Effect of cultivar, growth environment and developmental stage on phenolic compounds and ascorbic acid in potato tubers grown in Finland

Potato is the most important non-cereal crop worldwide. It has been consumed in the South American Andes for thousands of years and then introduced to Europe in the XVII century. Thanks to its nutritional value and high yield it was then expanded to the rest of the world. Since potato is a staple food crop for many countries, it plays a crucial role in maintaining food security and reducing malnutrition. Unfortunately, the sustainable production of this crop is threatened by climate change that causes rising global temperatures and altering weather conditions all over the world. The main purpose of this study was to understand how weather variables affected by latitude and year impact the biosynthesis of phenolic compounds and ascorbic acid in pigmented potato cultivars. The first aim of this work was to develop reliable extraction methods for anthocyanins and ascorbic acid, as previous studies showed contradictory information on the anthocyanin content when using fresh, freeze-dried or steamed potatoes. The second aim was to assess the effect of temperature, cultivar, and tuber developmental stage on the expression of genes involved in the biosynthesis of phenolic compounds and the content of anthocyanins, phenolic acids, and ascorbic acid in potato cultivars with purple or yellow flesh and/or skin. The third aim was to evaluate the effect of weather conditions (affected by latitude and year), cultivar, and tuber developmental stage also on the gene expression levels and on the content of anthocyanins, phenolic acids, and ascorbic acid in potato cultivars grown at two different latitudes and two consecutive years in Finland. The results showed that anthocyanins were most effectively extracted from freeze-dried potatoes using 70 % acidified methanol. Tris(2-carboxyethyl) phosphine hydrochloride was the most effective in reducing dehydroascorbic acid to ascorbic acid and was therefore the most suitable reducing agent for the determination of total ascorbic acid. Cultivar was the main variable that affected the gene expression levels of the enzymes involved in the biosynthesis of phenolic compounds as well as the anthocyanin and phenolic acid profile. The main anthocyanin in the purplefleshed and purple-skin cultivars was a petunidin derivative or malvidin derivate (depending on the cultivars), while the main anthocyanin in the red-skinned cultivar was a pelargonidin derivative. The effect of tuber developmental stage was evaluated in the second and third aim of this study. In both cases, it was found that the content of the main anthocyanins and phenolic acids as well as ascorbic acid tended to decrease with tuber maturation, although the content of minor anthocyanins and phenolic acids did not show a clear tendency to increase or decrease. The gene expression levels also remained relatively stable for most of the genes studied except for F3ʹH which showed a clear decreasing trend during tuber development in the purplefleshed cultivars. When potato tubers were cultivated under controlled temperatures (at 13 and 18 °C), it was found that the studied temperatures did not affect the content of anthocyanins, but mildly affected the content of phenolic acids and ascorbic acid during tuber development. However, when tubers reached full maturity no significant differences in the content of anthocyanins, phenolic acids or ascorbic acid were observed between the tubers grown at the two studied temperatures. Our third aim was to evaluate the impact of latitude on the content of phenolic compounds and ascorbic acid in potato tubers, and for that we evaluated two latitudes and replicated the experiment in two consecutive years for repeatability purposes. However, when we processed our data, we realized that the synthesis of the metabolites of interest were mainly affected by the interaction of “Latitude: Year” and less by the solo effect of “Latitude” or “Year”. So, when potato tubers were cultivated at different latitudes (61.2 and 64.8° N) and years (2014 and 2015) in Finland, potato plants cultivated at 61.2° N in 2014 (Kokemäki) were exposed to temperatures above 18 °C and reduced precipitation events. The pigmented potato tubers produced in this trial had the lowest expression levels of most of the genes involved in the phenylpropanoid pathway and the lowest content of phenolic compounds and ascorbic acid. On the other hand, when potato plants were cultivated at the same latitude (61.2° N) but in 2015 (Köyliö), the plants were exposed to temperatures between 13 and 18 °C and good precipitation events. These plants produced tubers with the highest gene expression levels, as well as the highest contents of anthocyanins and phenolic acids. The potato plants cultivated at 64.8° N in 2014 and 2015 (Muhos) produced tubers with intermediate contents of anthocyanins, phenolic acids, and ascorbic acid. Positive gene-gene, gene-anthocyanins and anthocyaninanthocyanin correlations were also stronger and more significant at 61.2° N in 2015 (Köyliö) than in the other field trials. In this study, we observed that a mild increment in temperature combined with poor precipitation events at 61.2° N in 2015 (Kokemäki) had a detrimental effect on the synthesis of bioactive compounds in potato tubers. However, during the last five years, temperatures in Finland have exceeded those of 2015 and Finnish potato growers have reported difficulties due to unexpected weather events. Further research is needed to better understand the potentially synergistic interactions of the main weather variables affecting the synthesis of bioactive compounds in potato tubers.----- Viljojen jälkeen peruna on maailman tärkein viljakasvi. Sitä on syöty ensin Etelä-Amerikan Andeilla tuhansien vuosien ajan, josta se tuotiin Eurooppaan XVII vuosisadalla. Ravintoarvonsa ja suuren satonsa ansiosta se levisi sitten muualle maailmaan. Koska peruna on monien maiden perusviljelykasvi, sillä on ratkaiseva merkitys elintarviketurvan ylläpitämisessä ja aliravitsemuksen vähentämisessä. Valitettavasti tämän viljelykasvin kestävää tuotantoa uhkaa ilmastonmuutos, joka nostaa maapallon lämpötiloja ja muuttaa sääolosuhteita kaikkialla maailmassa. Tämän tutkimuksen päätarkoituksena oli ymmärtää, miten leveyspiirin ja vuodenajan säämuuttujat vaikuttavat fenolisten yhdisteiden ja askorbiinihapon synteesiin pigmentoituneissa perunalajikkeissa. Työn ensimmäisenä tavoitteena oli luotettavan uuttomenetelmän kehittäminen antosyaaneille ja askorbiinihapolle. Aiemmissa tutkimuksissa oli antosyaanipitoisuuksista saatu ristiriitaisia tietoja, tutkittaessa tuoreita, kylmäkuivattuja tai höyrytettyjä perunoita. Toisena tavoitteena oli arvioida lämpötilan, lajikkeen ja mukulan kehitysvaiheen vaikutusta fenolisten yhdisteiden biosynteesiin osallistuvien geenien ilmentymiseen sekä antosyaanien, fenolihappojen ja askorbiinihapon pitoisuuksiin perunalajikkeissa, joiden malto ja/tai kuori on violetti tai keltainen. Kolmantena tavoitteena oli arvioida sääolosuhteiden (joihin vaikuttavat leveysaste ja vuosi), lajikkeen ja mukulan kehitysvaiheen vaikutusta antosyaanien, fenolihappojen ja askorbiinihapon pitoisuuksiin sekä näiden yhdisteiden biosynteesiin osallistuvien geenien ilmentymistasoihin perunalajikkeissa, joita kasvatettiin kahdella eri leveysasteella ja kahtena peräkkäisenä vuonna Suomessa. Tulokset osoittivat, että antosyaaneja saatiin eniten uuttamalla kylmäkuivattuja perunoita happamoidulla 70 % metanolilla. Tris(2-karboksietyyli) fosfiinihydrokloridi oli tehokkain pelkistämään dehydroaskorbiinihappo askorbiinihapoksi ja siten soveltui parhaiten askorbiinihapon kokonaismäärän määrittämiseen. Perunalajike oli tärkein muuttuja, joka vaikutti geeniekspressioprofiiliin sekä antosyaani- ja fenolihappoprofiiliin. Pääantosyaani violettimaltoisissa ja - kuorisissa lajikkeissa oli petunidiinijohdannainen tai malvidiinijohdannainen (lajikkeesta riippuen), kun taas punakuorisen lajikkeen pääantosyaani oli pelargonidiinijohdannainen. Mukulan kehitysvaiheen vaikutusta arvioitiin tämän tutkimuksen toisessa ja kolmannessa tavoitteessa, ja molemmissa tapauksissa havaittiin, että tärkeimpien antosyaanien ja fenolihappojen sekä askorbiinihapon pitoisuudet vähenivät yleensä kypsymisen myötä. Fenolihappojen pitoisuuksissa ei havaittu systemaattisia eroja kasvukauden aikana. Myös geenien ilmentymistasot pysyivät suhteellisen vakaina useimpien tutkittujen geenien osalta lukuun ottamatta F3ʹH:ta, jonka ilmeneminen selvästi väheni violettimaltoisissa lajikkeissa mukulan kypsyessä. Kolmantena tavoitteena oli arvioida leveysasteen vaikutusta perunan mukuloiden fenolisten yhdisteiden ja askorbiinihapon pitoisuuksiin. Perunoita kasvatettiin kahtena eri vuonna kahdella eri leveysasteella. Tulokset osoittivat, että tutkittavien parametrien "leveysaste" ja "vuosi" erillisvaikutukset aineenvaihduntatuotteiden synteesiin olivat vähemmän merkittäviä kuin ko. parametrien yhdysvaikutus "leveysaste: vuosi". Kun perunamukuloita viljeltiin eri leveysasteilla (61,2 ja 64,8° N) ja eri vuosina (2014 ja 2015), havaittiin, että perunakasvit, jotka kasvoivat kokeessa leveysasteella 61,2° N vuonna 2014 (Kokemäki), altistuivat yli 18 °C:n lämpötiloille ja vähäisemmille sateille. Tällöin kehittyi perunamukuloita, joissa fenyylipropanoidireittiin osallistuvien geenien ilmentymistasot olivat alentuneet ja antosyaanien, fenolihappojen ja askorbiinihapon pitoisuudet olivat vähentyneet. Toisaalta perunakasvit, jotka kasvoivat kokeessa leveysasteella 61,2° N vuonna 2015 (Köyliö), altistuivat runsaille sateille ja 13-18 °C:n lämpötiloille, ja ne tuottivat mukuloita, joiden geenien ilmentymistasot sekä antosyaanien ja fenolihappojen pitoisuudet olivat korkeimmat. Vuosina 2014 ja 2015 Muhoksella (64,8° N) kasvatetut perunat tuottivat mukuloita, joiden antosyaani-, fenolihappo- ja askorbiinihappopitoisuudet olivat keskitasoa. Positiiviset geeni-geeni-, geeni-antosyaani- ja antosyaani-antosyaani-korrelaatiot olivat myös vahvempia ja merkitsevämpiä kuin muissa kenttäkokeissa. Tässä tutkimuksessa havaitsimme, että vuonna 2015 lämpötilan lievä nousu yhdistettynä vähäisiin sademääriin leveysasteella 61,2° N (Kokemäki) vaikutti haitallisesti perunan mukuloiden bioaktiivisten yhdisteiden synteesiin. Viimeisten viiden vuoden aikana Suomen lämpötilat ovat kuitenkin ylittäneet vuoden 2015 lämpötilat, ja suomalaisten perunanviljelijöiden on raportoitu kohdanneen vaikeuksia odottamattomien sääilmiöiden vuoksi. Lisätutkimusta tarvitaan, jotta voidaan ymmärtää paremmin perunan mukuloiden bioaktiivisten yhdisteiden synteesiin vaikuttavien tärkeimpien säämuuttujien mahdollisesti synergistiset yhteisvaikutukset

Profiling beneficial phytochemicals in a potato somatic hybrid for tuber peels processing: phenolic acids and anthocyanins composition

The purpose of this study was to characterize the peels of a CN1 somatic hybrid obtained from two dihaploid potato lines (Cardinal H14 and Nicola H1) in terms of the health‐promoting phenolic compounds (phenolic acids and anthocyanins). The CN1 hybrid is defined by a pink tuber skin color making it different from the light‐yellow‐skinned “Spunta,” which is the most commonly grown potato cultivar in Tunisia. Oven‐dried peel samples derived from CN1 hybrid and cv. Spunta were ground, and phenolic compounds were extracted with water or methanol for quantification. Lyophilized peels were used for the phenolic acid and anthocyanin analyses. Higher total quantities of phenolic compounds were recovered in methanol extracts compared with water extracts. A slightly higher concentration of phenolic acids (100 mg/100 g DW) was obtained in the lyophilized peels extract of CN1 hybrid than in the cv. Spunta corresponding sample (83 mg/100 g DW). The profiles of the chlorogenic acid isomers were almost identical in both of CN1 hybrid and cv. Spunta. Caffeic acid (CA) and three caffeoylquinic acids (CQAs): 3‐CQA, 4‐CQA, and 5‐CQA, were identified from both genotypes, 5‐CQA being the dominant form in both potatoes. Since the CN1 hybrid has a pink skin color, its anthocyanin profile was also determined. The anthocyanin quantity in the CN1 peels was 5.07 mg/100 g DW, involving six different anthocyanins that were identified within the extract, namely, Pelargonidin‐3‐rutinoside‐5‐glucoside, peonidin‐3‐rutinoside‐5‐glucoside, coumaroyl ester of pelargonidin‐3‐rutinoside‐5‐glucoside, coumaroyl ester of peonidin‐3‐rutinoside‐5‐glucoside, feruloyl ester of pelargonidin‐3‐rutinoside‐5‐glucoside, and feruloyl ester of peonidin‐3‐rutinoside‐5‐glucoside. These results suggest that the peel waste of CN1 somatic hybrid can be considered as a promising source of high‐value compounds for food industry

Profiling beneficial phytochemicals in a potato somatic hybrid for tuber peels processing: phenolic acids and anthocyanins composition

The purpose of this study was to characterize the peels of a CN1 somatic hybrid obtained from two dihaploid potato lines (Cardinal H14 and Nicola H1) in terms of the health-promoting phenolic compounds (phenolic acids and anthocyanins). The CN1 hybrid is defined by a pink tuber skin color making it different from the light-yellow-skinned "Spunta," which is the most commonly grown potato cultivar in Tunisia. Oven-dried peel samples derived from CN1 hybrid and cv. Spunta were ground, and phenolic compounds were extracted with water or methanol for quantification. Lyophilized peels were used for the phenolic acid and anthocyanin analyses. Higher total quantities of phenolic compounds were recovered in methanol extracts compared with water extracts. A slightly higher concentration of phenolic acids (100 mg/100 g DW) was obtained in the lyophilized peels extract of CN1 hybrid than in the cv. Spunta corresponding sample (83 mg/100 g DW). The profiles of the chlorogenic acid isomers were almost identical in both of CN1 hybrid and cv. Spunta. Caffeic acid (CA) and three caffeoylquinic acids (CQAs): 3-CQA, 4-CQA, and 5-CQA, were identified from both genotypes, 5-CQA being the dominant form in both potatoes. Since the CN1 hybrid has a pink skin color, its anthocyanin profile was also determined. The anthocyanin quantity in the CN1 peels was 5.07 mg/100 g DW, involving six different anthocyanins that were identified within the extract, namely, Pelargonidin-3-rutinoside-5-glucoside, peonidin-3-rutinoside-5-glucoside, coumaroyl ester of pelargonidin-3-rutinoside-5-glucoside, coumaroyl ester of peonidin-3-rutinoside-5-glucoside, feruloyl ester of pelargonidin-3-rutinoside-5-glucoside, and feruloyl ester of peonidin-3-rutinoside-5-glucoside. These results suggest that the peel waste of CN1 somatic hybrid can be considered as a promising source of high-value compounds for food industry