Carotenoid retention and storage stability of spray-dried encapsulated paprika oleoresin using gum Arabic and Soy protein isolate as wall materials

LWT - Food Science and Technology 44 (2011) 549e557

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Carotenoid retention and storage stability of spray-dried encapsulated paprika oleoresin using gum Arabic and Soy protein isolate as wall materials Martha Paola Rascón a, César I. Beristain b, *, Hugo S. García a, Marco A. Salgado a a b

Unidad de Investigación y Desarrollo de Alimentos, Instituto Tecnológico de Veracruz, M.A. de Quevedo 2779, Veracruz, Ver, 91897 México Instituto de Ciencias Básicas, Universidad Veracruzana, A.P. 575, Xalapa, Veracruz, México

a r t i c l e i n f o

a b s t r a c t

Article history: Received 15 October 2009 Received in revised form 20 August 2010 Accepted 30 August 2010

The performance of gum arabic (GA) and soy protein isolate (SPI) on paprika oleoresin microcapsules preparation and their storage were evaluated. Paprika oleoresin emulsions with a ratio of paprika oleoresin/wall material of 1:4 (w/w) were prepared using high-pressure homogenization, and then spray dried. Both treatments showed that carotenoid retention in the microcapsules increased as inlet air temperature was increased from 160 to 200
C, and the yellow fraction was more stable than the red fraction at all temperatures tested. Microcapsules with the highest carotenoid retention were stored at different aw’s at 35
C. Maximal stability for carotenoid oxidation was found at aw’s of 0.274 and 0.710 for microcapsules prepared with GA and SPI respectively. In both treatments the lowest carotenoid degradation was associated to the minimum integral entropy zone and affected in the same way to the red and yellow pigments, during storage at 35
C. Additionally, in contrast to microcapsules prepared with SPI, GA microcapsules were unable to retain their structural integrity at water activities above 0.743. Ó 2010 Elsevier Ltd. All rights reserved.

Keywords: Spray drying Carotenoid retention Water activity Minimum integral entropy Degradation rate Maximal stability

1. Introduction Paprika oleoresin is a lipophilic matrix obtained by pepper fruits processing, it is mainly formed by glycerides, liposoluble poliphenolic antioxidants and carotenoid pigments. The coloring capacity of these carotenoid pigments makes paprika oleoresin to be commonly used in the food industry as additive. According to Mínguez-Mosquera, Jarén-Galán & Garrido-Fernández (1992) paprika carotenoid pigments can be divided in two isochromatic fractions: red (diesterified capsanthin and capsorubin) and yellow (b-carotene, esterified cryptoxanthin and diesterified zeaxanthin). The structural characteristic of all carotenoid pigments is its polyenoic chain, which is responsible for their physical and chemical properties, and provide this group of natural compounds with their coloring and antioxidant activities and their biological functions (Britton, 1995); nevertheless, this chain of conjugated double bonds also allows carotenoids to be degraded via oxidation processes originated by reactive species (singlet oxygen and free radicals often generated during lipid peroxidation) that are added to the polyenoic chain (Pérez & Mínguez, 2001). Thus, commercial quality of paprika oleoresin depends on a high concentration of carotenoids, the correct proportions between isochromatic fractions of these pigments, and sufficient stability to * Corresponding author. Tel.: þ52 228 841 8900; fax: þ52 228 841 89 32. E-mail address: [email protected] (C.I. Beristain). 0023-6438/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.lwt.2010.08.021

guarantee that the initial chromatic characteristics last throughout its useful life (Jarén & Mínguez, 1999). In industry, the pigment concentrate batch is not used immediately or completely. It is normally employed within a production process, with stock being withdrawn gradually from storage until it is consumed. Thus, the oleoresin may be in use for a long time after the date on which it was prepared (Jarén & Mínguez, 1999). Paprika oleoresin carotenoid degradation has been widely studied. Jarén & Mínguez (1999) found an overall loss of pigmentation in paprika oleoresin subjected to different heat treatments (40, 60, 80 and 100
C), which was more evident with increasing temperature. However, pigmentation loss was not qualitatively uniform. At temperatures below 60
C, the above authors found that the rate of destruction of the yellow pigment fraction was greater than that of the red pigments, and above 60
C, the order of lability of the two fractions was inverted and the red pigment became the more unstable fraction. The existence of such inversion implies an isokinetic point. In a subsequent work, Pérez, Jarén & Mínguez (2000) proved the existence of an isokinetic temperature (Tisok ¼ 82.5
C) through a kinetic study of carotenoid pigment degradation in the two isochromic fractions of six commercial oleoresins, under different reaction conditions (namely, higher temperatures). At temperatures above Tisok, degradation was preferentially towards the red fraction, while at lower temperatures, greater degradation was towards the yellow fraction.

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Pérez & Mínguez (2004) concluded that a more convenient strategy to prevent carotenoid degradation in oily food additives such as paprika oleoresins should be to minimize contact of food with oxygen. This could be achieved by applying vacuum, use of novel packaging materials, or by encapsulation techniques, thus avoiding oxygen-mediated auto-oxidation reactions. It has been established that oxidation of carotenoid pigments depends on the temperature and oxygen pressure under which pigment degradation takes place and on the structural properties of the pigment. Therefore, microencapsulation can be used in order to improve carotenoid stability. Microencapsulation is a method whereby liquid droplets or solid particles are packed into continuous individual walls. The walls or shells are designed to protect the encapsulated material from factors that may cause deterioration (Rosenberg, Kopelman, & Talmon, 1990). Spray drying has been used as an encapsulation method that entraps “active” material within a protective matrix (wall material), which is essentially inert to the material being encapsulated (core material) (Ré, 1998). Numerous materials are commercially available as wall materials (encapsulating agents) for spray drying microencapsulation. Gum arabic has been the encapsulating agent of choice for many years because it is an excellent emulsifier, has a bland flavor and provides very good volatiles retention during the drying process (Beristain & Vernon-Carter, 1994; Rosenberg et al., 1990; Shaikh, Bhosale & Singhal, 2006). However, more recently the use of proteins as wall materials has been proposed (Jimenez, García & Beristain, 2004; Keogh & O’Kennedy, 1999; Kim & Morr, 1996). On the other hand, in addition to a high core material retention by microcapsules, these composites must remain stable during long periods of time. Microcapsule morphology (shape, integrity, and porosity), glass transition temperature and moisture sorption characteristics are important variables involved in the stability of dehydrated foods (Ré, 1998, Sablani, Kasapis, & Rahman, 2007). Water activity has long been considered as one of the most important quality factors especially for long-term storage (Kaya & Kahyaoglu, 2005). Therefore, the determination of water activity and its relationship with the moisture content is significant, and this relationship is described by moisture sorption isotherms. Thermodynamic relationships between water and foodstuffs allows one to estimate heat requirements for certain process, and predict optimum storage conditions for maximal stability of dehydrated foods (Beristain & Vernon-Carter, 1994; Nunes & Rotstein, 1991). Certain thermodynamic parameters can be estimated from the sorption isotherms and this information is useful for understanding the physicochemical binding of water and packaging of dehydrated foods. The point of minimum integral entropy can be interpreted as the required moisture content for forming a monolayer and it is expected where strong bonds between water and food occur and therefore, water is less available to participate in spoilage reactions (Hill, Emmett, & Joyner, 1951; Nunes & Rotstein, 1991). There are several reports in the literature that use thermodynamics water sorption as a useful tool to predict the point of maximum stability of dehydrated foods (Azuara, & Beristain, 2006; Beristain, Azuara, & Vernon-Carter, 2002; Kaya & Kahyaoglu, 2005; Pérez-Alonso, Beristain, Lobato, Rodríguez, & Vernon-Carter, 2006; Rizvi & Benado, 1984). The purpose of the present study was to evaluate the performance of soy protein isolate in comparison to gum arabic on carotenoid retention during spray drying and its storage stability in paprika oleoresin microcapsules.

2. Materials and methods 2.1. Material, chemicals and reagents Paprika oleoresin was obtained from AMCO (Mexico City); soy protein isolate (SPI) and gum arabic (GA) were supplied by ZAVE (Xalapa, Veracruz, Mexico). Acetone and water (Baker) were both of HPLC grade. 2.2. Preparation of emulsions Emulsions were prepared by mixing paprika oleoresin into a suspension of each wall material in deionized water; at a proportion 1:4 (g paprika oleoresin:g wall material) and 0.3 g/L total solids in the case of gum arabic, or 0.125 g/L total solids for SPI, which due to its highly hydrophilic nature it was impractical to prepare at 0.3 g/L. The crude emulsions were then re-circulated through a twin-stage valve homogenizer (APV-1000, Albertslund, Denmark) at 30,000 kPa. 2.3. Emulsion particle size Particle size of the emulsions was determined using a BeckmaneCoulter particle size analyzer model LS230 (Bedford Hills, NY). This measurement was made prior to spray drying. Mean values of the volume percent distribution and the specific surface area were calculated. 2.4. Emulsion stability Emulsions were evaluated for stability using a procedure based on the report of Elizalde, De Kanterewicz, Pilosof, and Bartholomai (1988). In the modified procedure, emulsion stability is determined using stability ratings based on the extent of moisture homogeneity between initial and tested samples of an emulsion stored at 45
C  1
C for 24 h. The procedure consisted in placing 10 mL of the emulsion into a test tube; then, after allowed to stand for 24 h at 45
C  1, 5 mL of the emulsion were removed from the bottom and moisture content was determined (AOAC 1980). Emulsion instability (EI) after 24 h was calculated as follows:

EI ¼

q24h  q0 q0

!  100

(1)

Where “q24h” refers to the percent moisture content after 24 h, and “q0” represents the percent moisture content of the freshly prepared emulsion. Additionally, a visual method for determination of stability was carried out. This method consisted in placing 100 mL of the emulsion before spray drying in a test tube and kept in an oven for 16 h at 50
C (Beristain, García, & Vernon-Carter, 1999). After storage, the test tube was removed from the oven and analyzed for surface oil. 2.5. Preparation of microcapsules by spray-drying Emulsions were spray-dried in a Büchi 290 mini spray dryer (Flawil, Switzerland). The dryer was equipped with a 0.5 mm diameter nozzle. The operating conditions for the dryer were: inlet air temperatures of 160, 180 and 200  5
C and outlet air temperature of 110  5
C. Microcapsules were recovered from the collecting chamber. These powders were stored in a desiccator under vacuum, containing P2O5 to prevent moisture adsorption prior to further studies.

M.P. Rascón et al. / LWT - Food Science and Technology 44 (2011) 549e557

2.6. Carotenoid determination

P ¼ Carotenoid content was determined through a spectrophotometric method proposed by Hornero and Mínguez (2001). For oleoresin capsules, approximately 0.025 g were dissolved in a volumetric flask containing 100 mL of acetone, then filtered and absorbance measurements were made in a diode array spectrophotometer (Agilent model 8453) at 472 and 508 nm. In order to obtain both isochromic carotenoid and total carotenoid fractions; the absorbance values obtained were introduced in the following equations:

CR ¼

A508  2144:0  A472  403:3 270:9

ðmg=mlÞ

(2)

CY ¼

A472  1724:3  A508  403:3 270:9

ðmg=mlÞ

(3)

CT ¼ CR þ CY

ðmg=mlÞ

(4)

R

Where C represents the red isochromatic fraction content, CY represents the yellow isochromatic fraction content, and CT represents total carotenoid content. All carotenoid determinations were carried out in triplicate, before and after the spray drying process and during storage. 2.7. Vapor sorption isotherms Samples of the spray-dried encapsulated paprika oleoresin were placed in desiccators with vacuum (13 kPa) containing P2O5 for 8 d at room temperature (25
C). The moisture sorption data were obtained using the gravimetric method described by Lang, McCune, and Steinberg (1981). One to two g of sample was weighed in triplicate into standard weighing dishes with a circular section on the bottom. Samples were placed in separate desiccators containing saturated salt slurries in the range of water activity from 0.11 to 0.85 using the aw values reported by Labuza, Kaanane, and Chen (1985). The samples were held at 15, 25, and 35
C until equilibrium was reached. Values of water activity were generated using equations reported in the same paper. Equilibrium was assumed when the difference between 2 consecutive weightings was less than 1 mg/g of solids. The time to reach the equilibrium varied from 15 to 25 d. The Guggenheim-Anderson-De Boer (GAB) equation was used in modeling water sorption (Weisser, 1985):

M ¼

M0 Ckaw ð1  kaw Þð1  kaw þ Caw Þ

(5)

Where aw is water activity; M is water content of the sample on dry basis; M0 is the monolayer water content; C is the Guggenheim constant, given by C ¼ c’exp (hm  hn)/RT; where c0 is the equation constant; hm is the heat of sorption of the first layer; hn is the heat of sorption of the multilayer; R is the gas constant; T is the absolute temperature; and k is the constant correcting properties of multilayer molecules with respect to bulk liquid, and given by k ¼ k0 exp (h1  hn)/RT; where k’ is the equation constant; h1 is the heat of condensation of pure water. The parameters values of GAB equation (M0, C and k) were estimated by fitting the mathematical model to the experimental data, using non-linear regression using the Kaleidagraph 4.0 package (Synergy Software, 2457 Perkiomen Avenue Reading, PA 19606-2049, USA). Goodness of fit was evaluated using the average of the relative percentage difference between the experimental and predicted values of the moisture content or mean relative deviation modulus (P) defined by the following equation (Lomauro, Bakshi, & Labuza, 1985):

551

N jM  M j 100 X i pi N Mi

(6)

i¼1

where Mi is the moisture content at observation i; MPi is the predicted moisture content at that observations; and N is the number of observations. It is generally assumed that a good fit is obtained when P < 0.5. 2.8. Thermodynamic properties calculation The isosteric heat of sorption is a differential molar quantity derived from the temperature dependence of the isotherm, and it represents the energies for water molecules binding at a particular hydration level, in contrast to the integral heat, which is the average energy of all molecules already bound at that level (Schneider, 1981). The respective differential and integral entropies are obtained from their differential and integral heats, respectively. The usual entropy discussed qualitatively or quantitatively (statistical mechanics) in terms of order-disorder of the adsorbed molecules is the integral entropy and not the differential entropy (Hill et al., 1951; Rizvi & Benado, 1984). 2.8.1. Differential properties Changes in differential enthalpy at the wateresolid interface at different stages of the adsorption process were determined using Othmer’s equation (Othmer, 1940):

Hv ðTÞ

lnPv ¼

H0v ðTÞ

! lnP0v þ C

(7)

where Pv is vapor pressure of water in the food; P0v is vapor pressure of pure water at the same temperature; Hv(T) is the isosteric heat for water adsorption; H0v(T) is the heat of condensation of pure water; M is moisture; and C is an adsorption constant. A plot of lnPv against lnP0v gives a straight line if the ratio Hv(T)/ 0 Hv(T) is maintained constant in the range of temperatures studied. The net isosteric heat of adsorption or differential enthalpy is defined by:



DHdiff

 T

¼

Hv ðTÞ H0v ðTÞ

! H0v ðTÞ

1

(8)

M

by calculating Hv(T)/H0v(T) with Othmer’s equation and substituting into the last equation, it is possible to estimate the net isosteric heat of adsorption at different temperatures using steam tables. With values obtained for enthalpy changes, the variation in the molar differential entropy (DSdif)T may be estimated using:



DSdiff

 T

¼ S1  SL ¼

   DHdiff RTlnaw T

T

(9)

where S1 ¼ (vS/vN1)T,P is the molar differential entropy of water adsorbed in the food; SL is the molar entropy of pure water in equilibrium with the vapor; S is the total entropy of water adsorbed in the food; N1 is the number of moles of water adsorbed in the food; R is universal gas constant; aw is water activity; and T is temperature (K). 2.8.2. Integral properties Molar integral enthalpy is calculated using an expression similar to that for differential enthalpy, maintaining diffusion pressure constant:

ðDHint ÞT ¼

Hvi ðTÞ H0v ðTÞ

! H0v ðTÞ

1 f

(10)

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where Hvi(T) is integral molar heat of water adsorbed in food and f can be found by (Nunes & Rotstein, 1991).

Wap wv

f ¼ map  ma ¼ RT f ¼ a1 T

Zaw

Zaw Mdlnaw

(11)

0

Mdlnaw

(12)

0

where f is diffusion pressure or surface potential of the food; ma is chemical potential of the adsorbent in the condensed phase; map is chemical potential of the pure adsorbent; Wap is molecular weight of the adsorbent; wv is the molecular weight of water; f/a1 constant is similar to a process at f constant. When values for (DHint) are obtained, changes in molar integral entropy can be calculated using differential enthalpy equation:

ðDSint ÞT ¼ Ss  SL ¼

ðDHint ÞT RTlnaw T

(13)

where SS ¼ S/N1 is integral entropy of water adsorbed in the food. 2.9. Storage stability Fourteen samples containing ca. 1g of microcapsules elaborated with each wall material were placed in desiccators containing saturated solutions of LiCl, MgCl2, Mg(NO3)2 and NaCl for 35 days at 35
C, the water activities of the desiccants were 0.108, 0.318, 0.515 and 0.743 respectively. Two samples of each wall material were withdrawn every 5 d for spectrophotometric measurement. The samples were put into the desiccants immediately after they were spray-dried, and this was taken as the zero time. 2.10. Degradation reaction rate calculation For each isochromatic fraction of paprika oleoresin encapsulated in each wall material and for all water activities (0.108, 0.318, 0.515 and 0.743), the change in concentration was related to treatment time. The degradation reaction rate (Kv) was calculated as the percentage of color retained with time in hours (t). The system assayed followed theoretical kinetics of zero and first order. The result showing the best multiple correlation coefficient (R) was selected. For all microcapsules and water activities assayed, 16 regression lines were obtained for the degradation rate of red and yellow pigments. 2.11. Scanning electron microscopy (SEM) Structure of spray-dried microcapsules equilibrated at different water activities (0.108, 0.515 and 0.743) were evaluated with a scanning electron microscope, Model Jeol JSM-5600lv. The microcapsules were attached to SEM stubs of 2.54 cm diameter using 2-sided adhesive tape. The specimens were coated with goldepalladium (Plasma deposition method) and examined on the SEM at 15 kV. 3. Results and discussion 3.1. Emulsion particle size analysis The preparation of the emulsion to be processed is the first step involved into the process of encapsulation by spray drying. The ability of each encapsulating agent to produce small and uniform particle size is related with its ability to completely cover the oil drops during homogenization and prevents its coalescence after homogenization. In general, all emulsions homogenized at

30,000 kPa showed a log normal distribution which was predictable, because most emulsions prepared by pressure homogenization tend to produce size distribution curves skewed towards large globule sizes (Walstra, 1975). Values of an average particle size of 1.33  0.84 and 1.05  0.66 mm for GA and SPI emulsions respectively were obtained. These results are similar to those found by Kim, Morr, and Schenz (1996) for orange oil emulsions homogenized at 21,000 kPa; they reported average particle size values of 1.473 and 1.517 mm for emulsions elaborated with GA and SPI, respectively. Small particle average sizes prevents droplets coalescence during the dry process and make the emulsion more stable as it is described in the emulsion stability data below. An emulsion with a stable core material (material being encapsulated) into the wall material (encapsulating agent) solution is a critical factor on microencapsulation (Ré, 1998). 3.2. Emulsion stability Three different processes can be concomitantly involved in the rupture of emulsions: creaming, flocculation and coalescence (Elizalde, Bartholomai, & Pilosof 1996). Through stability visual test a volume decrease was appreciated in all emulsions, it is due to moisture less caused by thermal treatment, besides no oil layer separation occurred. Similar results for oil/water emulsions have been reported by Elizalde et al. (1996); under their experimental conditions, no oil layer separation occurred during aging of emulsions so authors suggest that flocculation and creaming were primarily involved in their destabilization. In addition, the small particle size obtained in all emulsions makes coalescence without an oil layer separation less likely. Otherwise, instability index (EI) was found as 8.03 and 0.67 for GA and SPI, respectively. Emulsions prepared with SPI had the smaller EI, the ability of proteins to aid the formation and stabilization of emulsions is well know; so the lower EI of SPI emulsions could be due to the fact that soy protein molecules performed better as mediators in the formation of a stable emulsion by binding both water and oil molecules to form thick barriers which prevented the oil particles from coalescing (Elizalde et al., 1988). EI obtained by Elizalde, Pilosof, & Bartholomai (1991) were between 24  0.3 and 31  1 for soy proteins isolates/corn oil emulsions stirred at 100 Hz, these values were considerably higher than our values, this could due to the homogenization method used; as it was discuses before high-pressure homogenization produce emulsions with small particle average sizes and hence produce a more stable emulsions with small EI. EI > 10 indicates an unstable emulsion, in general, EI of both emulsions were small with fewer tendencies towards instability. 3.3. Effect of inlet temperature on carotenoid retention Paprika oleoresin was encapsulated with both wall materials at 3 drying conditions (Tinlet ¼ 160, 180 and 200
C). The data showed that both isochromatic carotenoid fraction retentions increased with the increase of drying inlet air temperature (Fig. 1). Therefore, good carotenoid retention was obtained in microcapsules prepared with GA and SPI at 200
C. Similar results were obtained by Rosenberg et al. (1990) who worked with microencapsulation of volatiles using gum arabic as wall material. These authors concluded that higher drying temperature increased the encapsulation yield and volatile retention, and further elaborated that this could have been due to increasing air temperature that in turn increased drying rates and reduced the duration of the constant-rate stage of the drying process.

M.P. Rascón et al. / LWT - Food Science and Technology 44 (2011) 549e557

553

10

0.95

0

0.9

Entropy (kJ/mol K)

0

Carotenoid retention (C/C )

5

0.85

-5 -10 -15 -20

0.8

-25 -30

0.75 160

170

180

T

inlet

190

200

10

15

20

25

30

35

Moisture Content (g water /100g dry solids)

Additionally, wall material had influence in both fraction retentions since values obtain with APS were higher than those obtain with GA at 160
C and 180
C, however at 200
C there was no difference between treatments. Therefore, the improvement of carotenoid retention with the increase of the drying inlet air temperature is due to higher temperatures been able to increase the rate of film formation on the surface of powder particles. This crust is firmer and acts as a protective layer that limits core material migration of thermolabile and volatile compounds towards the surface. Independently of drying inlet air temperature, red fraction retentions resulted the most affected in microcapsules made with each wall material, which could be due to the different chemical structure of the two families of compounds (Fig. 1); all drying inlet air temperature used were higher than the isokinetic temperature (Tisok) reported by Pérez et al. (2000) and according with these authors at temperatures above Tisok, degradation is preferentially towards the red fraction. All the pigments of the red fraction have ketone groups in their structure, while no yellow pigment has this type of functional group. The presence of this group is probably the cause of the sharper increase in lability at elevated temperatures by the red pigments (Jarén & Mínguez, 1999). Based on these data, microcapsules of both wall materials obtained with a drying inlet air temperature of 200
C were selected to calculate the thermodynamic properties. Table 1 Parameters of the GAB equation for paprika oleoresin microcapsules, estimated by fitting the mathematical model to the experimental data, by non-linear regression.

SPI

5

(°C)

Fig. 1. Red and yellow carotenoid fraction retentions of paprika oleoresin encapsulated in GA and ISP at different conditions of inlet air temperature (Tinlet ¼ 1 60, 180 y 200
C); ) GA CR, ) GA CY, ) ISP CR, ) ISP CY. Means and standard deviations were calculated of triplicate experiments.

GA

0

210

T (
C)

M0 (g H2O/100 g dry solids)

C

k

R (J/mol K)

P

15 25 35 15 25 35

7.067 6.894 6.846 5.049 4.654 4.150

19.500 16.219 13.872 9.998 10.564 11.746

0.871 0.860 0.841 0.875 0.881 0.898

0.999 0.999 0.999 0.996 0.994 0.998

0.2877 0.2160 0.1784 0.4273 0.3601 0.2831

GA ¼ gum Arabic; SPI ¼ soy protein isolated; T ¼ temperature, Mo ¼ monolayer water content; C ¼ Guggenheim constant; k ¼ constant correcting properties of the multilayer molecules with respect to the bulk liquid; R ¼ universal gas constant; P ¼ mean relative deviation modulus.

Fig. 2. Differential and integral entropy changes as a function of moisture content for paprika oleoresin encapsulated in GA stored at 35
C; ) DSdif, ) DSint.

3.4. Thermodynamic properties The parameters obtained from fitting the GAB model were calculated (Table 1). The GAB model was found to fit the experimental data very well. The mean relative deviation values were less than 0.5 at 15, 25 and 35 for both GA and SPI treatment. The GAB model has provided important information for foodstuff samples, since it is well known that estimation of the monolayer moisture content (M0) and its respective water activity is important to define proper storage conditions (Kaya & Kahyaoglu, 2005). Therefore, it has also been assumed that the monolayer value is the critical water content where dehydrated foods are more stable. In our experiments, monolayer moisture content values for GA and SPI microcapsules at 35
C were 6.846 g H2O/100 g (aw ¼ 0.207) soluble solids and 4.150 g H2O/100 g soluble solids (aw ¼ 0.220), respectively.

30

20

Entropy (kJ/mol K)

150

10

0

-10

-20

0

5

10

15

20

25

30

Moisture Content (g water /100g dry solids) Fig. 3. Differential and integral entropy changes as a function of moisture content for paprika oleoresin encapsulated in SPI stored at 35
C; ) DSdif, ) DSint.

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M.P. Rascón et al. / LWT - Food Science and Technology 44 (2011) 549e557

Table 2 Kinetic parameters obtained from the fit of the concentration of both isochromatic fractions (red and yellow) to first-order kinetics for paprika oleoresin encapsulated with GA and SPI at 35
C. Red fraction

aw

GA

0.108 0.318 0.515 0.743 0.108 0.318 0.515 0.743

SPI

a

Yellow fraction

Kv x 10-3a

Origina

R

Kv x 10-3a

Origina

R

33.09  0.93 55.73  0.63 123.89  1.88 31.60  3.15 197.95  10.94 201.32  2.88 196.45  6.18 40.15  1.94

4.398  0.04 4.547  0.11 5.016  0.00 4.619  0.08 5.783  0.08 5.826  0.03 5.872  0.07 4.812  0.02

0.929 0.997 0.982 0.966 0.931 0.927 0.911 0.952

37.33  1.52 55.41  0.75 130.17  3.98 31.60  3.15 190.3  7.02 209.75  2.25 217.81  11.64 38.55  1.08

4.437  0.01 4.542  0.02 4.885  0.10 4.634  0.03 5.731  0.07 6.065  0.00 6.058  0.14 4.821  0.03

0.956 0.992 0.991 0.990 0.939 0.925 0.913 0.943

Means and standard deviations of triplicate experiments.

Changes occurring in the differential and integral entropies with respect to moisture content at 35
C for paprika oleoresin encapsulated in GA and SPI are depicted in Figs. 2 and 3, respectively. The integral entropy indicates the degree of grade order-disorder in which water molecules are absorbed in the surface of the dehydrated food. The intersection of the curves is found at the minimum integral entropy (DSint), and it can be observed in both cases that as the microcapsules absorb moisture, their integral entropy falls to a minimum. At this point, maximum stability can be assumed, since water molecules are more ordered within the microencapsulating material (Nunes & Rotstein, 1991). Encapsulated paprika oleoresin prepared with GA and SPI at 35
C had a minimum integral entropy value of approximately 7.127 g H2O/ 100 g soluble solids and 11.294 g H2O/100 g soluble solids, respectively. This minimum integral entropy is proposed as the most suitable variable for storage with its corresponding aw can be located from the isotherm and were 0.274 and 0.782, respectively. Paprika oleoresin microcapsules elaborated with SPI showed changes in the entropy in the vicinity of the point of the minimum integral entropy so small that a zone of maximum stability can be established that begins at moisture contents of 11.294 g water/ 100 g soluble solids (aw ¼ 0.721) and ends at 17.235 g water/100 g soluble solids (aw ¼ 0.851). Similar results were reported for canola oil encapsulated in soy protein isolate, which had

a minimum integral entropy value of 10.59 g H2O/100 (aw ¼ 0.68) and its zone of maximum stability begins at 8.00 g water/100 g soluble solids (aw ¼ 0.53) and ends at 16.37 g water/100 g soluble solids (aw ¼ 0.85) (Bonilla, Azuara, Beristain, and Vernon-Carter, 2010). The minimum integral entropy can be interpreted as the moisture content of the monolayer (Hill et al., 1951; Nunes & Rotstein, 1991); microcapsules elaborated with GA had a monolayer value calculated for the GAB equation similar to the point of the minimum integral entropy calculated through thermodynamic analysis. However, monolayer values calculated for microcapsules elaborated with SPI were different to their corresponding minimum integral entropy values. In fact, the moisture content corresponding to the minimum integral entropy value to achieve maximum stability was greater than that corresponding to the GAB monolayer value estimate. Similar results were calculated for orange peel oil encapsulated with mesquite gum, macadamia nuts and canola oil encapsulated in soy protein isolate (Beristain et al., 2002; Bonilla et al., 2010; Domínguez, Azuara, Vernon-Carter, & Beristain, 2007). Although for SPI, the GAB monolayer value was similar to the minimum differential entropy value (5.029 g water/100 g soluble solids), differential entropy does not mean order or disorder of the total system. Instead, differential entropy represents the algebraic sum of the integral entropy at a particular hydration level plus the 5

5 4.5

4 4

T

ln ( C / C

T

0

)

0

ln ( C/C )

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40 Time (days)

Time (days) Fig. 4. Effect of water activity on total carotenoid content degradation of paprika oleoresin encapsulated in gum arabic stored at 35
C and water activities of ) aw ¼ 0.108, ) aw ¼ 0.318, ) aw ¼ 0.575, ) aw ¼ 0.743. Means and standard deviations were calculated of triplicate experiments.

Fig. 5. Degradation of red and yellow carotenoid fraction of paprika oleoresin encapsulated in SPI and GA stored at 35
C and at aw corresponding to its minimum integral entropy respectively: ) CR SPI aw ¼ 0.743, ) CY SPI aw ¼ 0.743, ) CR GA aw ¼ 0.108, ) CY GA aw ¼ 0.108. Means and standard deviations were calculated of triplicate experiments.

M.P. Rascón et al. / LWT - Food Science and Technology 44 (2011) 549e557

change of order or disorder after new water molecules are absorbed by the system at the same hydration level. If the values of moisture content corresponding to minimum integral entropy and minimum differential entropy are different, this particular hydration level at the minimum differential entropy cannot be considered as the maximum stability point, because not all available active sites have been occupied at that particular water content, and therefore it is possible to obtain lower differential changes after this point that provide a better ordering of the water molecules adsorbed on food. Therefore, we assumed that the maximum stability of paprika oleoresin microcapsules corresponds to the minimum integral entropy zone, as in this zone the water molecules are best organized and less available to take part in spoilage reactions. 3.5. Kinetics of degradation of carotenoid content and microstructure morphology of microcapsules Microcapsules of paprika oleoresin were stored at 35
C at four different water activities: 0.108, 0.318, 0.515 and 0.743 during 35 days.

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Relating both isochromatic carotenoid fractions concentration to sample storage time, the pattern of change in concentration with time gives a better mathematical fit when the first-order kinetics model is used. Table 2 shows the kinetic parameters for the degradation of both isochromatic carotenoid fractions (CR and CY) in paprika oleoresin encapsulated with GA and SPI at the four water activities. As the kinetic model is first order, the ordinate at origin in the rate equation is the natural logarithm of the theoretical initial pigment concentration, which for a given oleoresin should be in principle identical at different water activities, although experimentally it ranges within a band of variability. A similar behavior was reported by Jarén & Mínguez (1999) in paprika oleoresin stored at the same water activity but different temperatures (40, 60, 80 and 100
C). The high level of significance in the correlation coefficients yielded by the model used to calculate the kinetic parameters means that the calculated equations reliably represent what really happens during the degradation reaction. The degradation rate constants (Kv) at each water activity allow oleoresin stability to be ranked, revealing similarities and differences in behavior between treatments.

Fig. 6. SEM Micrographs of paprika oleoresin encapsulated in a) gum arabic and b) isolated soy protein at different water activities. (Micron marker 5 mm, MAG  5000).

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In SPI treatments, degradation rate constant increased considerably as the water activity decreases, shown the lowest rate constant and therefore the highest stability at a water activity of 0.743 in both isochromatic carotenoid fractions. This water activity falls into the maximum stability zone calculated through thermodynamic properties. On the other hand, GA treatments showed a different behavior due to increased Kv as the water activity of the microcapsules increased from 0.108 to 0.515, and had the lowest Kv at a water activity of 0.108. Nevertheless, at a water activity of 0.743 the rate constant was almost as small as it was at 0.108. It can be easily see it in the Fig. 4, where degradation during storage of total carotenoid content of paprika oleoresin encapsulated in GA is depicted. However, scanning electron micrographs of GA microcapsules stored at 35
C, demonstrated that at a water activity of 0.743, microstructural changes exist and microcapsules become unable to keep their structural integrity, thus agglomeration occurs (Fig. 6). Similar results were reported by Bonilla et al. (2010) at water activities above of 0.76 evident caking and stickiness were shown by canola oil encapsulated in mesquite gum; whereas soy protein isolate microcapsules remained intact throughout the experimental aw range. Therefore, the low carotenoid degradation exhibited at aw ¼ 0.743 must be due to increased water content by the powder which provoked a change in their flow properties. At this humidity level, sufficient water was absorbed by the microcapsules to form a dough-like mass which acts as a shell opposed to oxygen diffusion into the microcapsule core, inasmuch as water is absorbed without initiating the wall dissolution process (Beristain et al., 2002). Therefore, lowest carotenoid degradation actually occurs at a water activity of 0.108, very close to the maximum stability point calculated through water sorption thermodynamic analysis. Additionally, in contrast with the GA treatment, SPI microcapsules were able to keep their structural integrity at all water activities proved as it can be observed in Fig. 6. The fact that when GA and SPI microcapsules are compared at the same water activities, they show a different degradation rates, indicates that the type of wall material modulate the degradation of the carotenoid pigments. The degradation rates of the yellow carotenoids (CY) were similar than those of the red ones (CR) for microcapsules elaborated with both wall materials at the four water activities proved, during storage at 35
C (Fig. 5). However, higher CY degradation rates were expected due to storage temperature used were lower than the isokinetic temperature (Tisok) and at temperatures under Tisok degradation is preferentially towards the yellow fraction (Pérez et al., 2000). Nevertheless, CY degradation was slightly lower than CR degradation in both treatments at the water activity corresponding to its respective minimum integral entropy point. The behavior obtained must be due to the good performance showed by both wall materials at these water activities to avoiding or limiting oxygen diffusion through microcapsule walls. 4. Conclusions In paprika oleoresin carotenoid pigment loss and therefore color loss takes place as a consequence of the temperature, water activity and oxygen. This study explored the use of microencapsulation to protect paprika oleoresin from degradation during storage, and through the use of thermodynamic properties the best storage conditions are recommended (as a function of temperature and water activity) to avoid carotenoid degradation. Microencapsulation proved to be a convenient strategy to prevent carotenoid degradation avoiding oxygen-mediated auto-oxidation reactions, but its good results

depend on wall material selected. The GAB equation was useful for modeling moisture sorption of GA and SPI in the water activity range studied. The minimum integral entropy can be interpreted as the water activity at which the microcapsules have the best stability to oxidation. On the other hand, degradation reaction rates provided relevant information about the shelf life of the microcapsules containing paprika. The degradation rate constant of carotenoid pigments in paprika oleoresin encapsulated in a wall material is a valid parameter for revealing the quantitative changes involved. Gum arabic showed to be stable at low water activities; however above aw ¼ 0.318, the degradation rate of carotenoid increased substantially and at aw ¼ 0.743 microcapsules became unable to keep their structural integrity and led the gradual dissolution of the walls. On the other hand SPI as wall material shown a very good protection against oxidation to paprika oleoresin microcapsules at high water activities in an interval from 0.721 to 0.851 and the structure of the capsules was not damaged at the water activity range covered in this study. Additionally, the use of certain wall materials as soy protein isolated may represent an improvement in the nutritional value of this preparation. In this way paprika oleoresin microcapsules can be used in the food industry as a colorant in the manufacturing of cheese powders, meat products, potato chips, popcorn, salads, mayonnaise, soups, garnishes, sauce, jellies, jams, beverages, conserves, sausage, and bakery additives, among others. References Azuara, E., & Beristain, C. I. (2006). Enthalpic and entropic mechanisms related to water sorption of yogurt. Drying Technology, 24, 1501e1507. Beristain, C. I., Azuara, E., & Vernon-Carter, E. J. (2002). Effect of water activity on the stability to oxidation of spray-dried encapsulated orange peel oil using mesquite gum (Prosopisjuliflora) as wall material. Journal of Food Science, 67, 206e211. Beristain, C. I., Garcia, H. S., & Vernon-Carter, E. J. (1999). Mesquite gum (Prosopis juli-ora) and maltodextrin blends as wall materials for spray-dried encapsulated orange peel oil. Food Science and Technology International, 5, 353e356. Beristain, C. I., & Vernon-Carter, E. J. (1994). Utililization of mesquite (Prosopisjuliflora) gum as emulsion stabilizing agent for spray-dried encapsulated orange. Drying Technology, 12(7), 1727e1733. Bonilla, E., Azuara, E., Beristain, C. I., & Vernon-Carter, E. J. (2010). Predicting suitable storage conditions for spray-dried microcapsules formed with different biopolymer matrices. Food Hydrocolloids, 24, 633e640. Britton, G. (1995). Structure and properties of carotenoids in relation to function. FASEB Journal, 9, 1551e1558. Domínguez, I. L., Azuara, E., Vernon-Carter, E. J., & Beristain, C. I. (2007). Thermodynamic analysis of the effect of water activity on the stability ofmacadamia nut. Journal of Food Engineering, 81, 566e571. Elizalde, B. E., De Kanterewicz, R. J., Pilosof, A. M. R., & Bartholomai, G. B. (1988). Physicochemical properties of food proteins related to their ability to stabilize oil-in water emulsions. Journal of Food Science, 53, 845e848. Elizalde, B. E., Pilosof, A. M. R., & Bartholomai, G. B. (1991). Prediction of emulsion inestability from emulsion composition and physicochemical properties of proteins. Journal of Food Science, 56, 116e120. Elizalde, B. E., Bartholomai, G. B., & Pilosof, A. M. R. (1996). The effect of pH on the relationship between hydrophilic/lipophilic characteristics and emulsification properties of soy proteins. Lebensmittel Wissenschaft und Technologie, 29, 334e339. Hill, T. L., Emmett, P. H., & Joyner, L. G. (1951). Calculation of thermodynamic functions of adsorbed molecules from adsorption isotherm measurements: nitrogen ongraphon. Journal of the American Chemical Society, 73, 5102e5107. Hornero, D., & Mínguez, M. I. (2001). Rapid spectrophotometric determination of red and yellow isochromic carotenoid fractions in paprika and red pepper oleoresins. Journal of Agricultural and Food Chemistry, 49, 3584e3588. Jarén, M., & Mínguez, M. I. (1999). Quantitative and qualitative changes associated with heat treatments in the carotenoid content of paprika oleoresins. Journal of Agricultural and Food Chemistry, 47, 4379e4383. Jimenez, M., García, H. S., & Beristain, C. I. (2004). Spray-drying microencapsulation and oxidative stability of conjugated linoleic acid. European Food Research and Technology, 219, 588e592. Kaya, S., & Kahyaoglu, T. (2005). Thermodynamic properties and sorption equilibrium of pestil (grape leather). Journal of Food Engineering, 71, 200e207. Keogh, M. K., & O’Kennedy, B. T. (1999). Milk fat microencapsulation using whey proteins. International Dairy Journal, 9, 657e663.

M.P. Rascón et al. / LWT - Food Science and Technology 44 (2011) 549e557 Kim, Y. D., & Morr, C. V. (1996). Microencapsulation properties of gum Arabic and several food proteins: Spray-dried orange oil emulsion particles. Journal of Agricultural and Food Chemistry, 44, 1314e1320. Kim, Y. D., Morr, C. V., & Schenz, T. W. (1996). Microencapsulation properties of gum Arabic and several food proteins: liquid orange oil emulsion particles. Journal of Agricultural and Food Chemistry, 44, 1308e1313. Labuza, T. P., Kaanane, A., & Chen, J. Y. (1985). Effect of temperature on the moisture sorption isotherms and water activity shift of two dehydrated foods. Journal of Food Science, 50, 385e391. Lang, K. W., McCune, T. D., & Steinberg, M. P. (1981). Proximity equilibration cell for rapid determination of sorption isotherms. Journal of Food Science, 46(3), 936e938. Lomauro, C. J., Bakshi, A. S., & Labuza, T. P. (1985). Evaluation of food moisture sorptionisotherm equations. Part I. Fruit, vegetable and meat products. Lebensmittel Wissenschaft Und Technologie, 28, 111e117. Mínguez-Mosquera, M. I., Jaren-Galán, M., & Garrido-Fernández, J. (1992). Color Quality in Paprika. Journal of Agriculture and Food Chemistry, 40, 2384e2388. Nunes, R. V., & Rotstein, E. (1991). Thermodynamics of the waterefoodstuff equilibrium. Drying Technology, 9(1), 113e117. Othmer, D. F. (1940). Correlating vapor pressure and latent heat data. A new plot. Industrial Engineering Chemistry, 32, 841e856. Pérez -Alonso, C., Beristain, C. I., Lobato, C., Rodríguez, M. E., & Vernon-Carter, E. J. (2006). Thermodynamic analysis of the sorption isotherms of pure and blended carbohydrate polymers. Journal of Food Engineering, 77, 753e760. Pérez, A., Jarén, M., & Mínguez, M. I. (2000). Effect of high-temperature degradative processes on ketocarotenoids present in paprika oleoresins. Journal of Agricultural and Food Chemistry, 48, 2966e2971.

557

Pérez, A., & Mínguez, M. I. (2001). Structure-reactivity relationship in the oxidation of carotenoid pigments of the pepper (Capsicum annuum L.). Journal of Agricultural and Food Chemistry, 49, 4864e4869. Pérez, A., & Mínguez, M. I. (2004). Degradation, under non-oxygen-mediated autooxidation, of carotenoid profile present in paprika oleoresins with lipid substrates of different fatty acid composition. Journal of Agricultural and Food Chemistry, 52, 632e637. Ré, M. I. (1998). Microencapsulation by spray drying. Drying Technology, 16(6), 1195e1236. Rizvi, S. S. H., & Benado, A. L. (1984). Thermodynamic properties of dehydrated food. Food Technology, 38(3), 83e92. Rosenberg, M., Kopelman, I. J., & Talmon, Y. (1990). Factors affecting retention in spray-drying microencapsulation of volatile materials. Journal of Agricultural and Food Chemistry, 38, 1288e1294. Sablani, S. S., Kasapis, S., & Rahman, M. S. (2007). Evaluating water activity and glass transitions concepts for food stability. Journal of Food Engineering, 78, 266e271. Schneider, A. S. (1981). Hydration of biological membranes. In L. B. Rockland, & StewartG.F. (Eds.), Water activity influences on food quality (pp. 338e405). New York: Academic Press. Shaikh, J., Bhosale, R., & Singhal, R. (2006). Microencapsulation of black pepper oleoresin. Food Chemistry, 94(1), 105e110. Walstra, P. (1975). Effect of homogenization on fat globule size in milk. Netherlands Milk and Dairy Journal, 29, 279. Weisser, H. (1985). Influence of temperature on sorption equilibria. In D. Simato, & J. L. Multon (Eds.), Properties of water in foods (pp. 133e151). Dordrecht, Netherlands: Martinus Nijhoff Publishers.