An investigation on the morphological, physicochemical, and thermal properties of

Transcription

1 CHAPTER 3 Physico chemicl rheologicl nd therml properties of njvr rice (Oryz Stiv) strch An investigtion on the morphologicl, physicochemicl, nd therml properties of Njvr rice strch ws crried out in this chpter. The properties were compred with ntive chm rice strch nd were found to e different from the ntive chm vriety rice strch.

2 3.1. Introduction Strch is reserve crohydrte in the plnt kingdom tht world wide 70 80% of the clories consumed y humns, nd is generlly deposited in the form of minute grnules or cells rnging from 1 to 100 µm or more in dimeter in the storge orgns [Wurzurg, 1986; Zoel et l., 1995; Whistler et l., 1997; Buleon et l., 1998; Freits et l., 2004]. Rice is one of the most importnt cerels nd more thn two thousnd vrieties of rice re grown commercilly throughout the world nd is the min food item in Asi. Strch is the min component in rice, nd s isolted from endosperm, hs een used for food nd nonfood pplictions in mny forms. It hs lso een used to produce modified strch, such s cross-linked, sustituted, cid-thinned, leched, nd oxidized strches [Xie et l., 2008]. Rice (Oryz stiv) strch hs mny unique ttriutes tht mke it one of the most interesting strches in the food industry. Rice strch is hypollergenic, lnd in tste, white in colour nd, s gel, is smooth in texture. However, rice strch, in common with other cerel strches, hs negtive spects, such s gel syneresis, retrogrdtion, nd tendency to exhiit rekdown, either from extended cooking, high sher or cidic conditions, producing wek-odied, cohesive, ruery pstes, nd undesirle gels [Viturwong et l., 2008]. The Ayurvedic Tretise (Indin Mteri Medic) records show the existence of mny medicinl rice vrieties in Indi. Njvr is the unique rice, short durtion cultivr grown only in certin pockets in Kerl stte, south Indi [Deep et l., 2008] nd elongs to the fmily Oryz. This is the only cultivr trditionlly used effectively in 68

3 the Ayurvedic system of medicine in certin specific tretments like Pnchkrm. It is interesting to note tht this tretment is now getting more nd more populr, not only in this region of the country ut lso in other prts of the ntion nd even in other countries. Njvr s specil cerel, reported to hve properties to rectify the sic ills ffecting the circultory, respirtory s well s the digestive system. Blck glumed njvr hs een used in Ayurved tretment from the ge of Chrk-ie, BC.600. njvr kizhi nd njvr theppu re two mjor tretments in Ayurved system of medicine in conditions of rthritis, prlysis, neurologicl complints, degenertion of muscles, tuerculosis, for children with Anemi, for women during lcttion, in certin ulcers, nd skin diseses. Njvr rice endosperm hs round 73 % of strch. Strches exhiit difference in vrious properties in ccordnce with the source nd genotype. The properties minly depend on physicl nd chemicl chrcteristics such s grnule size, mylose mylopectin rtio, the shpe nd size of strch grnules which is chrcteristics of their otnicl origin etc [Mdsen et l., 1996]. Strch exhiits unique viscosity ehviour with chnge of temperture, concentrtion nd sher rte [Lii et l., 1996]. Mny reserchers hve used the dynmic rheometer for studying the viscoelstic or rheologicl properties of strches [Tsi et l., 1997]. The rheologicl properties of different strches vry to lrge extent s function of grnule structure nd physico chemicl composition. Severl rheologicl chnges occur in strch, when strch wter systems re heted ove the geltiniztion temperture, the strch grnules loose their crystllinity, sor lrge mounts of wter, nd lech out 69

4 mylose, therey forming pste composed of swollen strch grnules dispersed in n mylose mtrix [Ring, 1985]. Strch geltiniztion refers to the disruption of the moleculr order within strch grnules when they re heted in the presence of wter. Evidence for the loss of n orgnized structure includes irreversile grnule swelling, loss of irefringence nd crystllinity. Geltiniztion is n energy-soring process tht cn e followed y differentil scnning clorimetry [Whistler et l., 1997]. We hve investigted into the unique properties of this njvr rice compred to common chm vriety of rice, which is the stple food of kerl nd hs found out the unique physico chemicl, therml, rheologicl nd texturl chrcteristics of this strch which mkes it preferred rice for the pnch krm tretment Experimentl Mterils Njvr (Blck glumed) nd chm (Jy) rice were purchsed from the locl mrket, Trivndrum, Kerl, Indi. Protese nd mylse enzyme were purchsed from Sigm Aldrich, USA Methods Properties of njvr strch nd ntive chm strch were studied y scnning electron microscope, TGA nd DSC, Rpid visco nlyzer, Rheometer, Food texture nlyser, X-ry diffrction pttern etc. 70

5 Strch isoltion Njvr rice nd Chm rice strch ws extrcted s descried in chpter Amylose content Njvr mylose ws seprted y lkli leching, purified nd used s stndrd. For this 10 g strch ws dispersed in 50 ml wter. This dispersion is dded to the 0.5N 500 ml NOH solution. The temperture ws mintined s 25 ºC 28 ºC, kept this lkline solution for 5minutes with mgnetic stirring. Then 100 ml 5% (w/v) NCl solution ws dded nd then the dispersion ws neutrlized with 1N HCl to ph 6.5 to 7.5. Kept this solution for settling down for 15 h, the gel settles nd it occupies out 1/3 rd of the totl volume. The superntnt ws the mylose which ws precipitted y ethnol nd purified. Amylose content of njvr rice ws determined ccording to the procedure of Sowhgy nd Bhttchry [Sowhgy et l., 1971]. According to this method ccurtely weighed 100 mg of the strch ws mixed with 1 ml lcohol. 10 ml (0.1N) of sodium hydroxide solution ws dded, nd left overnight t room temperture. Alterntively the mixture my e intermittently heted in oiling wter th for few minutes till the strch is dispersed, cooled nd diluted to 100 ml. Mixed thoroughly nd pipetted 5ml into 100ml volumetric flsk dded 3 drops of phenolphthlein nd out 50 ml of distilled wter. Added dilute hydrochloric cid drop wise with shking till the colour is just dischrged. Added 2 ml 1% (w/v) iodine solution nd mde up to 71

6 volume with oiled wter. Red the solutions fter 30 min in spectrophotometer t 600 nm ginst the lnk Soluility nd swelling power Soluility nd swelling power t vrious tempertures such s 60 C, 70 C, 80 C, 85 C nd 90 C were determined [Whistler, 1964]. Strch (0.1 g ) ws tken in previously tred ottle nd sufficient distilled wter ws dded to give totl volume of wter equivlent to 9 g. Heted in wter th for 30min t ny constnt temperture (60, 70, 80, 85, 90 C) with mgnetic stirring. After heting, the ottle ws rinsed with distilled wter to ring the volume to 10 g. Centrifuged the smple t 313 xg for 15 min. The cler superntnt, 5ml ws drwn off into clen dry dish. The dish ws dried in vccum oven for 4 h t 120 C. Cooled in desictor nd weighed. The superntnt ws completely decnted nd the swollen grnules were weighed. Percentge soluility nd swelling power were clculted using the formul Dry weight % Soluility = 100 Smple weight (3.1) weight of swollen grnule Swelling Power = 100 Smple weight (100 - % soluility) (3.2) Light trnsmittnce or gel clrity Strch suspensions (0.6% w/v in DMSO) were plced in wter th t 90 C for 30 min nd gitted well nd then cooled to room temperture. The percentge trnsmittnce of this geltinized strch ws determined t 640nm using 72

7 spectrophotometer. The gel clrity ws studied with time durtion (2h, 4h, 6h, 24h, 48h, 72h) [Bello-Perez et l., 1999] Freeze thw stility 50 ml of 6 % (w/v) strch solution ws heted to 95 C nd ws held t this temperture for 15 min nd the gel ws cooled down to room temperture. The gel ws frozen t < 0 C over night nd thwed to room temperture nd then centrifuged t 604 xg for 15 min nd mesurements ws tken for seprtion of wter (syneresis) from the strch gels nd the process ws repeted for 5 cycles Retrogrdtion properties of strch After conducting the therml nlysis, the smples were stored in the refrigertor t 4 C for 7 dys for retrogrdtion studies. These smples were left t room temperture, 28 C for 2 hour efore nlysis. Reheted t the rte of 10 C/min from 0 to 130 C. The enthlpies of retrogrdtion ws clculted utomticlly nd % retrogrdtion ws clculted s Enthlpy of retrogrdtion % R = 100 Enthlpy of geltiniztion (3.3) Enzymtic hydrolysis of strch The digestiility of strches ws studied using the enzyme lph mylse from Bcillus myloliquifciens. Strch (25% w/v) ws geltinized in 0.01M phosphte uffer of ph-7.0 in oiling wter th t 100 C. The strch gel ws then cooled to 73

8 Physico chemicl rheologicl nd therml properties of njvr rice (Oryz Stiv) strch Chpter 3 80 C. Incuted the gel t 80 C for 30 min with 200 units of enzyme nd 50 ppm of clcium chloride. After the digestion, the reducing sugr ws determined from n liquot of this smple. DNS ws used s the regent nd the sornce ws red t 540 nm using UV-Vis spectrophotometer Results nd discussion Morphology of the strch grnules The rice strch grnules re found to e hexgonl in shpe, which is typicl in mny of cerel strch. SEM shows tht the njvr strch grnule hs dimeter in the rnge of 5 6 µm, where s rice strch grnules ws smller, nd hd size of 1-2 µm (Figure 3.1). Figure 3.1. SEM imge of ) Njvr strch grnule, ) Ntive chm strch grnule. The vrition in strch grnule morphology my e due to the iologicl origin nd physiology of the plnt nd the iochemistry of the myloplst. This my e lso due to the vritions in the mylose nd mylopectin content nd its structure, which in turn ply n importnt role in the control of the strch grnule size nd shpe [Svegmrk et l., 1993; Kur et l., 2007]. Vrition in the ctivity of enzyme, such s 74

9 grnule ound strch synthse during growth hve lso een reported to ffect the strch grnule morphology in pottoes Amylose content Amylose content in njvr rice strch ws found to e 20 ± 2 % nd ws similr to the ntive rice vrieties were the mylose content is in the rnge of 20-22% [Deep et l., 2008] Swelling power nd soluility Swelling power nd soluility of rice strches t different tempertures were studied. Results were shown in Figure 3.2. In the cse of njvr strch, the swelling power increses steeply over the rnge of temperture studied. The pttern shows tht njvr strch swelled rpidly t out 76 C nd it exceeds the swelling of ntive rice strch grnules nd this strch grnule hs comprtively sturdy grnule structure. The swelling is due to the reking of intermoleculr hydrogen onds in the morphous region of the grnule tht llows irreversile nd progressive wter sorption [Bello- Perez et l., 1999]. In the cse of ntive rice strch, swelling pttern is less steep nd shows constnt increse in swelling power etween 60 C nd 76 C thn njvr. After 76 C, the swelling power vlue is higher for njvr. The low swelling power of njvr strch elow 76 C is minly due to its higher geltiniztion temperture. It is reported tht the swelling power is positively correlted to geltiniztion temperture, mylopectin chin length nd mylose content [Sski et l., 1998]. 75

10 Swelling power (%) Temperture ( C) Figure 3.2. Swelling power of () njvr strch, () ntive rice strch Solulity (%) Temperture ( C) Figure 3.3. Soluility of () njvr rice strch nd () ntive rice strch. Soluility of njvr strch shows sudden increse from 60 C nd soluility increses rpidly up to out 68 C then slowly etween 68 C -78 C (Figure 3.3). 76

11 Then it ecomes constnt. Soluility of ntive rice strch increses rpidly etween 70 C -80 C. Aove 76 C it shows slow increse. The soluility is due to the leching of mylose chins from the morphous prt of the swollen grnules. Swelling power nd the percentge solule re higher in njvr rice t 76 C. Below 76 C, it shows lower vlues thn ntive strch. The higher swelling power t higher temperture mkes this strch unique nd provides ppliction for pnchkrm in Ayurved system of medicl tretment Strch gel clrity Njvr rice strch gel hd less trnsmittnce vlue (87.45 %) compred to ntive rice (95.30 %) (Figure 3.4), ecuse of the reltively higher grnule size of the strch. The % trnsmittnce of gel decreses with n increse in storge time, due to the retrogrdtion of strch. In the cse of njvr strch gel, the decrese in trnsmittnce ws shrp up to 6 h then it remined lmost constnt. However the ntive rice strch lost its clrity significntly fter 2 h. The degree of trnsmittnce is directly correlted to the wter sorption cpcity. The njvr rice strch hs low wter sorption cpcity t lower tempertures compred to the ntive rice strch nd this my e the reson for the lower clrity of strch gel. In njvr, clrity of the gel is not much ffected y the storge time, where s in the cse of ntive rice strch, the gel ecomes opque fter 2 h due to rpid retrogrdtion. 77

12 Trnsmittnce (%) Time (h) Figure 3.4. Gel clrity of () njvr rice strch nd () ntive rice strch. From the studies it ws seen tht the clrity of gel from njvr strch is more stle thn rice strch nd hence cn e used with dvntge in food industry Freeze Thw stility Freeze thw stility is n importnt property tht is used to evlute the ility of strch to withstnd the undesirle physicl chnges tht my occur during freezing nd thwing. This property my e simply evluted y grvimetric mesurement of the wter of syneresis tht seprtes from strch pstes or gels nd the multiple freeze thw cycles tht involve sujecting smples to repeted freezing nd intermittent thwing to room temperture over period of 2 4 h, re known to drsticlly ccelerte retrogrdtion nd syneresis. In the freezing process, when strch pstes or gels re frozen, phse seprtion occurs upon formtion of ice crystls. Upon thwing, 78

13 phenomenon known s syneresis occurs, the wter cn e esily expressed out from the dense gel network. Repeting the cycle of freezing nd thwing enforces the phse seprtion nd ice growth. As the ice crystls ecome lrger, the syneresis nd sponge formtion occurs more redily. Syneresis in freeze thwed gel is due to the increse of moleculr ssocition etween strch chins, in prticulr retrogrdtion of mylose, expelling wter from the gel structure Synerisis (%) Time (Dys) Figure 3.5. Freeze thw stility of () njvr rice strch nd () ntive rice strch. Thus the mount of wter due to syneresis of the gel is useful indictor for the retrogrdtion tendency of strch [Srtrt et l., 2005]. It is well known tht when strch gel is frozen, strch-rich regions re creted in the mtrix, where wter remins prtilly unfrozen.. High solid concentrtion in the regions fcilittes the strch chins to ssocite forming thick filments, wheres wter molecules cogulte into ice crystls forming 79

14 seprted phse. These effects contriute to spongy structure of the gel [Ferrero et l., 2000; Lee et l., 2002; Arunynrt et l., 2008]Freeze thw stility of oth the strch gels hs sme pttern s shown in Figure 3.5. Njvr strch gel hd low syneresis compred to the ntive rice strch gel nd the % syneresis is inversely relted to the stility of the gel. Strch with high syneresis, redily sor nd eliminte wter like sponge. Njvr rice strch seprte less wter t the first cycle thn the ntive rice strch. Mximum wter ws seprted in the first cycle then it ws decresed over time. Compred to other strches, rice strch shows low freeze thw stility. Low synerisis rte of njvr strch indictes its superior qulity for its possile ppliction in food industry nd pnchkrm in Ayurved system of medicine Differentil scnning clorimetry The geltiniztion properties of the two strches were mesured y differentil scnning clorimetry, nd the DSC thermogrm of njvr nd ntive rice strches were depicted in Figure 3.6. Compred with ntive rice strch, njvr strch exhiited higher geltiniztion tempertures. The strch geltiniztion temperture depends on the prticle size distriution, where smll grnules usully hve lower geltiniztion temperture vlues thn the lrge grnules. However, there re conflicting reports out geltiniztion enthlpy for whet strch A nd B type grnules. 80

15 Het Flow (mw) Temperture ( C) Figure 3.6. Differentil scnning clorimetry of () njvr strch, () ntive rice strch. Some studies climed tht A-type strch possess higher geltiniztion enthlpy thn B- type grnules [Peng et l., 1999; Chiotelli et l., 2002], wheres, Wong nd Lelievre reported tht A-type grnules possess lower geltiniztion enthlpy [Wong et l., 1982; Xie et l., 2008]. Here we studied n A type rice strch. Geltiniztion endotherm of ntive rice strch ws roder thn njvr. The melting temperture rnge gives n indiction of the qulity nd heterogeneity of the recystllized mylopectin. Thus, wide melting rnge might imply lrge mount of crystls of vrying stility, wheres nrrow rnge could suggest crystls of more homogeneous qulity nd similr stility [Fredriksson et l., 1998]. Njvr rice hd high geltiniztion temperture (85 C) thn the ntive strch (70 C). Njvr strch required more energy to geltinize since its enthlpy of geltiniztion ws very high ( H=366.17j/g). The enthlpy of geltiniztion of ntive rice strch ws lower nd is 81

16 61.82j/g. The difference in geltiniztion temperture mong the rice strch my e influenced y the fctors like grnulr rchitecture nd moleculr structure of mylopectin [Gunrtne et l., 2002]. The rice strch prticles hve crystlline region within strch grnule tht is composed of smll crystllites with different crystl melting temperture which minly consists of mylopectin [Vsnthn et l., 1996] Het Flow (mw) Temperture ( C) Figure 3.7. Differentil scnning clorimetry of () njvr strch, () ntive rice strch fter retrogrdtion. The retrogrdtion properties of njvr nd ntive rice strches were studied fter storge of geltinized strches t 4 C for 7 dys. Strch retrogrdtion is cused y the moleculr interction fter cooling of the geltinized strch pste. During the retrogrdtion, mylose forms doule helicl ssocition, wheres mylopectin forms crystlline region y the ssocition of the outermost short rnches [Ring, 1985]. The vlues of enthlpy of retrogrded strch provide quntittive mesure of energy 82

17 trnsformtion tht occurs during the melting of re-crystlline structure. Retrogrdtion pek of njvr strch ws shifted in the higher temperture regions. (87 C) nd ntive rice strch shows the similr pttern s in the cse of geltiniztion endotherm (70 C) (Figure 3.7). The mylopectin nd the intermedite mterils ply significnt role in strch retrogrdtion during refrigerted storge. Recrystlliztion of mylopectin rnch chins hs een reported to occur in less ordered mnner in stored strch gels thn in ntive strches [Wrd et l., 1994]. The percentge of retrogrdtion (%R) ws less for njvr strch (85 %) s compred to ntive rice strch (90.56 %) Thermogrvimetric nlysis Njvr nd ntive strch ws sujected to therml degrdtion. Thermogrvimetric plot of njvr strch nd ntive strch were shown in Figure 3.8. In the cse of njvr strch, degrdtion strts t temperture of 275 C. But for ntive strch the degrdtion temperture strts t lower temperture of 225 C. This showed tht njvr strch ws thermlly more stle thn ntive rice strch. Temperture t which 5% weight loss of njvr strch nd ntive rice strch re t 59 C, nd 62 C respectively. Temperture corresponding to 10% weight loss of njvr nd ntive rice strch ws 85 C (njvr) nd 90 C (ntive rice). 83

18 100 Weight Loss (%) Temperture ( C) Figure 3.8. Thermogrvimetric nlysis of () njvr strch, () ntive rice strch Psting property Psting properties re reported to e influenced y grnule size, mylose/ mylopectin rtio, strch moleculr chrcteristics nd the condition of the therml process employed to induce geltiniztion [Zhou et l., 1998]. Psting profile of oth rice strches re similr nd ehves s typicl cerel strch. The results re presented in Figure 3.9. Njvr strch showed higher pek viscosity vlue (957 cp) thn ntive rice (632 cp), minly due to the igger grnule size which in turn increses the swelling rtio nd viscosity. Finl viscosity of these strches followed the sme pttern (Finl viscosity of njvr is 1054 cp nd ntive chm rice is 736 cp). Pek viscosity is mesure of the wter holding cpcity of the strch in terms of the resistnce of swollen grnules. The rekdown viscosity is regrded s mesure of degree of 84

19 disintegrtion of grnules nd shows pste stility. During rekdown, the grnules re disrupted nd mylose molecule will generlly lech out in to the solution. Figure 3.9. Psting profile of () njvr strch, () ntive rice strch Heting eyond the pek viscosity temperture provides further energy to rek down the residul crystlline structure, cusing the viscosity to decrese. Njvr strch showed higher rekdown vlue (324 cp) thn ntive strch (82 cp). The setck viscosity of njvr (421 cp) is higher due to high pek viscosity nd mylose content. The set ck is the viscosity increse resulting from the rerrngement of mylose molecules tht hve leched from the swollen strch grnules during cooling nd is generlly used s mesure of the gelling ility or retrogrdtion tendency of the strch [Ad Krim et l., 2000]. Njvr strch hd higher set ck viscosity while the ntive chm rice strch showed the lest. The strting of geltiniztion for oth njvr nd ntive strch were found to e the sme (54 C). But the psting 85

20 temperture of njvr rice strch ws higher nd found to e 84 C, where s ntive rice strch shows psting temperture of 78 C. These vlues re close to the geltiniztion temperture otined y DSC nlysis Enzyme digestility The digestiility of the strch is n importnt nutritionl fctor. The geltinized strches were hydrolysed using cteril lph mylse. Both njvr nd ntive strch re not highly digestile nd showed the sme rte of hydrolysis. Only 14% of strch ws hydrolysed in 30 minutes of incution t ph 7.0, t 80 C. The enzyme digestiility minly depends upon the interply of mny fctors such s strch source, grnule size, mylose mylopectin rtio etc. But here the grnule size lso did not ffect the lph mylolysis of the strch Rheologicl properties Effect of temperture Effect of heting of rice strch dispersion t constnt rte of temperture on sher modulus is shown in Figure Both strches shows sme pttern of sher modulus ginst temperture. Up to certin temperture oth moduli (storge [G ] nd loss [G ]) were sme. After this storge modulus shows shrp increse reches mximum then decreses. The temperture corresponds to higher storge modulus (G mx ) is the geltiniztion temperture. In njvr nd ntive chm rice these geltiniztion temperture is different. Njvr rice geltinizes t higher temperture of 68 C nd the geltiniztion strts t 59 C. But in ntive strch, geltiniztion 86

21 temperture ws found to e 58 C nd geltiniztion strts t lower temperture of 48 C. 4x10 5 3x10 5 A 4x10 5 3x10 5 B G', G" (P) 2x10 5 G', G" (P) 2x10 5 1x10 5 1x Temperture ( C) Temperture ( C) Figure Rheologicl nlysis. Temperture dependence of (A) njvr strch, (B) ntive rice strch ginst moduli.(- storge modulus, - loss modulus) Higher vlue of G compred to G indictes the formtion of the gel. The significnt increse in G vlue of rice strch on heting is cused y formtion of three dimensionl gel network developed y leched out mylose nd reinforced y strong interction mong the swollen strch prticle [Bilideris et l., 1980]. Further heting eyond G mx, the G decresed significntly, indicting dmge of gel nture during prolonged heting. The complete loss of gel nture of njvr strch occurs t higher temperture compred to the ntive rice strch. This indictes the stility of njvr strch gel with temperture. The dmge of structure could e due to the melting of the crystlline regions remining in the swollen strch grnule or resulted from the disentnglement of the mylopectin molecules in the swollen prticles tht softens the prticles. 87

22 Frequency dependence The dynmic rheologicl properties G nd G re presented s function of frequency in Figure The G, G nd complex modulus (G * ) decresed in the order G * > G > G, s commonly oserved for norml strch gels. The frequency dependence of G nd G gives vlule informtion out structure. A mteril tht is frequency independent over lrge time scle rnge is solid-like; true gel system is such mteril. In contrst, strong frequency dependence suggests mteril structure with moleculr entnglements tht ehves more like solid t higher frequencies nd more like liquid t lower frequencies. When swollen prticles re sujected to sher oscilltion t certin ngulr frequency nd mplitude, G nd G is proportionl to the dissipted or lost energy during the oscilltion process. It cn e seen from the figure tht with incresing frequency G nd G grdully increse. G is higher thn the G in the whole frequency rnge, the elstic ehvior of the smple predomintes over its viscous ehvior nd the swollen smple exhiits mechnicl rigidity. Both rice vriety show the sme pttern of modulii. But the difference etween the G nd G vlue is more in njvr strch compred to the ntive rice nd lso in the cse of njvr strch, the storge modulus is frequency independent. This indictes tht the gel rigidity is higher in the cse of njvr strch gel. For true gel the storge modulus is lwys higher thn loss modulus nd is independent throughout the experiment. This property is very useful for the ppliction of gels in food industries, dhesives, nd drug delivery etc. 88

23 G',G" (P) 100 G',G" (P) 100 A B Frequency (rd/s) Frequency (rd/s) Figure Rheologicl nlysis. Frequency dependence of (A) njvr strch, (B) ntive rice strch ginst moduli. (- storge modulus, - loss modulus) The rtio of loss nd storge moduli (loss tngent or tn δ) or phse ngle is mesure of the energy lost compred to energy stored in deformtion. Lower tn vlue of njvr indictes the formtion of strong gel compred to ntive rice strch. The results were shown in Figure Torque is the force required to rotte the smple. Figure 3.13 shows the vrition of torque with frequency. Both rice shows similr pttern. Torque increses with frequency to certin limit then it decreses. This my e due to the distortion gel structure t higher frequency. Njvr rice required more force to rotte the smple compred to ntive rice strch. Complex viscosity or the frequency dependent viscosity decreses with increse in frequency (Figure 3.14). 89

24 28 26 Phse ngle (deg) Frequency (rd/s) Figure Rheologicl nlysis. Phse ngle ginst frequency () njvr rice strch, () ntive rice strch Torque [µnm] Frequency (rd/s) Figure Rheologicl nlysis. Torque ginst frequency of () njvr strch, () ntive rice strch. 90

25 Complex viscosity (P s) Frequency (rd/s) Figure Rheologicl nlysis. Complex viscosity ginst frequency () njvr strch, () ntive rice strch. Both njvr nd ntive rice strch showed decrese in viscosity with sher. These results showed tht njvr rice ehves s non Newtonin fluid with pseudoplstic nture s in the cse other strches (Figure 3.15). Yield stress is the stress t which mteril egins to deform plsticlly. Aove the yield stress the mteril ct s elstic nd will return to its originl shpe when the pplied stress is removed. Once the yield stress point is crossed, the deformtion will e permnent nd non-reversile. The yield stress of njvr rice strch ws found to e P. But in the cse of ntive rice strch yield stress ws low ( P), Figure 3.14 nd This indictes the high gel strength of njvr strch ginst stress. 91

26 70 60 Sher stress (P) Sher rte (s -1 ) Figure Rheologicl nlysis. Newtonin ehviour of () njvr strch, () ntive rice strch. All rheologicl nlysis showed tht njvr stches hve good properties which cn e pplicle to food industries, medicl field, dhesives, compred to ntive rice strch. Its high gel strength, het cpcity nd high geltiniztion temperture my e the reson for its wide ppliction in Ayurved tretments Texture profile nlysis The hrdness (HA), dhesiveness (AD) springiness (SP), cohesiveness, nd chewiness of gels from njvr nd ntive rice strches were studied. The texturl properties were influenced y strch grnule size. The hrdness of geltinized strch gel hs relted to the mylose mtrix nd the filling effect of the swollen grnules [Morris, 1990]. Hrdness of njvr strch gel (0.289N) is less thn the ntive rice strch gel (0.391N). Adhesiveness is surfce chrcteristic nd depends on comined effect of dhesive nd cohesive forces, nd lso viscosity nd viscoelsticity. The negtive vlue for 92

27 dhesiveness of oth rice strches were for Njvr nd for ntive rice strch the vlue is Springiness or elsticity is sensitivity of gel rueriness in the mouth, nd is mesure of how much the gel structure is roken down y the initil compression. High springiness ppers when the gel structure is roken into few lrge pieces during the first texture profile nlyzer compression, wheres low springiness results from the gel reking into mny smll pieces. Less springy gels will rek down more esily during mstiction thn firm nd springy gel. Njvr rice strch (6.9368) showed 4 times higher vlue for springiness compred to the ntive rice strch (1.7849). Chewiness is the quntity to simulte the energy required for msticting semi-solid smple to stedy stte of swllowing process. It is the product of gumminess nd springiness. Chewiness of njvr rich gel (1.2923) ws three times higher compred to ntive rice strch (0.4017). Cohesiveness is n index tht how well the product withstnds second deformtion reltive to its ehviour under the first deformtion. Both the strch gel did not hve much difference in cohesiveness, even though the strch gel of Njvr rice showed slightly higher vlue thn ntive rice. Texture profile nlysis showed tht njvr strch hd good springiness nture. These properties my e very useful in food industries XRD nlysis Ntive strches generlly exhiit two min crystlline types, nmely, the A-type for cerel strches nd the B-type for tuer nd mylose-rich strches. The X-ry ptterns 93

28 of A type strches give the stronger diffrction peks t round d-vlues (5.9, 5.2, 4.9 & 3.84 Å) [Buleon et l., 1998]. Figure Xry diffrction pttern of () njvr strch, () ntive rice strch. These four d vlues re present in the cse of oth strches. The XRD pttern of oth rice strches re similr. The results re shown in Figure The % crystllnity of Njvr nd ntive chm rice strch ws found to e % nd % respectively Conclusion Physico chemicl properties of njvr strch ws studied nd compred with properties of ntive chm rice strch. The njvr strch hs high geltiniztion temperture, wter sorption cpcity, soluility nd swelling power. It degrdes t higher temperture nd the enthlpy of geltiniztion ws very high compred to 94

29 ntive rice strch. Psting properties showed tht it hs higher pek viscosity, rek down viscosity nd set ck vlues. These good therml properties mke it useful in products which need to e processed t high temperture. Becuse of its high het holding cpcity, the njvr rice is widely nd specificlly used in yurved tretments. Rheologiclly lso njvr rice strch ws superior. Temperture sweep nlysis showed tht njvr strch geltinizes t higher temperture (68 C) compred to the ntive rice strch (58 C). Njvr rice strch hd high gel strength thn the ntive rice strch, nd the difference etween the G nd G vlue is higher in the cse of njvr indicting the formtion of strong gel nd lso lower tn vlue nd higher torque vlue of njvr lso indictes the sme. Complex viscosity of oth strches decreses with sher rte. Texture properties like hrdness, gumminess, dhesiveness, cohesiveness, nd chewiness re similr in oth the rice strches. But the springiness nture of njvr strch gel is 3 times higher thn tht of ntive rice strch. X ry diffrction pttern showed tht oth strches re A type nd re similr in nture. 95