- Email: [email protected]
Amino acid composition of flesh-coloured potatoes as affected by storage conditions
Accepted Manuscript Amino acid composition of flesh-coloured potatoes as affected by storage conditions Anna Pęksa, Joanna Miedzianka, Agnieszka Nemś PII: DOI: Reference:
S0308-8146(18)30998-1 https://doi.org/10.1016/j.foodchem.2018.06.026 FOCH 22987
To appear in:
Food Chemistry
Received Date: Revised Date: Accepted Date:
8 January 2018 25 May 2018 5 June 2018
Please cite this article as: Pęksa, A., Miedzianka, J., Nemś, A., Amino acid composition of flesh-coloured potatoes as affected by storage conditions, Food Chemistry (2018), doi: https://doi.org/10.1016/j.foodchem.2018.06.026
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Amino acid composition of flesh-coloured potatoes as affected by storage conditions
Anna Pęksa, Joanna Miedzianka,* Agnieszka Nemś Department of Food Storage and Technology, Faculty of Biotechnology and Food Science, Wroclaw University of Environmental and Life Sciences
*Corresponding author: Joanna Miedzianka, Department of Food Storage and Technology, Faculty of Biotechnology and Food Science, Wroclaw University of Environmental and Life Sciences, Poland Email: [email protected]
Abstract The study determined nitrogen compounds and amino acid profile in dry matter of potatoes differing in flesh colour, stored at 2 °C and 5 °C for three and six months. With increased storage time, the total protein content and particularly amino acid content declined. The coagulable protein content increased at three months’ storage by 25%. The majority of the amino acid content decreased from 19 to 6% and from 38 to 21% after three and six months’ storage, respectively. Storage temperature did not influence the coagulable protein content or serine, glycine, cysteine, tyrosine and phenylalanine. However, potatoes stored at 2 ºC contained slightly more amino acids than tubers stored at 5 ºC. Independently of the storage conditions, potatoes of yellow-fleshed Fresco and red-fleshed Herbie 26 varieties were characterised by a relatively high nutritive value, limited by leucine (CS = 84), methionine plus cysteine (CS = 78) and leucine (CS = 72), respectively.
Keywords: coloured potatoes, storage, amino acids profile, protein quality
1. Introduction Potatoes are very popular as an inexpensive food product, available throughout the year due to their suitability for long-term storage. These vegetables are a valued raw material in starch and alcohol manufacture, for instance, and a valuable consumer product, mainly for their versatility of usage and favourable sensory and nutritional properties. Moreover, potatoes outperform other products, such as wheat, rice or corn, in terms of nutritional value, cost of cultivation and storage (Friedman, 1996; Lister & Munro, 2000). An increasing number of studies have described potato varieties with coloured flesh, notably purple and red. Despite similarities in chemical composition to traditional, yellow, creamy or white varieties (Jansen & Flamme, 2006; Lachman et al., 2012; Pęksa et al., 2013), coloured-fleshed potatoes contain anthocyanins, polyphenolic compounds with beneficial effects on human health. Tubers with purple or red flesh can be a profitable source of anthocyanins, similar to cranberries and superior to red cabbage. These compounds, besides displaying antioxidant properties, exhibit the activity in reducing the risk of chronic diseases of the nervous system; furthermore, they give tubers interesting functions not found in potatoes of traditional light colour. Potatoes with coloured flesh are similar to traditional fleshed tubers in terms of the content of nitrogen compounds (Jansen & Flamme, 2006). However, as has been shown in previous work (Pęksa et al., 2013), leucine is the amino acid limiting the quality of protein contained in purple- and red-fleshed varieties, whereas, in yellow-fleshed cultivars, it is primarily the sulfur amino acids, methionine and cysteine. Coloured-flesh potatoes cultivars allow long-term storage without notable loss of anthocyanins and belong to the so-called low-cost crops; their production and storage are well established. Coloured-flesh potatoes exhibit lower levels of anti-nutritional compounds, like glycoalkaloids, compared to yellow- and cream-fleshed varieties (Tajner-Czopek, Rytel, Kita, Pęksa, & Hamouz, 2012). Regardless of flesh colour, potatoes contain protein of high nutritive value which consists of two main fractions: coagulable protein (nitrogen compounds precipitable with trichloroacetic acid)
and non-protein organic compounds, such as free amino acids. This coagulable protein is a valuable foodstuff because of its well-balanced amino acid composition (van Gelder & Vonk, 1980). Potato protein is of great biological and nutritional value, comparable with egg white, and its chemical score (CS) ranges from 57 to 69 (Kapoor, Desbrough, & Li, 1975; Mitrus, Stankiewicz, Steć, Kamecki, & Starczewski, 2003; Pęksa, 2003; Pęksa, Rytel, Kita, Lisińska, & Tajner-Czopek, 2009). Potatoes contain significant amounts of aspartic and glutamic acids and their amides, as well as essential amino acids (EAAs) like leucine, lysine, phenylalanine, valine and tyrosine (Burton, 1989; Zimnoch-Guzowska & Flis, 2006; Pranaitiene, Danilcenko, Jariene, & Dabkevicius, 2008). About 50% of the total nitrogen presented in potatoes is derived from proteins (Eppendorfer, Eggum, & Bille, 1979; Kapoor et al., 1975); around 40% of the remaining soluble non-protein nitrogen consists of the above-mentioned free amino acids and their amides, while 10% comprises non-protein nitrogen associated with glycoalkaloids, some vitamins, purines, pyrimidines and secondary metabolites (Friedman, 1996). About 35% of the soluble protein is glycoprotein of 44–45 kDa molecular weight, known as patatin or tuberin, 25% of the protein includes protease inhibitors, and the remaining 40% contains other proteins with different properties (Deveaux-Gobert, 2008; Pęksa et al., 2009). Apart from their nutritional functions, amino compounds, such as amino acids, peptides and proteins, exhibit antioxidant activity and thus are considered important in plants and animals. Antioxidant amino acids include methionine, cysteine, tryptophan, tyrosine, histidine, lysine and proline. Storage of potatoes is aimed at extending the shelf-life while minimising quantitative and qualitative losses. The suitability of potatoes for long-term storage is associated with the genetic properties of the variety, which can be changed under the influence of the growing conditions and storage. Storage stability of varieties depends on the resting period of the tubers, the intensity of life processes occurring in the tubers, and the resistance to mechanical damage and susceptibility of tubers to fungal and bacterial diseases during vegetation and storage (Kołodziejczyk, 2016). During
storage, the chemical composition of potatoes is changed, mainly by the temperature. At increased storage temperature, respiration, transpiration and germ growth intensify, causing apparent increases in the dry matter (DM) content and loss of reducing sugars and starch. Most potato varieties exhibit low life activity when stored at 4–6 ºC. Table potatoes are usually stored at about 4ºC, which extends the period of dormancy, reduces the intensity of the growth of germs, stabilises the DM content of tubers and lowers the natural losses, also limiting the development of the majority of storage diseases (Czerko, Zgórska, & Grudzińska, 2012). However, this leads to the accumulation of reducing sugars, along with protein degradation, which is consistent with an increase in proteolytic enzyme activity, enhanced by low-temperature conditions (Brierley, Bonner, & Cobb, 1996). Both of these processes may act as determinants of potato processing quality. The research of various authors shows that long-term storage results in a decrease of the content of most amino acids and a similar downward trend can be seen in total protein (Brierley et al., 1996; Černá & Kráčmar, 2010). In these studies, it is also pointed out that amino acid composition of potatoes during long-term storage, usually, in low temperature conditions, depends primarily on the time of storage but also on the potato variety. The content and structure of nitrogen compounds is modified in yellow-fleshed varieties during long-term storage of potato tubers (Galdón, Mesa, Rodriquez, & Romero, 2010; Jansen & Flamme, 2006; Rexen, 1976), while potatoes with a coloured flesh in this regard are proportionally less tested. There is no information in published literature about the impact of the presence of anthocyanins in potato tubers on the variations in the content and composition of nitrogen compounds in potatoes during storage. It is worth learning the factors influencing the transformation of nitrogen compounds in potato varieties with red and purple flesh as affecting their nutritional value, both due to the growing interest of consumers and potato producers, but also due to the extensive research on varieties with coloured flesh in terms of their traits as raw materials in the food industry and dietetic food. The aim of this study was to investigate the magnitude and direction of changes in the content of nitrogen compounds in total, protein nitrogen, and amino
acids, and thus the nutritional value of potatoes differing in varietal characteristics, including the colour of flesh, originating from different growing conditions, during long-term storage at low temperature. 2. Materials and methods 2.1.
Raw material Six varieties of potato cultivated in the year 2014 were studied, including purple-fleshed
(Herbie 26 and Rote Emma), red-fleshed (Blaue Annelise and Blue Congo) and traditional yellowfleshed (Vineta and Fresco). The coloured-fleshed potatoes were grown in the test field at the station of The Central Institute for Supervising and Testing in Agriculture at Přerov nad Labem (the Czech Republic) and potatoes of the traditional yellow-fleshed varieties of Vineta and Fresco were obtained from a potato producing plant in Lower Silesia in Poland. The samples of potato tubers were harvested after reaching full maturity. Average laboratory samples of 20 kg tubers of each colour-fleshed variety were selected randomly from the collected field samples (40-50 kg). Mechanically damaged and green potatoes were rejected. Thereafter, the 20 kg samples of tubers of each variety were divided into two repetitions. Each sample of 10–15 tubers (weighing approximately 1.5 kg) was stored concurrently in paper bags for zero (at start of storage), three and six months at two low temperatures (2 ºC and 5 ºC), exposed to the air, at constant relative humidity (85% ±2%; thermohydrometer TH-130; Hama, Mannheim, Germany). After each storage period, the potatoes were analysed. Prepared material was stabilised by lyophilisation and stored below ‒18 ºC in closed polyethylene tubs for further analysis. 2.2.
Proximate analysis
The DM, starch, and total and coagulable nitrogen content were evaluated according to the Association of Analytical Chemists’ method (AOAC, 1995). Protein content was calculated using a conversion factor of 6.25. 2.3.
Determination of total polyphenols
The samples of freeze-dried potato were used for the extraction of polyphenols with 70% aqueous acetone, as described by Nemś et al. (2015). Total polyphenol content was determined using the Folin-Ciocalteu colorimetric method, as described by Gao, Bjork, Trajovski, & Uggla (2000). Polyphenol content, expressed as milligrams gallic acid equivalent (GAE), was calculated per 1 gram of DM. 2.4.
Assay of amino acid composition
Freeze-dried samples, milled and sieved, were used for amino acid determination. The amino acid composition was determined by ion-exchange chromatography after 23 hours’ hydrolysis with 6 N HCl at 110 °C. After cooling, filtering and washing, the hydrolyte was evaporated in a vacuum evaporator at a temperature below 50 °C. The dry residue was dissolved in a buffer of pH 2.2. The prepared sample was analysed using the ninhydrin method (Simpson, Neuberger, & Lin, 1976; Spackman, Stein, & Moore, 1958). The pH 2.6, 3.0, 4.25, and 7.9 buffers were applied. The ninhydrin solution was buffered at pH 5.5. The hydrolysed amino acids were determined using an AAA-400 analyser (INGOS, Prague, Czech Republic). A photometric detector was used, working at two wavelengths, 440 nm and 570 nm. A column of 350 × 3.7 mm, packed with ion exchanger Ostion LG ANB (INGOS) was utilised. Column temperature was kept at 60–74°C and detector at 121 °C. The calculations were carried out relative to an external standard. No analysis of tryptophan was carried out. During the 23 hours’ acid hydrolysis at 110 °C, Trp, Asn and Gln are totally lost (Asn and Gln turn to Asp and Glu, respectively). The losses of Cys, Met, Thr, Ser and Tyr reach up to 15%. 2.5.
Expression of the results The amino acid content in potatoes was calculated on a dry weight (DW) basis and the
composition of amino acids expressed on the nitrogen basis (g per 16 g N). Moreover, it was necessary to compare the amino acid composition of the coloured-flesh potatoes to a reference protein. The amino acid pattern for high-quality protein established by the Joint Food and Agriculture Organisation/World Health Organisation (FAO/WHO) Committee in 1991, according
to Young and Pellett (1991), was chosen. Levels were calculated on the basis of the essential amino acid composition of the chemical scores (CS), according to the Mitchell and Block method (Osborne & Voogt, 1978) and the integrated EAA index (Oser, 1951). 2.6.
Statistical analyses All data were statistically analysed using Statistica 10.0 (Statsoft, Inc., Tulsa, OK).
Homogenous groups and least significant difference (LSD) values were denoted using Duncan’s multiple comparison test. The significance level was set at α = 0.05, with one-way analysis of variance (ANOVA) for three variables. 3. Results and discussion 3.1.Chemical and amino acid composition The analysed coloured potato varieties were characterised by different DM, nitrogen and total polyphenol contents (Table 1). The total and coagulable protein content in the potatoes depended on the variety, not on the flesh colour. Purple-fleshed Blue Congo and red-fleshed Rote Emma contained a greater total protein content than the potatoes of other varieties studied (2.87 g and 2.63 g 100 g‒1 fresh weight (FW), respectively). The lowest content of total protein was noted in tubers of purple-fleshed Blaue Annelise and yellow-fleshed Fresco (2.01 g and 2.16 g 100 g‒1 FW, respectively). There were comparatively smaller differences among the studied samples of potatoes in respect of coagulable protein content. Potatoes of purple-fleshed Blaue Annelise and Blue Congo, red-fleshed Rote Emma and yellow-fleshed Vineta varieties had similar coagulable protein levels (from 0.55 g to 0.60 g 100 g‒1 FW). In contrast, the amount of coagulable protein was significantly higher in red-fleshed Herbie 26 (0.70 g 100 g‒1 FW) and lowest in tubers of the yellow-fleshed Fresco variety (0.34 g 100 g‒1 FW). Jansen & Flamme (2006) studied 18 potato varieties/breeding clones of white- and purplefleshed cultivars and reported no distinct differences concerning DM, starch and protein content, with comparable values to traditional white- or yellow-fleshed varieties. The total protein content is
said to depend mainly on the potato variety and fertilisation (Leszczyński, 2002; Mazur & Kreft, 1983; Rexen, 1976; Stankiewicz, Bombik, Rymsza, & Starczewski, 2008). Purple-fleshed Blaue Annelise and Blue Congo varieties presented the highest content of total polyphenols (2.50 mg and 1.84 mg g‒1 DM, respectively), whereas the lowest content was observed in Fresco tubers (0.58 mg g‒1 DM). Potato varieties with coloured flesh contain more polyphenolic compounds, including anthocyanins, which are not found in yellow- or cream-fleshed varieties. According to Brown (2005), purple- and red-fleshed potato varieties contain at least twice the levels of phenolic acid that yellow-fleshed potatoes contain. Both the variety and the storage conditions affected the protein and amino acid content of the analysed tubers of different flesh colours (Table 2). However, the biggest differences in the content of these compounds were observed among samples stored for different times and among different potato varieties, independently of flesh colour. There was no influence of storage temperature on the coagulable protein contents of the evaluated tubers. The studies showed that as the storage time increased, the total protein content (DM basis), the sum of all amino acid contents and that of all EAA contents declined. The loss of nitrogen compounds at three months’ storage amounted to about 6.4%, but at six months increased to 19% on average compared to the potato tubers before storage. The coagulable protein content (DM basis) of the analysed potatoes increased at three months storage by an average 25% that was maintained (3.61 g 100 g‒1 DW) at six months. Decreasing the total protein content but increasing the coagulable protein content at three months’ storage can be explained by the synthesis of proteins occurring especially in the first months of tuber storage (Brierley et al., 1996). On the other hand, increasing the total nitrogen and decreasing the coagulable protein content at six months’ storage was a result of protein hydrolysis, as the soluble nitrogen increased independently of temperature. According to Brierley et al. (1996), protein degradation is associated with the end of tuber dormancy and the mobilization of nitrogen reserves for sprout formation, while the breakdown of proteins is consistent with an increase in proteolytic enzyme activity.
The initial average of the sum of amino acids was 10.09 g 100 g ‒1 DW. At three months’ storage, it remained at 9.27 g 100 g‒1 DW, constituting 92% of the original amount. However, at six months’ storage, this had decreased relative to the initial value by, on average, 28%, with a maximum 7.29 g 100 g‒1 DW detected (Table 2). The total content of EAAs decreased, on average, by 30% at six months relative to the samples before storage. Some previous authors (Brierley et al., 1996; Stankiewicz et al., 2008) documented that a decrease in the content of amino acids in the DM of tubers under the influence of storage time was strictly connected to the accompanying decline in the total protein content. Additionally, an increase in total nitrogen concentration (DM basis) has been correlated with a reduction in the EAA content of the total protein (Danilchenko, Pranaitiene, Tarasieviciene, & Venskutoniene, 2008; Mitrus et al., 2003; Pęksa et al., 2013) and depends primarily on the potato variety, but also on the fertilisation. Moreover, from the results presented in Table 2, tubers of individual varieties differed significantly in their content of nitrogen compounds, including total and coagulable protein, as well as the sum of all and EAAs indices. Among all six potato varieties assessed, red-fleshed Herbie 26 and Rote Emma and yellow-fleshed Fresco tubers were characterised by higher total protein and sum of all amino acids (DM basis) after six months’ storage, whereas purple-fleshed Blaue Annelise variety had the lowest quantities of these compounds. Less diversity among samples of the analysed tubers was evident regarding the coagulable protein content (DM basis), which ranged from 3.04 g to 3.70 g 100 g‒1 DW. Galdón et al. (2010) observed relatively high variation in the amino acid data for all the potato cultivars grown in the Canary Islands. Thus, the genetic characteristics of the potato varieties decisively influenced the amino acid profile. The data did not indicate a significant influence of storage temperature on the content of almost all the determined amino acids. Potatoes stored at 2 ºC contained (DW basis) slightly more amino acids, mainly asparagine, glutamine, proline, leucine, lysine and arginine, than tubers stored at 5 ºC. However, there was a statistically significant difference for the amino acids valine and isoleucine. The tuber storage temperature did not impact on the serine, glycine, cysteine, tyrosine and
phenylalanine content. Likewise, Talley, Toma, and Orr (1984) stated that observed differences in the content of particular amino acids in potatoes stored at different temperatures (3.3 °C and 7.2 °C) were not significant. Moreover, these authors did not find significant differences for methionine, isoleucine and tyrosine content. However, content of asparagine, threonine, serine, proline, glycine, valine, leucine, phenylalanine, histidine, lysine, arginine and tryptophan increased during storage at 3.3 °C, while glutamine decreased. Throughout the six months’ storage, losses were observed in the majority of the potato amino acids (DM basis) (Table 2), both EAAs and non-essential amino acids (NEAAs). The storage time influenced the content of the individual amino acids more than the storage temperature, the differences at six months’ storage amounting to 21–38% relative to non-stored tubers. Furthermore, an increase (33%) in proline content occurred at three months’ storage. The storage time most affected the content of threonine, valine, arginine, leucine, histidine, lysine, isoleucine and asparagine. At three months’ storage, the examined tubers contained 6–18% less threonine, valine, methionine, isoleucine, leucine, tyrosine and lysine (EAAs) and, among the NEAAs, there were smaller amounts of asparagine, serine, glutamine, histidine and arginine. Losses of the remaining amino acids in the first period of storage were smaller than 16%. At six months’ storage of tubers of coloured flesh varieties, the content of individual amino acids (DM basis) decreased from 38% to 21% compared to the samples before storage. The smaller losses were observed for serine, glutamine, asparagine NEAAs and tyrosine or isoleucine EAAs; higher declines were noted for lysine, valine, leucine, threonine, histidine and arginine content. The amino acids content (DM basis) of tubers during long-term storage decreased along with the total nitrogen content. This relationship concurs with Eppendorfer and Eggum (1994), who assessed the quality of potatoes with traditional light-coloured flesh. The authors stated a close association between nitrogen content and the concentration (DM basis) of methionine, cysteine, threonine and lysine. According to Talley et al. (1984), the concentration of individual amino acids typically followed the same order as the nitrogen content. However, in many instances where the order was not followed, the values were
not significantly different. Stankiewicz et al. (2008) found that at seven months’ storage of Irga and Ekra potato tubers, the total protein content significantly decreased. There was significant differentiation among the contents of particular amino acids depending on the potato variety (Table 2). Yellow-fleshed Fresco potatoes contained more EAAs, such as threonine, methionine, tyrosine and phenylalanine, while among the NEAAs, asparagine, serine and proline contents were notably higher than in the other analysed tubers. The lowest values of amino acids, such as threonine, valine, lysine, asparagine and arginine, were found in purple-fleshed Blaue Annelise potatoes. Significant amounts of most amino acids were detected in potatoes of Rote Emma, Herbie 26 and Blue Congo varieties. The content of total protein (DM basis) of analysed tubers of Blaue Annelise, Blue Congo, Rote Emma, Vineta and Fresco varieties decreased during the six months’ storage, whereas in Herbie 26 no significant changes in the total nitrogen compounds occurred (Table 3). In potatoes of Blue Congo, Rote Emma and Vineta varieties, differing in flesh colour, decreasing total protein content was found at both three months’ and six months’ storage. Conversely, a significant decrease in total protein content was noticed only at three months’ storage in Fresco variety and six months’ storage in Blaue Annelise tubers. The highest loss of total nitrogen compounds at six months’ storage was found in the yellow-fleshed Vineta variety, which reached 38%; the smallest losses (average 1–8%) were recorded in red-fleshed Herbie 26 and yellow-fleshed Fresco varieties. The content of coagulable protein (DM basis) of the potato tubers significantly increased at three months’ storage, and changed slightly or plateaued during the next three months of storage (Table 3). The proportion of coagulable protein (DM basis) increased maximally in the Fresco variety (by about 42%) and minimally in Herbie 26 tubers (by about 6%). The presented studies showed that storage for six months contributed to a gradual decrease in the total amino acids (DM basis) of almost all potato samples, regardless of flesh colour (Table 2), and ranged from 22% to 40%. Only red-fleshed Herbie 26 variety, characterised by an insignificant increase in the total amino acids content at three months’ storage and at six months, retained the
same value as that of the respective tubers before storage. Černá and Kráčmar (2010) determined that the total quantity of amino acids in potatoes decreased by around 9% to 28% at 16 weeks’ storage, depending on the potato variety. There was observed an increase in dry matter content of most analysed potatoes. However, dry matter of Blue Congo and Herbie 26 did not change significantly during storage. The increase of dry matter content probably was the result of excessive evaporation of water from tubers stored in a proportionally low humidity (85 ± 2%). 3.2.Nutritive quality of the protein Potato protein is characterised by a high biological value, which is a measure of the proportion of protein from a specific food that can be utilised to synthesise the proteins of the organism. The nutritional value of proteins can be expressed by determining various indicators; for example, the essential amino acids index (EAAI) and the CS. The CS is a comparison of each EAA in a specific protein to the content of a standard protein, typically whole egg. The limiting EAA in the test protein is expressed as the percentage of the amount of the same amino acid in the reference protein. The CS of the EAAs and the EAAI were calculated with respect to the reference protein of the joint FAO/WHO (1991), taking into account all EAAs besides tryptophan, the storage temperature and time, as well as potato tuber variety. The storage temperature of the six potato tubers of coloured flesh varieties did not significantly influence the nutritional value of the protein, expressed as CS and EAAI (Table 4). In samples stored at 2 °C, the average CS was 74 and was identical for sulfur amino acids and leucine. The second limiting amino acid was threonine (CS = 85). In potatoes stored at 5 °C, the CS was 69–70 and concerned leucine and sulfur amino acids. The storage time significantly affected the nutritive value of the studied samples of differing flesh colour varieties (Table 4). The studies showed that the nutritional value indices of the protein contained in potatoes, both CS and EAAI, decreased at three and six months’ storage. Only the CS values of amino acids valine, phenylalanine and tyrosine, and isoleucine changed, but only slightly,
maintaining high levels. Similarly, Galdón et al. (2010) established the CS of all amino acids with respect to the reference protein of the joint FAO/WHO (1991) calculated for each cultivar and stated that the highest CS values were determined for aromatic amino acids (phenylalanine with tyrosine) and for branched amino acids, like isoleucine, leucine and valine. Before storage, the protein of the assessed potato samples characterised by CS, ranged from 84 to 156, whereas EAAI averaged 112. The limiting amino acids, before beginning the experiment, were leucine (CS = 84) and methionine + cysteine (CS = 92). At three months’ storage, the CS values ranged from 67 (for sulfur amino acids) to 147 (for aromatic amino acids). Extending the storage time to six months contributed to further lowering the nutritional value of the protein contained in the analysed tubers of the six potato varieties. This behaviour was reflected in the EAAI, which decreased by over 30% relative to the EAAI of the potatoes before storage. The CS (55 and 65 for sulfur amino acids and leucine, respectively) also limited the potato quality. The analysed potato tubers of the different coloured flesh varieties showed significant differentiation in terms of the nutritional value of the protein contained regardless of storage conditions (Table 3). On average, Fresco, Rote Emma and Herbie 26 varieties were characterised by the highest EAAI of protein, with values of 118, 110 and 96, respectively; leucine (CS = 84), methionine + cysteine (CS = 78), and leucine (CS = 72) were the amino acids limiting the protein quality of these potato varieties. The nutritional value of the potato varieties, expressed as CS relative to the referenced standard protein (FAO/WHO, 1991), changed depending on the storage time and variety (Figure 1). Before storage, the yellow-fleshed Fresco potatoes contained full-valued protein (CS = 142), which contrasted with the tubers of the other varieties, wherein the amino acid limiting the protein quality was leucine, and CS, which ranged between 67 and 85. Our results corroborate the data published by Eppendorfer and Eggum (1994), who found that methionine + cysteine and leucine were the most limiting amino acids in the studied potato tubers. Conversely, Sotelo, Contreras, Soussa, and
Hernández (1998) reported that the sulfur amino acids were the limiting amino acids in all investigated potato varieties. The nutritional value of protein contained in potatoes of the evaluated varieties decreased during storage, depending on the variety. This was particularly the case for purple-fleshed Blue Congo and yellow-fleshed Fresco potatoes at six months’ storage, and for Blaue Annelise at three months’ storage (Figure 1). At three months’ storage, the CS of the protein nutritional value decreased in these varieties by, on average, over 30%; in tubers of the Blue Congo and Fresco varieties, it decreased by a further 12–18% at six months. Leucine was the amino acid limiting the quality of protein of stored potatoes of the Fresco variety (CS range 69–57). Conversely, Blue Congo was limited by methionine + cysteine (CS range 49–43), while the quality of Blaue Annelise protein was limited by methionine + cysteine at three months’ storage (CS = 54) and threonine at six months (CS = 70). Relatively small changes in the nutritional value at six months’ storage in comparison to their non-stored counterparts were observed for the protein of red-fleshed Herbie 26 and yellow-fleshed Vineta varieties. The nutritional value of protein of these potatoes, expressed as CS, maintained a similar level to the samples before storage. At three months’ storage, the limiting amino acids were, proportionally, leucine (CS = 58) and methionine + cysteine (CS = 59); at six months, these were methionine + cysteine (CS = 65) and leucine (CS = 71). At six months’ storage, the CS of all analysed varieties was 43–71. However, the protein of Vineta and Blaue Annelise tubers presented the highest nutritional value, despite containing less total nitrogen compounds than the other tubers. The data are consistent with van Gelder and Vonk (1980), who studied the amino acid composition of the protein of 34 potato varieties and stated that the slight variation in the amino composition of coagulable protein hardly affects the EAAI. Additionally, the amino acid composition of coagulable potato protein was largely the same in varieties with low and high protein content. Similar findings were also confirmed by our previous research (Pęksa et al., 2013) and by other authors (Eppendorfer & Eggum, 1994; Rexen, 1976).
4. Conclusion The presented study found that during storage of the six potato samples of varieties with different coloured flesh (DM basis), the nitrogen compounds decreased, along with the amino acid content (except proline). However, an increase in the coagulable protein content occurred, to the greatest extent in tubers of the yellow-fleshed Fresco variety (by about 42%) and to the least extent in the DM of red-fleshed Herbie 26 tubers (by about 6%). The storage temperature did not significantly influence the coagulable protein content and only insignificantly affected some of the amino acid content: samples stored at a lower temperature (2 ºC versus 5 ºC) contained less valine and isoleucine, for instance. The storage time mostly impacted the content of amino acids, such as threonine, valine, arginine, leucine, histidine, lysine, isoleucine and asparagine. Among the samples of tubers of the six potato varieties, there was lower diversity regarding the coagulable protein (DM basis) than the total protein and the sum of all amino acid content. The highest losses of total nitrogen compounds, following six months’ storage, were found in yellow-fleshed potatoes of the Vineta variety, which reached 38%; in tubers of red-fleshed Herbie 26 and yellow-fleshed Fresco varieties, however, this value was lower than 8%. The increase in the coagulable protein content (DM basis) of potatoes during long-term storage did not impact its increased quality, as confirmed by the decreasing values of the nutritional value indicators (EAAI, CS) determined at three and six months of storage, independently of potato variety and flesh colour. Before storage, the limiting amino acid was leucine (CS = 84), but at three and six months’ storage, it was the sulfur amino acids, with CS values of 67 and 55, respectively. After storage at 2 ºC and 5 ºC, leucine and sulfur amino acids limited the protein quality of the studied potatoes. In samples stored at 2 ºC, the average CS was 74; in potatoes stored at 5 ºC, it was 69–70. After six months of storage, the CS of all analysed varieties ranged between 43 and 71. However, the proteins of Vineta and Blaue Annelise were characterised by the highest nutritional value, despite containing fewer total nitrogen compounds than the other tubers.
Acknowledgements This project was financed by the National Science Centre, granted on the basis of decision DEC-2013/11/N/NZ9/00117. This publication was supported by the Wroclaw Centre for Biotechnology programme at the Leading National Research Centre (KNOW) for the years 2014–2018. The authors declare no commercial or financial conflict of interest.
References AOAC. (1995). Official methods of analytical chemist. Washington, DC: Association of Official Analytical Chemists. Brierley, E. R., Bonner, P. L. R., & Cobb, A. H. (1996). Factors influencing the free amino acid content of potato (Solanum tuberosum L) tubers during prolonged storage. Journal of the Science of Food and Agriculture, 70, 515–525. Brown, C. R. (2005). Antioxidants in potato. American Journal of Potato Research, 82(2), 163– 172. Burton, W. G. (1989). The potato. New York, NY: Longman Scientific and Technical. Černá, M., & Kráčmar, S. (2010). The effect of storage on the amino acids composition in potato tubers. Acta Universitatis Agriculturae et Silviculturae Mendelianae Brunensis, 58, 49–55. Czerko, Z., Zgórska, K., & Grudzińska, M. (2012). Porównanie odmian ziemniaka pod względem reakcji na stosowanie inhibitorów kiełkowania (Comparison of potato varieties in terms of response to inhibitors of sprouting). Biuletyn Instytutu Hodowli i Aklimatyzacji Roślin, 266, 121–130. Danilchenko, H., Pranaitiene, R., Tarasieviciene, Z., & Venskutoniene, E. (2008). The effect of inhibitors on the amino acid content in the stored potato tubers. Zeszyty Problemowe Postępów Nauk Rolniczych, 530, 301–316.
Deveaux-Gobert, V. (2008). Potato proteins: Towards new value-added markets? Cahiers Agricultures, 17, 407–411. Eppendorfer, W. H., & Eggum, B. O. (1994). Effects of sulphur, nitrogen, phosphorus, potassium, and water stress on dietary fibre fractions, starch, amino acids and on the biological value of potato protein. Plant Foods for Human Nutrition, 45, 299–313. Eppendorfer, W. H., Eggum, B. O., & Bille, S. W. (1979). Nutritive value of potato crude protein as influenced by manuring and amino acid composition. Journal of the Science and Food Agriculture, 30, 361–368. FAO/WHO. (1991). Protein quality evaluation. Report of the joint FAO/WHO Expert Consultation. FAO Food and Nutrition Paper 51. Rome, Italy: World Health Organization. Friedman, M. (1996). Nutritional value of proteins from different food sources. A review. Journal of Agriculture and Food Chemistry, 44, 6–29. Galdón, B. R., Mesa, D. R., Rodriquez, E. M. R., & Romero, C. D. (2010). Amino acid content in traditional potato cultivars from the Canary Islands. Journal of Food Composition and Analysis, 23, 148–153. Gao, X., Björk, L., Trajkovski, V., & Uggla, M. (2000). Evaluation of antioxidant activities of rosehip ethanol extracts in different test systems. Journal of the Science of Food and Agriculture, 80, 2021–2027. Jansen, G., & Flamme, W. (2006). Coloured potatoes (Solanum tuberosum L.)—anthocyanin content and tuber quality. Genetic Resources and Crop Evolution, 53, 1321–1331. Kapoor, A. C., Desborough, S. L., & Li, P. H. (1975). Potato tuber proteins and their nutritional quality. Potato Research, 18, 469–478. Kołodziejczyk, M. (2016). Effect of nitrogen fertilisation and microbial preparations on quality and storage losses in edible potato. Acta Agrophysica, 23(1), 67–78.
Lachman, J., Hamouz, K., Orsák, M., Pivec, V., Hejtmánková, K., Pazderů, K., Dvořák, P., & Čepl, J. (2012). Impact of selected factors: Cultivar, storage, cooking and baking on the content of anthocyanins in coloured-flesh potatoes. Food Chemistry, 133, 1107–1116. Leszczyński, W. (2002). Zależność jakości ziemniaka od stosowania w uprawie nawozów i pestycydów (The dependence of potato quality on fertilizer and pesticide cultivation). Zeszyty Problemowe Postępów Nauk Rolniczych, 489, 47–64. Lister, C. E., & Munro, J. (2000). Nutrition and health qualities of potatoes— a future focus. In Crop & Food Research Confidential Report No. 143 (pp. 1–53). Christchurch, New Zealand: New Zealand Institute for Crop & Food Research Limited Provate Bag 4704. Mazur, T., & Kreft, L. (1983). Zawartość związków azotowych w bulwach pięciu odmian ziemniaka w zależności od nawożenia azotem w rejonie Olsztyna (The content of nitrogen compounds in tubers of five potato varieties depending on nitrogen fertilisation in the Olsztyn region). Biuletyn Instytutu Ziemniaka, 30, 29–40. Mitrus, J., Stankiewicz, C., Steć, E., Kamecki, M., & Starczewski, J. (2003). The influence of selected cultivation on the content of total protein and amino acids in the potato tubers. Plant Soil Environmental, 4(3), 131–134. Nemś, A., Pęksa, A., Kucharska, A.Z., Sokół-Łętowska, A., Kita, A., Drożdż, W., & Hamouz, K. (2015). Anthocyanin and antioxidant activity of snacks with coloured potato. Food Chemistry, 172, 175–182. Osborne, B. L., & Voogt, P. (1978). The analysis of nutrients in food. London: Academic Press. Oser, B. L. (1951). Method for integrating essential amino acid content in the nutritional evaluation of protein. Journal of the American Dietetic Association, 27, 396–402. Pęksa, A. (2003). Białko ziemniaczane charakterystyka właściwości (Potato protein, the profile of properties). Postępy Nauk Rolniczych, 5, 79–94. Pęksa, A., Kita, A., Kułakowska, K., Aniołowska, M., Hamouz, K., & Nemś, A. (2013). The quality of protein of coloured fleshed potatoes. Food Chemistry, 141, 2960–2966.
Pęksa, A., Rytel, E., Kita, A., Lisińska, G., & Tajner-Czopek, A. (2009). The properties of potato protein. In: Potato: Food, nutrition and health (pp. 79–87). Japan: Global Science Books, Food 3 (Special Issue 1). Pranaitiene, R., Danilcenko, H., Jariene, E., & Dabkevicius, Z. (2008). The effect of inhibitors on the changes of potato tuber quality during the storage period. Journal of Food, Agriculture and Environment, 6, 231–235. Rexen, B. (1976). Studies of protein of potatoes. Potato Research, 19, 189–202. Simpson, R. J., Neuberger, M. R., & Lin, T. Y. (1976). Complete amino acid analysis of proteins from a single hydrolysate. Journal of Biological Chemistry, 251, 1936–1940. Sotelo, A., Contreras, E., Soussa, H., & Hernández, V. (1998). Nutrient composition and toxic factor content of four wild species of Mexican potato. Journal of Agriculture and Food Chemistry, 46, 1355–1358. Spackman, D. H., Stein, W. H., & Moore, S. (1958). Automatic recording apparatus for use in the chromatography amino acid. Analytical Chemistry, 30, 1190–1206. Stankiewicz, C., Bombik, A., Rymsza, K., & Starczewski, J. (2008). An impact of selected agrotechnological operations on protein and exogenous amino acid content in potato tubers of Irga and Ekra cultivars during their storage (in Polish). Zeszyty Problemowe Postępów Nauk Rolniczych, 530, 281–291. Tajner-Czopek, A., Rytel, E., Kita, A., Pęksa, A., & Hamouz, K. (2012). The influence of thermal process of coloured potatoes on the content of glycoalkaloids in the potato products. Food Chemistry, 133, 1117–1122. Talley, E. A., Toma, R. B., & Orr, P. H. (1984). Amino acid composition of freshly harvested and stored potatoes. American Potato Journal, 61(5), 267–279. van Gelder, W. M. J., & Vonk, C. R. (1980). Amino acid composition of coagulable protein from tubers of 34 potato varieties and its relationship with protein content. Potato Research, 23, 427– 434.
Young, V. R., & Pellett, P. L. (1991). Protein evaluation, amino acid scoring and the food and drug administration’s proposed food labeling regulations. Issues and opinions in nutrition. Journal of Nutrition, 121, 145–150. Zimnoch-Guzowska, E., & Flis, B. (2006). Genetyczne podstawy cech jakościowych ziemniaka (Genetic basis of potato quality traits). Zeszyty Problemowe Postępów Nauk Rolniczych, 511, 23–36.
0-month 120 F
100
RE
BA
80
BC
H26
60
V
40 20 0
0
2
4
6
8
10
12
14
Total protein (g·100g-1 DW)
3-month 120 100 80
V
60
F
RE H26
BA
40 BC
20 0 0
2
4
6
8
10
12
14
Total protein (g·100g-1 DW)
6-month 120 100 80 60 40 20 0
H26
V BA
0
2
4
6
BC
8
RE
10 Total
F
12
protein (g·100g-1
14 DW)
Fig 1. CS values of the protein contained in potatoes of different flesh colour varieties after 0, 3 and 6-month storage in relation to total protein content. The first limited amino acid: (0-month) Leu; (3-month) Met+Cys (BA, BC, RE, V), Leu (H26, F); (6-month) Thr (BA), Met+Cys (BC, H26, RE), Leu (V, F)
Table 1. Chemical composition of experimental potatoes at the beginning of storage variety
Blaue Annelise
colour of flesh
purple
Blue Congo Herbie 26
red
Rote Emma Vineta Fresco
yellow
dry matter
total protein
coagulable protein
total polyphenols
g·100g‒1 FW
g·100g‒1 FW
g·100g‒1 FW
mg·g‒1 DM
20.55 ±0.22
d
2.01 ±0.01
f
0.61 ±0.03
b
2.50 ±0.08
23.57 ±0.71
a
2.87 ±0.01
a
22.05b±0.05
0.61 ±0.02
b
1.84 ±0.08
2.45c±0.02
0.70a±0.05
1.21c±0.20
21.42c±0.35
2.63b±0.06
0.60b±0.01
0.83d±0.09
19.92d±0.15
2.35d±0.01
0.55b±0.02
0.66e±0.07
e
2.16 ±0.01
17.34 ±0.24
e
c
0.34 ±0.01
a
b
f
0.58 ±0.08
Values are mean ± SD of three determinations; a,b,c,d,e,f – means in a column with the same letter are not significantly different (p < 0.05)
Table 2 Amino acid concentration and protein content (g·100 g‒1 DW) in potatoes of different flesh colour varieties as influenced by storage conditions and variety. storage temperature (°C) 5 2 a
0 b
3 a
b
c
d
0.32 ±0. 10
0.39 ±0. 10
Ser
0.34± 0.07
0.34± 0.07
0.38 ±0.
0.35 ±0.
0.30 ±0
0.31
04
08
.06
±0.0
a
b
Glu
1.50 ±0. 32
Pro
0.40 ±0. 16
a
1.34 ±0. 29 b
0.33 ±0. 08
a
1.58 ±0. 26 b
0.31 ±0. 07 a
Gly
0.3± 0.09
0.3± 0.09
Ala
0.28 ±0. 07
0.27 ±0. 05
0.29 ±0. 04
Cys *
0.05± 0.01
0.05±0.0 1
0.06 ±0. 01
Val *
0.45 ±0. 17
Me t*
0.15 ±0. 06
Ile*
0.32 ±0. 10
Leu *
0.53 ±0. 17
0.49 ±0. 13
0.60 ±0. 12
Tyr *
0.32± 0.09
0.31±0.0 6
0.36 ±0. 07
Phe *
0.66±0.2 2
0.64±0.1 8
0.70 ±
a
b
a
b
a
a±
His
0.20 0. 06
Lys *
0.55 ±0. 18
Arg
0.58 ±0. 22
a
a
a
0.34 ±0. 07 b
a
0.48 ±0. 13 b
0.14 ±0. 05 a
0.34 ±0. 08 b
b
0.19 ±0. 04 b
0.51 ±0. 13 b
0.55 ±0. 20 b
a
a
a
0.53 ±0. 14 a
0.19 ±0. 05 a
0.38 ±0. 08 a
a
a
0.23 0.22
a
±0.03 a
0.62 ±0. 14 a
0.68 ±0. 20 a
9,15 ±1, 98
8.61 ±1. 88
∑eaa
3,39±1,0 4
3.22 ±0. 83
TP
10,81 ±1 ,63
10.44 ±1 .81
11.6 ±0. 95
CP
3,33±0,6 6
3.28±0.6 9
2.70 ±0. 38
a
b
10.09 ±1 .45 a
3.85 ±0. 91 a
b
b
b
1.48 ±0. 29 a
0.46 ±0. 17 a
0.33 ±0. 11 a
0.29 ±0. 08 c
0.04 ±0. 02 b
0.50 ±0. 16 b
0.14 ±0. 04 b
0.33 ±0. 10 b
0.53 ±0. 16 b
0.31 ±0. 08 a
0.69 ± 0.22 b
∑aa
b
b
0.32 ±0. 05
1.73 ±0. 36
BC
0.31 ±0. 09
a
2.18 ±0. 41
BA
Thr *
a
2.43 ±0. 19
6
2.15 ±0. 39 b
2.08 ±0. 49
variety
Asp
a
ami no acid
storage time (month)
c
0.24 ±0. 05 c
c
1.20 ±0. 27 b
0.32 ±0. 06 b
0.24 ±0. 04 b
0.25 ±0. 05 b
0.05 ±0. 01 c
0.35 ±0f .07 c
0.10 ±0. 02 c
0.27 ±0. 04 c
0.40 ±0. 07 c
0.27 ±0. 04 b
b
9.27 ±1. 84 b
3.41 ±0. 96 b
d
1.16 ±0. 17 bc
0.35 ±0 .13 d
0.26 ±0. 04 c
0.26 ±0. 04 b
0.05 ±0. 02 e
0.35 ±0. 06 c
0.12 ±0. 05 d
0.28 ±0. 05 d
0.44 ±0. 09 d
0.27 ±0. 05 d
.08
c
.03
b
4
0.11 0.15 ±0
0.57 ±0. 21
c
0.53 ±0
06 b
d
0.26 ±0. 07
0.55 ±
0.20 ±0.
0.55 ±0. 17
1.77 ±0. 37
c
0.43 ±0. 08 c
0.45 ±0. 16 c
7.29 ±1. 32 c
2.66 ±0. 45 c
d
0.16 ±0. 03 d
0.41 ±0. 07 e
0.36 ±0. 06 e
7.33 ±1. 09 e
2.70 ±0. 45 e
10.86 ±1 .45
9.42 ±1. 89
8.81 ±1. 69
a
3.61a±0 .56
3.24 ±0. 38
3.61 ±0. 62
c
H26 c
2.07 ±0. 57 c
0.28 ±0. 08 c
RE
b
2.32 ±0. 22 c
0.30 ±0. 03 b
V c
2.08 ±0. 33 b
0.34 ±0. 06 b
F c
2.06 ±0. 51 c
0.30 ±0. 08 c
a
2.39 ±0. 35 a
0.42 ±0. 01 a
0.30 ±0.
0.38 ±0.
0.36 ±0.
0.31 ±0.
0.41 ±0.
08
06
06
07
06
b
1.60 ±0. 41 d
0.30 ±
0.06 d
0.26 ±0. 07 c
0.25 ±0. 05 b
0.05 ±0. 02 c
0.43 ±0. 12 c
0.11 ±0. 04 c
0.31 ±0. 08 d
0.44 ±0. 12 c
0.31 ±0. 08 c
0.60 ±0. 12 c
0.18 ±0. 04 c
0.48 ±0. 10 b
0.66 ±0. 24 c
8.64 ±2. 09 d
3.02 ±0. 74 c
10.24 ±1 .52 cd
3.13 ±0 .41
c
1.46 ±0. 18 b
0.37 ±0. 08 c
0.30 ±0. 04 c
0.26 ±0. 03 a
0.06 ±0. 01 b
0.47 ±0. 10 b
0.15 ±0. 03 b
0.34 ±0. 05 c
0.51 ±0. 07 c
0.31 ±0. 05 c
0.60 ±0. 10 b
0.21 ±0. 04 b
0.55 ±0. 09 b
0.64 ±0. 11 b
9.22 ±1. 09 c
3.29 ±0. 52 b
11.47 ±0 .81 a
3.70 ±0. 43
a
1.66 ±0. 29 bc
0.35 ±0 .02 a
0.39 ±0. 13 a
0.34 ±0. 08 a
0.06 ±0. 02 a
0.55 ±0. 17 b
0.15 ±0. 04 a
0.39 ±0. 10 a
0.63 ±0. 18 b
0.35 ±0. 08 b
0.77 ±0. 23 a
0.23 ±0. 06 a
0.63 ±0. 19 a
0.82 ±0. 15 a
10.10 ±1 .85 b
3.88 ±1. 02 b
11.53 ±0 .74 b
3.58 ±0. 76
d
1.20 ±0. 21 c
0.33 ±0. 14 cd
0.27 ±0 .05 d
0.23 ±0. 02 b
0.05 ±0. 01 d
0.39 ±0. 09 c
0.12 ±0. 04 d
0.27 ±0. 05 d
0.45 ±0. 08 d
0.28 ±0. 06 d
0.50 ±0. 08 d
0.16 ±0. 03 c
0.47 ±0. 09 d
0.41 ±0. 12 d
7.81 ±1. 57 de
2.84 ±0 .56 d
9.94 ±2. 12 c
3.16 ±0. 88
c
1.44 ±0. 24 a
0.47 ±0. 21 b
0.34 ±0. 10 b
0.30 ±0. 06 a
0.06 ±0. 02 a
0.58 ±0. 18 a
0.19 ±0. 07 a
0.37 ±0. 13 b
0.60 ±0. 19 a
0.37 ±0. 09 a
0.87 ±0. 24 b
0.21 ±0. 06 a
0.64 ±0. 19 c
0.51 ±0. 12 a
10.19 ±1 .99 a
4.10 ±1. 24 a
11.77 ±0 .91 d
3.04 ±0. 85
Values are means ±SD of six determinations.. a,b,c,d,e – means in a row with the same letter are not significantly different (p < 0.05) * Essential amino acid; ∑aa – sum of amino acids; ∑eaa - sum of essential amino acids; TP - total protein; CP - coagulable protein; potato varieties: Blaue Annelise (BA), Blue Congo (BC), Herbie 26 (H26), Rote Emma (RE), Vineta (V), Fresco (F)
Table 3 The content of protein, the sum of amino acids (g·100 g‒1 DW) in potatoes of six varieties and their dry matter (g·100 g‒1 FW) as influenced by storage time and variety (mean values of the storage temperature).
attrib ute
vari ety
Blaue Annelise
Blue Congo
0
3
6
0
3
6
0
3
6
0
3
6
0
3
6
0
3
6
9.7 h 7 ±0. 07
9.5 h 6
7.11
12. b 19 ±0. 04
9.70
8.8 i 3 ±0. 40
11.1 e 2 ±0.1 2
12. 27
11.0 ef 3 ±0.7 2
12. 26
11.5 d 1 ±0.4 6
10. g 83
11. 78
10. g 77 ±1. 25
7.27
12. j 48 ±0. 10
11. d 36 ±1. 08
11. d 46 ±0. 91
coagu lable protei n
2.8 h 4 ±0. 16
3.2 fg 9
2.6 i 0
3.39
3.3 ef 9 ±0. 10
3.17
3.3 ef 9 ±0. 15
4.00
2.8 hi 0 ±0. 10
3.84
4.1 a 2
3.8 bc 0 ±1. 10
2.84
1.9 j 9
3.4 ef 3 ±0. 46
3.7 cd 2 ±0. 39
Σaa
8.6 e 8 ±0. 07
7.0 h 2 ±0. 30
6.30
6.8 h 0 ±0. 20
8.49
10. c 45 ±0. 79
8.74
10. c 60 ±0. 09
11.4 b 5 ±0.9 0
8.2 7
8.3 ef 7 ±0. 39
5.78
12. 34
10. 38
a
c
±0.1 7
±0. 76
±0. 72
7.8 3g ±0. 21
3.2 ef 4
2.5 hi 3
2.34
3.04
3.8 c 9
2.95
3.0 fg 3
±0.4 4
±0.2 0
±0.8 1
±0. 49
2.9 fg 2 ±0. 22
5.6 a 4
±0.3 5
3.4 de 3 ±0. 07
2.17
b
±0. 10
3.7 cd 8 ±0. 09
4.82
±0. 13
2.4 hi 2 ±0. 11
3.6 cd 4 ±0. 41
3.0 fg 4 ±0. 12
20. ef 55
23. ab 06
24.1 bcd 8
23. bc 57
23.1 cde 7
24. ab 68
22.0 cde 5
24. ab 21
23.7 abc 1
21. de 42
22.0 cde 2
25. a 51
19. f 92
20. ef 85
21.9 cde 1
17. g 34
20. f 03
24. ab 06
±0. 22
±0. 66
±0.7 8
±0. 71
±0.9 9
±1. 12
±0.0 5
±0. 81
±0.9 8
±0.9 8
±1. 13
±0. 15
±0. 54
±1.1 8
±0. 24
±0. 89
±1. 31
time of stor age
Herbie 26
Rote Emma
Vineta
Fresco
(mo nth) total protei n
Σeaa
dry matte r
±0. 90
±0. 20
j
±0.1 7
3.58 de
±0.3 2
i
±0.5 2
hi
±0. 10
h
±0.4 3
ef
±0.2 7
11. b 13 ±0. 46
7.98
3.9 c 5
2.68
±0. 16
fg
±0.4 4
gh
g
±0.2 2
e
±0.3 6
fg
±0.1 4
ab
±0. 80
±0. 45
ab
±0.2 5
e
±0.7 8
fg
ab
±0. 29
bc
±0.3 4
c
±0. 61
±0. 50
±0. 02 2.8 h 5
±0. 10 9.7 d 2
efg
±0. 99
±0. 23
j
±0.1 2
h
±0.2 0
j
i
±0.1 1
±0. 09
±0. 82
f
±0. 35
Values are mean ±SD of three determinations; a,b,c,d,e,f, g,h,i,j – means in a row with the same letter are not significantly different (p < 0.05)
Table 4 Essential amino acid index (EAAI) and chemical scores of essential amino acids present in potatoes of different flesh colour varieties in relation to temperature, time of storage and variety.
storage temperature (°C) storage time (month)
variety
EAAI 96
85
Met+Cys 74
Val 119
essential amino acids Ile Leu 106 74
5
95
87
70
127
112
69
140
81
0
112
106
92
140
125
84
156
99
3
97
87
67
132
109
74
147
88
6
76
65
55
93
89
56
121
69
Blaue Annelise
79
71
63
93
92
63
118
65
Blue Congo
86
76
59
114
102
63
134
77
Herbie 26
96
82
78
125
112
72
134
88
Rote Emma
110
93
78
146
129
88
165
101
Vineta
82
82
63
103
89
63
115
75
Fresco
118
115
92
154
122
84
182
102
3.4
2.5
3.5
2.8
6.6
6.3
5.8
factor 2
protein standard FAO/WHO (1991) (g/16 g N)
Thr
Phe+Tyr 144
88
Lys
HIGHLIGHTS >Amino acids profile and protein quality of stored coloured potatoes were analysed >Storage temperature did not affected protein content and its nutritive quality >Losses of Lys, Val, Leu, Thr, His and Arg amino acids occurred in stored potatoes >The protein of stored potatoes of Fresco and Herbie 26 varieties was of the highest quality
28
S0308-8146(18)30998-1 https://doi.org/10.1016/j.foodchem.2018.06.026 FOCH 22987
To appear in:
Food Chemistry
Received Date: Revised Date: Accepted Date:
8 January 2018 25 May 2018 5 June 2018
Please cite this article as: Pęksa, A., Miedzianka, J., Nemś, A., Amino acid composition of flesh-coloured potatoes as affected by storage conditions, Food Chemistry (2018), doi: https://doi.org/10.1016/j.foodchem.2018.06.026
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Amino acid composition of flesh-coloured potatoes as affected by storage conditions
Anna Pęksa, Joanna Miedzianka,* Agnieszka Nemś Department of Food Storage and Technology, Faculty of Biotechnology and Food Science, Wroclaw University of Environmental and Life Sciences
*Corresponding author: Joanna Miedzianka, Department of Food Storage and Technology, Faculty of Biotechnology and Food Science, Wroclaw University of Environmental and Life Sciences, Poland Email: [email protected]
Abstract The study determined nitrogen compounds and amino acid profile in dry matter of potatoes differing in flesh colour, stored at 2 °C and 5 °C for three and six months. With increased storage time, the total protein content and particularly amino acid content declined. The coagulable protein content increased at three months’ storage by 25%. The majority of the amino acid content decreased from 19 to 6% and from 38 to 21% after three and six months’ storage, respectively. Storage temperature did not influence the coagulable protein content or serine, glycine, cysteine, tyrosine and phenylalanine. However, potatoes stored at 2 ºC contained slightly more amino acids than tubers stored at 5 ºC. Independently of the storage conditions, potatoes of yellow-fleshed Fresco and red-fleshed Herbie 26 varieties were characterised by a relatively high nutritive value, limited by leucine (CS = 84), methionine plus cysteine (CS = 78) and leucine (CS = 72), respectively.
Keywords: coloured potatoes, storage, amino acids profile, protein quality
1. Introduction Potatoes are very popular as an inexpensive food product, available throughout the year due to their suitability for long-term storage. These vegetables are a valued raw material in starch and alcohol manufacture, for instance, and a valuable consumer product, mainly for their versatility of usage and favourable sensory and nutritional properties. Moreover, potatoes outperform other products, such as wheat, rice or corn, in terms of nutritional value, cost of cultivation and storage (Friedman, 1996; Lister & Munro, 2000). An increasing number of studies have described potato varieties with coloured flesh, notably purple and red. Despite similarities in chemical composition to traditional, yellow, creamy or white varieties (Jansen & Flamme, 2006; Lachman et al., 2012; Pęksa et al., 2013), coloured-fleshed potatoes contain anthocyanins, polyphenolic compounds with beneficial effects on human health. Tubers with purple or red flesh can be a profitable source of anthocyanins, similar to cranberries and superior to red cabbage. These compounds, besides displaying antioxidant properties, exhibit the activity in reducing the risk of chronic diseases of the nervous system; furthermore, they give tubers interesting functions not found in potatoes of traditional light colour. Potatoes with coloured flesh are similar to traditional fleshed tubers in terms of the content of nitrogen compounds (Jansen & Flamme, 2006). However, as has been shown in previous work (Pęksa et al., 2013), leucine is the amino acid limiting the quality of protein contained in purple- and red-fleshed varieties, whereas, in yellow-fleshed cultivars, it is primarily the sulfur amino acids, methionine and cysteine. Coloured-flesh potatoes cultivars allow long-term storage without notable loss of anthocyanins and belong to the so-called low-cost crops; their production and storage are well established. Coloured-flesh potatoes exhibit lower levels of anti-nutritional compounds, like glycoalkaloids, compared to yellow- and cream-fleshed varieties (Tajner-Czopek, Rytel, Kita, Pęksa, & Hamouz, 2012). Regardless of flesh colour, potatoes contain protein of high nutritive value which consists of two main fractions: coagulable protein (nitrogen compounds precipitable with trichloroacetic acid)
and non-protein organic compounds, such as free amino acids. This coagulable protein is a valuable foodstuff because of its well-balanced amino acid composition (van Gelder & Vonk, 1980). Potato protein is of great biological and nutritional value, comparable with egg white, and its chemical score (CS) ranges from 57 to 69 (Kapoor, Desbrough, & Li, 1975; Mitrus, Stankiewicz, Steć, Kamecki, & Starczewski, 2003; Pęksa, 2003; Pęksa, Rytel, Kita, Lisińska, & Tajner-Czopek, 2009). Potatoes contain significant amounts of aspartic and glutamic acids and their amides, as well as essential amino acids (EAAs) like leucine, lysine, phenylalanine, valine and tyrosine (Burton, 1989; Zimnoch-Guzowska & Flis, 2006; Pranaitiene, Danilcenko, Jariene, & Dabkevicius, 2008). About 50% of the total nitrogen presented in potatoes is derived from proteins (Eppendorfer, Eggum, & Bille, 1979; Kapoor et al., 1975); around 40% of the remaining soluble non-protein nitrogen consists of the above-mentioned free amino acids and their amides, while 10% comprises non-protein nitrogen associated with glycoalkaloids, some vitamins, purines, pyrimidines and secondary metabolites (Friedman, 1996). About 35% of the soluble protein is glycoprotein of 44–45 kDa molecular weight, known as patatin or tuberin, 25% of the protein includes protease inhibitors, and the remaining 40% contains other proteins with different properties (Deveaux-Gobert, 2008; Pęksa et al., 2009). Apart from their nutritional functions, amino compounds, such as amino acids, peptides and proteins, exhibit antioxidant activity and thus are considered important in plants and animals. Antioxidant amino acids include methionine, cysteine, tryptophan, tyrosine, histidine, lysine and proline. Storage of potatoes is aimed at extending the shelf-life while minimising quantitative and qualitative losses. The suitability of potatoes for long-term storage is associated with the genetic properties of the variety, which can be changed under the influence of the growing conditions and storage. Storage stability of varieties depends on the resting period of the tubers, the intensity of life processes occurring in the tubers, and the resistance to mechanical damage and susceptibility of tubers to fungal and bacterial diseases during vegetation and storage (Kołodziejczyk, 2016). During
storage, the chemical composition of potatoes is changed, mainly by the temperature. At increased storage temperature, respiration, transpiration and germ growth intensify, causing apparent increases in the dry matter (DM) content and loss of reducing sugars and starch. Most potato varieties exhibit low life activity when stored at 4–6 ºC. Table potatoes are usually stored at about 4ºC, which extends the period of dormancy, reduces the intensity of the growth of germs, stabilises the DM content of tubers and lowers the natural losses, also limiting the development of the majority of storage diseases (Czerko, Zgórska, & Grudzińska, 2012). However, this leads to the accumulation of reducing sugars, along with protein degradation, which is consistent with an increase in proteolytic enzyme activity, enhanced by low-temperature conditions (Brierley, Bonner, & Cobb, 1996). Both of these processes may act as determinants of potato processing quality. The research of various authors shows that long-term storage results in a decrease of the content of most amino acids and a similar downward trend can be seen in total protein (Brierley et al., 1996; Černá & Kráčmar, 2010). In these studies, it is also pointed out that amino acid composition of potatoes during long-term storage, usually, in low temperature conditions, depends primarily on the time of storage but also on the potato variety. The content and structure of nitrogen compounds is modified in yellow-fleshed varieties during long-term storage of potato tubers (Galdón, Mesa, Rodriquez, & Romero, 2010; Jansen & Flamme, 2006; Rexen, 1976), while potatoes with a coloured flesh in this regard are proportionally less tested. There is no information in published literature about the impact of the presence of anthocyanins in potato tubers on the variations in the content and composition of nitrogen compounds in potatoes during storage. It is worth learning the factors influencing the transformation of nitrogen compounds in potato varieties with red and purple flesh as affecting their nutritional value, both due to the growing interest of consumers and potato producers, but also due to the extensive research on varieties with coloured flesh in terms of their traits as raw materials in the food industry and dietetic food. The aim of this study was to investigate the magnitude and direction of changes in the content of nitrogen compounds in total, protein nitrogen, and amino
acids, and thus the nutritional value of potatoes differing in varietal characteristics, including the colour of flesh, originating from different growing conditions, during long-term storage at low temperature. 2. Materials and methods 2.1.
Raw material Six varieties of potato cultivated in the year 2014 were studied, including purple-fleshed
(Herbie 26 and Rote Emma), red-fleshed (Blaue Annelise and Blue Congo) and traditional yellowfleshed (Vineta and Fresco). The coloured-fleshed potatoes were grown in the test field at the station of The Central Institute for Supervising and Testing in Agriculture at Přerov nad Labem (the Czech Republic) and potatoes of the traditional yellow-fleshed varieties of Vineta and Fresco were obtained from a potato producing plant in Lower Silesia in Poland. The samples of potato tubers were harvested after reaching full maturity. Average laboratory samples of 20 kg tubers of each colour-fleshed variety were selected randomly from the collected field samples (40-50 kg). Mechanically damaged and green potatoes were rejected. Thereafter, the 20 kg samples of tubers of each variety were divided into two repetitions. Each sample of 10–15 tubers (weighing approximately 1.5 kg) was stored concurrently in paper bags for zero (at start of storage), three and six months at two low temperatures (2 ºC and 5 ºC), exposed to the air, at constant relative humidity (85% ±2%; thermohydrometer TH-130; Hama, Mannheim, Germany). After each storage period, the potatoes were analysed. Prepared material was stabilised by lyophilisation and stored below ‒18 ºC in closed polyethylene tubs for further analysis. 2.2.
Proximate analysis
The DM, starch, and total and coagulable nitrogen content were evaluated according to the Association of Analytical Chemists’ method (AOAC, 1995). Protein content was calculated using a conversion factor of 6.25. 2.3.
Determination of total polyphenols
The samples of freeze-dried potato were used for the extraction of polyphenols with 70% aqueous acetone, as described by Nemś et al. (2015). Total polyphenol content was determined using the Folin-Ciocalteu colorimetric method, as described by Gao, Bjork, Trajovski, & Uggla (2000). Polyphenol content, expressed as milligrams gallic acid equivalent (GAE), was calculated per 1 gram of DM. 2.4.
Assay of amino acid composition
Freeze-dried samples, milled and sieved, were used for amino acid determination. The amino acid composition was determined by ion-exchange chromatography after 23 hours’ hydrolysis with 6 N HCl at 110 °C. After cooling, filtering and washing, the hydrolyte was evaporated in a vacuum evaporator at a temperature below 50 °C. The dry residue was dissolved in a buffer of pH 2.2. The prepared sample was analysed using the ninhydrin method (Simpson, Neuberger, & Lin, 1976; Spackman, Stein, & Moore, 1958). The pH 2.6, 3.0, 4.25, and 7.9 buffers were applied. The ninhydrin solution was buffered at pH 5.5. The hydrolysed amino acids were determined using an AAA-400 analyser (INGOS, Prague, Czech Republic). A photometric detector was used, working at two wavelengths, 440 nm and 570 nm. A column of 350 × 3.7 mm, packed with ion exchanger Ostion LG ANB (INGOS) was utilised. Column temperature was kept at 60–74°C and detector at 121 °C. The calculations were carried out relative to an external standard. No analysis of tryptophan was carried out. During the 23 hours’ acid hydrolysis at 110 °C, Trp, Asn and Gln are totally lost (Asn and Gln turn to Asp and Glu, respectively). The losses of Cys, Met, Thr, Ser and Tyr reach up to 15%. 2.5.
Expression of the results The amino acid content in potatoes was calculated on a dry weight (DW) basis and the
composition of amino acids expressed on the nitrogen basis (g per 16 g N). Moreover, it was necessary to compare the amino acid composition of the coloured-flesh potatoes to a reference protein. The amino acid pattern for high-quality protein established by the Joint Food and Agriculture Organisation/World Health Organisation (FAO/WHO) Committee in 1991, according
to Young and Pellett (1991), was chosen. Levels were calculated on the basis of the essential amino acid composition of the chemical scores (CS), according to the Mitchell and Block method (Osborne & Voogt, 1978) and the integrated EAA index (Oser, 1951). 2.6.
Statistical analyses All data were statistically analysed using Statistica 10.0 (Statsoft, Inc., Tulsa, OK).
Homogenous groups and least significant difference (LSD) values were denoted using Duncan’s multiple comparison test. The significance level was set at α = 0.05, with one-way analysis of variance (ANOVA) for three variables. 3. Results and discussion 3.1.Chemical and amino acid composition The analysed coloured potato varieties were characterised by different DM, nitrogen and total polyphenol contents (Table 1). The total and coagulable protein content in the potatoes depended on the variety, not on the flesh colour. Purple-fleshed Blue Congo and red-fleshed Rote Emma contained a greater total protein content than the potatoes of other varieties studied (2.87 g and 2.63 g 100 g‒1 fresh weight (FW), respectively). The lowest content of total protein was noted in tubers of purple-fleshed Blaue Annelise and yellow-fleshed Fresco (2.01 g and 2.16 g 100 g‒1 FW, respectively). There were comparatively smaller differences among the studied samples of potatoes in respect of coagulable protein content. Potatoes of purple-fleshed Blaue Annelise and Blue Congo, red-fleshed Rote Emma and yellow-fleshed Vineta varieties had similar coagulable protein levels (from 0.55 g to 0.60 g 100 g‒1 FW). In contrast, the amount of coagulable protein was significantly higher in red-fleshed Herbie 26 (0.70 g 100 g‒1 FW) and lowest in tubers of the yellow-fleshed Fresco variety (0.34 g 100 g‒1 FW). Jansen & Flamme (2006) studied 18 potato varieties/breeding clones of white- and purplefleshed cultivars and reported no distinct differences concerning DM, starch and protein content, with comparable values to traditional white- or yellow-fleshed varieties. The total protein content is
said to depend mainly on the potato variety and fertilisation (Leszczyński, 2002; Mazur & Kreft, 1983; Rexen, 1976; Stankiewicz, Bombik, Rymsza, & Starczewski, 2008). Purple-fleshed Blaue Annelise and Blue Congo varieties presented the highest content of total polyphenols (2.50 mg and 1.84 mg g‒1 DM, respectively), whereas the lowest content was observed in Fresco tubers (0.58 mg g‒1 DM). Potato varieties with coloured flesh contain more polyphenolic compounds, including anthocyanins, which are not found in yellow- or cream-fleshed varieties. According to Brown (2005), purple- and red-fleshed potato varieties contain at least twice the levels of phenolic acid that yellow-fleshed potatoes contain. Both the variety and the storage conditions affected the protein and amino acid content of the analysed tubers of different flesh colours (Table 2). However, the biggest differences in the content of these compounds were observed among samples stored for different times and among different potato varieties, independently of flesh colour. There was no influence of storage temperature on the coagulable protein contents of the evaluated tubers. The studies showed that as the storage time increased, the total protein content (DM basis), the sum of all amino acid contents and that of all EAA contents declined. The loss of nitrogen compounds at three months’ storage amounted to about 6.4%, but at six months increased to 19% on average compared to the potato tubers before storage. The coagulable protein content (DM basis) of the analysed potatoes increased at three months storage by an average 25% that was maintained (3.61 g 100 g‒1 DW) at six months. Decreasing the total protein content but increasing the coagulable protein content at three months’ storage can be explained by the synthesis of proteins occurring especially in the first months of tuber storage (Brierley et al., 1996). On the other hand, increasing the total nitrogen and decreasing the coagulable protein content at six months’ storage was a result of protein hydrolysis, as the soluble nitrogen increased independently of temperature. According to Brierley et al. (1996), protein degradation is associated with the end of tuber dormancy and the mobilization of nitrogen reserves for sprout formation, while the breakdown of proteins is consistent with an increase in proteolytic enzyme activity.
The initial average of the sum of amino acids was 10.09 g 100 g ‒1 DW. At three months’ storage, it remained at 9.27 g 100 g‒1 DW, constituting 92% of the original amount. However, at six months’ storage, this had decreased relative to the initial value by, on average, 28%, with a maximum 7.29 g 100 g‒1 DW detected (Table 2). The total content of EAAs decreased, on average, by 30% at six months relative to the samples before storage. Some previous authors (Brierley et al., 1996; Stankiewicz et al., 2008) documented that a decrease in the content of amino acids in the DM of tubers under the influence of storage time was strictly connected to the accompanying decline in the total protein content. Additionally, an increase in total nitrogen concentration (DM basis) has been correlated with a reduction in the EAA content of the total protein (Danilchenko, Pranaitiene, Tarasieviciene, & Venskutoniene, 2008; Mitrus et al., 2003; Pęksa et al., 2013) and depends primarily on the potato variety, but also on the fertilisation. Moreover, from the results presented in Table 2, tubers of individual varieties differed significantly in their content of nitrogen compounds, including total and coagulable protein, as well as the sum of all and EAAs indices. Among all six potato varieties assessed, red-fleshed Herbie 26 and Rote Emma and yellow-fleshed Fresco tubers were characterised by higher total protein and sum of all amino acids (DM basis) after six months’ storage, whereas purple-fleshed Blaue Annelise variety had the lowest quantities of these compounds. Less diversity among samples of the analysed tubers was evident regarding the coagulable protein content (DM basis), which ranged from 3.04 g to 3.70 g 100 g‒1 DW. Galdón et al. (2010) observed relatively high variation in the amino acid data for all the potato cultivars grown in the Canary Islands. Thus, the genetic characteristics of the potato varieties decisively influenced the amino acid profile. The data did not indicate a significant influence of storage temperature on the content of almost all the determined amino acids. Potatoes stored at 2 ºC contained (DW basis) slightly more amino acids, mainly asparagine, glutamine, proline, leucine, lysine and arginine, than tubers stored at 5 ºC. However, there was a statistically significant difference for the amino acids valine and isoleucine. The tuber storage temperature did not impact on the serine, glycine, cysteine, tyrosine and
phenylalanine content. Likewise, Talley, Toma, and Orr (1984) stated that observed differences in the content of particular amino acids in potatoes stored at different temperatures (3.3 °C and 7.2 °C) were not significant. Moreover, these authors did not find significant differences for methionine, isoleucine and tyrosine content. However, content of asparagine, threonine, serine, proline, glycine, valine, leucine, phenylalanine, histidine, lysine, arginine and tryptophan increased during storage at 3.3 °C, while glutamine decreased. Throughout the six months’ storage, losses were observed in the majority of the potato amino acids (DM basis) (Table 2), both EAAs and non-essential amino acids (NEAAs). The storage time influenced the content of the individual amino acids more than the storage temperature, the differences at six months’ storage amounting to 21–38% relative to non-stored tubers. Furthermore, an increase (33%) in proline content occurred at three months’ storage. The storage time most affected the content of threonine, valine, arginine, leucine, histidine, lysine, isoleucine and asparagine. At three months’ storage, the examined tubers contained 6–18% less threonine, valine, methionine, isoleucine, leucine, tyrosine and lysine (EAAs) and, among the NEAAs, there were smaller amounts of asparagine, serine, glutamine, histidine and arginine. Losses of the remaining amino acids in the first period of storage were smaller than 16%. At six months’ storage of tubers of coloured flesh varieties, the content of individual amino acids (DM basis) decreased from 38% to 21% compared to the samples before storage. The smaller losses were observed for serine, glutamine, asparagine NEAAs and tyrosine or isoleucine EAAs; higher declines were noted for lysine, valine, leucine, threonine, histidine and arginine content. The amino acids content (DM basis) of tubers during long-term storage decreased along with the total nitrogen content. This relationship concurs with Eppendorfer and Eggum (1994), who assessed the quality of potatoes with traditional light-coloured flesh. The authors stated a close association between nitrogen content and the concentration (DM basis) of methionine, cysteine, threonine and lysine. According to Talley et al. (1984), the concentration of individual amino acids typically followed the same order as the nitrogen content. However, in many instances where the order was not followed, the values were
not significantly different. Stankiewicz et al. (2008) found that at seven months’ storage of Irga and Ekra potato tubers, the total protein content significantly decreased. There was significant differentiation among the contents of particular amino acids depending on the potato variety (Table 2). Yellow-fleshed Fresco potatoes contained more EAAs, such as threonine, methionine, tyrosine and phenylalanine, while among the NEAAs, asparagine, serine and proline contents were notably higher than in the other analysed tubers. The lowest values of amino acids, such as threonine, valine, lysine, asparagine and arginine, were found in purple-fleshed Blaue Annelise potatoes. Significant amounts of most amino acids were detected in potatoes of Rote Emma, Herbie 26 and Blue Congo varieties. The content of total protein (DM basis) of analysed tubers of Blaue Annelise, Blue Congo, Rote Emma, Vineta and Fresco varieties decreased during the six months’ storage, whereas in Herbie 26 no significant changes in the total nitrogen compounds occurred (Table 3). In potatoes of Blue Congo, Rote Emma and Vineta varieties, differing in flesh colour, decreasing total protein content was found at both three months’ and six months’ storage. Conversely, a significant decrease in total protein content was noticed only at three months’ storage in Fresco variety and six months’ storage in Blaue Annelise tubers. The highest loss of total nitrogen compounds at six months’ storage was found in the yellow-fleshed Vineta variety, which reached 38%; the smallest losses (average 1–8%) were recorded in red-fleshed Herbie 26 and yellow-fleshed Fresco varieties. The content of coagulable protein (DM basis) of the potato tubers significantly increased at three months’ storage, and changed slightly or plateaued during the next three months of storage (Table 3). The proportion of coagulable protein (DM basis) increased maximally in the Fresco variety (by about 42%) and minimally in Herbie 26 tubers (by about 6%). The presented studies showed that storage for six months contributed to a gradual decrease in the total amino acids (DM basis) of almost all potato samples, regardless of flesh colour (Table 2), and ranged from 22% to 40%. Only red-fleshed Herbie 26 variety, characterised by an insignificant increase in the total amino acids content at three months’ storage and at six months, retained the
same value as that of the respective tubers before storage. Černá and Kráčmar (2010) determined that the total quantity of amino acids in potatoes decreased by around 9% to 28% at 16 weeks’ storage, depending on the potato variety. There was observed an increase in dry matter content of most analysed potatoes. However, dry matter of Blue Congo and Herbie 26 did not change significantly during storage. The increase of dry matter content probably was the result of excessive evaporation of water from tubers stored in a proportionally low humidity (85 ± 2%). 3.2.Nutritive quality of the protein Potato protein is characterised by a high biological value, which is a measure of the proportion of protein from a specific food that can be utilised to synthesise the proteins of the organism. The nutritional value of proteins can be expressed by determining various indicators; for example, the essential amino acids index (EAAI) and the CS. The CS is a comparison of each EAA in a specific protein to the content of a standard protein, typically whole egg. The limiting EAA in the test protein is expressed as the percentage of the amount of the same amino acid in the reference protein. The CS of the EAAs and the EAAI were calculated with respect to the reference protein of the joint FAO/WHO (1991), taking into account all EAAs besides tryptophan, the storage temperature and time, as well as potato tuber variety. The storage temperature of the six potato tubers of coloured flesh varieties did not significantly influence the nutritional value of the protein, expressed as CS and EAAI (Table 4). In samples stored at 2 °C, the average CS was 74 and was identical for sulfur amino acids and leucine. The second limiting amino acid was threonine (CS = 85). In potatoes stored at 5 °C, the CS was 69–70 and concerned leucine and sulfur amino acids. The storage time significantly affected the nutritive value of the studied samples of differing flesh colour varieties (Table 4). The studies showed that the nutritional value indices of the protein contained in potatoes, both CS and EAAI, decreased at three and six months’ storage. Only the CS values of amino acids valine, phenylalanine and tyrosine, and isoleucine changed, but only slightly,
maintaining high levels. Similarly, Galdón et al. (2010) established the CS of all amino acids with respect to the reference protein of the joint FAO/WHO (1991) calculated for each cultivar and stated that the highest CS values were determined for aromatic amino acids (phenylalanine with tyrosine) and for branched amino acids, like isoleucine, leucine and valine. Before storage, the protein of the assessed potato samples characterised by CS, ranged from 84 to 156, whereas EAAI averaged 112. The limiting amino acids, before beginning the experiment, were leucine (CS = 84) and methionine + cysteine (CS = 92). At three months’ storage, the CS values ranged from 67 (for sulfur amino acids) to 147 (for aromatic amino acids). Extending the storage time to six months contributed to further lowering the nutritional value of the protein contained in the analysed tubers of the six potato varieties. This behaviour was reflected in the EAAI, which decreased by over 30% relative to the EAAI of the potatoes before storage. The CS (55 and 65 for sulfur amino acids and leucine, respectively) also limited the potato quality. The analysed potato tubers of the different coloured flesh varieties showed significant differentiation in terms of the nutritional value of the protein contained regardless of storage conditions (Table 3). On average, Fresco, Rote Emma and Herbie 26 varieties were characterised by the highest EAAI of protein, with values of 118, 110 and 96, respectively; leucine (CS = 84), methionine + cysteine (CS = 78), and leucine (CS = 72) were the amino acids limiting the protein quality of these potato varieties. The nutritional value of the potato varieties, expressed as CS relative to the referenced standard protein (FAO/WHO, 1991), changed depending on the storage time and variety (Figure 1). Before storage, the yellow-fleshed Fresco potatoes contained full-valued protein (CS = 142), which contrasted with the tubers of the other varieties, wherein the amino acid limiting the protein quality was leucine, and CS, which ranged between 67 and 85. Our results corroborate the data published by Eppendorfer and Eggum (1994), who found that methionine + cysteine and leucine were the most limiting amino acids in the studied potato tubers. Conversely, Sotelo, Contreras, Soussa, and
Hernández (1998) reported that the sulfur amino acids were the limiting amino acids in all investigated potato varieties. The nutritional value of protein contained in potatoes of the evaluated varieties decreased during storage, depending on the variety. This was particularly the case for purple-fleshed Blue Congo and yellow-fleshed Fresco potatoes at six months’ storage, and for Blaue Annelise at three months’ storage (Figure 1). At three months’ storage, the CS of the protein nutritional value decreased in these varieties by, on average, over 30%; in tubers of the Blue Congo and Fresco varieties, it decreased by a further 12–18% at six months. Leucine was the amino acid limiting the quality of protein of stored potatoes of the Fresco variety (CS range 69–57). Conversely, Blue Congo was limited by methionine + cysteine (CS range 49–43), while the quality of Blaue Annelise protein was limited by methionine + cysteine at three months’ storage (CS = 54) and threonine at six months (CS = 70). Relatively small changes in the nutritional value at six months’ storage in comparison to their non-stored counterparts were observed for the protein of red-fleshed Herbie 26 and yellow-fleshed Vineta varieties. The nutritional value of protein of these potatoes, expressed as CS, maintained a similar level to the samples before storage. At three months’ storage, the limiting amino acids were, proportionally, leucine (CS = 58) and methionine + cysteine (CS = 59); at six months, these were methionine + cysteine (CS = 65) and leucine (CS = 71). At six months’ storage, the CS of all analysed varieties was 43–71. However, the protein of Vineta and Blaue Annelise tubers presented the highest nutritional value, despite containing less total nitrogen compounds than the other tubers. The data are consistent with van Gelder and Vonk (1980), who studied the amino acid composition of the protein of 34 potato varieties and stated that the slight variation in the amino composition of coagulable protein hardly affects the EAAI. Additionally, the amino acid composition of coagulable potato protein was largely the same in varieties with low and high protein content. Similar findings were also confirmed by our previous research (Pęksa et al., 2013) and by other authors (Eppendorfer & Eggum, 1994; Rexen, 1976).
4. Conclusion The presented study found that during storage of the six potato samples of varieties with different coloured flesh (DM basis), the nitrogen compounds decreased, along with the amino acid content (except proline). However, an increase in the coagulable protein content occurred, to the greatest extent in tubers of the yellow-fleshed Fresco variety (by about 42%) and to the least extent in the DM of red-fleshed Herbie 26 tubers (by about 6%). The storage temperature did not significantly influence the coagulable protein content and only insignificantly affected some of the amino acid content: samples stored at a lower temperature (2 ºC versus 5 ºC) contained less valine and isoleucine, for instance. The storage time mostly impacted the content of amino acids, such as threonine, valine, arginine, leucine, histidine, lysine, isoleucine and asparagine. Among the samples of tubers of the six potato varieties, there was lower diversity regarding the coagulable protein (DM basis) than the total protein and the sum of all amino acid content. The highest losses of total nitrogen compounds, following six months’ storage, were found in yellow-fleshed potatoes of the Vineta variety, which reached 38%; in tubers of red-fleshed Herbie 26 and yellow-fleshed Fresco varieties, however, this value was lower than 8%. The increase in the coagulable protein content (DM basis) of potatoes during long-term storage did not impact its increased quality, as confirmed by the decreasing values of the nutritional value indicators (EAAI, CS) determined at three and six months of storage, independently of potato variety and flesh colour. Before storage, the limiting amino acid was leucine (CS = 84), but at three and six months’ storage, it was the sulfur amino acids, with CS values of 67 and 55, respectively. After storage at 2 ºC and 5 ºC, leucine and sulfur amino acids limited the protein quality of the studied potatoes. In samples stored at 2 ºC, the average CS was 74; in potatoes stored at 5 ºC, it was 69–70. After six months of storage, the CS of all analysed varieties ranged between 43 and 71. However, the proteins of Vineta and Blaue Annelise were characterised by the highest nutritional value, despite containing fewer total nitrogen compounds than the other tubers.
Acknowledgements This project was financed by the National Science Centre, granted on the basis of decision DEC-2013/11/N/NZ9/00117. This publication was supported by the Wroclaw Centre for Biotechnology programme at the Leading National Research Centre (KNOW) for the years 2014–2018. The authors declare no commercial or financial conflict of interest.
References AOAC. (1995). Official methods of analytical chemist. Washington, DC: Association of Official Analytical Chemists. Brierley, E. R., Bonner, P. L. R., & Cobb, A. H. (1996). Factors influencing the free amino acid content of potato (Solanum tuberosum L) tubers during prolonged storage. Journal of the Science of Food and Agriculture, 70, 515–525. Brown, C. R. (2005). Antioxidants in potato. American Journal of Potato Research, 82(2), 163– 172. Burton, W. G. (1989). The potato. New York, NY: Longman Scientific and Technical. Černá, M., & Kráčmar, S. (2010). The effect of storage on the amino acids composition in potato tubers. Acta Universitatis Agriculturae et Silviculturae Mendelianae Brunensis, 58, 49–55. Czerko, Z., Zgórska, K., & Grudzińska, M. (2012). Porównanie odmian ziemniaka pod względem reakcji na stosowanie inhibitorów kiełkowania (Comparison of potato varieties in terms of response to inhibitors of sprouting). Biuletyn Instytutu Hodowli i Aklimatyzacji Roślin, 266, 121–130. Danilchenko, H., Pranaitiene, R., Tarasieviciene, Z., & Venskutoniene, E. (2008). The effect of inhibitors on the amino acid content in the stored potato tubers. Zeszyty Problemowe Postępów Nauk Rolniczych, 530, 301–316.
Deveaux-Gobert, V. (2008). Potato proteins: Towards new value-added markets? Cahiers Agricultures, 17, 407–411. Eppendorfer, W. H., & Eggum, B. O. (1994). Effects of sulphur, nitrogen, phosphorus, potassium, and water stress on dietary fibre fractions, starch, amino acids and on the biological value of potato protein. Plant Foods for Human Nutrition, 45, 299–313. Eppendorfer, W. H., Eggum, B. O., & Bille, S. W. (1979). Nutritive value of potato crude protein as influenced by manuring and amino acid composition. Journal of the Science and Food Agriculture, 30, 361–368. FAO/WHO. (1991). Protein quality evaluation. Report of the joint FAO/WHO Expert Consultation. FAO Food and Nutrition Paper 51. Rome, Italy: World Health Organization. Friedman, M. (1996). Nutritional value of proteins from different food sources. A review. Journal of Agriculture and Food Chemistry, 44, 6–29. Galdón, B. R., Mesa, D. R., Rodriquez, E. M. R., & Romero, C. D. (2010). Amino acid content in traditional potato cultivars from the Canary Islands. Journal of Food Composition and Analysis, 23, 148–153. Gao, X., Björk, L., Trajkovski, V., & Uggla, M. (2000). Evaluation of antioxidant activities of rosehip ethanol extracts in different test systems. Journal of the Science of Food and Agriculture, 80, 2021–2027. Jansen, G., & Flamme, W. (2006). Coloured potatoes (Solanum tuberosum L.)—anthocyanin content and tuber quality. Genetic Resources and Crop Evolution, 53, 1321–1331. Kapoor, A. C., Desborough, S. L., & Li, P. H. (1975). Potato tuber proteins and their nutritional quality. Potato Research, 18, 469–478. Kołodziejczyk, M. (2016). Effect of nitrogen fertilisation and microbial preparations on quality and storage losses in edible potato. Acta Agrophysica, 23(1), 67–78.
Lachman, J., Hamouz, K., Orsák, M., Pivec, V., Hejtmánková, K., Pazderů, K., Dvořák, P., & Čepl, J. (2012). Impact of selected factors: Cultivar, storage, cooking and baking on the content of anthocyanins in coloured-flesh potatoes. Food Chemistry, 133, 1107–1116. Leszczyński, W. (2002). Zależność jakości ziemniaka od stosowania w uprawie nawozów i pestycydów (The dependence of potato quality on fertilizer and pesticide cultivation). Zeszyty Problemowe Postępów Nauk Rolniczych, 489, 47–64. Lister, C. E., & Munro, J. (2000). Nutrition and health qualities of potatoes— a future focus. In Crop & Food Research Confidential Report No. 143 (pp. 1–53). Christchurch, New Zealand: New Zealand Institute for Crop & Food Research Limited Provate Bag 4704. Mazur, T., & Kreft, L. (1983). Zawartość związków azotowych w bulwach pięciu odmian ziemniaka w zależności od nawożenia azotem w rejonie Olsztyna (The content of nitrogen compounds in tubers of five potato varieties depending on nitrogen fertilisation in the Olsztyn region). Biuletyn Instytutu Ziemniaka, 30, 29–40. Mitrus, J., Stankiewicz, C., Steć, E., Kamecki, M., & Starczewski, J. (2003). The influence of selected cultivation on the content of total protein and amino acids in the potato tubers. Plant Soil Environmental, 4(3), 131–134. Nemś, A., Pęksa, A., Kucharska, A.Z., Sokół-Łętowska, A., Kita, A., Drożdż, W., & Hamouz, K. (2015). Anthocyanin and antioxidant activity of snacks with coloured potato. Food Chemistry, 172, 175–182. Osborne, B. L., & Voogt, P. (1978). The analysis of nutrients in food. London: Academic Press. Oser, B. L. (1951). Method for integrating essential amino acid content in the nutritional evaluation of protein. Journal of the American Dietetic Association, 27, 396–402. Pęksa, A. (2003). Białko ziemniaczane charakterystyka właściwości (Potato protein, the profile of properties). Postępy Nauk Rolniczych, 5, 79–94. Pęksa, A., Kita, A., Kułakowska, K., Aniołowska, M., Hamouz, K., & Nemś, A. (2013). The quality of protein of coloured fleshed potatoes. Food Chemistry, 141, 2960–2966.
Pęksa, A., Rytel, E., Kita, A., Lisińska, G., & Tajner-Czopek, A. (2009). The properties of potato protein. In: Potato: Food, nutrition and health (pp. 79–87). Japan: Global Science Books, Food 3 (Special Issue 1). Pranaitiene, R., Danilcenko, H., Jariene, E., & Dabkevicius, Z. (2008). The effect of inhibitors on the changes of potato tuber quality during the storage period. Journal of Food, Agriculture and Environment, 6, 231–235. Rexen, B. (1976). Studies of protein of potatoes. Potato Research, 19, 189–202. Simpson, R. J., Neuberger, M. R., & Lin, T. Y. (1976). Complete amino acid analysis of proteins from a single hydrolysate. Journal of Biological Chemistry, 251, 1936–1940. Sotelo, A., Contreras, E., Soussa, H., & Hernández, V. (1998). Nutrient composition and toxic factor content of four wild species of Mexican potato. Journal of Agriculture and Food Chemistry, 46, 1355–1358. Spackman, D. H., Stein, W. H., & Moore, S. (1958). Automatic recording apparatus for use in the chromatography amino acid. Analytical Chemistry, 30, 1190–1206. Stankiewicz, C., Bombik, A., Rymsza, K., & Starczewski, J. (2008). An impact of selected agrotechnological operations on protein and exogenous amino acid content in potato tubers of Irga and Ekra cultivars during their storage (in Polish). Zeszyty Problemowe Postępów Nauk Rolniczych, 530, 281–291. Tajner-Czopek, A., Rytel, E., Kita, A., Pęksa, A., & Hamouz, K. (2012). The influence of thermal process of coloured potatoes on the content of glycoalkaloids in the potato products. Food Chemistry, 133, 1117–1122. Talley, E. A., Toma, R. B., & Orr, P. H. (1984). Amino acid composition of freshly harvested and stored potatoes. American Potato Journal, 61(5), 267–279. van Gelder, W. M. J., & Vonk, C. R. (1980). Amino acid composition of coagulable protein from tubers of 34 potato varieties and its relationship with protein content. Potato Research, 23, 427– 434.
Young, V. R., & Pellett, P. L. (1991). Protein evaluation, amino acid scoring and the food and drug administration’s proposed food labeling regulations. Issues and opinions in nutrition. Journal of Nutrition, 121, 145–150. Zimnoch-Guzowska, E., & Flis, B. (2006). Genetyczne podstawy cech jakościowych ziemniaka (Genetic basis of potato quality traits). Zeszyty Problemowe Postępów Nauk Rolniczych, 511, 23–36.
0-month 120 F
100
RE
BA
80
BC
H26
60
V
40 20 0
0
2
4
6
8
10
12
14
Total protein (g·100g-1 DW)
3-month 120 100 80
V
60
F
RE H26
BA
40 BC
20 0 0
2
4
6
8
10
12
14
Total protein (g·100g-1 DW)
6-month 120 100 80 60 40 20 0
H26
V BA
0
2
4
6
BC
8
RE
10 Total
F
12
protein (g·100g-1
14 DW)
Fig 1. CS values of the protein contained in potatoes of different flesh colour varieties after 0, 3 and 6-month storage in relation to total protein content. The first limited amino acid: (0-month) Leu; (3-month) Met+Cys (BA, BC, RE, V), Leu (H26, F); (6-month) Thr (BA), Met+Cys (BC, H26, RE), Leu (V, F)
Table 1. Chemical composition of experimental potatoes at the beginning of storage variety
Blaue Annelise
colour of flesh
purple
Blue Congo Herbie 26
red
Rote Emma Vineta Fresco
yellow
dry matter
total protein
coagulable protein
total polyphenols
g·100g‒1 FW
g·100g‒1 FW
g·100g‒1 FW
mg·g‒1 DM
20.55 ±0.22
d
2.01 ±0.01
f
0.61 ±0.03
b
2.50 ±0.08
23.57 ±0.71
a
2.87 ±0.01
a
22.05b±0.05
0.61 ±0.02
b
1.84 ±0.08
2.45c±0.02
0.70a±0.05
1.21c±0.20
21.42c±0.35
2.63b±0.06
0.60b±0.01
0.83d±0.09
19.92d±0.15
2.35d±0.01
0.55b±0.02
0.66e±0.07
e
2.16 ±0.01
17.34 ±0.24
e
c
0.34 ±0.01
a
b
f
0.58 ±0.08
Values are mean ± SD of three determinations; a,b,c,d,e,f – means in a column with the same letter are not significantly different (p < 0.05)
Table 2 Amino acid concentration and protein content (g·100 g‒1 DW) in potatoes of different flesh colour varieties as influenced by storage conditions and variety. storage temperature (°C) 5 2 a
0 b
3 a
b
c
d
0.32 ±0. 10
0.39 ±0. 10
Ser
0.34± 0.07
0.34± 0.07
0.38 ±0.
0.35 ±0.
0.30 ±0
0.31
04
08
.06
±0.0
a
b
Glu
1.50 ±0. 32
Pro
0.40 ±0. 16
a
1.34 ±0. 29 b
0.33 ±0. 08
a
1.58 ±0. 26 b
0.31 ±0. 07 a
Gly
0.3± 0.09
0.3± 0.09
Ala
0.28 ±0. 07
0.27 ±0. 05
0.29 ±0. 04
Cys *
0.05± 0.01
0.05±0.0 1
0.06 ±0. 01
Val *
0.45 ±0. 17
Me t*
0.15 ±0. 06
Ile*
0.32 ±0. 10
Leu *
0.53 ±0. 17
0.49 ±0. 13
0.60 ±0. 12
Tyr *
0.32± 0.09
0.31±0.0 6
0.36 ±0. 07
Phe *
0.66±0.2 2
0.64±0.1 8
0.70 ±
a
b
a
b
a
a±
His
0.20 0. 06
Lys *
0.55 ±0. 18
Arg
0.58 ±0. 22
a
a
a
0.34 ±0. 07 b
a
0.48 ±0. 13 b
0.14 ±0. 05 a
0.34 ±0. 08 b
b
0.19 ±0. 04 b
0.51 ±0. 13 b
0.55 ±0. 20 b
a
a
a
0.53 ±0. 14 a
0.19 ±0. 05 a
0.38 ±0. 08 a
a
a
0.23 0.22
a
±0.03 a
0.62 ±0. 14 a
0.68 ±0. 20 a
9,15 ±1, 98
8.61 ±1. 88
∑eaa
3,39±1,0 4
3.22 ±0. 83
TP
10,81 ±1 ,63
10.44 ±1 .81
11.6 ±0. 95
CP
3,33±0,6 6
3.28±0.6 9
2.70 ±0. 38
a
b
10.09 ±1 .45 a
3.85 ±0. 91 a
b
b
b
1.48 ±0. 29 a
0.46 ±0. 17 a
0.33 ±0. 11 a
0.29 ±0. 08 c
0.04 ±0. 02 b
0.50 ±0. 16 b
0.14 ±0. 04 b
0.33 ±0. 10 b
0.53 ±0. 16 b
0.31 ±0. 08 a
0.69 ± 0.22 b
∑aa
b
b
0.32 ±0. 05
1.73 ±0. 36
BC
0.31 ±0. 09
a
2.18 ±0. 41
BA
Thr *
a
2.43 ±0. 19
6
2.15 ±0. 39 b
2.08 ±0. 49
variety
Asp
a
ami no acid
storage time (month)
c
0.24 ±0. 05 c
c
1.20 ±0. 27 b
0.32 ±0. 06 b
0.24 ±0. 04 b
0.25 ±0. 05 b
0.05 ±0. 01 c
0.35 ±0f .07 c
0.10 ±0. 02 c
0.27 ±0. 04 c
0.40 ±0. 07 c
0.27 ±0. 04 b
b
9.27 ±1. 84 b
3.41 ±0. 96 b
d
1.16 ±0. 17 bc
0.35 ±0 .13 d
0.26 ±0. 04 c
0.26 ±0. 04 b
0.05 ±0. 02 e
0.35 ±0. 06 c
0.12 ±0. 05 d
0.28 ±0. 05 d
0.44 ±0. 09 d
0.27 ±0. 05 d
.08
c
.03
b
4
0.11 0.15 ±0
0.57 ±0. 21
c
0.53 ±0
06 b
d
0.26 ±0. 07
0.55 ±
0.20 ±0.
0.55 ±0. 17
1.77 ±0. 37
c
0.43 ±0. 08 c
0.45 ±0. 16 c
7.29 ±1. 32 c
2.66 ±0. 45 c
d
0.16 ±0. 03 d
0.41 ±0. 07 e
0.36 ±0. 06 e
7.33 ±1. 09 e
2.70 ±0. 45 e
10.86 ±1 .45
9.42 ±1. 89
8.81 ±1. 69
a
3.61a±0 .56
3.24 ±0. 38
3.61 ±0. 62
c
H26 c
2.07 ±0. 57 c
0.28 ±0. 08 c
RE
b
2.32 ±0. 22 c
0.30 ±0. 03 b
V c
2.08 ±0. 33 b
0.34 ±0. 06 b
F c
2.06 ±0. 51 c
0.30 ±0. 08 c
a
2.39 ±0. 35 a
0.42 ±0. 01 a
0.30 ±0.
0.38 ±0.
0.36 ±0.
0.31 ±0.
0.41 ±0.
08
06
06
07
06
b
1.60 ±0. 41 d
0.30 ±
0.06 d
0.26 ±0. 07 c
0.25 ±0. 05 b
0.05 ±0. 02 c
0.43 ±0. 12 c
0.11 ±0. 04 c
0.31 ±0. 08 d
0.44 ±0. 12 c
0.31 ±0. 08 c
0.60 ±0. 12 c
0.18 ±0. 04 c
0.48 ±0. 10 b
0.66 ±0. 24 c
8.64 ±2. 09 d
3.02 ±0. 74 c
10.24 ±1 .52 cd
3.13 ±0 .41
c
1.46 ±0. 18 b
0.37 ±0. 08 c
0.30 ±0. 04 c
0.26 ±0. 03 a
0.06 ±0. 01 b
0.47 ±0. 10 b
0.15 ±0. 03 b
0.34 ±0. 05 c
0.51 ±0. 07 c
0.31 ±0. 05 c
0.60 ±0. 10 b
0.21 ±0. 04 b
0.55 ±0. 09 b
0.64 ±0. 11 b
9.22 ±1. 09 c
3.29 ±0. 52 b
11.47 ±0 .81 a
3.70 ±0. 43
a
1.66 ±0. 29 bc
0.35 ±0 .02 a
0.39 ±0. 13 a
0.34 ±0. 08 a
0.06 ±0. 02 a
0.55 ±0. 17 b
0.15 ±0. 04 a
0.39 ±0. 10 a
0.63 ±0. 18 b
0.35 ±0. 08 b
0.77 ±0. 23 a
0.23 ±0. 06 a
0.63 ±0. 19 a
0.82 ±0. 15 a
10.10 ±1 .85 b
3.88 ±1. 02 b
11.53 ±0 .74 b
3.58 ±0. 76
d
1.20 ±0. 21 c
0.33 ±0. 14 cd
0.27 ±0 .05 d
0.23 ±0. 02 b
0.05 ±0. 01 d
0.39 ±0. 09 c
0.12 ±0. 04 d
0.27 ±0. 05 d
0.45 ±0. 08 d
0.28 ±0. 06 d
0.50 ±0. 08 d
0.16 ±0. 03 c
0.47 ±0. 09 d
0.41 ±0. 12 d
7.81 ±1. 57 de
2.84 ±0 .56 d
9.94 ±2. 12 c
3.16 ±0. 88
c
1.44 ±0. 24 a
0.47 ±0. 21 b
0.34 ±0. 10 b
0.30 ±0. 06 a
0.06 ±0. 02 a
0.58 ±0. 18 a
0.19 ±0. 07 a
0.37 ±0. 13 b
0.60 ±0. 19 a
0.37 ±0. 09 a
0.87 ±0. 24 b
0.21 ±0. 06 a
0.64 ±0. 19 c
0.51 ±0. 12 a
10.19 ±1 .99 a
4.10 ±1. 24 a
11.77 ±0 .91 d
3.04 ±0. 85
Values are means ±SD of six determinations.. a,b,c,d,e – means in a row with the same letter are not significantly different (p < 0.05) * Essential amino acid; ∑aa – sum of amino acids; ∑eaa - sum of essential amino acids; TP - total protein; CP - coagulable protein; potato varieties: Blaue Annelise (BA), Blue Congo (BC), Herbie 26 (H26), Rote Emma (RE), Vineta (V), Fresco (F)
Table 3 The content of protein, the sum of amino acids (g·100 g‒1 DW) in potatoes of six varieties and their dry matter (g·100 g‒1 FW) as influenced by storage time and variety (mean values of the storage temperature).
attrib ute
vari ety
Blaue Annelise
Blue Congo
0
3
6
0
3
6
0
3
6
0
3
6
0
3
6
0
3
6
9.7 h 7 ±0. 07
9.5 h 6
7.11
12. b 19 ±0. 04
9.70
8.8 i 3 ±0. 40
11.1 e 2 ±0.1 2
12. 27
11.0 ef 3 ±0.7 2
12. 26
11.5 d 1 ±0.4 6
10. g 83
11. 78
10. g 77 ±1. 25
7.27
12. j 48 ±0. 10
11. d 36 ±1. 08
11. d 46 ±0. 91
coagu lable protei n
2.8 h 4 ±0. 16
3.2 fg 9
2.6 i 0
3.39
3.3 ef 9 ±0. 10
3.17
3.3 ef 9 ±0. 15
4.00
2.8 hi 0 ±0. 10
3.84
4.1 a 2
3.8 bc 0 ±1. 10
2.84
1.9 j 9
3.4 ef 3 ±0. 46
3.7 cd 2 ±0. 39
Σaa
8.6 e 8 ±0. 07
7.0 h 2 ±0. 30
6.30
6.8 h 0 ±0. 20
8.49
10. c 45 ±0. 79
8.74
10. c 60 ±0. 09
11.4 b 5 ±0.9 0
8.2 7
8.3 ef 7 ±0. 39
5.78
12. 34
10. 38
a
c
±0.1 7
±0. 76
±0. 72
7.8 3g ±0. 21
3.2 ef 4
2.5 hi 3
2.34
3.04
3.8 c 9
2.95
3.0 fg 3
±0.4 4
±0.2 0
±0.8 1
±0. 49
2.9 fg 2 ±0. 22
5.6 a 4
±0.3 5
3.4 de 3 ±0. 07
2.17
b
±0. 10
3.7 cd 8 ±0. 09
4.82
±0. 13
2.4 hi 2 ±0. 11
3.6 cd 4 ±0. 41
3.0 fg 4 ±0. 12
20. ef 55
23. ab 06
24.1 bcd 8
23. bc 57
23.1 cde 7
24. ab 68
22.0 cde 5
24. ab 21
23.7 abc 1
21. de 42
22.0 cde 2
25. a 51
19. f 92
20. ef 85
21.9 cde 1
17. g 34
20. f 03
24. ab 06
±0. 22
±0. 66
±0.7 8
±0. 71
±0.9 9
±1. 12
±0.0 5
±0. 81
±0.9 8
±0.9 8
±1. 13
±0. 15
±0. 54
±1.1 8
±0. 24
±0. 89
±1. 31
time of stor age
Herbie 26
Rote Emma
Vineta
Fresco
(mo nth) total protei n
Σeaa
dry matte r
±0. 90
±0. 20
j
±0.1 7
3.58 de
±0.3 2
i
±0.5 2
hi
±0. 10
h
±0.4 3
ef
±0.2 7
11. b 13 ±0. 46
7.98
3.9 c 5
2.68
±0. 16
fg
±0.4 4
gh
g
±0.2 2
e
±0.3 6
fg
±0.1 4
ab
±0. 80
±0. 45
ab
±0.2 5
e
±0.7 8
fg
ab
±0. 29
bc
±0.3 4
c
±0. 61
±0. 50
±0. 02 2.8 h 5
±0. 10 9.7 d 2
efg
±0. 99
±0. 23
j
±0.1 2
h
±0.2 0
j
i
±0.1 1
±0. 09
±0. 82
f
±0. 35
Values are mean ±SD of three determinations; a,b,c,d,e,f, g,h,i,j – means in a row with the same letter are not significantly different (p < 0.05)
Table 4 Essential amino acid index (EAAI) and chemical scores of essential amino acids present in potatoes of different flesh colour varieties in relation to temperature, time of storage and variety.
storage temperature (°C) storage time (month)
variety
EAAI 96
85
Met+Cys 74
Val 119
essential amino acids Ile Leu 106 74
5
95
87
70
127
112
69
140
81
0
112
106
92
140
125
84
156
99
3
97
87
67
132
109
74
147
88
6
76
65
55
93
89
56
121
69
Blaue Annelise
79
71
63
93
92
63
118
65
Blue Congo
86
76
59
114
102
63
134
77
Herbie 26
96
82
78
125
112
72
134
88
Rote Emma
110
93
78
146
129
88
165
101
Vineta
82
82
63
103
89
63
115
75
Fresco
118
115
92
154
122
84
182
102
3.4
2.5
3.5
2.8
6.6
6.3
5.8
factor 2
protein standard FAO/WHO (1991) (g/16 g N)
Thr
Phe+Tyr 144
88
Lys
HIGHLIGHTS >Amino acids profile and protein quality of stored coloured potatoes were analysed >Storage temperature did not affected protein content and its nutritive quality >Losses of Lys, Val, Leu, Thr, His and Arg amino acids occurred in stored potatoes >The protein of stored potatoes of Fresco and Herbie 26 varieties was of the highest quality
28