BERBERT, P. A.

BERBERT-MOLINA, M. A.

GRAVINA, G. de A.

QUEIROZ, L. R.

QUEIROZ, V. A. V.

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Brazil, August 31 to September 4,2008 •-11CIGR - Intemational Conference of Agricultural EngineeringXXXVII Congresso Brasileiro de Engenharia AgrícolaZINC LOSS DURING DEWATERING-IMPREGNATION SOAKING OF GUAV AVALÉRIA APARECIDA VIElRA QUEIROZ I; PEDRO AMORIM BERBERT2; MARÍLIAAMORIM BERBERT-MOLINA2; GERALDO DE AMARAL GRAVINA2; LUCIANORODRIGUES QUE[ROZ3IResearcher, DS, EMBRAPA/Sete Lagoas - Brazil. e-mail: valeria@cnpms.embrapa.br2 LecturerlResearcher, PhD, UENF/Campos dos Goytacazes - Brazil.3 DS, Crop Production, CCTAlUENF/Campos dos Goytacazes - Brazil.Presented atCIGR INTERNATIONAL CONFERENCE OF AGRICULTURAL ENGINEERINGXXXVII CONGRESSO BRASILEIRO DE ENGENHARIA AGRÍCOLA - CONBEA 2008Brazil, August 31 to September 4, 2008ABSTRACT: This work investigated the loss of zinc to the osmotic solution during the dewatering-impregnation soaking of guava slices. The dehydration was conducted at 50°C, for 2 h, using a fruit tosyrup ratio of 10:1 (w/w), and a single leveI of agitation of the solution, 60 min -I. Guava slices wereimmersed into solutions of sucrose, sucrose + sucralose, and inverted sugar. lnverted sugar wasresponsible for a lesser degree of zinc retention in fruit tissue than sucrose. Reductions from 26 to 47%in zinc content were observed during the osmotic dehydration of guava slices in the hypertonicsolutions.KEYWORDS: Psidium guajava, osmotic dehydration, food conservation, mineraIsINTRODUCTION: Zinc is essential for human health and plays a key role in human metabolismoAccording to MAFRA & COZZOLlNO (2004) zinc is vital for the proper functioning of enzymes,participates in cell div ision, genetic expression, physiological processes like growth and development,genetic transcription, as well as programmed cell death. Furthermore, zinc affects the immune functionand cognitive development. Symptoms of zinc deficiency include oxidative damage, reduced sense oftaste and smell, skin disorders, reduced fertility, and neuropsychological impairment such as mentallethargy. TORREGGIANI (1993) stated that the dewatering and impregnation soaking processes(DIS), a food pre-treatment also known as osmotic dehydration, is capable of improving the nutritionaland sensory characteristics of fruit which will be further submitted to convective air drying. The DISconsists of the immersion of fruit pieces in a hypertonic solution. During the DIS process, three typesof mass transfer occur: water flows from the product to the solution; the solute is transferred fromsolution to the product and the product's own solutes, such as sugars, organic acids, mineraIs andvitamins, leach out to the solution (PEIRÓ-MENA et aI., 2007). Few studies have been conducted toidentify and quantify the losses of mineraIs during the DIS processo On this basis, the object of thiswork was to assess the loss of zinc during the osmotic dehydration of guava is sucrose- and inverted-sugar solutions.METHODOLOGY: This work was carried out at the Agricultural Engineering Laboratory, NorthemRio de Janeiro State University (UENF), Campos dos Goytacazes, Brazil. Twenty guavas (fsidiumguajava L.) of the Pedro Sato variety were harvested with a similar degree of ripening, i.e., skin hueangle between 113 and 116°, and care was taken to avoid selecting individual guavas with injuries,bruises, rots and apparent softening ofthe tissue. Upon arrival at the laboratory fruits were stored at 7°C until reaching a ripening stage characterised by skin hue angles between 108 e 112°. At the end ofthe storage period, the selected fruits had a mean weight of 185.5±37.3 g, total soIuble solids contentof 8.6±1.3 °Brix, and water content of 86.7±1.l% w.b. The fruits were removed from storage andsubsequent1y washed and immersed in a 10 ppm sodium hypochlorite solution for 15 mino DistilledBrazil, August 31 to September 4,2008 •-11CIGR - International Conference of Agricultural EngineeringXXXVII Congresso Brasileiro de Engenharia Agrícolaand deionised water was used throughout. Fruits were manually peeled and cut in halves with astainless steel knife, the central pulp was removed with a spoon, and the remaining flesh of each fruitwas cut in eight slices of similar size (Figure I). Blanching was performed by exposing the fruit sIicesto steam for 1 min at atmospheric pressure, and then cooled in ice bath for 1 mino Fruit slices weresubsequently immersed in a 1% ascorbic acid solution. The DIS process was performed employingtwo types of solute: sucrose and inverted sugar. Food grade sucrose was produced and supplied byUsina Sapucaia, and the experiment was conducted using osmotic solutions prepared with distilledwater to the following concentrations: 0.5 g m.L-1 (TI), 0.4 g mL -I (T2), 0.3 g mL -I (T3). To this lattertreatment, 0.2 g of sucralose was added per Iitre of solution. lnverted sugar, with a degree of inversionhigher than 90%, was provided by Dulcini S.A. Treatments with this solute comprised a 41% (w/w)solution (T4), and undiluted syrup (T5). The experiment was carried out by immersing guava sIices(each slice corresponding to IIgth of a whole fruit, as shown in Figure I) in the hypertonic solutionseontained in 1000 mL beakers mounted on temperature- and agitation-controlled shakers (B.BraunBioteeh, model Certomat U / Certomat HK). ln an attempt to assure uniform temperature (50°C) andconcentration of the solution around the fruit samples, and at the same time to reduce externalresistance and increase overall mass transfer rate, osmotic dehydration was conducted using a singleleveI of agitation of the solution, 60 min", Ali beakers were closed to avoid evaporative losses andspilling of water. The syrup to fruit ratio was 10:I (w/w). The samples were osmo-dehydrated for aperiod of 2 h; preliminary tests have shown that this period was enough to reach equilibriumeonditions concerning water loss and solids gain. Besides, osmotic treatments with immersion periodslarger then 2 h resulted in tissue collapse making it difficult to handle the guava slices. At the end ofthe immersion period in the hypertonic solutions, the fruit slices were quickly rinsed with distilledwater to partial1y remove adhering solutes and excess solution and then were gently blotted dry withtissue paper.FIGURE 1. (a) Longitudinal eut ofa fresh guava with tips removed; (b) Eight working samplesobtained from a single fresh guava.The zine content of the guava slices was detennined by atomic absorption spectrophotometry (AAS)after the samples were dry mineralised for 4 h, at 450°C. The obtained ash was dissolved in a 50%HCI solution, whic h was subsequently placed in a sand bath at 180°C until complete evaporation ofthe acid. This latter operation was repeated, and after the crucible was cooled the residue wasdissolved in deionised water to 20 mL. A calibration curve prepared with zinc standard solutions wasused to determine zinc concentration in guava slices, which was determined directly from mineralisateon a Zeiss AA-S4 spectrophotometer (AOAC, 1990). Zinc content was expressed as mg.l00 gl on adry basis. The content was determined for fresh guavas slices, guava slices after immersion in citrieacid, and for osmo-dehydrated slices.The experiment was set up according to a randomised cornplete-block design with factorial treatments(dehydration and process steps) in four replications. Data were analysed by ANOVA and differencesbetween mean values of zinc content in each treatment were assessed by Tukey's test (P < 0.05).Group treatments were also compared through orthogonal contrasts which allows multiple pairwise ormore complex comparisons among groups. Significance ofthe contrasts was evaluated by the F test (P< 0.05). The group oftreatments contrasted were: sucrose vs inverted sugar (Cl), 41% (w/w) invertedBrazil, August 31 to September 4,2008 •-11CIOR - lnternational Conference of Agricultural EngineeringXXXVII Congresso Brasileiro de Engenharia Agrícolasugar solution vs undiluted inverted sugar (C2), sucrose 0.5 g mL·1 vs sucrose 0.4 g ml." (C3), sucrose0.5 g roL·I vs sucrose 0.3 g rol-I + sucralose 0.2 g L-I (C4).RESULTS AND DISCUSSION: Table I shows the rnean zinc content (mg.lOO ~ed.b.) of slices offresh guavas (FG), guava siices after immersion in citric acid (lCA), and for osmo-dehydrated slices(DIS) for all the treatments studied. A significant reduction of zinc content was observed in alltreatments (but 0.5 g mL-I sucrose solution) when values obtained for fresh fruit were compared withthose obtained after the D1S processoTABLE 1. Zinc content (mg.IOO gl d.b.) in samples of fresh guavas (FG), guava samples afterimmersion in citric acid (ICA), and in osmo-dehydrated samples (DIS) for ali the treatments studied.Process step TreatmentSucrose0.3 g mL-1 +sucralose0.2 g L-ISucrose0.4 g mL-1Inverted sugar41%(w/w)Undiluted invertedsugarFO 0.87aB 1.23aAB 1.31aAB 1.35aA 1.16aABICA 0.76 aA 0.99 aA 1.04 abA 1.04 aA 0.94 aADIS 0,56 aA 0.51 bA 0.7 bA 0.56 bA 0.53 bAMeans in the same column followed by the same lower-case letter, and in the same line followed by the samecapital letter, are not significantly different according to the Tukey test (P < 0.05).In order to compensate for the differences in initial moisture content and moisture content afterimmersion in ascorbic acid solution, the results were norrnalised making it possible to compare zinclosses among treatments on a percentage basis. Figure 2 shows the percentage reduction in zinccontent for all treatments studied Leaching of zinc from fruit tissues to the osmotic soIutions duringthe DIS process was more pronounced (47%) in the following treatments: sucrose 0.4 g mL-1 (T2),41% (w/w) inverted sugar solution (T4) and undiluted inverted sugar syrup (T5). The lowest zinc loss(26%) was recorded during dehydration in 0.5 g mL-1 sucrose solution. Table 2 shows the orthogonalcontrasts under consideration and their estimates.60--"$. 50"---c.Q 40U::s" 30<I)...c<I) 20.•..cou 10cNoSucrose0.5 g/ml,a aaSucrose Sucrose Inverted0.4 g/rnl, 0.3 g/ml. + sugarsucralose solution0.2g/L 41%(w/w)UndilutedinvertedsugarsyrupFIGURE 2. Zinc percentage reduction during the osmotic dehydration of guava slices. Meansfollowed by the same letter are not significantly different according to the Tukey test (P < 0.05).Brazil, August 31 to September 4,2008 •-11ICIGR -International Conference of Agricultural EngineeringXXXVII Congresso Brasileiro de Engenharia AgrícolaTABLE 2. Contrast comparison for the following treatments: sucrose 0.5 g rnL·I (m.), sucrose 0.4 gmL-I (m-), sucrose 0.3 g rnL-I + sucralose 0.2 g L-I (rn.), 41% (w/w) inverted sugar solution (m.), andundiluted inverted sugar syrup (rn.). Contrasts were calculated with mean values of zinc percentageloss (m) during DIS.Group contrast C\ C2 C3 C4Contrast estimates -67,49* _1,21"s -2\ ,32* _6,720'os = not statistically significant at the 5% levei, * = statistically significant at the 5% leveI.Contrast C I shows that inverted sugar is responsible for a lesser degree of zinc retention in fruit tissuethan sucrose. This same behaviour was noticed by QUElROZ (2006) for magnesium and potassium,using the same experimental conditions. One can infer that the higher the concentration of thesolution, the higher the degree of water loss and mass reduction during osmotic dehydration of thefruit. This may have lead to a higher zinc loss (which is a water soluble mineral) to the hypertonicsolution. Nonetheless, according to contrast C4, treatment T2 (sucrose 0.4 g mL -I) prompted a higherloss ofzinc than TI (sucrose 0.5 g ml.").PEIRÓ et aI. (2006) observed losses ofNa, K, Ca and Mg between 23 to 51%, 48 to 68%, 23 to 68%and 19 to 35%, respectively, after osmotic dehydration of grapefruit. They also analysed the content ofthese minerais in the osmotic medium, and proved that there was a flow of nutrients from the fruittissues to the solution. RODRIGUEZ (1993) and BOGNAR (1998), quoted by KRESIC et aI. (2004),also described losses of minerais from 25 to 50% in candied celeriac. However, the zinc content wasnot evaluated by these authors nor was found in the literature any data conceming the reduction ofthismineral in the osmotic dehydration of fruit.CONCLUSIONS: Inverted sugar was responsible for a lesser degree of zinc retention in fruit tissuethan sucrose Reductions from 26 to 47% in zinc content were observed during the osmoticdehydration of guava siices in sucrose and inverted sugar solutions.ACKNOWLEDGEMENTS: Authors are indebted to the Intemational Foundation for Science - IFS;Minas Gerais state Research Foundation - FAPEMIG; Rio de Janeiro state Research Foundation -FAPERJ, Brazilian Council for Scientific and Technological Development _. CNPq, and BrazilianResearch and Projects Financing - FINEP.REFERENCES:AOAC. Association of Official Analytical Chemists. Official Methods of Analysis. 151h Edition.Arlington: AOAC, 1990, 1298p.BOGNAR, A. Comparative study of frying to other cooking techniques influence on the nutritivevalue. Grasas y aceites, 49(3-4):250-260, 1998.KRESIC, G.; LELAS, Y.; SIMUNDIC, B. Effects of processing on nutritional composition andquality evaluation of candied celeriac. Sadhana, 29( 1):1-12, 2004.MAFRA, D.; COZZOLINO, S.M.F. Importância do zinco na nutrição humana. Revista de Nutrição,17(1):79-87,2004.PEIRÓ, R.; DIAS, V.M.C.; CAMACHO, M.M.; MARTÍNEZ-NA VARRETE, N. Micronutrient flowto the osmotic solution during grapefruit osmotic dehydration. Journal of Food Engineering, 74(3):299-307, 2006.PEIRÓ-MENA, R.; CAMACHO, M.M.; MARTÍNEZ-NA VARRETE, N. Compositional andphysicochemical changes associated to successive osmodehydration cycles of pineapple (Ananascomosus). Journal of Food Engineering, 79(3):842-849, 2007.QUEIROZ, V.A.V. Nutritional quality of guava (Psidium guajava L.) as affected by the dewateringand impregnation soaking process followed by convective drying. Ph.D. thesis. AgriculturalEngineering Laboratory. Northem Rio de Janeiro State University. 2006.Brazil, August 31 to Septern ber 4, 200811 CIGR - International Conference of Agricultural EngineeringXXXVII Congresso Brasileiro de Engenharia AgrícolaRODRIGUEZ, T. Mineral losses in hot water blanched and microwave blanched green dry whitebeans. Journal of Agriculture of the University of Puerto Rico, 77: 129-135, 1993.TORREGGIANI, D. Osmotic dehydration in fruit and vegetable processing. Food TI csca rchInternational, 26: 59-68, 1993.

Zinc loss during dewatering-impregnation soaking of guava.

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