Extraction and Some Functional Properties of Protein Extract from Rice Bran

Transcription

1 Ksetsrt J. (Nt. Sci.) 40 : (2006) Extrction nd Some Functionl Properties of Protein Extrct from Rice Brn Chockchi Theerkulkit*, Siree Chiseri nd Siriwt Mongkolknchnsiri ABSTRACT Rice brn protein extrct (RBPE) ws prepred from lbortory deftted rice brn (milled nd sieved through 50 mesh screen) by lkli extrction. The extrcting conditions tht provided the mximum protein extrctbility were: extrction rice brn to wter t rtio of 1:4 (w/v) t ph 9.5, gitting speed of 500 rpm for 45 min. The protein extrctbility ws 44.4%of totl protein in rice brn used for extrction. Protein solubility, emulsifying ctivity nd emulsion stbility index of RBPE were determined. The results showed tht protein solubility, emulsifying ctivity nd emulsion stbility index of RBPE were the highest t ph 9 compred t other phs (p 0.05) with the vlues of 66.74%, (A 500nm ) nd min, respectively, while the lowest t ph 4 (p 0.05) with the vlues of 10.75%, (A 500nm ) nd min, respectively. Key words: rice brn, protein extrct, extrction, solubility, emulsion properties INTRODUCTION Protein is the key ingredient in mny food products which contributes the nutritionl vlue, flvor nd other importnt functionl properties of food system (Giese, 1994). Rice brn is n under-utilized milling by-product of rough rice nd hs high nutritionl vlue with 12-15% protein content; however, it hs been sold primrily s niml feed (Houston, 1972; Sunders, 1990). Moreover, rice brn is lso considered s source of hypollergenic proteins nd dietry fibre (Azizh nd Yu, 2000). It lso contined phytochemicls tht hve positive effects on humn helth such s tocopherols, tocotrienols, nd gmm-oryznol (Chen nd Bergmn, 2005). Rice brn protein is higher in lysine content thn rice endosperm protein or ny other cerel brn proteins (Julino, 1985). Protein is widely used in mny kinds of food products which contribute the development of vlue dded foods or used s functionl food ingredients tht re currently in high demnd. By understnding functionl properties of rice brn protein extrct, it could be used wider in food pplictions with higher consumer cceptnce. However, the informtion of extrction nd functionl properties of rice brn protein extrct prepred from Thi rice brn is limited. Therefore, the study of extrction nd functionl properties of protein extrct from Thi rice brn will provide the informtion for production of rice brn protein concentrte nd use for food industry in Thilnd nd other rice growing countries in the future. The objectives of this reserch were to study the effect of gitting speed nd extrction time during extrction on Deprtment of Food Science nd Technology, Fculty of Agro-Industry, Ksetsrt University, Bngkok 10900, Thilnd. * Corresponding uthor, e-mil: fgicct@ku.c.th

2 210 Ksetsrt J. (Nt. Sci.) 40(5) protein extrctbility nd to determine some functionl properties of protein extrct prepred from rice brn; including protein solubility, emulsion ctivity nd emulsion stbility index. MATERIALS AND METHODS Preprtion of deftted rice brn Rice brn smple ws obtined from rice milling industry in Thilnd. Rice brn tht milled nd sieved through 50 mesh screen ws dispersed t 1:3 (w/v) in hexne for 30 min., nd centrifuged t 4,000 xg t 20 C for 10 min. The sediment ws re-extrcted by the sme procedure. Deftted rice brn smples were ir dried overnight under hood. Proximte compositions were nlyzed with AOAC stndrd methods (AOAC, 1995) nd compred with tht of full-ft rice brn. Alkli extrction of rice brn protein extrct Rice brn protein ws extrcted by dispersing milled deftted rice brn in distilled wter (mentioned t bove) t rtio of 1:4 (w/v) t ph 9.5 nd gitted ll the time during extrction, then, centrifuged t 15,200 xg t 25 C for 30 min. The superntnt obtined ws rice brn protein extrct (RBPE). Using the generl procedure described bove, the extrcting conditions, including speed of gitting (400, 500, 600, 700, 800 nd 1,000 rpm) nd extrction time (15, 30, 45 nd 60 min) were investigted on percent protein extrctbility of totl protein in rice brn used for extrction. The percent protein extrctbility ws defined s totl protein in rice brn extrct divided by totl protein in the rice brn used for extrction nd multiplied by 100 (modified from Betschrt et l., 1977). Then, RBPE ws prepred by using the conditions tht provided the mximum percent protein extrctbility. The protein extrct ws determined for its functionl properties, including protein solubility, emulsion ctivity nd emulsion stbility index. Protein solubility determintion Protein solubility of RBPE ws determined by the procedure of Gnnsmbndm nd Hettirchchy (1995) nd nlyzed for protein by Kjeldhl method (AOAC, 1995). Protein solubility ws clculted by dividing the mount of protein in superntnt by the mount of protein in 100g smple nd multiplied by 100. Emulsion ctivity nd emulsion stbility index determintion Emulsion ctivity nd emulsion stbility index of RBPE were determined by the turbidimetric method of Perce nd Kinsell (1978). Emulsion ws formed by mixing 45 ml of rice brn protein extrct with 15 ml of soyben oil using Tissuemizer Ultr Turrx T-25 for 3 min t 25 C, then 1 ml of emulsion ws diluted with 0.1% (w/v) sodium dodecyl sulfte (SDS) solution t rtio of 1:25 (v/v). Absorbnce of emulsion ws mesured immeditely fter emulsion formtion t 500 nm nd expressed s emulsion ctivity of protein. For emulsion stbility index determintion, the emulsion ws left t 25 C for 10 min then 1 ml of emulsion ws diluted with 0.1% (w/v) SDS solution t rtio of 1:25 (v/v) nd mesured the bsorbnce t 500 nm. Emulsion stbility index ws clculted by dividing the bsorbnce t 500 nm of emulsion t 0 min by the chnge in bsorbnce t 500 nm of emulsion between t 0 nd 10 min nd multiplied by the time intervl, l of 10 min. Sttisticl nlysis Three replictions of the experiment were performed. Anlysis of Vrince nd Duncn s New Multiple Rnge Test (DMRT) were used to seprte mens tht were significntly different t p RESULTS AND DISCUSSION Proximte compositions of rice brn

3 Ksetsrt J. (Nt. Sci.) 40(5) 211 Proximte compositions of full-ft nd deftted rice brn re shown in Tble 1. The protein content in deftted rice brn ws significntly higher thn tht of full-ft rice brn nd the ft content ws much lower in deftted smple (p 0.05). Therefore, the results showed tht deftting step ws successful in removing ft nd incresing the protein concentrtion in the rice brn smple prior to protein extrction by lkli solution. Effects of extrcting conditions on protein extrctbility Agitting speed According to preliminry investigtion, the percent protein extrctbility t ph 9.5 ws the highest nd ws not significntly different from tht t ph 10.0; however, it ws significntly higher tht of ph 9.0, 8.0 nd 7.0, respectively (p 0.05). At ph 9.5, it ws found tht extrction of deftted rice brn (milled nd sieved through 50 mesh screen) with wter t the rtio of 1:4 (w/ v) showed the highest percent protein extrctbility bsed on totl protein in rice brn used for extrction (dt not shown). Therefore, the experiment ws further performed by using the bove conditions. The effect of gitting speed of turbine mixer for extrcting protein from deftted rice brn on percent protein extrctbility ws studied by using the rtio of deftted rice brn to wter t 1:4 (w/v) nd extrcted t ph 9.5 for 30 min with vrying gitting speed from 400 to 1,000 rpm. The results re shown in Figure 1. Tble 1 Chemicl composition of full-ft nd deftted rice brn 1/ Rice brn Chemicl compositions 2/ (%dry wt.) Protein Ft Ash ns/ Crude fiber ns/ Crbohydrte Full-ft 14.1b b Deftted b / The experiment ws done in tripliction 2/ Men vlues with different letters in the sme column re significntly different (p 0.05) ns/ Men vlues in the sme column re not significntly different (p >0.05) %Protein extrctbility b b b b b Agitting speed (rpm) Figure 1 Percent protein extrctbility of the extrction from deftted rice brn t vrious gitting speed. b Men vlues with different letters re significntly different (p 0.05).

4 212 Ksetsrt J. (Nt. Sci.) 40(5) From Figure 1, the percent protein extrctbility of the tretments using gitting speed in the rnge of 500 to 1,000 rpm ws not significntly different from ech other (p>0.05), while the tretment using gitting speeds of 400 rpm ws significntly lower thn the others (p 0.05). Thus, the gitting speed of 500 rpm ws chosen s the lowest speed with the highest percent protein extrctbility, nd used for next studies. Extrction time Protein from deftted rice brn ws extrcted with wter t rtio of 1:4 (w/v) nd djusted ph to 9.5, nd then gitted t 500 rpm for 15, 30, 45 nd 60 min. The percent protein extrctbilities of protein extrcts t vrious extrction times re shown in Figure 2. The percent protein extrctbility incresed with incresed extrction time from 10 to 45 min. However, the percent protein extrctbility t 45 min ws not significntly different from tht extrcted for 60 min (p>0.05). Therefore, the extrction time of 45 min ws selected nd used for preprtion of RBPE by extrcting deftted rice brn using turbine mixer with wter t the rtio of 1:4 (w/v) t ph 9.5, nd gitted t 500 rpm. This condition yielded the protein extrctbility of 44.4%. However, the the protein extrctbility ws not very high. This might be due to the poor solubility of some portions of protein with n extensive disulfide bonding nd ggregtion (Hmd, 1997). Moreover, the protein in rice brn re complex mixture nd could bind with other compounds in rice brn such s phytte, fiber (Betschrt et l., 1977; Julino, 1985; Hmd, 1997). The RBPE ws prepred nd used for determintion of its functionl properties. Some functionl properties of RBPE Protein solubility Protein solubility t ph 2.0, 4.0, 7.0 nd 9.0 of protein extrct (extrcted t ph 9.5) prepred from deftted rice brn ws determined. At ph 9 nd ph 4, RBPE showed the highest nd the lowest protein solubility with the vlues of 66.74% nd 10.75%, respectively. The protein solubility t ph significntly incresed s ph incresed (p 0.05). At ph 9, the higher protein solubility might be due to the negtive chrges of molecules of protein t tht ph which resulted in the increse of repulsing force nd interctions with wter molecules (Zys, 1997). However, t ph 9, the protein solubility ws not very high s expected; it might be becuse of the interction or binding of protein with other components tht extrcted from rice brn (Hmd, 1997 nd Julino,1985). %Protein extrctbility c b Extrction time (min) Figure 2 Percent protein extrctbility of the extrction from deftted rice t vrious extrction time. b Men vlues with different letters re significntly different (p 0.05)

5 Ksetsrt J. (Nt. Sci.) 40(5) 213 The protein solubility t ph 2.0 ws significntly higher thn tht t ph 4.0 (p 0.05) s shown in Figure 3. This indicted tht the isoelectric point of rice brn protein is closed to ph 4.0, which greed with the reserch of Ber nd Mukherjee (1989); Gnnsmbndm nd Hettirchchy (1995). Emulsion ctivity nd emulsion stbility index The emulsion ctivity nd emulsion stbility index of RBPE re shown in Tble 2. The emulsion ctivity nd emulsion stbility index incresed s ph incresed. At ph 9, RBPE hd the highest emulsion ctivity nd emulsion stbility index with the vlues of (A 500nm ) nd min, respectively, wheres t ph 4, RBPE hd the lowest emulsion ctivity nd emulsion stbility index with the vlues of (A 500nm ) nd min, respectively. The emulsion properties re closely relted with protein 80 surfce hydrophobicity nd protein solubility (Dmodrn, 1996). The high vlue of bsorbnce t 500 nm indicted the high number of smll oil droplet size in the emulsion (Perce nd Kinsell, 1978). Emulsion ctivity nd emulsion stbility index of RBPE were lowest t cidic ph nd incresed with ph. This might be tht protein hd higher solubility t higher phs (Mngino, 1994). CONCLUSION RBPE could be prepred by extrcting with lkline condition tht provided the protein extrctbility of 44.4%. The protein solubility, emulsion ctivity nd emulsion stbility index of RBPE tended to increse when the ph incresed. However, for using s functionl ingredients, the extrcting conditions nd functionl properties might be improved by other mens. %Protein Solubility b d ph c Figure 3 Protein solubility t different phs of protein extrct prepred from deftted rice brn (using the rtio of rice brn to wter t 1:4 (w/v) nd extrcted t ph 9.5 with the gitting speed of 500 rpm for 45 min) bcd Men vlues with different letters re significntly different (p 0.05) Tble 2 Emulsifying properties of RBPE t vrious phs. ph Emulsion ctivity (A 500nm ) Emulsion stbility index (min) c 18.58c b 29.80b bc Men vlues in the sme columns with different letters re significntly different (p 0.05)

6 214 Ksetsrt J. (Nt. Sci.) 40(5) ACKNOWLEDGEMENTS The uthors would like to express sincere grtitude to the Ksetsrt University Reserch nd Development Institute (KURDI) for the finncil support of this reserch. Specil thnks to Ptum Rice Mill nd Grnry Public Co. Ltd. for kindly supporting rice brn smple. LITERATURE CITED AOAC Officil Methods of Anlysis. 16th ed. Assocition of Officil Anlyticl Chemists, Arlington, Virgini. 467 p. Azizh A.H. nd S.L. Yu Functionl properties of dietry fibre prepred from deftted rice brn. Food Chem. 68: Betschrt A.A., R.Y. Fong nd R.M. Sunders Rice by-products: Comprtive extrction nd precipittion of nitrogen from U.S. nd Spnish brn nd germ. J. Food Sci. 42: Ber M.B. nd R.K. Mukherjee Solubility, emulsifying, nd foming properties of rice brn protein concentrtes. J. Food Sci. 54: Chen M.H. nd C.J. Bergmn Influence of kernel mturity, milling degree, nd milling qulity on rice brn phytochemicl concentrtions. Cerel Chem. 82:4-8 Dmodrn S Functionl property, pp In S. Nki nd H.W. Modler (eds.). Food Protein Properties nd Chrcteriztion. VHC Publishers, New York. Giese J Protein s ingredients: Types, functions, pplictions. Food Technol. 68 (10): Gnnsmbndm R. nd N.S. Hettirrchchy Protein concentrtes from unstbilized nd stbilized rice brn : Preprtion nd properties. J. Food Sci. 60: Hmd, J.S Chrcteriztion of protein frctions of rice brn to devise effective methods of protein solubiliztion. Cerel Chem. 74(5): Houston D.F Rice brn nd polish, pp In D.F. Houston (ed.). Rice: Chemistry nd Technology. Americn Assocition of Cerel Chemists : St. Pul, MN. Julino, B.O Rice brn, pp In O. Julino (ed.). Rice: Chemistry nd Technology. 2nd ed. Americn Assocition Of Cerel Chemists: St. Pul, MN. Mngino, M.E Protein interctions in emulsions: protein-lipid Interctions, pp In N.S. Hettirchchy nd G.R. Ziegler (eds.). Protein Functionlity in Food System. Mrcel Dekker, Inc., New York. Perce K.N. nd J.E. Kinsell Emulsifying properties of proteins: Evlution of turbidimetric technique. J. Agric. Food Chem. 26: Sunders R.M The properties of rice brn s food stuff. Cerel Foods World 35: Zys J.F Functionlity of Proteins in Food. Springer-Verlg Heidelberg, New York. 373 p.