Karel Hamouz

Effect of peeling and three cooking methods on the content of selected phytochemicals in potato tubers with various colour of flesh

The impact of peeling and three cooking treatments (boiling, baking and microwaving) on the content of selected phytochemicals in white-, yellow-, red- and purple-fleshed potatoes was investigated. Ascorbic acid and chlorogenic acid contents were determined by HPLC-DAD, total anthocyanin content by pH-differential spectrophotometry, glycoalkaloid, α-chaconine and α-solanine contents by HPLC-ESI/MS/MS. All cooking treatments reduced ascorbic and chlorogenic acid contents, total glycoalkaloids, α-chaconine and α-solanine with the exception of total anthocyanins. The losses of ascorbic and chlorogenic acids were minimised with boiling and total anthocyanin levels retained the highest. Boiling of peeled tubers decreased contents of total glycoalkaloids (α-chaconine and α-solanine) and appeared as the most favourable among the three tested methods. Moreover, due to higher initial levels, red- and purple-fleshed cultivars retained higher amounts of antioxidants (ascorbic acid, chlorogenic acid and total anthocyanin) after boiling and may be healthier as compared with white or yellow cultivars.

Anthocyanin and antioxidant activity of snacks with coloured potato.

Coloured-fleshed potatoes of four varieties were used as raw material for coloured flour and fried snack production. The effects of thermal processes traditionally used in dried potato processing and in snack pellet manufacturing on anthocyanin profiles, total polyphenols and antioxidant properties of obtained half- and ready products were studied. There was a significant influence of potato variety on the experimental flour and snack properties. Flours with the highest antioxidant activities were obtained from Salad Blue and Herbie 26 potatoes; however, the flour prepared from the Blue Congo exhibited a much higher total polyphenol and anthocyanin content. Snacks produced with coloured flour had 2-3 times higher antioxidant activities, 40% higher contents of polyphenols, attractive colour and better expansion compared to control samples. The lowest losses of anthocyanins during snack processing were in snacks with flour from the purple-fleshed Blue Congo and red-fleshed Herbie 26.

Content of polyphenols in coloured and yellow fleshed potatoes during dices processing.

The purpose of the research was to examine the effect of the laboratory production of dried potato dice on the content of phenolic compounds in one yellow-fleshed potato variety and four blue-fleshed potatoes varieties. Coloured-flesh potato varieties were characterised by about three times higher amount of total phenolic content than traditional yellow-fleshed ones. The predominating phenolic acids in potato were chlorogenic acid and its isomers, which account about 90% of total phenolic content in tubers. The phenolic acid content decreased by 80% after peeling the blue-fleshed potatoes and by 60% after peeling the yellow variety. The dried potato dice obtained from yellow-fleshed potatoes had no content of phenolic acids but produced from colour-fleshed potatoes contained about 4% of the original phenolic content of the raw material. Chlorogenic acid amounted about 97% of total phenolic acid content, and the rest was neochlorogenic acid.

The quality of protein of coloured fleshed potatoes

Potatoes of purple varieties and red flesh colour were estimated as the important food product containing valuable protein. Amino acids concentration and protein nutritive value of coloured potatoes were analysed and compared with traditional yellow-fleshed varieties. Studies comprised potatoes of 13 varieties: 7 of purple-fleshed, four of red-fleshed and two of yellow-fleshed. There were observed differences between studied potatoes with respect to dry matter, starch and protein content as well as to amino acids concentration and protein quality independently on flesh colour. Potatoes of low as well of high content of total protein, independently on flesh colour, characterised similar protein quality, like for example varieties of Blaue Anneliese and Highland B. Red or Blue Congo and Salad Blue. Leucine limited the quality of majority of coloured fleshed potato varieties used for the experiment. The best amino acid profiles and protein quality confirmed by chemical scores and EAA index values characterised purple fleshed Vitelotte and Blaue Anneliese, yellow fleshed Verdi as well as red fleshed Herbie 26, Highland B. Red and Rosemarie.

Carotenoid profile and retention in yellow-, purple- and red-fleshed potatoes after thermal processing.

This research aimed to investigate the effect of thermal processing on carotenoid profile, quantity and stability in 22 colour-fleshed potato cultivars grown in the Czech Republic. The total of nine carotenoids was analysed by HPLC using a C30 column and PDA detection. The total carotenoid content for all cultivars ranged from 1.44 to 40.13 μg/g DM. Yellow cultivars showed a much higher average total carotenoid content (26.22 μg/g DM) when compared to red/purple-fleshed potatoes (5.69 μg/g DM). Yellow cultivars were dominated by antheraxanthin, whereas neoxanthin was the main carotenoid in red/purple cultivars. Thermal processing significantly impacted all potato cultivars. Boiling decreased the total carotenoids by 92% compared to baking (88%). Lutein was the most stable carotenoid against thermal processing (decreased by 24-43%) followed by β-carotene (decreased by 78-83%); other carotenoids were degraded nearly completely. Increased formation of (Z)-isomers by thermal processing has not been confirmed.

The influence of dehydrated potatoes processing on the glycoalkaloids content in coloured-fleshed potato.

The aim of this study was to determine the effect of different temperatures of blanching and pre-drying used in the laboratory production of dried potato dice on the content of glycoalkaloids in red and blue fleshed potato varieties. Studied potatoes of coloured fleshed varieties were characterised by a low glycoalkaloids content at 5.47 mg 100 g(-1). The production of dehydrated potato dice influenced on the decrease in glycoalkaloids content in potato products. The majority of these compounds were removed during the peeling (70%) and blanching process (29%). Potato dice blanched at the highest temperature (85 °C) and pre-dried at 120 °C was characterised by the lowest quantity of glycoalkaloids content, whereas the highest content of these compounds was found in dice blanched potato at the lowest temperature (65 °C) and pre-dried at 120 °C. The blanching process much influenced on the decrease in glycoalkaloids content than pre-drying process.

Impact of Phenolic Content on Antioxidant Activity in Yellow and Purple-fleshed Potatoes Grown in the Czech Republic

ABSTRACT Purple-fleshed potatoes cultivars are new on the Czech market. Intensive trials about growing purple-fleshed potato cultivars in the Czech Republic are currently being carried out. Recently many articles deal with phenolic antioxidants and their contribution to the human health; thus the aim of this study was to determine the differences in total phenolic (TP) content and antioxidant activity (AA) between yellow (cvs. Impala, Karin, Dita, Saturna) and purple-fleshed (cvs. Valfi, Violette) potatoes grown in the Czech Republic in 2004 in four locations in field trials. TP content was determined by Folin-Ciocalteau assay and AA by DPPH assay both in freeze-dried tuber matter. Results showed a statistical significant difference in TP content and AA between yellow- and purple-fleshed potatoes. Purple-fleshed cultivars showed 60% higher TP content than yellow-fleshed cultivars and AA content was double in purple-fleshed cultivars. A significant linear correlation between TP and AA was found (r2 = 0.747). Average TP content in yellow-fleshed cultivars was 2.96 GAE (gallic acid mg g−l DM) and in purple-fleshed cultivars 4.68 GAE was found. Average AA in yellow-fleshed cultivars was 11.26 AAE (ascorbic acid equivalent mg 100 g−1 DM) and in purple-fleshed cvs. 24.79 AAE. Purple-fleshed potatoes showed a lower variation among localities (6 % only). The results showed that AA of freeze-dried tuber matter is very low when compared to other plants or sources (wine, tea, chocolate and blueberries) although a high potato intake in humans by Czechs (72 kg capita−1 year−1) is considered.

Effect of cultivar, flesh colour, locality and year on carotenoid content in potato tubers

In this study, twelve cultivars of potato with different flesh colour (yellow, purple and red) were cultivated in 2012 and 2013 in two trial localities in the Czech Republic and evaluated for the main individual carotenoids. The con tent of total carotenoids (TC) in analysed cultivars ranged in 1.1–12.2 mg/kg in dry matter (DM) and was influ enced by genotype cultivar, locality and year. Cv. Agria (yellow flesh) reached 1.8 to 11.8 times higher levels of TC compared with cultivars of coloured flesh. Locality and year of higher average temperatures during the growing season produced higher TC contents in tubers. Genotype significantly influenced the content and composition of individual carotenoids. As in cv. Agria, violaxanthin (41%) and lutein (55–78%) dominated in all cultivars with coloured flesh. The relative content of β-carotene in cv. Agria represented 2% of TC, in cultivars with coloured flesh 5–12% TC.

Changes in anthocyanidin levels during the maturation of color-fleshed potato (Solanum tuberosum L.) tubers

Certain potato cultivars are capable of producing anthocyanin pigments in the potato skin and flesh and those pigments have been shown, together with other phytochemicals, to promote good health. Six common anthocyanidins (cyanidin, delphinidin, petunidin, pelargonidin, malvidin and peonidin) were analyzed weekly for 15weeks in red- and purple-fleshed potato cultivars (Red Emma, Königspurpur, Valfi and Blaue de la Mancha) grown in field conditions using a validated LC-(+ESI)MS/MS method. Pelargonidin was the major type detected in red-fleshed cultivars whereas petunidin was the major type detected in the purple ones. Neither cyanidin nor delphinidin were found in any of the cultivars. The anthocyanidin levels observed were as high as 78mg/100g FW during tuber growth; however, fully matured tubers contained only 10-39mg anthocyanidins/100gFW. Anthocyanidin levels were moderately correlated with global solar irradiation (r<0.6252) but not with rainfall or daily temperature.

Determination of Antioxidant Activity and Polyphenols Content in Chips by Raman and IR Spectroscopy

The application of vibrational spectroscopy for the determination of total polyphenols content, antioxidant activity, colour parameters, and fat level in chips originated from yellow-, red- and purple-fleshed potato varieties is reported. Raman, infrared (IR) and near-infrared (NIR) spectra of the laboratory-prepared chips were collected. Combining spectral data with the results of reference analyses, partial least squares regression models were built. To characterise and compare the elaborated models, the relative standard errors of prediction were calculated for calibration and validation sets. In the case of total phenolics quantification by Raman/IR/NIR techniques, these errors (%) amounted to 4.0/7.0/7.1 and 6.4/8.5/8.4 for calibration and validation samples, respectively, whereas they were 4.9/7.7/4.8 and 6.6/8.3/6.8 for antioxidant activity. The obtained results demonstrate that both infrared and Raman spectroscopy can effectively replace commonly used extraction methods. It follows that Raman spectroscopy has the highest potential to be adopted for the online potato-derived product analysis.