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Abant Izzet Baysal University, 14280 Golkoy Campus, Bolu, Turkey. Tel: +90-374-2541000 (Ext. 4220); Fax: +90-374-2534558. E-mail: yalcin_e@ibu.edu.tr.
Food Sci. Biotechnol. 19(3): 735-742 (2010) DOI 10.1007/s10068-010-0103-1

RESEARCH ARTICLE

Effect of Partial Removal of Prolamins on Some Chemical and Functional Properties of Barley Flours Erkan Yalçın

Received: 6 January 2010 / Revised: 27 February 2010 / Accepted: 4 March 2010 / Published Online: 30 June 2010 © KoSFoST and Springer 2010

Abstract In this study, some chemical and functional prolamins (alcohol soluble), and glutelins (soluble in properties of hulled (BF-1) and hull-less (BF-2) barley flours and their partial prolamin removed forms (PPRF-1 and PPRF-2, respectively) were determined. Total dietary fiber and resistant starch values increased on dry weight basis, conversely β-glucan levels slightly decreased after partial prolamin removing (PPR). Sodium dodecyl sulphatepolyacrylamide gel electrophoresis (SDS-PAGE) patterns of PPRF-1 and PPRF-2 exhibited that PPR was highly achieved. Rapid visco analyzer (RVA) peak and breakdown viscosity values of PPRF-1 and PPRF-2 were higher than BF-1 and BF-2, conversely their setback, trough, and final viscosity values were lower than that of the BF-1 and BF2, respectively. PPR also caused an increase in water binding capacity and resulted in a decrease on water solubility values of barley flours. Protein solubility of PPRF-1 and PPRF-2 were lower than BF-1 and BF-2, respectively. Emulsifying properties of PPRF-2 were affected negatively from the PPR.

Keywords: barley, prolamin, extraction, pasting, functional property

Introduction Cereals are the most important foods of mankind and they provide the major portion of energy and protein and much of the other nutrients needed (1). Cereal seed endosperm proteins are usually classified according to their solubilities into albumins (water soluble), globulins (salt soluble), Erkan Yalçın ( ) Department of Food Engineering, Faculty of Engineering & Architecture, Abant Izzet Baysal University, 14280 Golkoy Campus, Bolu, Turkey Tel: +90-374-2541000 (Ext. 4220); Fax: +90-374-2534558 E-mail: [email protected]

diluted acid/base) as indicated in Silano and De Vincenzi (1), Osborne (2), and Helm et al. (3). Prolamins are the

main storage proteins of the majority of some cereals (including wheat, barley, and rye), where they account for 30-50% of total protein content (4,5). However, some people have intolerance to the prolamins of wheat, rye, and barley. Those prolamins are described as gliadin, secalin, and hordein, respectively. They are responsible for damaging mucosa of the small intestine, leading to the malabsorption of nutrients (6). This sickness is called as celiac desease and celiac patients should avoid from the consumption of wheat, rye, and barley which contain prolamins. Proteins causing celiac desease were commonly extracted with 40 or 60% ethanol for the immunological assays. These conditions were efficient for wheat prolamins, but not necessarily best for barley and rye prolamins (7). Barley (Hordeum vulgare L.) is an ancient cereal grain which is an important agricultural crop in several countries. The grain is used for animal feed and malt production, but there is a growing interest in barley for production of functional foods due to its concentration of bioactive compounds and for industrial use (3,8,9). Barley contains total dietary fibers, especially high amount of soluble dietary fibers such as β-glucans, arabinoxylans, and resistant starch due to the processing of amylose and phenolic compounds (10). There has been recent interest in barley foods in African and Asian countries. Today, pearled barley is known as the most common form of barley food. Additionally, barley soups, hot porridges, pilafs, pasta, snack, and breads of many types can be made from barley. Barley can also be replaced with white or whole-grain wheat flour in order to increase the nutritional value and quality of many food products (10). Most of cultivated barley is hulled. Hull-less barley is a genetically improved variety and it is mostly used in swine and poultry feeding

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by livestock industry (3). The chemical composition of barley is about 60% starch, 20% dietary fiber, and 11% protein (11). Hull-less barley usually has a higher crude protein and amino acid content. In addition, hull-less barley is more digestible than hulled barley (3). Barley proteins can be classified by their sequential extractabilities by the procedure introduced by Osborne (2) as described above. In barley, generally the amount of albumins is relatively low (3-5% of the total protein), and considerable quantity of globulins (10-20% of the total protein) occurs in the endosperm. The main storage protein fractions in barley are hordein (also called as prolamins) and glutelin, accounting for 35-55 and 35-45% of the storage protein pool, respectively (3, 8). The hordein fraction is extracted with alcohol in the presence of a reducing agent (8). Barley hordeins are divided into 5 groups based on their electrophoretic mobilities and amino acid compositions: the B-hordeins (70-80%), C-hordeins (10-20%), D- and γhordeins (less than 5% of the total hordein fraction), and finally A-hordeins is the smallest polypeptides having average molecular weight of 15 kDa (8). Some studies related to rice have indicated that protein could play a role in determining the pasting properties (1214). Lim et al. (13) reported that reducing the protein content in rice flour resulted in increased peak viscosity and hot paste viscosity. Baxter et al. (14) studied the effect of addition and removal of rice prolamins on starch pasting properties. It was found that addition of prolamin to rice starch caused a significant increase in rapid visco analyser (RVA) breakdown viscosity, similarly when prolamin was removed from rice flour, exactly the opposite effect was observed. Hamaker and Griffin (12) claimed that proteins with intact disulphide bonds inhibited the water uptake by starch granules and that resulted in a decrease on peak viscosity. Similar investigations on barley flour were not clearly studied well. Therefore, barley flour should be investigated in order to understand the effect of prolamins on its physicochemical properties before and after removing. After removing the prolamin proteins, barley flours may find extensive applications in the preparation of gluten-free products, and may also be applied as a functional food ingredient. Thus, the objective of this study was to investigate the effect of partial prolamin removing with ethanol on some chemical, pasting, and functional properties of hulled (BF-1) and hull-less (BF-2) barley flours. Materials and Methods

Materials Hulled barley (cvs. Bülbül) and hull-less

barley (advanced line, Ç-738) samples used in this study were obtained from the Field Crops Improvement Center,

E. Yalçın

Ankara, Turkey. Hulled barley is an alternative type 2rowed barley cultivar commonly grown for malting in Turkey. Hull-less barley was developed by cross-breeding of winter and summer type barleys. The hulled and hullless barley samples were cleaned on a Carter Dockage Tester (Carter Day Int., Minneapolis, MN, USA), tempered to 14.5% moisture content and milled into straight-grade flour in a laboratory mill (Bühler AG, Uzwil, Switzerland).

Analytical methods Moisture, ash, and crude oil contents of flour samples were determined according to American Association of Cereal Chemists (AACC) Standard Methods No. 44-01, No. 08-01, and No. 30-25 with slight modifications, respectively (15). Nitrogen contents of barley samples were determined by using AACC Standard Method No. 46-12 and converted to protein content (N×6.25) (15). For β-glucan analysis by an enzymic method, Megazyme β-glucan assay kit (Megazyme International Ireland Limited, Wicklow, Ireland) was used. β-Glucan contents were assessed using McCleary enzymic method for barley samples (16,17). Total dietary fibre (TDF) contents of barley samples were determined by using Megazyme TDF assay kit (Megazyme International Ireland Limited). TDF residue values were corrected for protein, ash, and blank. Resistant starch and non-resistant starch contents of barley samples were also determined by using Megazyme resistant starch assay kit (Megazyme International Ireland Limited). All of the tests on the barley samples were performed in duplicate and the average values were reported. Preparation of partial prolamin removed forms of barley flours Partial prolamin removed forms of barley

samples were prepared from both BF-1 and BF-2 according to the methods of Ewart (18) and Heisel et al. (19) with slight modifications. Barley flours were extracted with 70%(v/v) ethanol (Merck, Darmstadt, Germany) at the solvent to flour ratio of 3:1. L-Cysteine (Merck) was included in the extractions, at a concentration of 1%(w/v), as a food grade reducing agent in order to break the disulphide bonds. Extraction was carried out at 20ºC for 2 hr with constant mixing on the magnetic stirrer (MR HeiStandard; Heidolph, Schwabach, Germany). The slurry was then centrifuged (NF 1200 model; Nüve, Ankara, Turkey) at room temperature at 900×g for 30 min. The supernatant including prolamin proteins were discarded and precipitate including other flour components was saved and rinsed with deionized water 3 times. After lyophilization (Alpha 1-2 LDplus model; Christ, Osterode, Germany), precipitates obtained from BF-1 and BF-2 were called later as PPRF-1 and PPRF-2, respectively, and stored at 4oC before analyzing some chemical and functional properties.

Partial Removal of Prolamins from Barley

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Sodium dodecyl sulphate-polyacrylamide gel electro- dried (ED-E2 model; Binder GmbH, Tuttlingen, Germany) phoresis (SDS-PAGE) method SDS-PAGE was performed at 100oC for 4 hr and WS was calculated as follows:

based on the original procedure of Laemmli (20) modified by Fu and Sapirstein (21). BF-1, BF-2, PPRF-1 and PPRF2 samples were weighed as 80 mg and mixed with 1 mL of buffer solution (pH 6.8) containing 0.063 mol/L Tris-HCl, 2%(w/v) SDS, 7%(v/v) 2-mercaptoethanol, 20%(w/v) glycerol (Merck), and 0.01%(w/v) Pyronine Y (SigmaAldrich, St. Louis, MO, USA). The blend was vortexed (Reax Top; Heidolph) for 1 min every 10 min during 2 hr. Dissolved samples were heated (WNB 7-45 model; Memmert, Schwabach, Germany) in boiling water for 3 min and then applied (12.5 µL) to the SDS-PAGE which was carried out in a cooled slab gel unit (Protean II xi Cell; Bio-Rad, Hercules, CA, USA). The gels were stained overnight with Coomassie brillant blue G-250 (Merck) according to Ng and Bushuk (22). Apparent molecular weights (Mw) were estimated using the wide range molecular weight markers (Sigma-Aldrich).

Pasting properties Pasting properties of the barley samples

were determined using a rapid visco analyzer (RVA 4; Newport Scientific, Warriewood, Australia). The RVA is a controlled shear rate instrument that applies a constant shear rate (rpm) and then measures the resultant torque (force, shear stress). Torque and displacement are then converted to rheological format by means of the measuring system constants (23). In this assay, approximately 3.1 g (14% moisture basis) of sample was dispersed in about 25 mL distilled water in an aluminium sample canister. The RVA pasting curve was obtained by using a 23 min test profile: initial equilibrium at 30ºC for 3 min, heating to 95ºC over 10 min, holding at 95ºC for 5 min, cooling to 50ºC over 3 min, and holding at 50ºC for 2 min. Peak, final, trough, breakdown ( ) and setback ( ) viscosity values and pasting temperature were evaluated with the data analysis software (Thermocline for Windows, Newport Scientific). The results were obtained as centipoise (cp) and converted to rapid visco unit (RVU) by dividing by 12. Each analysis was performed as duplicate. peak

viscosity-trough

final viscosity-trough

Functional properties Water solubility (WS, %) and

water binding capacity (WBC, %) values of the BF-1, BF2, PPRF-1, and PPRF-2 samples were determined using a method based on Singh and Singh (24) with slight modifications. A 1 g of sample was added to 10 mL distilled water and vortexed (Reax Top; Heidolph) for 15 sec every 5 min. After 90 min, it was centrifuged (NF 1200 model; Nüve) at 4,000×g for 10 min. Supernatant was

WS (%)=(weight of dried supernatant/weight of sample) ×100 Precipitate was weighed and then dried at 100ºC for 24 hr. WBC was calculated as follows: WBC (%)=[(weight of wet precipitate-weight of dried precipitate)/weight of sample]×100 Protein solubility of barley samples were investigated according to the method of Yalçin and Çelik (25) with slight modifications. Barley flour suspensions were prepared in distilled water. Solubilities of all suspensions were tested at 1.0%(w/v) flour concentration. The suspensions were stirred at room temperature for 1 hr on a magnetic stirrer (MR Hei-Standard; Heidolph). At the end of mixing period, pH of the suspension was recorded (SevenEasy pH meter S20; Mettler Toledo GmbH, Schwerzenbach, Switzerland). Then, they were centrifuged (NF 1200 model; Nüve) at 3,200×g for 10 min at room temperature and the supernatant was filtered through a Whatman No. 1 filter paper to obtain a clear filtrate. The amount of soluble protein in the filtrate was determined by the method of Lowry (26) with bovine serum albumin (SigmaAldrich) as the standard. The solubility was expressed as a percentage of total protein concentration. Emulsifying capacity (EC) and emulsifying stability (ES) were determined according to Koksel (27) as modified by Bilgi and Celik (28). The samples were prepared according to Abdul-Hamid and Luan (29) with some modifications. Barley sample (0.25 g) was mixed with 5 mL of 0.05% whey protein isolate (Prolacta 90; BBA Lactalis Industrie, Bourgbarre, France) solution and vortexed (Reax Top; Heidolph) for 15 sec. Then, the solution was mixed with 5 mL of corn oil (provided from local market) and homogenized (Miccra D-9 Digitronic; Art Moderne Labortechnik, Müllheim, Germany) at 25,000 rpm for 90 sec. Next, it was centrifuged (NF 1200 model; Nüve) at 2,770×g for 20 min. The ratio of the height of the emulsified phase to the height of total liquid was expressed as EC (%). For the determination of ES, homogenized sample was incubated (WNB 7-45 model; Memmert) at 80oC for 30 min and then centrifuged at 2,770×g for 20 min. The ratio of the height of the emulsified phase to the height of total liquid was expressed as ES (%). et al.

et al.

Statistical analysis All experiments were performed as

duplicate determinations and the mean values and corresponding standard deviations (SD) were reported.

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36 kDa) for both PPRF-1 and PPRF-2. The overall electrophoresis result indicated that relative band intensities of BF-1 and BF-2 decreased due to ethanol extraction, regardless of barley genotype. On the other hand, SDS-PAGE electrophoresis shown that partial removing of prolamin proteins with ethanol treatment was more effective for the sample of hulled barley than that of hull-less barley, since the relative bands intensities of PPRF-1 were generally less intense than that of PPRF-2.

Chemical properties Some chemical properties of BF-1,

Fig. 1. SDS-PAGE pattern of barley flours before (BF-1 and BF-2) and after (PPRF-1 and PPRF-2, respectively) partial prolamin removing. M, Wide-range protein markers; 1, BF-1; 2, PPRF-1; 3, BF-2; 4, PPRF-2

Results and Discussion

SDS-PAGE patterns of barley samples SDS-PAGE

patterns of BF-1 and BF-2 and their partial prolamin removed forms (PPRF-1 and PPRF-2, respectively) are presented in Fig. 1 (lane 1-4). Efficiency of prolamin protein extraction from barley flours was evaluated in this study by using SDS-PAGE technique. According to the SDS-PAGE result, some changes on the electrophoregrams of barley flours occurred after ethanol extraction of prolamins. That was seen with the samples of PPRF-1 and PPRF-2 (lane 2 and 4). In this electrophoregram, groups of barley proteins were termed as described in Shewry and Tatham (4) and Shewry (30). Relative protein band intensities of the PPRF-1 and PPRF-2 were generally less intense than those of the BF-1 and BF-2, respectively. The reduction in relative band intensities of PPRF-1 and PPRF2 occurred due to relative dilution of prolamin proteins during ethanol extraction (Fig. 1, lane 2 and 4). This indicated that ethanol extraction caused a decreasing effect on the intensity of prolamin bands. The decrease was more obvious at the smaller molecular weight regions (below et al.

BF-2, PPRF-1, and PPRF-2 samples were presented on dry weight basis (d.w.b.) in Table 1. The moisture contents of BF-1 and BF-2 were 9.9 and 11.2%, respectively. After partial removing of prolamin proteins, remaining precipitants called as PPRF-1 and PPRF-2 were lyophilized and their moisture contents were found as 2.7 and 3.7%, respectively. The protein contents of PPRF-1 and PPRF-2 were inherently lower than the samples of BF-1 and BF-2, respectively. The protein contents of PPRF-1 and PPRF-2 were found as 5.4 and 8.6%, respectively. The ash contents of PPRF-1 and PPRF-2 were lower than the samples of BF-1 and BF-2, respectively. The crude oil contents of the samples of BF-1 and BF-2 slightly decreased after ethanol treatment of the flours, due to the solubilization of oil in ethanol. TDF and resistant starch contents of PPRF-1 were higher than BF-1. However, although PPR seems to have caused an increase in TDF and resistant starch contents of BF-2, the increase was not significant according to standard deviations. β-Glucan contents of PPRF-1 and PPRF-2 were slightly lower than the samples of BF-1 and BF-2 on d.w.b., respectively. It was indicated that some amount of soluble β-glucan were removed while extracting the prolamins with 70% ethanol. Besides, non-resistant starch contents of PPRF-1 and PPRF-2 were found almost similar compared to BF-1 and BF-2, respectively on d.w.b.

Pasting properties RVA pasting properties of BF-1 and

BF-2 and their respective partial prolamin removed forms, PPRF-1 and PPRF-2, are presented in Table 2 and their pasting profiles according to temperature changing shown in Fig. 2. There were some differences in the RVA viscosity values of BF-1 and BF-2. The highest peak, trough, breakdown, setback, and final viscosity values were obtained with the sample of BF-2 which was the hullless barley flour. Those differences may arise from genotypic variances and chemical constitutions, such as amylose/ amylopectin ratio, waxy or non-waxy starch types. There were also some differences between PPRF-1 and PPRF-2 samples in terms of RVA viscosity values. The highest peak, trough, breakdown, setback, and final viscosity values were obtained with the sample of PPRF-2. After partial removing of prolamin proteins, peak and breakdown

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Table 1. Some chemical properties of hulled (BF-1) and hull-less (BF-2) barley flours and their respective partial prolamin removed forms (PPRF-1 and PPRF-2) Chemical properties Moisture (%) Protein (%, N×6.25) Ash (%) Crude oil (%) Total dietary fiber (%) β-Glucan (%) Non-resistant starch (%) Resistant starch (%) 1)

1)

1)

1)

1)

1)

1)

BF-1 10.0±0.01 9.0±0.01 3.10±0.160 2.0±0.07 6.5±0.88 3.2±0.14 81.0±0.480 3.8±0.23

2)

BF-2 11.0±0.01 13.7±0.05 1.51±0.02 02.2±0.02 08.4±1.05 04.4±0.00 73.3±1.83 03.6±0.29

PPRF-1 2.7±0.20 5.4±0.02 2.28±0.030 1.5±0.15 8.8±0.15 2.6±0.04 79.7±1.130 4.2±0.10

PPRF-2 3.7±0.25 8.6±0.02 1.11±0.000 1.5±0.16 10.1±1.620 3.5±0.25 71.7±2.080 4.0±0.23

Dry weight basis Results are given as mean±SD.

1) 2)

viscosity values rapidly increased. However, trough, setback, and final viscosity values of BF-1 and BF-2 decreased after partial extraction of prolamin proteins as indicated with samples of PPRF-1 and PPRF-2, respectively. The decrease in the final viscosity value of hull-less barley was 32% while that of hulled barley was 62%. As indicated before, hull-less barley had more protein content than hulled barley on d.w.b. That was also same in the samples of partially prolamin removed ones. Fitzgerald (31) found in their work that removal of proteins from rice flours caused a decrease in final viscosity. They explained that the amount of breakdown relative to the peak height was proportionally higher without proteins than in flour, and final viscosity was lower than in flour. Similar findings were observed with barley samples in this study. Fitzgerald (31) also indicated that many storage proteins become sticky when hydrated, so differences in proteins between varieties could easily contribute to viscosity of either the dispersed or the continuous phase. The remaining proteins after partial prolamin removing in both barley types could contribute to the existing breakdown and final viscosities differently. The pasting temperatures of the barley samples, where the pasting viscosity began to increase, were almost similar (around 64oC). The effect of partial removal of prolamin proteins on gelatinization is very clearly related to the altered viscosity patterns in treated barley flours. Recent studies suggested that protein could play a role in determining the pasting and textural properties of rice. Lim (13) reported that reducing the protein content in rice flour increases its peak viscosity. This was confirmed by Tan and Corke (32) who advised that protein content was negatively correlated to peak viscosity and hot paste viscosity. While these studies have suggested a link between total protein and physical properties of rice, it is not clear how individual protein fractions contribute to rice pasting and texture (14). It is generally accepted that the increase in viscosity that occurs during heating of starch suspension is mainly due to the swelling of the starch granules (with lesser contributions et al.

et

al.

et al.

Fig. 2. RVA pasting profiles of barley flours before (BF-1 and BF-2) and after (PPRF-1 and PPRF-2, respectively) partial prolamin removing.

from hydration of protein if present) and breakdown of viscosity is caused by rupture of the swollen granules (14). It is therefore likely that the observed increase in breakdown viscosity following the removal of prolamins was due to an increased rate of starch granule rupturing during RVA processing. This may be caused by an increase in the rate of water absorption by starch granules (14). The decreased final viscosity values of PPRF-1 and PPRF-2 revealed that the 3-dimensional network might be weakened by the removal of prolamins. Baxter (14) indicated according to the results of Champagne (33) that cultivars with similar starch contents and composition could have rather different pasting and textural properties, suggesting that components other than starch may contribute to pasting and textural traits. In this study, the results obtained with 2 different barley flours were confirmed with the previous works. et al.

et al.

Some functional properties of the barley flours (BF-1 and BF-2) and their partial prolamin removed forms (PPRF-1 and PPRF-2, respectively) were Functional properties

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Table 2. Pasting properties of hulled (BF-1) and hull-less (BF-2) barley flours and their respective partial prolamin removed forms (PPRF-1 and PPRF-2) Pasting properties Peak viscosity (RVU) Trough 1 (RVU) Breakdown (RVU) Final viscosity (RVU) Setback (RVU) Pasting temperature (oC)

BF-1 0327±1.6 139±0.1 188±1.5 300±0.2 161±0.2 062±0.0

1)

BF-2 345±5.0 143±0.2 202±4.8 321±1.2 178±1.1 064±0.0

2)

PPRF-1 345±2.4 048±1.1 297±1.4 115±2.3 067±1.2 064±0.0

PPRF-2 414±1.4 084±4.7 330±3.4 217±1.4 133±6.1 064±0.1

RVU=rapid viscoanalyzer unit=centipoise (cp)/12 Results are given as mean±SD.

1) 2)

Table 3. Water solubility (WS) and water binding capacity (WBC) of hulled (BF-1) and hull-less (BF-2) barley flours and their respective partial prolamin removed forms (PPRF-1 and PPRF-2)

Table 4. Protein solubility of hulled (BF-1) and hull-less (BF-2) barley flours and their respective partial prolamin removed forms (PPRF-1 and PPRF-2) at 1%(w/v) sample concentration and end pH values after mixing for 1 hr in distilled water

BF-1 BF-2 PPRF-1 PPRF-2 WS (%) 007.1±0.16 010.2±0.11 004.8±0.00 007.4±0.81 WBC (%) 112.1±0.640 110.7±1.58 165.9±1.03 184.2±1.36

BF-1 BF-2 PPRF-1 PPRF-2 End pH 05.7±0.00 05.6±0.01 03.6±0.01 3.9±0.00 Protein solubility 12.1±0.000 10.4±0.00 11.7±0.14 9.5±0.00 (%)

1)

Results are given as mean±SD.

1)

Results are given as mean±SD.

1)

presented in Table 3 and 4. WS and WBC results of barley flours (BF-1 and BF-2) and their partial prolamin removed forms (PPRF-1 and PPRF-2, respectively) were shown in Table 3. According to the results, WS value of BF-2 was higher than that of BF-1, while WBC values of both type barley flours were almost similar to each other. WS and WBC values of PPRF-2 were higher than that of PPRF-1. In this study, it was also observed that PPRF-2 exhibited higher peak viscosity than PPRF-1. The results generally showed that WS values of BF-1 and BF-2 decreased after partial prolamin removing. On the contrary, WBC values of BF1 and BF-2 considerably increased after partial prolamin removing. This can be explained with increased total starch contents on dry weight basis after partial prolamin removing for PPRF samples. It is known that the structure of starch granule and concentration of starch are effective in WBC and WS values. Koksel (27) reported in their work that lyophilized starch samples did not have compact structures and their water binding values were significantly higher. Sing (34) also reported that WBC and WS values of plant flours affected from morphological structure of starch granules, lipid content, and amylose content. Gupta (35) reported that the peak viscosity indicates the water holding capacity of starch and refers to the maximum viscosity reached during the heating and holding cycle. It can be affected by the molecular structure of amylopectin, starch-water concentration, lipids, residual proteins, granule size, and instrument operating conditions (35). After mixing the samples at room temperature for 1 hr, the end pH value was recorded for each sample and protein et al.

et al.

et al.

1)

solubility was detected at that pH value. End pH and protein solubility of barley flours (BF-1 and BF-2) and their partial prolamin removed forms (PPRF-1 and PPRF2, respectively) were shown in Table 4. The end pH values of BF-1 and BF-2 were 5.7 and 5.6, respectively. Protein solubility values of the barley flours at those pHs were found as 12.1 and 10.4%, respectively. Those pH values were closed to isoelectric point of barley proteins which was indicated as pH 5.4 (36). Besides, the end pH values of PPRF-1 and PPRF-2 were recorded as 3.6 and 3.9, respectively. Protein solubility values of these samples were found as 11.7 and 9.5%, respectively. According to those results, partial prolamin removing did not cause any considerable change on protein solubility, although the protein profile and end pH values of remaining barley flours varied. Barley flour includes whole storage proteins and other flour components. It has a unique structure and has a certain pH value in distilled water. PPRF was obtained after treating the barley flour with 70% ethanol and therefore, natural flour structure and protein profile changed, such as distribution of acidic and basic characters of storage proteins. As a consequence, all those may have created the pH difference between BF and PPRF. EC and ES of barley flours (BF-1 and BF-2) and their respective partial prolamin removed forms (PPRF-1 and PPRF-2) were detected in oil/water type emulsion system. EC and ES values of 0.05%(w/v) whey protein isolate were found as 47.4±0.92 and 56.0±1.27%, respectively. EC values of BF-1 and BF-2 were 49.3 and 56.4%, respectively. In addition, after partial prolamin removing, EC values of PPRF-1 and PPRF-2 were found as 50.7 and

Partial Removal of Prolamins from Barley

7.5%, respectively. ES values of BF-1 and BF-2 were found as 51.1 and 60.2%, respectively. Furthermore, after partial prolamin removing, ES values were found as 52.8 and 30.0% with the samples of PPRF-1 and PPRF-2, respectively. These results also indicated that emulsion properties of BF-2 were higher than that of BF-1. Partial prolamin removing caused slightly an increase in both EC and ES values of hulled barley. However, emulsion properties of hull-less barley flour (BF-2) considerably decreased after partial prolamin removing (PPRF-2). This was more obvious in EC value. In the sample of PPRF-2, EC probably decreased due to starch/whey protein isolate precipitation or change in hydrophilic/hydrophobic balance of remaining proteins. Consequently, the interfacial film between oil and water phases could not be built appropriately. After partial prolamin removing, the relative starch portion of barley flours was increased on dwb. Although proteins are commonly used as emulsion forming and stabilizing agents, starch can not remarkably produce emulsion. Native starch is in granular form and does not have capacity for remaining at oil/water interface. However, it might affect emulsion properties (27,37). Therefore, in the present study, effect of partial prolamin removing on the emulsifying properties of barley flours was investigated in the presence of whey protein isolate. In conclusion, to the best of my knowledge, the present work was the first study that has demonstrated such effect on pasting and some functional properties of different barley flours. The results suggested that partial prolamin removal with 70% ethanol could considerably change the pasting properties of barley flours, particularly hull-less barley flour. That could be explained with the substantial reduction of prolamins from barley flours on dry weight basis. In most cereals, the types and amounts of protein significantly affect the end-use of the grain. The change in viscosity properties by removing prolamins could provide us insight about its actual effect. The prolamins located in the endosperm matrix influence the pasting and some functional behaviors of barley flours. Barley flours without prolamin proteins may find extensive industrial applications as a thickener, colloidal stabilizer, gelling agent, water retention agent, and adhesive agent. Those properties should be studied in detail in further researches.

Acknowledgments This work was financed by Abant

Izzet Baysal University Scientific Research Projects Coordination Unit (Project No. BAP- 2007.09.01.266).

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