Review

Coconut water preservation and processing: a reviewAlexia PRADES1*, Manuel DORNIER1,2, Nafissatou DIOP3, Jean-Pierre PAIN4

* Correspondence and reprints

Received 31 March 2011Accepted 20 June 2011

Fruits, 2012, vol. 67, p. 157–171© 2012 Cirad/EDP SciencesAll rights reservedDOI: 10.1051/fruits/2012009www.fruits-journal.org

RESUMEN ESPAÑOL, p. 171

Article published by EDP Sciences

Coconut water preservation and processing: a review.

Abstract — The product. Coconut water (Cocos nucifera L.) is an ancient tropical beveragewhose original properties have drawn the attention of manufacturers as a natural functionaldrink. Preservation. This refreshing liquid comes mainly from immature coconuts which aredifficult to collect, store and thus to commercialise. Nevertheless, some studies, mostly fromAsian countries, tend to prove that the shelf life of immature coconut fruits could be pro-longed thanks to post-harvest treatments. Processing. Coconut water itself, extracted fromthe nut, is obviously easier to handle but is also very sensitive to biological and chemical inju-ries. Thermal treatment combined with chemical additives are already used by the industrybut other technologies such as micro- and ultrafiltration are not yet available on an industrialscale. Whatever the process, taste, aroma and colour (linked to enzymatic activities) are stilldifficult to control. Discussion. Results of former and recent investigations are discussed.Finally, suggestions are made for further research to increase our knowledge of this originaltropical juice.

France / Cocos nucifera / coconuts / coconut water / plant developmentalstages / maturation / quality / storage / preservation / keeping quality /processing

Conservation et transformation de l'eau de noix de coco : une synthèse.

Résumé — Le produit. L’eau de coco (Cocos nucifera L.) est un breuvage tropical dont lespropriétés fonctionnelles naturelles intéressent aujourd’hui les industriels. Conservation. Celiquide rafraîchissant provient des noix de coco immatures dont la récolte et le stockage res-tent délicats. Toutefois, certaines études menées essentiellement en Asie tendent à prouverque des traitements post-récoltes pourraient prolonger la durée de vie des noix immatures.Transformation. L’eau de coco extraite de la noix est évidemment plus simple à manipuleret transporter, mais sa composition la rend particulièrement sensible aux dégradations biolo-giques et chimiques. Des traitements thermiques combinés à l’usage d’additifs sontaujourd’hui utilisés dans l’industrie mais d’autres technologies comme la micro ou l’ultrafiltra-tion ne sont toujours pas disponibles pour ce produit. Quel que soit le procédé de stabilisa-tion utilisée, le goût et la flaveur originels de l’eau de coco restent très difficiles à préserver.Discussion. Dans cette synthèse, pour la première fois, les recherches sur l’eau de coco, desplus anciennes aux plus récentes, sont présentées ; elles conduisent à proposer des pistespour améliorer notre connaissance de ce jus de fruit tropical atypique.

France / Cocos nucifera / noix de coco / eau de coco / stade de développementvégétal / maturation / qualité / stockage / préservation / aptitude à laconservation / traitement

1 Cirad-Persyst, UMR 95Qualisud, TA B-95 / 16,73 rue Jean-François Breton,F-34398 Montpellier cedex 5,France, alexia.prades@cirad.fr

2 Montpellier SupAgro,UMR 95 Qualisud,TA B-95 / 16, 73 rueJean-François Breton,F-34398 Montpellier Cedex 5,France,manuel.dornier@cirad.fr

3 Inst. Technol. Aliment. (ITA),route des Pères Maristes,BP 2765, Dakar, Sénégal,ndiop@ita.sn

4 Univ. Montpellier II,UMR 95 Qualisud, PlaceEugène Bataillon, F-34090Montpellier, France,jppain@polytech.univ-montp2.fr

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1. Introduction

Coconut (Cocos nucifera L.) is one of themost important and extensively grown palmtrees worldwide. The inner part of the nut(endosperm) is divided into two edibleparts: a white kernel and a clear liquid:coconut water [1]. Both parts can be proc-essed in many different ways and lead tovarious products such as copra, virgin coco-nut oil, coconut cream, coconut milk, des-iccated coconut, coconut water, nata decoco, etc. [2]. The market for canned coco-nut milk, coconut cream and coconut juice/water is increasing considerably [3–5]. Coco-nut is no longer only an international oilcommodity but is becoming a valuable freshfruit.

Coconut water (CW), also called coconutjuice (not to be confused with coconutmilk), is a sweet refreshing drink takendirectly from the inner part of coconut fruits[6]. It differs from coconut milk, which is theoily white liquid extracted from the gratedfresh kernel. The coconut water consumedas a beverage usually comes from immaturecoconut fruits [7]. Due to its unique charac-teristics, coconut water is considered as anatural functional drink [8]. Its sugar contentand mineral composition make it an idealrehydrating and refreshing drink after phys-ical exercise [9]. Previously considered as asimple tropical refreshment or occasionallyas a medicine, coconut water is progres-sively becoming a natural healthy drink. Asa beverage being extracted in few tropicaland subtropical areas and only processed insome Brazilian or Asian industrial manufac-turing plants, coconut water remains a tra-ditional and under-used resource. In mostcases, coconut water comes from small andscarce coconut tree plantations more relatedto “gardens”, except in Brazil where thegrowing market demand led growers to cre-ate, a few years ago, large commercial coco-nut plantations. An increasing internationaldemand for this product could be a highlypositive issue for thousands of African andAsian small farmers. However, to competeon the international beverage market, coco-

nut water still has to be carefully processed,packed, transported and stored.

After suitable varieties have been identi-fied, coconut palms have to be harvested atthe right stage of maturity and in optimalconditions [10]. The immature fruits areoften consumed immediately after harvestor sold, either on a local market (75% of theproduction) or dispatched, with or withoutpre-treatment, to the international market.Most whole young tender coconuts from theAsian and Pacific Coconut Community passthrough Hong Kong or Singapore marketsbefore being transported by plane to Tai-wan, the US or the EU. However, a tendercoconut can be heavy [(0.8 to 2) kg], leadingto considerable air freight costs.

Apart from the market for whole youngtender coconuts, whose transport can beexpensive, thus limiting exports, coconutwater is also removed from the nut andprocessed. Although coconut water is sterileas long as it remains in the inner cavity ofthe nut [11], it is very difficult to preserve.As soon as the nut is opened, its biochemicalcomposition and physical appearancechange. Thermal and non-thermal treat-ments, sometimes combined with additives,have been tried with varying degrees of suc-cess. In Asian countries and in Brazil,canned, bottled or tetra-packed coconutwater is available. But those who havetasted these manufactured juices are awarethat they differ from fresh coconut juice.Prolonging the coconut water shelf life with-out modifying its flavour and nutritiousproperties remains a technical challenge.Fermentation processes are also encoun-tered but lead to fully different final prod-ucts which do not resemble natural coconutwater. We drew a flow diagram of the dif-ferent manufactured products made ofyoung coconut water (figure 1).

Current research on the post-harvest sec-tor of coconut water is rare. Two differentfields have to be taken into account: pres-ervation of the whole nut (the Young TenderCoconut, YTC market) and processing ofcoconut water. Nevertheless, we found inthe literature these two approaches that wedescribe in detail in our review.

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Coconut water preservation and processing

2. Preservation and saleof young tender coconuts

Young tender coconuts are still the best wayto preserve coconut water (inside its naturalcontainer) but the nuts cannot be stored formore than 6 days at ambient temperature[12]. In Sri Lanka, the Coconut ResearchInstitute suggested some technical guide-lines for the shipping of King Coconuts forexport [13]. Following their advice on prep-aration, young tender coconuts can remainfresh and safe for 3 weeks at (13 to 15) °Cand 70% RH (reefer containers). Similarly, aproject funded by the Indian CoconutDevelopment Board has provided a com-plete supply chain for young tender coco-nuts from the field to the kiosks andretailers. The minimum processing consistsof dipping partially husked nuts in a solution

of 0.5% citric acid and 0.5% of potassiummetabisulphite for 3 min. The final product,wrapped with polypropylene cling film, canbe stored for up to 24 days at (5 to 7) °C [14].

As for many tropical fruits, reducing thetemperature below 12 °C results in chillinginjury: the coconut skin rapidly browns. Forthe whole nut without any treatment, pres-ervation for 28 days at either 12 °C or 17 °Cgave the best results reported in the litera-ture [15–17]. For the whole nut with treat-ment such as sanitisation, i.e., immersion ina specific solution for a few minutes [18], thebest result was obtained after 21 days at12 °C [19]. Surprisingly, sanitisation did notimprove the shelf life of the nut. For thewhole nut with film wrapping, results wereequivalent or even better: 28 days at 12 °Cwith PE film [16] and 30 days at 12 °C withPVC film [19]. The longest shelf life for

FFmc

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igure 1.low diagram of the differentethods of processing young

oconut fruit.

) 159

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A. Prades et al.

whole young tender coconuts was obtainedwith paraffin wrapping stored for 49 days at12 °C [17].

The most common method to promotethe sale of young tender coconuts on localmarkets, in supermarkets, or in restaurantsis to partially remove the tender mesocarp(husk) up to the outer shell. The partiallyhusked young tender coconuts havebecome so famous on Asian markets, espe-cially in Thailand, that a prototype machinehas been designed to trim and open youngcoconut fruits [20, 21].

However, the exposed trimmed huskquickly turns brown, reducing the commer-cial value of the fruit even though the coco-nut water remains of good quality inside.Without any packing or sanitisation, thesepartially husked nuts can only be stored for7 days at 17 °C. To overcome the problem,the freshly-cut nut can be immersed in asolution of anti-browning agent such assodium metabisulphite at a concentration ofabout 2 g·L–1 for (5 to 10) min [22]. Withanti-browning treatment and a film wrap-ping, the shelf life is estimated at 24 days at5 °C [23]. Finally, immersion in carnaubawax emulsion maintains the freshness ofpartially husked young tender coconuts forup to 30 days at 12 °C [24].

In conclusion, the best method for pro-longing shelf life was obtained using waxcoatings: paraffin for whole young tendercoconuts for up to 49 days at 12 °C, and car-nauba for partially husked fruits for up to30 days at 12 °C. Other waxes should betested to preserve young tender coconutsand to optimise conditions for the sale of thisnatural product. Additional work is alsoneeded to optimise coatings and packaging.A better understanding of the coconut fruitripening process and senescence could alsohelp design suitable storage conditions suchas modified atmosphere packaging (MAP).

3. Coconut water processing

3.1. Mature coconut waterprocessing

As early as 1977, Sison raised the questionof the disposal of the mature coconut water

[25]. Until now mature coconut water hasbeen considered as waste, especially incoconut processing plants (desiccated coco-nut factories, coconut milk factories, etc.).Pramith estimated the total volume of coco-nut water discarded by the Sri Lankan coco-nut mills at 261 Mt per year [26]. The liquidcauses environmental pollution and is alsoa waste of a valuable food [27].

3.1.1. An environmental problem

A desiccated coconut factory which splitsabout 300,000 coconuts a day throws outapproximately 5.3 m3 of pure coconut waterplus 44 m3 of wash water, giving a total of50 m3 of effluent per day. Pure coconut waterhas a BOD (Biological Oxygen Demand) of29,000 mg·L–1 and wash water about3,000 mg·L–1 so that the global liquid wastefrom the factory has about 5,800 mg·L–1 ofBOD, which has to be reduced to theaccepted level of 50 mg·L–1 [25]. Severalconventional techniques can be used in SriLankan conditions including letting thecoconut water settle and skimming off thesurface oily layer, which can be processedinto soap. Anaerobic treatment in an UpflowAnaerobic Sludge Blanket (UASB) and aer-obic treatment in ponds have also been sug-gested [27]. The quality of the effluent todischarge into inland surface waters includesa pH of 6.5 to 8 and maximum allowedamount of 300 mg·L–1, 30 mg·L–1 and10 mg·L–1 for COD (Chemical OxygenDemand), BOD and oil, respectively [28].

3.1.2. A valuable food

First attempts to make use of the liquidwaste as food failed due to technical diffi-culties involved in removing the residualoil from the liquid. A membrane was testedto separate the residual oil. The maturecoconut water was previously heated to95 °C to precipitate the protein. Then pas-teurisation gave a relatively high flux of upto 42 L·h–1·m–2 at 60 °C and up to 245 kPawith a 0.45-µm hydrophilic PVDF mem-brane [26]. Fresh mature coconut waterwas also concentrated by plate-and-framereverse osmosis using composite mem-branes (DDS type HR98 with a cut-off ofless than 500 Da) at (2, 3 and 4) MPa inletpressures [29].

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The most economical and practical waysto enhance the value of coconut water arestill making vinegar [30], using it as a growthmedium for yeasts [25], for xanthan gumproduction [31], for the culture for variouslactic acid bacteria [32] or for Nata de cocoproduction [33]. Nata de coco is pure cellu-lose, free of lignin and hemicellulose, pro-duced by Acetobacter xylinum [34–36].Besides its use as a food, the gel-like sub-stance is also considered to impart extraor-dinary mechanical strength when processedinto film or sheets [37, 38]. Nata de coco wasalso tested as a natural coating for minimallyprocessed fruits [39]. Coatings containing 1%and 2% of carboxymethyl cellulose fromNata de coco, referred to as carboxymethyl-nata, were applied to bell peppers to eval-uate the effect of the polysaccharide coatingon the post-harvest life of the fruits. Theresults suggested that this coating signifi-cantly reduced the ripening rate. Jagannathet al. studied the production of Nata de cocoby Acetobacter xylinum using tender coco-nut water as a medium instead of the usualmature coconut water [40].

3.2. Young coconut waterprocessing

Although some publications addressed theprocessing of young coconut water beforethe mid-1990s [41–43], the first paper pre-senting detailed scientific results of thermaltreatment of young coconut water was pub-lished in 1996. Since then, ten articles havebeen published on pasteurisation and twoon sterilisation. Two additional publicationsby the University of Sao Paulo, Brazil,described microwave treatment of coconutwater. Besides conventional thermal tech-niques, cooling and freezing are the twoprocesses currently used in the industry.Surprisingly, they are only cited ordescribed in three articles and one manual.As far as we know, membrane filtrationtechniques, mentioned in seven papers,have not yet been used industrially foryoung coconut water.

No information was found in the litera-ture on young coconut water aseptic extrac-tion, whereas it is the first crucial operationin coconut water processing. It is probably

due to the fact that this opening step is thekey issue to obtain a high-quality raw mate-rial and each company wants to preserve itsknow-how. Another explanation could bethat it is still a highly challenging technicalproblem because of the rapid discolorationand fermentation occurring just after thecoconut cracking.

3.2.1. Thermal treatments

3.2.1.1. Pasteurisation, sterilisationand combined treatments

The first paper on the preservation of tendercoconut water was Indian [43]. Additivessuch as nisin, minimum heating, and pack-ing in polymeric pouches and metal canswere cited as being used to achieve com-mercial sterility. A more detailed process todevelop shelf-stable ready-to-serve greencoconut water was described by Chowd-hury et al. [44]. The authors filtered thefreshly extracted coconut water, pasteurisedit at 85 °C for 10 min and cooled it. Thecoconut water was then poured into metalcans or glass bottles. Cans and bottles weresterilised at 121 °C for 30 min and at 100 °Cfor 15 min, respectively.

An experimental hot-fill process was alsocompared with other commercial coconutwater subjected to cooling, freezing, asepticfilling of cartons and industrialised hot-fillprocessing [45]. The experimental processconsisted of filtration, addition of citric acidto reduce the pH to 4.5, addition of fructoseto standardise the soluble solids content at70 g·L–1 and sodium metabisulphite(0.45 g·L–1), addition of sodium benzoate(1.24 g·L–1) and ascorbic acid (0.0013 g·L–1),pasteurisation at 90 °C for 2 min and pour-ing into 200-mL glass bottles. Samples werestored at ambient temperature (28 °C). Theexperimental hot-fill samples were accept-able even though they did not resembleother commercial samples in terms of phys-icochemical attributes.

In Taiwan, sterilisation is commonly usedas a thermal treatment to stabilise coconutwater and frequently causes non-enzymaticbrowning of the liquid [46]. In order toremove the brown colour, active carbon,cation exchange resin, sulphur compounds

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such as sulphite, acetyl-cysteine, glutathi-one and cysteine were successfully tested.

3.2.1.2. Thermal treatmentand microbiological effects

The main objective of the thermal treatmentsis to stop or eradicate the microbiologicalload for consumer safety [47]. Thermal treat-ments were applied to buko, a mix of coco-nut water/distilled water (80/20) and,respectively, (60 and 20) g of maceratedsolid endosperm and refined sugar per litreof beverage. Glass test tubes were immersedin a hot water bath at (60, 70 and 80) °C fordifferent lengths of time. According to thedifferent temperatures and time treatments,a D value was determined, i.e. the time (inminutes) required for a 1 log10 reduction ofthe survival of the reference strain. The cal-culated D values forEscherichiacoli on bukoranged from (0.26 ± 0.01) min at 80 °C to(0.56 ± 0.08) min at 60 °C.

3.2.1.3. Thermal treatmentand thermophysical properties

Before the design or adaptation of specificfood processing equipment, an importantstep is often left out: assessment of the effectof temperature on the thermophysical prop-erties of the raw material. Food compositionand temperature are important factorswhich affect the thermal behaviour of a trop-ical fluid such as coconut water. The density,dynamic viscosity, thermal diffusivity, ther-mal conductivity and specific heat of thewater of green Bahia coconuts (presumedto be the Brazilian Green Tall or Dwarf vari-ety) bought from a local market in Brazilwere measured using a range of tempera-tures from 5 °C to 80 °C [48]. Temperaturesignificantly affected the above properties,which displayed linear trends, except fordynamic viscosity, which displayed anexponential curve. Different equations andmodels were proposed to fit the experimen-tal data (table I).

3.2.1.4. Thermal treatmentand enzymatic browning control

The major problem encountered in coconutwater stabilisation is apparently not micro-biological or chemical stability, since these

objectives have already been partiallyachieved [44, 45], but the fact that enzymesneed to be inactivated to stabilise the colourand taste of the final product. As is true formany fruit juices, polyphenol oxydase(PPO) and peroxydase (POD) enzymes arepresent in young coconut water.

The consequence of PPO or POD activi-ties in coconut water is discoloration. Yel-low, brown or pink discoloration of thecoconut water can occur a few minutes ora few hours after the nut is cracked. Discol-oration can also occur after several weeksof storage of processed coconut water. Eventhough the mechanisms of PPO and PODactivities are well described from a bio-chemical point of view [49], the same mech-anisms remain to be explained duringripening of the fruit and post-harvest. Arange of different factors affect the levels ofactivities of the enzymes and are often dif-ficult to control (temperature, pH, mechan-ical impacts, oxygen concentration, etc.). Toprevent the consequences of PPO and PODactivities in coconut water, several authorssuggested inactivating the enzymes by ther-mal treatments either using conventionalmethods (pasteurisation, sterilisation) or bymicrowave heating.

At a low temperature (90 °C), total inac-tivation was obtained after 550 s for PPOand after 310 s for POD [50]. At a tempera-ture of 139 °C for 10 s combined with200 mg·L–1 of ascorbic acid, PPO wasentirely inactivated, whereas POD was stillactive at 40% of its original level [51]. Con-trary to Campos et al., who underlined thefact that PPO was more resistant than PODto pasteurisation [50], Abreu and Faria con-cluded that POD was inversely more ther-mostable using sterilisation [51]. Attemperatures below 90 °C, the POD of thecoconut water is less thermostable thanPPO, like strawberry [52], but unlike apple[53] or pineapple [54].

Other investigations of the kinetics ofinactivation of the two enzymes indicatedthat the situation is more complex [55, 56].In fact, two isoenzymes for PPO and PODare present in young coconut water. Thethermal behaviour of the different fractionswas analysed and quantified during pas-teurisation. Two different mathematical

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Coconut water preservation and processing

equations were developed to predict thethermal resistance of PPO and POD frac-tions using the same type of multicompo-nent first-order model (table II).

The thermal resistance of POD can beestimated by a D value, i.e., the timerequired to reduce the enzyme activity to10% of its initial value. The temperaturerequired for a D value of 5 min, which was81.2 °C for coconut water POD [57], wasshown to be higher than the 44.5 °C

required for pepper [58], 75 °C for grape [59]and 80.3 °C for carrot [60], but slightly lowerthan the 83.2 °C for potato [60].

Apart from classical thermal treatments,an unconventional technique, microwaveheating, has been used to inactivate PPOand POD enzymes [57, 61]. First, the thermalbehaviour of solutions simulating the chem-ical constituents of coconut water (PPO/water, PPO/sugars, PPO/salts and PPO/sug-ars/salts, and equivalent for POD) was

Table I.Experimental values of thermophysical properties of coconut water and equations for tfrom Fontan et al. [48]).

Temperature(°C)

Density(ρ)

Thermal diffusivity(α)

Dynamic viscosity(μ)

Specific heat(cp)

(kg·m–3) (10–7 m2·s–1) (10–3 Pa.s) (J·kg–1·°C–1)

5 1021.72 1.36 1.54 4056.5

20 1016.75 1.39 1.00 4056.5

35 1011.33 1.46 0.69 4056.5

50 1007.12 1.50 0.45 4056.5

65 1000.03 1.55 0.43 4056.5

80 996.72 1.58 0.36 4056.5

Thermophysical properties Equations

Density ρ = 1023·4651 – 0.3416 · T

Thermal diffusivity α = 1.343·10–7 + 3.119·10–10 · T

Dynamic viscosity μ = 2.838·10–4 + 1.540·10–3 · exp(–3.956·10–2 · T)

Specific heat

with

Thermal conductivity K = 0.5581 + 1.08·10–3 · T

Ccal: calorific capacity of calorimeter (J.°C–1); cw: specific heat of water (J.kg–1.°C–1); mc: cold watermass (kg); mh: hot water mass (kg); ms: sample mass (kg); mw : mass of water inside the calorimeter(kg); Tc: calorimeter + cold water temperature (°C); Teq: equilibrium temperature (°C); Th: hot watertemperature (°C); T0: calorimeter + initial temperature of water (°C); Ts: initial temperature of thesample (°C).

Cpcw mw⋅ Ccal+( ) T eq T 0–( )

ms T s T eq–( )------------------------------------------------------------------=

Ccalmh cw⋅ T h T eq–( )– mc cw⋅ T eq T c–( )––

T eq T c–( )----------------------------------------------------------------------------------------------------------=

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heir prediction (adapted

Thermal conductivity(K)

(W·m–1·°C–1)

0.56

0.57

0.60

0.61

0.63

0.64

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A. Prades et al.

characterised. The influence of sugars andsalts on enzyme activity was demonstrated.Sugars, especially fructose, were more det-rimental to POD than to PPO inactivation.Salts significantly affected PPO and POD sta-bility. At temperatures above 77 °C, PPOwas found to be more thermally resistant tomicrowave heating than POD, corroborat-ing the results of Campos et al. [50]. Thepresence of salts in the simulated solutionscombined with microwave heating reducedboth enzymatic activities to undetectablelevels. In addition, the thermal behaviour ofnatural coconut water was compared withthat of the simulated solutions [57]. Itappeared that natural enzymes were morethermo-resistant than commercial ones. Theauthors used a first-order kinetic model todescribe the experimental results and deter-mined D parameters for PPO, D92.20 °C =52 s, and for POD, D92.20 °C = 16 s. The ther-mal inactivation of both enzymes was faster

with microwave processing than with con-ventional pasteurisation.

3.2.1.5. A simple thermal treatment:refrigeration

Cold preservation of young coconut waterhas been studied by the FAO for a fewyears with the aim of extending the shelflife of this fragile product. A manual enti-tled “Good practice for the small-scale pro-duction of bottled coconut water” [62] wasdesigned for use as a learning resource forsmall and micro-entrepreneurs as well as atraining resource for extension workersand trainers. The manual describes meth-ods for harvest, storage conditions and san-itisation of the coconut fruits. It thenexplains how to extract, filter on cheese-cloth, pour into bottles and store the coco-nut water at 4 °C. No peer-reviewed articlewas found on international databases on

f polyphenoloxydase (PPO) and peroxydase (POD) thermal inactivation in coconut

tivity–1)

T(°C)

Model[55]

Coefficient of multicomponent first-order model

α k1 (s–1) k2 (s–1) R2

80 0.6559 1.70E–03 1.98E–03 0.938

80 0.5826 2.19E–02 –7.12E–04 0.893

85 0.2068 1.28E+00 3.01E–03 0.953

90 0.5983 2.36E–02 2.39E–02 0.970

Model[56]

Coefficient of multicomponent first-order model

Tref(°C)

α(% of activity

of isoenzyme 1)

D1(s)

z1(°C)

D2(min)

z2(°C)

R2

86.9 0.88 6.0 5.7 11.3 5.5 0.82

86.9 0.95 8.6 3.4 26.3 6.9 0.74

min–1); A0: initial enzymatic activity (U·mL–1·min–1); α: fraction of the initial activity of the isoenzyme 1temperature (°C); D: decimal reduction time (min); z: temperature increase that reduces D-value by 90%.

AA0

------ ek1t–( )⋅ 1 –( ) e

k2t–( )⋅+= α α

AA0

------ A1

A01

---------⎝ ⎠⎛ ⎞⋅ 1 –( ) A2

A02

---------⎝ ⎠⎛ ⎞⋅+= α α

A1

A01

---------⎝ ⎠⎛ ⎞log t

D1

------–=A2

A02

---------⎝ ⎠⎛ ⎞log t

D2

------–=

1 Dref1a

T ref T–z1

-------------------⎝ ⎠⎛ ⎞log⋅= D2 Dref2

aT ref T–

z2

-------------------⎝ ⎠⎛ ⎞log⋅=

Table II.Mathematical models owater.

Enzyme Enzymatic ac(U·mL–1·min

PPO 16.5

POD 3.6

Enzyme Activity(U·mL–1·min–1)

T(°C)

PPO 0.15–34.8 75

80

85

POD 0.13–6.18 75

80

85

A: enzymatic activity (U·mL–1·(%); t: time (s); Tref: reference

D

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Coconut water preservation and processing

this popular and frequently-used proce-dure for the preservation of coconutwater.

3.2.2. Non-thermal treatments

Non-thermal treatments such as membranefiltration are interesting alternatives to sta-bilise delicate aromatic fruit juices. The orig-inal flavour of coconut water is sensitive totemperature and microfiltration (MF) couldhelp to pasteurise the product at ambienttemperature while preserving its aroma.Moreover, ultrafiltration (UF) is used for theextraction of small molecules from a solu-tion and enzymes, such as PPO and POD,are small molecules of, respectively,73.8 kDa and 49.2 kDa [63].

Several authors tried to stabilise coconutwater using either MF or UF (table III). TheFAO has also taken out a patent [64] claimingthat high-speed centrifugation followed by

microfiltration and aseptic packaging canpreserve young coconut water for a periodof at least 6 months.

Working on a semi-industrial microfiltra-tion unit, Diop observed relatively highsteady-state flux at 150 L·h–1·m–2 and a lossof only 3% of coconut water at a VRF (Volu-mic Reduction Factor) of 25 [65].

To prevent enzymatic discoloration, afew authors tried to use ultrafiltration imme-diately after microfiltration to remove PPOand POD from the coconut water. Ultrafil-tration retained 92% and 91% of PPO andPOD activity thanks to a 10 kDa cut-offmembrane [65]. In all cases, PPO activity wasconsiderably reduced and POD activity wasundetectable. Equations were developedfor ultrafiltration to estimate and predict itsperformance [66].

Another way to cope with coconut waterpinking is to mix it with a coloured fruit juicesuch as cashew apple juice [67–69], acerola

Table III.Microfiltration and ultrafiltration conditions of immature coconut water.

Treatment Membraneporosity

(µm)

Membranemolecular

cut-off(kDa)

Surface(m²)

Membrane Temperature(°C)

TransmembranePressure

(kPa)

Filtrty

Microfiltration(MF)

0.2 – Notavailable

Not available 6 Not available Nava

0.1 – 0.72 Plate and framepolysulphone

25 200 Dea

0.2 – 0.22 Tubular ceramic 20–25 140–158 Cros7 m

0.2 – 0.013 Plate and framecellulose nitrate

20 16 Dea

Ultrafiltration(UF)

0.1,0.025

– Notavailable

Plate and framecellulose ester

Not available Not available Dea

– 10, 30, 50 0.09 Plate and frameregenerated

cellulose (10 kDA)and

polyethersulphone(30 and 50 kDa)

25 60 Dea

– 20, 50, 100 0.72 Plate and framepolysulphone

25 200 Dea

– 50 0.0035 Plate and frame thinfilm composite

polyamide

Ambienttemperature

276–690 Stirre80

160

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ationpe

Permeateflux

(L·h–1·m–2)

References

otilable

Notavailable

[64]

d-end 20 [75]

s Flow·s–1

150 [65]

d-end Notavailable

[76, 77]

d-end Notavailable

[78]

d-end Notavailable

[65]

d-end 5 [75]

d cell0–

0 rpm

25–130 [66]

) 165

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[70] or maracuja [71]. The association of thetwo fruit juices combines their sensory andnutritional properties, while cumulatingtheir respective advantages.

Other investigations tried to prevent“pinking” of coconut water by using differ-ent types of food-grade resins: polyvinyl-polypyrrolidone (PVPP), calcium bentoniteand gelatin [72], as commonly used in wineand beer processing. None of the tested res-ins was successful in controlling discolora-tion but further investigations are requiredto improve the experimental methodology.Continuous dense-phase CO2 (DPCD), avery recent technology, also failed to pre-vent discoloration at ambient temperature[73].

Hence, from a microbiological point ofview, microfiltration appears to be a satis-factory way to stabilise coconut water buthas no effect on enzyme activity since theenzymes cross the membrane. Ultrafiltrationretains PPO and POD enzymes. The discol-oration of coconut water is still notcompletely elucidated. Thus, emergingtechnologies such as high-pressure, pulsedelectric field or ohmic heating should beinvestigated.

3.2.3. Shelf life and qualityof processed young coconut water

Few studies have dealt with the quality andshelf life of processed coconut water. Con-cerning shelf life, it is clear that neitherclassical thermal pasteurisation, nor sterili-sation, nor microfiltration were sufficient toobtain a shelf-stable product without addi-tives. Efficient results were obtained byadding molecules such as nisin [43], ascorbicacid [50] or citric acid and sodium metabi-sulphite [74]. In these cases only, it waspossible to preserve pasteurised coconutwater for 2 to 3 months at ambient temper-ature or refrigerated. Sterilisation prolongedthe shelf life of coconut water to 10 monthsat ambient temperature and to 12 months at4 °C [44]. The storage stability of the cannedand bottled green coconut water was satis-factory but the addition of citric acid didchange the taste of the processed product.

Microfiltration did not significantly influ-ence pH, acidity, total soluble solids or totalsolids of clarified coconut water but

increased clarity (measured as luminance Lwith a Hunter-Lab system), decreased tur-bidity and protein content by 24% [75]. Withdifferent equipment and membranes, a sim-ilar increase in clarity, and a decrease of 13%in protein content and turbidity were alsoobserved in clarified coconut water [76, 77].Furthermore, microfiltration caused a signif-icant decrease in the ash content of the per-meate. K, Mg, Ca, Fe and Cu concentrationsdecreased by, respectively, (10, 16, 19, 20and 22)%. Only calcium concentrationsremained stable. Physical properties such assurface tension and viscosity changed,whereas the specific gravity was not affected[76, 77].

Microfiltration obviously did not stop thepink coloration of the clarified coconutwater. The pink coloration occurred inmicrofiltered coconut water from Dwarfvarieties but not from Tall varieties whenstored at ambient temperature. When storedat 9 °C to 10 °C just after processing, discol-oration did not occur in any of the samples.However, the samples from Dwarf varietiesstill became pink when placed at ambienttemperature after cold storage [64, 65].

Finally, the taste of the microfilteredcoconut water was found to be very similarto that of fresh coconut water but the aromawas lost during processing, even though theoverall acceptability of the final product bya panel of consumers was good [76, 77].

Ultrafiltration retained PPO and PODenzymes. Retention percentages of proteinof, respectively, (25, 38 and 43)% for the(100, 50 and 20) kDa cut-off membraneswere confirmed [66, 75]. The assessment ofthe effect of three different processes (ultra-filtration, pasteurisation and freezing) onthe mineral composition of young coconutwater showed that the ultrafiltration mem-brane retained most of the minerals presentin coconut water. In contrast, pasteurisationtended to increase Cu, Fe and Zn concen-trations, whereas freezing completelychanged the mineral distribution [78]. Ultra-filtration was able to retain PPO and PODenzymes but also retained minerals, andthese are major quality criteria and a strongmarketing argument for the young coconutwater beverage.

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As the market for processed coconutwater is constantly growing in Brazil,Luvielmo et al. performed a quantitativedescriptive analysis of Brazilian brandedcoconut waters to compare the effects of dif-ferent types of processing: freezing,pasteurisation and microwave heating [79].Contrary to microwave-heated samples, thefrozen coconut water samples showed thebest values for typical characteristics ofgreen coconut water. This is the first time alist of twelve descriptors has been drawn upfor green coconut water by an expert jury.Unfortunately, this study was performedusing commercialised samples of differentorigin and without a reference sample (i.e.,fresh coconut water without treatment).Four other articles compared, respectively,9, 3, 3 and 26 different coconut water brandssold in Brazilian supermarkets. Marked var-iability of the analysed samples wasobserved: De Sousa et al. in mineral com-position [80], Abreu et al. in organolepticquality [81], and Pinheiro et al. and Forteset al. in physicochemical and organolepticcharacteristics [82, 83]. This variability wasnevertheless in accordance with the Brazil-ian standard. On the other hand, 100% of theanalysed samples were microbiologicallycontaminated beyond legal limits.

Nunes et al. studied the hygienic condi-tions and characteristics of commercialfoods marketed in Brazil and especially fruitjuices [84]. They confirmed the previousresults of Fortes et al. regarding the badhygienic conditions during processing andhandling of young coconut fruits [83]. Theyalso confirmed the results of an investiga-tion by Walter et al., who demonstrated thatListeria monocytogenes was a possible con-taminant of young coconut water and greweasily on this media even at 4 °C [85]. There-fore, better care needs to be paid to pack-aging [86] and storage [87], training of theprocessors and vendors and adequate man-agement of wastes during fruit juice process-ing.

Attention also needs to be paid to con-trolling the physicochemical and microbio-logical quality of young coconut productsold. As far as we know, only Brazil [83] andIndia [88] already have or will soon have

official standards for processed young coco-nut water.

4. Conclusion and futureprospects

Coconut water is not a common fruit juiceand thus not easy to stabilise. Since its pHis high, it is subject to rapid deterioration.TheYoungTenderCoconutmarket could bea solution for regional markets but researchon the preservation of the fruits will needfuture efforts, especially in the coating andpackaging fields. Concerning coconut wateritself, thermal treatment combined withchemical additives are already used by theindustry but other technologies such asmicro- and ultrafiltration are not yet availa-ble on an industrial scale for coconut water.Microfiltration and ultrafiltration can pre-serve the taste of the fresh coconut water butnot the aroma. Ultrafiltration can drasticallychange the mineral composition of coconutwater. Whatever the process, taste, aromaand colour (linked to enzymatic activities)are still difficult to control. Therefore,emerging technologies such as high-pres-sure, pulsed electric field or ohmic heatingshould be investigated.

Coconut water extracted from youngcoconut fruits appears to be a naturalhealthy beverage and a good alternative toartificial sport drinks. Despite the lack of sci-entific knowledge on this raw material, themarket for it is continuously expandingworldwide.

To satisfy demand, coconut producingcountries have been planting Dwarf coco-nut palm trees for more than 10 years.Green Dwarf in Brazil, King coconut in SriLanka, Aromatic Green Dwarf (Nam hon) inThailand and Chowgat Orange Dwarf inIndia are some of the most popular cultivarsfor tendernut consumption around theworld. In the future, combined efforts bybreeders, biochemists and food processingscientists accompanied by innovative man-ufacturers will probably increase the qualityof young coconut water and give a chanceto millions of coconut smallholders toincrease the value of their production.

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Acknowledgements

The authors wish to acknowledge Dr.Olivier Gibert and Mrs Daphne Goodfellowfor the English revision of the manuscript.

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Conservación y transformación del agua de coco: una síntesis.Resumen — El producto. El agua de coco (Cocos nucifera L.) es un refresco tropical, cuyas propiedadesfuncionales naturales interesan hoy a los industriales. Conservación. Este líquido procede de los cocosinmaduros, cuya cosecha y almacenamiento son delicados. No obstante, algunos estudios llevados a cabosobre todo en Asia, tienden a demostrar que podrían existir tratamientos posteriores a la cosecha paraprolongar la duración de vida de los cocos inmaduros. Transformación. Lógicamente, el agua de cocoextraída del fruto es más fácil de manipular y transportar, pero su composición hace que sea particular-mente sensible a las degradaciones biológicas y químicas. Hoy en día, en la industria, se emplean tra-tamientos térmicos combinados con el uso de aditivos, sin embargo, otros tratamientos, tales como lamicro o la ultrafiltración, aún no están disponibles para este producto. Independientemente del procesode estabilización empleado, sigue siendo difícil preservar el sabor y el aroma originales del agua del coco.Discusión. En la presente síntesis, por primera vez, se presentan los estudios sobre el agua de coco,desde los más antiguos hasta los más recientes. Éstos dan lugar a proponer ideas para mejorar nuestroconocimiento acerca de este singular zumo de frutas tropical.

Francia / Cocos nucifera / coco / agua de coco / etapas de desarrollo de la planta /maduración / calidad / almacenamiento / preservación / aptitud para la conservación /procesamiento

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