Arabinoxylan and Arabinogalactan Content in Different Spring Wheats

Abstract

In the present study, an effort has been made to characterize eight different spring wheats for arabinoxylan and arabinogalactan content. For the purpose, non-starch polysaccharides were extracted, derivitized with hexamethyldisalazine, and further analyzed through a gas chromatograms flame ionization detector. Arabinose, xylose, and galactose content ranged from 21.66 to 40.02 g/100 g, 23.95 to 48.09 g/100 g, and 37.44 to 50.02 g/100 g, respectively. The arabinoxylan and arabinogalactan content in whole wheat flour ranged from 2.93 to 4.68 g/100 g and 0.47 to 0.93 g/100 g, respectively, while in bran it contained 11.71 to 18.38 g/100 g and 1.07 to 4.43 g/100 g, respectively. Conclusively, significant variations regarding arabinoxylan and arabinogalactan content were estimated among all spring wheat varieties and their bran fraction.

Keywords:

• Spring wheats
• Non-starch polysaccharides
• Arabinoxylan
• Arabinogalactan

INTRODUCTION

Phytochemicals are in use since immemorial times in various cultures to improve the quality and health-endorsing aspects of baked products. People consuming diets rich in functional/bioactive components are at lower risk of chronic illnesses, thus reducing the risk of various maladies.[1] The plant species containing esteemed quantities of nutritive and non-nutritive components include cereal grains (rice, wheat, oat, barley, and maize), fruits and vegetables, and psyllium husk.[2,3] In this regard, the extraction of bioactive components and their impact on product development demand systematic research investigations to have a persuasive and meticulous awareness for customers.[4]

Cereals are a staple diet for human nourishment and they can be processed into a broad range of products that have enormous economic worth. Among cereals, wheat grains are inimitable owing to certain characteristics of its flour, which form consistent dough that is further utilized in baked products.[5] Globally, wheat covers a maximum area and gives more production as compared to other food grain crops. The area and production of wheat in Pakistan are 9046 thousand hectares and 25 million tons, respectively.[6,7] Wheat is comprised of numerous valuable constituents. The prime components of interests in the grain are starch (60–70 g/100 g), proteins (10–15 g/100 g), and non-starch polysaccharides.[8,9] Among these, proteins and carbohydrates are crucial nutritive components, while minerals, vitamins, and dietary fiber are non-nutritive in nature.[10,11]

Overall, dietary fiber is comprised of non-starch polysaccharides and several other plant components, such as pectin, lignin, β-glucan, and xylo-oligosacchrides. These components have a major effect on the functional utility of cereal grain (milling, baking, and animal feed) owing to their high viscosity in aqueous solution. Among non-starch polysaccharides (NSP), arabinoxylans (AX), arabinogalactans (AG), and β-glucans[12] are of considerable importance. These non-starch polysaccharides are also a major component of dietary fiber in cereals[13] and vital structural elements of cereal's cell wall.[14]

Arabinoxylans are mainly present in the bran of cereals and further categorized into water-extractable arabinoxylans (WEAX) and water-unextractable arabinoxylans (WUEAX). They have xylose backbone and arabinose side chains.[15] The chemical structure of AX is based on a chain of linear (1-4)-b-D-xylopyranose units, which is substituted with L-arabinofuranose in the O-2 or O-3 position, or both. On the contrary, research on cereal AG has been concentrated mainly on spring wheat[16–19] and durum wheat.[19] Arabinogalactans are dry, caramel-like powder with a slightly sweet taste with mild pine odor. They dissolve completely in water, having low viscosity and, consequently, are easy to be incorporated in complementary foods for children.[17]

MATERIALS AND METHODS

Materials

Eight commercially available spring wheat varieties, namely, Lasani-08, Faisalabad-08 (FSD-08), Mairaj-08, Shafaq-06, Sehar-06, Bhakkar-02 (Bk-02), Uqab-2000, and Inqalab-91 were procured from Wheat Research Institute, Ayub Agriculture Research Institute (AARI), Faisalabad and Regional Agriculture Research Institute (RARI), Bahawalpur. The environmental variables influence the quality attributes of grains, so in order to check seasonal variations, these varieties were analyzed for 2 years.

Milling

The grains of each wheat variety free from dockage and foreign matter were subjected to tempering at 14.5 g/100 g moisture level. The tempering of wheat was carried out in plastic containers at room temperature for 24 h in order to equilibrate the moisture within the grains. The amount of water required for tempering was calculated as per the procedure given in AACC[20] method No. 26-95.

The tempered wheat was milled through a Brabender Quadrumate Senior Mill (C.W. Brabender Instruments, Inc.) to obtain different milling fractions, i.e., bran, shorts, break, and reduction flour. Then these fractions were weighed and their percentage was calculated on the basis of total material recovered according to AACC[20] method No. 26-21A. Straight grade flour (SGF) yield was determined by blending the break roll flour and reduction roll flour fractions.

Characterization of NSP

Extraction

Arabinoxylans and arabinogalactans were extracted from whole flour by an enzymatic method[21] and from bran fraction using an alkali extraction method.[22]

Derivatization

Derivatization was the first step for preparation of a sample to run on gas chromatograms flame ionization detector (GC-FID).[23] A 0.6-mg extracted AX sample was placed on a 16 × 75-mm test tube. Then, 0.5 mg of phenyl β-d-glucopyranoside (Sigma-Aldrich) was added, which is used as an internal standard. Hydroxylamine (12.5 mg) hydrochloride (Sigma-Aldrich) and 0.5 ml of undiluted pyridine (Sigma-Aldrich; 99 g/100 g purity) were also added in test tubes. For sealing purposes, Teflon-lined caps were used, which were stirred and kept at 70°C in a water bath for 5 min. Then test tubes were removed, mixed, and allowed to cool to 22°C. Each tube subsequently received 0.5 ml of hexamethyldisilazane (Pierce Chemical Co., Rockford, IL, USA) and 0.4 ml of undiluted trifluoro-acetic acid (Sigma-Aldrich; 98 g/100 g purity), was continuously shaken, and permitted to react at 22°C for 10 min. Next, 0.5 ml of undiluted isooctane (Sigma-Aldrich; 99 g/100 g purity) and 4 ml of deionized water were added in each test tube and then mixed to dissolve residual salts into the aqueous phase. The isooctane layer was pipetted into gas chromatography vials for analysis.

Determination of monosaccharides through GC-FID

A gas chromatograph equipped with a flame ionization detector (Agilent 6890) was used to determine monosaccharide content, which was acquired through extraction. A 30-m-long DB-5 fused silica capillary column with a film thickness of 1.0 μm and a diameter of 0.25 mm was used. A multi-ramp column oven temperature program was used to separate the monosaccharides.[23] An initial temperature of 180°C was held for 4 min, then increased to 200°C at a rate of 1.5°C/min, held for 1 min, increased to 260°C at a rate of 10°C/min, held for 2 min, then increased to 290°C at a rate of 6°C/min increments and held for 8 min. The detector and injection port temperatures were 300 and 280°C, respectively. Nitrogen was used as the carrier gas with a flow rate of approximately 1.5 ml/min. A 2.0-μl splitless sample was injected to quantitate individual sugars.

RESULTS AND DISCUSSION

Arabinoxylans and Arabinogalactans Content in Whole Flour

Mean values regarding arabinose and xylose content have been depicted in Table 1. Arabinose content ranged from 21.66 to 40.02 g/100 g and 21.05 to 36.02 g/100 g between crop years 2008–2009 and 2009–2010, respectively. Analysis revealed that during crop year 2008–2009, Shafaq-06 showed higher arabinose content (40.02 g/100 g) while the minimum (21.66 g/100 g) was observed in Uqab-2000 followed by Lasani-08, Inqalab-91, Bk-02, and FSD-08. Shafaq-06 with 36.02 g/100 g again showed the highest results for arabinose while Lasani-08 had the lowest (20.48 g/100 g) during crop year 2009–2010. Uqab-2000 showed the highest xylose content (58.16 g/100 g) while Bk-02 was at the bottom with 35.87 g/100 g followed by Inqalab-91, Mairaj-08, and Sehar-06. Results regarding xylose content of all these varieties revealed that Uqab-2000 showed the highest value at 50.08 g/100 g while Lasani-08 was the lowest with 33.04 g/100 g. During crop year 2009–2010, analysis revealed that Sehar-06 with 36.1 g/100 g showed the highest content while Bk-02 showed the lowest (31.5 g/100 g) during crop year 2009–10. All wheat varieties were also analyzed for their galactose content (Table 2). Analysis revealed that Sehar-06 with 36.1 g/100 g showed the highest content while Bk-02 showed the lowest at 31.50 g/100 g. Arabinose content of other varieties defined their position after Sehar-06 as meticulous, Shafaq-06 (34.50 g/100 g), Lasani-08 (33.90 g/100 g), Uqab-2000 (33.50 g/100 g), and FSD-08 (33.40 g/100 g). These varieties were also investigated for their galactose content. The highest galactose content of 48.8 g/100 g was found in Sehar-06 followed by Uqab-2000 (48.7 g/100 g), Shafaq-06 (48.00 g/100 g), and FSD-08 (45.20 g/100 g) while during crop year 2009–10, arabinose content of other varieties define their position after Sehar-06 as meticulous, Shafaq-06 (34.5 g/100 g), Lasani-08 (33.9 g/100 g), Uqab-2000 (33.5 g/100 g), FSD-08 (33.4 g/100 g), Mairaj-08 (32.0 g/100 g), Inqalab-91 (31.6 g/100 g), and Bk-02 (31.50 g/100 g). The highest galactose content (50.02 g/100 g) was found in Uqab-2000 and the lowest (38.94 g/100 g) in Inqalab-91. During analysis, it was observed that other varieties followed Uqab-2000 for galactose content, such as Mairaj-08 (40.19 g/100 g), Shafaq-06 (48.79 g/100 g), FSD-08 (47.22 g/100 g), Sehar-06 (47.07 g/100 g), Lasani-08 (43.59 g/100 g), Bk-02 (40.10 g/100 g), and Inqalab-91 (38.94 g/100 g).

Table 1 Arabinose and xylose content (g/100 g) in flour and bran fraction of different spring wheats

	Flour portion				Bran portion
	2008–2009		2009–2010		2008–2009		2009–2010
Varieties	Arabinose	Xylose	Arabinose	Xylose	Arabinose	Xylose	Arabinose	Xylose
Shafaq-06	40.02	41.13	36.02	42.23	19.07	23.95	36.02	42.23
FSD-08	28.60	46.90	30.26	38.88	37.17	48.09	30.26	38.88
Lasani-08	24.08	38.32	20.48	33.04	23.18	39.02	20.48	33.04
Sehar-06	32.30	44.09	30.13	47.79	19.07	40.8	30.13	47.79
Inqalab-91	26.50	47.84	21.05	35.84	24.25	33.07	21.05	35.84
Uqab-2000	21.66	58.16	24.59	50.08	23.78	47.86	24.59	50.08
Bk-02	28.47	35.87	32.38	36.74	29.63	39.99	32.38	36.74
Mairaj-08	33.38	45.09	23.43	36.18	20.73	34.49	23.43	36.18

Table 2  Arabinose and galactose content (g/100 g) in flour and bran of different spring wheats

	Flour portion				Bran portion
	2008–2009		2009–2010		2008–2009		2009–2010
Varieties	Arabinose	Galactose	Arabinose	Galactose	Arabinose	Galactose	Arabinose	Galactose
Shfaq-06	34.50	48.00	31.37	49.98	20.65	48.69	31.37	49.98
FSD-08	33.40	45.20	33.98	50.02	25.67	47.22	33.98	50.02
Lasani-08	33.90	44.90	32.07	46.65	21.35	40.17	32.07	46.65
Sehar-06	36.10	48.80	35.54	43.49	31.79	47.47	35.54	43.49
Inqalab-91	31.60	44.40	29.23	37.44	23.19	38.94	29.23	37.44
Uqab-2000	33.50	48.70	33.39	48.58	21.54	47.76	33.39	48.58
BK-02	31.50	40.10	24.07	43.97	24.08	43.23	24.07	43.97
Mairaj-08	32.00	44.90	30.45	47.67	19.21	41.3	30.45	47.67

Varieties illustrated deviations in their galactose and arabinose content due to environment as they bear variation in genes pool and soil type. In the current study, there has been much focus on determination of non-starch polysaccharides in different spring wheats in subsequent years (Table 3). Arabinoxylans content ranged from 2.93 to 4.43 g/100 g and 3.23 to 5.02 g/100 g while arabinogalactans ranged from 0.47 to 0.88 g/100 g and 0.39 to 0.87 g/100 g among crop years 2008–2009 and 2009–2010, respectively. Lasani-08 showed maximum arabinoxylan content (4.68 g/100 g) while Shafaq-06 with 2.93 g/100 g was at the bottom position. Arabinogalactans content for these spring wheats were also examined through the same procedure. Arabinogalactans was found to be the highest (0.93 g/100 g) in Inqalab-91 and the lowest (0.47) was recorded in Bk-02. Gas chromatography-mass spectrometry (GC-MS) results revealed that varieties following Inqalab-91 for arabiogalactans content are as follows: Sehar-06 (0.88 g/100 g), Shafaq-06 (0.78 g/100 g), and Lasani-08 (0.71 g/100 g).

Table 3  Arabinoxylans and arabinogalactans content (g/100 g) in flour and bran of different spring wheats

	Flour portion				Bran portion
	2008–2009		2009–2010		2008–2009		2009–2010
Varieties	AX	AG	AX	AG	AX	AG	AX	AG
Shafaq-06	2.93	0.78	3.23	0.71	18.38	2.97	17.02	2.13
FSD-08	4.29	0.57	4.09	0.87	15.23	3.45	13.68	3.45
Lasani-08	4.68	0.71	5.38	0.79	14.98	1.07	14.67	2.19
Sehar-06	3.37	0.88	3.23	0.67	10.47	2.89	12.23	2.30
Inqalab-91	3.58	0.93	5.02	0.83	11.71	4.43	14.89	3.18
Uqab-2000	3.01	0.56	3.65	0.69	17.00	3.02	15.35	4.89
Bk-02	4.43	0.47	4.08	0.39	15.67	3.67	16.13	2.87
Mairaj-08	3.23	0.64	4.87	0.75	12.68	2.39	13.89	3.34

Variations for arabinoxylans and arabinogalactans content are owing to different genetic potential of verities; environmental factors such as sunlight, rain, and temperature, etc.; and soil also has an impact on crops. Varieties exhibited a difference in their arabinose and xylose content owing to various environmental alterations as all varieties belong to divergent areas. Some genetic attributes are also affected as they are established from their parent, and soil composition's nutrient nearby in soil may change a crop's composition. The present results are also matched with the previous findings of Morris et al.,[16] Saulnier et al.,[9] Delcour et al.,[24] and Sowa,[25] who observed that presence of AX in wheat mainly depends upon variety, soil, and method of isolation. Environmental factors, such as climate, also affect the content of AX in wheat. Average totals of AX and WEAX content in common wheat are 6.7 and 0.7 g/100 g, respectively.[23,26] The range of total AX of whole grain was 5.55–7.51 g/100 g, with hard wheat cultivars exhibiting higher concentrations than soft wheat.[25] The distribution and structural variation of AX and WEAX of 19 milling fractions ranged from 1.44 to 30.66 g/100 g and 0.3 to 1.38 g/100 g, respectively.[24]

Arabinoxylans and Arabinogalactans Content in Bran

Analysis regarding bran portion for arabinose and xylose content in bran fraction of eight different wheat varieties by GC-MS has been shown in Table 1. Bran analysis demonstrated that during crop year 2008–2009, FSD-08 with 37.17 g/100 g was at the top while Shafaq-06 and Uqab-2000 were at the bottom position with 19.07 g/100 g each. Analysis for other varieties occupy their position after FSD-08 concerning arabinose content as given: Bk-02 (29.63 g/100 g), Inqalab-91 (24.25 g/100 g), Uqab-2000 (21.66 g/100 g), Lasani-08 (23.18 g/100 g), Mairaj-08 (20.73 g/100 g), Sehar-06 (19.07 g/100 g), and Shafaq-06 (19.07 g/100 g). Bran fraction of these varieties was also analyzed for xylose content. The value of 48.09 g/100 g for xylose content was found to be highest in FSD-08 and lowest at 23.95 g/100 g in Shafaq-06. However, other varieties regarding their xylose content remained in the sequence: Uqab-2000 (47.86 g/100 g), Sehar-06 (40.80 g/100 g), and Bk-02 (39.99 g/100 g). During 2009–2010, analysis revealed that Sehar-06 with 35.54 g/100 g showed higher results while Bk-02 had the lowest value (24.07 g/100 g). Sehar-06 contained 35.54 g/100 g arabinose content followed by FSD-08 (33.98 g/100 g), Uqab-2000 (33.39 g/100 g), Lasani-08 (32.07 g/100 g), and Shafaq-06 (31.37 g/100 g). FSD-08 showed maximum values (50.02 g/100 g) whereas Bk-02 was reported at the bottom position (35.87 g/100 g).

Analysis regarding bran portion for arabinose and galactose content in different wheat varieties has been presented in Table 2. The maximum arabinose content (31.79 g/100 g) for bran was observed in Sehar-06 followed by the FSD-08 (25.67 g/100 g), Bk-02 (24.08 g/100 g), and Inqalab-91 (23.19 g/100 g) while the minimum content was recorded for Mairaj-08 (19.21) during crop year 2008–2009. These selected varieties were also evaluated for their galactose content. Shafaq-06 was found to be the highest galactose content (48.69 g/100 g) and was preceded by Uqab-2000 (47.76 g/100 g), Sehar-06 (47.47 g/100 g) FSD-08 (47.22 g/100 g), Bk-02 (43.23 g/100 g), Mairaj-08 (41.30 g/100 g), Lasani-08 (40.17 g/100 g), and Inqalab-91 (38.94 g/100 g); Mairaj-08 had the lowest content (19.21 g/100 g). Bran of various wheat varieties, grown during 2009–2010, was investigated to find the arabinose and galactose content. Results regarding these aspects have been given in Table 2, revealing that the highest arabinose content (35.54 g/100 g) was recorded in Sehar-06 followed by FSD-08 (33.98 g/100 g), Uqab-2000 (33.39 g/100 g), and Lasani-08 (32.07 g/100 g) whereas the lowest (24.07 g/100 g) for this trait was observed in Bk-02. The maximum galactose contents were observed in FSD-08 (50.02 g/100 g) followed by Shafaq-06 (49.98 g/100 g) and Uqab-2000 (48.58 g/100 g). The galactose content of Inqalab-91 was found to be the lowest (37.44 g/100 g) as compared to all other wheat varieties.

The results regarding arabinoxylans content among all varieties of different wheat verities have been given in Table 3. Shafaq-06 illustrated a higher content (18.38 g/100 g) for arabinoxylans while Sehar-06 was reported to have lowest (10.47 g/100 g). Other varieties fall between Shafaq-06 and Sehar-06 and it was found that Uqab-2000 (17.00 g/100 g) ranked at the 2nd position and onwards Bk-02 (15.67 g/100 g), FSD-08 (15.23 g/100 g), Lasani-08 (14.98 g/100 g), Mairaj-08 (12.68 g/100 g), Inqalab-91 (11.71 g/100 g), and Sehar-06 (10.47 g/100 g). The present investigations demonstrated that maximum content (4.43 g/100 g) was found in Inqalab-91 and minimum content (1.07 g/100 g) was recorded for Lasani-08. The results regarding arabinoxylans and arabinogalactans content of bran of eight different wheat varieties grown during 2009–2010 are presented in Table 3. Bran portions of various wheat varieties were also evaluated by the GC-MS for the determination of respective traits. In the present study, maximum arabinoxylans (17.02 g/100 g) were exhibited by the Shafaq-06 followed by Bk-02 (16.13 g/100 g), Uqab-2000 (15.35 g/100 g), and Inqalab-91 (14.89 g/100 g) while minimum arabinoxylans content was noted in the bran portion of the Sehar-06 as compared to the rest of the brans of all spring wheats. The results exposed that the highest arabinogalactans content was recorded in bran fraction of Uqab-2000 (4.89 g/100 g) and the lowest for this trait (2.13 g/100 g) was noticed in the Shafaq-06. However, the values 3.45 g/100 g, 2.19 g/100 g, 2.3 g/100 g, 3.18 g/100 g, 2.87 g/100 g, and 3.34 g/100 g were observed for FSD-08, Lasani-08, Sehar-06, Inqalab-91, Bk-02, and Mairaj-08, respectively.

Numerous factors are involved, which creates differences among these varieties regarding arabinoxylans and arabinogalactans. Most important factors that modify characteristics of varieties are the environmental changes, which vary from one variety to another, as well as genetic potential, which are very important in this aspect. Soil type, e.g., sandy soil, clay soil, and loamy soil, affects crop growth and brings discrepancy in its nutrient composition. Previous studies have also identified genotype differences in arabinoxylans' content of grain.[8,27 ⁻ 32] The environment can play a large role in variation for arabinoxylans content of spring wheats, often being an order of magnitude or greater than that contributed by genotype.[23,33]

CONCLUSION

The presence of bioactive molecules in the plants renders them as an important position in diet-based regimens. However, an appreciable quantity of these bioactive molecules is being lost during food processing. Additionally, some of them hold multifarious perspectives for their utilization to add value to the foods. Cereal, especially wheat, is one example in this respite as it contains several nutrients and phytochemicals. In this regard, the presence of non-starch polysaccharides are of significant value, e.g., arabinoxylans (AX) and arabinogalactan (AG). In 2008–2009, the arabinoxylan contents in whole wheat flours ranged between 2.93 to 4.68 g/100 g while arabinogalactan ranged from 0.47 to 0.93 g/100 g. Likewise, in 2009–2010, arabinoxylan ranged from 3.23 to 5.02 g/100 g while arabinogalactan varied from 0.39 to 0.87 g/100 g. In 2008–09, the arabinoxylans contents in bran fraction ranged between 10.47 to 18.38 g/100 g while arabinogalactan ranged from 1.07 to 4.43 g/100 g. Likewise, in 2009–2010, arabinoxylans in bran fraction ranged from 12.23 to 17.02 g/100 g while arabinogalactan varied from 2.13 to 4.89 g/100 g. These ingredients possess several functional and nutritional properties and, in this project, efforts were only directed to extract AX and AG from different spring wheat varieties of Pakistan.