Bioresource Technology 98 (2007) 1278–1284

Optimization of native agar extraction from Hydropuntia corneafrom Yucatan, Mexico

F. Pereira-Pacheco a,1, D. Robledo a, L. Rodrıguez-Carvajal b, Y. Freile-Pelegrın a,*

a CINVESTAV-Unidad Merida, A.P. 73 Cordemex, 97310 Merida, Yucatan, Mexicob Facultad de Matematicas, Universidad Autonoma de Yucatan, A.P. 172 Cordemex, 97110 Merida, Yucatan, Mexico

Received 2 April 2004; received in revised form 5 May 2006; accepted 5 May 2006Available online 23 June 2006

Abstract

Response surface methodology (RSM) was used to determine optimum extraction conditions for yield, gelling temperature, meltingtemperature and apparent viscosity of native agar from the red alga Hydropuntia cornea. Two independent variables were selected duringextraction, temperature (80, 90 and 100 �C) and time (2, 3 and 4 h). The extraction procedure using 100 �C and 3 h produced the greatestyield (43.3%), the greatest gelling temperature (32 �C) and the greatest melting temperature (78 �C). The extraction using 65 �C and 4 hproduced the optimum statistical apparent viscosity (80.73 cPs), though agar yield under these conditions had low quality for industrialpurposes. Temperature and time do not affect melting temperature, but do play an important role in gelling temperature. From the inde-pendent variables studied, extraction temperature is most important in producing an increase in yield, and time is the only variable thatcontributes significantly to increasing viscosity. Most of the physicochemical properties found in the native agar from H. cornea extractedat 100 �C/3 h were similar to commercial samples. These findings suggest the feasibility of using this colloid in spreads and soft-texturefood products.� 2006 Elsevier Ltd. All rights reserved.

Keywords: Agar; Hydropuntia cornea; Native agar; Optimization

1. Introduction

Agar is a hydrophilic colloid extracted from seaweeds ofthe Rhodopyceae, including order Gelidiales (Gelidium andPterocladia) and order Gracilariales (Gracilaria and Hydro-

puntia). This colloid is industrially important because of itsexcellent thickening and gelling properties. Agars with gelstrengths greater than 700 g cm�2 in a 1.5% solution arereferred to as high quality agars and are required by theinternational market (Armisen, 1995). Moreover, agarswith gel strengths less than these values would be rejectedfor industrial applications and are destined solely for tradi-tional domestic use in Asia. Nevertheless, high gel strength

0960-8524/$ - see front matter � 2006 Elsevier Ltd. All rights reserved.

doi:10.1016/j.biortech.2006.05.016

* Corresponding author. Fax: +52 999 9812917.E-mail address: freile@mda.cinvestav.mx (Y. Freile-Pelegrın).

1 Present address: Facultad de Ingenierıa Quımica, Universidad Auto-noma de Yucatan, A.P. 26 Suc, Las Fuentes Merida, Yucatan, Mexico.

is not always the most desirable quality for hydrocolloidssince agars with lesser gel strength (30–200 g cm�2) mayhave potential uses in new industrial applications, includ-ing liquid and spread foods, soft-texture confectionery,fat replacers (Hurtado-Ponce, 1992; Wilkinson et al.,2000), and as cryoprotectants that minimize damage inthe freezing-thawing process (Downey, 2002). In general,the gel strength is proportional to the agar concentrationin a solution. However, when the agar concentration islowered to a certain level, water removal (syneresis) occursand some physical properties are lost (Stanley, 1995). Inorder to prevent the above mentioned problems, a lessergel strength agar could be required that produces a softgel without a significant loss of water.

The order Gracilariales is the largest world-wide agarsource. This is due to its abundance of biomass and thenature of the chemical structure of its agars that have dif-ferent, but unique, properties and allow new uses in the

F. Pereira-Pacheco et al. / Bioresource Technology 98 (2007) 1278–1284 1279

food industry (Murano, 1995; Abbott, 1996). Gracilarialesare of particular interest because of the large quantitiesavailable in temperate and tropical regions and their highpotential for mariculture, with respect to the traditionalsources from Gelidiales. Species of the genus Gracilaria

was initially employed to compensate for the lack of suffi-cient quantities of species of Gelidium, allowing for anincrease in agar production. Because native agars isolatedfrom Gracilaria species are typically more sulphated, andtherefore have a lower gelling capacity than those obtainedfrom Gelidium species, the use of Gracilaria species requiresan alkaline hydrolysis as a pre-treatment to eliminatesulphate groups and, consequently, enhance their gel form-ing ability (Armisen and Galatas, 1987). However, at anindustrial level, this alkali pre-treatment must be carefullycontrolled in order to avoid the considerable pollution gen-erated by outflows of alkaline residues and large quantitiesof ‘sodium agaropectinates’ (Armisen, 1995). Although thequality of agar is usually judged in terms of its technicalperformance as a gelling agent (gel strength), other param-eters are also important to determine its use in food indus-try, such as gelling and melting temperature, viscosity andsyneresis index (lost of water during ageing). The low gelstrength of native agars from species of Gracilaria, togetherwith their low syneresis compared with Gelidium, makethem useful in other applications, such as low fat andsoft-texture products. An important factor in the use ofGracilaria species for industry to consider is that the chem-ical composition of its agar can be significantly affected bydifferent extraction processes. This means that extractiontemperature and time influence the rheological propertiesof the resulting polymer. A notable loss of yield anddecrease in gel strength are frequently associated with thephycocolloid extracted at an elevated temperature or forprolonged extraction time, and these changes depend onthe seaweed source (Hurtado-Ponce, 1992; Lai and Lii,1998).

Hydropuntia cornea (J. Agardh) M.J. Wynne (as Graci-laria cornea J. Agardh) from the Yucatan Peninsulahas been described as a potential agar source, yieldingapproximately 40% native agar and a weak gel that canbe dramatically improved after a suitable alkali treat-ment (Freile-Pelegrın and Robledo, 1997a). According toMcHugh (2001), processing industries in developing coun-tries can produce agar using low technology methods forconsumption in their internal markets. On this regard,Kapraun (1999) suggested that the solution of the problemof the waste water in phycocolloid industry is to process atsmall scale in rural areas, where the residues can be incor-porated into agricultural production. With the future com-mercial and industrial development of H. cornea agar fromYucatan in mind, by using low technology, it is importantto determine the optimum conditions for native agarextraction. Moreover, if an agar for industrial purposescan be obtained without an alkaline treatment step, itmay be more attractive from both an ecological and aneconomic point of view.

In this study, a multifactorial design and response sur-face analysis was used to determine the effects of extractionvariables on the yield, gelling and melting temperaturesand apparent viscosity of native agar from H. cornea fromYucatan. To consider the potential applications of nativeagar in the food industry, other chemical and physicalproperties (gel strength, syneresis index, sulfate, 3,6 anhy-drogalactose content, and viscosimetric molecular weight)were measured at the optimal extraction conditions.

2. Methods

Hydropuntia cornea was collected by SCUBA divingfrom natural stocks between 1 and 3 m depth at TelchacPuerto (21�1 0N, 89�14 0W), in the state of Yucatan, Mexico,in May 1999. Algal biomass was washed with tap water toremove excess salts and sand, submerged overnight in 10%formaldehyde to prevent enzymatic hydrolysis and thegrowth of microorganisms that hydrolyze agar during stor-age (Armisen, 1995; Freile-Pelegrın, 2000), dried and finallymilled prior to extraction.

2.1. Agar extraction with multifactorial experimental

design

Extraction of native agar from H. cornea was performedusing a response surface methodology (RSM; Montgom-ery, 1991). Based on previous studies (Freile-Pelegrın andRobledo, 1997b; Lai and Lii, 1998), two independent vari-ables were selected; X1 for extraction temperature (80, 90and 100 �C) and X2 for extraction time (2, 3 and 4 h),and two practical levels for each variable were determined.In the first experimental series, nine extraction conditionswere carried out: four factorial points and five replicatesfor the center point (Table 1). A first order model was fittedto these results. The center point replicates were used toestimate experimental error and check the fit. The experi-ments with data fitted to a first order model suggesteduse of the steepest ascent method (trial 10–13, Table 1),where the distance of the axial points was ±1.4142, calcu-lated from the following equation (Montgomery, 1991):

X ¼ �ðN fÞ1=4

X is the distance of the axial points; Nf is the number offactorial points.

Then, a new first order model was fitted. When theresults reached the vicinity of optimum, indicated by thelack of a first order model fit, a second order model was fit-ted. The optimum point was defined using a canonical formof the model.

Multifactor variance analysis (ANOVA), first and sec-ond order polynomials and response surface plots werecomputed using a statistical software program (Statgraph-ics Plus 2.1.). Optimum extraction condition was obtainedusing a canonical form of the model.

The effect sum of squares of temperature and time aswell as the interactions between them on the yield, gelling

Table 1Coded levels and real values for the factorial design and yield, gelling temperature, melting temperature and apparent viscosity obtained from the nativeagar extraction from Hydropuntia cornea

Trial no. Coded values Real values Results

X1 X2 Temp. (�C) Time (h) Yield (%) Gelling temp. (�C) Melting temp. (�C) Apparent viscosity (cps)

1 �1 �1 80.0 2.0 28.8 25.0 65.0 3.82 �1 1 100.0 2.0 41.9 30.6 75.5 7.03 1 �1 80.0 4.0 30.9 31.3 78.0 91.54 1 1 100.0 4.0 40.4 29.9 77.5 57.05 0 0 90.0 3.0 33.7 31.5 76.5 53.16 0 0 90.0 3.0 34.6 30.5 78.3 52.57 0 0 90.0 3.0 33.9 31.8 79.0 53.18 0 0 90.0 3.0 32.1 31.9 77.5 56.39 0 0 90.0 3.0 32.6 32.1 77.0 58.5

10 0 +1.4142 90.0 4.4 36.5 30.0 73.5 5.811 +1.4142 0 100.0 3.0 43.4 31.4 76.9 38.312 �1.4142 0 75.9 3.0 27.3 30.0 76.6 63.413 0 +1.4142 90.0 1.6 35.0 25.8 73.3 5.8

1280 F. Pereira-Pacheco et al. / Bioresource Technology 98 (2007) 1278–1284

and melting temperature and apparent viscosity were deter-mined by ANOVA analysis. The p-value was used to con-firm the significance of factors studied. The quadratic effectof the independent variables was not considered importantbecause it does not have any meaning from the technicalpoint of view.

For agar extraction, dry algae (10 g) were soaked in1.8 L distilled water and pH was adjusted between 6.3and 6.4. The mixture was heated in a water bath at the tem-perature and time indicated by the experimental design.The extract was mixed with diatomaceous earth (CELITE,Mexico) and pressure filtered. The filtrate was allowed togel at room temperature, frozen for two days and thenthawed. Finally, the agar was oven-dried at 60 �C, cooledand weighed to calculate percent agar yield.

2.2. Physico-chemical properties

Gelling and melting temperatures were measured asdescribed by Freile-Pelegrın and Robledo (1997a). Appar-ent viscosity was measured at 60 �C in a Cole Parmer (Ver-non Hills, IL) viscosimeter model 98936-10 using a lowcentipoise adaptor (spindle number 8) at 50 rpm, and18 mL of a 1% agar dispersion in 0.1 M NaCl. Gel strengthwas determined in a 4442 Instron apparatus (Norwood,MA) and measured as the resistance of an agar gel(15 mL) to the penetration of a plunger (1.05 cm diameter).The agar solutions (1% w/v) were poured into plastic vials(31 mm diameter and 48 mm height) and left for 24 h atroom temperature. The syneresis index was determinedusing 10 g of agar gel (1%) left for 24 h at 7 �C. The indexwas measured as the volume of water released after centri-fuging at 13,000g for 20 min at 20 �C.

Agar sulfate content was analyzed with the spectropho-tometric method described by Jackson and McCandless(1978) using K2SO4 as a standard. The 3,6 anhydrogalac-tose content (3,6 AG) was determined following themethod of Matsuhiro and Zanlungo (1983).

Intrinsic viscosities [g] of agar samples in an aqueous0.75 M NaSCN solution were measured using a Cannon-Ubbelohde (State College, PA) capillary viscometer at35 �C ± 0.5 �C. Viscosimetric molecular weight (M) wascalculated according to the Mark–Houwink equation(Rochas and Lahaye, 1989):

½g� ¼ 0:07M0:72

3. Results and discussion

For agar yield, the first order model ANOVA showedthat lack of fit was not significant (p > 0.05), and, therefore,the steepest ascent method was applied. However, thismethod suggested high times (>10 h) and temperatures(above 100 �C), that are impractical in industrial applica-tions. In response, all experiments (Table 1) were done todetermine which extraction condition produced the highestyield. The ANOVA of all the yields exhibited significantdifferences (p < 0.05), probably due to a quadratic effect,assuming a maximum. On the contrary, the response sur-face showed a minimum (Fig. 1). The greatest agar yieldswere obtained with the extractions at 100 �C/2 h and100 �C/3 h (Table 1). To verify the maximum obtainedyields, five replicates of these conditions were done and aStudent’s t-test applied. Agar yield at 100 �C/2 h was40.3% ± 0.02 and for 100 �C/3 h yield was 43.3% ± 0.03.A significant difference (p < 0.05) was observed betweenthe treatments, and the 100 �C/3 h treatment was chosenas producing the maximum agar yield. The effect of tem-perature and time and their interaction on agar propertiesrevealed that temperature was the most relevant variableaffecting agar yield (p < 0.05).

For gelling temperature, the second order modelANOVA exhibited significant difference (p < 0.05) due toa quadratic effect, and the response surface showed a max-imum (Fig. 2). The statistically optimum gelling tempera-ture (32.0 �C) was also that at 100 �C/3 h. Optimum

Fig. 2. Response surface of gelling temperature of native agar fromHydropuntia cornea from Yucatan.

Fig. 3. Response surface of melting temperature of native agar fromHydropuntia cornea from Yucatan.

Fig. 1. Response surface of yield of native agar from Hydropuntia cornea

from Yucatan.

F. Pereira-Pacheco et al. / Bioresource Technology 98 (2007) 1278–1284 1281

gelling temperature was obtained from the canonical formof the model using the following second order model:

Y ¼ 31:56þ 0:772489X 1 þ 1:43716X 2 � 0:456875X 21

� 1:84938X 22 � 1:75X 1X 2

X1 is temperature; X2 is time.For melting temperature, the lack of fit in the first order

model ANOVA showed significant differences (p < 0.05),probably due to a quadratic effect. Based on this, all theremaining experiments were carried out (Table 1). The lackof fit in the second order model ANOVA also showed sig-nificant difference (p < 0.05), indicating that the methodusing the steepest temperature ascent should be used. Thismethod, however, suggested the use of times greater than10 h and temperatures above 100 �C, which are impractical

in industrial applications. Therefore, all melting tempera-ture values (Table 1) were analyzed, with the optimum(78 �C) at 80 �C/4 h and 90 �C/3 h (77.7 �C on average)(Fig. 3). Because the treatment at 100 �C/3 h producedthe best results for yield and gelling temperature, a Stu-dent’s t-test was performed on five replicates for treatmentsat 90 �C/3 h and 100 �C/3 h. Melting values were recordedof 77.7 for 90 �C/3 h and 78 �C for 100 �C/3 h. There wasno significant difference (p > 0.05) between the treatments,and the 100 �C/3 h extraction condition was selected asproducing the maximum melting temperature (78 �C).The corresponding ANOVA revealed that temperatureand time, as well as the interaction between them had aremarkable effect on the gelling temperature. However, thiswas not found for the melting temperature where thesevariables were not statistically significant (p > 0.05).

For apparent viscosity, a significant difference (p < 0.05)was detected using the second order model of ANOVA dueto a quadratic effect, and the response surface showed amaximum (Fig. 4). Optimum apparent viscosity wasobtained using the canonical form of the model and the fol-lowing second order model:

Y ¼ 54:708þ 13:6498X 1 þ 17:2X 2 � 4:67396X 21

� 19:714X 22 � 9:44X 1X 2

According to the canonical form of the model, the max-imum feasible apparent viscosity that could be attained was80.7 cPs at 65 �C during 4 h of extraction. Nevertheless, theexperimental viscosity produced under this condition was139.2 cPs (Table 2), though yield was low (14.0%) forindustrial purposes. The RSM result predicts the maxi-mum, feasible data that can be attained, though in somecases greater or lesser values can be obtained. In this case,higher apparent viscosity values were obtained in theexperimental assay, meaning that the predicted value was

Fig. 4. Response surface of apparent viscosity of native agar fromHydropuntia cornea from Yucatan.

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far from the real apparent viscosity value, probably due todata dispersion. The ANOVA showed that time was themost relevant variable concerning to the viscosity at 90%of confidence interval.

Montano et al. (1999) reported apparent viscosities of14 cPs for Gracilaria tenuistipitata C.F. Chang and B.M.Xia native agars and 2090 cPs for Gracilaria arcuata Zan-ardini native agars, both extracted for 1 h at boiling tem-perature. These authors indicated that the analysis wasdone at 75 �C but did not mention the agar concentration,or the measurement conditions (spindle and rpm). As aresult, it is difficult to compare the present results withthose obtained by these authors.

Optimal extraction condition for yield, gelling and melt-ing temperature were found at 100 �C/3 h, whereas extrac-tion condition at 65 �C/4 h resulted in greatest apparentviscosity. These conditions were chosen to evaluate H.

cornea native agar properties. A commercial agar fromGelidium robustum (Gardner) Hollenberg and Abbott(Agarmex no. 010103) was used for comparison; this spe-cies is the only agarophyte exploited and industrialized in

Table 2Physical and chemical properties of native agars from Hydropuntia cornea extrGelidium robustum (n = 3)

Property Native agar (100 �C/3 h) N

Yield (%) 43.3 ± 0.05a 14Gelling temp. (�C) 30.7 ± 0.01a 27Melting temp. (�C) 78.0 ± 1.30a 75Gelling hysteresis (�C) 47.3 ± 1.30a 47Apparent viscosity (cPs) 96.0 ± 1.90a 13Gel strength (g cm�2) 127.0 ± 13.60a 70Syneresis (mL/100 g) 0.50 ± 0.01a 0.Visc. molecular weight 342,072 37Sulfate (%) 6.2 ± 0.10a 6.3,6 AG (%) 35.2 ± 1.00a 31

N.R. = not reported; different letters indicate significant differences (p < 0.05).

Mexico (Robledo, 1998). The agar yield obtained was43.3% at 100 �C/3 h and 14.0% at 65 �C/4 h (Table 2).Under the latter conditions, the temperature did not allowfor the complete extraction of the colloid and yield wasconsequently less. Not surprisingly, industrial yields varydepending on raw material quality. However, they alsovary depending on the species used for agar extractionand even on the locality and collection date for a specificspecies. Within these conditions, yields between 15% and25% are accepted worldwide (Armisen, 1995). The maxi-mum agar yield obtained in the present study was greaterthan those required for industrial applications, and greaterthan that of other native agar yields (Aponte-Dıaz andLemus, 1989; Bird and Hinson, 1992; Oyieke, 1993).

For gelling temperature, the statistical value was similarto the experimental value of 30.7 �C obtained at 100 �C/3 h, and comparable to that obtained from commercialagar (Table 2). Gelling temperature was less under the sec-ond experimental condition (65 �C/4 h). A similar patternwas seen in melting temperature, where, at 100 �C/3 h, itwas greater than that obtained at 65 �C/4 h but less thancommercial agar (Table 2). The functionality of agar inthe food industry depends almost exclusively on its abilityto form thermoreversible gels; therefore, the gelling andmelting temperatures, as well as gelation hysteresis, arecritical parameters in agar quality control (Stanley, 1995).The gelling temperatures in the present study ranged from25 �C to 32.1 �C, and the optimization process indicatedthat the maximum possible gelling temperature was32 �C. Bird and Hinson (1992) extracted native agar fromGracilaria blodgettii Harvey and obtained a similar gellingtemperature (33.5 �C), though Oyieke (1993) reportedlower temperatures (29.5 �C) for Gracilaria gracilis (Stack-house) M. Steentoft, L.M. Irvine and W.F. Farnham (asGracilaria verrucosa Hudson Papenfuss). Montano et al.(1999) extracted native agars from G. tenuistipitata andG. arcuata for 1 h at boiling temperature and recorded gel-ling temperatures of 42.3 �C for G. tenuistipitata and63.5 �C for G. arcuata. These authors mentioned that thehigh gelling temperature of G. arcuata is uncommon andis likely due to the colloid’s high molecular weight.

acted at 100 �C/3 h and 65 �C/4 h compared with AGARMEX agar from

ative agar (65 �C/4 h) Commercial agar from AGARMEX

.0 ± 1.30b N.R.

.2 ± 0.10b 30.5 ± 0.10a

.0 ± 0.40b 80.7 ± 0.61c

.8 ± 0.40a 50.2 ± 0.50b

9.2 ± 7.70b 8.3 ± 0.01c

.0 ± 2.40b 466.1 ± 28.40c

50 ± 0.01a 5.00 ± 0.01b

1,808 121,8866 ± 0.04b 2.8 ± 0.03c

.3 ± 0.09b 45.0 ± 0.60c

F. Pereira-Pacheco et al. / Bioresource Technology 98 (2007) 1278–1284 1283

The maximum melting temperature (78.0 �C) obtainedin the present study was similar to that of native agar fromG. blodgetti (Cote and Hanisak, 1986). Bird and Hinson(1992) extracted native agars from Gracilaria tikvahiae

McLachlan and G. blodgetti, reporting melting tempera-tures of 78.0 �C and 92.0 �C, respectively. Oyieke (1993)worked with Gracilaria species and obtained melting tem-peratures from 79.8 �C to 94.8 �C, which are greater thanthose of H. cornea.

Gel strengths of H. cornea native agar recovered underthe present experimental conditions were comparable withnative agar from other species. At 95 �C for 3 h, Oyieke(1993) reported native agar gel strengths ranging from 60to 99 g cm�2 for Gracilaria canaliculata Sonder (as Graci-laria crassa Harvey ex J. Agardh), from 60 to 198 g cm�2

for Gracilaria millardettii (Montagne) J. Agardh, from125 to 205 g cm�2 for Gracilaria corticata (J. Agardh) J.Agardh, from 199 to 203 g cm�2 for G. gracilis and from205 to 220 g cm�2 for Gracilaria salicornia (C. Agardh)E.Y. Dawson.

An increase in 3,6 AG content corresponds to anincrease in gel strength (Murano, 1995). This relationshipwas also observed in the present study (Table 2). H. cornea

native agar had 21.8% less 3,6 AG than commercial agar at100 �C/3 h, and 30.4% less at 65 �C/4 h. These values weregreater, however, than those noted by other authors usingGracilaria species. Cote and Hanisak (1986) reported val-ues of 25.2% for Gracilaria lemanaeformis (Bory de Saint-Vincent) Greville native agar and 33.9% for Gracilaria

mammillaris (Montagne) M.A. Howe native agar. Birdand Hinson (1992) reported contents of 24.0% for G. tikva-

hiae native agar and Oyieke (1993) reported concentrationsof 15.2% for G. millardetti native agar and 23.0% for G.

gracilis native agar.The H. cornea native agar extracted at 65 �C exhibited

greater sulfate content than commercial agar from Geli-

dium and even than that extracted under the 100 �C/3 hconditions. Cote and Hanisak (1986) observed high sulfateconcentrations in native agars from G. mammillaris (5.6%)and G. tikvahiae (6.8%). Rebello et al. (1997), however,noted values between 2.2% and 3.4% in native agars fromdifferent Gracilaria species from five different countries.Bird and Hinson (1992) and Oyieke (1993), in comparison,studied the sulfate composition of native agars from differ-ent Gracilaria species and reported lesser values (between1.3% and 3.0%) than those obtained in the present study.Freile-Pelegrın and Robledo (1997a) noted that a mildalkali treatment (0.5% of NaOH) at 90 �C slightly reducesthe sulfate content of H. cornea native agar from Yucatanwithout affecting other agar properties.

An important feature of an agar gel is syneresis, inwhich a gel loses water during aging. This is attributed tocontraction of the polymer network through a slow aggre-gation of helices. This property is not as pronounced foragars containing charged groups and is inversely relatedto agar concentration (Stanley, 1995). In the present study,commercial agar from Gelidium showed higher syneresis

than the H. cornea native agar. Montano et al. (1999) eval-uated syneresis in native and treated agars from G. arcuata

and G. tenuistipitata and observed that native agars hadless syneresis than the treated ones. This property is impor-tant when a weaker binding force is required, and the useof less agar leads to excess syneresis.

It is concluded from the ANOVA results that optimumextraction conditions depend on the desired properties ofthe colloid. Neither temperature nor time affect meltingtemperature, but they do play an important role in gellingtemperature. To produce a yield increase, only temperatureis important, and to produce a viscosity increase, time isthe only variable that contributes significantly. The extrac-tion process using 100 �C and 3 h produced the greatestyield (43.3%) and the greatest gelling (32 �C) and meltingtemperatures (78 �C). Though extraction at 65 �C and 4 hproduced the greatest apparent viscosity (139.2 cPs), theagar yield (14.0%) is less attractive for industrial applica-tions than that obtained at 100 �C/3 h.

There are a number of thickeners and gels on the marketwhich have multiple uses, particularly in the food industry.Their physicochemical properties depend on the specificchemical nature of their different colloids and each one isthus more adequate for certain uses. Most of the propertiesexhibited in the H. cornea native agar extracted at 100 �C/3 h could have industrial applications. Gel strength underthis condition is less than that of commercial agar. How-ever, its apparent viscosity, gelation hysteresis and synere-sis index, together with an excellent agar yield, suggest thatuse of this colloid in the food industry is feasible, mainly inspreads and soft-texture food products. This study, andothers like it addressing H. cornea agar, highlight thepotential exploitation of H. cornea from Yucatan. In addi-tion, mariculture of this species has been successfully donein conjunction with fishermen cooperatives in severalresearch projects (Robledo, 1998). If the H. cornea nativeagar extraction method reported here and the results ofproduction experiments is any indication, this algae speciesholds the potential for rural production and/or industrialscale use in the future, and could prove a significant addi-tional income source for the people of Yucatan.

Acknowledgements

This study was supported by the CONACYT-SAGA-RPA 2002-C01-1057 project. Appreciation is also extendedto CONACYT for the Ph.D. scholarship 129275. Theauthors wish to thank C. Chavez-Quintal for technicalassistance and Oc. David Lora (AGARMEX) for supply-ing commercial agar samples.

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