, were assessed. The BEH C18 column showed best separation and sensitivity for the alkaloids. Validation data (inter-day and intra-day combined) for accuracy and recovery ranged from 94.3 to 107.7% and 97.0 to 103.5%, respectively. The accuracy data were within the acceptable range of 15% as outlined in the United States Food and Drug Administration (USFDA) guidelines. The recovery data were consistent and reproducible with a coefficient of variation (CV) ranging from 6.2 to 9.7%. In addition, precision of the method also met the criteria of the USFDA with CV values lower than 15% even at lower limit of quantification (LLOQ), while the permissible variation is considered acceptable below 20%. The limit of detection and LLOQ of the four alkaloids were in the range of 0.001-0.004μg/mL whereas the linearities of the standard curves were between 0.980 and 0.995.

Chlorogenic Acid Biosynthesis Appears Linked with Suberin Production in Potato Tuber (Solanum tuberosum)

Potato (Solanum tuberosum L.) is a good source of dietary antioxidants. Chlorogenic acid (CGA) and caffeic acid (CA) are the most abundant phenolic acid antioxidants in potato and are formed by the phenylpropanoid pathway. A number of CGA biosynthetic routes that involve hydroxycinnamoyl-CoA quinate hydroxycinnamoyl transferase (HQT) and/or hydroxycinnamoyl-CoA shikimate/quinate hydroxycinnamoyl transferase (HCT) have been proposed, but little is known about their path in potato. CA production requires a caffeoyl shikimate esterase (CSE), and CA serves as a substrate of lignin precursor ferulic acid via the action of caffeic/5-hydroxyferulic acid O-methyltransferase (COMT I). CGA is precursor of caffeoyl-CoA and, via caffeoyl-CoA O-methyltransferase (CCoAOMT), of feruloyl-CoA. Feruloyl-CoA is required for lignin and suberin biosynthesis, crucial for tuber development. Here, metabolite and transcript levels of the mentioned and related enzymes, such as cinnamate 4-hydroxylase (C4H), were determined in the flesh and skin of fresh and stored tubers. Metabolite and transcript levels were higher in skin than in flesh, irrespective of storage. CGA and CA production appear to occur via p-coumaroyl-CoA, using HQT and CSE, respectively. HCT is likely involved in CGA remobilization toward suberin. The strong correlation between CGA and CA, the correspondence with C4H, HQT, CCoAOMT2, and CSE, and the negative correlation of HCT and COMT I in potato tubers suggest a major flux toward suberin.

Recovery of steroidal alkaloids from potato peels using pressurized liquid extraction

A higher yield of glycoalkaloids was recovered from potato peels using pressurized liquid extraction (1.92 mg/g dried potato peels) compared to conventional solid–liquid extraction (0.981 mg/g dried potato peels). Response surface methodology deduced the optimal temperature and extracting solvent (methanol) for the pressurized liquid extraction (PLE) of glycoalkaloids as 80 °C in 89% methanol. Using these two optimum PLE conditions, levels of individual steroidal alkaloids obtained were of 597, 873, 374 and 75 µg/g dried potato peel for α-solanine, α-chaconine, solanidine and demissidine respectively. Corresponding values for solid liquid extraction were 59%, 46%, 40% and 52% lower for α-solanine, α-chaconine, solanidine and demissidine respectively.

Purification, characterization and antioxidant activities of polysaccharides from thinned-young apple

Purification, characterization and antioxidant activities of polysaccharides from thinned-young apple (TYA) were investigated in the study. A water-soluble polysaccharide (TYAP) was obtained with hot water extraction, which was further purified by chromatography of Cellulose DEAE-52 and Sephadex G-150 to get three purified fractions of TYAP-1, TYAP-2 and TYAP-3. HPLC analysis showed that the three fractions were mainly composed of galactose and arabinose with the average molecular weights of 115 kDa, 479 kDa and 403 kDa, respectively and the monosaccharide compositions of TYAP-2 and TYAP-3 were more complicated than that of TYAP-1. Moreover, TYAP fractions of three had no absorptions at 260 nm and 280 nm in the UV spectrum, indicating the absence of protein and nucleic acid. Their structure properties were further confirmed by FT-IR. In vitro antioxidant activities of three fractions were characterized by DPPH(•), HO(•), O2(•-) and ferric-reducing antioxidant power systems. The results indicated that TYAP-1, TYAP-2 and TYAP-3 possessed significant antioxidant effects in a concentration-dependant manner in the tested concentration range of 0.25-5.0mg/mL. Among the fractions tested, TYAP-3 showed significantly higher antioxidant activity than that of TYAP-1 and TYAP-2. All of these findings provide a scientific basis for the further use of polysaccharides from thinned-young apple.

Phenolic profiling in the pulp and peel of nine plantain cultivars (Musa sp.)

The present study investigated the phenolic profiles of the pulp and peel of nine plantain cultivars and compared them to those of two dessert bananas of commercial interest (Grand Nain and Gros Michel), alongside a newly created hybrid, resistant to black sigatoka disease (F568). Identification and quantification of phenolic compounds were performed by means of HPLC-ESI-HR-MS and HPLC-DAD. Hydroxycinnamic acids, particularly ferulic acid-hexoside with 4.4-85.1 μg/g of dry weight, dominated in the plantain pulp and showed a large diversity among cultivars. Flavonol glycosides were predominant in plantain peels, rutin (242.2-618.7 μg/g of dry weight) being the most abundant. A principal component analysis on the whole data revealed that the phenolic profiles of the hybrid, the dessert bananas and the pure plantains differed from each other. Plantain pulps and peels appeared as good sources of phenolics, which could be involved in the health benefits associated with their current applications.

Ultrasonic extraction of steroidal alkaloids from potato peel waste

Potato processors produce large volumes of waste in the form of potato peel which is either discarded or sold at a low price. Potato peel waste is a potential source of steroidal alkaloids which are biologically active secondary metabolites which could serve as precursors to agents with apoptotic, chemopreventive and anti-inflammatory properties. The present study investigated the relative efficacy of ultrasound assisted extraction (UAE) and solid liquid extraction (SLE) both using methanol, to extract steroidal alkaloids from potato peel waste and identified optimal conditions for UAE of α-solanine, α-chaconine, solanidine and demissidine. Using response surface methodology optimal UAE conditions were identified as an amplitude of 61 μm and an extraction time of 17 min which resulted the recovery of 1102 μg steroidal alkaloids/g dried potato peel (DPP). In contrast, SLE yielded 710.51 glycoalkaloid μg/g DPP. Recoveries of individual glycoalkoids using UAE yielded 273, 542.7, 231 and 55.3 μg/g DPP for α-solanine, α-chaconine, solanidine and demissidine respectively. Whereas for SLE yields were 180.3, 337.6, 160.2 and 32.4 μg/g DPP for α-solanine, α-chaconine, solanidine and demissidine respectively. The predicted values from the developed second order quadratic polynomial equation were in close agreement with the experimental values with low average mean deviation (E<5%) values. Predicted models were highly significant (p<0.05) for all parameters studied. This study indicates that UAE has strong potential as an extraction method for steroidal alkaloids from potato peel waste.

Optimisation of antioxidant extraction from Solanum tuberosum potato peel waste by surface response methodology

This study reports the optimised conditions (temperature, ethanol concentration and processing-time) for antioxidant extraction from potato peel (Agria variety) waste. At short extraction times (34 min), optimal yields of phenolic (TP) and flavonoid (Fv) compounds were reached at 89.9°C and ethanol concentrations of 71.2% and 38.6%, respectively. The main phenolic compounds identified in the extracts were chlorogenic (Cl) and ferulic (Fer) acids. A significant positive correlation was found between antioxidant activity and TP, Fv, Fer and Cl responses. Potato peel extracts were able to stabilize soybean oil under accelerated oxidation conditions, minimising peroxide, totox and p-anisidine indices. The production of hexanal and 2-hexenal in soybean oil samples was maximal for extracts obtained at intermediate temperatures and ethanol concentrations. Our results demonstrate potato peel waste is a good source of antioxidants able to effectively limit oil oxidation, while contributing to the revalorisation of these agrifood by-products.

Dietary factors affecting polyphenol bioavailability

While many epidemiological studies have associated the consumption of polyphenols within fruits and vegetables with a decreased risk of developing several chronic diseases, intervention studies have generally not confirmed these beneficial effects. The reasons for this discrepancy are not fully understood but include potential differences in dosing, interaction with the food matrix, and differences in polyphenol bioavailability. In addition to endogenous factors such as microbiota and digestive enzymes, the food matrix can also considerably affect bioaccessibility, uptake, and further metabolism of polyphenols. While dietary fiber (such as hemicellulose), divalent minerals, and viscous and protein-rich meals are likely to cause detrimental effects on polyphenol bioaccessibility, digestible carbohydrates, dietary lipids (especially for hydrophobic polyphenols, e.g., curcumin), and additional antioxidants may enhance polyphenol availability. Following epithelial uptake, polyphenols such as flavonoids may reduce phase II metabolism and excretion, enhancing polyphenol bioavailability. Furthermore, polyphenols may act synergistically due to their influence on efflux transporters such as p-glycoprotein. In order to understand polyphenol bioactivity, increased knowledge of the factors affecting polyphenol bioavailability, including dietary factors, is paramount.

The impact of in vitro digestion on bioaccessibility of polyphenols from potatoes and sweet potatoes and their influence on iron absorption by human intestinal cells

The composition of potatoes as determined by chemical extraction has been described extensively. It is thus quite well known that, among other compounds, potato is rich in polyphenols, vitamins and in some minerals. This paper underlines the important role of simulated gastro-intestinal in vitro digestion in the bioaccessibility of polyphenols (chlorogenic acid and derivatives, and rutin) from potatoes and sweet potatoes and their impact on iron uptake. Concentrations of polyphenols in the flesh of two potato cultivars (Nicola, white potato, and Vitelotte, purple potato) and sweet potato were measured by Ultra Performance Liquid Chromatography after boiling and after in vitro digestion. Chemical extraction underestimates polyphenol amounts that can be released during digestion and that are actually bioaccessible. Iron uptake, as evaluated by a ferritin assay, by intestinal human cells was decreased after incubation with the intestinal phase of in vitro digestion, presumably due to the presence of polyphenols.