Nutritional Value of Coloured Flesh Potato Tubers in Terms of Their Micronutrient Content

Abstract

The aim of this study was to compare Fe, Zn, Mn, Al and Li contents in table potato tubers, obtained from seven potato cultivars with different flesh colour, and one cultivar characterised by light-coloured flesh. The study material consisted of potato tubers produced in a one-factor field experiment carried out at the Agricultural Experimental Station in Zawady belonging to the University of Siedlce, Poland (52°03′ N, 22°33′ E) in 2021–2023. The following cultivars were tested: Eurostar (light yellow flesh), Rote Emmalie and Herbie 26 (red flesh), Provita, Salad Blue, Blaue Annelise, Vitelotte Noire and Bora Valley (purple and blue flesh). The study showed that the genetic characteristics of the cultivars determined the nutrient content and uptake with tuber yield. Of the tested minerals which are important for human nutrition (Fe, Zn, Mn), red and purple cultivars accumulated more Fe than the light yellow-fleshed Eurostar. Zn content was the highest in red-fleshed cultivars compared with light and purple-fleshed cultivars. Mn content was the highest in the tubers of the light yellow-fleshed Eurostar and lowest in red Rote Emmalie. Fe, Zn, Mn and Al contents and uptake with tuber yield were influenced by weather conditions during the growing season.

1. Introduction

Alongside wheat, rye and maize, the potato (Solanum tuberosum L.) is the most popular food source for the world’s population. The crop, thanks to its relatively high harvest tuber yield per hectare, is a clear leader in tuber production in the world, which was 359 million tonnes in 2020 [1,2]. In the current global food system, it is referred to as a food security crop by many researchers [3,4]. Tubers are of high nutritional value due to their content of carbohydrates, high-quality protein, vitamins, dietary fibre and numerous macronutrients and micronutrients [5,6,7,8]. In addition, potato cultivars with yellow, red and purple flesh contain bioactive compounds—carotenoids and anthocyanins—which are of great interest because of their health-promoting properties [9,10,11]. Potato occupies an important position in nutrition because of its nutritional value and its wide range of minerals. The tubers contain between 0.5 and 2.0% of macronutrients and micronutrients, which are important for the human body [5,12,13,14]. Macronutrients, the most abundant being potassium, magnesium, phosphorus and calcium, are mainly involved in physiological processes and have structural functions [6,12,15]. Micronutrients are involved in the metabolism of organic compounds, and, above all, they are components of enzymes that activate biochemical and physiological processes [16,17,18]. A lack of minerals in the human diet leads to serious health problems, which is why many of these nutrients are often given as dietary supplements [2]. Hence, it is important to provide the body with raw materials and natural products that are minimally processed and contain a wide range of nutrients and minerals. Potato tubers with different coloured flesh are among these products. Many factors determine the micronutrient content of a potato tuber including cultivar, climatic conditions, soil physico-chemical characteristics, and agrotechnological treatments [17,19,20,21]. At present, some breeding programmes focus on increasing tubers’ mineral content as they are an important source of minerals in the diet and can be made even healthier, more nutritious and flavourful [18]. However, there are few publications reporting results of comparative studies on the micronutrient content of potato tubers whose flesh is of varied colours [9,20]. Hence, it was hypothesised that potato cultivars with red and purple flesh may accumulate similar or greater amounts of the most important micronutrients than those with light-coloured flesh. The research reported here aimed to provide information on the content of the health-important micronutrients (Fe, Zn and Mn) and the harmful ones (Al and Li) in the tubers of potato cultivars with light, red and purple flesh (including one new cultivar Provita registered in Poland in 2021) grown in three different growing seasons.

2. Materials and Methods

2.1. Experimental Site and Materials

The study material consisted of potato tubers obtained in a one-factor field experiment carried out in 2021–2023 at the Agricultural Experimental Station in Zawady, Poland. The experimental field was located at 52°03′ N latitude and 22°33′ E longitude, and 160 m above sea level. Each year, the experiment was in a different field of a four-year rotation system.

The field experiment was set up on Haplic Luvisol/LV-ha with a sandy clay loam texture according to the World Reference Base for Soil Resources [22]. Analyses of soil samples taken from the experimental fields were performed using standard methods at a certified laboratory of the National Chemical and Agricultural Station in Warsaw. Soil analyses were conducted every year, and its characteristics in 2021–2023 are presented in

Table 1. Soil properties on the layer of 0–30 cm in the field experiment.

Properties	Description
	2021	2022	2023
pH (in 1 M KC)	5.48	5.62	5.00
Organic matter (g·kg−1)	22.0	22.8	15.9
Phosphorus—available (mg·kg−1)	72.0	66.0	69.9
Potassium—available (mg·kg−1)	151.0	159.0	123.2
Magnesium—available (mg·kg−1)	64.0	63.0	46.0
Iron—total forms (mg·kg−1)	886.0	1620.0	897.0
Zinc—total forms (mg·kg−1)	17.4	18.1	11.3
Manganese—total forms (mg·kg−1)	58.4	56.1	104.0

. In 2023, organic matter was lower than in 2021 and 2022 due to different crop yields in preceding years.

2.2. Characteristics of Potato Cultivars

The main criterion for the selection of potato cultivars for the experiment was flesh colour. The differences between the selected cultivars centre around the following features: earliness (length of the vegetation period), flesh colour, peel colour, taste, yield of tubers, country of origin and year of registration. The description of the cultivars is presented in

Table 2. Characteristics of the tested cultivars.

Cultivar	Earliness	Flesh Colour	Peel Colour	Taste	Yield of Tubers	Country of Origin	Year of Registration
Eurostar	medium late	light yellow	light yellow	good	large	The Netherlands	2013
Rote Emmalie	early	red	red	distinctive	large	Germany	2004
Herbie 26	medium late	red	red	good	medium	Czech Republic	-
Provita	early	purple	purple	good	medium	Poland	2021
Salad Blue	medium early	purple	blue	good nutty	medium	United Kingdom	1900
Blue Annelise	medium early	purple	dark purple	delicate	medium	Germany	2007
Vitelotte Noire	medium late/late	purple	purple	slightly bitter, nutty	medium	France	-
Bora Valley	medium late	dark purple	dark purple	good delicate	very large	Korea	-

[23,24].

An experiment with potatoes whose tubers have coloured flesh is an innovative one and the only one in Eastern Poland. Tubers of coloured-flesh potato cultivars contain 2–3 times as much polyphenolic compounds, including anthocyanins, compared to white or yellow-fleshed cultivars. Polyphenols are natural components of the potato which perform vital functions in the plant. Due to their antioxidant properties, they can be an important part of enriching our diet with these valuable components. It should be noted that the publication about nutritional value of potatoes with different flesh colour can contribute to increasing the diversity of the market offer and promoting a healthy lifestyle among consumers.

2.3. Experimental Design—Cultivation and Protection

A three-year experiment, carried out in 2021–2023, was set up as a one-factor randomised block design with three replicates, which is a standard number in field experiments. Eight table potato cultivars of varying flesh colour—light yellow, red and purple—were grown. Seed potatoes for the study were obtained in vitro at the Plant Breeding and Acclimatisation Institute—National Research Institute, which were bought by Podlasie Vodka Distillery ‘Polmos’ S.A. Siedlce. The seed potatoes for the experiment were obtained through the co-operation with this company. The forecrop of the potato was winter triticale. Farmyard manure was applied in the autumn at the rate of 25 t·ha⁻¹, and mineral fertilisation with phosphorus and potassium was applied at the following rates: 44.0 kg·ha⁻¹ P (as 46% triple superphosphate) and 124.5 kg·ha⁻¹ K (in the form of 60% potassium chloride salt, granulated). In the spring, before planting the tubers, nitrogen was applied in the amount of 100 kg N per 1 ha (in the form of 34% ammonium salt). Weeds were controlled using the herbicide Bandur 600 SC, whose active substance is aclonifene, at a rate of 2.5 dm³·ha⁻¹. The herbicide was applied approximately 7–10 days prior to potato plant emergence. To control potato blight, three fungicides were applied: Cabrio Duo 112 EC (dimetomorph and pyraclostrobine), Infinito 687.5 SC (propamocarb hydrochloride and fluopicolide) and Carial Star 500 SC (mandiopropamide and difenoconazole). Colorado potato beetle was controlled by means of the insecticide Coragen 200 SC (chlorantraniliprole) and Decis Mega 50 EW (deltamethrin). The season crop management was performed as normally done in the area. Plant protection products were used in accordance with the recommendations of the Institute of Plant Protection—National Research Institute [25]. Potato harvesting was conducted in early and mid-September (technical maturity 99° on the BBCH scale) [26]. The agrotechnological treatments were carried out in accordance with methodological, national recommendations [27,28].

2.4. Meteorological Conditions

Air temperature and rainfall were recorded during the three years of the field experiment. Based on the collected data, the Sielianinow hydrothermal index (K) was calculated (Figure 1) [29].

Weather conditions in the years studied varied, which is reflected in the K index values. In 2021 and 2022, the values of the K index were similar (1.19 and 1.14, respectively), indicating these were relatively dry periods. Rainfall in July, August and September (the months decisive for yield formation) was better distributed in 2021 than in 2022 (

Table 3. Mean air temperature and rainfall total during the potato growing season.

Years	Months
	April (IV)	May (V)	June (VI)	July (VII)	August (VIII)	September (IX)	April–September (IV–IX)
Air temperature (°C)
2021	6.6	12.4	20.4	22.7	17.1	12.9	15.4 mean
2022	7	13.6	19.9	19.3	21	11.8	14.8 mean
2023	8.7	13.4	18	20.3	21.3	18	16.6 mean
Long-term mean (1980–2009)	7.9	11.2	16.7	19.3	18.0	13.0	14.4 mean
Rainfall (mm)
2021	42.0	29.5	33.8	50.0	95.4	42.1	292.8 sum
2022	31.5	31.4	26.5	95.7	39.3	64.9	289.0 sum
2023	12.4	46.5	53.6	31.4	25.0	16.6	185.5 sum
Long-term mean (1980–2009)	49.6	48.2	60.7	45.7	53.0	50.7	307.9 sum

). However, the growing season of 2023 was warm and very dry.

2.5. Tuber Sampling and Laboratory Analyses

Tubers were harvested and their weight per plot was determined in the first half of September, and then the yield per 1 hectare was calculated. Moreover, the tuber sample was taken (10 kilos) to determine yield structure. Just before the potato harvest, random samples were collected from each plot by digging 10 potato plants. Tubers with diameters ≥35 mm and without external and internal defects were considered marketable yield. Marketable quality traits important in the preparation of goods for marketing (packaging) include tuber size [30]. Defective tubers with visible external defects, potatoes with internal defects and tubers below 35 mm in diameter were qualified as by-product yield. Yield determination was the same for all the cultivars. After the potato harvest, tubers were sampled for chemical determinations in the laboratory: 10 tubers with a diameter of 35–60 mm were taken and the dry weight of the tubers and contents of micronutrients, such as iron (Fe), zinc (Zn), manganese (Mn), aluminium (Al) and lithium (Li), were determined. The tubers were carefully washed with tap water and left to dry on paper towel. Then they were cut into smaller pieces and dried in an oven (SIMPLE, producer POL-ECO, Poland) at an initial temperature of 60 °C, and then dried at 105 °C until a constant weight was achieved. The dry matter (DM) content of the tubers was determined according to the Polish standard [31]. Fe, Zn, Mn, Al and Li contents were determined in three replicates. Dry samples of approximately 0.2–0.3 g were digested with 6 mL HNO₃ and 2 mL HCl. The samples and acid mixture were placed in a rotor and heated in the microwave digestion system. Mineralised samples were transferred to the 50 mL flasks through filtering paper and diluted to 50 mL with ultra-pure water. Micronutrients contents were determined with the inductively coupled plasma optical emission spectrometry ICP-OES Spectro Blue (producer—Spectro Inc., Chelmsford, MA, USA, Mid-America Instruments LLC, Edgerton, MO, USA). The micronutrients were quantified by reference to the calibration curve of a multi-element standard solution (VHG, Standard, LGC) in its linear range. Mean micronutrient contents were expressed as milligrams per one kilogram of potato tuber dry matter (DM). The uptake of micronutrients was calculated as the product of the yield of potato tuber dry matter and the content of individual elements (Fe, Zn, Mn, Al, Li).

2.6. Statistical Analysis

The factors tested in the experiment were potato cultivars (eight cultivars with different flesh colour) and years (three growing seasons). The obtained research results were tested via analysis of variance (ANOVA). The significance of differences between mean values was determined using Tukey’s HSD (Honestly Significant Difference) test at the level of p ≤ 0.05. The relationship between the analysed micronutrients (Fe, Zn, Mn and AL) and total amount of water during the growing season, as well as the soil micronutrients content (Fe, Zn and Mn), was determined using the correlation index [32]. For micronutrients in the potato tubers, no correlation was calculated for Li, as the analysis of variance was not significant for this nutrient.

For micronutrient content in the soil, no correlation was calculated for Al and Li, as these micronutrients were not determined in the soil.

3. Results

3.1. Iron Content in Potato Tuber Yield

Iron content in potato tubers depended significantly on the tested cultivars and weather conditions during the growing seasons, and ranged from 37.52–99.33 mg·kg⁻¹ dry matter (Table 3 and

Table 4. The effect of weather conditions on iron (Fe) content in tubers (mg·kg⁻¹ DM) and its uptake with the potato tuber yield (g·ha⁻¹).

Cultivars	Content of Fe				Uptake of Fe
	2021	2022	2023	Mean	2021	2022	2023	Mean
Eurostar	38.95 D	39.93 E	38.72 D	39.20 e	460.4 AB	387.7 ABC	286.1 A	378.1 a
Rote Emmalie	60.59 B	63.27 C	56.30 A	60.05 bc	399.9 AB	361.9 ABC	166.1 AB	309.3 abc
Herbie 26	86.15 A	99.33 A	47.47 BC	77.65 a	319.6 ABC	458.9 A	258.7 AB	345.7 ab
Provita	61.73 B	65.22 C	57.97 A	61.64 b	475.3 AB	431.8 AB	205.5 AB	370.9 a
Salad Blue	50.78 C	52.90 D	49.03 BC	50.90 d	262.0 BC	279.8 BC	223.6 AB	255.1 bc
Blaue Annelise	40.92 D	45.36 E	39.56 D	41.95 e	184.5 C	220.4 C	207.3 AB	204.1 c
Vitelotte Noire	57.10 BC	60.63 C	55.17 AB	57.63 c	268.4 BC	330.5 ABC	157.2 AB	252.0 bc
Bora Valley	70.20 A	75.14 B	37.52 D	60.95 bc	530.0 A	435.8 AB	110.7 B	358.8 a
Mean	58.30 a	62.27 a	47.72 b	56.25	362.5 a	363.3 a	201.9 b	309.2

Means followed by the same letters do not differ significantly at p ≤ 0.05. Means in columns followed by capital letters refer to interactions between cultivars and years. The values in the last ‘Mean’ column and the values in the last ‘Mean’ row (followed by lower case letters) refer to cultivars and years.

). The highest mean values of this trait were obtained for cultivars: Herbie 26 (red flesh), Provita (purple flesh) and Bora Valley (purple flesh), and the lowest being recorded for cultivars: Eurostar (light yellow flesh) and Blaue Annelise (purple flesh). The iron content of potato tubers was significantly affected by weather conditions during the crop’s growing season (Table 3 and Table 4, and Figure 1) The highest iron content was accumulated in 2022, which was relatively dry (mean 62.72 mg·kg⁻¹), followed by 2021 with a similar Sielianinov index (K) (mean 58.30 mg·kg⁻¹). In contrast, moisture and thermal conditions in 2023, which was very dry, did not favour iron accumulation (mean 47.72 mg·kg⁻¹). An interaction of cultivars with the years studied confirms that an accumulation of the component in tubers depended on the meteorological conditions. The highest amount of Fe was found for cultivar Herbie 26 in the favourable year 2022, and the lowest in the tubers of cultivar Bora Valley in 2023.

3.2. Iron Uptake with the Potato Tuber Yield

The uptake of Fe with tuber yield was significantly affected by cultivar and weather conditions during the years studied (Table 3 and Table 4, and Figure 1). Cultivar Eurostar took up the highest average amounts of Fe, whereas the uptake by Blaue Annelise was the lowest. The years 2021 and 2022 were favourable for iron uptake with the potato crop, while 2023 was unfavourable. The highest uptake in 2022 could also be due to the highest total content of this micronutrient in the soil—1620 mg·kg⁻¹ (Table 1). There was also a significant interaction of cultivars with the years studied, which was also largely determined by tuber yields, with the highest Fe uptake recorded for cultivar Eurostar in 2021.

3.3. Zinc Content in Potato Tuber Yield

Zinc content in tubers depended significantly on cultivars and weather conditions during the potato growing season, and ranged from 11.31 to 19.22 mg·kg⁻¹ dry matter (Table 3 and

Table 5. The effect of weather conditions on zinc (Zn) content in tubers (mg·kg⁻¹ DM) and its uptake with the potato tuber yield (g·kg⁻¹).

Cultivars	Content of Zn				Uptake of Zn
	2021	2022	2023	Mean	2021	2022	2023	Mean
Eurostar	17.00 A	19.22 A	9.39 D	15.20 bc	200.9 A	186.6 A	69.4 A	152.3 a
Rote Emmalie	16.93 A	17.85 A	15.80 A	16.86 a	111.7 B	102.1 B	46.61 B	86.8 bc
Herbie 26	16.45 AB	18.92 A	12.48 BC	15.95 a	61.0 B	87.4 B	68.0 B	72.1 bcd
Provita	14.95 BC	15.53 B	14.21 A	14.90 cd	115.1 B	102.8 B	50.4 B	89.4 b
Salad Blue	13.20 C	14.14 BC	11.88 BCD	13.07 e	68.1 B	74.8 B	54.2 B	65.7 bcd
Blaue Annelise	16.97 A	19.16 A	6.73 E	14.29 d	76.5 B	93.1 B	35.3 B	68.3 bcd
Vitelotte Noire	13.38 C	13.42 C	13.37 AB	13.39 e	62.9 B	73.1 B	38.1 B	58.0 d
Bora Valley	12.27 C	11.31 D	11.91 BCD	11.83 f	92.6 B	65.6 B	35.1 B	64.4 bcd
Mean	15.14 a	16.19 a	11.97 b	14.43	98.6 a	98.2 a	49.6 b	82.1

Means followed by the same letters do not differ significantly at p ≤ 0.05. Means in columns followed by capital letters refer to interactions between cultivars and years. Values in the last ‘Mean’ column and the values in the last ‘Mean’ row (followed by lower case letters) refer to cultivars and years.

). The highest average content was recorded in the red-fleshed cultivars Rote Emmalie and Herbie 26, and the light yellow-fleshed cultivar, Eurostar. The lowest accumulation of the mineral in question was found in the warmest and very dry year 2023, and significantly higher in the other years studied. An interaction between cultivars and years indicates a different response of cultivars to environmental conditions.

3.4. Zn Uptake with Potato Tuber Yield

Similar to the previous micronutrients, Zn uptake was influenced by cultivars and years studied, and by an interaction between the discussed factors (Table 3 and Table 5, and Figure 1). The highest mean Zn uptake in all years studied was found for cultivar Eurostar, and the lowest for cultivar Bora Valley. The lowest amount of this nutrient was taken up by tubers in 2023, it being affected by the content and yield harvested, and probably also by the lowest soil Zn content. Significantly higher, yet very similar, amounts of Zn were taken up by tubers in 2021 and 2022.

3.5. Manganese Content in Potato Tuber Yield

In the experiment reported here, manganese content varied, ranging from 1.84 to 16.49 mg·kg⁻¹ dry matter, and was significantly affected by cultivar, weather conditions and cultivar x year interaction (Table 3 and

Table 6. The effect of weather conditions on manganese (Mn) content in tubers (mg·kg⁻¹ DM) and its uptake with the potato tuber yield (g·kg⁻¹).

Cultivars	Content of Mn				Uptake of Mn
	2021	2022	2023	Mean	2021	2022	2023	Mean
Eurostar	9.10 A	8.78 A	16.49 A	11.46 a	107.6 A	85.3 A	121.9 A	104.9 a
Rote Emmalie	2.20 G	1.84 G	7.10 F	3.71 h	14.5 B	10.5 B	20.9 D	15.3 d
Herbie 26	4.61 D	4.64 C	14.70 C	7.98 d	17.1 B	21.4 B	80.1 B	39.5 bc
Provita	5.40 C	5.29 B	15.14 B	8.61 c	41.6 B	35.0 B	53.7 BC	43.4 b
Salad Blue	6.10 B	5.38 B	15.24 B	8.91 b	31.5 B	28.5 B	69.5 B	43.2 b
Blaue Annelise	3.20 F	2.20 F	10.16 E	5.19 g	14.4 B	10.7 B	53.2 BC	26.1 cd
Vitelotte Noire	3.23 EF	2.86 E	13.23 D	6.44 f	15.2 B	15.6 B	37.7 CD	22.8 d
Bora Valley	3.50 E	3.67 D	14.53 C	7.23 e	26.4 B	21.3 B	42.9 CD	30.2 bcd
Mean	4.67 b	4.33 b	13.32 a	7.44	33.5 b	28.5 b	60.0 a	40.7

Means followed by the same letters do not differ significantly at p ≤ 0.05. Means in columns followed by capital letters refer to interactions between cultivars and years. Values in the last ‘Mean’ column and the values in the last ‘Mean’ row (followed by lower case letters) refer to cultivars and years.

). The highest average Mn accumulation in tubers was determined for the light yellow-fleshed Eurostar (11.46 mg·kg⁻¹). This cultivar accumulated the highest Mn amount in all the years studied. In contrast, the lowest quantity of this micronutrient was recorded in the tubers of the Rote Emmalie cultivar, which had red flesh.

An analysis of the impact of weather conditions showed that these marked variation. In 2023 year, which was very dry, Mn accumulation in tubers was about three times as high as in the other years, which were relatively dry. The confirmed interaction of cultivars and years studied indicates a significant response of cultivars to air temperatures and rainfall that occurred during crop growth and development.

3.6. Manganese Uptake with Potato Tuber Yield

Similar results were observed for Mn uptake with tuber yield. Cultivars Eurostar and Rote Emmalie took up, respectively, the most and the least Mn, the highest amounts being taken up with tuber yield in 2023, and significantly lower quantities in 2021 and 2022 (about twice as low). There was also confirmed a significant interaction of cultivars with years studied (Table 3 and Table 6, and Figure 1).

3.7. Aluminium Content in Potato Tuber Yield

In the present study, aluminium accumulation in tubers fell within the range of 38.37 to 99.97 mg·kg⁻¹, and the values were significantly affected by test cultivars and weather conditions during the study period (Table 3 and

Table 7. The effect of weather conditions on the aluminium (Al) content in tubers (mg·kg⁻¹ DM) and its uptake with the potato tuber yield (g·kg⁻¹).

Cultivars	Content of Al				Uptake of Al
	2021	2022	2023	Mean	2021	2022	2023	Mean
Eurostar	60.13 C	61.87 E	38.74 C	53.58 f	710.7 A	600.8 A	286.3 A	532.6 a
Rote Emmalie	64.20 BC	65.37 DE	63.17 A	64.25 cd	423.7 BC	373.9 BC	186.4 A	328.0 bcd
Herbie 26	66.13 BC	70.00 CD	38.37 C	58.17 e	245.3 CD	323.4 BC	209.1 A	259.3 cd
Provita	70.10 B	70.83 CD	60.89 A	67.27 c	539.8 A	468.9 AB	216.2 A	408.3 ab
Salad Blue	68.21 B	70.12 CD	43.68 BC	60.67 de	352.0 BC	370.9 BC	199.2 A	307.4 bcd
Blaue Annelise	42.88 D	44.03 F	46.26 B	44.39 g	193.4 D	214.0 C	242.4 A	216.6 d
Vitelotte Noire	96.40 A	80.50 B	65.67 A	80.86 a	453.1 BC	438.7 B	187.2 A	359.7 bc
Bora Valley	99.07 A	91.00 A	39.52 BC	76.53 b	748.0 A	527.8 A	116.6 A	464.1 ab
Mean	70.89 a	69.22 a	49.54 b	63.22	458.2 a	414.8 a	205.4 b	359.5

Means followed by the same letters do not differ significantly at p ≤ 0.05. Means in the columns followed by capital letters refer to interactions between cultivars and years. Values in the last ‘Mean’ column and the values in the last ‘Mean’ row (followed by lower case letters) refer to cultivars and year.

).

The highest average amounts of Al were determined in the tubers of cultivar Vitelotte Noire (80.86 mg·kg⁻¹) and the lowest in cultivar Blaue Annelise (44.39 mg·kg⁻¹). The relatively dry years 2021 and 2022 contributed to an accumulation of this nutrient, while in the very dry year 2023, the Al content was significantly lower. An interaction between cultivars and years studied was found, confirming that the lowest Al amounts were in cultivar Herbie 26 tubers in 2023, and the highest in cultivar Bora Valley in 2021.

During all three years studied, the light yellow-fleshed cultivar Eurostar accumulated the highest amounts of Al in yield, it being the lowest for the purple-fleshed Blaue Annelise (Table 7).

3.8. Aluminium Uptake with the Potato Tuber Yield

The smallest amounts of aluminum were taken up with the potato tuber yield in 2023, with them being significantly higher in 2021 and 2022.

3.9. Lithium Content in Potato Tuber Yield

Lithium content in potato tubers ranged from 0.70 to 0.83 mg·kg⁻¹, and it was significantly affected only by the cultivar grown (

Table 8. The effect of weather conditions on lithium (Li) content in tubers (mg·kg⁻¹ DM) and its uptake with the potato tuber yield (g·kg⁻¹).

Cultivars	Content of Li				Uptake of Li
	2021	2022	2023	Mean	2021	2022	2023	Mean
Eurostar	0.75 A	0.77 A	0.70 A	0.74 b	8.86 A	7.48 A	5.17 A	7.17 a
Rote Emmalie	0.71 A	0.71 A	0.70 A	0.71 c	4.69 BC	4.06 B	2.07 B	3.61 b
Herbie 26	0.81 A	0.83 A	0.71 A	0.78 a	3.01 C	3.84 B	3.82 B	3.56 b
Provita	0.70 A	0.71 A	0.70 A	0.70 c	5.39 B	4.70 B	2.49 B	4.19 b
Salad Blue	0.71 A	0.72 A	0.70 A	0.71 c	3.66 C	3.81 B	3.19 B	3.55 b
Blaue Annelise	0.71 A	0.70 A	0.70 A	0.70 c	3.20 C	3.40 B	3.67 B	3.42 b
Vitelotte Noire	0.75 A	0.77 A	0.70 A	0.74 b	3.53 C	4.20 B	2.00 B	3.24 b
Bora Valley	0.78 A	0.79 A	0.70 A	0.76 ab	5.89 B	4.58 B	2.07 B	4.18 b
Mean	0.74 a	0.75 a	0.70 a	0.73	4.78 a	4.51 a	3.06 a	4.12

Means followed by the same letters do not differ significantly at p ≤ 0.05. Means in columns followed by capital letters refer to interactions between cultivars and years. Values in the last ‘Mean’ column and the values in the last ‘Mean’ row (followed by lower case letters) refer to cultivars and years.

).

3.10. Lithium Uptake with Potato Tuber Yield

Analysis of variance showed that an uptake of lithium with tuber yield depended significantly on cultivar and the interaction of cultivars with years studied (Table 3 and Table 8). Cultivar Eurostar accumulated the highest Li amount (mean 7.17 g·ha⁻¹), while the other cultivars took up significantly less lithium (mean 3.24–4.19 g·ha⁻¹). The response of cultivars to weather conditions showed that cultivar Eurostar took up the most Li in all the years studied, whereas the uptake by cultivar Vitelotte Noire was the lowest in the very dry year of 2023.

3.11. Correlation Index

The correlation results presented in

Table 9. The correlation index between the analysed micronutrients (Fe, Zn, Mn and AL) and total amount of water during the growing season, as well as soil micronutrients content (Fe, Zn and Mn).

Studied Feature	Fe	Zn	Mn	Al
Total rainfall in the years studied 2021–2023	+0.94906	+0.96106	−0.99751	+0.99918
Soil nutrients content (Fe, Zn, Mn)	−0.47930	+0.98800	+0.99999	-

showed a significant, positive relationship between total rainfall in the study seasons and the Fe, Zn and Al content of potato tubers. The correlation between total rainfall and the amount of Mn in the tubers was negative, which means that the higher the amount of rainfall, the lower the content of this micronutrient in the potato tubers.

A significant correlation was also found between the micronutrients content of the soil and their content in the potato tubers. For Zn and Mg, it was a significant correlation, and for Fe it was a negative one (Table 9).

3.12. Mean Daily Intake of Iron, Zinc and Manganese with a Potato Diet

In the study reported here, iron content in the tubers of test potato cultivars averaged 56.25 mg·kg⁻¹ dry matter, or 1.15 mg·100 g⁻¹ fresh matter. According to the European Food Safety Authority [33], the daily requirement for Fe is 7.0–16.0 mg, and according to Polish standards [34], it is 10–18 mg. Consumption of 100 g of potato tubers therefore constitutes, respectively, 7–16% and 6–11.5% of the required amount (

Table 10. Mean daily intake of iron, zinc and manganese with a potato diet.

Micronutrient	Mean in Dry Matter (mg·kg−1)	Mean in Fresh Matter (mg·100 g−1)	Dietary Reference Intake/Day * (mg)	Dietary Reference Intake/Day ** (mg)	Percent of Realisation
					[33,35,36]	[34]
Iron	56.25	1.15	7.0–16.0	10–18	7–16	6–11.5
Zinc	14.43	0.30	7.5–16.3	8–11	2–4	3–4
Manganese	7.44	0.15	3.0	1.8–2.3	5	6.5–8

* [33,35,36], ** [34].

).

Mean zinc content was 0.30 mg·100 g⁻¹ fresh weight, and the reference intake/day in mg is 7.5–16.3 mg according to the European Food Safety Authority [35], and 8–11 mg according to Polish standards [34]. Thus, a portion of 100 g of tubers consumed per day supplies the human body with 2–4% and 3–4% Zn, respectively, which are very similar amounts (Table 10).

Manganese content was, on average, 0.15 mg in 100 g⁻¹ fresh weight, and the daily human requirement for these elements is 3.0 mg [36] and 1.8–2.3 mg per day [34]. With the given recommended daily standard, the consumption of 100 g of potatoes covers the daily requirement for Mn in 5 and 6.5–8% (Table 10).

4. Discussion

Mineral nutrients are an important part of a healthy diet, and their deficiency can lead to hidden hunger, which is becoming a global health problem [37]. These nutrients participate in the structural processes of the body [7]. Humans require at least 22 mineral elements for well-being [38]. Hence, Solanum tuberosum, as a major table crop due to its relatively high content of some macroelements and a small amount of micronutrients essential for the human body, can play an important role in offsetting deficiencies of minerals such as Fe, Zn and Mn [15]. Iron is essential for all living organisms. Among other things, it is involved in cellular respiration and electron transport, and is an essential component of hemoglobin and respiratory enzymes. Fe is also essential for the proper conduction of impulses in the central nervous system, and its deficiency can lead to anemia, cognitive dysfunction, or memory impairment [16,21,37,38]. In the study reported here, Fe content in potato tubers ranged from 37.52 to 99.33 mg·kg⁻¹ dry matter, and it was higher in red-fleshed tubers than in white- and purple-fleshed tubers. It was also demonstrated that red-fleshed tubers accumulated more Fe than white-/cream- and yellow-fleshed cultivars [39]. Similar Fe content in potatoes was found by other researchers who reported ranges from 63.24 to 94.57 mg·kg⁻¹ dry matter, depending on cultivar [40], 23.96–30.99 mg·kg⁻¹ dry matter [20], and 40.68–63.42 mg·kg⁻¹ dry matter, according to Wierzbowska et al. [17]. The research discussed here showed that the concentration of Fe and its uptake with tuber yield were influenced by cultivars and weather conditions in the years studied. A significant effect of cultivars and weather conditions on this trait was reported by Gugała et al. [19], Zhou et al. [20], Sawicka et al. [40] and Mystkowska [41]. Furthermore, Wierzbicka and Trawczyński [42], as well as Lal et al. [21], reported that the micronutrient content of potato cultivars and their uptake were significantly influenced by environmental growing conditions and soil abundance. This is in line with the present study as both Fe content and uptake were the highest in 2022 and when soil Fe abundance was also the highest. Karan [2], Dereje and Chibuzo [15], Karan [2] and Pandey et al. [18] highlighted that, unlike cereals and many vegetables, the bioavailability of iron contained in Solanum tuberosum tubers is high due to very low levels of phytic acid which limits iron absorption, thus making them a good source of this nutrient. Bioavailability is a measure of the extent to which nutrients provided in food are absorbed and utilised by the human body.

After iron, zinc is the next micronutrient that has many functions in the body: it is an activator of various enzymes, it participates in the metabolism of proteins and carbohydrates, as well as the synthesis and degradation of necrotic acids; it also contributes to flavour [12,16,43]. In the present study, Zn content ranged from 11.31 to 19.22 mg·kg⁻¹ dry matter, which is consistent with the results of Zhou et al. [20] (20.02–30.73 in 14 cultivars), Saar-Reismaa et al. [9] (9.81–26.01—in 21 cultivars) and Singh et al. [37] (12.33–33.87 mg·kg⁻¹ DM in 37 cultivars). In the research reported here, the content of this nutrient and its uptake with the tuber yield depended on cultivar and weather conditions in the years studied. On average, tubers accumulated 14.43 mg·kg⁻¹ of Zn, the highest amount being determined in cultivars with red and light yellow flesh. According to Saar-Reismaa et al. [9], cultivars with yellow and red flesh had a higher amount of Zn than those with purple flesh, which matches the results of the present study. In contrast, Dalamu et al. [39] showed that cultivars with red and purple flesh accumulated more Zn than those with yellow and white/cream flesh. Similar amounts of Zn were contained in the tubers in the study by Mystkowska and Rogóż-Matyszczak [44], with an average of 13.39 mg·kg⁻¹; these authors [44] also found that Zn content and uptake with yield depended on cultivar and weather conditions, with the highest values being obtained in the year with the highest rainfall and lowest average air temperature, which confirms the present results.

Manganese is a component and activator of numerous enzymes involved in the synthesis of proteins and fatty acids. As a component of antioxidant enzymes, it provides the body’s defence shield against free radicals, and thus against oxidative stress. It is essential for the proper functioning of the nervous system, the formation of connective tissue and the maintenance of normal skin condition. Therefore, Mn is an ingredient in many dietary supplements [34,45,46]. In the study discussed here, Mn concentration ranged from 1.84 to 16.49 mg·kg⁻¹ and depended significantly on cultivar, weather conditions in the years studied and their interaction with the cultivars. The greatest amounts of Mn were accumulated and taken up with the yield by cultivar Eurostar tubers in all years studied, and the smallest by tubers of the Rote Emmalie cultivar which had red flesh. The highest content and uptake with yield was recorded in a very dry year. Also, Sawicka et al. [40] showed that the amount of this component depended on cultivar, production system and conditions in the years studied. Zhou et al. [20] found higher amounts of Mn in yellow-fleshed cultivars compared with white-fleshed ones, which ranged from 8.15 to 14.95 mg·kg⁻¹. In the experiments of Saar-Reismaa et al. [9], Mn content was relatively low (5.26–12.04 mg·kg⁻¹), similar to the present study. The aforementioned authors [9] observed more Mn in dark violet and dark yellow-fleshed cultivars compared with other colours. Singh et al. [37], studying 37 cultivars that were grown under uniform conditions, reported substantial differences in Mn content (from 7.27 to 29.67 mg·kg⁻¹), with higher amounts being found in tubers with white and cream flesh than in those with darker flesh. They also claimed that differences in mineral concentrations indicate that different cultivars have different genetic capacities for micronutrient accumulation. Wekesa et al. [47] emphasised that the accumulation and uptake of minerals in tubers depend on soil type, soil content and climatic conditions. Pandey et al. [18] stated that the genetic basis of mineral content in potatoes with different flesh colours is still poorly understood, and their study was one of the few genome-wide studies on mineral content in tetraploid potatoes. Hence, Singh et al. [37] believe that, with modern agronomic practices and plant-breeding strategies, mineral-rich potato cultivars should be sought. Chemical elements are often an essential part of the diet. However, many of them, including aluminium and lithium, do not provide proven nutritional benefits, and their consumption in excess causes health risks, while in large quantities they can be toxic [48,49,50]. Aluminium is one of the most common metals on Earth, ranking third after oxygen and silicon, and first among metals, making it a common component of plants. The negative effects of Al on plants are associated, among other things, with adverse impacts on the availability of calcium and magnesium ions, and excess Al causes stunted root growth and reduced plant weight gain. Table plants also contain Al, including spinach (104), oats (82), onions (63) and potatoes (45 mg·kg⁻¹ of dry matter), but its excess poses a risk to human health [51]. According to the medical literature, the accumulation of aluminium can be found in people with renal impairment or undergoing haemodialysis [52,53]. In the study reported here, Al content ranged from 42.88 to 99.07 mg·kg⁻¹ dry matter and was affected by cultivar and weather conditions during the growing season. There are few studies on the presence of Al in potato tubers. Vidlak [54] reported an Al value of 76.0 mg·kg⁻¹ dry matter, Melnikov et al. [55] found the level of 1.99 mg·kg⁻¹ wet weight in potato tubers, Gunko et al. [56] determined a range of 18.76–51.89 mg·kg⁻¹ dry matter, depending on cultivar, and Bedoya-Perales et al. [57] reported a range of 3.65–30.80 mg·kg⁻¹ dry matter, depending on cultivar and location of the study. The results of the study discussed here were similar to those AL values in potato tubers.

Lithium is the lightest metal widely distributed in nature [51,58]. It is toxic to plants and animals when it occurs in high concentrations in soil and plants. Various studies have reported negative and positive effects of Li on plant growth. Hawrylak-Nowak [59] and Shahzad et al. [60] found that Li interferes with numerous metabolic processes, such as photosynthesis, DNA biosynthesis, enzyme activation in plants and the breakdown of chloroplast structure; its high concentration causes a significant reduction in plant growth. Jiang et al. [61] noted that, at low concentrations, Li showed various positive effects, including increased root and shoot biomass. According to Tanveer et al. [62], Li is a non-essential element for plants and its biological relevance has not yet been fully identified. Emsley [51] stated that the human body has no biological requirement for lithium, but it is found in every-day food. However, only some is absorbed and most is excreted. After ingestion, lithium is moderately toxic, but there are large differences in tolerance. Długaszek et al. [63] claims that Li is an element that is needed for the normal functioning of the human body, but there is little information about the amount of Li in food and the quantity consumed. The main Li sources in the diet are cereals, potatoes, tomatoes, spinach, cabbage and some mineral waters. According to Emsley [51], plants in the Solanaceae family, which includes the potato, have the highest Li content, up to 30 mg·kg⁻¹ dry matter, corn grain about 0.05, lettuce 0.3 and cabbage 0.5 mg·kg⁻¹ dry matter. In the present study, Li content averaged 0.74 mg·kg⁻¹ dry matter, and it was stable in all the years studied. Rogóż and Wiśniowska-Kielian [64] reported that Li content in the storage organs of vegetables was: 0.63, 0.81 and 1.08 mg·kg⁻¹ dry matter in parsley, carrot and beetroot, respectively, and these values were similar to the results of the study reported here. Currently there are no data on Li content in potato tubers.

Potato tubers have been in the human diet for thousands of years. Solanum tuberosum tubers are readily available throughout the year and have become a staple food in the world. Moreover, potatoes are a staple of diets, are the most widely consumed vegetable and have the highest daily intake compared to other vegetables [13,65]. The nutritional value of potato tubers, in addition to protein, carbohydrates and vitamins, is also determined by the content of macronutrients and micronutrients which, after digestion and absorption into the bloodstream, are used for the proper maintenance of the body [66]. According to the European Food Safety Authority [33,35,36], the human body’s requirement for iron, zinc and manganese is 7–16, 7.5–16.3 and 3.0 mg per day, respectively. In the presented studies, consumption of 100 g of potato tubers covered the daily demand for these micronutrients in 7–16, 2–4 and 5%, respectively. On the other hand, according to Polish standards [34], the daily coverage of the requirement for the mentioned elements was, respectively: 6–11.5, 3–4 and 6.5–8%. In Poland, potato consumption in 2022 was 86 kg per capita per year, i.e., 235 g per day, which means coverage of the demand for the minerals in question was higher [1]. According to Leszczyński [67], it was shown many years ago that the consumption of 200 g of potato covers up to 30% of the daily iron requirement. Other authors have also investigated to what extent the consumption of 100 g of tubers per day makes it possible to achieve the standard for the more important micronutrients [15,19,66,68,69]. Rubio et al. [68] found that the potato covers the human requirement for Fe and Mn at 6 and 9%, and Wierzbicka [66] noted the realisation of the daily requirement for Fe, Zn and Mn was 12, 2–3 and 6–8%, respectively. Gugala et al. [19] reported that for Fe and Mn, the realisations were 9 and 21%, Dereje and Chibuzo [19] found that for Fe and Zn these were 6 and 2%, and Zarzecka et al. [69] found that for Mn this was 7–9.1%. The coverage levels of Fe, Zn and Mn requirements calculated in our work are close to the literature values given above. In addition, Dereje and Chibuzo [15] emphasised the importance of the fact that most minerals are stable and they are well-preserved after cooking and roasting potato tubers.

Al and Li, which were also determined in the present study, are not considered essential and, in higher amounts, are harmful and pose a risk to human health [50,52]. According to the Bundesinstitut für Risikobewertung—BfR [70] (Federal Institute for Risk Assessment), for the risk assessment of aluminium intake, the tolerable weekly intake (TWI) established by the European Food Safety Authority (EFSA) is 1 milligram of aluminium per one kilogram of body weight [49]. Walton [53] stated that this is a dose that most residents of modern industrialised societies routinely exceed. According to Simonsen et al. [71], aluminium is formally classified as a substance with pronounced neurotoxic effects. Li is also listed as a mineral pollutant, and in the future it could become a serious, dangerous soil and plant pollutant [60]. However, a fundamental challenge in relation to the chemical composition of raw plant materials and food is the long-standing principle in medicine of ‘first do no harm’ (Latin: primum non nocere) [72].

5. Conclusions

The study showed that the genetic characteristics of the cultivars determined the content and uptake with tuber yield of the determined micronutrients. In the group of tested minerals that are important for human nutrition (Fe, Zn, Mn), red- and purple-fleshed cultivars accumulated more Fe than the light yellow-fleshed Eurostar. Red-fleshed cultivars contained more Zn than light- and purple-fleshed cultivars, while Mn content was the highest in the tubers of the light yellow-fleshed Eurostar, and the lowest in the red-fleshed Rote Emmalie. The content and uptake with yield of Fe, Zn, Mn and Al were influenced by weather conditions during the growing season. Significantly higher values for these characteristics were found in 2021 and 2022, which were relatively dry years, except for Mn, compared with the very dry 2023. Information about minerals in potato cultivars with different flesh colours can help increase consumer acceptance and sales potential of these cultivars and newly registered cultivars being introduced into cultivation.

The cultivation of potato with coloured flesh can be an interesting alternative to traditional cultivars, offering farmers an opportunity to diversify their crops and attract new customers. Due to their unique aesthetic qualities, such potatoes can attract the attention of restaurants, health food shops and consumers looking for unusual products. Their health benefits and variety of flavours are worth promoting. Potatoes which have coloured flesh are rich in antioxidants such as anthocyanins providing health benefits due to their anti-cancer, anti-inflammatory and antioxidant properties. For this reason, they can be particularly important for breeding programs that use crossbreeding techniques to combine the best characteristics of different cultivars. Breeding potatoes with coloured flesh often requires international collaboration, and this approach accelerates the breeding progress and enables new cultivars to be brought to the market more quickly. These programs contribute to increasing crop diversity and providing products of high nutritional value.

Potatoes with coloured flesh have great potential in the food industry due to their unique sensory, health and aesthetic characteristics. They can be an attractive addition to a variety of dishes and can be used for various types of snack (e.g., chips). They can also offer a component in frozen vegetables.