Comparative Study of the Quality of New Potatoes Imported from the Mediterranean Area

This paper presents the comparison of the quality of new potatoes imported from the Mediterranean area during the winter­spring period. The study material included the new potatoes imported from Cyprus, Egypt, Israel, Spain and Morocco, purchased in Poland, from the beginning of February to the end of May. The laboratory analyses were performed on a total of 162 potato samples. The dry matter content in the new potatoes imported from Spain and Morocco was higher than in the potatoes originating from Cyprus, Egypt or Israel. The dry matter content in the new potatoes imported from Cyprus, Egypt, and in the majority of new potatoes imported from Israel did not differ significantly. PCA showed that the potatoes which had more dry matter contained more L ascorbic acid but less total sugars. The least L-ascorbic acid content and the lowest protein content were determined in the ‘Nicola’ potatoes imported from Israel and ‘Excellency’ tubers imported from Spain. The amounts of L-ascorbic acid and protein in the remaining potato samples tested were at a similar level. The potatoes of the same variety imported from different countries did not differ in terms of L-ascorbic acid content. The ‘Maris Peer’ tubers imported from Spain had more protein than those originating from Israel. The starch contents in new potatoes imported from Israel and Cyprus were lower compared with the tubers from Egypt, Spain and Morocco. The potatoes which had more starch had higher dry matter contents and more monosaccharides. The highest starch content was de­ termined in the ‘Excellency’ potatoes, which represent the floury cooking type, imported from Spain or Morocco. The ‘Excellency’ tubers imported from Morocco had more total sugars and monosaccharides than the potatoes imported from Spain. All of the tested potato varieties had a very low susceptibility to the after­cooking darkening.


INTRODUCTION
Early potato is a typical product of Medi terra nean countries exported to central and northern European markets (Foti, 1999, Timpanaro, 2003, Ierna, 2010).In the climate of the Mediterranean area, potatoes are mainly grown as an off-season crop growing over the winterspring months (planting from December to January and har vesting from March to early June) or summer autumn months (planting in early September and harvesting from November to the end of January).Frequently, two crops are grown a year (Timpanaro, 2003, Ierna, 2010, Sgroi et al., 2014).The different climate conditions can have an ef fect on the tuber quality.The potato tuber quality is influenced by many factors including produc tion area, variety, soil and climate, agronomic practices, harvest time and commercialisation conditions (Mustonen, 2004, Ierna and Melilli, 2014, Trawczyński, 2016, Wegener et al., 2017).The production of two early potato harvests in the Mediterranean area requires the varieties which can adapt to the climatic conditions (Frusciante et al., 1999).Cultivation is carried out over the sum merautumn period and based on the seedtubers produced locally in the previous spring, and over the winterspring period when the seedtubers of foreign varieties from northern European coun tries like Belgium, Holland or Germany are used (Timpanaro, 2003, Ierna, 2010).'Spunta' is the most common variety grown in the Mediterranean area in both the summerautumn and winterspring seasons (Ierna andMauromicale, 2006, Buono et al., 2009).Potatoes are an excellent source of many bioactive components in the human diet.In our diet, a typical meal of 200 g of boiled po tatoes (at least three medium sized tubers) will contribute 9% of the Guideline Daily Amount (GDA) of protein, 11% of carbohydrates, 11% of dietary fibres, up to 28% of potassium, 18% of phosphorus and 15% of magnesium as well as 47% of the Recommended Dietary Allowance (RDA) of vitamin C (Haase, 2008, Leszczyński, 2012, Visvanathan et al., 2016).In the early po tato production in the Mediterranean area, in both off season crops, delaying the tuber harvest in creased yield and improved the tuber quality by an increase in dry matter content (Ierna, 2010).When the harvest time is delayed, the ascorbic acid content increases in a winterspring crop, but decreases in a summerautumn crop.The re verse is observed for nitrates (Ierna, 2010, Ierna andMelilli, 2014).This reversed trend could be caused by a reduction in sunlight intensity and daylength during the potato season (Ierna, 2010, Lee andKader, 2000).When the harvest date was delayed, phenolics in tubers decreased in both growing seasons (Ierna and Melilli, 2014).Harvest time affects sucrose and reducing sugar content in tubers (Mustonen, 2004).The nutrient content in potatoes depends on a number of fac tors, with variety being among the most important (Burlingame et al., 2009).New potatoes are har vested at an early growth stage, and have higher concentrations of some phytonutrients than ma ture tubers (Navarre et al., 2010).In recent years, there has been an increase in demand for new potatoes imported from the Mediterranean area which prompts a need to analyse their nutritional value in the aspect of a healthy diet.The aim of the study was to compare the quality of new pota toes imported from the Mediterranean area during the winterspring period.

Plant material
The study material included the new potatoes imported from the Mediterranean area.The po tatoes were sampled from small local greengro cer's shops and from supermarkets belonging to the major food retail chains in Poland, located in Siedlce.The samples were taken once a week from the beginning of February to the end of May.On each occasion, three samples of each variety of new potato imported from various countries, each weighing approximately 1.5 kg, were pur chased.The laboratory analyses were performed on a total of 162 potato samples.In total, six po tato varieties imported from five countries were analysed (Table 1).The potatoes purchased in February originated from Cyprus (n=15), in March and April from Cyprus (n=45), Egypt (n=18) and Israel (n=33), and in May from Cyprus (n=27), Spain (n=15), Israel (n=6) and Morocco (n=3).Over fifty percent of the examined sam ples of new potatoes were grown in Cyprus.Only the potatoes imported from Cyprus exhib ited the characteristics of early potatoes, consis tent with United Nations Economic Commission for Europe Standard FFV52 (UNECE Standard FFV52) concerning the marketing and commer cial quality control of early and ware potatoes, i.e. they were harvested before they reached complete maturity, marketed immediately after their har vesting, and whose skin could be easily removed without peeling.The other potatoes introduced to the market as new potatoes were harvested after completely mature, had corky skins, and were washed and packed.

Laboratory analysis
Fresh potatoes were analysed immediate ly after sampling.The dry matter content was All analyses were performed twice, and the re sults were expressed as g or mg per 1 kg of fresh weight (FW) of potatoes.The after-cooking dark ening of potatoes was also determined.The as sessment of potato aftercooking darkening was performed after 10 minutes and 2 hours following boiling in water, using the 9point Danish scale on which 9 means no darkening and 1 denotes the strongest darkening.The assessment of potato aftercooking darkening was conducted on ten tubers (Roztropowicz 1999).All analyses were carried out at the laboratory of Department of Vegetable Crops, Siedlce University of Natural Sciences and Humanities, Poland.

Statistical analysis
The results of the study were analysed statis tically by means of onefactor ANOVA in which the cultivars from different countries (Spunta from Egypt, Excellency from Spain, Excellency from Morocco, Maris Peer from Spain, Maris Peer from Israel, Nicola from Israel, Orchestra from Israel, and Sifra from Israel) were the ex perimental factor.The significance of differences was checked using Tukey's test at p=0.05.
A multidimensional principal component analysis (PCA) and cluster analysis (Badenes et al., 2000, Lotti et al., 2008) were carried out to compare the quality of new potatoes imported from various countries.As the variables used in the analysis had different units, they were stan dardised.The number of components considered was selected based on the Kaiser's criterion ac cording to which only the variables with the value greater than 1 are analysed (Iezzoni andPritts, 1991, Lotti et al., 2008).Such components carry only the most significant information which re flects variation of the objects so they were used in the second part of the analysis -cluster anal ysis.Euclidean distance was used as a measure of distance between objects and Ward's proce dure as an agglomeration method (Nikolic et al., 2010).The intersection point was determined ap plying the Mojena's rule (Rymuza and Bombik, 2012).Statistical analysis was performed using Statistica 12.0 PL for Windows.

RESULTS AND DISCUSSION
The dry matter content in the tested new po tato samples ranged from 14.4 to 21.36%, de pending on the cultivar and country of origin (Table 2).The least dry matter was determined in the 'Maris Peer' and 'Nicola' tubers imported from Israel.The 'Orchestra' and 'Sifra' potatoes imported from the same country contained more dry matter, on average, by 2.12% and 2.78%, re spectively, compared with 'Maris Peer'.The dry matter content in 'Maris Peer' potatoes originat ing from Spain was higher, on average, by 4.76% than in the potatoes of the same variety imported from Israel.The 'Excellency' potatoes imported from Spain and Morocco had a similar dry mat ter content, the same finding being detected for the 'Spunta' potatoes imported from Cyprus and Egypt.In general, the dry matter content in the new potatoes imported from Cyprus, Egypt and in most tubers imported from Israel did not differ significantly.The dry matter content in the new potatoes imported from Spain and Morocco was higher than in the tubers originating from Cyprus, Egypt or Israel.The new potatoes imported from Spain and Morocco contained a similar amount of dry matter.The dry matter content is one of important characteristics of new potatoes.When tubers are harvested very early, low dry matter content can result in a soggy tuber texture, and decrease the quality of new potatoes (Mustonen, 2004).The dry matter content in potato tubers depends on variety and harvest time.Under the environmental conditions of southern Italy, the dry matter content in the 'Spunta' potatoes amounted to 168 g kg 1 FW at 90 days after plant ing in the winterspring crop and 153 g kg 1 FW at 80 days after planting in the summerautumn crop.Potato harvest delayed by 25-30 days re sulted in an increase in the dry matter content of 10 g kg 1 FW (6%) in the winter-spring crop, and of 15 g kg 1 FW (10%) in the summer-autumn crop (Ierna, 2010).The dry matter content in potato tubers is affected by temperature and day-length during the potato growing season, radiationuse efficiency (Kooman et al., 1996) as well as some physiological indicators of plant growth such as assimilation leaf area and the chlorophyll content in leaves (Sawicka et al., 2015).When the potato production in the Mediterranean area takes place over the winterspring period, potatoes begin to grow when temperatures are relatively low and daylengths short, and growth continues at in creasing temperatures, daylength and irradiation (Ierna, 2010).
The L-ascorbic acid content in the tested po tato samples ranged from 115.6 to 133.4 mg kg 1 FW, and protein content from 15.00 to 21.26 g kg 1 FW (Table 2).Assuming that daily potato consumption is approximately 150-200 g (at least three mediumsized tubers), the new potatoes con tributed to 22-33% of the Recommended Dietary Allowance (RDA) of vitamin C and 4-6% of pro tein in the daily human diet.The least L-ascorbic acid and the most protein was determined in the 'Nicola' potatoes imported from Israel, and the 'Excellency' imported from Spain.The amount of L-ascorbic acid and protein in the remaining po tato samples tested was at a similar level.The po tatoes of the same variety, imported from differ ent countries, did not differ in terms of L-ascorbic acid content.The protein content in 'Maris Peer' potatoes imported from Spain was by 5.45 g kg 1 FW higher, on average, compared with the tubers of the same variety originating from Israel.The protein content in the 'Maris Peer' tubers im ported from Israel was the lowest of all the potato samples tested.Potatoes are an important source of vitamin C (mainly L-ascorbic acid and small amounts of dehydroascorbic acid) in human diet (Love and Pavek, 2008).The vitamin C content insignificantly decreases after cooking of a new potato (Navarre et al., 2010).The ascorbic acid content in the new potatoes from Mediterranean countries depends, besides variety, on the growing season and harvest date.When the harvest time is delayed, the ascorbic acid content increases over the winterspring months, and decreases during the summerautumn growing season (Ierna and Melilli 2014).This is related to sunlight intensity and daylength during the period of potato growth.The higher the light intensity during the potato growing season, the greater the ascorbic acid con tent in plant tissues (Lee and Kader, 2000).The 'Spunta' and 'Nicola' are the most common vari eties grown in the Mediterranean area in both the winterspring months and the summerautumn season (Timpanaro 2003, Buono et al., 2009).Under the conditions of southern Italy, the ascor bic acid contents in the tubers of these varieties were very similar in both the growing seasons (Ierna and Melilli 2014).In the present study, the L-ascorbic acid content and protein content in the 'Spunta' potatoes imported from Cyprus were similar to the tubers of this variety originating from Egypt.The protein content in potato tuber depends on leaf assimilation area and chlorophyll a content in leaves, while vitamin C accumulation is only associated with the chlorophyll a content in leaves (Sawicka et al., 2015).
The starch content in the tested potato sam ples ranged from 71.00 to 142. 00 g kg 1 FW depending on cultivar and country of origin (Table 3).The new potatoes imported from Israel and Cyprus were lower in the starch compared with the tubers imported from Egypt, Spain and Morocco.The most starch was determined in the floury 'Excellency' potatoes imported from Spain or Morocco.According to Pereira et al. (2008), starch content is the most stable characteristic of the potato tuber chemical composition.In the present study, the starch content in 'Maris Peer' potatoes imported from Spain was higher, on  2015).The harvest time and variety affected the content of sucrose and reducing sugars in potato tubers.The content of sucrose and reducing sug ars, in particular glucose, was lower at the later dates of potato harvest (Mustonen, 2004).
The aftercooking darkening is one of the most important characteristics of potato quality.It is caused by nonenzymatic oxidation reac tion of the colourless ferrouschlorogenic acid compound formed during cooking, exposure to air and coloured ferri-dichlorogenic acid (Wang-Pruski and Nowak, 2004).All of the tested potato varieties were characterised by very low suscep tibility to aftercooking darkening, both immedi ately and two hours after cooking (Table 4).The  Principal component analysis (PCA) demon strated that the quality of new potatoes was asso ciated with the first three components: PC1, PC2, PC3.The components explained over 88.18% of the total variance -that is overall multidimen sional variation of traits (Table 5).The first prin cipal component, accounting for over 46.62% of total variation, was the most closely correlated with darkening of cooked tubers after 10 minutes following boiling in water (0.894), protein con tent (r = 0.821), and darkening of cooked tubers after 2 hours following boiling in water (-0.768).The values of correlation coefficients indicated that the potato varieties rich in protein do not tend to darken after cooking.The second princi pal component, strongly associated with the con tent of starch (r = -0.916),dry matter (r = -0.788)and monosaccharides (r = 0.608), explained over 27% of total variation.The potato varieties which accumulated more starch had higher con tents of dry matter and monosaccharides.Similar relations were reported by Ahmadizadeh and Felenja (2011) (2011) reported similar findings and concluded that dry matter and starch contents are the main factors determining the culinary value of potato tubers.The third principal component is mainly the carrier of information about the content of dry matter (0.539), total sugars (-0.569) and L ascorbic acid (0.572).The potatoes which had more dry matter were higher in L ascorbic acid and had less total sugars (Table 5).
As can be seen in Figure 2 which demon strates the distribution of the tested potato va rieties, they differed in terms of the examined characteristics.The PCA scatter plot showed that the potato varieties were characterised by con tinuous genetic diversity for the most important quality traits.The 'Sifra' and 'Maris Peer' pota toes imported from Israel were characterised by negative values for PC1 and positive values for PC2.These potatoes displayed low aftercook ing darkening, and had a low protein, dry matter and starch contents.The 'Maris Peer' tubers im ported from Israel and Spain, and 'Spunta' po tatoes imported from Egypt had negative inter mediate (near zero) values of PC1 and PC2.The 'Excellency' potatoes imported from Morocco and Spain were more diverse.The present study confirmed the substantial differences among the genotypes from different and similar geographic origins, and wide variability was detected for most potato varieties tested.Cluster analysis, based on the principal com ponents discussed above, yielded a dendrogram presented in Figure 2. The tested varieties of new potatoes were divided into 3 groups with dif ferent properties.Mean values of traits for each group are compiled in Table 6.The first group was made up of five varieties: 'Spunta' import ed from Cyprus and Egypt, 'Maris Peer' origi nating from Spain, and 'Orchestra' and 'Sifra' imported from Israel.Those potatoes had the highest vitamin C contents and were the least susceptible to aftercooking darkening.The sec ond group included two varieties: 'Maris Peer' imported from Israel and 'Excellency' originat ing from Morocco.Tubers of the cultivars had the most total sugars and monosaccharides.The third group consisted of the following two potato varieties: 'Excellency' imported from Spain and 'Nicola' grown in Israel.These potatoes had the highest dry matter, starch and protein contents and were the lowest in L-ascorbic acid, total sug ars and monosaccharides.

CONCLUSIONS
The quality of new potatoes imported from the Mediterranean countries and produced during the winterspring period depended on variety and country of origin.The dry matter content in the new potatoes imported from Spain and Morocco was higher than in the tubers originating from Cyprus, Egypt or Israel.The dry matter content in the new potatoes imported from Cyprus, Egypt and in the majority of new potatoes imported from Israel did not differ significantly.The potatoes which had more dry matter contained more L-ascorbic acid and less total sugars.The lowest L ascorbic acid content and the highest protein content were de termined in the 'Nicola' potatoes imported from Israel, and 'Excellency' originating from Spain.The amount of L-ascorbic acid and protein in the remaining potato samples tested was at a similar level.The potatoes of the same variety imported from different countries did not differ in terms of L-ascorbic acid content.The 'Maris Peer' tubers imported from Spain had more protein than the potatoes grown in Israel.The starch content in the new potatoes imported from Israel and Cyprus was lower than in tubers originating from Egypt, Spain and Morocco.The potatoes which had more starch contained more dry matter and monosac charides.Floury cookingtype 'Excellency' pota toes imported from Spain or Morocco were the starchiest.'Excellency' tubers imported from Morocco had more total sugars and monosac charides than those imported from Spain.All of the tested new potatoes had a very low suscepti bility to after cooking darkening.Cluster analy sis showed that the 'Spunta' potatoes imported from Cyprus and Egypt, 'Maris Peer' imported from Spain, and 'Orchestra' and 'Sifra' imported from Israel had the most vitamin C and were the least susceptible to aftercooking darkening.The 'Maris Peer' potatoes imported from Israel, and 'Excellency' imported from Morocco had the most total sugars and monosaccharides, whereas the 'Excellency' tubers imported from Spain, and 'Nicola' imported from Israel had the most dry matter, starch and protein and were the lowest in L-ascorbic acid, total sugars and monosaccharides.

Figure 1 .Figure 2 .
Figure 1.Distribution of 9 potato varieties in terms of 8 traits in the system of two components (PC1, PC2)

Table 1 .
Characteristics of potato varieties (The European Cultivated Potato Database)

Table 2 .
Dry matter, L-ascorbic acid and protein contents in potato tubers

Table 4 .
Aftercooking darkening of cooked tubers (9point Danish scale) * Means followed by the same letters do not differ significantly at p=0.05.

Table 5 .
Factor loads, eigenvalues and proportion of the total variance in potato varieties, as explained by the first three principal components

Table 6 .
Means of the examined characteristics of potato varieties divided into three groups based on cluster analysis