ARTICLE IN PRESS

0023-6438/$30.0

doi:10.1016/j.lw

�CorrespondE-mail addr

LWT 39 (2006) 492–495

www.elsevier.com/locate/lwt

Thermal inactivation of polyphenoloxidase in pineapple puree

Benjar Chutintrasria, Athapol Noomhormb,�

aFood Technology Department, Faculty of Science, Ramkhamhaeng University, Bangkok 10240, ThailandbFood Engineering and Bioprocess Technology, School of Environment, Resources and Development, Asian Institute of Technology,

Pathumthani, Klongluang 12120, Thailand

Received 3 December 2004; received in revised form 31 March 2005; accepted 12 April 2005

Abstract

Prevention of browning in pineapple puree by thermal inactivation of enzyme, Polyphenoloxisase (PPO), was examined between

40 and 90 1C and in relation to exposure time. The amount of inactivation was measured as a function of time and temperature

under isothermal conditions. Reaction rate constant and activation energy (Ea) as well as Decimal reduction time (D) and z-value of

thermal inactivation, were determined. The rate of inactivation varied with temperatures and follows a logarithmic law. Kinetic

studies showed that the thermal inactivation (40–90 1C) of the PPO followed first-order kinetics.

r 2005 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved.

Keywords: Pineapple puree; Polyphenoloxidase; Enzymatic browning; Thermal inactivation; Kinetics

1. Introduction

Pineapple is an important tropical fruit (Bartholo-mew, Paul, & Rohrbach, 2002), particularly in the formof processed products. Of these, pineapple puree,derived from crushing those portions of the fruit nototherwise used and thermally processing in cans oraseptic packs, is marketed as a high value-addedproduct at a premium price. Important to the prepara-tion of stable fruit purees is the inactivation of theenzyme, polyphenoloxidase (PPO), that catalyzes dete-rioration reactions after tissue is damaged in the sizereduction process. Among these reactions is the forma-tion of a brown pigment that is undesirable with respectto color, flavor and market value.

The pineapple PPO was found in three isoforms (Das,Boht, & Eowda, 1997), with the major isoform being atetramer of identical subunits of 25 kDa and havingoptimum activity between pH 6 and 7. The PPO is stableto heat when extracted, but loses over 50% of its activity

0 r 2005 Swiss Society of Food Science and Technology. P

t.2005.04.006

ing author. Tel.: +662 524 5476; fax: +66 2 524 6200.

ess: athapol@ait.ac.th (A. Noomhorm).

following 20min exposure to 60 1C in vivo (Teisson,1977).

Natural phenolic compounds in fruit and vegetablesin the presence of PPO and oxygen are oxidized to o-quinone that subsequently polymerizes nonenzymati-cally to brown pigments (Golan-Goldhirsh & Whitaker,1984; Sapers, 1993). This browning process leads also toa change in flavor and a reduction in nutritional quality,especially ascorbic acid. (Vamos-Vigyazo, 1981; Golan-Goldhirsh & Whitaker, 1984). The most importantfactors that determine the rate of the enzymaticbrowning of fruit and vegetables are the concentrationsof both active PPO and phenolic compounds present,the pH, the temperature and the oxygen availability ofthe tissue. pH and oxygen also influence subsequentnonenzymatic browning (Martinez & Whitaker,1995).

In general, exposure of PPO to temperatures of70–90 1C destroys their catalytic activity (Vamos-Vigya-zo, 1981). Thermal inactivation profiles of PPO in fruitand vegetable processing follow first-order reactionkinetics with the time required varying with the product.Of the studies on heat inactivation of PPO only a fewhave included the calculations of Arrhenius and thekinetic parameters of heat inactivation of PPO from

ublished by Elsevier Ltd. All rights reserved.

ARTICLE IN PRESSB. Chutintrasri, A. Noomhorm / LWT 39 (2006) 492–495 493

various foods. These include apple (Strubi, Escher, &Neukom, 1975), Sultana grapes (Aquilera, Oppermann,& Sanchez, 1987), apricot (Heil, McCarthy, & Merson,1988), rice (Ansah, 1989) and mango (Askar, El-Ashwah, Omran, & Labib, 1994). No information isavailable for pineapple puree on the quantitative effectsof temperature and time on the inactivation of PPOwhich was the subject of this study.

2. Materials and methods

Pineapple puree samples (20 l) were obtained from acommercial plant in Rayong Province, Thailand. Thepuree samples were sampled from the same productionlot after size reduction process and kept in industrialplastic bags with metalized plastic layer on the outside(Scholle # 800465) at �20 1C until used in experiments.The physical–chemical characteristics of the sample were:1Brix (20 1C) ¼ 15.070.1; total acidity (g citric acid/100 g sample) ¼ 0.6370.07; pH ¼ 3.7270.04; % pulp ¼68.6772.31; moisture content (% wet basis) ¼83.770.2.

PPO was assayed according to the procedure ofPalou, Lopez-Malo, Barbosa-Canovas, Welti-Chanes,and Swanson (1999). An aliquot of puree (10 g) wasmixed with McIlvaine citric-phosphate buffer (10ml, pH6.5) at 3000 rpm for 60 s. The homogenate wascentrifuged (3960g, 4 1C, 30min) and the supernatantwas filtered (Whatman no.1). To the filtrate (0.5ml) wasadded 1ml of 0.175mol/l catechol solution and 2ml ofMcIlvaine buffer (pH 6.5) and optical density at 420 nmwas measured every 15 s up to 1 and 2min in freshand treated purees using a 1-cm glass cuvette and aUV/VIS spectrophotometer as described by Pizzocaro,Torreggiani, and Gilardi (1993). This duration time wasbased on preliminary test results that no changes in theoptical density were found after those specified timeintervals. PPO activity was calculated on the basis of theslope from the linear portion of the curve of DA420 vs.time for fresh and treated puree, respectively. One unitof PPO activity was defined as 0.001 DA420 min�1 (ml ofextract)�1. Residual PPO activity was expressed as theratio between treated and fresh pineapple puree.

Thermal inactivation experiments were conducted in awater bath at constant temperature between 40 and90 1C. Samples were exposed to each temperature for0–30min (5min interval). Puree samples (10 g) werefilled in Pyrex screw-capped test tubes (15� 1.6 cm, wallthickness 1.8mm) held in the water bath for the assignedtime after the geometric center of sample had reachedthe desired temperature measured by thermocouples(Type T). Immediately afterwards, samples were im-mersed in an ice bath and enzyme activity measured. Ateach combination of temperature and time, threesamples were analysed.

Results of the thermal experiments were processedinto kinetic parameter values, decimal reduction times,D, inactivation rate constants, k, z-values and activationenergy, Ea. Decimal reduction time was calculated fromthe equation (Stumbo, 1973):

DT ¼t

ðlog Ai � log Af Þ,

where Ai is the initial activity, Af , the residual activityafter treatment and t, time of thermal treatment inminutes. Z was derived from logDT values in relation totreatment temperature:

Z ¼�ðT1 � T2Þ

log D1 � log D2,

where T1 and T2 represent the lower and highertemperatures, 1C or 1K, and D1 and D2, D-values atthe lower and higher temperatures in minutes.

First-order reaction rates, k were obtained from thelinear portion of the relation between ln activityretention and treatment time. The z and Ea values wereestimated from the linear regression of logD andtemperature and ln k and 1=T , respectively.

3. Results and discussion

The extent of PPO denaturation increased withtemperature and treatment time (Table 1). PPO activ-ities were reduced by approximately 60% after exposureto 40–60 1C for times to 30min. Denaturation increasedrapidly above 75 1C. Thus, residual activity was onlyabout 7% after 5min at 85 1C and 1.2% after 5min at90 1C.

The logarithmic linear relationship between PPOactivity and treatment time for the temperature rangeof 40–90 1C followed first-order kinetics and wasconsistent with the relationships found in earlier studieson fruits and vegetables (Dimick, Ponting, & Makower,1951; Demeaux & Biden, 1967; Chan & Yang, 1971;Benjamin & Montgomery, 1973; Halim & Montgomery,1978; Lee, Smith, & Pennesi, 1983; McCord & Kilara,1983). Rate of PPO inactivation (Table 2), after lntransformation, decreased linearly with the inverse oftemperature. This relationship is described by theequation:

ln k ¼ �9955:6ð1=TaÞ þ 24:49

ðn ¼ 5; R2 ¼ 0:991; Pp0:05Þ,

where Ta represents absolute temperature (K). Simi-larly, decimal reduction time, D (Table 3) afterlogarithmic transformation declined linearly with tem-perature increase:tvs

log D ¼ �0:0466ðT cÞ þ 5:2466

ðn ¼ 5; R2 ¼ 0:996; Pp0:05Þ,

ARTICLE IN PRESS

Table 1

Effect of treatment temperature and time on the inactivation of polyphenoloxidase in pineapple puree

Temp (1C) % Enzyme remaining at each treatment time (min)

5 10 15 20 25 30

40 99.771.6a 88.171.8 81.871.9 80.970.9 78.870.9 69.670.6

45 85.571.8 83.771.2 81.570.3 73.370.9 70.971.3 65.670.8

50 81.471.6 80.670.9 73.771.9 71.972.6 70.871.8 62.670.6

55 74.670.3 74.071.6 72.370.6 71.571.8 68.971.6 61.570.9

60 68.271.3 67.871.1 67.571.3 66.970.9 66.171.8 56.770.6

65 62.671.2 60.970.3 59.871.8 59.671.8 59.271.6 47.870.6

70 59.170.6 56.271.6 51.570.9 51.071.9 50.470.9 47.070.7

75 59.071.3 56.171.3 51.571.1 51.070.9 50.370.8 47.070.5

80 31.071.8 26.571.1 23.470.9 22.770.6 21.270.3 18.370.3

85 7.070.3 6.170.2 4.070.2 3.870.2 3.570.2 2.070.1

90 1.270.3 1.170.2 1.170.3 0.770.1 0.870.2 0.370.1

The PPO activity in fresh pineapple puree was 0.4470.02mUAbs�min�1.aMean (n ¼ 3)7standard deviation.

Table 2

Rate constants for heat inactivation of polyphenoloxidase in pineapple

puree at 40–90 1C

Temp (1C) k (min�1) R2

40 0.004770.0005a 0.966

45 0.004870.0003 0.967

50 0.006270.0002 0.964

55 0.007470.0004 0.962

60 0.008770.0003 0.975

65 0.009870.0002 0.981

70 0.01170.007 0.986

75 0.01270.007 0.987

80 0.02470.005 0.991

85 0.04170.002 0.994

90 0.05270.003 0.992

aMean (n ¼ 3)7standard deviation.

Table 3

D, z- and Ea-values for thermal inactivation of polyphenol oxidase in

pineapple puree at low-temperature range (40–70 1C) and high-

temperature range (70–90 1C)

D, z and Ea Values

Low-temperature range (40–70 1C)

D40 (min) 190.373.6a

D45 (min) 164.373.2

D50 (min) 146.872.7

D55 (min) 142.472.5

D60 (min) 121.972.2

D65 (min) 97.472.3

D70 (min) 93.772.1

z (40–70 1C) 104.270.7

Ea (kJ/mol) )(40–70 1C) 23.771.7

High-temperature range (70–90 1C)

D75 (min) 91.371.9

D80 (min) 40.770.6

D85 (min) 17.870.5

D90 (min) 11.470.2

z (70–90 1C) 21.570.0

Ea(kJ/mol) )(70–90 1C) 82.872.7

aMean (n ¼ 3)7standard deviation.

B. Chutintrasri, A. Noomhorm / LWT 39 (2006) 492–495494

where Tc is temperature as 1C. The Ea value for thermalinactivation of pineapple puree PPO at 70–90 1C( Table3) was 82.8 kJ/ mol, much higher than that reported forrice, 23.3 kJ/mol (Aquilera et al., 1987) but lower thanthat for other fruit purees which have ranged from276 kJ/mol for grape to 502 kJ/mol for peach (Chan &Yang, 1971). Ea values reported for whole banana andcranberry, 413 and 116 kJ/mol, respectively, (Dimicket al., 1951; Lee et al., 1983) are within the rangereported for purees. High activation energy reflects agreater sensitivity of PPO to temperature change. Thus,the PPO of pineapple puree is more sensitive to heatthan wild rice but less than the other fruit examined todate.

The z-value for pineapple puree, 21.5 1C, at 70–90 1C,was high relative to values reported for other fruitswhich have ranged from 8.5 to 10.1 1C (Strubi et al.,1975; Vamos-Vigyazo, 1981). In general, low z- valuesare thought to indicate greater sensitivity to heat(Barrett, Gryison, & Lewis, 1999). Interestingly, z-values

may be influenced by the degree of ripeness andpreparation method. Thus, Heil et al. (1988) reporteda wide variance in z-value of 16 and 61.5 1C for PPO ofripe and soft apricot prepared for canning. Differencesin the kinetics of heat activation of PPO for differentproducts may result from differences in their composi-tion, reflective of their variety or the agronomic andclimatic conditions under which they were grown.

In summary, the efficient and effective heat treatmentto reduce PPO and enzymatic browning in pineapplepuree can be derived from any of D, z, Ea or k values.However, to achieve the optimum heat treatment,further studies should be carried out to find the loss ofdesirable characteristics from selected conditions and to

ARTICLE IN PRESSB. Chutintrasri, A. Noomhorm / LWT 39 (2006) 492–495 495

investigate the effects of residual enzyme on the productstability during subsequent storage to validate thethermal inactivation process.

References

Ansah, Y. J. O. (1989). Polyphenol oxidase in wild rice (Zizania

palustris). Journal of Agricultural and Food Chemistry, 37, 901–904.

Aquilera, J. M., Oppermann, K., & Sanchez, F. (1987). Kinetics of

browning of Sultana grapes. Journal of Food Science, 52,

990–993,1025.

Askar, A., El-Ashwah, F. A., Omran, H. T., & Labib, A. A. S. (1994).

Color stability of Tropical nectars and a simple method and its

determination. Fruit Processing, 1, 14–20.

Barrett, N. E., Gryison, A. S., & Lewis, M. J. (1999). Contribution of

the lactoperoxidase system to the keeping quality of pasteurized

milk. Journal of Dairy Research,, 66, 73–80.

Bartholomew, D. C., Paul, R. E., & Rohrbach, K. G. (2002). The

pineapple: botany, production and uses. Wallingford.

Benjamin, N. D., & Montgomery, M. W. (1973). Polyphenol oxidase

of Royal Ann cherries; purification and characterization. Journal of

Food Science, 38, 799–806.

Chan, H. T., & Yang, H. Y. (1971). Identification and characterization

of some oxidizing enzymes of the McFarlin cranberry. Journal of

Food Science, 35, 169.

Das, J. R., Boht, S. G., & Eowda, LR. (1997). Purification and

characterization of a polyphenol oxidase from the Kew cultivar of

Indian pineapple fruit. Journal of Agricultural and Food Chemistry,

45, 2031–2035.

Demeaux, M., & Biden, P. (1967). Etude de l’inactivation par la

chaleur de la polyphenoloxydase du jus de raisin. Annales de

Technologie Agricole, 16(2), 75–79.

Dimick, K. P., Ponting, J. D., & Makower (1951). Heat inactivation of

polyphenolase in fruit purees. Food Technology, 6, 237–241.

Golan-Goldhirsh, A., & Whitaker, J. R. (1984). Effect of ascorbic acid,

sodium bisulfite and thiol compounds on mushroom polyphenol

oxidase. Journal of Agricultural and Food Chemistry, 32,

1003–1009.

Halim, D. H., & Montgomery, M. W. (1978). Polyphenol oxidase of

d’Anjou Pears (Pyrus communis L.). Journal of Food Science, 43,

603–608.

Heil, J. R., McCarthy, M. J., & Merson, R. L. (1988). Influence of

gluconic acid on enzyme inactivation and color retention in canned

apricots and peaches. Journal of Food Science, 53, 1717–1719.

Lee, C. Y., Smith, N. L., & Pennesi, A. P. (1983). Polyphenoloxidase

from DeChaunac Grapes. Journal of the Science of Food and

Agriculture, 34, 987–991.

Martinez, M. V., & Whitaker, J. R. (1995). The biochemistry and

control of enzymatic browning. Trends in Food Science and

Technology, 6, 195–200.

McCord, J. D., & Kilara, A. (1983). Control of enzymatic browning in

processed mushrooms (Agaricus bisporus). Journal of Food Science,

48, 1479–1484.

Palou, E., Lopez-Malo, A., Barbosa-Canovas, G. V., Welti-Chanes, J.,

& Swanson, B. G. (1999). Polyphenoloxidase activity and color of

blanched and high hydrostatic pressure treated banana puree.

Journal of Food Science, 64(1), 42–45.

Pizzocaro, F., Torreggiani, D., & Gilardi, G. (1993). Inhibition of

apple polyphenoloxidase (PPO) by ascorbic acid, citric acid and

sodium chloride. Journal of Food Processing and Preservation, 17,

21–30.

Sapers, G. M. (1993). Browning of foods: Control by sulfites,

antioxidants and other means. Food Technology, 47, 75–84.

Strubi, P., Escher, F., & Neukom, H. (1975). Neuere Arbeiten uber die

Technologie der Apfelnektar Herstellung. Industrie Obst-Gemuse-

verwert, 60, 349–351.

Stumbo, C. R. (1973). Thermobacteriology in food processing (2nd ed).

New York: Academic Press.

Teisson, C. (1977). Le brunissement interne de l’ananas. Docteur es

sciences naturelles these, presentee a la Faculte des Sciences de

l’Universite d’ Abidjan, 184pp.

Vamos-Vigyazo, L. (1981). Polyphenol oxidase and peroxidase in

fruits and vegetables. CRC Critical Reviews in Food Science and

Nutrition, 15, 49–127.