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Color and chemical stability of spray-dried blueberry extract using mesquite gum as wall material
Journal of Food Composition and Analysis 24 (2011) 889–894
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Original Article
Color and chemical stability of spray-dried blueberry extract using mesquite gum as wall material D.M. Jime´nez-Aguilar a, A.E. Ortega-Regules b, J.D. Lozada-Ramı´rez c,*, M.C.I. Pe´rez-Pe´rez d, E.J. Vernon-Carter e, J. Welti-Chanes a a
Department of Biotechnology and Food Engineering, Instituto Tecnolo´gico de Estudios Superiores de Monterrey, Eugenio Garza Sada Ave 2501, CP 64849, Monterrey, NL, Mexico Department of Biotechnology Engineering, Universidad Polite´cnica de Tlaxcala, Avenida Universidad Polite´cnica No. 1, CP 90180, San Pedro Xalcaltzinco, Tlaxcala, Mexico Department of Chemical and Biological Sciences, Universidad de las Ame´ricas Puebla, Sta. Catarina Ma´rtir, C.P. 72820, Cholula, Puebla, Mexico d Department of Biochemistry Engineering, Instituto Tecnolo´gico de Celaya, Avenida Tecnolo´gico s/n, C.P. 38010, Celaya, Gto, Mexico e Department of Hydraulic Processes, Universidad Auto´noma Metropolitana-Iztapalapa, Av. San Rafael Atlixco No. 186, Vicentina, Iztapalapa, Me´xico D.F., Mexico b c
A R T I C L E I N F O
A B S T R A C T
Article history: Received 31 October 2010 Received in revised form 26 April 2011 Accepted 27 April 2011 Available online 8 May 2011
Blueberry is an important source of anthocyanins, which are highly colored substances recognized for their antioxidant activity. One of the drawbacks of using anthocyanins as food colorant is their low stability. The objective of this study was to evaluate the variations found in color and concentration of the compounds (which produce the color) on spray-dried powders, obtained from blueberry extracts with added mesquite gum. Ethanolic blueberry extracts were concentrated until reaching 35% of soluble solids. They were then spray-dried using mesquite gum as an encapsulating agent at 140 and 160 8C of air inlet temperature and 8.5, 9.1 and 9.6 mL/min of feeding rates. The lowest losses in the content of total phenolics, total anthocyanins, and color of the samples were found in samples dried at 140 8C and 9.1 mL/min. The microencapsulates that were stored for 4 weeks at 4 8C in the absence of light presented low degradation of phenolics (10%), anthocyanins (7%) and antioxidant activity (15%). Final color values were L = 39.87, C = 47.83 and H8 = 28.59, with a total color difference DE = 5. ß 2011 Elsevier Inc. All rights reserved.
Keywords: Color Anthocyanins Phenolics Spray dried Mesquite gum Stability Antioxidant activity Blueberry extracts Food analysis Food composition
1. Introduction Color is one of the most important appearance attributes of food materials, since it influences consumer acceptance (Maskan, 2001). Synthetic food colorants have been related to toxic effects; also, it has been suggested that their consumption affects behavior in children, for example attention-deficit hyperactivity disorder (ADHD) (McCann et al., 2007); therefore consumers are steadily replacing them with natural pigments (Maier et al., 2009; MalienAubert et al., 2001). Anthocyanins are colorant candidates (Maier et al., 2009), because they are representative pigments widely distributed in nature, and are responsible for the attractive red, purple and blue color in many fruits and flowers (Xiong et al., 2006). Anthocyanins also exhibit antioxidant activity (Malien-Aubert et al., 2001) and they possess characteristics known to be effective against cancer, ˜ an et al., 2011). heart and inflammatory diseases (Estupin
* Corresponding author. Tel.: +52 222 229 20 67x4388. E-mail address: [email protected] (J.D. Lozada-Ramı´rez). 0889-1575/$ – see front matter ß 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.jfca.2011.04.012
Blueberry is the fruit of the genus Vaccinium, which belongs to the Ericaceae family. It is recognized for its anthocyanin and flavonoid content, antioxidant activity (Prior et al., 1998; Smith et al., 2000), and for its potential health benefits (Smith et al., 2000). Anthocyanins and phenolics compounds are located at the cellular vacuole (Kalt et al., 1999), mainly at the fruit rind (Lee and Wrolstad, 2004). The main drawback of the use of anthocyanins as food colorants is their low stability (Malien-Aubert et al., 2001). Factors which affect their color and stability are pH, temperature, light, oxygen, ascorbic acid, enzymes, sugars, degradation products and metallic ions (Rodrı´guez-Saona et al., 1999; Xiong et al., 2006). Encapsulation of anthocyanin extracts using spray drying may enhance their stability for them to be used as food colorants. The main objective of the encapsulation process is to build a barrier between the component in the particle and the environment. The barrier is made of compounds with chains that create a network. Its protection or controlled release efficiency depends on the composition and structure of the established wall but also on the operating conditions during the production and storage of these particles (Fuchs et al., 2006).
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Proteins, carbohydrates, fibers and gums are encapsulating agents (Fuchs et al., 2006). Mesquite gum, a natural exudate from the mesquite tree, is a neutral salt of a complex acidic branched polysaccharide formed by a core of b-D-galactose residues, comprising a (1–3)-linked backbone with (1–6)-linked branches, bearing L-arabinose, L-rhamnose, b-D-glucuronate and 4-O-methyl-b-D-glucuronate as single sugar or oligosaccharide side chains. It also contains a small amount of protein (up to 6%) (Lo´pez-Franco et al., 2008), and has been reported to be a good encapsulating agent (Beristain et al., 2002). Although few studies of microencapsulation of anthocyanins by spray drying exist, they show that their compounds have great stability under determined storage conditions (Ersus and Yurdagel, 2007; Tonon et al., 2010). Therefore, the objective of this study was to evaluate changes in color and concentration of the compounds responsible of it on spray-dried powders, which were obtained from blueberry extracts added with mesquite gum. 2. Material and methods
soluble solids and 64 0.4% of moisture) in proportions of 67:33 (v/ v). The resultant slurry (24.5 0.5% of soluble solids and 77 0.3% of moisture) was divided in three parts, and each one was spray-dried. Drying conditions were the following: air inlet temperature 140 2 and 160 3 8C, air flow 7.32 L/min, and feeding rates of 8.5, 9.1 and 9.6 mL/min. For each drying condition described in this work, an independent extraction was performed. 2.4. Preparation of control sample The blueberry concentrated extract was a thick viscous liquid with a large amount of dissolved sugars (35% of soluble solids), which was impossible to spray dry without mesquite gum, due to the sample being adhered to the drying chamber walls, which did not allow the recovery of it. Due to the reasons explained earlier, the control sample was prepared in triplicate by freeze drying, 25 mL of blueberry concentrated extract was placed in a plastic plate and frozen at 40 2 8C, then it was dehydrated for 30 h in a freeze-dryer Lyph-Lock 6 (Labconco, USA) at 90 mm Hg with a chamber temperature of 18 0.5 8C, and a condenser at 66 1 8C.
2.1. Reagents, standards and material 2.5. Moisture sorption isotherms Gallic acid, Folin-Ciocalteu reagent, 2, 2-azino-bis-3-ethylbenzothiazoline-6-sulphonic acid (ABTS), Trolox, potassium persulphate and sodium carbonate were purchased from Sigma-Aldrich (USA). Ethanol (96%) was bought from Quimicam (Me´xico). Salts anhydrous to be used in the moisture sorption determination were lithium chloride, potassium acetate, magnesium chloride, potassium carbonate, magnesium nitrate, sodium bromide, strontium chloride, sodium chloride, potassium chloride, and barium chloride. All reagents and standards used in this work were obtained from Fermont (Me´xico). A total of 15 kg of blueberry (Vaccinium ashei) var. Rabbiteye were collected in Zacatlan, Puebla, Me´xico. Portions of 250 g of the fruit were mashed, mixed and stored in polyethylene bags at 42 8C until extraction. Mesquite gum (Prosopis laevigata) was collected in San Luis Potosı´, Me´xico. Purification of mesquite gum was performed following the technique developed by Beristain et al. (2002). Mesquite gum (160 g) was dissolved in distilled water at room temperature (20 8C), until a volume of 1 L was reached. The mixture was filtered using Whatman paper No 1 and dehydrated in Mini Spray Dryer Bu¨chi B-290 (Switzerland), under the following conditions: inlet temperature 180 2 8C; outlet temperature 92 4 8C, air flow 7.32 L/min, and a feeding rate of 9 mL/min. Powders were stored in polyethylene bags at room temperature until they were about to be used. 2.2. Extraction and concentration of anthocyanins of blueberry Anthocyanins were extracted following the methodology described by Ersus and Yurdagel (2007), with some modifications. Ethanol (96%) was mixed with 1.2 kg of blueberry until a volume of 2 L was reached, then it was stirred in a dark environment at 25 2 8C for 2 h. The resulting extracts were later filtered. Concentration of the blueberry ethanolic extract was performed in a rotavapor Bu¨chi 461 (Switzerland), at 35 8C and a vacuum pressure of 56 cm of Hg, until a level of 35 0.5% of soluble solids was reached (around 700 mL). 2.3. Preparation of microencapsulates by spray drying A solution was prepared at 17% weight/volume (w/v) of mesquite gum in distilled water, which showed levels of 17 1% of soluble solids and 85 0.3% of moisture. Later, the solution was diluted with the blueberry concentrated extract (35% of
Moisture sorption isotherms of microencapsulates were determined at 25 0.1 8C in hermetically sealed glass jars containing salt solutions. Salts used to control relative humidity were LiCl (11.3%), CH3COOK (22.5%), MgCl2 (32.8%), K2CO3 (44.3%), Mg (NO3)2 (53.6%), NaBr (56.6%), SrCl2 (70.1%), NaCl (75.3%), KCl (84.3%), and BaCl2 (90.3%). Samples (0.5 g) in triplicate were placed in glass pans and they were kept inside the glass jars. The weight of samples was registered every two days for four weeks. Experimental moisture sorption data was adjusted to the models of GAB and BET (Venturi et al., 2007). Moisture content was measured according to AOAC method (AOAC, 1997). 2.6. Samples analysis For the quantification of total phenolics content, total anthocyanins content and antioxidant activity, 1.35 g of the microencapsulates or the control sample were dissolved in 5 mL of water, and for the evaluation of the color, 5.36 g were dissolved until reaching a volume of 20 mL. Samples were analyzed in triplicate. 2.6.1. Total phenolics and total monomeric anthocyanins Total phenolic content found in samples was obtained using the Folin-Ciocalteu method, according to Singleton and Rossi (1965). The method presented a linearity (R2 = 0.9971 0.0015) between 3 and 15 ppm of standard gallic acid (final concentration), limit of detection (LOD) 0.40 ppm, limit of quantification (LOQ) 1.30 ppm, repeatability RSD (relative standard deviation) < 2.08%, reproducibility RSD < 2.96%, and an accuracy of 98.67 3.31%. Results were expressed as mg of acid equivalents per g of soluble solids of the extract of blueberry (mg GAE/g ss BE). A solution with 35% of the main sugars (50% glucose and 50% fructose) found in blueberry (Wang et al., 2008) was considered the blank. The content of total anthocyanins of the samples was measured using the pH differential method, according to Lee et al. (2005). Repeatability RSD (relative standard deviation) and reproducibility RSD were lower than 2.81% and 2.78%, respectively. Pigment content was calculated using the molecular weight and molar extinction coefficient of cyanidin-3-glucoside (lmax = 510 nm; 449.2 g/mol; 26 900 L/mol cm). Water was used as blank. Results were expressed as mg of cyanidin-3-glucoside equivalents per g of soluble solids of the extract of blueberry (mg c3 g/g ss BE).
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Table 1 Phenolics, antochyanins, and antioxidant activity of slurries of blueberry obtained before and after spray drying at different air inlet temperatures and feeding rates. Air inlet temperature (˚C)
Air outlet temperature (˚C)
Feeding rate (mL/min)
Moisture of microencapsulates (%)
Total phenolics*
Total anthocyanins**
Antioxidant activity***
140
81 2 80 2 80 2
8.5 9.1 9.6
16.2 0.5a 17.6 0.5ab 20.5 0.9b
19.71 1.73a 22.78 1.68ab 23.69 1.16ab
13.56 1.05a 15.70 0.08b 15.61 0.47b
102.05 3.72a 101.89 2.93ab 102.22 0.62a
160
95 2 95 2 92 2
8.5 9.1 9.6
15.3 0.2c 16.1 0.3c 18.9 1.1ab
18.33 0.89ac 18.24 0.67ac 18.77 0.99ac
12.54 0.76a 12.42 0.48a 11.98 0.42c
96.14 2.91bc 95.89 0.43c 97.7 0.54ac
24.12 1.21ad 24.92 2.64ad
16.52 0.78d 16.42 1.13d
Blueberry concentrated extract (freeze dried sample without mesquite gum) Slurry of blueberry prior spray drying
115.41 1.69d 116.2 2.3d
Different letters in the same column indicate significant differences (P < 0.05). Results expressed in *mg GAE/g soluble solid of blueberry extract (g ss BE), **mg c3g/g ss BE, and *** mmol Trolox/g ss BE. Samples were re-diluted with water, except for the slurry (blueberry concentrated extract with mesquite gum) obtained before spray drying.
2.6.2. Antioxidant activity Antioxidant activity was evaluated using the ABTS method ˜ an et al. (2011). The method presented a described by Estupin linearity (R2 = 0.9992 0.0010) over the concentration range 3– 20 mM of standard Trolox (final concentration), LOD 0.75 mM, LOQ 2.5 mM, repeatability RSD 2.17%, reproducibility RSD < 4.45%, and an accuracy of 100.29 2.46%. Results were expressed as mmol of Trolox per g soluble solids of the extract of blueberry (mg TE/g ss BE). Water was used as blank. In order to compare the results obtained for the spray dried samples with the control sample (freeze-dried without mesquite gum); phenolics, anthocyanins and antioxidant activity were expressed based on the content of soluble solids of the extract of blueberry. 2.6.3. Color Hunter L, a, and b values were determinate using a colorimeter (Color Gard System 05, USA.) with 1 cm of path length optical glass cell (20 mL of the sample). The equipment was set to measure total transmittance using illuminant C, and a 28 observation angle. Hue angle [tan 1 (b/a)], Chroma [(a2 + b2)1/2] and total color difference DE = [square ((Lo L)2 + (ao a)2 + (bo b)2)] were calculated from Hunter a and b values (Maskan, 2001). Lo, ao and bo, represent reference values. 2.7. Storage of powders Petri dishes (55 mm 10 mm) were completely filled with microencapsulated and sealed with Parafilm. Control sample was stored at 25 8C in presence of light (3000 lx), while the samples were maintained at 25 8C in presence and absence of light; for the later samples which were also maintained at 4 8C. Changes in the content of total phenolics, total anthocyanins, antioxidant activity and color were analyzed in triplicate weekly during one month. 2.8. Statistical analysis Data was reported as mean standard deviation for determinations by triplicate. Analysis of variance and Tukey’s tests to identify differences among means were performed and determined using MINITAB (Version 14, Minitab Inc., PA, USA). The level of confidence required for significance was selected at P 0.05. 3. Results and discussion 3.1. Effect of spray drying Dehydrated mesquite gum (10.3 0.5% moisture) has 13.8 0.2 mg GAE and 0.8 2.1 mmol TE of total phenolics content and antioxidant activity per g of soluble solids of mesquite gum, respectively; also total monomeric anthocyanins were not detected.
Although the presence of tannins (phenolic compounds with antioxidant activity) has been reported (0.5–2%, w/w) in mesquite gum (Lo´pez-Franco et al., 2008), low levels of those parameters were found compared with the blueberry concentrated extract. Due to this fact, those parameters were ignored in the determinations. As expected, with increased spray drying temperatures, the higher the quantity of evaporated water, the lower the moisture content of the samples. The moisture of the powders was not significantly affected when the air inlet temperature and the feeding rate were the same (Table 1), this could be explained because all the samples were exposed to the same air outlet temperature, being this parameter responsible for the humidity content of the final product (Lafuente and Welti, 1985). The highest losses of phenolics, anthocyanins and antioxidant activity were obtained at 160 8C with a feed flow rate of 8.5 and 9.1 mL/min, being of 26%, 24% and 17%, respectively. While the samples spray dried at 140 8C with a feeding rate of 9.1 and 9.6 mL/min showed the lowest losses of total anthocyanins (4%) and antioxidant activity (12%). These results reveal that the losses of total phenolics, total anthocyanins, and antioxidant activity are directly related with the air outlet temperature (Table 1). During the spray drying process food products are exposed to the air outlet temperature (Lafuente and Welti, 1985). In spite of the fact that blueberry is a fruit with high content of phenolics compounds (22.7–27.7 mmol GAE/g wet weigh) and low content of vitamin C (0.35–0.49 mmol ascorbic acid/g wet weigh) (Kalt et al., 1999), values obtained with the Folin-Ciocalteu assay for total phenolic quantification (Table 1), could have been lightly overestimated due to the presence of ascorbic acid in the samples (Prior et al., 2005). In Table 1, it can be observed that when there is a reduction in the concentration of phenolics and anthocyanins in the samples, the antioxidant activity is also diminished. It is then concluded that the content of those compounds found in the samples was directly related to its respective antioxidant activity, as previously demonstrated in blueberry (Kalt et al., 1999; Lee and Wrolstad, 2004; Prior et al., 1998; Smith et al., 2000). The color was evaluated in liquid samples and, because of that, the powders were re-diluted with water. Slurry of blueberry with mesquite gum (Table 2) presented a high value of total color change (DE = 7.25), in respect to the extract of blueberry. This effect was produced by the dilution of the extract of blueberry (33%, v) with mesquite gum in solution (67%, v) which was a yellowish fluid (L = 85.90 0.45, a = 1.23 0.34 and b = 35.24 1.45), although, is also possible that anthocyanins did interact with other compounds present in the blueberry extract and/ or mesquite gum (copigmentation) (Rodrı´guez-Saona et al., 1999) since great changes of Hue angle were found. Samples had high values of color parameter a, which is attributed to anthocyanins content (Table 2). Also, it can be observed that with a lower loss of anthocyanins, the lower total
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Table 2 Color parameters of the slurries of blueberry before and after spray drying at different air inlet temperatures and feeding rates. Air inlet temperature (˚C)
Air outlet temperature (˚C)
Feeding rate (mL/min)
Color parameters L
a
B
C
H˚
DE
140
81 2 80 2 80 2
8.5 9.1 9.6
38.27 0.60a 35.80 0.75b 35.87 0.90b
32.88 0.81a 33.33 0.21a 33.46 0.12a
3.06 0.13a 3.40 0.03b 4.15 0.06c
33.02 0.82a 33.50 0.21a 33.71 0.12a
5.31 0.10a 5.33 0.08a 7.07 0.12b
5.66 0.13a 3.49 0.26b 3.25 0.09b
160
95 2 95 2 92 2
8.5 9.1 9.6
39.48 0.50a 37.83 0.03c 36.21 0.56b
34.46 0.05b 33.24 0.25a 33.53 0.28a
3.67 0.09d 4.88 0.05e 5.89 0.02f
34.55 0.05b 33.60 0.05a 34.04 0.08c
6.09 0.14c 8.35 0.11d 9.96 0.34e
6.04 0.23c 4.87 0.34d 3.62 0.31b
30.23 0.53
41.07 0.19
8.26 0.14
41.89 0.18
33.70 0.61c
35.82 0.07c
4.66 0.39e
36.12 0.09d
Blueberry concentrated extract (freeze dried sample without mesquite gum) Slurry of blueberry prior spray drying
11.38 0.21 7.71 0.60b
7.25 0.28 –
Different letters in the same column indicate significant differences (P < 0.05). Samples were re-diluted with water, except for the slurry (blueberry concentrated extract with mesquite gum) obtained prior spray drying. DE was calculated using L, a and b of the slurry obtained prior spray drying (Lo, ao and bo) as reference.
color change (DE) was obtained. As result, the microencapsulates dried at 160 8C showed higher changes of color parameters than samples dried at 140 8C in respect to the sample not dehydrated. The chroma value was proportional to the strength of the color and indicates its degree of saturation (Maskan, 2001), this result suggests higher stability of red color in microencapsulates obtained mainly at 140 8C (Table 2). The Hue angle value is the attribute of color that is perceived (Lee, 2000), and all samples show Hue angle values < 108, therefore they can be described as red samples (Lee, 2000; Rodrı´guez-Saona et al., 1999). Powders obtained at 140 8C of inlet air temperature and 9.1 mL/ min of feeding rate were selected for evaluating the storage stability, because these samples did show lower degradation of total anthocyanins and total phenolics, the loss of antioxidant activity and total color difference were at a low level (3.49), also, it was one of the samples with lower moisture (17.6%). These microencapsulates are shown in Fig. 1. It was also noted that they showed an intense red color.
of microencapsulates were adjusted to the mathematical models of BET and GAB. The prediction made is shown in Fig. 2, where it can be observed that the BET model was only adequate until the value of aw was closer to 0.5, while the model of GAB provided a more accurate prediction of the equilibrium data during the whole interval of aw. BET model presented an error of 4% and a value of the lineal regression coefficient (R2) or polynomial R2 of 0.99, while GAB model had an error of 4.9% and a value of R2 of 0.95. The value of the monolayer moisture content (Xm) indicates the amount of water that is strongly absorbed to specific sites at the surface and is considered as the optimum value at which food is more stable (Gabas et al., 2007; Pe´rez-Alonso et al., 2006). In this study, the values of Xm obtained with the models BET and GAB were similar, 18.9 and 20.9 g water/100 g dry solids, respectively. Those values were higher than those reported for similar products (Pe´rez-Alonso et al., 2006), nevertheless, microencapsulates had a moisture of 17.6% (Table 1), which is closer to the values of Xm recommended for these samples. Therefore it is assumed that the microencapsulates are stable.
3.2. Sorption isotherms 3.3. Storage stability evaluation Microencapsulates spray dried (140 8C of air inlet temperature and 9.1 mL/min of feeding rate) were highly hygroscopic. The moisture of the product rises when the water activity (aw) increases, the rise observed was between 0.264 and 0.957 g of water/g dry solids in aw range of 0.11–0.9. Moisture sorption data
Fig. 1. Spray-dried blueberry extracts obtained at 140˚ C of air inlet temperature and 9.1 mL/min of feeding rate.
Stability of total phenolic content, total anthocyanins, antioxidant activity and color was evaluated under different storage conditions. Selected powders (140 8C of air inlet temperature and 9.1 mL/min of feeding rate) stored in darkness at 4 8C had losses of 10% of total phenolics content (Fig. 3i), 7% of total anthocyanins (Fig. 3ii), and 15% of antioxidant activity (Fig. 3iii) after 4 weeks of storage; meanwhile microencapsulates stored at 25 8C and light had losses of 33%, 24% and 33%, respectively. Losses of phenolic
Fig. 2. Sorption isotherm of blueberry microencapsulates at 25˚ C adjusted to BET and GAB models.
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content, total anthocyanins and antioxidant activity of microencapsulates ware higher in the samples stored at 25 8C and light; similar results were observed in microencapsulates of gelatin gel and pectin gel (Maier et al., 2009). Microencapsulates kept at 25 8C (with and without light) presented statistically similar losses (P < 0.05) of total phenolics, and antioxidant activity (Fig. 3), also an increment of similar of L during the 4 weeks of the study. Nevertheless C and H8 only showed similar features during the 3 first weeks (Fig. 4). It can be inferred that the storage temperature was the factor of greatest impact in the loss of the evaluated compounds, and also of the color. The control sample (stored at 25 8C and light) had the highest losses of phenolics (65%), anthocyanins (65%) and antioxidant activity (75%); this result revealed that mesquite gum was an effective protector wall against degradation by temperature and light. Due to the fact that anthocyanins are the compounds responsible for color, their kinetics of degradation was monitored over the storage period, also, rate constants and half life values of reactions were determined using the equations of first order reaction kinetics: log (Co/Ct) = k t and t1/2 = ln 2/k, where k is the reaction kinetics coefficient, Co is the initial anthocyanin content, Ct is the anthocyanin content at a specific tome and t is the time (weeks) (Ersus and Yurdagel, 2007; Tonon et al., 2010).
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The half-life (t1/2) of the anthocyanins in the powders stored in darkness at 4 8C is about 37 weeks (Table 3), meanwhile, the value for the samples exposed to light at 25 8C is about 10 weeks. These values tell that in presence of light and with an increase in temperature during storage, the degradation rate of anthocyanins increases. On the other side, the data obtained reveal that anthocyanins were successfully protected with the mesquite gum, because the control sample showed only 3 weeks of half-life. The half-life time of anthocyanins in the microencapsulates used in this study was lower compared to the results described by Ersus and Yurdagel (2007), who reported t1/2 = 25–28 months (48 C) and t1/2 = 9–10 months (25 8C) of anthocyanins of black carrots spray dried with maltodextrines (10DE, 20–23DE and 28–31DE); and by the data reported by Tonon et al. (2010) t1/2 = 20–42 months (25 8C) for anthocyanins of ac¸ai juice spray dried with maltodextrin (10DE and 20DE), gum Arabic and Tapioca starch. These differences in the losses of total anthocyanins could be due to the nature of the encapsulating agent, the conditions of storage, the moisture of microencapsulates, and the morphology of the particles (Tonon et al., 2009, 2010). Changes in the color parameter of microencapsulates are shown in Fig. 4. After 4 weeks of storage, the samples presented an increase in lightness (Fig. 4i), especially the ones stored at 25 8C and light. Although the increase in L is less than the one reported in Table 3 Anthocyanin degradation rate constants of blueberry extracts microencapsulates during storage at different light and temperature conditions.
Fig. 3. Changes in total phenolics (i), total anthocyanins (ii), and antioxidant activity (iii) of microencapsulates at different storage conditions.
Storage condition
k (week
Dark at 4˚ C Light at 25˚ C Dark at 25˚ C
0.0185 0.0681 0.0415
1
)
t1/2 (week) 37 10 17
Fig. 4. Changes in L (i), C (ii) and H˚ (iii) of microencapsulates of blueberry extracts at different storage conditions.
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the control sample (10 units), increase in L value is interpreted as an indication of discoloration, which could be provoked by the ˜ an et al., 2011). degradation of anthocyanins (Estupin The C values changed lightly during the storage (Fig. 4ii), this suggests stability of red color in microencapsulates. Powders maintained H8 < 458 (Fig. 4iii), samples conserved the red color (Lee, 2000; Rodrı´guez-Saona et al., 1999). In relation with zero time, samples stored in darkness at 4 8C, light at 25 8C, and darkness at 25 8C, showed DE values of 5, 11 and 7, respectively, showing that light and temperature have some effect on the color changes. The control sample showed a value of DE = 19, so, it is concluded that mesquite gum is a good color protector. In this study, color was no related to the loss of monomeric anthocyanins, because of that, the possibility that polymerization reactions occurred at a low level exists due to the fact that no major variations of Hue angle (9–298) were found in samples (Maier et al., 2009). 4. Conclusions Microencapsulation by spray drying employing mesquite gum as a wall to avoid losses of phenolics, anthocyanins, antioxidant activity and color of blueberry extracts has been evaluated, mainly in products dried at outlet temperature of 80 8C and feeding rate of 9.1 mL/min. The red color of the samples was directly related to the content of anthocyanins found in them. Mesquite gum serves as a good protection agent for the color because it reduces anthocyanin degradation in the microencapsulates exposed to light (3000 lx) and temperatures of 4 and 25 8C. After 4 weeks of storage at 4 8C in darkness, the sample showed minimal changes in color (DE = 5), demonstrating that this process provides an advantage in the conservation of colorants. Acknowledgments Authors acknowledge the financial support from Tecnolo´gico de Monterrey (Research Chair Funds CAT-005), and CONACYT (Post Doctoral and Scholarship Program). References AOAC, 1997. Official Methods Of Analysis of Official Analytical Chemists, 20 ed. AOAC, Gaythersburg, MD, USA, pp. 1110–1117. Beristain, C.I., Azuara, E., Vernon-Carter, E.J., 2002. Effect of water activity on the stability to oxidation spray-dried encapsulated orange peel oil using mesquite gum (Prosopis Juliflora) as wall material. Journal of Food Science 67, 206–211. Ersus, S., Yurdagel, U., 2007. Microencapsulation of anthocyanins pigments of black carrot (Daucuscarota L.) by spray drier. Journal of Food Engineering 80, 805–812. ˜ an, D.C., Schwartz, S.J., Garzo´n, G.A., 2011. Antioxidant activity, total pheEstupin nolics content, anthocyanin, and color stability of isotonic model beverages colored with andes berry (Rubus glaucus Benth) anthocyanin powder. Journal of Food Science 76, S26–S34. Fuchs, M., Turchiuli, C., Bohin, M., Cuvelier, M.E., Ordonnaud, C., Peyrat-Maillard, M.N., Dumoulin, E., 2006. Encapsulation of oil in powder using spray drying and fluidized bed agglomeration. Journal of Food Engineering 75, 27–35. Gabas, A.L., Telis, V.R.P., Sobral, J.A., Telis-Romero, J., 2007. Effect of maltodextrin and Arabic gum in water vapor sorption thermodynamic properties of vacuum dried pineapple pulp powder. Journal of Food Engineering 82, 246–252.
Kalt, W., Forney, F.C., Martin, A., Prior, R.L., 1999. Antioxidant capacity, vitamin C, phenolics, and anthocyanins after fresh storage of small fruits. Journal of Agricultural and Food Chemistry 47, 4638–4644. Lafuente, B., Welti, J., 1985. Quality of spray-dried comminuted orange products as influenced of process variables. In: Proceedings of the Symposium of Advances in the Fruit and Vegetable Juice Industry, (Tel Aviv, March). Juris Druck and Verlag, pp. 239–260. Lee, H., 2000. Objective measurement of red grapefruit juice color. Journal of Agricultural and Food Chemistry 48, 1507–1511. Lee, J., Durst, R.W., Wrolstad, R.E., 2005. Determination of total monomeric anthocyanin pigment content of fruit juices, beverages, natural colorants, and wines by the pH differential method: collaborative study. Journal of AOAC International 88 (5), 1269–1278. Lee, J., Wrolstad, R.E., 2004. Extraction of anthocyanins and polyphenolics from blueberry processing waste. Journal of Food Science 69, C564–C573. Lo´pez-Franco, Y.L., Calderon de la Barca, A.M., Valdez, M.A., Peter, M.G., Rinaudo, M., Chambat, G., Goycoolea, F.M., 2008. Structural characterization of Mesquite (Prosopis velutina) gum and its fractions. Macromolecular Bioscience 8, 749– 757. McCann, D., Barrett, A., Cooper, A., Crumpler, D., Dalen, L., Grimshaw, K., Kitchin, E., Lok, K., Porteous, L., Prince, E., Sonuga-Barke, E., Warner, J., Stevenson, J., 2007. Food additives and hyperactive behaviour in 3-year-old and 8/9-year-old children in the community: a randomised, double-blinded, placebo-controlled trial. The Lancet 370, 1560–1567. Maier, T., Fromm, M., Schieber, A., Kammerer, D.R., Carle, R., 2009. Process and storage stability of anthocyanins and non-anthocyanin phenolics in pectin and gelatin gels enriched with grape pomace extracts. European Food Research and Technology 229, 949–960. Malien-Aubert, C., Dangles, O., Amiot, M.J., 2001. Color stability of commercial anthocyanin-based extracts in relation to the phenolic composition. protective effects by intra and intermolecular copigmentation. Journal of Agricultural and Food Chemistry 49, 170–176. Maskan, M., 2001. Kinetics of color change of kiwifruits during hot air and microwave drying. Journal of Food Engineering 48, 169–175. Pe´rez-Alonso, C., Beristain, C.I., Lobato-Calleros, C., Rodriguez-Huezo, M.E., VernonCarter, E.J., 2006. Thermodynamic analysis of the sorption isotherm of pure and blended carbohydrate polymers. Journal of Food Engineering 77, 753–760. Prior, R.L., Cao, G., Martin, A., Sofic, E., McEwen, J., O’Brien, C., Lischner, N., Ehlenfeldt, M., Kalt, W., Krewer, G., Mainland, C.M., 1998. Antioxidant capacity as influenced by total phenolic and anthocyanin content, maturity, and variety of Vaccinium species. Journal of Agricultural and Food Chemistry 46, 2686–2693. Prior, R.L, Wu, X., Schaich, K., 2005. Standardized methods for the determination of antioxidant capacity and phenolics in foods and dietary supplements. Journal of Agricultural and Food Chemistry 53, 4290–4302. Rodrı´guez-Saona, L.E., Giusti, M.M., Wrolstad, R.E., 1999. Color and pigment stability of red radish and red-fleshed potato anthocyanins in juice model systems. Journal of Food Science 64, 451–456. Singleton, V.L., Rossi, J.A., 1965. Colorimetry of total phenolics with phosphomolybdic–phosphotungtic acid reagents. American Journal of Enology and Viticulture 16, 144–158. Smith, M.A.L., Marley, K.A., Seigler, D., Singletary, K.W., Meline, B., 2000. Bioactive properties of wild blueberry. Journal of Food Science 65, 352–356. Tonon, R.V., Brabet, C., Pallet, D., Brabet, C., Hubinger, M.D., 2009. Physicochemical and morphological characterisation of ac¸ai (Euterpe oleraceae Mart.) powder produced with different carrier agents. International Journal of Food Science and Technology 44, 1950–1958. Tonon, R.V., Brabet, C., Hubinger, M.D., 2010. Anthocyanin stability and antioxidant activity of spray-dried ac¸ai (Euterpe oleracea Mart.) juice produced with different carrier agents. Food Research International 43, 907–914. Venturi, L., Rocculi, P., Cavani, C., Placucci, G., Dalla Rosa, M., Cremonini, M.A., 2007. Water absorption of freeze-dried meat at different water activities: an multianalytical approach using sorption isotherm, differential scanning calorimetry, and nuclear magnetic resonance. Journal of Agricultural and Food Chemistry 55, 10572–10578. Wang, S., Chen, C.T., Sciarappa, W., Wang, C.Y., Camp, M.J., 2008. Fruit quality, antioxidant capacity, and flavonoid content of organically and conventionally grown blueberries. Journal of Agricultural and Food Chemistry 56, 5788–5794. Xiong, S., Melton, L.D., Easteal, A.J., Siew, D., 2006. Stability and antioxidant activity of black currant anthocyanins in solution and encapsulated in glucan gel. Journal of Agricultural and Food Chemistry 54, 6201–6208.
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Original Article
Color and chemical stability of spray-dried blueberry extract using mesquite gum as wall material D.M. Jime´nez-Aguilar a, A.E. Ortega-Regules b, J.D. Lozada-Ramı´rez c,*, M.C.I. Pe´rez-Pe´rez d, E.J. Vernon-Carter e, J. Welti-Chanes a a
Department of Biotechnology and Food Engineering, Instituto Tecnolo´gico de Estudios Superiores de Monterrey, Eugenio Garza Sada Ave 2501, CP 64849, Monterrey, NL, Mexico Department of Biotechnology Engineering, Universidad Polite´cnica de Tlaxcala, Avenida Universidad Polite´cnica No. 1, CP 90180, San Pedro Xalcaltzinco, Tlaxcala, Mexico Department of Chemical and Biological Sciences, Universidad de las Ame´ricas Puebla, Sta. Catarina Ma´rtir, C.P. 72820, Cholula, Puebla, Mexico d Department of Biochemistry Engineering, Instituto Tecnolo´gico de Celaya, Avenida Tecnolo´gico s/n, C.P. 38010, Celaya, Gto, Mexico e Department of Hydraulic Processes, Universidad Auto´noma Metropolitana-Iztapalapa, Av. San Rafael Atlixco No. 186, Vicentina, Iztapalapa, Me´xico D.F., Mexico b c
A R T I C L E I N F O
A B S T R A C T
Article history: Received 31 October 2010 Received in revised form 26 April 2011 Accepted 27 April 2011 Available online 8 May 2011
Blueberry is an important source of anthocyanins, which are highly colored substances recognized for their antioxidant activity. One of the drawbacks of using anthocyanins as food colorant is their low stability. The objective of this study was to evaluate the variations found in color and concentration of the compounds (which produce the color) on spray-dried powders, obtained from blueberry extracts with added mesquite gum. Ethanolic blueberry extracts were concentrated until reaching 35% of soluble solids. They were then spray-dried using mesquite gum as an encapsulating agent at 140 and 160 8C of air inlet temperature and 8.5, 9.1 and 9.6 mL/min of feeding rates. The lowest losses in the content of total phenolics, total anthocyanins, and color of the samples were found in samples dried at 140 8C and 9.1 mL/min. The microencapsulates that were stored for 4 weeks at 4 8C in the absence of light presented low degradation of phenolics (10%), anthocyanins (7%) and antioxidant activity (15%). Final color values were L = 39.87, C = 47.83 and H8 = 28.59, with a total color difference DE = 5. ß 2011 Elsevier Inc. All rights reserved.
Keywords: Color Anthocyanins Phenolics Spray dried Mesquite gum Stability Antioxidant activity Blueberry extracts Food analysis Food composition
1. Introduction Color is one of the most important appearance attributes of food materials, since it influences consumer acceptance (Maskan, 2001). Synthetic food colorants have been related to toxic effects; also, it has been suggested that their consumption affects behavior in children, for example attention-deficit hyperactivity disorder (ADHD) (McCann et al., 2007); therefore consumers are steadily replacing them with natural pigments (Maier et al., 2009; MalienAubert et al., 2001). Anthocyanins are colorant candidates (Maier et al., 2009), because they are representative pigments widely distributed in nature, and are responsible for the attractive red, purple and blue color in many fruits and flowers (Xiong et al., 2006). Anthocyanins also exhibit antioxidant activity (Malien-Aubert et al., 2001) and they possess characteristics known to be effective against cancer, ˜ an et al., 2011). heart and inflammatory diseases (Estupin
* Corresponding author. Tel.: +52 222 229 20 67x4388. E-mail address: [email protected] (J.D. Lozada-Ramı´rez). 0889-1575/$ – see front matter ß 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.jfca.2011.04.012
Blueberry is the fruit of the genus Vaccinium, which belongs to the Ericaceae family. It is recognized for its anthocyanin and flavonoid content, antioxidant activity (Prior et al., 1998; Smith et al., 2000), and for its potential health benefits (Smith et al., 2000). Anthocyanins and phenolics compounds are located at the cellular vacuole (Kalt et al., 1999), mainly at the fruit rind (Lee and Wrolstad, 2004). The main drawback of the use of anthocyanins as food colorants is their low stability (Malien-Aubert et al., 2001). Factors which affect their color and stability are pH, temperature, light, oxygen, ascorbic acid, enzymes, sugars, degradation products and metallic ions (Rodrı´guez-Saona et al., 1999; Xiong et al., 2006). Encapsulation of anthocyanin extracts using spray drying may enhance their stability for them to be used as food colorants. The main objective of the encapsulation process is to build a barrier between the component in the particle and the environment. The barrier is made of compounds with chains that create a network. Its protection or controlled release efficiency depends on the composition and structure of the established wall but also on the operating conditions during the production and storage of these particles (Fuchs et al., 2006).
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Proteins, carbohydrates, fibers and gums are encapsulating agents (Fuchs et al., 2006). Mesquite gum, a natural exudate from the mesquite tree, is a neutral salt of a complex acidic branched polysaccharide formed by a core of b-D-galactose residues, comprising a (1–3)-linked backbone with (1–6)-linked branches, bearing L-arabinose, L-rhamnose, b-D-glucuronate and 4-O-methyl-b-D-glucuronate as single sugar or oligosaccharide side chains. It also contains a small amount of protein (up to 6%) (Lo´pez-Franco et al., 2008), and has been reported to be a good encapsulating agent (Beristain et al., 2002). Although few studies of microencapsulation of anthocyanins by spray drying exist, they show that their compounds have great stability under determined storage conditions (Ersus and Yurdagel, 2007; Tonon et al., 2010). Therefore, the objective of this study was to evaluate changes in color and concentration of the compounds responsible of it on spray-dried powders, which were obtained from blueberry extracts added with mesquite gum. 2. Material and methods
soluble solids and 64 0.4% of moisture) in proportions of 67:33 (v/ v). The resultant slurry (24.5 0.5% of soluble solids and 77 0.3% of moisture) was divided in three parts, and each one was spray-dried. Drying conditions were the following: air inlet temperature 140 2 and 160 3 8C, air flow 7.32 L/min, and feeding rates of 8.5, 9.1 and 9.6 mL/min. For each drying condition described in this work, an independent extraction was performed. 2.4. Preparation of control sample The blueberry concentrated extract was a thick viscous liquid with a large amount of dissolved sugars (35% of soluble solids), which was impossible to spray dry without mesquite gum, due to the sample being adhered to the drying chamber walls, which did not allow the recovery of it. Due to the reasons explained earlier, the control sample was prepared in triplicate by freeze drying, 25 mL of blueberry concentrated extract was placed in a plastic plate and frozen at 40 2 8C, then it was dehydrated for 30 h in a freeze-dryer Lyph-Lock 6 (Labconco, USA) at 90 mm Hg with a chamber temperature of 18 0.5 8C, and a condenser at 66 1 8C.
2.1. Reagents, standards and material 2.5. Moisture sorption isotherms Gallic acid, Folin-Ciocalteu reagent, 2, 2-azino-bis-3-ethylbenzothiazoline-6-sulphonic acid (ABTS), Trolox, potassium persulphate and sodium carbonate were purchased from Sigma-Aldrich (USA). Ethanol (96%) was bought from Quimicam (Me´xico). Salts anhydrous to be used in the moisture sorption determination were lithium chloride, potassium acetate, magnesium chloride, potassium carbonate, magnesium nitrate, sodium bromide, strontium chloride, sodium chloride, potassium chloride, and barium chloride. All reagents and standards used in this work were obtained from Fermont (Me´xico). A total of 15 kg of blueberry (Vaccinium ashei) var. Rabbiteye were collected in Zacatlan, Puebla, Me´xico. Portions of 250 g of the fruit were mashed, mixed and stored in polyethylene bags at 42 8C until extraction. Mesquite gum (Prosopis laevigata) was collected in San Luis Potosı´, Me´xico. Purification of mesquite gum was performed following the technique developed by Beristain et al. (2002). Mesquite gum (160 g) was dissolved in distilled water at room temperature (20 8C), until a volume of 1 L was reached. The mixture was filtered using Whatman paper No 1 and dehydrated in Mini Spray Dryer Bu¨chi B-290 (Switzerland), under the following conditions: inlet temperature 180 2 8C; outlet temperature 92 4 8C, air flow 7.32 L/min, and a feeding rate of 9 mL/min. Powders were stored in polyethylene bags at room temperature until they were about to be used. 2.2. Extraction and concentration of anthocyanins of blueberry Anthocyanins were extracted following the methodology described by Ersus and Yurdagel (2007), with some modifications. Ethanol (96%) was mixed with 1.2 kg of blueberry until a volume of 2 L was reached, then it was stirred in a dark environment at 25 2 8C for 2 h. The resulting extracts were later filtered. Concentration of the blueberry ethanolic extract was performed in a rotavapor Bu¨chi 461 (Switzerland), at 35 8C and a vacuum pressure of 56 cm of Hg, until a level of 35 0.5% of soluble solids was reached (around 700 mL). 2.3. Preparation of microencapsulates by spray drying A solution was prepared at 17% weight/volume (w/v) of mesquite gum in distilled water, which showed levels of 17 1% of soluble solids and 85 0.3% of moisture. Later, the solution was diluted with the blueberry concentrated extract (35% of
Moisture sorption isotherms of microencapsulates were determined at 25 0.1 8C in hermetically sealed glass jars containing salt solutions. Salts used to control relative humidity were LiCl (11.3%), CH3COOK (22.5%), MgCl2 (32.8%), K2CO3 (44.3%), Mg (NO3)2 (53.6%), NaBr (56.6%), SrCl2 (70.1%), NaCl (75.3%), KCl (84.3%), and BaCl2 (90.3%). Samples (0.5 g) in triplicate were placed in glass pans and they were kept inside the glass jars. The weight of samples was registered every two days for four weeks. Experimental moisture sorption data was adjusted to the models of GAB and BET (Venturi et al., 2007). Moisture content was measured according to AOAC method (AOAC, 1997). 2.6. Samples analysis For the quantification of total phenolics content, total anthocyanins content and antioxidant activity, 1.35 g of the microencapsulates or the control sample were dissolved in 5 mL of water, and for the evaluation of the color, 5.36 g were dissolved until reaching a volume of 20 mL. Samples were analyzed in triplicate. 2.6.1. Total phenolics and total monomeric anthocyanins Total phenolic content found in samples was obtained using the Folin-Ciocalteu method, according to Singleton and Rossi (1965). The method presented a linearity (R2 = 0.9971 0.0015) between 3 and 15 ppm of standard gallic acid (final concentration), limit of detection (LOD) 0.40 ppm, limit of quantification (LOQ) 1.30 ppm, repeatability RSD (relative standard deviation) < 2.08%, reproducibility RSD < 2.96%, and an accuracy of 98.67 3.31%. Results were expressed as mg of acid equivalents per g of soluble solids of the extract of blueberry (mg GAE/g ss BE). A solution with 35% of the main sugars (50% glucose and 50% fructose) found in blueberry (Wang et al., 2008) was considered the blank. The content of total anthocyanins of the samples was measured using the pH differential method, according to Lee et al. (2005). Repeatability RSD (relative standard deviation) and reproducibility RSD were lower than 2.81% and 2.78%, respectively. Pigment content was calculated using the molecular weight and molar extinction coefficient of cyanidin-3-glucoside (lmax = 510 nm; 449.2 g/mol; 26 900 L/mol cm). Water was used as blank. Results were expressed as mg of cyanidin-3-glucoside equivalents per g of soluble solids of the extract of blueberry (mg c3 g/g ss BE).
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Table 1 Phenolics, antochyanins, and antioxidant activity of slurries of blueberry obtained before and after spray drying at different air inlet temperatures and feeding rates. Air inlet temperature (˚C)
Air outlet temperature (˚C)
Feeding rate (mL/min)
Moisture of microencapsulates (%)
Total phenolics*
Total anthocyanins**
Antioxidant activity***
140
81 2 80 2 80 2
8.5 9.1 9.6
16.2 0.5a 17.6 0.5ab 20.5 0.9b
19.71 1.73a 22.78 1.68ab 23.69 1.16ab
13.56 1.05a 15.70 0.08b 15.61 0.47b
102.05 3.72a 101.89 2.93ab 102.22 0.62a
160
95 2 95 2 92 2
8.5 9.1 9.6
15.3 0.2c 16.1 0.3c 18.9 1.1ab
18.33 0.89ac 18.24 0.67ac 18.77 0.99ac
12.54 0.76a 12.42 0.48a 11.98 0.42c
96.14 2.91bc 95.89 0.43c 97.7 0.54ac
24.12 1.21ad 24.92 2.64ad
16.52 0.78d 16.42 1.13d
Blueberry concentrated extract (freeze dried sample without mesquite gum) Slurry of blueberry prior spray drying
115.41 1.69d 116.2 2.3d
Different letters in the same column indicate significant differences (P < 0.05). Results expressed in *mg GAE/g soluble solid of blueberry extract (g ss BE), **mg c3g/g ss BE, and *** mmol Trolox/g ss BE. Samples were re-diluted with water, except for the slurry (blueberry concentrated extract with mesquite gum) obtained before spray drying.
2.6.2. Antioxidant activity Antioxidant activity was evaluated using the ABTS method ˜ an et al. (2011). The method presented a described by Estupin linearity (R2 = 0.9992 0.0010) over the concentration range 3– 20 mM of standard Trolox (final concentration), LOD 0.75 mM, LOQ 2.5 mM, repeatability RSD 2.17%, reproducibility RSD < 4.45%, and an accuracy of 100.29 2.46%. Results were expressed as mmol of Trolox per g soluble solids of the extract of blueberry (mg TE/g ss BE). Water was used as blank. In order to compare the results obtained for the spray dried samples with the control sample (freeze-dried without mesquite gum); phenolics, anthocyanins and antioxidant activity were expressed based on the content of soluble solids of the extract of blueberry. 2.6.3. Color Hunter L, a, and b values were determinate using a colorimeter (Color Gard System 05, USA.) with 1 cm of path length optical glass cell (20 mL of the sample). The equipment was set to measure total transmittance using illuminant C, and a 28 observation angle. Hue angle [tan 1 (b/a)], Chroma [(a2 + b2)1/2] and total color difference DE = [square ((Lo L)2 + (ao a)2 + (bo b)2)] were calculated from Hunter a and b values (Maskan, 2001). Lo, ao and bo, represent reference values. 2.7. Storage of powders Petri dishes (55 mm 10 mm) were completely filled with microencapsulated and sealed with Parafilm. Control sample was stored at 25 8C in presence of light (3000 lx), while the samples were maintained at 25 8C in presence and absence of light; for the later samples which were also maintained at 4 8C. Changes in the content of total phenolics, total anthocyanins, antioxidant activity and color were analyzed in triplicate weekly during one month. 2.8. Statistical analysis Data was reported as mean standard deviation for determinations by triplicate. Analysis of variance and Tukey’s tests to identify differences among means were performed and determined using MINITAB (Version 14, Minitab Inc., PA, USA). The level of confidence required for significance was selected at P 0.05. 3. Results and discussion 3.1. Effect of spray drying Dehydrated mesquite gum (10.3 0.5% moisture) has 13.8 0.2 mg GAE and 0.8 2.1 mmol TE of total phenolics content and antioxidant activity per g of soluble solids of mesquite gum, respectively; also total monomeric anthocyanins were not detected.
Although the presence of tannins (phenolic compounds with antioxidant activity) has been reported (0.5–2%, w/w) in mesquite gum (Lo´pez-Franco et al., 2008), low levels of those parameters were found compared with the blueberry concentrated extract. Due to this fact, those parameters were ignored in the determinations. As expected, with increased spray drying temperatures, the higher the quantity of evaporated water, the lower the moisture content of the samples. The moisture of the powders was not significantly affected when the air inlet temperature and the feeding rate were the same (Table 1), this could be explained because all the samples were exposed to the same air outlet temperature, being this parameter responsible for the humidity content of the final product (Lafuente and Welti, 1985). The highest losses of phenolics, anthocyanins and antioxidant activity were obtained at 160 8C with a feed flow rate of 8.5 and 9.1 mL/min, being of 26%, 24% and 17%, respectively. While the samples spray dried at 140 8C with a feeding rate of 9.1 and 9.6 mL/min showed the lowest losses of total anthocyanins (4%) and antioxidant activity (12%). These results reveal that the losses of total phenolics, total anthocyanins, and antioxidant activity are directly related with the air outlet temperature (Table 1). During the spray drying process food products are exposed to the air outlet temperature (Lafuente and Welti, 1985). In spite of the fact that blueberry is a fruit with high content of phenolics compounds (22.7–27.7 mmol GAE/g wet weigh) and low content of vitamin C (0.35–0.49 mmol ascorbic acid/g wet weigh) (Kalt et al., 1999), values obtained with the Folin-Ciocalteu assay for total phenolic quantification (Table 1), could have been lightly overestimated due to the presence of ascorbic acid in the samples (Prior et al., 2005). In Table 1, it can be observed that when there is a reduction in the concentration of phenolics and anthocyanins in the samples, the antioxidant activity is also diminished. It is then concluded that the content of those compounds found in the samples was directly related to its respective antioxidant activity, as previously demonstrated in blueberry (Kalt et al., 1999; Lee and Wrolstad, 2004; Prior et al., 1998; Smith et al., 2000). The color was evaluated in liquid samples and, because of that, the powders were re-diluted with water. Slurry of blueberry with mesquite gum (Table 2) presented a high value of total color change (DE = 7.25), in respect to the extract of blueberry. This effect was produced by the dilution of the extract of blueberry (33%, v) with mesquite gum in solution (67%, v) which was a yellowish fluid (L = 85.90 0.45, a = 1.23 0.34 and b = 35.24 1.45), although, is also possible that anthocyanins did interact with other compounds present in the blueberry extract and/ or mesquite gum (copigmentation) (Rodrı´guez-Saona et al., 1999) since great changes of Hue angle were found. Samples had high values of color parameter a, which is attributed to anthocyanins content (Table 2). Also, it can be observed that with a lower loss of anthocyanins, the lower total
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Table 2 Color parameters of the slurries of blueberry before and after spray drying at different air inlet temperatures and feeding rates. Air inlet temperature (˚C)
Air outlet temperature (˚C)
Feeding rate (mL/min)
Color parameters L
a
B
C
H˚
DE
140
81 2 80 2 80 2
8.5 9.1 9.6
38.27 0.60a 35.80 0.75b 35.87 0.90b
32.88 0.81a 33.33 0.21a 33.46 0.12a
3.06 0.13a 3.40 0.03b 4.15 0.06c
33.02 0.82a 33.50 0.21a 33.71 0.12a
5.31 0.10a 5.33 0.08a 7.07 0.12b
5.66 0.13a 3.49 0.26b 3.25 0.09b
160
95 2 95 2 92 2
8.5 9.1 9.6
39.48 0.50a 37.83 0.03c 36.21 0.56b
34.46 0.05b 33.24 0.25a 33.53 0.28a
3.67 0.09d 4.88 0.05e 5.89 0.02f
34.55 0.05b 33.60 0.05a 34.04 0.08c
6.09 0.14c 8.35 0.11d 9.96 0.34e
6.04 0.23c 4.87 0.34d 3.62 0.31b
30.23 0.53
41.07 0.19
8.26 0.14
41.89 0.18
33.70 0.61c
35.82 0.07c
4.66 0.39e
36.12 0.09d
Blueberry concentrated extract (freeze dried sample without mesquite gum) Slurry of blueberry prior spray drying
11.38 0.21 7.71 0.60b
7.25 0.28 –
Different letters in the same column indicate significant differences (P < 0.05). Samples were re-diluted with water, except for the slurry (blueberry concentrated extract with mesquite gum) obtained prior spray drying. DE was calculated using L, a and b of the slurry obtained prior spray drying (Lo, ao and bo) as reference.
color change (DE) was obtained. As result, the microencapsulates dried at 160 8C showed higher changes of color parameters than samples dried at 140 8C in respect to the sample not dehydrated. The chroma value was proportional to the strength of the color and indicates its degree of saturation (Maskan, 2001), this result suggests higher stability of red color in microencapsulates obtained mainly at 140 8C (Table 2). The Hue angle value is the attribute of color that is perceived (Lee, 2000), and all samples show Hue angle values < 108, therefore they can be described as red samples (Lee, 2000; Rodrı´guez-Saona et al., 1999). Powders obtained at 140 8C of inlet air temperature and 9.1 mL/ min of feeding rate were selected for evaluating the storage stability, because these samples did show lower degradation of total anthocyanins and total phenolics, the loss of antioxidant activity and total color difference were at a low level (3.49), also, it was one of the samples with lower moisture (17.6%). These microencapsulates are shown in Fig. 1. It was also noted that they showed an intense red color.
of microencapsulates were adjusted to the mathematical models of BET and GAB. The prediction made is shown in Fig. 2, where it can be observed that the BET model was only adequate until the value of aw was closer to 0.5, while the model of GAB provided a more accurate prediction of the equilibrium data during the whole interval of aw. BET model presented an error of 4% and a value of the lineal regression coefficient (R2) or polynomial R2 of 0.99, while GAB model had an error of 4.9% and a value of R2 of 0.95. The value of the monolayer moisture content (Xm) indicates the amount of water that is strongly absorbed to specific sites at the surface and is considered as the optimum value at which food is more stable (Gabas et al., 2007; Pe´rez-Alonso et al., 2006). In this study, the values of Xm obtained with the models BET and GAB were similar, 18.9 and 20.9 g water/100 g dry solids, respectively. Those values were higher than those reported for similar products (Pe´rez-Alonso et al., 2006), nevertheless, microencapsulates had a moisture of 17.6% (Table 1), which is closer to the values of Xm recommended for these samples. Therefore it is assumed that the microencapsulates are stable.
3.2. Sorption isotherms 3.3. Storage stability evaluation Microencapsulates spray dried (140 8C of air inlet temperature and 9.1 mL/min of feeding rate) were highly hygroscopic. The moisture of the product rises when the water activity (aw) increases, the rise observed was between 0.264 and 0.957 g of water/g dry solids in aw range of 0.11–0.9. Moisture sorption data
Fig. 1. Spray-dried blueberry extracts obtained at 140˚ C of air inlet temperature and 9.1 mL/min of feeding rate.
Stability of total phenolic content, total anthocyanins, antioxidant activity and color was evaluated under different storage conditions. Selected powders (140 8C of air inlet temperature and 9.1 mL/min of feeding rate) stored in darkness at 4 8C had losses of 10% of total phenolics content (Fig. 3i), 7% of total anthocyanins (Fig. 3ii), and 15% of antioxidant activity (Fig. 3iii) after 4 weeks of storage; meanwhile microencapsulates stored at 25 8C and light had losses of 33%, 24% and 33%, respectively. Losses of phenolic
Fig. 2. Sorption isotherm of blueberry microencapsulates at 25˚ C adjusted to BET and GAB models.
D.M. Jime´nez-Aguilar et al. / Journal of Food Composition and Analysis 24 (2011) 889–894
content, total anthocyanins and antioxidant activity of microencapsulates ware higher in the samples stored at 25 8C and light; similar results were observed in microencapsulates of gelatin gel and pectin gel (Maier et al., 2009). Microencapsulates kept at 25 8C (with and without light) presented statistically similar losses (P < 0.05) of total phenolics, and antioxidant activity (Fig. 3), also an increment of similar of L during the 4 weeks of the study. Nevertheless C and H8 only showed similar features during the 3 first weeks (Fig. 4). It can be inferred that the storage temperature was the factor of greatest impact in the loss of the evaluated compounds, and also of the color. The control sample (stored at 25 8C and light) had the highest losses of phenolics (65%), anthocyanins (65%) and antioxidant activity (75%); this result revealed that mesquite gum was an effective protector wall against degradation by temperature and light. Due to the fact that anthocyanins are the compounds responsible for color, their kinetics of degradation was monitored over the storage period, also, rate constants and half life values of reactions were determined using the equations of first order reaction kinetics: log (Co/Ct) = k t and t1/2 = ln 2/k, where k is the reaction kinetics coefficient, Co is the initial anthocyanin content, Ct is the anthocyanin content at a specific tome and t is the time (weeks) (Ersus and Yurdagel, 2007; Tonon et al., 2010).
893
The half-life (t1/2) of the anthocyanins in the powders stored in darkness at 4 8C is about 37 weeks (Table 3), meanwhile, the value for the samples exposed to light at 25 8C is about 10 weeks. These values tell that in presence of light and with an increase in temperature during storage, the degradation rate of anthocyanins increases. On the other side, the data obtained reveal that anthocyanins were successfully protected with the mesquite gum, because the control sample showed only 3 weeks of half-life. The half-life time of anthocyanins in the microencapsulates used in this study was lower compared to the results described by Ersus and Yurdagel (2007), who reported t1/2 = 25–28 months (48 C) and t1/2 = 9–10 months (25 8C) of anthocyanins of black carrots spray dried with maltodextrines (10DE, 20–23DE and 28–31DE); and by the data reported by Tonon et al. (2010) t1/2 = 20–42 months (25 8C) for anthocyanins of ac¸ai juice spray dried with maltodextrin (10DE and 20DE), gum Arabic and Tapioca starch. These differences in the losses of total anthocyanins could be due to the nature of the encapsulating agent, the conditions of storage, the moisture of microencapsulates, and the morphology of the particles (Tonon et al., 2009, 2010). Changes in the color parameter of microencapsulates are shown in Fig. 4. After 4 weeks of storage, the samples presented an increase in lightness (Fig. 4i), especially the ones stored at 25 8C and light. Although the increase in L is less than the one reported in Table 3 Anthocyanin degradation rate constants of blueberry extracts microencapsulates during storage at different light and temperature conditions.
Fig. 3. Changes in total phenolics (i), total anthocyanins (ii), and antioxidant activity (iii) of microencapsulates at different storage conditions.
Storage condition
k (week
Dark at 4˚ C Light at 25˚ C Dark at 25˚ C
0.0185 0.0681 0.0415
1
)
t1/2 (week) 37 10 17
Fig. 4. Changes in L (i), C (ii) and H˚ (iii) of microencapsulates of blueberry extracts at different storage conditions.
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the control sample (10 units), increase in L value is interpreted as an indication of discoloration, which could be provoked by the ˜ an et al., 2011). degradation of anthocyanins (Estupin The C values changed lightly during the storage (Fig. 4ii), this suggests stability of red color in microencapsulates. Powders maintained H8 < 458 (Fig. 4iii), samples conserved the red color (Lee, 2000; Rodrı´guez-Saona et al., 1999). In relation with zero time, samples stored in darkness at 4 8C, light at 25 8C, and darkness at 25 8C, showed DE values of 5, 11 and 7, respectively, showing that light and temperature have some effect on the color changes. The control sample showed a value of DE = 19, so, it is concluded that mesquite gum is a good color protector. In this study, color was no related to the loss of monomeric anthocyanins, because of that, the possibility that polymerization reactions occurred at a low level exists due to the fact that no major variations of Hue angle (9–298) were found in samples (Maier et al., 2009). 4. Conclusions Microencapsulation by spray drying employing mesquite gum as a wall to avoid losses of phenolics, anthocyanins, antioxidant activity and color of blueberry extracts has been evaluated, mainly in products dried at outlet temperature of 80 8C and feeding rate of 9.1 mL/min. The red color of the samples was directly related to the content of anthocyanins found in them. Mesquite gum serves as a good protection agent for the color because it reduces anthocyanin degradation in the microencapsulates exposed to light (3000 lx) and temperatures of 4 and 25 8C. After 4 weeks of storage at 4 8C in darkness, the sample showed minimal changes in color (DE = 5), demonstrating that this process provides an advantage in the conservation of colorants. Acknowledgments Authors acknowledge the financial support from Tecnolo´gico de Monterrey (Research Chair Funds CAT-005), and CONACYT (Post Doctoral and Scholarship Program). References AOAC, 1997. Official Methods Of Analysis of Official Analytical Chemists, 20 ed. AOAC, Gaythersburg, MD, USA, pp. 1110–1117. Beristain, C.I., Azuara, E., Vernon-Carter, E.J., 2002. Effect of water activity on the stability to oxidation spray-dried encapsulated orange peel oil using mesquite gum (Prosopis Juliflora) as wall material. Journal of Food Science 67, 206–211. Ersus, S., Yurdagel, U., 2007. Microencapsulation of anthocyanins pigments of black carrot (Daucuscarota L.) by spray drier. Journal of Food Engineering 80, 805–812. ˜ an, D.C., Schwartz, S.J., Garzo´n, G.A., 2011. Antioxidant activity, total pheEstupin nolics content, anthocyanin, and color stability of isotonic model beverages colored with andes berry (Rubus glaucus Benth) anthocyanin powder. Journal of Food Science 76, S26–S34. Fuchs, M., Turchiuli, C., Bohin, M., Cuvelier, M.E., Ordonnaud, C., Peyrat-Maillard, M.N., Dumoulin, E., 2006. Encapsulation of oil in powder using spray drying and fluidized bed agglomeration. Journal of Food Engineering 75, 27–35. Gabas, A.L., Telis, V.R.P., Sobral, J.A., Telis-Romero, J., 2007. Effect of maltodextrin and Arabic gum in water vapor sorption thermodynamic properties of vacuum dried pineapple pulp powder. Journal of Food Engineering 82, 246–252.
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