Zeszyty Problemowe Postępów Nauk Rolniczych nr 577, 2014, 63–71
Corresponding author – Adres do korespondencji: Krzysztof Konrad Jadwisieńczak, Uniwersytet Warmińsko-Mazurski w Olsztynie, Wydział Nauk Technicznych, Katedra Maszyn Roboczych i Metodologii Badań, ul. Michała Oczapowskiego 11, 10-719 Olsztyn, e-mail: krzychj@moskit.
uwm.edu.pl
THE CONTENT OF ORGANIC COMPOUNDS IN PEA (PISUMSATIVUM L.) SEEDS
Krzysztof K. Jadwisieńczak, Dariusz J. Choszcz, Stanisław Konopka, Joanna Majkowska-Gadomska, Katarzyna Głowacka
Uniwersytet Warmińsko-Mazurski w Olsztynie
Summary. The aim of this study was to determine the content of organic compounds in pea (cv. ‘Kelvedon Wonder’) seeds intended for planting. Chemical analyses were performed to determine density, the content of dry matter, total sugars, protein, fat, dietary fi ber and ash in eight seed fractions separated at different velocities of the air stream. Seed surface struc- ture was analyzed by scanning electron microscopy. The levels of organic compounds were found to be optimal for pea seeds. Seed fractions separated at the highest air stream velocity were characterized by signifi cantly higher density and a signifi cantly higher protein and fat content. They also tended to accumulate higher amounts of total sugars and therefore had higher germination capacity. A microscopic analysis revealed no signifi cant differences in seed coat structure and the number of starch grains between dry and imbibed pea seeds.
Key words: seeds, pea, chemical composition, seed coat structure
INTRODUCTION
The pea (Pisumsativum L.) is one of the oldest cultivated vegetables in the world. Peas are also a traditional crop in Poland – they have been widely grown in our country for centuries and are included in many commonly-used proverbs in the Polish language. Peas are also very important in human nutrition. Both green garden peas, immature and fresh, and sugar pea pods are eaten. Dry seeds are less commonly consumed, but they are still a valuable protein source for humans and animals [Wierzbicka 2007, Remiszewski et al.
2007, Klimek and Zając 2009].
Pea seeds can be smooth or wrinkled, depending on the variety. Usefulness of pea varieties for cultivation and food processing is genetically determined [Kumar et al. 2013, Sharma and Bora 2013].
Commercial pea cultivars intended for the processing industry should be character- ized by uniformity of pod setting, filling and ripening, and high yield stability, including under adverse weather conditions, with seed yield above 20% of total green matter; they should also be well suited for mechanical harvesting. ‘Kelvedon Wonder’ is a popular commercial pea cultivar, resistant to lodging, with plant height of 40÷80 cm, upright stems and small delicate leaves [Stelling 1994].
Pea seeds can be planted directly in the field. In Poland, planting takes place in early spring, when the soil is moist and cold. The rate of seed germination and seedling emer- gence is very slow, which increases the risk of infection and pathogen attack [Pięta and Pastucha 2008]. Seed material should be characterized by specific purity of 99% and minimum germination capacity of 80%. Adverse weather conditions during the growing season, including too high or low temperatures and high relative air humidity, contribute to uneven ripening and yield decrease, thus deteriorating seed quality. After harvest, the planting value of seeds is significantly affected by drying rate and temperature [Gugała and Zarzecka 2009, Klimek and Zając 2009].
The aim of this study was to determine the content of organic compounds in pea (cv.
‘Kelvedon Wonder’) seeds intended for planting, and to analyze their coat structure.
MATERIALS AND METHODS
The experimental materials comprised pea cv. ‘Kelvedon Wonder’ seeds supplied by a farm located in Gronówko, Kujawy-Pomerania Province. The seeds were planted on 10 April 2010. The recommended cultivation practices for peas were applied. Due to ad- verse weather conditions (heavy rainfalls), harvest was preceded by desiccant application (Reglone 200 SL). After seven days, on 8 July, peas were harvested using a conventional combine harvester. Dry seeds (ca. 5 tons) were placed into 25 kg bags and transported to Przedsiębiorstwo Nasiennictwa Ogrodniczego i Szkółkarstwa “TORSEED” S.A. (Horti- cultural Seed Production and Nursery Co., Ltd) in Toruń, to perform a laboratory analysis which revealed low germination capacity of seeds, at ca. 37%. The seeds could not be used as breeding material. Due to the high market value of seeds, an attempt was made to increase their germination capacity by cleaning with the use of the Petkus K-541 seed cleaner equipped with an upper screen measuring ≠ 5.5÷8.0 mm and a lower screen with a mesh size of ø 3.75÷4.25 mm. Cleaned and sized seeds still had low germination capac- ity of 53%. Repeated grading did not improve seed germinability and led to considerable loss of choice-quality seeds, which constituted a serious problem for the seed processing plant.
An average seed sample (ca. 5 kg) collected at ‘TORSEED’ [PN-EN ISO 13690:2007]
was transported to the laboratory of the Department of Separation Processes, University of Warmia and Mazury in Olsztyn, where preliminary analyses were performed. The seeds were uniform in size, and their diameter ranged from 5.9 to 6.5 mm. The experimental procedure was divided into several stages. At the first stage, pea seeds were separated
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into fractions [Choszcz et al. 2011]. Seed density ρ, defined as mass [m] of the material per unit volume V , was determined by the indirect method. At successive stages, seed fractions separated at eight different velocities of the air steam were subjected to chemical analyses and evaluated under a scanning electron microscope. Analytical sam- ples were collected from each batch of seeds, according to Polish Standard [PN-EN ISO 13690:2007]. The first samples was used to determine the content of: dry matter – by drying the collected plant material at 105°C to constant weight [PN-90/A-75101/03], total sugars – by the Tillmans method modified by Pijanowski [PN-90A-75101/11], pro- tein, fat, dietary fiber and ash – with the use of a MPA 0620 spectrometer. The second sample was divided into two subsamples, to evaluate the coat structure of dry (Fig. 1) and imbibed (Fig. 2) seeds. The surface of dry seeds was analyzed under a JSM-5310LV scanning electron microscope (JEOL, Japan) at 15 kV. Prior to the analysis, specimens had been sputter coated with gold in the presence of argon (Fine Coater, JCF-1200). Im- bibed seeds, cut along the micropyle, were stained with iodine-potassium iodide solution (v/v, 1/2) (Fig. 4 and 5) and were evaluated under a LEICA M205C stereo microscope equipped with a DFC 425C digital camera. The first and second datasets were processed using the NSS Version 3.0 (Thermo Fisher Scientific) program and the LAS V3.8 pro- gram, respectively.
Fig. 1. Dry pea seeds (scale 5 mm) Rys. 1. Suche nasiona grochu (skala 5 mm)
Fig. 2. Imbibed pea seeds (scale 5 mm) Rys. 2. Spęczniałe nasiona grochu (skala 5 mm)
Fig. 3. Longitudinal sections of imbibed seeds showing the embryo; k.z. – radicle, m.k. – root apical meristem, h – hypocotyl, cz.p. – epicotyl, m.p. – shoot apical me- ristem, z.l. – leaf primordia; l – cotyle- dons (scale 1 mm) Rys. 3. Przekroje przez zarodki napęczniałych nasion grochu; k.z. – korzeń zarodkowy, m.k. – merystem wierzchołka wzrostu korzenia, h – hipokotyl, cz.p. – część pę- dowa zarodka, m.p. – merystem wierz- chołka wzrostu pędu, z.l. – zawiązki liści, l – liścienie (podziałka 1 mm) Fig. 4. Fragment of a pea cotyledon stained with I/KI solution (v/v, 1 : 2). Starch grains violet-blue (scale 200 μm) Rys. 4. Fragment liścienia grochu wybarwio- nego I w KI (v/v, 1 : 2). Ziarna skrobi wybarwione na kolor fi oletowo-grana- towy. Podziałka 200 μm
Fig. 5. Pea seed surface observed under a scanning electron microscope at 15 kV (scale 250 μm) Rys. 5. Powierzchnia nasion grochu obser wowana w mikroskopie elektrono- wym skaningowym przy napięciu 15 kV (podziałka 250 μm)
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The results were processed statistically by ANOVA followed by Duncan’s (post-hoc) test to identify homogeneous subsets of means, with the use of Statistica PL v. 10 soft- ware. Table 1 shows significant differences in seed density and chemical composition (dry matter, protein and fat content) resulting from an increase in the critical velocity of the air stream. Homogeneous subsets were denoted by the same letters. The relationships between the studied parameters were determined by correlation and regression analyses.
Table 1. Chemical composition of pea seeds from different fractions Tabela 1. Skład chemiczny nasion grochu z różnych frakcji
Air stream velocity Prędkość strumienia powietrza [m·s–1] Density – Gęstość [g·cm–3] Dry matter – Sucha masa [%] Germination capacity Zdolność kiełkowania [%] Total sugars – Cukier ogółem [g·100 g–1] Protein – Białko [g·100 g–1] Fat – Tłuszcz [g·100 g–1] Dietary fi ber Błonnik pokarmowy [g·100 g–1] Ash – Popiół [g·100 g–1]
11.00 1.15a 93.6a 13 15.6 23.9a 2.1a 10.6 4.3
11.55 1.16a,b 93.5a 39 15.7 24.7b 2.1a 10.1 4.2
12.10 1.17a,b,c 93.1b 51 15.4 24.8bc 2.2b 11.1 4.6
12.65 1.18a,b,c,d 92.5c 69 15.8 24.8c 2.3c 10.8 4.6
13.20 1.19b,c,d,e 92.3c,d,e 71 16.2 25.1d 2.4c.d 11.5 5.2
13.75 1.21d,e,f 92.2d,e,f 77 16.0 25.1d 2.5d 10.1 4.4
14.30 1.23f,g 92.1d,e,f 81 16.9 25.2d 2.6e 8.8 4.2
14.85 1.25g 92.0f 87 16.9 24.5e 2.7e 8.6 3.8
Mean 1.19 92.7 61 16.1 24.8 2.4 10.2 4.4
a, b, c, d, e – average valuas in columns determined with the same letters do not differ statistically signifi cantly (uniform groups) / wartości średnie w kolumnach oznaczone tymi samymi literami nie różnią się statystycznie istotnie (grupy jednorodne).
RESULTS AND DISCUSSION
In Poland, habitat conditions are conducive to growing peas [Baraniak and Niezab- itowska 2004]. However, the seedling field emergence index does not always meet pro- ducers requirements. Seedling emergence is determined by many factors, including seed quality which is affected by seed production technology, seed vigor viability, germinabil- ity and age, as well as air temperature and humidity, and cultivation practices [Bujak and Frant 2010]. The germination capacity of seeds depends, among others, on their chemical composition [Andrzejewska et al. 2002, Klimek and Zając 2009]. Loss of seed vigor and viability may be caused by three functionally interrelated factors: damage to the cell membrane, inactivation of multiple enzymes and genome damage [Kopcewicz and
Lewak 2002]. During storage, the dissimilation process occurs in seeds which increases acidity and soluble sugar content, and decreases protein content. As a result, reducing sugars undergo the Maillard reaction with proteins [Górecki and Grzesiuk 2002].
The density of pea seeds varied significantly between fractions, and it was found to increase with increasing velocity of the air stream, from 1.15 g·cm–3 to 1.25 g·cm–3 (Ta- ble 1).
Dry legume seeds are a rich source of organic compounds [Remiszewski et al. 2007].
An analysis of the chemical composition of pea cv. ‘Kelvedon Wonder’ showed that the dry matter content of seeds ranged from 92.0% in the fraction separated at air stream velocity v = 14.85 m·s–1 to 93.6% in the fraction separated at v = 11.00 m·s–1. The noted differences were significant are similar to those reported by [Kunachowicz et al. 2006].
A comparison of the dry matter content and germinability of pea seeds [Choszcz et al.
2011] indicates that seeds with a lower dry matter content are characterized by higher germination capacity. There were no significant differences in total sugar concentrations between seed fractions. The nutritional value of legume seeds is determined by protein content [Messina 1999]. Research results show that the protein content of dry pea seeds ranges from 23.8 to 30.0 g·100 g–1 [Kulig et al. 1997, Kunachowicz et al. 2006, Sabanis et al. 2006, Wójtowicz 2009].
In our study, the protein content of pea seeds was within the above range, but signifi- cant differences were observed between seed fractions. The lowest protein content was noted in seeds separated at air stream velocity of 11.00 m·s–1, while seeds separated at v = 13.20÷14.30 m·s–1 had the highest protein concentrations. A comparison of the present results with previous findings [Choszcz et al. 2011] shows that pea seeds from the frac- tions separated at higher air stream velocities were characterized by higher germination capacity. A similar trend was noted with respect to the fat content of seeds, which ranged from 2.1 g·100 g–1 to 2.6 g·100 g–1, and increased with increasing velocity of the air stream. The dietary fiber content of seeds decreased as air stream velocity was increased in the separation process. According to [Kunachowicz et al. 2006], the dietary fiber con- tent of dry pea seeds should oscillate around 15 g·100 g–1. The values noted in our study were lower. The highest dietary fiber content was observed in seed fractions separated at air stream velocities of 11.00 to 13.20 m·s–1, and the lowest – in the fractions separated at v = 14.30 and 14.85 m·s–1. The ash content of pea seeds cv. ‘Kelvedon Wonder’ varied from 3.8 g·100 g–1 to 5.2 g·100 g–1, with no significant differences between fractions.
Table 2 presents the coefficients of correlation between the air stream velocity, seed density and germination capacity vs. the nutrient content of seeds.
Variables affecting germination capacity (organic compounds) were selected and a regression equation was derived. Decision variables that had the most significant ef- fect on the germination capacity of seeds were dry matter (r > 0.96) and protein content (r > 0.72).
A microscopic analysis revealed no significant differences in seed coat structure be- tween dry and imbibed seeds (Fig. 4 and 5). In all analyzed groups, seed embryos had similar structure, with normally developed radicles, hypocotyls and epicotyls, shoot api- cal meristems and leaf primordia. Starch grains in the cotyledon cells of pea seeds stained violet-blue with iodine-potassium iodide solution (Fig. 4). No significant differences in the number of starch grains were observed between groups.
Table 2. Coeffi cients of correlation between the analyzed parameters and the results of regression analysis
Tabela 2. Współczynniki korelacji między analizowanymi parametrami i wynikami analizy regresji
Air stream velocity Prędkość strumienia powietrza [m·s–1] Density – Gęstość [g·cm–3] Germination capacity Zdolność kiełkowania [%] Dry matter – Sucha masa [%] Total sugars – Cukier ogółem [g·100g–1] Protein – Białko [g·100g–1] Fat – Tłuszcz [g·100g–1] Dietary fi ber – Sucha masa [g·100g–1] Ash – Popiół [g·100g–1]
Air stream velocity Prędkość strumienia powietrza [m·s–1]
1.0000 – – – – – – – –
Density Gęstość [g·cm–3]
0.8655 1.0000 – – – – – – –
Germination capacity Zdolność kiełkowania [%]
0.8390 0.8784 1.0000 – – – – – –
Dry matter Sucha masa [%]
–0.8424 –0.8972 –0.9631 1.0000 – – – – –
Total sugars Cukier ogółem [g·100g–1]
0.7983 0.9140 0.7361 –0.7894 1.0000 – – – –
Protein Białko [g·100 g–1]
0.5021 0.4239 0.7242 –0.6328 0.3330 1.0000 – – –
Fat Tłuszcz [g·100 g–1]
0.9090 0.9850 0.8961 –0.9395 0.9050 0.4639 1.0000 – –
Dietary fi ber Błonnik pokarmowy [g·100 g–1]
–0.5701 –0.7510 –0.4361 0.4292 –0.7779 –0.0228 –0.6667 1.0000 –
Ash Popiół [g·100 g–1]
–0.2275 –0.4022 –0.0391 0.0072 –0.3838 0.3765 –0.2877 0.8611 1.0000
Statistical analysis – Analiza statystyczna:
Signifi cance level (α) / Poziom istotności (α) 0.05 Percentage of explained variation / Procent wyjaśnionej zmienności 94.96 Coeffi cient of multiple correlation / Współczynnik korelacji wielokrotnej 0.974 Calculated value of F statistic / Obliczona wartość statystyki F 56.5651 Probability level in p-test / Poziom prawdopodobieństwa testu 0.0001
Regression equation – Równanie regresji:
y = 2812.8599 – 32.7384 x1 + 11.3822 x2 x1 – Dry matter/Sucha masa [%]
x2 – Protein content/Zawartość białka [g·100 g–1] y – Germination capacity/Zdolność kiełkowania [%]
CONCLUSIONS
1. The highest coefficients of correlation (exceeding 0.9) were noted between the fat content of pea seeds vs. density, dry matter and total sugars. A high coefficient of cor- relation was observed between fat content and air stream velocity during the separation process. A significant correlation was also found between the germination capacity of pea seeds vs. the concentrations of dry matter and total sugars.
2. Among the analyzed organic compounds, the concentrations of dry matter and protein had the most significant effect on the germination capacity of pea seeds, which was further validated by a mathematical formula describing the relationships between changes in the analyzed parameters. The suitability of the proposed equation for pre- dicting the germination capacity of pea seeds was also confirmed by a high percentage of explained variation (nearly 95%) and a high probability of exceeding the calculated p-value (0.0001).
3. A microscopic analysis revealed no significant differences in seed coat structure and the number of starch grains between dry and imbibed pea seeds.
LITERATURE
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ZAWARTOŚĆ SKŁADNIKÓW ORGANICZNYCH W NASIONACH GROCHU ŁUSKOWEGO (PISUM SATIVUM L.) PRZEZNACZONEGO DO WYSIEWU
Streszczenie. W pracy podjęto próbę określenia zawartości składników organicznych w nasionach grochu łuskowego odmiany Cud Kelwedonu przeznaczonych do siewu. Prze- prowadzono analizy chemiczne, w których oznaczono gęstość, suchą masę, cukry ogó- łem, białko oraz tłuszcz, błonnik pokarmowy i popiół dla 8 frakcji nasion wydzielonych przy różnych prędkościach strumienia powietrza. Przebadano również ich strukturę, wy- korzystując mikroskop skaningowy. Zawartość poszczególnych składników organicznych kształtowała się na optymalnym poziomie dla nasion grochu. Frakcje nasion pozyskane przy największej prędkości charakteryzowały się istotnie większą gęstością oraz zawar- tością białka i tłuszczu, jednocześnie wykazywały tendencję zwiększonego gromadzenia cukrów ogółem, co miało odzwierciedlenie w zwiększeniu zdolności ich kiełkowania. Ana- liza mikroskopowa nie wykazała znaczących różnic w budowie okrywy nasiennej zarówno na powierzchni suchych, jak i spęczniałych nasion grochu oraz nie zaobserwowano różnic w występowaniu czy też liczbie ziaren skrobi.
Słowa kluczowe: nasiona, groch, skład chemiczny, struktura powierzchni
