CRUDE FAT CONTENT AND FATTY ACID PROFILE IN THE SEEDS OF POLISH LINES AND CULTIVARS OF FIELD PEA (PISUM SATIVUM L.): PILOT STUDY

Jadwiga Andrzejewska¹, Stanisław Ignaczak¹, Agnieszka Katańska-Kaczmarek², Paweł Barzyk^3
1 Department of Agrotechnology, University of Science and Technology in Bydgoszcz, Poland
² Danko Plant Breeders LTD, Szelejewo Department, Poland
³ Poznańska Hodowla Roślin LTD, Plant Breeding Station Wiatrowo, Poland

ABSTRACT

In Poland and other European countries studies are conducted over replacing soya bean meal with domestic species of legumes. In these studies the problem of the amount and quality of oil is generally underestimated. The aim of this work is to review and assess the Polish lines and cultivars of species from the genus Pisum in regard to the oil content in seeds and the profile of their fatty acids. Field pea genotypes that were analysed comprised 9 with colourful blossom and 38 with white blossom. Mean crude fat content in both groups of cultivars was the same and amounted to 2.0%, but the coefficient of variation in the group of cultivars with colourful blossom amounted to 0.22, whereas with white blossom 0.10. The highest percentage in the fatty acid profile had linoleic acid (44–48%), and then oleic acid (22–26%). The highest variation in both groups of cultivars was shown by alpha-linolenic acid, and its content ranged from 0.08 to 0.13. From the nutritional point of view, oil from pea seeds, and particularly from the cultivars with white blossom, is characterized by a very favourable n-6/n-3 acids ratio in respect of nutritional value, staying within the range from 2.9 to 5.9.

Key words: colourful blossom pea, white blossom pea, alpha-linolenic acid, linolic acid, oleic acid.

INTRODUCTION

Leguminous plants are regarded as a source of protein in fodder and food. Less attention, however, is focused on the content and quality of oil. The exception is only soybean, which has the highest content of oil among the leguminous plants (12.2–23.6%), with the high proportion of necessary unsaturated fatty acids, i.e. linoleic acid and alpha-linolenic acid [8, 14]. Another species from this group is also South American lupine, whose seeds contain 14.1–15.6% of oil [18]. In the seeds of the other species of annual moderate zone legumes there is most often from 1.5 to 10% of oil [2, 3, 5, 18, 25].

The available literature indicates that the problem of quality of oil from legumes was first undertaken by Grela and Günter [9], who compared fatty acid profiles of 9 cultivars representing 7 species. In recent years, information can be found in the literature about the quality of oil from seeds of plants from the genus Lupinus [2, 3, 5], Pisum [13, 21, 24, 25], Vicia [12, 16, 23], Lens and Lathyrus [13]. This is, among other things, the effect of looking in the world of plants for oil raw materials with the high content of unsaturated acids with health supporting properties. The monounsaturated oleic acid affects a reduction in the cholesterol level [4]. Polyunsaturated linoleic acid (LA C18:2, n-6) and alpha-linolenic acid (ALA C18:3, n-3) belong to the group of necessary unsaturated fatty acids. These are precursors of long-chain acids (EPA, DPA) formed in the pathways of enzymatic transformations called, respectively, the omega-6 and omega-3 pathways [7]. Favourable effect of EPA and DPA acids on curbing and reducing risk of many diseases, particularly those of the cardiovascular system, is well documented in the literature [7, 10]. Not only the presence of those precursors is important in the human diet, but also keeping their proper ratio, which should amount to no more than 5:1 [20].

Animal food products are commonly criticized for too high content of saturated fatty acids (SFA), which are believed, among others, to have to cause increased cholesterol level [22]. Presently it is known that by modification of animals’ diet it is possible to raise the proportion of unsaturated fatty acids (UFA) in meat, milk and eggs [22], and also to affect a change in the omega-6 to omega-3 acid ratio [19]. Even at a low fat content in a fodder, its quality may be of utmost importance in animal feeding. At present, when research is done in the European countries on replacing soybean meal, derived from genetically modified cultivars, with native legumes, not only the content and quality of protein but also the content and quality of oil is taken into account [6, 17, 19, 22]. Oil content in the seeds of leguminous plants is similar or higher than that in soybean oil meal [1, 6].

Due to the yield potential, the content and quality of protein, field pea is regarded as the species that should be the basic source of plant protein under conditions of moderate climate, especially as the achievements of native breeding are impressive [11, 15]. Total protein content in pea seeds ranges, depending on the cultivar, from 20 to 26%. Oil content usually stays within the range 1.43–2.38% [18, 25]. Nowadays Canada is the greatest pea producer in the world. A research program was initiated there aiming to obtain pea cultivars with high oil content. A the first stage, of 198 cultivars 30 were selected for further studies, with the oil content in seeds ranging from 1.15 to 6.31% [21].

The fatty acid profile of pea may be differentiated by the genotype, since according some authors linoleic acid predominates in it [13, 21, 24, 25], but according to others, the proportions of oleic and linoleic acids are similar [18]. Unique feature of pea oil is a high content of linolenic acid, which according to different authors stays within the range 11.8–13.8% [18, 25], which causes that the linoleic to linolenic acid ratio is close to 5 or lower.

The studies carried out so far concern a relatively small number of field pea cultivars. According to the authors’ knowledge, there is no data either concerning possible differences in the quantity and quality of oil from the field pea cultivars with colourful and white flowers.

The aim of this pilot study is to review and assess Polish lines and cultivars of field pea with white and colourful flowers with respect to oil content in seeds and the profiles of their fatty acids.

MATERIAL AND METHODS

Material for the study was obtained from the company Danko Plant Breeders LTD, Department in Szelejewo, and the Poznańska Hodowla Roślin Plant Breeding Station at Wiatrowo. The seeds derived from the harvest of 2011. They were dried at 50ºC and stored under the same conditions at 18ºC. The oil (crude fat) content and the fatty acid profiles of 47 pea lines and cultivars were analysed, including 9 with colourful flowers and 38 with white flowers.

The crude fat content was determined using the apparatus for fast extraction ASE 150 by Dionex. Fragmented material was dried to the constant weight at 105ºC, and then it was cooled and stored in the desiccator. Weighed sample for the desiccator cell was 0.5 g. Extraction was performer at 130ºC, using a changing high pressure of inert gas – nitrogen 5.0 and solvents hexane:acetone (4:1). Time of extraction amounted to 40 minutes. After extraction the cell was cooled in the desiccator for at least 24 h, and the nit was weighted together with the sample. The loss of the sample weight related to the weight of the initial sample determined the proportion of oil in the initial sample. Weighing was performer to an accuracy of 0.001 g.

Oil extracted from seeds was subjected to esterification. At the first stage, oil was saponified using 0.5N of methanol solution of KOH at 70ºC until obtaining the solution clarity. Esterification with methanol was carried out in the presence of sulphuric acid as the catalyst. Obtained esters were suspended in n-hexane.

The chromatographic analysis was carried out on the gas chromatograph DANI GC equipped in detector of Split/Splitless type, the polar column Thermo Scientific TRACE™ TR-FAME (a length of 50 m, a diameter of 0.22 mm and a film width of 0.25 µm) and a flame-ionization detector (FID). The carrying gas was helium, with the flow set at 1.2 ml/min. The temperature of the dispenser was 230ºC. There was proportioned 1 µl of the sample, which was divided in the dispenser in a ratio of 1:15. The following temperature program was applied: 140ºC for 4 min.; increase in  temp. 3.5ºC/min. up to 170ºC; an increase in temp. 2.0ºC/min. up to 230ºC and keeping it for 1 min. The temperature in the detector amounted to 250ºC. Identification of fatty acid esters was performer using 37-component standard Supelco FAME Mix.

Analyses for the content of crude fat were performer in three replications, and for the fatty acid composition in one replication. However, if the results differed from the others, the analyses were repeated. Results of oil content in each cultivar were given together with the standard deviation. Results of fatty acid content were given as means from all cultivars together with the standard deviation. Moreover, variation coefficients were used to compare cultivars within the group of colourful or white flowers.

RESULTS

The average content of oil in seeds of pea cultivars with white and colourful flowers was the same and accounted for 2.0% (Tab. 1). However, differentiation within genotypes with colourful flowers was higher than within genotypes with white flowers, because the difference between the line WTD 591 (the highest oil content of the genotypes with colourful flowers) and the cultivar Klif (the lowest oil content of the genotypes with colourful flowers) was 1.39 percentage points (p.p.), and respectively, between the genotypes with white flowers – DS. 3044 and DS. 3037 – 0.84 p.p. This is also confirmed by variation coefficients. Although the number of cultivars with colourful flowers was 4 times lower, the variation coefficient amounted to 0.22, whereas for the group of cultivars with white flowers it was 0.10.

The basic fatty acid in pea oil was the polyunsaturated linoleic acid (C18:2), and its percentage in the profile was 48.1% in cultivars with colourful flowers and 44.25% in cultivars with white flowers (Tab. 2). There was also a large proportion of: monounsaturated oleic acid (C18:1) – in the group of cultivars with colourful and white flowers, respectively, 22.15 and 26.32%, and then, the saturated palmitic acid (C16:0) – 13.30 and 12.28%, and the polyunsaturated alpha-linolenic acid (C18:3) – 10.37 and 11.13%. Taking into account the values of standard deviation, it can be stated that oils from both groups of cultivars did not differ in respect of the total amount of saturated fatty acids (SFA). Oil from the cultivars with colourful flowers, as compared with oil from cultivars with white flowers, contained considerably less monounsaturated fatty acids (MUFA), and slightly more polyunsaturated fatty acids (PUFA). It was also characterized by a slightly wider ratio of n-6/n-3 acids.

Differentiation of the content of basic fatty acids in oil from compared lines and cultivars of field pea with colourful flowers to the largest degree referred to linolenic acid, and consequently, also the total of n-3 acids, and palmitic acid (Tab. 3). The cultivars Wiato and Turnia were distinguished by the profiles of fatty acids, since they contained about 13% of alpha-linolenic acid, which resulted in a narrow n-6/n-3 acid ratio. Moreover, oil from the cultivar Wiato was characterized by the content of palmitic acid lower by 2 p.p. from the other cultivars. The oil from the cultivar Sokolik was distinguished by the widest n-6/n-3 acid ratio, which resulted from the low content of alpha-linolenic acid, as compared with other cultivars.

The contents of linoleic acid in oils from lines and cultivars with white flowers were very similar (variation coefficient – 0.05) (Tab. 4). The contents of the other basic fatty acids varied within the range from 10 to 14%, whereas 14% referred to alpha-linolenic acid. The line WTD 5811 was distinctive in this group of cultivars, because the oil contained the largest proportion of oleic acid (32.3%) and the total of monounsaturated acids (32.8%), and the smallest of linoleic acid (38.5%). It was also characterized by the narrowest n-6/n-3 acid ratio (2.9). The oil from the cultivar Wenus was characterized by the widest ratio of these acids (5.3), and at the same time it contained the smallest amount of alpha-linolenic acid (8.1%).

DISCUSSION

Oil content in the seeds of Polish lines and cultivars of field pea is similar to the content in cultivars grown in Asia [24, 25]. In no Polish cultivars, however, oil content did not exceed 3.5 %, and such Canadian genotypes are reported by Villalobos Solis et al. [21].

It was proved that in respect of oil content a higher differentiation occurred within the cultivars with colourful flowers than those with white flowers. Of the fatty acids, alpha-linolenic acid was subject to the highest variability in both groups, but mostly in the group of cultivars with colourful flowers.

Both the results of the present study and the studies by other authors [24, 25] prove that the basic fatty acid profile of pea oil is very similar to the fatty acid profile of soybean oil, and the content of alpha-linolenic acid in pea oil may be higher even by about 3 p.p. than in soybean oil [7, 8]. Moreover, pea oil is a richer source of vitamin E than soybean oil, although the content of tocopherols is lower [9].

Basic fatty acids in oil from both studied groups of cultivars on average were arranged in the sequence C18:2>C18:1>C16:0>C18:3>C18:0, that is the same as it also reported by another authors [13, 21, 24, 25]. However, among 38 Polish lines and cultivars of pea with white flowers, in as many as 13 the content of the desirable alpha-linolenic acid was equal or higher than the content of palmitic acid. Of 9 lines and cultivars of pea with colourful flowers, a higher content of alpha-linolenic acid than palmitic acid occurred only once and referred to the cultivar Wiato. Rybiński et al. [18] also studied other Polish lines and cultivars of field pea and according to their data, the content of alpha-linolenic acid was always higher than that of palmitic. Moreover, the oil of all the lines and cultivars of pea tested in the presented study, and particularly forms with white flowers, was characterized by the n-6/n-3 acid ratio favourable from the nutritional point of view.

Although the oil content in pea seeds is low, the literature data indicate that this however is important in animal feeding. In the experiment with broiler chicken it was indicated that replacing about half of the feed ration of soybean meal with ground pea seeds did not affect the result of fattening and most meat qualities, but in chicken meat there was found an increase in the content of unsaturated fatty acids-oleic and linoleic [6].

Taking up breeding work aiming to obtain pea cultivars with a higher oil content would be a very ambitious and long-term task, but due to adapting pea to the climatic conditions of North Europe, its potential economic value, as well as oil quality, this is certainly worth consideration. Among Polish lines and cultivars there are those which are characterized by the fatty acid composition very desirable by nutritional specialists. However, initial forms for further breeding for higher fat content should be looked for e.g. among Canadian genotypes.

CONCLUSION

1. Average fat content in the seeds of Polish lines and cultivars of field pea amounts to 2%, but the range of variability is higher within the genotypes with colourful flowers than those with white flowers.
2. Fatty acid profile of the oil from pea seeds is very similar to the fatty acid profile of soya oil. Moreover, oil from most Polish lines and cultivars of pea with white flowers has a very narrow n-6/n-3 acid ratio, which is favourable from nutritional point of view.
3. Orienting breeding work towards an increase in fat content in pea seeds could be an important economic asset of this species.

ACKNOWLEDGES

This publication was made using the equipment purchased within the project “Realization of the 2nd stage of the Regional Innovation Centre” co-financed from the means of the European Regional Fund within the framework of the Regional Operational Program of the Kuyavian-Pomeranian Voivodeship for the years 2007–2013.

This work was funded from the means for Statutory Research of the Department of Agrotechnology, UTP in Bydgoszcz.

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Accepted for print: 30.10.2015

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