Scallion (Allium fistulosum L.) Chemistry Affected by Variety and Environmental Conditions (Light and CO 2 )

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1 Scllion (Allium fistulosum L.) Chemistry Affected y Vriety nd Environmentl Conditions (Light nd CO 2 ) Lnfng Levine, Jn Buer, Shron Edney, Jeffrey Richrds, nd Neil Yorio Dynmc Corportion, Spce Life Sciences Lortory, Mil Code DYN-3, Kennedy Spce Center, FL 32899, USA Copyright 25 SAE Interntionl Kunyu Li nd Pul W. Pré Deprtment of Chemistry nd Biochemistry, Texs Tech University, Luock, TX 7949, USA Ry Wheeler NASA Biologicl Sciences, Mil Code YA-E4-B, Kennedy Spce Center, FL 32899, USA ABSTRACT To fcilitte the selection of pltle nd functionl foods, eight green onions grown under either cool-white fluorescent lmps (CWF) or high pressure sodium lmps (HPS) were compred for their pungency, tissue nitrte nd sulfte sttus. The influence of light intensity nd tmospheric CO 2 levels on pungency of the selected cultivrs ws lso investigted. Results demonstrte tht there ws difference in pungency not only mong cultivrs, ut lso etween tissue types nd developmentl stges. Pseudouls were more pungent thn leves except for cultivr Pcific Perl tht hd similr levels in oth pseuoduls nd leves. EG Hrdy White ws the most pungent, while Deep Purple ws the lest pungent. The pungency ws inversely correlted with nitrte level in the tissue. Light sources (CWF versus HPS) did not influence plnt growth or pungency, ut hd cler impct on tissue nitrte levels with nitrte in CWF-grown onions higher thn HPSgrown plnts. Light nd CO 2 levels hd positive effect on pungency, i.e. incresing light nd CO 2 levels incresed the net ccumultion of flvor precursors nd/or lliinse ctivity (pungency fctors). This study rised severl interesting questions. For instnce, should green onion e consumed immeditely fter hrvest due to the high nitrte level, or should different horticulturl prctices (nutrient nd light regime) e implemented to reduce nitrte levels? Wht effect would these strtegies hve on the vegetle s other qulity trits? Does lterntive lighting hve repercussion for food qulity, prticulrly in nitrte levels? INTRODUCTION Plnts re n integrl component of our sustinle life support system on Erth, nd will ply n importnt role in spce explortion to initilly provide dietry supplements, nd eventully more complete diet with concomitnt ir nd wter revitliztion (Wheeler et l. 21). Vegetles with minimum processing requirements re considered for oth short term (e.g. ISS, CEV) nd long term plnetry sed hitts. Scllion or unching onion (Allium fistulosum L.) hs een considered s one of the NASA s Advnced Life Support cndidte crops ecuse of its chrcteristic flvor, short cropping cycle, suitility in dense plnting compred with ul onion, nd ese of hydroponic culturing (Thompson et l. 24). Onion is lso well known for its helth enefit. Consumption of onion nd relted Alliums is ssocited with reduction in lood lipids, cholesterol nd pltelet ctivity (Block 1992), contriuting to decrese risk of crdiovsculr disese (Sinni et l 1976, Kendler 1987, Augusti 199). The iologicl ctivity nd humn helth enefit re thought to e ttriutle to suite of orgnosulfur compounds (Mundy nd Mundy 1999 nd 24). However, re ll onions eqully effective? In n effort to select onion cultivr for inclusion in spce menu, in ddition to yield, quntum efficiency (g yield mol -1 light) nd growth chrcteristics, onion flvor or pltle feture nd its helth enefits including potentil protection ginst ionizing rditions need e evluted. Studies on Allium production (minly ul onion, Allium cep L.) indicte tht onion flvor nd pungency re governed y oth genetic nd environmentl fctors such s wter supplies, temperture nd growth medium fertility especilly nitrogen nd sulfur (Rndle 1992, 1999). However unching onions re less studied; little is known whether or how rtificil lighting (qulity nd intensity), nd tmospheric CO 2 levels tht re likely encountered in spce environment could ffect these qulity trits. Moreover, differences in food composition exist etween field grown nd closed environments (Thompson et l. 24 nd references cited within). Preliminry studies y (Thompson et l. 24)

2 suggested tht elevted CO 2 incresed totl flvonols content in ul onions, ut not in chives or unching onions with n exception of cultivr Choesty. Elevted CO 2 hs lso een shown to increse onion hydrocron emissions (Jsoni et l. 24). Onion develops its flvor nd pungency when the enzyme lliinse intercts with sulfur-sustituted mino cids, collectively known s S-lk(en)yl-L-cysteine sulfoxide (ACSO) fter cutting or crushing the onion tissue (Lncster nd Bolnd 199). The products of this rection nd susequent spontneous rerrngements generte pyruvic cid, mmoni, nd thiosulfintes. In the erly 196s, significnt correltion etween enzymticlly developed pyruvic cid nd sensory evlution of onion pungency ws reported (Schwimmer nd Gudgni 1962). Since then, enzymticlly developed pyruvic cid hs een used s quntittive pungency indictor, nd is often used to ssess the culinry qulity of onions. Pungency my lso e n indirect mesure of medicinl qulity (Briggs nd Goldmn 22). In order to fcilitte the selection of pltle nd functionl food, comprtive study on eight green onions in terms of their pungency, tissue nitrte nd sulfte sttus under either cool white fluorescent lmp (CWF) or high pressure sodium lmp (HPS) were conducted in reltion to commercil ul onions. The effect of lighting intensity nd tmospheric CO 2 levels on these ttriutes ws lso investigted. MATERIALS AND METHODS PLANT MATERIALS Cultivr evlution Eight green onions (Allium fistulosum L. cv. Kink, Kruncho, Choetsu, Gurdsmn, Choho, Pcific Perl, Evergreen Hrdy White, Deep Purple) were hydroponiclly grown in ½ strength Hoglnd s solution using recirculting nutrient film technique within n environmentl chmer. The environmentl conditions were controlled to 23 C, 12 µmol mol -1 CO 2, nd 3 µmol m -2 s -1 light using either cool white fluorescent lmp (CWF) or high pressure sodium lmps (HPS) with photoperiod of 16/8 light/drk (i.e. dily integrl light 17.3 mol m -2 d -1 ). Detiled horticulturl conditions were descried in Edney et l. (23). On 34 dy fter plnting (DAP), three representtive onion plnts were hrvested. The third lef nd 3 cm pseudoul ove the root were dissected from ech plnt nd immeditely frozen in LN 2 nd stored t 8 C for pungency ssys. In ddition, the third lef nd 3 cm pseudoul segments from 4-6 plnts were pooled for ech cultivr, frozen in LN 2 nd freeze-dried followed y grinding to pss 4 mesh screen. Freeze-dried ground smples were nlyzed for inorgnic nutrient composition. Two experiment replictes were smpled. Sptil distriution of pungency Green onion cv. Kruncho grown under the conditions descried in cultivr evlution ws smpled. Pseudouls were dissected into five 1 cm-long segments strting from the interfce etween the root nd stem, nd lef numers 2, 3 nd 4 (progressively younger) were collected from two experimentl replictes, three plnts per experiment. Effect of light intensity nd tmospheric CO 2 level For this experiment, only cultivr Kink ws investigted. Green onion, Kink, ws grown under comintion of three lighting intensities (15, 3, 45 µmol m -2 s -1 of CWF nd three CO 2 levels (4, 12, 4 µmol mol -1 ) with photoperiod of 16/8 light/drk t 25 C (Richrds et l. 24). These conditions corresponded to dily light integrl 8.6, 17.3, 25.9 mol m -2 respectively. At DAP 34, smples were tken exctly the sme wy s in cultivr evlutions for pungency, while the entire plnt except the root ws frozen in LN 2 freeze-dried nd ground to fine powder for determintion of inorgnic nutrients. Bul Onions (Allium cep L.) Red onion nd sweet white onion were purchsed from locl grocery store. Three firm red or white onions were selected, nd the dried shell long with the immeditely djcent lyer ws peeled off; the top nd se were lso removed.. The onion ws cut into four qurters, nd ech qurter ws further cut into three pproximtely equl wedges. One wedge ws used for pungency ssys, one for inorgnic nutrient mesurements nd the third section for wter content determintions. PUNGENCY ASSAY Pungency development Enzymticlly developed pyruvic cid ws used s mesure of pungency. Briefly, 1-3 grm of frozen green onion ws ground in LN 2 with pestle nd mortr; susequently, 5 ml of.1 M sodium pyrophosphte uffer (ph 9.) ws dded. The thwed slurry ws quntittively trnsferred to 15 ml conicl centrifuge tue. The slurry ws then incuted for 3 min in 37 C wter th to llow complete enzymtic conversion of flvor precursors to flvor compounds nd pyruvic cid. The rection ws terminted y incuting in 1 C wter th for 1 min. The mixture ws cooled to room temperture, nd filtered through two lyers of pre-wshed cheesecloth fitted onto Buckner funnel followed y two rinses. The filtrte nd rinses were comined nd diluted to totl volume of 5 ml with DI wter. For ul onion, freshly cut wedge (15-25 g) ws directly lended in 9 ml of the sodium pyrophosphte uffer for 3 s. Homogenized onion ws then incuted the sme wy s ove. The filtrte ws diluted for the determintion of pyruvte concentrtion. Quntifiction of the enzymticlly developed pyruvic cid (Schwimmer nd Weston 1961) 1. ml of the ove filtrte tht hs een further clrified y centrifugtion ws mixed with 1. ml of.125% 2, 4- dinitrophenylhydrzine in 2N HCl nd 1. ml de-ionized wter. After incution in wter th t 37 C for 1 minutes, 5 ml of.6 N sodium hydroxide ws dded.

3 Following thorough mixing nd temperture equilirtion to room temperture, sornce t 42 nm ws red. Five different concentrtions of pure sodium pyruvte were treted the sme wy s smples nd correltion etween pyruvte mount nd sornce ws estlished to determine the enzymticlly developed pyruvte in the test smples. ANION CONCENTRATION IN TISSUES Freeze-dried nd ground tissue (25-3mg) ws quntittively extrcted with de-ionized wter. The wter extrct ws filtered through.45 µm syringe filter nd diluted 5 times with ion chromtogrphic nlysis eluent (3.5 mm N 2 CO mm NHCO 3 ). The filtered nd diluted extrct ws nlyzed for nion concentrtions y n ion chromtogrphy/suppressed conductivity detector (Dionex DX-5 IC/HPLC system, Dionex, Sunnyvle, CA) using procedure descried in Dionex ppliction note 135 (Dionex). DATA ANALYSIS Plnt cultivrs were rrnged in growth chmers in rndomized design under defined light sources nd cron dioxide concentrtions. A minimum of four replicte mesurements were mde for ech tretment. Dt were nlyzed y the GLM procedure in the SAS sttisticl progrm nd mens seprted using t-test Lest Significnt Difference (LSD) t the 5% level. RESULTS AND DISCUSSION PUNGENCY DIFFERS IN CULTIVARS AND TISSUE TYPES Enzymticlly developed pyruvte in eight green onions grown under HPS nd CWF s shown in Figure 1 for pseudouls nd Figure 2 for the third lef, were used s pungency indictors. In generl, there ws no difference in pungency of either tissue types etween CWF nd HPS, ut pungency differed mong cultivrs nd tissue types. The level of pyruvte in pseudouls ws significntly higher thn tht in leves with n exception of Pcific Perl tht hd roughly equl intensity of pungency in the pseudoul nd lef. EG Hrdy White pseudouls were the most pungent, while Deep Purple pseudouls (under CWF only) were the lest pungent mong the eight cultivrs. The pseudouls of other six cultivrs hd similr level of enzymticlly developed pyruvte. On the other hnd, the leves of Kink, Kruncho, Choetsu, Pcific Per nd EG hrdy were more pungent thn Choho, Gurdsmn nd Deep Purple, nd Deep Purple leves under CWF were once gin the lest pungent. When sttisticl nlysis ws performed on the comined pungency of pseudouls nd leves of n individul cultivr, nd compred mong cultivrs, EG Hrdy White lso turned to e the most pungent overll. Pyruvic Acid (µmol g -1 FW) Kink cde CWF- Grown Pseudoul HPS - Grown Pseudoul c Kruncho cdecd cde Choetsu Gurdsmn cde cd def cde ef Choho Pcific Perl EG Hrdy g Deep Purple Figure 1: Enzymticlly developed pyruvte in green onion pseudouls grown under cool white fluorescent nd high pressure sodium lmps. The letters ove the rs designte the outcome of sttisticl nlysis. The formtion of pyruvte upon mcertion or chewing of onion is lso ccompnied y the relese of thiosulfintes, the primry flvor compounds for Allium plnts (Block 1992, Lwson 1998). Thiosulfintes not only render onion the chrcteristic flvor, ut lso vrious iologicl ctivities including nticrcinogenecity (Rndle 1997, nd references therein, Sinni et l 1976, Kendler 1987, Augusti 199). Although thiosulfintes were not directly mesured, it is hypothesized tht more pungent onion my e more flvorful nd my provide greter helth enefit. Considering plnt s composition/undnce of eneficil phytochemicls when selecting sld crops s prt of supplementl diet for stronuts my e especilly importnt. Flight crews re t n elevted helth risk due to incresed exposure to ionizing rdition nd microgrvity (Todd, 23; Schimmerling et l., 23; Schimmerling, 23). Indeed phytochemicls from fruits nd vegetles over recent yers hve gined stture for their generl helth promoting effects nd specificlly s rdioprotectors to llevite rdition dmge (Weiss nd Lnduer 23). In ddition, necdotl evidences imply tht stronuts with extended sty in spce experience some shifts in the threshold levels for detection of tstes nd flvors nd desire for more flvorful food (Lne nd Schoeller 2). From the perspectives of pltility nd potentil helth enefit, pprently EG Hrdy White outperformed other cultivrs. Ironiclly Kink ws previously selected nd recommended for further testing under spce-relevnt environment (Edney et l. 23) t Kennedy Spce Center sed on other criteri (more uniform nd compct growth chrcteristics). Our findings here nd the fct tht there ws no sttisticl difference in iomss production or quntum efficiency etween EG Hrdy White nd Kink prompt the need for investigtion of oth productivity nd food qulity side y side during cultivr evlutions. fg

4 Pyruvic Acid (µmol g -1 FW) Kink def Kruncho CWF- Grown Lef HPS - Grown Lef cd ccd Choetsu Gurdsmn def efg cde cde Choho Pcific Perl EG Hrdy g Deep Purple Figure 2: Enzymticlly developed pyruvte in green onion leves grown under cool white fluorescent nd high pressure sodium lmps. The letters ove the rs designte the outcome of sttisticl nlysis. SPATIAL DISTRIBUTION OF PUGNENCY Figure 3 shows tht the first cm of the pseudoul ws the lest pungent nd tht there ws no significnt difference in the remining stem. The younger leves (i.e. lef 4) were more pungent thn the older leves (lef 2 nd 3); which grees with findings y Schwimmer nd Weston (1961). There ws no difference etween leves 2 nd 3 tht were oth fully expnded nd hd not yet reched senescence. Pyruvic cid (µmol g -1 FW) Exp. #1 Pseudoul Exp. #2 Pseudoul Exp. #1 Lef Exp. #2 Lef Distnce (cm) from Pseudoul Bse or Lef Numer Figure 3. Pungency grdient long the pseudoul nd development stge of leves in cv Kruncho. Brs represent stndrd devition of three plnt replictes. PUNGENCY IN BULB ONIONS How does the level of green onion pungency compre to tht of ul onion? Although it is known tht the pungency of ul onion vries gretly from 2 to 2 µmol g -1 (Schwimmer nd Weston 1961, Kopsell nd Rndle 1997), in order to vlidte our procedure nd provide direct comprison, two types of ul onion with distinct sensory vlue were nlyzed. Tle 1 indictes tht the store-purchsed gf red onion ws strongly pungent with vlue of 12.2 µmol g -1, while store-purchsed sweet white onion ws reltively mild with vlue of 5.4 µmol g -1. Most of green onions tested in this study fell etween these two extremes. EG Hrdy White pseudouls were equivlent to the red onion ul in terms of pungency. This implies tht some green onions could mesure up to ul onion in terms of pungency nd potentil helth enefit without the disdvntges such s low plnting density, twice the growing cycle (12 weeks vs. 6 weeks or short for green onions) nd longer light/drk photoperiod (Lncster 1996) required in producing ul onions. More interestingly, the more pungent onion coincided with lower nitrte nd sulfte, ut higher phosphte concentrtion in the tissue (Tle 1). At first glnce, this finding ppers to contrdict with previous oservtion tht incresing nitrogen nd sulfur fertility results in more flvorful onion (Rndle 2; Rndle et l. 1995). It is importnt to note tht the ul onions exmined in this study hve een commercilly stored nd shipped post hrvest, nd tht more pungent onion cultivrs my hve greter genetic potentil to continuously utilize reserved nitrte nd sulfte for the production of nitrogen nd sulfur contining compounds, resulting in lower nitrte nd sulfte concentrtion in tissues. Tle 1. Pyruvte nd Anion Concentrtion of Commercil Bul Onion. Vlues re the mens of 9 replictes nd stndrd devitions. Red Onion Sweet White Pyruvic Acid* 12.2 ± ±.9 Nitrte**.6 ± ±.6 Sulfte** 2.2 ± ±.6 Phosphte** 8.1 ± ± 1.1 * µmol g -1 fresh weight; ** mg g -1 dry weight TISSUE NITRATE AND SULFATE STATUS IN GREEN ONIONS In ll instnces, nitrte level (Tle 2) in the leves were higher thn tht in pseudouls, which is consistent with findings in other vegetles (Mynrd et l 1976), nd inversely correlted with the pungency. The inverse correltion etween pyruvte concentrtion nd nitrte ws lso found mong cultivrs. Pseudouls of Deep Purple with the lowest pungency hd the highest nitrte concentrtion, while the most pungent green onion (EG Hrdy White pseuoduls) hd the lowest nitrte level excluding Kink. The nitrte in Kink my e underestimted ecuse of some procedurl difficulties. In ddition, CWF lmps consistently incresed the nitrte level in green onions, ut the enhncement vried from 2-35% in pseudouls nd 4-58% in the leves of different cultivrs. The tissue nitrte level represents the difference etween sorption nd ssimiltion nd is ffected y genetic progrmming, environmentl fctors nd nutrient supply. It is well known tht the light intensity hs profound impct on nitrte levels, primrily due to the ltertion of nitrte reductse (NR)

5 ctivity (Mynrd et l 1976). On the other hnd, the evidence nd interprettion of the effect of light qulity, on nitrte level is tenuous. A study y Hrper nd Pulsen (1968) indictes tht nitrte concentrtions of whet leves (Triticum estivum L.) were lower under lue light (38-47 nm), nd NR ctivity ws mrkedly higher thn in red light (68-74 nm). However, in Hrper nd Pulsen s report, neither light level nor growth dt were shown. Overly of the light spectr of two lighting sources used in our experiment shows tht HPS hs more red, while CWF hs more lue, which would result in lower nitrte level in CWF-grown plnts sed on Hrper nd Pulsen s oservtion. It is importnt to note tht the light intensity of oth HPS nd CWF in our experiment ws djusted to the sme level (3 µmol m -2 s -1 ), nd there ws not significnt difference in iomss ccumultion under these lights (Edney et l 23). The finding here is significnt nd requires further investigtion to understnd the iochemicl nd physiologicl implictions of this enhnced ccumultion under CWF. Lstly the nitrte level in these green onions ws much higher thn in ul onions. Although differences in uptke potentil etween ul onions nd green onions could not e ruled out, the discrepncy might e prtly due to the fct tht the green onions investigted here were grown under excess nitrte supply (nitric cid ws used to mintin the ph of growth medium), nd iologicl ctivities were rrested t the time of hrvest, preventing ny post hrvest ssimiltion. Tle 2. Nitrte Concentrtion (mg g -1 DW) in Green Onion Tissue (n=4). Superscript letters designte the outcome of sttisticl nlysis HPS- Bul CWF- Bul HPS- Lef CWF- Lef Kink 22.1 g 43.6* 48.8 ef 67. Kruncho 28.8 fg 38 cde 69.2 c 9.7 Choetsu 3.8 f 38.1 cde 66.4 cd 94.9 Gurdsmn 33.8 def 41.2 c 59.9 cde 3.3 cde Choho 31.1 ef 38.9 cd 69.1 c 1.9 Pcific Perl 38. cde g 48.4 ef EG Hrdy 29.5 f 33.4 def Deep Purple fg 53.4 de *Insufficient degree of freedom for meningful sttistic nlysis. These results rise the question whether green onion should e consumed immeditely fter hrvest s well s whether storge cn hve n dverse effect on onion flvor nd helth promoting properties. The ingestion of vegetles with high nitrte levels presents potentil risk to humn helth due to the formtion of nitrite, which cuses methemogloinemi (Wright nd Dvison 1964). The presence of nitrite in lood might lso result in the formtion of nitrosmine, crcinogenic compound (Crddock 1983). Previous studies on ul onions (Smittle 1998, Lncster nd Shw 1991, Deene et l. 1999, Glmrini et l. 21) demonstrted tht pungency increses over post hrvest storge, however the response vries mong cultivrs (Kopsell nd Rndle 1997, Glmrini et l. 21). Bsed on previous findings on wht controls the nitrte ccumultion, it is conceivle tht nitrte level in edile iomss my e lowered y implementing one of the following prctices few dys prior to hrvest: ) incresing light level, ) incresing photoperiods, nd/or c) withdrwing the nitrogen supply from the growth medium. How these prctices ffects the onion s qulity trits remins to e determined. Tle 3 shows the sulfte concentrtion in tissues of eight green onions grown under either HPS or CWF. Sulfte concentrtions exhiited the sme trend s nitrte, nd were higher in leves thn in pseudouls. Unlike nitrte, there were no significnt cultivr differences or lighting source effects. The genetic potentil of cultivr to sor nd utilize sulfte for the synthesis of the flvor precursors determines onion flvor to lrger extent (Rndle 1997). The inverse correltion etween pungency nd nitrte in different cultivrs, nd the lck of difference in tissue sulfte t the sme time leds us to conclude tht higher pungency of EG Hrdy White is due to the higher efficiency of sulfur utiliztion nd/or lliinse ctivity Tle 3. Sulfte Concentrtion (mg g -1 DW) in Green Onion Tissue (n=4); Superscript letters designte outcome of sttistic nlysis HPS- Bul CWF- Bul HPS- Lef CWF- Lef Kink 6.3 cd 6.5* 7. e 6.8* Kruncho cd 8.7 c Choetsu 6.6 c cde 8.7 Gurdsmn defg cde Choho 6.4 cd 6.3 cdef 7.4 de 7.2 de Pcific Perl 5. g 5.9 cdef 6.9 e 8.9 EG Hrdy 5.9 cdef 6.3 cde Deep Purple 5.4 efg 5.4 efg 6.9 e 8.1 cde * Insufficient degree of freedom for meningful sttistic nlysis. EFFECT OF LIGHT INTENSITY AND ATOMSPHERIC CO 2 LEVEL ON ONION BIOMASS AND PUNGENCY Richrds et l (24) previously reported the results of 4 ppm (ppm ws used in text insted of µmol mol -1 for its simplicity) nd 12 ppm CO 2 tretments. Figure 4 included the results of 4 ppm CO 2, nd shows tht iomss production incresed with incresing light intensity regrdless of CO 2 levels. At ny of three given light levels, iomss ccumultion incresed s CO 2 level incresed from 4 ppm to 12 ppm, ut not when it incresed from 12 to 4 ppm, which suggests tht CO 2 sturtion nd yield potentil ws

6 reched t 12 ppm under these light intensities. Pungency of the onion pseudouls grown under 4 ppm CO 2 incresed with the increse of light level from 8.6 to 17.3 mol m -2 d -1 (lue grphic rs in Figure 5). Further increses of light levels from 17.3 to 25.9 mol m - 2 d -1 filed to enhnce pungency. These results suggest tht pungency incresed t greter rte thn iomss ccumultion from light levels of 8.6 to 17.3 mol, while t similr rte from 17.3 to 25.9 mol. At 12 ppm (red grphic rs) nd 4 ppm (yellow grphic rs) CO 2 tretments, pungency per grm sis in the pseudouls remined unchnged regrdless of light intensity. Bsed on the ner liner increse in iomss with the increse of light intensity, the pungency must hve incresed t the sme rte s the iomss t these two CO 2 levels. Edile Fresh Weight (g plnt -1 ) µmol mol -1 CO 2 12 µmol mol -1 CO 2 4 µmol mol-1 CO Dily Light Integrl (mol m -2 d -1 ) Figure 4. Edile iomss ccumultion (g plnt -1 ) of onion grown with dily integrl light set t 8.6, 17.3, nd 25.9 mol m -2 d -1 nd either 4, 12 or 4 µmol mol -1 CO 2 levels. When comprison is mde on pungency of onion pseudouls etween different CO 2 levels t given light level, elevted CO 2 hd no negtive or positive impct on pungency t either 8.6 or 17.3 mol m -2 d -1 light. This suggests the pungency incresed in prllel with the iomss. At higher light level (i.e mol m - 2 d -1 ), incresing CO 2 from 4 ppm to 12 ppm resulted in decresed pungency, while further increse of CO 2 level from 12 ppm to 4 ppm resulted in enhnced pungency in pseudouls. Considering tht iomss douled when CO 2 levels incresed from 4 to 12 ppm (Figure 4), the decrese of pungency in these pseudouls is likely dilution effect. On the other hnd, even though incresing CO 2 from 12 to 4 ppm filed to promote continued enhncement of iomss (Figure 4), this CO 2 increse significntly enhnced pungency, restoring pungency to level of tht under 4 ppm CO 2. In lef tissue (Figure 6), the effect of light intensity nd CO 2 levels on pungency ws mrkedly different. Under 8.6 mol m -2 d -1 light, there ws shrp decline in pungency s CO 2 incresed from 4 ppm to 12 ppm, ut leveled off etween 12 ppm nd 4 ppm CO 2 coinciding with the CO 2 sturtion of growth. The decline in pungency is not net decrese of pungency precursors or lliinse ctivity, rther greter dilution effect due to the fct tht leves ccount for more thn 8% of the totl edile iomss, nd consequently ccount for mjor portion of the iomss increse resulted from tripled CO 2 level. No CO 2 impct on pungency t other two light intensities signifies prllel increse in flvor precursor nd iomss. Pyruvic Acid (µmol g-1 FW) c 4 µmol mol-1 12 µmol mol-1 4 µmol mol-1 c c c c Dily Light Integrl (mol m -2 d -1 ) Figure 5: Enzymticlly developed pyruvte in green onion cv. Kink pseudouls developed under dily integrl light 8.6, 17.3, 25.9 mol m -2 d -1 CWF nd 4, 12 nd 4 µmol mol -1 CO 2. The letters ove the rs designte sttistic tretment outcomes. Pyruvic Acid (µmol g-1 FW) µmol mol-1 12 µmol mol-1 4 µmol mol Dily Light Integrl (mol m -2 d -1 ) Figure 6: Enzymticlly developed pyruvte in green onion cv. Kink lef developed under 15, 3 nd 45 µmol m -2 s -1 cool-white fluorescent lmps nd 4, 12 nd 4 µmol mol -1 CO 2. The letters ove the rs designte sttistic tretment outcomes. These initil experimentl dt indicte tht the comintion of low light (due to power constrints) nd high CO 2 conditions nticipted in enclosed spce c

7 environment hve no dverse effect on onion iomss nd qulity in terms of pungency equivlent to tht produced under the conditions of high light nd mient CO 2. CONCLUSIONS Results indicte the onions tested in this study were reltively strong, especilly the pseudouls of the mjority of cultivrs were one level more pungent (6-8 µmol g -1 FW) thn tht of the lef (4-6 µmol g -1 FW). EG Hrdy White ws the most pungent (8-1 µmol g -1 FW in pseudouls), nd outperformed other cultivrs in terms of pungency nd prole helth enefit. The nitrte level in green onions ws mrkedly higher thn ul onion (1-5 folds depending on cultivrs). For instnce, nitrte-n in Kink leves ccounts for 1.1% dry mss. Becuse of the helth hzrd of nitrite from consuming vegetles with high nitrte content, further study is deemed to ddress questions whether green onion should e consumed immeditely fter hrvest or horticulturl mnipultion of light level, photoperiod or nitrogen withdrwl prior to hrvest should e exercised to reduce nitrte level in edile iomss; s well s wht effect would these strtegies hve on green onion flvor nd helth enhncing trits. Nitrte level in edile iomss ws lso drmticlly influenced y light qulity. Although light sources did not hve ny effect on the iomss ccumultion or onion pungency, CWF-grown onions hd 2-35% higher nitrte in pseudouls nd 4-58% higher in leves compred to HPS-grown onions. Light nd CO 2 levels hd positive effect on pungency, i.e. incresing light nd CO 2 levels incresed the net ccumultion of flvor precursors nd/or lliinse ctivity (pungency fctors). However, the rte of ccumultion of pungency fctors seemed to lg ehind iomss efore the CO 2 sturtion point (12 ppm), resulting in n pprent decrese in pungency. Accumultion of pungency fctors continued eyond 12 ppm fter iomss reched its yield potentil. The environment of low light nd high CO 2 nticipted in enclosed spce hitts could still provide sld crops such s onion with equivlent quntity nd qulity (in terms of pungency) to those grown under mple high light nd mient CO 2. ACKNOWLEDGMENTS This reserch ws conducted s prt of ongoing studies for NASA in order to enhnce the diet diversity for the stronuts. Funding ws provided in prt y grnt from NASA (JSC ). REFERENCES 1. Augusti K.T. (199). Therpeutic nd medicinl vlues of onion nd grlic. In Alliums nd Allied Crops. Ed y Rinowitch H. nd Brewster J. Vol III, pp CRC Press, Boc Rton, FL, US. 2. Block A. (1992). The orgnosulfur chemistry of the genus Allium: implictions for the orgnic chemistry of sulfur. Angew. Chem. Int. Ed. Eng. 31: Briggs W.H. nd Goldmn I.L. (22) Vrition in economiclly nd ecologiclly importnt trits in onion plnt orgns during reproductive development. Plnt Cell nd Environment 25: Crddock, V.M. (1983). Nitrosmines nd humn cncer: proof of n ssocition? Nture 36: Deene J.P., Goldmn I.L., Yndell B. (1999). Post hrvest flux nd genotype x environment effects for onion induced ntipltelet ctivity, pungency, nd solule solids in long-dy onion during post hrvest cold storge. J. Amer. Soc. Hort. Sci. 124: Dionex. AN 135 determintion of inorgnic nions in wstewter y ion chromtogrphy. 7. Edney S.L.; Yorio N.C. Stutte G.W., Monje O.A. nd Wheeler R.M. (23). Comprison of unching onion (Allium fistulosum L.) grown under high pressure sodium nd cool white fluorescent lmps. pp in Proceedings of 3 rd plnt growth regultion society of Americ, August 3-6, Vncouver, British Columi, Cnd. 8. Glmrini C.R.; Goldmn I.L.; Hvey M.J. (21). Genetic nlyses of correlted solids, flvor nd helth-enhncing trits in onion (Allium cep L.). Mol Genet Genomics 265: Hrper J.E. nd Pulsen G.M. (1968). Crop Sci. 8: Jsoni R, Kne C, Green C, Peffley P, Tissue D, Thompson L, Pyton, P, Pré PW (24). Altered lef nd root emissions from onion (Allium cep L.) grown under elevted CO 2 conditions. Environ. Exper. Bot. 51: Kendler B.S. (1987). Grlic (Allium stivum) nd onion (Allium cep): A review of their reltionship to crdiovsculr disese. Pre. Med. 16: Kopsell D.E., Rndle W.M. (1997). Onion cultivrs differ in pungency nd ul qulity chnges during storge. Hort. Sci. 32: Lncster J. E. nd Shw M. (1996). Metolism of gmm-glutmyl peptides during development, storge nd sprouting of onion uls. Phytochemitry 3: Lncster J.E. (1996). Buling in onions: Photoperiod nd temperture requirements nd prediction of uli size nd mturity. Annls of Botny 78(4): Lne, H. W. nd D. A. Schoeller (2). Overview: History of nutrition nd spceflight, Chpter 1 in Nutrition in Spceflight nd weightlessness models

8 Eds y H. W. Lne nd D. A. Schoeller, P13 CRC press, Boc Rton, Lwson L.D. (1998). Grlic: review of its medicinl effects nd indicted ctive compounds. ACS Symp. Ser. 691: Mynrd D.N., Brker A.V., Minotti P.L. nd Peck N.H. (1976). Nitrte ccumultion in vegetles. Advnces in Agronomy 28: Mundy R. nd Mundy C. M. (1999). Low doses of dilly disulfide, compound derived from grlic, increses tissue ctivities of quinone reductse nd glutthione trnsferse in the gstrointestinl trct of the rt. Nutrition nd Cncer 34(1): Mundy R. nd Mundy C. M. (24). Induction of phse II enzymes y liphtic sulfides derived from grlic nd onions: n overview. Methods in Enzymology 382: Rndle W.M. (1992). Onion germplsm intercts with sulfur fertility for plnt sulfur utiliztion nd ul pungency. Enphyticl 59: Rndle W.M., Lncster J.E., Shw M.L., Sutton K.H., Hy R.L. nd Bussrd M.L. (1995). Quntifying onion flvor compounds responding to surlfur fertility-sulfur increse levels of lke(en)yl cysteine sulfoxides nd iosynthetic intermedites. J. Amer. Soc. Hort.Sci. 12(6): Rndle W.M. (1997). Onion flvor chemistry nd fctors influencing flvor intensity. pp in Spices: Flvor chemistry nd ntioxidnt properties, ACS symposium series 66, ed y Risch S.J. nd Ho C.T., Americn Chemicl Society, Wshington. 23. Rndle W.M., Kopsell D.E., Kopsell, D.A., Snyder R.L. (1999). Totl sulfur ccumultion in onion is ffected y sulfur fertility. J. Plnt Nutr. 22: Rndle W.M. (2). Incresing nitrogen concentrtion in hydroponic solutions ffects onion flvor nd ul qulity. J. Amer. Soc. Hort. Sci. 125(2): Richrds, J.T., Edney, S.L., Yorio, N.C., Stutte, G.W., Crnston, N., Wheeler, R.M. nd Goins G.D. (24). Effects of lighting intensity nd supplementl CO 2 on yield of potentil slds crops for ISS. Pper# , Proceedings of the 34 th interntionl conferences on Environmentl systems (ICES), July, 24, Colordo Springs, Colordo. 26. Sinni G.S., Desi D.B. More K.N. (1976). Onion, grlic, nd rtherosclerosis. Lncet. 2: Schimmerling W., Cucinott F. A. nd Wilson J. W. (23). Rdition risk nd humn spce explortion. Adv. Spce Res. 31(1): Schimmerling W. (23). Overview of NASA s spce rdition reserch progrm. Grvittionl nd Spce Biology Bulletin 16(2): Schwimmer, S. nd W.J. Weston (1961). Enzymtic Development of Pyruvic Acid in Onion s Mesure of Pungency. Journl of Agriculturl nd Food Chemistry. 9: Schwimmer, S nd Gudgni D.G. (1962). Reltion etween olfctory threshold concentrtion nd pyruvic cid content of onion juice. J. Food Sci. 27: Smittle D.A. (1998). Evlution of storge methods for Grnex onions. J. Amer. Soc. Hort. Sci. 113: Thompson, L., Peffley, E., Green, C., Pre, P. nd Tissue D. (24). Biomss, flvonol levels nd sensory chrcteristics of Allium cultivrs grown hydroponiclly t mient nd elevted CO 2. Pper# , Proceedings of the 34 th interntionl conferences on Environmentl systems (ICES), July, 24, Colordo Springs, Colordo. 33. Todd P. (23). Spce rdition helth: rief primer. Grvittionl nd Spce Biology Bulletin 16(2): Weiss J. F. nd Lnduer M. R. (23). Protection ginst ionizing rdition y ntioxidnt nutrients nd phytochemicls. Toxicology 189: Wheeler R.M., Stutte G.W., Suro G.V. nd Yorio N.C. (21). Plnt growth nd humn life support for spce trvel in: M. Pssrki (ed.), Hndook of plnt nd Crop Physiology, 2 nd Edition, pp Wright, M.G. nd K.L. Dvison (1964). Nitrte ccumultion in crops nd nitrte poisoning of nimls. Advnces in Agronomy 16: DEFINITIONS, ACRONYMS, ABBREVIATIONS ACSO: CEV: CWF: DAP: HPS: ISS: LN 2 : PPF: ppm: S-lk(en)yl-L-cysteine sulfoxide Crewed Explortion Vehicle cool-white fluorescent dys fter plnting high pressure sodium Interntionl Spce Sttion liquid nitrogen photosynthetic photo flux prts per million (this unit ws used in the text interchnging with µmol mol -1 )