TSNAs in Burley and Dark Tobacco

Transcription

1 t this time. Stlk choppers tht incorporte conveyers, so tht they re fed continuously s workers strip the tocco, offer the est gins in efficiency for stripping opertions ecuse they eliminte the need for ccumulting re stlks nd crrying them out of the stripping room nd mnully loding them on wgons or in mnure spreders. Chopping the stlks cn hve significnt dvntges on the loding nd spreding end s well, especilly if the chopped stlk is loded directly into mnure spreders. Lor requirements for spreding re considerly reduced compred to hving to throw whole stlks off wgon mnully, nd uniformity is much etter thn if whole stlks re spred with mnure spreder. Videos of the opertion of some of the mechniztion innovtions mentioned, s well s informtion out the sources of some of the equipment, re shown on the UK BAE tocco wesite: Check the BAE wesite for periodic updtes. References Sperry, R.G., J.H. Wilhoit, nd G.A. Duncn Development of semi-utomted tocco stripping mchine utilizing string trimmers. Applied Engineering in Agriculture 29(2): Dy V, G.B., T.D. Smith, nd L.G. Wells. High-cpcity mrket preprtion for urley tocco. Presenttion nd strct, 45th Tocco Workers Conference, Willimsurg, VA. Jnury 16-19, Wells, L.G., J.L. Goudouneche, T.D. Smith, G.B. Dy V, nd M. Hrpring. Mechnicl hrvesting of urley tocco in Frnce. Presenttion nd strct, 45th Tocco Workers Conference, Willimsurg, VA. Jnury 16-19, Wilhoit, J.H., nd G.A. Duncn Evlution of lor requirements for urley tocco stlk-notching hrvesters. Tocco Science (2012) 49: Wilhoit, J.H., nd G.A. Duncn Lor productivity nd requirements for stripping urley tocco. Tocco Science 50:1-10. Wht Are TSNAs? Nitrosmines re nitrogenous compounds, some of which re crcinogenic. They re found in wide rnge of food nd cosmetic products, s well s in tocco. TSNAs, tocco-specific nitrosmines, re so clled ecuse they re formed only from tocco lkloids nd found only in tocco leves nd in the prticulte phse of tocco smoke. With the current emphsis on the helth risks of tocco, TSNA reduction hs ecome mjor issue for the tocco industry. Severl TSNAs hve een identified, ut interest hs focused on the four most importnt: NNK, NNN, NAT, nd NAB. Of these, NNN is the most importnt in urley nd drk tocco. How Are TSNAs Formed? Negligile mounts of TSNAs re present in freshly hrvested tocco. They re minly formed during curing, specificlly during the lte yellowing to erly rowning stge. Typiclly this occurs over two-week period etween the third nd fifth week fter hrvest ut cn e erlier or lter depending on curing conditions. TSNAs re formed y the nitrostion of tocco lkloids (ddition of nitrogen nd n oxygen tom to the lkloid molecule). NNN is formed y the nitrostion of the lkloid nornicotine. The nitrosting gent in ir-cured tocco is usully nitrite, derived from the reduction of lef nitrte y the ction of microes during curing. In fire-cured tocco, the nitrosting gents re oth nitrite nd ny of severl nitrogen oxides (NOx) formed during the fire-curing process. Both the lkloid nd the nitrosting gent re necessry for the formtion of TSNAs. Any prctices or conditions tht increse the ccumultion of either of these groups of compounds would e expected to increse TSNAs. TSNAs in Burley nd Drk Tocco Anne Jck, Lowell Bush, nd Andy Biley Fctors Affecting TSNA Accumultion Three min fctors ffect the mount of TSNA ccumultion: The mount of specific lkloid precursor. In the cse of urley nd drk toccos, this precursor is nornicotine, nd it is minly determined y the mount of conversion of nicotine to nornicotine in the seedlot used. Screened or LC seed hs een selected for low conversion, nd we hve shown tht selecting screened or LC seed results in significntly lower TSNAs. The mount of nitrosting gent. Nitrite, NO 2-, is the min nitrosting gent for ir-cured tocco nd is determined y the microil popultions reducing the lef nitrte to nitrite. The microil popultions re ffected y curing conditions, prticulrly during the first 35 dys of curing. The mount of lef nitrte, determined y ville soil nitrogen, hs little direct effect on the mount of lef nitrite; ny effect is indirect, through the effect of nitrte on the thickness nd drying rte of the lef. With the levels of nitrte found in the norml production rnge, the min effect of pplied nitrogen fertilizer on TSNAs is through the effect on lkloid level. During fire-curing, nitrogen oxides (NOx) re the nitrosting gent nd re the result of comustion of wood during firing. The mount of totl lkloids/nicotine. The reltive mount of nornicotine depends on conversion, nd the solute mount depends on the mount of nicotine originlly present. The higher the nicotine, the higher the solute mount of nornicotine (ecuse there is more nicotine ville to e converted to nornicotine) nd consequently the higher the potentil for TSNA ccumultion. The mount of totl lkloid is determined prtly y environmentl conditions, such s rinfll, nd prtly y gronomic prctices, such s fertiliztion, topping, mturity t hrvest, etc. If ny of these fctors (conversion, nitrosting gent, totl lkloids) re reduced, TSNAs re reduced (Figure 1). 49

2 Seed Screening Reducing the mount of nornicotine precursor for NNN is the single most effective step in reducing TSNA ccumultion. Figure 2 illustrtes the difference in NNN etween two vrieties, non-commercil high converter nd screened low converter. There re very low inherent levels of nornicotine in the green plnt; it is minly formed y the conversion of nicotine to nornicotine during curing. The ility of plnts to convert nicotine is under genetic control, nd most modern vrieties hve een selected for minimum conversion. In the U.S., ll the pulic vrieties hve een screened; i.e., the foundtion seed ws selected for low conversion, which is indicted y LC (low converter) in the vriety nme (for exmple, TN 90LC, KT 204LC). Mny other vrieties lso hve this designtion. Some vrieties do not hve the LC designtion, ut screened seed is indicted on the seed pck. All seed of commercilly vile vrieties hs now een screened, nd there should e no unscreened seed sold in the domestic seed mrket. Prior to universl seed screening, mny seedlots hd reltively high conversion, nd consequently the potentil for high TSNA formtion. There hs een considerle reduction in TSNAs in recent yers s direct result of seed screening. The most importnt step in TSNA reduction, the use of LC or screened seed, hs een tken for U.S. tocco growers. All seed on the domestic mrket is now screened, nd ll contrcts with mjor tocco compnies now require the grower to use LC or screened seed. Vriety To some extent, there seem to e inherent differences etween some urley vrieties in their potentil to ccumulte TSNAs, differences tht re not explined y conversion levels. These differences re smll, ut they do pper to e rel. For exmple, it ppers tht KT 204LC often hs lower TSNA levels thn some other vrieties (Figure 3). We do not yet understnd the mechnism for these vrietl differences. Like ll fctors ffecting TSNAs, these differences re not lwys pprent. They re dependent to lrge extent on the environmentl growing nd curing conditions; differences re more likely to e pprent under conditions conducive to higher TSNA ccumultion. To dte, no vrietl differences in TSNA ccumultion hve een oserved in drk tocco vrieties. Vriety choice is minor considertion in reltion to TSNA ccumultion. Choose the vriety most suited to locl conditions, pying prticulr ttention to the disese spectrum. If KT 204LC meets the requirements, the choice of this vriety my contriute to lowering TSNAs. Fertiliztion Nitrogen fertiliztion hs considerle impct on TSNA ccumultion in the lef, ut the effect is indirect; nitrte is not directly involved in TSNA synthesis in the lef. Nitrte ffects TSNA levels minly through its effect on lkloid levels, nd lso through the effect on the ody nd drying rte of the lef. However, high nitrte in the lef is undesirle ecuse dditionl TSNAs my e produced during storge nd cigrette smoking. Mny studies hve found lrge differences in TSNAs etween very high nd very low nitrogen rtes. However, within the norml production rnge, the effect ws oserved to e much smller nd often inconsistent. Growing nd curing conditions cn ply lrge role in determining how nitrogen rtes ffect TSNAs, even when the rtes re extreme. Only when mny studies were pooled were reserchers le to show cler reltionship etween the mount of pplied nitrogen nd TSNA ccumultion. Figure 4 shows the strong liner trend for TSNAs to increse with incresing nitrogen. On verge, TSNAs will increse 0.05 ppm for every 10 pound per cre increse in pplied nitrogen. The totl mount of pplied nitrogen is the criticl fctor, regrdless of whether it is ll pplied s pretrnsplnt ppliction or is split etween pretrnsplnt nd sidedressing. Sidedressing does not pper to cuse significnt increse in TSNAs, s long s it is pplied t the recommended time. Applying sidedress nitrogen lter thn six weeks fter trnsplnting could increse TSNA levels under some conditions. Figure 1. NNN formtion. nicotine* conversion* nitrte curing* wood comustion nornicotine + nitrite or NO x fire-curing* NNN *Trgets for TSNA reduction. NNN (ppm) Figure 2. NNN (ppm) for high converter (HC) nd low converter (LC) urley vrieties over two yers. Within ech yer, rs with different letters re significntly different t the 5% level HC LC Totl TSNAs (ppm) Figure 3. Totl TSNAs (ppm) for KT 204LC nd NCBH 129LC; men over two yers. Brs with different letters re significntly different t the 5% level KT 204LC NCBH 129LC

3 There is no cler link etween nitrogen source nd TSNAs. Ft stems cn increse TSNAs y retining moisture in the lef stem. Ft stems cn e cused y lte uptke of nitrogen (lte sidedressing or dry period followed y rin shortly efore hrvest) nd y the use of murite of potsh fertilizers. Judicious fertilizer ppliction is one of the more fesile steps grower cn tke to reduce TSNAs. Apply no more nitrogen thn is necessry for the crop. In ddition to minimizing TSNAs, there re mny other good resons to void excessive nitrogen not the lest of which is cost. Excess nitrogen cn lso cuse disese prolems nd contriute to groundwter pollution, nd it does not increse yield. If sidedressing, pply nitrogen within four to five weeks fter trnsplnting. Avoid spring pplictions of murite fertilizers. If murite fertilizers re used, they should e pplied in the fll. Chloride lso hs n dverse effect on qulity nd cuses the cured lef to e more hygroscopic (moisture soring). Topping Any effect of topping on TSNAs is indirect through the effect on lkloid levels. Topping erly nd/or low increses lkloids nd would e expected to increse TSNAs. We do not hve much dt on this topic, ut indictions re tht differences re smll nd unlikely to hve much impct, especilly with low converters. The effect of topping on TSNA ccumultion is reltively minor. Top s recommended for est yield nd qulity (see Topping section of this puliction). Mturity t Hrvest Severl studies hve shown tht TSNAs increse with incresed mturity t hrvest. Erlier studies used unscreened seed, nd we know tht conversion increses with incresed mturity. Current results show similr ut smller response with the low converter vrieties now in use. The increse in TSNAs with incresed mturity is due minly to the higher lkloids in lter hrvested tocco; lkloids increse stedily fter topping. Wether nd vilility of lor to cut the crop often limit the grower s choice of hrvest dte, ut to the extent possile, hrvest t the mturity for est yield nd qulity. Burley. Typiclly the est compromise etween yield nd qulity is pproximtely three nd hlf to four weeks fter topping. Drk ir-cured. Hrvest five to six weeks fter topping; some erly mturing vrieties my require erlier hrvest. Drk fire-cured. Hrvest six to seven weeks fter topping; some erly mturing vrieties my require erlier hrvest. Figure 4. TSNAs vs. nitrogen rtes for three yers, five loctions. TSNA (ppm) Every 10 units N rise, 0.05 ppm TSNA rise ON AVERAGE N Rte, l/a Bush, Tem TSNA Hrvesting Prctices Field-wilting longer thn necessry cn, under some conditions, increse TSNAs. Figure 5 shows the TSNA ccumultion in urley tocco field-wilted for three nd six dys. These increses re smll nd re not lwys pprent, ut it is dvisle not to field-wilt urley longer thn three dys, s this cn hve detrimentl effect not only on TSNA ccumultion ut lso on lef qulity.. Wether nd vilility of lor often dictte when the tocco cn e housed, ut house urley tocco s soon s possile, idelly within few dys of cutting. Air-Curing Growing seson nd curing environment ply very lrge role in TSNA ccumultion. Figure 2 shows the effect of seson on high nd low converter vriety. At this site, 2005 ws yer very conducive to TSNA ccumultion; 2004 ws not. The more thn tenfold difference etween yers ws due solely to environmentl differences, s the sme seed nd growing prctices were used in oth yers. Note tht the low converter vriety in 2005 (when conditions were highly conducive) still hd lower TSNAs thn the high converter in 2004 (when conditions were very unfvorle for TSNA formtion). The min fctors ffecting ir-curing in reltion to TSNAs re temperture, reltive humidity, nd ir movement. Higher tempertures increse TSNAs ecuse iologicl nd chemicl rections re fster t higher tempertures. Higher humidity increses TSNAs ecuse it is fvorle for the nitrite-producing microes nd the lef Figure 5. Totl TSNAs (ppm), mens cross vrieties, for urley tocco field-wilted for 3 nd 6 dys fter cutting. Brs with different letters re significntly different t the 5% level Totl TSNAs (ppm) dys field wilting dys field wilting Miller 51

4 remins live nd ctive longer during curing, llowing more conversion of nicotine to nornicotine. Thus, with the incresed nitrite nd nornicotine ville, more TSNA is formed. Incresed ir movement decreses TSNAs minly y incresing the drying rte of the lef. High humidity nd high tempertures result in high TSNAs nd often in houseurn. Low tempertures or low humidity result in low TSNAs ut green or pield tocco. The conditions est for optiml qulity (moderte tempertures nd 72 to 75% reltive humidity, i.e., long, slow cure) re lso fvorle for TSNA ccumultion. Under these conditions, TSNAs levels will e uncceptle if there is ny pprecile mount of conversion. However, TSNAs will usully e cceptle if conversion is low nd curing is well mnged. Low converters cn hve significnt mounts of TSNAs in conducive conditions if the curing is not properly mnged (see Figure 2, low converter in 2005). The chllenge is to produce qulity tocco with cceptle levels of TSNAs. Tests hve shown tht TSNAs in outdoor urley curing structures re very similr to those in conventionl rn (Figure 6) if they re in the sme vicinity nd experience similr environmentl conditions. The loction nd orienttion of rn cn hve considerle effect on TSNAs y ffecting the mount of ventiltion. There cn e ig differences in TSNAs etween toccos cured in different rns. TSNAs will tend to e lower in exposed rns on ridges nd higher in rns in protected hollows with limited ir movement. Vrious rn modifictions hve een tested, ut none hve yet resulted in prcticl nd economicl system to consistently reduce TSNAs while producing qulity tocco. Attention hs focused on ventiltion, ecuse there is little tht grower cn do to control mient humidity nd temperture during ir-curing. However, ventiltion cn e mnipulted to limited extent to mintin qulity. Mnging curing specificlly for very low TSNAs will often result in poor qulity tocco, so the est curing mngement is lnce etween enough humidity for good qulity nd enough ventiltion to minimize TSNA formtion. Tke the following steps: Spce plnts evenly on sticks, nd spce sticks evenly on the rils. Avoid pcking sticks too closely (ctul stick spcing will vry with rn design nd size of tocco). Mnge vents to ensure dequte ut not excessive ventiltion. Fire-Curing Fire-curing of drk tocco involves the urning of hrdwood sls nd swdust on the floor of the rn during curing. Although fire-curing rns hve ottom nd top ventiltors, they re typiclly much tighter thn ir-cured rns nd most hve metl siding. Mny fire-cured rns re lso equipped with fns in the top of the rn tht cn e used to increse ventiltion erly in the cure. Although differences in rn design nd the fire-curing process itself llow more control over curing conditions nd less influence of outside wether conditions, the growing seson nd curing environment still ply mjor role in TSNA ccumultion in fire-cured tocco. Fire-curing llows more potentil for TSNA ccumultion thn ir-curing. Higher tempertures re involved, which increses the speed of iologicl nd chemicl rections, nd nitrogen oxide (NO x ) gses re produced y the urning of wood, which increses nitrostion of tocco lkloids. However, some sic mngement prctices for fire-curing cn reduce the potentil for high TSNA formtion. Avoid pcking sticks too closely in the rn, s this cn led to poor cured lef qulity, losses in cured lef weight, poor or uneven smoke finish on leves, nd higher TSNAs. Idelly, strt firing within seven dys fter housing. Avoid firing the tocco more or longer thn necessry to produce cured lef with cceptle qulity nd mrketility. Growers should strive to keep rn tempertures elow 130 F, even during the drying stge of the cure. Idelly, tocco should not e kept t 130 F longer thn four to five dys; y seven dys t this temperture, TSNAs would e expected to increse. Artificil csing with overhed misting systems or stemers is often required for tkedown in drk fire-cured tocco due to the extremely dry condition of the tocco fter curing is complete. This is prticulrly true with first cures in doule-crop curing, where tkedown needs to occur quickly following curing. Reserch hs shown tht use of overhed misting systems t tkedown my result in lower TSNAs thn stem. The most effective steps grower cn tke re to minimize the effects of high tempertures (which increse the speed of TSNA-forming rections) nd wood comustion (which increses the mount of nitrosting gent). Do the following: Fire drk tocco no more thn necessry. Idelly, strt firing within seven dys fter housing. Strive to keep rn tempertures in fire-cured rns elow 130 F. Idelly, do not keep tempertures t 130 F for longer thn four to five dys. Spce plnts evenly on sticks, nd plce sticks evenly on the rils. Figure 6. NNN (ppm) in conventionl rn (left) nd outdoor curing structure (right). 52

5 Avoid pcking sticks too closely. Use miniml rtificil csing. Consider using overhed misting systems insted of stem when rtificil csing is needed in fire-cured tocco. Control of Microes The nitrite-producing microes re uiquitous nd cnnot e voided. They re endophytic (inside the lef ), which mkes ppliction of ny tretment very difficult. Mny chemicls nd iologicl gents hve een tested, ut none of them hs resulted in prcticl control method. Correct curing will help to control microes. At this point, there is no tretment to directly control the nitrifying microes. Mnge curing for production of high qulity, full flvor nd rom tocco nd void houseurn conditions tht re conducive to microil ctivity. Moisture nd Storge Studies hve shown tht housing wet tocco cn increse TSNAs, s cn storing high-moisture tocco. It is difficult to control the moisture content of tocco when using rtificil methods of csing such s stem or wter sprys, nd overppliction of wter to cured lef cn result in unsfe moisture levels during storge. For this reson, it is etter to use nturl csing if possile. TSNAs generlly increse with time in storge, lthough this is less evident in low converter tocco. Tocco should therefore not e left in storge longer thn necessry. The following steps will help to minimize the effects of moisture on the nitrite-producing microes: To the extent possile, do not house tocco with free moisture on the leves. Allow ir-cured tocco to come into cse nturlly if possile. If using rtificil csing, void over-pplying moisture. Use miniml rtificil csing for fire-cured tocco, nd consider using overhed misting systems insted of stem. Strip, le, nd deliver tocco s soon s possile to void ny extr time in storge. Keep moisture in the cured tocco s low s possile, ensuring tht it is elow the level specified in the contrct. Best Mngement Prctices for Minimizing TSNAs TSNA formtion is very complex process, nd one cnnot consider ny of the fctors contriuting to it in isoltion. All of these fctors interct, sometimes resulting in TSNA differences nd sometimes do not. These prctices will contriute to lowering TSNAs: Use LC or screened seed. Choose the most suitle vriety with the pproprite disese resistnce pckge. (If KT 204LC meets other requirements, the choice of this vriety my help to lower TSNAs.) Use no more nitrogen thn necessry to optimize yield. Avoid spring pplictions of murite fertilizers. If sidedressing, pply nitrogen within four to five weeks fter trnsplnting. Top correctly. Hrvest t correct mturity, idelly out three nd hlf to four weeks fter topping for urley, out five to six weeks for drk ir-cured, nd out six to seven weeks for drk fire-cured. House urley tocco s soon s possile, idelly within few dys of cutting. To the extent possile, do not cut or house tocco with free moisture on the leves. Mnge ir-curing crefully, ensuring dequte ut not excessive ventiltion, nd void houseurn. Avoid overpcking the rn, nd spce sticks nd plnts on the sticks evenly. Fire drk tocco no more thn necessry. Idelly, strt firing drk fire-cured tocco within seven dys fter housing. Strive to keep rn tempertures in fire-cured rns elow 130 F. Idelly, do not keep tempertures in fire-cured rns t 130 F for longer thn four to five dys. Allow urley tocco to come into cse nturlly nd use miniml rtificil csing for drk tocco, idelly misting systems insted of stem. Do not leve tocco in storge longer thn necessry; strip, le, nd deliver tocco s soon s possile. Keep moisture in the lef s low s possile; do not put highmoisture tocco into storge, nd do not deliver tocco with moisture higher thn specified in the contrct. 53