Sensory quality of soymilk and tofu from soybeans lacking lipoxygenases

Transcription

1 ORIGINAL RESEARCH Sensory qulity of soymilk nd tofu from soyens lcking lipoxygenses Aijun Yng 1, Hether Smyth 2, Mridusmit Chlih 3 & Andrew Jmes 1 1 CSIRO Agriculture, 36 Crmody Rod, St Luci, Queenslnd 467, Austrli 2 Queenslnd Allince for Agriculture nd Food Innovtion, The University of Queenslnd, St Luci, Queenslnd 472, Austrli 3 Deprtment of Agriculture, Fisheries nd Forestry, Coopers Plins, Queenslnd 418, Austrli Keywords Lipoxygense, sensory qulity, soy milk, soyen, tofu Correspondence Aijun Yng, CSIRO Agriculture, 36 Crmody Rod, St Luci, Queenslnd 467, Austrli. Tel: ; Fx: ; E-mil: Aijun.Yng@csiro.u Funding Informtion Grins Reserch nd Development Corportion, Austrli. Received: 2 June 215; Revised: 26 July 215; Accepted: 2 August 215 Food Science & Nutrition 216; 4(2): doi: 1.12/fsn3.274 Astrct The oxidtion of unsturted lipids y lipoxygenses in soyens cuses undesirle flvors in soy foods. Using trditionl nd nontrditionl soy food user group, we exmined the culturl difference in perceiving the sensory chrcteristics of soymilk nd tofu produced from soyens with or without lipoxygenses (Lx123). The two groups descried the smples using similr terms. The trditionl users preferred the control soy milk nd lipoxygense- free tofu while the nontrditionl users preferred the lipoxygense- free soymilk with no preference for tofu. In seprte study, trined descriptive tste pnel compred the odor of soymilk nd tofu from control soyens or those lcking lipoxygense- 1 nd lipoxygense- 2 (Lx12) or ll three isomers (Lx123). The rncid/grssy odor ws rted the lowest in Lx123 products, followed y Lx12 products with the control products given the highest rting. The Lx12 nd Lx123 products were lso sweeter nd less itter thn the controls. Tken together, our results demonstrted tht soyens lcking lipoxygenses cn produce soy foods with less undesirle roms nd re therefore likely more cceptle to the consumers. Introduction Soy foods produced from whole soyen seeds such s soymilk nd tofu hve een prt of the trditionl foods in Est Asi for long time. Soyen is lso n importnt ingredient in mny processed foods. Its production nd use hs incresed rpidly due to its high nutritionl vlue nd potentil helth enefits. Utiliztion of soyen seeds s food mterils, however, hs sometimes een limited, prticulrly in Western societies, ecuse of their grssy/ eny flvor (Krishn et l. 23) nd certin consumers prefer lnd or neutrl flvor in soy products. The consumers from trditionl soy food consumption countries, on the other hnd, generlly fvorly ssocite eny flvor with soy products such s soymilk nd tofu. Cross- culturl vritions in food preferences re well known nd culturl differences in consumption of soy products might ccount for some differences in perception of sensory ttriutes. These undesirle flvors, chrcterized s eny, green, grssy, pinty, stringent, nd itter, hve een ssocited with off- flvors from the oxidtion of polyunsturted lipids y lipoxygenses (LOX) present in soyens. Soyens re known to e rich source of LOX nd mture soyen seeds contin three mjor lipoxygenses: LOX-1 (lipoxygense-1), LOX-2 (lipoxygense-2), nd LOX- 3 (lipoxygense- 3). Soyen lso contins high mount 215 The Authors. Food Science & Nutrition pulished y Wiley Periodicls, Inc. This is n open ccess rticle under the terms of the Cretive Commons Attriution License, which permits use, distriution nd reproduction in ny medium, provided the originl work is properly cited. 27

2 Sensory Qulity of Soy Foods without Lipoxygenses A. Yng et l. of polyunsturted ftty cids (PUFA), predominntly linoleic cid (C18:2) t round 5% nd linolenic cid (C18:3) up to 11% (King et l. 1998; Gerde nd White 28). Both C18:2 nd C18:3 contin cis,cis-1,4-pentdiene structure potentilly leding to the production of hydroperoxides when oxidized, which in turn re converted into voltile compounds ssocited with undesirle flvors (Kitmur 1984). Full- ft soy flour is especilly prone to such deteriortion nd hs disgreele tste tht is difficult to msk. Before ens re crushed or ground, LOX nd PUFA re seprted within the cell, ut following soking nd homogeniztion in the process of mking soymilk, they re mixed nd egin to rect to form the oxidtion products nd voltile compounds. Among the voltile compounds detectle in soy products, hexnl is primrily responsile for the ojectionle flvor or rom of soy foods nd hs very low detection threshold (Wilkens nd Lin 197). The removl of ll or some of the LOX present in soyens through reeding hs produced soyen lines lcking LOX nd susequent lower levels of voltiles responsile for the rncid flvor, which could e useful in improving the cceptnce of Western consumers. While LOX- free soyen hs een shown to produce lower hydroperoxide nd hexnl levels thn tht with LOX or lcking LOX- 1, - 2, or - 3 isozyme (Hildernd et l. 1991; Koyshi et l. 1995; Furut et l. 1996), there hve lso een mixed results in the literture on the impct of these LOX- free soyen lines on controlling the eny flvor of soy foods produced. For exmple, using GC- MS, Koyshi et l. (1995) showed tht lmost ll voltiles in soymilk produced from mutnts lcking LOX were mrkedly lower thn those from norml vriety. Wilson (1996) reported tht tofu mde from LOX- 2 null lines of soyens were less eny thn their respective controls s evluted y sensory pnel. However, while LOX- free soyens reduced the eny flvor in certin types of soy products such s soymilk nd tofu (Wilson 1996; Torres- Penrnd et l. 1998), they showed no effect in oils, reds, nd met ptties (King et l. 1998, 21; Liu et l. 28). Besides improved flvor nd rom, soyens null in LOX could e more resistnt to dverse storge conditions thn the norml soyens with regrd to chnges in ph nd solid content of the soymilk (Lmrecht et l. 1996), lthough Torres- Penrnd nd Reitmeier (21) reported significnt sensory differences etween soymilks from soyens lcking LOX stored for 3 months nd 15 months nd no difference for the soymilks from the norml soyens stored for these times. The LOX- null lines, including those developed in Austrli, hve een shown to hve similr gronomic trits including yield (Nrvel et l. 1998; Reinprecht et l. 26) (A. Jmes, 213 unpul. dt). However, the LOXfree lines from Austrli hve not een evluted for their effect on storge stility, eny flvor, nd other qulity ttriutes in soy foods. There re two types of commercil soymilk in Austrli, one mde from imported soy protein isoltes nd one mde from domesticlly sourced whole soyen. The grssy/eny flvor of the whole en soymilk is reported to e limittion on the uptke of this type y the mrket. Therefore, soyen without lipoxygense my offer n opportunity to expnd the mrket for Austrlin- grown soyens. Studies using pnels from different culturl ckgrounds to evlute the smple product my give some indiction s to whether such differences should e considered. The Austrlin mrket for soy products hs consumers of mny culturl nd ethnic ckgrounds. The ojectives of this study were therefore to compre soymilk nd silken tofu from norml nd lipoxygense- free soyens using predominntly ntive Chinese pnel ( trditionl soy users ) nd n Anglo- Austrlin pnel ( nontrditionl soy users ) in Austrli nd to investigte the impct of LOX- free soyens developed in Austrli on sensory ttriutes of soy products in order to improve our understnding of the potentil utility of these trits for the Austrlin mrket. Mterils nd Methods Soyens, soymilk nd tofu Norml soyens nd soyen lines selected for LOX- null in Austrli were used in these studies. All the lines used were grown, hrvested, nd stored together efore use. In the preliminry study, commercil line nd genotype lcking ll three mjor LOX isozymes (Lx123) were used. In the following sensory study, norml soyens nd lines lcking LOX- 1 nd LOX- 2 (Lx12) or ll three isomers (Lx123) were selected. The LOX- 1 nd LOX- 2 genes re tightly linked nd inherited together, while the LOX- 3 gene is independently inherited (Dvies nd Nielsen 1986). All the mterils were kept t round 22 C until use. All soyen lines were checked for LOX using screening method (Sud et l. 1995; Nrvel et l. 2) nd SDS- PAGE (sodium dodecyl- polycrylmide gel electrophoresis) (Yng nd Jmes 213) to confirm the sence of LOX- 1 nd LOX- 2 or ll three LOX isomers. A typicl SDS- PAGE profile of soyen seed proteins with or without LOX isozymes is presented in Figure 1. Soymilk nd silken tofu were produced ccording to the procedure optimized y Yng nd Jmes (213) nd stored t 4 C overnight efore use in sensory nd focus group ssessments. Briefly, the ens were soked overnight efore they were ground in domestic lender. The slurry ws cooked t 98 C nd then filtered using juice extrctor to otin soymilk. The required mount of the soymilk for ssessment ws trnsferred to 4 C. The The Authors. Food Science & Nutrition pulished y Wiley Periodicls, Inc.

3 A. Yng et l. Sensory Qulity of Soy Foods without Lipoxygenses Lipoxygenses (kd 94 97) β-conglycinin (7S) Glycinin (11S) Control Lx12 Lx123 nd to rte the overll cceptility of ech smple on n unstructured 15- cm hedonic line scle nchored from dislike extremely to like extremely. The individul ssessments were mde under controlled conditions (light, temperture) nd smples were leled with 3- digit codes. Presenttion order of smples ws identicl cross the prticipnts s follows: control soy milk, LOX- free soy milk, control silken tofu, nd LOX- free tofu. Smples (15 2 g ech) were presented in disposle plstic pots (tofu) nd cups (milks). Prticipnts were lso sked to complete short demogrphic questionnire nd indicte their soy product knowledge nd consumption ehvior. Following the tste session, focus group discussion ws held in which prticipnts were sked to shre nd discuss their thoughts on the sensory properties nd cceptility of the smples nd their pst soy product experiences nd consumption ehvior. Figure 1. Sodium dodecyl- polycrylmide gel electrophoresis profile of seed proteins from control, Lx12 or Lx 123 soyens. remining soymilk ws mde into silken tofu y dding.3% cogulnt (nigri, mostly mgnesium chloride) nd llowing the curd to form t 85 C. The soymilk nd tofu were kept t 4 C until use. Preliminry study of soymilk nd tofu from control nd LOX- free soyens Sensory evlution using pnels of trditionl nd nontrditionl soy users Two semiforml focus groups were held (ech of 1 h durtion) involving two trget groups nmely nontrditionl soy users (the Austrlin pnel) nd trditionl soy users (the Chinese pnel). The profiles of the prticipnts for ech group re given in Tle 1. The prticipnts in ech group were presented smples of soy milk nd silken tofu mde from commercil ens (control) nd lipoxygensefree soyens (LOX- free) together with pper questionnires. Prticipnts were sked to descrie the ppernce, rom, texture nd mouth feel, flvor, nd ftertste of smples Tle 1. Profiles of prticipnts involved in soy focus group study. Nontrditionl soy product users Trditionl soy product users 2 mle 5 femle 1 mle 5 femle Age rnge (yers) Ethnicity 2 7 Anglo- Austrlin Soy product consumption Dily never 4 Chinese Dily weekly Instrumentl nlysis of voltile compounds y GC-MS Replicted smples of soy milk nd silken tofu (control nd LOX- free) fter 1 dy nd 8 dys stored t 4 C were smpled nd frozen ( 19 C) for voltile nlysis. Aliquots of 5 ml of soy milk or 5 g of silken tofu were plced in 25 ml glss vils for SPME (solid phse microextrction) nd immeditely closed with screw cps with PTFE/ silicone sept (Supelco, Bellefonte, PA). The method used for voltile nlysis ws modified version of the method reported y Achouri et l. (26). Smples were nlyzed with 689N GC (gs chromtogrph) equipped with 5975 MSD (mss spectrometric detector) (Agilent Technologies, Plo Alto, CA). The GC ws fitted with DB- WAX column (J&W Science, i.d. =.25 μm, length = 3. m, film thickness =.25 μm), nd helium (BOC gses, ultrhigh purity) ws used s crrier gs t liner velocity of 56 cm/min nd t flow rte of 2.4 ml/min. The polydivinylenzene nd crowx nd polydimethylsiloxne (DVB CAR PDMS, Gry, 5/3 μm, Supelco) fier ws introduced into the hedspce of the smple vil nd ws llowed to incute t 45 C for 2 min. After the incution, the fier ws retrcted into needle nd desored into the injection port of the GC for 6 min. The fier remined in the injection port for 6 min to eliminte the possile residues on the fier. Extrction ws supported y mgnetic stirring t 25 rpm/s nd fier lnk experiment ws performed. The mss spectrometer ws operted in the electron impct ion mode with source temperture of 25 C. The electron energy ws 7 ev nd the mss rnge ws 35 3 m/z. The GC oven temperture strted t 35 C for 3 min, ws incresed t 6. C/min to 22 C, nd ws held for 1 min. 215 The Authors. Food Science & Nutrition pulished y Wiley Periodicls, Inc. 29

4 Sensory Qulity of Soy Foods without Lipoxygenses A. Yng et l. Dt nlysis ws crried out with MSD ChemSttion Dt Anlysis softwre (Agilent Technologies) to otin pek responses of voltiles. Pek identifiction ws chieved y comprison of spectr nd retention times with uthentic reference stndrds. Sensory study on compring control, Lx12, nd Lx123 soy products Soyen seed chrcteriztion The moisture, oil, nd protein content of the soyens were determined s descried y Yng nd Jmes (213). The seeds were nlyzed for their ftty cid composition using GC. Briefly, soyen seeds were ground to fine powder nd oil ws extrcted twice with n- hexne. The comined hexne extrctions were evported under nitrogen. The oil,.1 g, ws methylted with.5 mol/l sodium methoxide solution t 8 C for 1 min. After cooling to room temperture,.5 ml of glcil cetic cid, 2.5 ml of distilled wter, nd 2.5 ml of petroleum spirit (or hexne) were dded. The mixture ws vortexed nd.5 μl of the cler upper phse ws used for nlysis. The seprtion nd distriution of ftty cid methyl esters were otined using GC (Perkin Elmer Autosystem Gs Chromtogrph, MA, USA) fitted with FID (flme ioniztion detector) nd cpillry column (SGE BPX7, 25 m.22 mm). The crrier gs ws helium t 15 psi. The injector temperture ws 24 C nd detector temperture ws 28 C. The oven temperture strted t 15 C efore reching 2 C. The ground full- ft soyen mel ws lso stored t 37 C for 1 week nd the totl voltiles were mesured using SPME- GC- FID procedure. Sensory evlution Three replictes of ech silken tofu nd soy milk smple were prepred from the composite smples of soyens the dy prior to the commencement of sensory testing nd trining nd forml ssessments were completed within 3 dy period to ensure freshness of smples. Sensory descriptive nlysis techniques were pplied to ssess nd quntify the mjor sensory properties of six smples including tofu nd soy milk mde from commercil soyens (control), from triple- null soyens (Lx123), nd from doule- null soyens (Lx12). A totl of 11 pnelists (four mle, seven femle), who were experienced in descriptive sensory studies nd who were stff nd students t the Helth nd Food Sciences Precinct, Coopers Plins, Queenslnd, prticipted in the study. Their profiles re listed in Tle 1. Two trining sessions were conducted in ord- room style round tle suitle for discussions. The first trining session involved presenttion of ll smples to pnelists, individul rom nd tste ssessments, nd voculry development through discussion (Tle 2). The second trining session involved prcticing rting ttriutes for ech of the smples nd developing concise list of ttriutes, scles, nd definitions. Attriutes selected during trining, together with their definitions, re shown in Tle 3. Forml ssessments were conducted in the sensory lortory of the Helth nd Food Sciences Precinct, Coopers Plins, Queenslnd. The lortory consists of individul tsting ooths equipped with computers, dylight equivlent lighting, nd temperture control. Three replicte sessions were held wherey ll six smples were presented nd ssessed ccording to lnced presenttion design. Dt were collected using sensory softwre Compusense five (version 5., Compusense Inc., Guelph, ON, Cnd) nd dt were exported nd nlyzed using XLSTAT (version , Addinsoft , CA, USA). During trining nd forml sessions, smples of tofu nd milk (~1 15 g) were presented to pnelists in smll plstic cups covered with plstic lids. Milks were freshly stirred nd tofu ws freshly sliced prior to serving. Tle 2. Sensory descriptors nd voculry from the trining session in the preliminry evlution of control nd LOX- free soymilk nd tofu. LOX-free soymilk Control soymilk Yellowish Cooked pst, floury, evported milk, cooked, sour, grssy, rw, less intense/sutle, eny, sweet florl, rw soy Soy, pinty, potto, lflf sprouts, snow pe, green- sweet, mcdmi, svory, soft- nutty sourness, sweeter, less intense Off- white, lighter color, thicker looking Typicl Chinese- style, strong, stle- erthy, strchy, rw ens, green, florl, nutty, chlky, rncid, flour nd wter pste, rw green pe Rw ens, soy, fresh veg, grssy, ged oil/rncid, pinty, green stringent, erthy, itterness, legume, dry milk, more intense LOX-free tofu Control tofu Lighter, yellower Cremy, eige More sutle, less intense, green en, fresh en, grssy, green- florl, More intense, rncid, rw en, strch, nutty, grin, pinty, old ruer tree, sppy, fermented, legume, plesnt rncid whet rn, floury Bitter, metllic, nutty, sourness, potto, diry, uttery, rw en, Rncid, ged oil, sour, low- intensity flvors, itterness, rw tste, sweeter, fresher, clen ftertste metllic, green, legume, pinty, oxidized, potto The Authors. Food Science & Nutrition pulished y Wiley Periodicls, Inc.

5 A. Yng et l. Sensory Qulity of Soy Foods without Lipoxygenses Tle 3. Sensory ttriutes nd definitions developed nd used in the sensory descriptive study of control nd LOX- free soymilk nd tofu. Attriute Arom intensity Fresh pe rom Grssy rncid rom Floury rom Flvor intensity Sweetness Bitterness Sttisticl nlysis All mesurements in this study were replicted three times. The dt were suject to nlysis of vrince to exmine the effect of genotypes on ech of the sensory ttriutes exmined in soymilk nd tofu. The mens were seprted using lest squre difference t the 5% significnce level. Results Definition The overll intensity of the smples rom from sutle to intense A fresh pe, cucumer, melon- like or lettuce rom A grssy rncid rom, sppy, sour, rw nd pinty, like rncid oil A floury, strchy, potto- like rom, reminiscent of cly nd erth The overll flvor intensity of the smple when in the mouth The perceived sweetness of smples experienced in the mouth The perceived itterness of smples experienced in the mouth Preliminry study using pnels of trditionl nd nontrditionl soy users Typiclly, the prticipnts from ech trget group descried the smples using similr terms. The control soy milk ws pler in color thn the LOX- free soy milk. Both groups descried the LOX- free milk s eing less intense nd more sutle with more floury, cooked pst- type roms which lso cme through on the plte together with some sweet green snow pe- like flvors. The LOXfree milk ws lso descried s sweeter thn the control nd less intense in flvor overll. The control soy milk ws stronger in odor with rw green pe/en, stle- erthy, nd rncid- type roms. The flvor ws lso stronger, rw, nd grssy with some rncid oil, pinty, nd ittertype flvors. Similrly for the silken tofu smples, the control ws descried overll s eing more intense in odor nd flvor. The LOX- free tofu ws descried s hving fresher/clener, more sutle ttriutes, while the control ws descried s eing rncid (not fresh) nd more intense rom nd flvor. Interestingly, the Chinese pnel ( trditionl soy users ) descried the control soy milk s typicl Chinese- style wheres they descried the LOXfree milk s unusul. Overll, the Chinese pnel preferred the control soymilk nd the LOX- free tofu while the Austrlin pnel ( nontrditionl soy users ) preferred the LOX- free soymilk nd did not seem to like either of the tofu products (Fig. 2). The presence or sence of the three mjor lipoxygenses ws confirmed using SDS- PAGE (Fig. 1) nd screening method. The soymilk from the control nd LOX- free soyen hd similr solid content in soymilk (~11%). The mjor voltiles in these products s determined y GC- MS were hexnl with some 1- hexnol nd utnol. A GC- MS profile showing the difference in the mjor voltiles in soymilk stored t 4 C for 1 dy is presented in Figure 3. The pek re dt ( 1,) reveled tht ll three voltiles in the control products were much higher thn tht in the LOX- free products, 1.85, 2.75, nd 1.22 for control soymilk nd.6, 2.5, nd.42 for LOX- free soymilk for hexnl, 1- hexnol, nd utnol, respectively; 4.5, 2.15, nd 1.3 for control tofu nd 1.25, 1.75, nd.4 for LOX- free tofu for hexnl, 1- hexnol, nd utnol, respectively. The difference in the mjor voltile, hexnl, etween control nd LOXfree products seemed to hve incresed fter 8 dys of refrigerted storge (Fig. 4). Sensory study on compring control nd Lx12 nd Lx123 soy products The seed chrcteristics of the soyens contining the three mjor lipoxygenses, lcking LOX- 1 nd LOX- 2 (Lx12) or lcking ll three isomers (Lx123) re presented in Tle 4. The similr genetic ckground of the three soyen types, except for lipoxygenses, ws expected to yield products with similr chrcteristics other thn the eny rom/flvor. While the seeds of Lx12 were smller nd, compred with the controls, contined more protein, Chinese pnel ("trditionl soy users") Austrlin pnel ("nontrditionl soy users") Control milk LOX-free milk Control tofu LOX-free tofu Figure 2. Difference in preference etween n Austrlin (n = 8) nd ntive Chinese (n = 6) pnel for control nd LOX- free soymilk nd tofu. 215 The Authors. Food Science & Nutrition pulished y Wiley Periodicls, Inc. 211

6 Sensory Qulity of Soy Foods without Lipoxygenses A. Yng et l. 5 Hexnl, Control 4 Aundnce 3 2 Butnol, Control 1 1-Hexnol Hexnl, LOX-free Butnol, LOX-free Time (min) Figure 3. Mjor voltiles in control soymilk nd LOX- free soymilk. Pek re 6, 5, 4, 3, 2, 1, Control soymilk LOX-free soymilk Control tofu LOX-free tofu Dys of storge t 4 o C Figure 4. Hexnl pek re for tofu nd soymilk fter 1 nd 8 dys of storge t 4 C the three groups hd similr oil content nd ftty cids profiles, in prticulr totl sturted ftty cids, totl PUFA, nd the rtio of linoleic to linolenic ftty cids. As rncidity results from the oxidtion of PUFA, the similr ftty cid composition provided n importnt sis for compring differences in the sensory ttriutes or storge stility. After 1 week s storge t 37 C, the totl pek re for the mjor voltiles detected using SPME- GC- FID incresed over fourfold for the control full- ft soyen mel while the increse for doule- null nd triple- null smples ws only 1.3- fold (P <.5). The sensory nlysis of the soy products mde from control soyens or those lcking LOX- 1 nd LOX- 2 (Lx12) or ll three isomers (Lx123) showed cler nd significnt differences in the mjor rom notes etween these three groups for soymilk (Fig. 5A) or silken tofu (Fig. 5B). The Tle 4. Seed chrcteristics of control, Lx1-2 null nd Lx1-3 null smples. Control Lx12 Lx123 Seed wt (g/1 seeds) * Oil (%) Protein (%) Mjor ftty cids C16: C18: C18:1c C18: C18: PUFA rtio (18:2/18:3) (PR) Totl SFA Totl PUFA Totl PUFA/Totl SFA (PI) Totl voltile increse in full- ft soy mel fter 1 week storge t 37 C SFA, sturted ftty cids; PUFA, polyunsturted ftty cids; PR, polyunsturtion rtio; PI, polyunsturtion index. *Mens with the sme superscripts within the sme row re not sttisticlly different, P >.5. ojectionle rncid/grssy odors were rted the lowest y the tste pnel in oth soymilk nd tofu from Lx123 soyens, followed y Lx12 products with the control products given the highest rncid odor rting. The difference etween these three soyens ws sttisticlly significnt for oth soymilk nd tofu (P <.5). Bitterness, nother negtive sensory note, ws rted significntly lower in the soymilk nd tofu mde from the soyens lcking two or three lipoxygenses compred with those mde from the soyen contining ll three isozymes (P <.5). Arom intensity The Authors. Food Science & Nutrition pulished y Wiley Periodicls, Inc.

7 A. Yng et l. Sensory Qulity of Soy Foods without Lipoxygenses (A) Bi erness Sweetness Arom intensity c Fresh pe rom Grssy/rncid rom (B) Bi erness Sweetness Arom intensity c Fresh pe rom Grssy/rncid rom Flvour intensity Floury rom Flvour intensity Floury rom Control milk Doule-null milk (Lx12) Triple-null milk (Lx123) Control tofu Doule-null tofu (Lx12) Triple-null tofu (Lx123) Figure 5. Plot of sensory scores for soymilk (A) nd silken tofu (B) smples. n = 3 11, for ech sensory ttriute, the scores with different letter re significntly different (P <.5). ws lso scored significntly lower for tofu produced from Lx12 nd Lx123 soyens, lthough this difference ws not sttisticlly significnt for soymilk. On the other hnd, sweetness, positive sensory note, ws rted significntly higher in the Lx12 nd Lx123 products thn the controls for oth soymilk nd tofu (P <.5). Fresh pe rom ws lso rted higher in the Lx12 nd Lx123 products thn the controls, lthough this difference ws only significnt for tofu. Flvor intensity ws rted differently y the tste pnels for soymilk nd tofu. It ws scored lower for the control soymilk (P <.5) nd higher for the control tofu, lthough this difference ws not sttisticlly different. Discussion Culturl difference nd preference, s result of longterm or trditionl consumption of soy foods, hs een reported in the perception of sensory ttriutes of soy foods, lthough the results re not cler- cut (Torres- Penrnd et l. 1998). The preference for control soymilk from n lmost- ntive Chinese pnel in this study ws therefore expected s trditionl soy users would ssocite the eny flvor with the typicl flvor of soy milk. It is possile tht consumers of trditionl soy foods such s soymilk nd tofu my find the products without lipoxygenses too lnd due to the sence of the fmilir eny flvor nd tste. As result, while soyen vrieties lcking lipoxygenses hve een developed in countries of trditionl soy food consumption such s Kore nd Chin, these vrieties hve not een widely tken up (K. Lee 214 nd M. Zhng 213, pers. comm.). For nontrditionl soy users, the trditionl tofu is usully too lnd in flvor nd mushy in texture to their liking. They my still prefer the sesoned nd hrder products irrespective of lipoxygenses. Among the voltile compounds contriuting to the eny/ rncid/off- flvor in soy products, hexnl is the mjor voltile responsile nd hs een studied most. The lower hexnl level oserved in this study in the soymilk nd tofu mde from the LOX- free soyens ws consistent with the results from mny studies which reported tht LOX- free soyens produce lower hydroxyperoxide nd hexnl levels thn those with LOX or lcking the LOX- 1, - 2, or - 3 isozyme lone (Hildernd et l. 1991; Koyshi et l. 1995; Furut et l. 1996; King et l. 1998; M et l. 22, 215). There hve lso een ttempts to link soyen oil profile, lipoxygense sttus, nd off- flvor development in soy foods nd direct reltionship etween the degree of oil polyunsturtion, voltile compounds, hexnl level in prticulr, nd off- flvor determining prmeters hs een reported (Furut et l. 1996; Yun nd Chng 27; Mndl et l. 214). The significntly lrger increse in the totl voltiles in the full- ft soy mel fter 1 week s storge t 37 C ws similr to those reported y Koyshi et l. (1995), lthough King et l. (1998) oserved no difference in hexnl level etween control nd LOX- free oils nd n incresed hexnl level nd peroxide vlues in LOX- free oil fter 2 weeks storge t 35 C nd 5% humidity. The uthors ttriuted these results to the differences in initil ftty cid composition. The effects of removing lipoxygenses from soyens on the sensory ttriutes, in prticulr on the ojectionle eny/grss flvor, of soy products re mixed nd seem to e product- dependent. For exmple, Torres- Penrnd et l. (1998) reported significnt less cooked 215 The Authors. Food Science & Nutrition pulished y Wiley Periodicls, Inc. 213

8 Sensory Qulity of Soy Foods without Lipoxygenses A. Yng et l. eny rom nd flvor in soy milk mde from the LOXfree soyen thn tht from the norml line, lthough no difference ws oserved in tofu in the sme study. They lso found significnt interctions etween soyen types nd pnelist ethnic ckgrounds for rw eny rom nd flvor, which ws ttriuted to the low intensity of the rw rom nd flvor mking differentition etween soymilk from norml nd LOX- free soyens difficult. Wilson (1996) lso reported tht tofu mde from LOX- 2 null lines of soyens were less eny thn their respective controls s evluted y sensory pnel. LOX- free soyens, however, showed no effect in oils, reds, nd met ptties (King et l. 1998, 21; Liu et l. 28). It is possile tht the eny flvor ws eing msked y other stronger sensory notes in these products. In evluting 7 genotypes including two series of ner isogenic lines with or without lipoxygense isozymes, no effect of lipoxygense sence ws oserved on soymilk flvor prmeters (M et l. 215). Our results clerly showed tht soyens null in two or three of the mjor lipoxygenses positively reduced the negtive sensory notes including rncidity, itterness, nd rom intensity nd improved the positive sensory notes such s sweetness nd fresh pe rom in soymilk nd tofu. Soyens lcking ll three mjor isomers seemed to hve n dditive effect on reducing the negtive notes in these soy products. Tken together, our results demonstrted tht soyen seeds lcking lipoxygenses cn produce whole- en- sed soy foods such s soymilk nd tofu with improved flvor nd rom which re likely more cceptle to the consumers, prticulrly nontrditionl soy users, nd perhps llow their utiliztion into other products. The soyen lines lcking lipoxygenses will lso provide the Austrlin food industry with dditionl ingredients tht would roden nd increse the utiliztion of soyens nd soy proteins in wide rnge of food pplictions. Acknowledgments This reserch ws funded in prt y the Grins Reserch nd Development Corportion in Austrli under the uspices of the Ntionl Soyen Breeding Progrm. Conflict of Interest None declred. References Achouri, A., J. I. Boye, nd Y. Zmni. 26. Identifiction of voltile compounds in soymilk using solid- phse microextrction- gs chromtogrphy. Food Chem. 99: Dvies, C. S., nd N. C. Nielsen Genetic- nlysis of null- llele for lipoxygense- 2 in soyen. Crop Sci. 26: Furut, S., Y. Nishi, M. Hjik, K. Igit, nd I. Sud DETBA vlue nd hexnl production with the comintion of unsturted ftty cids nd extrcts prepred from soyen seeds lcking two or three lipoxygense isozymes. J. Agric. Food Chem. 44: Gerde, J. A., nd P. J. White. 28. Lipids. Pp In L. A. Johnson, P. J. White nd R. Gllowy, eds. Soyens: chemistry, production, processing nd uniliztion. AOCS Press, Chmpign, IL. Hildernd, D. F., R. T. Versluys, nd G. B. Collins Chnges in lipoxygense isozyme levels during soyen emryo development. Plnt Sci. 75:1 8. King, J. M., L. K. Svendsen, W. R. Fehr, J. M. Nrvel, nd P. J. White Oxidtive nd flvor stility of oil from lipoxygense- free soyens. J. Am. Oil Chemists Soc. 75: King, J. M., S. M. Chin, L. K. Svendsen, C. A. Reitmeier, L. A. Johnson, nd W. R. Fehr. 21. Processing of lipoxygense- free soyens nd evlution in foods. J. Am. Oil Chemists Soc. 78: Kitmur, K Biochemicl- chrcteriztion of lipoxygense lcking mutnts, l- 1- less, l- 2- less, nd l- 3- less soyens. Agric. Biol. Chem. 48: Koyshi, A., Y. Tsud, N. Hirt, K. Kuot, nd K. Kitmur Arom constituents of soyen glycinemx (l) merril milk lcking lipoxygense isozymes. J. Agric. Food Chem. 43: Krishn, A., G. Singh, D. Kumr, nd K. Agrwl. 23. Physico- chemicl chrcteristics of some new vrieties of soyen. J. Food Sci. Tech.- Mysore 4: Lmrecht, H. S., S. S. Nielsen, B. J. Lisk, nd N. C. Nielsen Effect of soyen storge on tofu nd soymilk production. J. Food Qulity 19: Liu, C., X. Wng, H. M, Z. Zhng, W. Go, nd L. Xio. 28. Functionl properties of protein isoltes from soyens stored under vrious conditions. Food Chem. 111: M, H., C. Gun, X. He, G. Zhng, nd A. Din. 22. Effects of lipoxygense null genes of soyen in controlling eny- flvor of soymilk nd soyflour. Agric. Sci. Chin 1: M, L., B. Li, F. Hn, S. Yn, L. Wng, nd J. Sun Evlution of the chemicl qulity trits of soyen seeds, s relted to sensory ttriutes of soymilk. Food Chem. 173: Mndl, S., A. Dhuj, A. Kr, nd I. M. Snth In vitro kinetics of soyen lipoxygense with comintoril ftty sustrtes nd its functionl significnce in off flvour development. Food Chem. 146: The Authors. Food Science & Nutrition pulished y Wiley Periodicls, Inc.

9 A. Yng et l. Sensory Qulity of Soy Foods without Lipoxygenses Nrvel, J. M., W. R. Fehr, nd G. A. Welke Agronomic nd seed trits of soyen lines lcking seed lipoxygenses. Crop Sci. 38: Nrvel, J. M., W. R. Fehr, nd L. C. Weldon. 2. Anlysis of soyen seed lipoxygenses. Crop Sci. 4: Reinprecht, Y., V. W. Poys, I. Rjcn, G. R. Alett, nd K. P. Puls. 26. Agronomic performnce of soyen with seed lipoxygense nulls nd low linolenic cid content. Cn. J. Plnt Sci. 86: Sud, I., M. Hjik, Y. Nishi, S. Furut, nd K. Igit Simple nd rpid method for the selective detection of individul lipoxygense isozymes in soyen seeds. J. Agric. Food Chem. 43: Torres-Penrnd, A. V., nd C. A. Reitmeier. 21. Sensory descriptive nlysis of soymilk. J. Food Sci. 66: Torres-Penrnd, A. V., C. A. Reitmeier, L. A. Wilson, W. R. Fehr, nd J. M. Nrvel Sensory chrcteristics of soymilk nd tofu mde from lipoxygense- free nd norml soyens. J. Food Sci. 63: Wilkens, W. F., nd F. M. Lin Gs chromtogrphic nd mss spectrl nlyses of soyen milk voltiles. J. Agric. Food Chem. 18: Wilson, L. A Comprison of lipoxygense-null nd lipoxygense-contining soyens for foods. Pp In G. Pizz, ed. Lipoxygense nd lipoxygense pthwy enzymes. AOCS Press, Chmpign, IL. Yng, A., nd A. T. Jmes Effects of soyen protein composition nd processing conditions on silken tofu properties. J. Sci. Food Agric. 93: Yun, S., nd S. K.-C. Chng. 27. Selected odor compounds in soymilk s ffected y chemicl composition nd lipoxygenses in five soyen mterils. J. Agric. Food Chem. 55: The Authors. Food Science & Nutrition pulished y Wiley Periodicls, Inc. 215