Development of infrared heating technology for tomato peeling

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1 Development of infrred heting technology for tomto peeling Zhongli Pn,, Xun Li, Yong Wng,c, Griffiths Atungulu, Tr H. McHugh, Michel Delwiche Processed Foods Reserch Unit, Western Regionl Reserch Center, USDA-ARS, Alny, CA 94710, USA Deprtment of Biologicl nd Agriculturl Engineering, University of Cliforni Dvis, Dvis, CA 95616, USA c College of Engineering, Chin Agriculturl University, Beijing, Chin ABSTRACT The commercil lye nd stem peeling methods used in tomto processing industry re wter- nd energyintensive nd hve negtive impct on environment. To develop lterntive peeling methods, we conducted comprehensive studies of using infrred (IR) heting for tomto peeling. The three mjor reserch ojectives were (1) to compre the efficcy of IR peeling nd conventionl lye peeling, (2) to investigte the dynmic therml-mechnicl properties of tomto skins heted with IR nd lye solution, nd (3) to model the geometricl chrcteristics of processing tomto fruits. It ws discovered tht IR heting significntly reduced the tomto peeling loss y 9% nd produced firmer product with similr ese of peeling nd heting time compred to lye peeling method. The reduced peeling loss nd improved product qulity men tht more premium products cn e produced. Since no wter/stem nd chemicls re used, the IR peeling is nmed s IR dry-peeling method. To elucidte the IR dry-peeling mechnism, Dynmic Mechnicl Anlysis (DMA) technique ws used to determine the reltionship mong the texturl prmeters, IR heting time, nd the degree of tomto tissue deteriortion. It ws found tht the texturl ehvior of tomto skin ws sensitive to temperture nd frequency scn nd hd significnt chnge fter IR heting s compred to fresh tomto skin. A 3D model of tomto shpe ws developed to chrcterize the shpe nd size of processing tomto fruits sed on mss nd hd high ccurcy of prediction. The new model lso provided importnt geometric informtion vitl for designing commercil IR dry-peeler to chieve desired peeling performnce. Bsed on the reserch results, it is concluded tht IR dry-peeling hs promising potentil for commerciliztion. A proto-type commercil tomto IR peeling system is currently eing developed. Keywords: Infrred heting; Lye peeling; Processing tomto; Dynmic mechnicl nlysis; Geometric model; INTRODUCTION The long-term wter supply nd wstewter disposl prolems ssocited with lye nd stem peeling methods hve ecome criticl concerns to the sustinility of tomto processing industry. Prticulrly, the widely used lye peeling process is wter nd energy-intensive opertion nd results in lrge mount of wstewter with high slinity nd orgnic lods. The stem peeling does not use chemicls, ut it produces softer products nd hs more peeling loss thn lye peeling. It is vitl to develop sustinle peeling technology, which cn eliminte or reduce wter nd chemicl usge, menwhile delivering high qulity peeled tomto products. To ddress these criticl chllenges, our reserch hs imed t developing sustinle dry-peeling method which uses infrred (IR) het without wter nd chemicls in the heting stge [1, 2]. This pper provides rief report on our recent studies of developing IR dry-peeling technology. The reserch hd three mjor ojectives: (1) compring the efficcy of IR dry-peeling nd conventionl lye peeling methods; (2) investigting the dynmic therml-mechnicl properties of tomto skins heted with IR nd lye solution; nd (3) modelling the geometricl chrcteristics of processing tomtoes. MATERIALS & METHODS Tomto Fruits Three populr peeling cultivrs (cvs.), Sun6366, CXD179 nd AB2, of processing tomtoes were used for the peeling evlution studies. They were grown y Clifornin commercil growers nd only tomtoes with uniform sizes nd no visul defects were used through the experiments. The verge dimeter of tomtoes t the lrgest trnsverse section ws 49±3mm nd the tomto weights were in the rnge of 70 to 110g. Different tomtoes cultivrs were used for different sets of tests depending on their hrvest dte nd experimentl

2 schedule. To chrcterize the morphometric ttriutes of processing tomtoes, some physicl properties were determined in three consecutive hrvesting sesons. The mesured physicl ttriutes included fruit mss (m), fruit density, surfce re, totl height (H), mximum dimeter (W), the position of mximum dimeters (P), shoulder height (s), rdius of curvture t the lossom end of tomtoes (R 90 ). IR Dry-peeling Method, Evlutions of Peeling Performnce nd Product Qulity An IR heting system equipped with two ctlytic IR emitters (Ctlytic Drying Technologies LLC, Independence, KS), nd powered y nturl gs, ws used in this reserch. The schemtic digrm of the experimentl setup is shown in Figure 1. The IR emitter hs heting surfce of cm nd the distnces etween two emitters were selected s 90±2mm, 110±2 mm nd 120±2 mm for the tests. Tomtoes were heted with IR for 30, 45, 60 nd 75 s nd rotted for 90 degree every 15s to improve heting uniformity. Regulr lye peeling with NOH ws used s control for compring with the IR peeling. Tomtoes were dipped into 10% (w/v) NOH solution t 95±2 C for 30, 45, 60 nd 75s. The rtio of lye solution to tomto ws 5:1. Figure 1 Schemtic digrm of IR heting system for tomto peeling Peeling performnce evlutes the outcomes nd efficiency of tomto peeling process from three spects, peelility, ese of peeling, nd peeling loss. Peelility ws clculted s un-removed peel per unit weight (cm 2 /g). According to FDA stndrd (21CFR ), un-removed peel per grm of the rw product should e less thn [3]. The ese of peeling, grding system sed on scle of 1 (unle to peel) to 5 (esy to peel), ws used to descrie the esiness of peeling of tomtoes. A score greter thn 4 ws considered s n cceptle level [3]. Peeling loss ws clculted percentge in terms of the tomto weight chnge efore nd fter peeling, where lower peeling loss is desirle for peeling process. The surfce temperture of tomtoes ws nother importnt processing prmeter, which ws mesured immeditely fter IR heting using non-contct IR Thermometer (Lesmn Instrument Compny, USA). For lye peeling, the surfce temperture of tomtoes ws ssumed to e equl to the temperture of peeling solution. Texture nd ppernce of peeled products re the most importnt qulity indictors. The firmness of tomtoes ws mesured using fruit texture nlyzer FTA GS-14 (Texture Technologies Corp., Scrsdle, USA) through compression test [4]. The color of peeled tomto ws determined t three different loctions long the trnsverse direction in CIE L ** color spce using Minolt Chrom Meter (Model CR200, Minolt Crop., Rmsey, NJ, USA). Hue vlues re reported nd vlue closer to zero indictes redder tomto. Anlysis of vrince (ANOVA) nd Duncn s multiple rnge tests (p 0.05) were pplied to compre peeling performnces using SAS softwre pckge. All reported peeling results re the verge of ten replictes. All tests were completely rndomized so s to otin independent oservtions. Dynmic Therml Anlysis of Tomto Skin The chnges in properties of tomto peels treted y IR nd hot lye solution under different tretment times (30, 45, 60, 75 s) were exmined y using Dynmic Mechnicl Anlysis (DMA) method (DMA 8000, Perkin-Elmer, Wlthm, Msschusetts, US) under two modes, frequency sweep mode nd temperture rmp mode. In the frequency sweep test, smples experienced frequency scn in rnge from 0.01Hz to10 Hz with constnt prelod displcement of 0.05 mm. Ten dt points were collected t ech frequency decde nd ll dt were comined together in determining storge modulus nd loss modulus for ech smple ccording to the Powel Lw model. Under the temperture rmp mode, the smple ws heted from 22 C to 120 C t heting rte of 5 C/min. The frequency ws mintined t 1 Hz through the entire temperture rmp tests nd constnt prelod displcement of 0.05 mm ws pplied. All smples of tomto peel were cut with customdesigned die-cutter to otin smple dimension of mm (length width thickness). To prevent the moisture loss during ll of the tests, smples were crefully wrpped with plstic preservtion film nd

3 luminium foil. All DMA tests were performed immeditely fter IR or lye tretment with t lest six replictes for ech condition nd fresh peels were used s control. Tomto Geometric Modelling nd Sttisticl Anlysis A three-dimensionl geometric model of tomto shpe ws nlyticlly developed sed on the mesurements of tomto cv. AB2. The vlidtion of the developed 3D model ws conducted y compring predicted nd mesured mss nd surfce re of the sme cultivr tomtoes from different sesons. RESULTS & DISCUSSION Peeling Evlutions For cv. Sun6366, the ese of peeling nd peeling loss incresed with the increse of dipping time for lye peeling (Tle 1). Even though ll tretments met the required cm 2 /g peelility stndrd, we oserved tht heting for t lest 45 seconds is needed to chieve cceptle level of the esiness of peeling. Due to the vriety difference, the cv. CXD179 needed less dipping time to chieve similr peeling esiness nd showed higher firmness. Tle 1 Effects of heting time on tomto peeling with hot lye solution for tomto Sun6366 nd CXD 179 Cultivr Methods nd Peelility Ese of Peeling Loss Peeled Tomto Peeled Tomto Conditions (cm 2 /g) Peeling (%) Color (Hue ) Firmness (kg) Sun6366 Lye s Lye s , Lye s Lye s c CXD 179 Lye s Lye s Note: Suscript 10 indictes the percentge concentrtion of the lye solution. Men seprtion with different letter in ech column of two sections re significntly different t the 0.05 level. Sme nottions were used in Tle 2 nd 3. When IR ws used for peeling with n emitter distnce of 120 mm (Tle 2), the required IR heting time to chieve n ese of peeling score ove 4 ws 60 seconds which ws out 15 seconds longer thn the lye peeling. We recently found tht the required IR heting time cn e significntly reduced y incresing IR emitter temperture. Compred to the control, the IR peeled tomtoes hd much firmer texture nd much less peeling loss. For exmple, when the ese of peeling ws ove 4, the IR nd lye peeled tomtoes hd firmnesses of nd kg, respectively, nd the corresponding peeling losses of % nd %. The rottion seemed to slightly improve the esiness of peeling nd firmness nd lso reduced peeling loss. Tle 2 Effects of time nd rottion on tomto peeling with IR for tomto Sun6366 Peeling Performnce Time (s) Rottion with 120mm gp Yes No Men Ese of peeling ± ± ± ± ± ± c ± ± d Peeling loss (%) ± ± ± ± ± ± ± ± Peeled Firmness (kg) ± ± ± ± ± ± , ± ± For cv. CXD179, ll IR peeled tomtoes met the peelility requirement (Tle 3). The heting rte nd firmness of peeled products were slightly improved when the emitter gp ws reduced from 110 to 90 mm. Therefore, in order to provide higher het fluxes to rpidly het the surfce of tomtoes, reltively smller

4 gp etween emitters is generlly recommended. The vlue of the ese of peeling reched to 4.8 nd ws significntly higher thn the control (4.5) when heting time ws 45 s. However, the firmness of IR peeled tomtoes ws in the rnge of 1.3 to 1.6 kg, while the control gve 1.7 kg (dt shown in Tle 1). The slightly lower firmness of IR peeled tomtoes could e due to over exposure to IR heting. The verge peeling loss of IR treted tomtoes ws pproximtely 9% which ws significntly lower thn tht of control which ws round 10.7%. The colour of IR peeled tomtoes ws similr to the control (dt not shown). Tle 3 Effect of time nd emitter gp on tomto peeling using IR heting for CXD 179 Peeling Performnce Time (s) 90mm gp 110mm gp RTN NRTN RTN NRTN Ese of peeling ± ± ± ± ± ± ± ± ± ± ± ± Peeling loss (%) ± ± ± ± ± ± ± ± ± ± ± ± Peeled Firmness (kg) ± ± ± ± ± ± ± ± ± ± ± ± Note: RTN mens with rottion nd NRTN indictes without rottion. Therml-Mechnicl Properties of Tomto Skin The results of temperture rmp test re shown in Figure 2. The storge modulus of ll smples decresed t the eginning with the increse of temperture nd turned to increse fter reching the trnsition points, which re the lowest points in the plots. This tendency ws consistent with previous study of tomto skin properties y Mts et l [5]. Figure 2 lso revels tht tomto peels fter IR heting hd higher modulus vlues thn the fresh control (Figure 2), while the storge modulus of lye treted smples were lower thn tht of fresh smples, especilly t the low temperture rnge (Figure 2). These differences in storge modulus indicted tht IR nd lye peeling methods my hve different mechnism for tomto peel removl. In this studies, the trnsition tempertures of tomto peels were found to e in rnge from out 50 C to 85 C, depending on the tretment time nd methods. All IR treted smples hd significntly lower trnsition temperture thn fresh control, which indicted the chnges in mechnicl properties occurred within tomto skin due to IR heting. IR treted smples showed similr trnsition temperture of out 70 C. Sttisticlly no significnt difference ws oserved for the otined trnsition tempertures with different IR heting times. This my indictes tht s long s the trnsition point of tomto skin is chieved, further increse of IR tretment time is not necessry. Men Figure 2 Storge modulus (E') chnge of tomto skin under different temperture: ) IR tretment; ) Lye tretment Figure 3 shows the frequency response of the storge modulus of tomto peels s ffected y IR or lye tretment. All modulus vlues incresed with the increse of frequency. The IR treted smples hd higher storge modulus thn tht of the control (Figure 3), while ll the lye treted skins hd lower modulus thn the control (Figure 3). This trend is very similr to the modulus differences found in temperture rmp tests. A possile reson is tht the cuticulr memrnes of tomto peels were prtly destroyed y the lye tretment

5 Storge modulus (MP) Storge modulus (MP) [6]. The pectin in cuticulr memrnes which contriute much to the mechnicl strength, most likely hve een prtly destroyed y the hot lye solution. The IR tretment could reduce the moisture content within the tomto peels nd increse the modulus vlues. The moisture content ws found to hve negtive effect on the mechnicl strength of tomto peels [7]. 120 Control 30s 45s 60s 75s Control 30s 45s 60s 75s Frequency (Hz) Frequency (Hz) Figure 3 Storge modulus (E') of tomto skin under different frequency: ) IR tretment; ) Lye tretment Tomto Geometric Model Processing tomtoes generlly hve elongted ovl shpe nd re different from round-shped fresh mrket tomtoes. We derived tomto shpe eqution under polr coordintes, which descried the representtive processing tomto geometricl profile in terms of tomto dimensionl informtion nd shpe coefficients. R(θ) = 1+c 1sin (θ)+c 2 sin 3 (θ) (1) 2 cos (θ ) 2+ sin (θ ) where R(θ) is the rdius distnce from the origin to the tomto surfce; θ is the ngle of polr coordintes; nd denote the semi-mjor xis nd the semi-minor xis, respectively; c 1 nd c 2 re shpe coefficients. The four tomto shpe descriptors (,, c 1 nd c 2 ) cn e mthemticlly determined from minimum of five mesurements (H, W, P, s nd R 90 ) of tomto geometric ttriutes [8]. The determintion cn lso e simplified sed on the regression reltionship etween tomto msses nd tomto shpe descriptors of nd. Figure 4 depicts three tomto geometric profiles differing with distinct tomto msses. From the lrgest to the smllest mss of tomtoes, the corresponding vlues of nd were 31, 29, 26 respectively for nd 26, 22, 18 respectively for. The vlues of c 1 nd c 2 were selected s 0.24 nd 0.38 for ll the three mss levels. Figure 4 demonstrtes 3D geometric model of tomto with medium mss. The model cn e used for further computer simultion studies (Figure 4). Figure 4 Processing tomto shpes nd 3D geometricl model: () Geometric profiles t three mss levels; () Computer generted 3D tomto geometry with finite element meshes. The model vlidtion ws crried out sed on tomto mss nd surfce re. In generl, the predicted nd mesured vlues hd resonly good greement (Figure 5). The developed 3D model will lso llow the clcultions of other geometric chrcteristics of tomtoes, such s volume, rdii of curvture etc.

6 CONCLUSION Figure 5 Vlidtion of model etween predicted vlues nd mesured vlues ) mss ) surfce re The studies showed tht IR peeling yielded lower peeling loss nd firmer peeled product with similr peeling esiness compred to regulr lye peeling method. DMA nlysis of tomto skins reveled tht the mechnism of IR nd lye peeling methods were different. The chnges in dynmic mechnicl properties of tomto skin due to IR heting were quntified. Estlished 3D model provided n effective tool for generting geometric representtion of tomtoes, which cn e used for the design of IR dry-peeling system nd ssocited het trnsfer simultion. The new peeling technology hs gret potentil to replce the conventionl lye peeling method for tomtoes nd could lso e extended to other fruits nd vegetles. REFERENCES [1] Pn, Z., X. Li, G. Bingol, T. H. McHugh, nd G. Atungulu Development of Infrred Rdition Heting Method for Sustinle Tomto Peeling. Applied engineering in griculture 25(6): [2] Pn, Z., R. Khir, L. D. Godfrey, R. Lewis, J. F. Thompson, nd A. Slim Fesiility of simultneous rough rice drying nd disinfesttions y infrred rdition heting nd rice milling qulity. Journl of Food Engineering 84(3): [3] Li, X., Z. Pn, G. Bingol, T. H. McHugh, nd G. Atungulu Fesiility Study of Using Infrred Rdition Heting s Sustinle Tomto Peeling Method In Proceedings of the Americn Society of Agriculturl nd Biologicl Engineers Interntionl Pper No ASABE, ed. Reno, Nevd: St. Joseph, Michign.: ASABE. [4] Cntwell, M Report to the Cliforni Tomto Commission Tomto Vriety Trils: Posthrvest Evlutions for Dvis. Aville t: [5] Mts, A. J., López-Csdo, G., Curtero, J., & Heredi, A Reltive Humidity nd Temperture Modify the Mechnicl Properties of Isolted Tomto Fruit Cuticles. Americn Journl of Botny, 92(3), [6] Mts, A. J., Co, E. D., Brtsch, J. A., Polillo, D. J., & Nikls, K. J Biomechnics nd Anotomy of Lycopersicon Esculentum Fruit Peels nd Enzyme-treted Smples. Americn Journl of Botny, 91(3), [7] Lopez-Csdo, G., Mts, A. J., Dominguez, E., Curtero, J., & Heredi, A Biomechnics of Isolted Tomto (Solnum lycopersicum L.) Fruit Cuticles: the Role of the Cutin Mtrix nd Polyscchrides. Journl of Experimentl Botny, 58(14), [8] Li, X., Z. Pn, S. K. Updhyy, G. Bingol, G. Atungulu, X. Zheng, nd T. H. McHugh Geometricl Chrcteristics nd Model Development of Processing Tomtoes. In Proceedings of the Americn Society of Agriculturl nd Biologicl Engineers Interntionl Pper No ASABE, ed. Pittsurgh, Pennsylvni: St. Joseph, Michign.: ASABE.