&nbsp;In Drying characteristic for infrared drying of tomato slices were investigated. The drying experiments were carried out using Kerewa local varieties of tomato at five infrared drying power (150, 250, 300, 400 and 500 W) with slice thickness of 10 mm. For all drying powers there was a reduction in moisture content with increased drying time, the drying took place in the falling rate period. The drying time reduced as the infrared heating power increased from 150 to 500W. The diffusivity obtained for the tomato slices were within the range specified for fruits and vegetables with a value of 5.6132 x 10-7 m/s2.&nbsp; Blanched tomato varieties had better rehydration capacities than all unblanched samples

Abimbola, M.

Adeleke, E. A.

Adeosun, O. J.

Dada, O.

Dairo, O. U.

Dairo, R. B.

Omotainse, P. O.

Yusuf, B.

LAUTECH Journal of Engineering and Technology (LAUJET)

Dairo O.U.  et. Al./LAUTECH Journal of Engineering and Technology 11(2) 2017: 66-7166DRYING CHARACTERISTICS OF KEREWA TOMATO UNDER INFRAREDDRYING1Dairo, O. U*, 1Adeosun O, J., 2Adeleke, E. A, 1Omotainse, P. O., 1Abimbola M., 1YusufB., 1Dada Omolara, and 3Dairo R. B1Department of Agricultural Engineering, College of Engineering, Federal University ofAgriculture. Abeokuta. Ogun State, Nigeria2Mechanical Engineering Department, Faculty of Engineering, Federal University Oye Ekiti,Ekiti State, Nigeria3Department of Nutrition & Dietetics, Federal University of Agriculture Abeokuta. Ogun State,Nigeria*Corresponding author: dairoou@funaab.edu.ngABSTRACTIn Drying characteristic for infrared drying of tomato slices were investigated. The drying experiments werecarried out using Kerewa local varieties of tomato at five infrared drying power (150, 250, 300, 400 and 500 W)with slice thickness of 10 mm. For all drying powers there was a reduction in moisture content with increaseddrying time, the drying took place in the falling rate period. The drying time reduced as the infrared heating powerincreased from 150 to 500W. The diffusivity obtained for the tomato slices were within the range specified for fruitsand vegetables with a value of 5.6132 x 10-7 m/s2.  Blanched tomato varieties had better rehydration capacities thanall unblanched samples.Keywords: Infrared, Kerewa, Tomato, Drying, Diffusivity,IntroductionTomato (solanum, lycopersicum) is one of the mostscientifically investigated vegetable, because of itscommercial importance, its highly perishable and postharvesting losses reach 25 – 50%, with high watercontent of 93-95%. In tropical countries, there is a lossof 20-50% from harvesting to consumption. It is lowin calories and rich in vitamin A, C, and E andminerals such as calcium, potassium and phosphorus.Tomatoes grow in lowland and highland areas, butthey cannot survive for a long period of time afterharvested. After three days in storage, tomatoesrespiration and transpiration will cause increase ofCO2 and H2O content. This triggers the growth ofbacteria that cause rotting of tomato (Cahyono, 1998).The quality of tomatoes depends on its freshness whilelow water content in tomatoes discourages the growthof bacteria. In order to make the tomatoes last longerafter harvesting, preservation method is needed todrying tomatoes while retaining flavor. Drying is animportant process to preserve raw food materials. Thedrying process occurs when water vapour is removedfrom its surface into the surrounding space, resultingin a dried material with an extended shelf life andreduced water activity of food products. Duringdrying, the moisture content can be reduced to a levelranging from 1 to 5%, which avoids microbial spoilageand undesirable enzymatic reactions. In addition tosubstantial reduction in weight and volume, itminimizes packaging, storage and transportation costs(Fumagalli and Silveira, 2005; Falade and Solademi,2010). Drying can be carried out by the application ofheat either by conduction, convection or radiation. Itinvolves both heat transfer (application of heat) andmass transfer (removal of water).The use of artificial drying to preserve agriculturalproducts has expanded widely, creating a need formore rapid drying techniques and methods that reducethe large amount of energy required in dryingprocesses. New and or innovative techniques thatincrease drying rates and enhance product quality haveachieved considerable attention. New dryingtechniques and dryers must be designed and studied tominimize the energy cost in the drying process(Kocabiyik and Tezer 2009).Several methods are used in the drying industry suchas sun drying, hot air, microwave, vacuum andinfrared radiation. Infrared Drying (IR) drying is basedon the action of infrared wavelength radiation from asource, which interacts with the internal structure ofLAUTECH Journal of Engineering and Technology 11(2) 2017: 66-71Dairo O.U.  et. Al./LAUTECH Journal of Engineering and Technology 11(2) 2017: 66-7167the sample and thus increases its temperature andfavors the evaporation of its moisture content. IRdrying technique is particularly valid for products withsignificant moisture content, for which long waveradiation (over 3μm) is almost totally absorbed bymoisture, while dry material is highly permeable tosuch radiation. IR heating presents some advantageswith respect to conventional drying: decreasing dryingtime, high energy efficiency and lower air flowthrough the sample product (Togrul, 2005).IR drying has been investigated as a potential methodfor the drying of numerous foodstuffs, including fruit,vegetables and grains, and of some derived subproducts, as described in the works on the IR drying ofcashew kernel (Hebbar and Rastogi, 2001), of carrot(Togrul, 2006), of onion (Sharma et al., 2005) and ofwet olive husk (Ruiz Celma et al., 2008).Until recently, one of the most commonly used dryingtechniques was the convective hot air drying.However, in this drying technique, food material areexposed to elevated temperature, which leads to anincrease in shrinkage and toughness, reduction in boththe bulk density and rehydration capacity of the driedproduct, and it also causes serious damage to flavor,colour and nutrient content. There is scarce literatureon infrared drying of the local Kerewa tomatoevariety; hence the main objective was to investigatethe effect of infrared power on drying characteristics(moisture ratio, drying rate, and diffusivity andactivation energy) of Kerewa tomato slicesMaterials and MethodsThe Yoruba-Kerewa tomato variety used for theexperiment was procured at local market in Ogunstate. Tomatoes that appeared damaged was removedby hand picking. Red, fresh and ripe tomatoes with thesame grade were sorted out and wash with water toremove dirt and soil. The fresh ripe tomato sampleswere stored in a refrigerator until drying experimentwas conducted. The tomato was washed and slicedinto 10 mm thickness using a stainless steel knife. Thedirection of cut was perpendicular to the vertical axisof the tomato. A micrometer was used to check thethickness and uniformity of each slice at threedifferent locations, and acceptance was being based onmean value and deviation from the desired thicknessof 10mm.All tomatoes varieties were divided into two batches;one batch was blanched in water at 80oC for threeminutes and drained for five minutes. This wasregarded as blanched samples while the other batchwas used fresh without any pre-treatment and wasreferred to as raw or unblanched samples. Each batchslices of tomato were subjected to drying at fiveinfrared energy levels (150W, 250W, 300W, 400Wand 500W).The weight change was recorded at every 5 minutesfrom the LED display of the digital balance. The initialmoisture content of the tomato samples wasdetermined using AOAC (1990) standard oven dryingmethod at an air temperature of 105 ± 2oC until therewill be no appreciable weight change as reported byDairo et al., (2017). The drying experiment wasterminated be when there is no appreciable change inweight.Equipment setup and drying proceduresThe drying setup used by Dairo et al (2017) consistingof a rectangular infrared drying chamber box (500 mmx 500 mm x 300 mm) made of 12 mm thick plywoodwas used as the infrared drying. The inner chamber ofthe box was lined with aluminum sheet to prevent heatloss. Three outlets (one at each end and one at thecenter) were provided at the underside of the chambertop for installation of infrared bulbs which convertselectrical energy to infrared energy. Two InfraredBulbs (150 and 250 W, Philip Bulbs) were arrangedboth as combination and singly to provide 150, 250,300, 400, and 500W of heat source from the infraredbulbs. A front door with a viewing glass for loadingand offloading of sample was also provided. A fan wasattached to one side of the chamber while an exit formoist air was provided at the opposite end. A digitalinfrared thermometer was used to monitor the chambertemperature. A tray covering the length of the cabinetwas provided at about 150mm below the bulb end fordrying of samples.Three sample trays (10 cm in diameter and 1 cm deepmade of steel wire mesh) containing the sample werearranged on the horizontal tray within the radius ofeach infrared bulb rays to allow good absorption of theinfrared energy. The change in mass during themicrowave drying was recorded by removing thesample from the cabinet and weighed on a digitalbalance (Model PE1600, Mettler InstrumentsCorporation, Zurich, Switzerland) with a resolution of± 0.01g at 5 min intervals of drying time until therewas no appreciable change in weight for threeconsecutive readings. All experiments were carriedout in triplicates for both blanched and unblanchedsamples and the mean value was used for analysis. Thesamples were uniformly arranged on the tray as a thinlayer and moisture loss was recorded at 5minsintervals during the drying process in order todetermine the drying curves. The drying process wascontinued until no moisture content was recorded.Samples were thus completely dried in order to carryout the mathematical modelling of kinetics of thedrying process.Dairo O.U.  et. Al./LAUTECH Journal of Engineering and Technology 11(2) 2017: 66-7168Experimental data from the different drying runs wereexpressed as moisture ratio versus drying time, dryingrate versus drying time and drying rate versus moisturecontent. The change in moisture content of tomatoslices was calculated and moisture ratio was obtainedfrom equation 1=(1)Where Mt and Mo are the moisture content at anygiven time and the initial moisture content,respectively, since in IR drying, samples may be driedas much as dry matter content.Determination of Rehydration ratio (RR)The rehydration characteristics of a dried product arewidely used as indicators of quality. Rehydration is acomplex process that is influenced by both physicaland chemical changes associated with drying and thetreatments preceding dehydration.  The rehydrationratio of dried tomato was determined as reported by(EL-Mesery and Mwithiga, 2012) by immersing ofdried sample in water at a temperature of 100oC andafter 20 minutes, samples were drained and weighed.The rehydration ratio (RR) was calculated as the ratioof the mass of the rehydrated sample to that of drysample using equation (2)=(2)Where Ma is mass of sample after rehydration and Miis initial mass of sample before rehydrationDetermination of effective DiffusivityDiffusivity is used to indicate the flow of moisture outof the material being dried (Cui, et al., 2005). Moisturediffusivity is influenced mainly by moisture contentand temperature of the material. Fick’s second law ofdiffusion equation was used to fit the experimentaldrying data for the determination of diffusivitycoefficients.= ∇(4)The diffusion equation (Eqn 3) was solved for infiniteslab assuming uni-dimensional moisture movement,volume change, constant temperature and diffusivitycoefficients, and negligible external resistance (Crank,1975):MR = = ∑ ( ) ( )(4)Where Deff is the effective coefficient (m2s-1), H is thethickness of the slab (m) and n is a positive integer.Only the first term of eqn 3 as presented in Equation 4can be used with a small error (Doymaz, 2005)MR =(4)The slope is determined by plotting (MR) against timeaccording to eqn (4) and the diffusivity determinedfrom Equation 5Slope =(5)RESULTS AND DISCUSSIONThe drying curve for Kerewa tomato variety of 10 mmthickness at all infrared power (150, 250, 300, 400, and500W) are presented in Fig. 1 and 2 for blanched andunblanched samples respectively. The averageKerewa 94.63 % (w.b.) was reduced to an average of14.8, % (w.b.) after infrared drying. The average timeof drying ranges between 55 min to 240 min with150W infrared power having the longest dryingperiod.The drying curves showed that there was a reductionin drying time with increased in infrared drying powerof 150 to 500W. This could be attributed the increasein available energy to dry the tomato slices. It wasobserved that an increase in infrared power output ledto reduction in drying time. This is in corroborationwith findings by El-Mesery and Mwithiga (2014)Drying curves for infrared drying tomato slicesshowed that the rate of moisture removal was higheras infrared power increased. This shows that infraredpower output had significant influence the rate ofmoisture removal. This is in line with findings ofSorour and El-Mesery (2014), Kozabiyik and Tezer(2009). The drying curve revealed that moisture ratiodecreased with time. Drying rate increased withincrease in infrared output power, indicating thatinfrared power has effect on drying rate of the crop.This is in line with research findings by Kocabiyik andTezer (2009)Dairo O.U.  et. Al./LAUTECH Journal of Engineering and Technology 11(2) 2017: 66-7169.Drying rate curves (Fig.3) shows the higher drying rate was observed at initial phase of drying, this may be due to thehigh moisture content of the crop at initial phase of drying. As moisture reduced with time, the drying rates began todecrease. Drying rate increased with increase in infrared output power, indicating that infrared power has effect ondrying rate of the crop. This is in line with research findings by Gabel et al. (2006). Drying rate at 500W00.20.40.60.811.20 50 100 150 200Moisture RatioDrying Time (min)Fig. 1: Drying Curve for Blanched Kerewa tomato variety at differentinfrared PowerMR150_B MR250_BMR300_B MR400_BMR500_B00.20.40.60.811.20 50 100 150 200Moisture RatioDrying Time (min)Fig. 2: Drying Curve for Unblanched Kerewa tomato variety at differentinfrared PowerMR150_UB MR250_UBMR300_UB MR400_UBMR500_UB050100150200250300350-10 10 30 50 70 90 110 130 150Drying Rate (kg/kg DM. min)Drying Time (min)Fig. 3: Drying Rate Characteristics of Blanched Kerewa under different  InfraredPowerDR150_B DR250_BDR300_B DR400_BDR500_BDairo O.U.  et. Al./LAUTECH Journal of Engineering and Technology 11(2) 2017: 66-7170output power had the highest drying rate of waterremoval with the shortest drying time while the 150Winfrared power had the longest drying time with thelowest drying rate. The blanched samples had aslightly higher drying rate than fresh unblanchedsamplesDiffusivity of Infra-red DryingThe variation of Ln (MR) against drying time forblanched Kerewa using infra-red power of 150, 250,300, 400 and 500 W is presented in Fig. 4. It wasobserved that the plot of In (MR) against timefollowed a straight line with negative slopes, where theeffective diffusivity (Deff) was obtained from thesevalues. The slope was found to increase with increasein infra-red power while the effective diffusivity Deffalso increased with the infra-red power for bothunblanched and blanched samples indicating increaseddrying rate with increase in infra-red power.The range of Deff for both blanched and unblanchedof kerewa slices was between 1.844 E-7 and4.08324E-7 the values for blanched samples wereconsistently higher than corresponding blanchedsamples indication that drying would be accomplishedfaster with blanched samples as evident in the dryingcurvesCONCLUSIONFrom the study conducted the following could beconcluded.i. For all drying powers there was areduction in moisture content withincreased drying time and drying tookplace in the falling rate period.ii. The drying time reduced as the infraredheating power increased from 150 to500Wiii. There were no significant differences indrying times but the pre-treated samplesalways had a slightly lower drying timesthan the raw or fresh tomato slices.iv. The diffusivity obtained for the tomatoslices were with the range specified forfruits and vegetables with value of5.61319 E -7 m2/sv. Blanched tomato varieties had betterrehydration capacities than allunblanched samples.REFERENCES-8-7-6-5-4-3-2-10120 20 40 60 80 100 120 140 160 180Ln(MR) kg/kg DMDrying Time (min)Fig. 4: Diffusivity chart for Blanched Kerewa Tomato Slices at different Infrared PowerLN(MR)150_B LN(MR)250_B LN(MR)300_BLN(MR)400_B LN(MR)500_B Linear (LN(MR)150_B)Linear (LN(MR)250_B) Linear (LN(MR)300_B) Linear (LN(MR)400_B)Linear (LN(MR)400_B) Linear (LN(MR)500_B)Dairo O.U.  et. Al./LAUTECH Journal of Engineering and Technology 11(2) 2017: 66-7171Alaei, B., Chayjan, R. A. (2015). Modelling ofnectarine drying under near infrared -Vacuum conditions. Acta Sci Pol TechnolAliment. 14(1):15-27. doi:10.17306/J.AFS.2015.1.2AOAC (1990). Official method of analysis (12th ed.)association of official analytical chemist,Washington ,Dc , moisture content in plant,I,949Cahyono L. 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DRYING CHARACTERISTICS OF KEREWA TOMATO UNDER INFRARED DRYING

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DRYING CHARACTERISTICS OF KEREWA TOMATO UNDER INFRARED DRYING

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