Avelar, M. L. C. M.

Ferreira, J. P. M.

Morais, A. M. M. B.

Morais, R. M. S. C.

English

Repositório Institucional da Universidade Católica Portuguesa

    Polyphenoloxidase Activity of Pear (cv. Rocha) Reduced byControlled Atmosphere StorageA. M. M. B. Morais l*, M. L. C. M. Avelar2, J. P. M. Ferreiral , R. M. S. C. MoraisllEscola Superior de Biotecnologia da Universidade CatOlica Portuguesa2Estarylo Nacional de Fruticultura Vieira NatividadeThe enzymatic browning of fruits during storage may cause undesirable quality changes,specially of colour. During storage of fruits, polyphenoloxidase (PPO) activity and browning werereported by several authors to vary in different ways, depending on species, cultivar, pickingmaturity, storage conditions, etc (Amiot et al., 1992). PPO soluble content and browning were, inmost cases, found to increase during normal atmosphere. According to Burton (1982), sincephenolases have a low oxygen-affinity, oxidation of phenolic substrates can be avoided or at leastreduced at 02 levels of 5% or less. Therefore, the use of controlled atmosphere (CA) storage maysucceed to reduce these processes.Although there are studies in literature on PPO of pears (Espfn et al., 1997; Halim andMontgomery, 1978; Smith and Montgomery, 1985; Zhou and Feng, 1992), very scarce, if none,information is available on PPO of 'Rocha' pear.The objective of this work was to evaluate the effects of controlled atmosphere storage (lowoxygen and carbon dioxide contents) on PPO activity of 'Rocha' pear, in comparison to storage innormal atmosphere.Material and MethodsPlant material. Pears (cv. Rocha) were grown at West region of Portugal, harvested in August28, 1996 and stored at 0°C (relative humidity 85-90%) either in normal atmosphere or controlledatmosphere (4.21 %02 and 1.01 %CO2). The fruits were removed from the cold on February 16,1997 and stored in normal atmosphere. The pears were supplied by Estagdo Nacional de FruticulturaVieira Natividade (ENFVN) for this research work and on February 19 the fruits were transportedfrom the ENFVN in Alcobaca to the laboratory in Porto within approximately 4 hours. They werestored at 2°C and 80 % of relative humidity.*Rua Dr. Ant6nio Bernardino de Mmeida, 4200 PORTO, PortugalFax: 351-2-5580063, e-mail: amorais @esb.ucp.ptTreatment and storage conditions. Pears from each atmosphere storage were divided randomlyinto two samples. On February 21 the fruits of the first sample were cut into pieces, immediatelyfrozen with liquid nitrogen and stored at -80°C. Two weeks later, the same procedure was followedfor the second sample. Pear samples were stored for five months until used in the enzymatic assays.Extraction of PPO. The method was based on the procedure described by Galeazzi et al.(1981). Pear samples were homogenized in the extraction buffer (0.2 M sodium phosphate buffer, pH6.5) with 2% insoluble PVP and 0.25% Triton Xinn in an external ice bath for 3 min in 1 minintervals. The ratio buffer / pear sample used was 3 (mL/ g). The homogenate was centrifuged at 4°Cfor 30 min at 14, 000 x g (Sorvall RC-5C, Instruments Dupont). The supernatant was filtered throughcheesecloth and its volume determined. Each extraction was performed in triplicate.Assay for PPO activity. Enzymatic activity was assayed by measuring the rate of increase inabsorbance at 420 rim and 28°C in a double beam model UVNIS sprectrophotometer. The substratesolution contained 2.8 mL of substrate solution (0.16 M catechol prepared in 0.05 sodium phosphatebuffer, pH 6.5) and 20 	 of enzyme extract. The reference Gu yette contained only substrate solution.The unit of the enzyme activity was defined as the change of 0.001 in the absorbance value. Alldeterminations were performed in triplicate.ResultsTable 1. Polyphenoloxidase activity (U/ g of fruit/ min) of 'Rocha' pear after storagein different atmospheresStorage atmosphere Date of freezing Polyphenoloxidase activity(U/ g of fruit/ min)NormalControlledNormalControlledFebruary 21February 21March 7March 77200aY4534b8058a3892bzData are means of 10 fruitsYMean separation in columns by Duncan's multiple range test, P=0.05Polyphenoloxidase activity of CA (4.21 %02 and 1.01 %CO2) stored pears was found to besignificantly lower than in the fruits stored in air. With the enzymatic assay performed in this study,no significant difference was detected between the samples frozen 5 days after being removed fromcold storage and those frozen 20 days after.ConclusionThere was a reduction of polyphenoloxidase activity by controlled atmosphere storage (4.21%02 and 1.01 %CO2).Information regarding the response of PPO activity of pears (cv. Rocha) to different CAconditions would be very useful in order to help understand colour changes during storage, and toselect the best CA composition for this cultivar preservation. Therefore, further research is requiredconcerning the enzyme activity of the fruits stored under different sets (oxygen and carbon dioxidelevels) of CA composition.AcknowledgmentsThis work was funded by the project PAMAF 6034 (INIA, Portugal).ReferencesAmiot, M. J. , Tacchini, M., Aubert, S., Nicolas, J. 1992. Phenolic composition and browningsusceptibility of various apple and pear cultivars at maturity. Acta Horticulturae 343, 67-71.Burton, W. G. 1982. Postharvest physiology of food crops, Longman, London.Espial, J. C., Morales, M., Var6n, R., Tudela, J., Garcia-Catiovas, F. 1997. Monophenolase activityof polyphenol oxidase from Blanquilla pear. Phytochemistry 44, 17-22.Galeazzi, M. A. M., Sagarbieri, V. C. J., Constantidines, S. M. 1981. Isolation, purification andphysicochemical characterization of polyphenoloxidase from a dwarf variety of banana(Musa Cavendishii, L.). J. Food Sci. 46, 150-155.Halim, D. H. and Montgomery, M. W. 1978. Polyphenol Oxidase of d'Anjou pears (Pyrusconununis L.). J. Food Sci. 43, 603-608.Smith, D. M. and Montgomery, M. W. 1985. Improved methods for the extraction of polyphenoloxidase from d'Anjou pears. Phytochemistry, 24, 910-904.Zhou, H. and Feng, X. 1991.Polyphenol Oxidase from Yali Pear (Pyrus bretschneideri). J. Sci.Food Agric. 57, 307-313.

Polyphenoloxidase Activity of Pear (cv. Rocha) Reduced by Controlled Atmosphere Storage

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Polyphenoloxidase Activity of Pear (cv. Rocha) Reduced by Controlled Atmosphere Storage

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