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Effect of Different Carrier Agents on Physicochemical Properties of Spray-dried Pineapple (Ananas comosus Merr.) Powder


Abstract

The main purpose of this study is to examine the different physicochemical properties of spray-dried products. The carrier agents and powders after the spray-drying process were analyzed for encapsulation yield, moisture content, color parameters, total polyphenol content (TPC), antioxidant capacity (AC), bulk density, flowability, wettability, hygroscopicity, water solubility index (WSI), particle size and microstructure. The spray-drying process was carried out with different carrier agents including maltodextrin (MD) and the combination of maltodextrin and gum arabic (MD-GA) with MA/GA ratio of 70/30, dried at the inlet/outlet air temperature of 160 °C/70 °C, 4 bar, airflow rate of 70 m3·h-1 and feed flow rate of 750 mL·h-1. The results showed that the different carrier agents have significant influences on the physicochemical properties of the powder produced by the spray-drying method. In there, while the values of recovery efficiency and flowability of spray-dried products from MD are higher than those of spray-dried products from MD-GA combination, the opposite is true for the values of TPC, AC, bulk density and wettability, whereas hygroscopicity and WSI values are equally represented in both products.


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INTRODUCTION

Pineapple has a latin name is Ananas comosus and is the only species in the Bromeliaceae family. Pineapple plants originated in South America, mainly in southern Brazil, northern Argentina and Paraguay. In Vietnam, the pineapple varieties are currently grown in Ananas comosus species. This species is divided into 7 groups including 3 main groups: Cayen, Queen and Spanish pineapple.1 Pineapples are nonclimacteric fruits and should be harvested when ready to eat. The skin color changes from green to yellow at the base of the fruit. A soluble solids content and an acidity in pineapple are approximately 12% and 1%, respectively. In addition, this fruit contains many nutrients such as vitamin C, vitamin B complex, fiber, manganese, copper, calcium, zinc, bromelain, and β-carotene. The flesh is free of fat and cholesterol leading to low calories. Therefore, this delicious tropical fruit is consumed fresh, canned, dehydrated in jams and juice. Besides, pineapple can improve the immune system, aids digestion of proteins, reduce symptoms of the common cold and strengthens bones.2

Although, pineapple has many benefits to human health and was widely applied in the food industry but this fruit has high moisture content and highly perishable because of the growth of microorganisms that leads to the low lifespan of fruit. The rapid deterioration in the quality of pineapple was shown at a decline in sugar content, flavor reduction, excessive softening, and an increase in susceptibility to microorganisms during the storage period. Hence, this fruit should be dried to surmount these postharvest losses and to extend the shelf-life for its availability during the off-season.3 Dried products such as powder bring about a significant reduction in volume and weight, minimize the packaging and storage, leading to reducing transportation costs. Currently, there are many drying methods that can produce dried products, for instance, vacuum drying, freezing drying, spray-drying, foam mat drying, etc.4 In there, the spray-drying was widely used in food technology with various materials from plants or spice, for instance, Polygonum multiflorum Thunb. root,5 guava leaves,6 jaboticaba peels,7 etc.

The spray-drying process is the common method and applied in the production and stabilization of bioactive compounds, especially phenolic compounds, natural colorants. Because of their sensitivity to temperature, oxygen, light and enzymatic activities, this method needs to be used for storage and processing.8 Besides, the spray-drying method also can keep the quality of the product, maintains low water activity, extends the shelf-life of the product and would make easier to transport and store.9 Nowadays, the most commonly used carrier agent is maltodextrin with various dextrose equivalent values (DE 1-20). However, other carrier agents were also used such as gum arabic,5 skim milk powder,10 tapioca starch,11 etc. or a combination of these carrier agents. The addition of carrier agents into the feed solution dramatically affects the properties and stability of powder products. Until now, there are many studies on the spray-dried powder of pineapple.12,13 However, there is limited scientific information about how various carrier agents and drying conditions may affect the physicochemical properties of pineapple fruit powder. Hence, this study was carried out to evaluate the physicochemical properties of pineapple fruit powder with emphasis on TPC, AC, recovery efficiency, wettability, water solubility index (WSI), bulk density, flowability, hygroscopicity, the particle size and shape by some types of encapsulating agents (MD and MD-GA). other carrier agents were also used such as gum arabic,5 skim milk powder,10 tapioca starch,11 etc. or a combination of these carrier agents. The addition of carrier agents into the feed solution dramatically affects the properties and stability of powder products. Until now, there are many studies on the spray-dried powder of pineapple.12,13 However, there is limited scientific information about how various carrier agents and drying conditions may affect the physicochemical properties of pineapple fruit powder. Hence, this study was carried out to evaluate the physicochemical properties of pineapple fruit powder with emphasis on TPC, AC, recovery efficiency, wettability, water solubility index (WSI), bulk density, flowability, hygroscopicity, the particle size and shape by some types of encapsulating agents (MD and MD-GA).

EXPERIMENTAL

Chemicals and reagents

Maltodextrin (MD) (DE 16-19) was purchased from GPC company (USA) and gum arabic (GA) was supplied by Xiamen Ditai Chemicals company (China). Folin Ciocalteu and DPPH (2,2-diphenyl-1-picrylhydrazyl) reagents were bought from Merck. Trolox reagent (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic) was bought from Sigma-Aldrich (USA) and other chemicals used were of analytical grade.

Sample preparation

The pineapples were harvested from Tien Giang province (Vietnam) and have a yellow to golden yellow pulp, uniform size (approximately 1 kg/unit) and free of physical damage and fungal infection. They were washed, peeled, removed eyes and cut into small pieces with a size of 3×3 cm. Then the pineapple flesh was crushed in a Philips blender about 30 seconds. The mixture was added 1.5% enzyme Pectinex (v/w) and incubated in the thermostatic baths at 50 °C for 1.5 hours. After that, it was hydraulically pressed to squeeze out the juice. The received solutions were adjusted the total soluble solids (TSS) to 12° Brix and preserved at 4 °C. In this study, the pineapple juice was added MD (DE 16-19) or MD-GA (70:30) with the same concentration of 16% (w/w). Then, this mixture was filtered through Whatman No. 4 filter paper and spray-dried by LabPlant SD-Basic Spray Dryer (England) at the inlet/outlet air temperature of 160 °C/70 °C, 4 bar, airflow rate of 70 m3·h-1 and feed flow rate of 750 mL·h-1.

Encapsulation yield (EY)

According to Roccia et al. (2014),14 EY was calculated as the ratio of the powder weight collected after every spray-drying experiment to the initial amount of solids in the sprayed dispersion volume.

H = m 1 m 2 × 100 %

where

m1

The total soluble solids of the spray-dried powders (g)

m2

The total soluble solids of the feed weight (g)

Total polyphenol content (TPC)

The TPC was determined according to the Folin Ciocalteu method.15 The results were based on a standard curve obtained with gallic acid. TPC was expressed as mg of gallic acid equivalents per gram of dry weight (mg GAE·g-1 DW).

Antioxidant capacity (AC)

The AC of material and product were determined by DPPH assay.16 Trolox was used as the standard. AC was expressed in TEAC (Trolox equivalent antioxidant capacity) determined as μmol of Trolox per gram of dry weight (μmol TE·g-1 DW).

Bulk density

Powder (2 g) was added into an empty graduated cylinder (10 mL) and shook for 1 min. The result was determined by the ratio of mass of the powder and the final volume occupied by the powder in the cylinder.17

Flowability

Flowability was determined by using the measurement of the angle of repose (AOR). AOR was calculated by the height and radius of the powder on the flat base when the powder had been poured slowly through the funnel which was held at a fixed height above the flat base.18

Wettability

This parameter was determined by the method of Freudig et al. (1999) with slight modifications.19 The powders were poured into the funnel which is held at a fixed height and fallen down a volume of 100 mL water in a beaker (250 mL) at room temperature. After that, the time for the whole amount of powder to visibly sink beneath the water surface was recorded as an indicator of wettability.

Hygroscopicity

About 1.5 g samples of each powder were placed at 25 °C in an airtight plastic container containing the saturated solution of sodium carbonate. These samples were weighed after 7 days. Eventually, hygroscopicity was determined by gram of adsorbed moisture per 100 g solids (g·100 g-1).20

Water solubility index (WSI)

The method to determine WSI was adapted from Anderson et al. (1969) with some small changes.21 Powder (1 g) and deionized water (10 mL) were vigorously mixed for 1 min. Then, the mixture was made up to 15 mL by deionized water, moved to the centrifuge tube and incubated for 30 minutes at 37 °C. After that, it was centrifuged for 30 minutes at 8000 rpm; the supernatant was separated and dried at 103 °C in an oven. The WSI (%) was expressed as the percentage of dried supernatant to the amount of the original powder.

Color parameters

The color parameters consist of L*(lightness), a*(redness and greenness) and b*(yellowness and blueness) values, which were determined using a Chroma Meter CR-400 (Minolta, Japan).

Scanning electron microscopy (SEM)

The morphology of the material and the spray-dried powder was examined by a Jeol/JSM-7401F scanning electron microscope system. Samples were observed at magnification of 1000X.

Particle size and distribution analysis

A laser scattering particle size distribution analyzer (Horiba LA-960, Japan) was used to determine the particle sizes of the spray-dried powder.

Statistical analysis

The experimental data was analyzed by the one-way analysis of variance (ANOVA) method and significant differences among the means from triplicate analysis at p<0.05 were determined by Fisher’s least significant difference (LSD) procedure using Statgraphics software (Centurion XV). The values obtained were expressed in the form of a mean±standard deviation (SD).

RESULTS AND DISCUSSION

EY, moisture, TPC and AC of powder

Table 1 shows that the EY of MDe (maltodextrin and extract after spray-drying) was higher than MD-GAe (the combination of maltodextrin, gum arabic and extract after spray-drying) at the same concentration of 16% (w/w) because GA has the short-chain branched structure and the high hydrophilic nature leading to powder stickiness on the chamber wall. The EY of MDe is higher than that of Krishnaiah et al. (2012),22 the EY of spray-dried powder from Morinda citrifolia L. reached 39.16% when using 5% MD. While the EY of MD-GAe of the received result is lower than in the study of Bazaria and Kumar (2017) (73.27%),23 who worked with spray-dried beetroot juice when using 10% MD and 10% GA. Thereby, the EY depends on various factors such as inlet/outlet temperature, type of carrier agent, feed flow rate, airflow speed, etc. In addition, the EY of the spray-drying process cannot reach the maximum level because of the wet powder stuck to the upper part of the chamber wall.

Table1.

EY, moisture, TPC and AC of carrier agents and powder products

Sample EY, % Moisture, % TPC, mg GAE·g-1 DW AC, μmol TE·g-1 DW
Fresh pineapple - 84.41±0.70e 2.64±0.09d 6.97±0.07d
MD - 5.98±0.40c - -
MD-GA - 7.12±0.32d 0.16±0.01a 1.38±0.26a
MDe 51.65±0.7b 2.66±0.10a 1.99±0.02b 5.24±0.22b
MD-GAe 47.31±0.78a 3.31±0.19b 2.20±0.06c 5.70±0.10c

Different lowercase letters in the same column indicate a statistically significant difference (p<0.05) between various samples.

Essentially, TPC and AC of the spray-dried product were lower than that of fresh material because of the degradation of bioactive compounds at high temperature. However, the results also showed that there was an increase in the TPC and AC of products compared to the initial carrier agent. Typically, the TPC of MD-GA increased from 0.16 to 2.20 mg GAE·g-1 DW and that of MD increased from 0 to 1.99 mg GAE·g-1 DW. While the AC of MD-GA increased from 1.38 to 5.70 μmol TE·g-1 DW and that of MD increased from 0 to 5.24 μmol TE·g-1 DW. This suggests that this method is capable of keeping precious bioactive compounds in herbs and fruits, especially phenolic compounds. The TPC and AC in fresh pineapple of this study are higher than that of study of Almeida et al. (2011)24 (TPC and AC were 0.381 mg GAE·g-1 DW and 1.33 μmol TE·g-1 DW, respectively) and the TPC of MDe is also higher than that of study of Saikia et al. (2015)25 (0.257 mg GAE·g-1 DW), who spray-dried watermelon juice using MD as carrier agent (DE ≤ 20). These differences may be due to different original materials, types of carrier agent and different spray-drying conditions.

The moisture content of carrier agents after spray-drying is lower than that of carrier agents before spray-drying and the moisture of MDe obtains the lowest value (2.66%). These results are similar to the study of Quoc and Muoi (2018).5 Besides, Righetto and Netto (2005) also believed that MD is more effective in reducing the moisture content of acerola powder by spray-drying.26 This is probably due to the difference between the chemical structure of both carrier agents; GA is a complex heteropolysaccharide with a highly dispersed structure, containing shorter chains and more hydrophilic groups. Generally, the moisture content of spray-drying products is quite low (<4%) and it caused a reduction of the water activity. Therefore, these products are quite safe to preserve. In addition, the moisture of product was influenced by drying temperature, feed flow rate, airflow speed, etc., especially the combination of carrier agents at different ratios.7

Bulk density, flowability, wettability and hygroscopicity of powder

Bulk density of the original carrier agents decreases rapidly after the spray-drying. MDe and MD-GAe ranged from 0.5 to 0.53 g·mL-1, similar to those reported in other studies.5,27 In the spray-drying process, grain formation occurs quickly at high temperatures, the surface of the liquid droplets dries quickly and forms a waterproof layer on the surface, then the formation of vapor bubbles and droplets are increased in size resulting in a reduction in bulk density. In addition, some studies also suggest that the bulk density of spray-dried product could be influenced by many other factors such as input flow rate, hot airflow, spray pressure, amount of dissolved solids,28 dextrose equivalent value and moisture.9

Flowability of before and after spray-drying carrier agents are evaluated through an angle of repose (AOR). AOR of MD increases slowly from 37.57 to 40.54° after the spray-drying process while that of MD-GA decreases sharply from 39.45 to 34.23°. The increase in AOR means that the flowability will decrease and vice versa. This result contrasts with the observation of Carr (1970),29 this author noticed that MDe has a very good flowability (AOR<30°). In this case, adding GA can change significantly the AOR (or flowability) of the initial material and power product. Besides, the flowability of powders can also be significantly affected by the storage temperature, moisture content of the powder and the relative moisture content of the surrounding air. The hygroscopic particle will tend to dissolve the compounds on the surface, forming a bond between the particles increases the cohesion leading to reduced flowability.30 In addition, flowability depends on the size and shape of particles.31 As the particle size decreases with an increase in the surface area per unit volume and this leads to a decrease in the flowability of the powder. The flow was resisted by frictional forces and the surface bonding particles.

Table 2 shows that the wet-tability of MD increased sharply from 87.33 to 179.33 seconds, whereas that of MD-GA also dropped significantly from 1153.67 to 298.67 seconds. This proved that adding GA into MD as a carrier agent strongly affects their wettability. Besides, the wettability could depend on the shape, particle size, moisture and structure of carrier agent. The fluctuations of wettability can be explained according to the assumption of Buffo et al. (2002) and Fernandes et al. (2014), the water penetrates easily into the pores of the powder with various levels depended on the structure of carrier agents and changes the wettability time.32,33 In addition, the result of MD-GA is contrary to the study of Quoc and Muoi (2018),5 the wettability MD and GA after spray-drying are higher than that of initial materials. The mixture of the initial material (MD-GA) in this study is agglomerated, which means the aggregation of dispersed materials to material units of larger size, its sink-ability would spend a lot of time.

Table2.

Bulk density, flowability, wettability and hygroscopicity of carrier agents and powder products

Sample Bulk density, g·mL-1 Flowability (AOR), ° Wettability, s Hygroscopicity, g·100 g-1
MD 0.67±0.0a 37.57±0.75a 87.33±19.35a 10.5±1.11a
MD-GA 0.71±0.0b 39.45±0.89b 1153.67±13.01b 8.74±0.43a
MDe 0.50±0.01c 40.54±0.62c 179.33±7.51c 24.30±0.88b
MD-GAe 0.53±0.01d 34.23±0.61d 298.67±23.97d 22.83±2.14b

Different lowercase letters in the same column indicate a statistically significant difference (p<0.05) between various samples.

Hygroscopicity of MDe and MD-GAe are 24.3 and 22.83 g·100 g-1, respectively. They are higher than that of original powder (nearly 2.5 times). The results of this study also are higher than that of Bazaria and Kumar (2017),23 who spray-dried beetroot juice with MD (DE 10), MD (DE 20), MD (DE 10) - GA and MD (DE 20) - GA (Hygroscopicity ranges from 14.09% to 19.33%). These differences are due to the use of various carrier agents; in addition, the difference in water absorption is thought to be the effect of the drying temperature and moisture content of the product. The adsorption of water by a carbohydrate was attributed to the links between the hydrogen present in water molecules and the hydroxyl groups available in the surface crystalline regions of the substrate and as well as the amorphous regions. MD and GA have a large number of ramifications with the hydrophilic groups in molecular. For this reason, they were easily adsorbed the moisture from the surrounding air.9 High hygroscopicity can be considered a disadvantage for the preservation of these products. The type and particle size of carrier agent strongly affect the hygroscopicity. The smaller the particle size is, the greater the hygroscopicity capacity achieve. Moreover, the spray-drying temperature increases with a decrease in the moisture content of the product, leading to an increase of hygroscopicity because the product was also easily adsorbed the moisture from the ambient air.

Water solubility index (WSI) and color parameters of powder

The WSI of carrier agents before and after the spray-drying were significantly different (p<0.05) (Table 3). The WSI of MD and MD-GA strongly increase, nearly 1.5 times (WSI ranges from 92 to 93.67%). These results were lower than another study of Bazaria and Kumar (2017),23 who spray-dried beetroot juice with MD as carrier agent (WSI achieved from 97.47 to 98.54%). However, it was in agreement with that of the study of Quoc and Muoi (2018), who produced the spray-dried powder from P. multiflorum Thunb. root extract.5 Adding GA into MD did not change the WSI of the initial material and powder product in this study. WSI may be influenced by the type of carrier agent, the spray-drying temperature,34 and the airflow rate.9 In addition, particle size also affected WSI because smaller particle size resulted in the bigger exposed surface, increased contact with the continuous phase and high value WSI.

Table3.

Water solubility index (WSI) and color parameters of carrier agents and powder products

Sample Water solubility index (WSI), % L* a* b*
MD 68.36±3.07a 97.40±1.76a -0.25±0.02a 1.59±0.09a
MD-GA 64.60±4.14a 90.97±3.36b 0.26±0.11b 10.75±1.05b
MDe 93.67±1.95b 95.78±0.46a -1.14±0.12c 10.23±0.42b
MD-GAe 92±1.48b 94.65±0.66a -0.61±0.02d 11.61±1.37b

Different lowercase letters in the same column indicate a statistically significant difference (p<0.05) between various samples.

The color of the product differs from the original carrier agent color. The L* and a* values decreased slightly, whereas b* value increased gradually but that of MD-GA and MD-GAe changed insignificantly. The changes in carrier agent color may be due to browning reactions that occur during the spray-drying process, especially the non-enzymatic browning reactions (caramelization, Maillard reactions and pigment oxidation). These reactions occur due to high sugar concontent in pineapple juice and heat supply in the drying chamber. Besides, the color parameters were affected by inlet temperature, feed flow rate, airflow rate, soluble solid content,35 and concentration of carrier agent.12

Microstructure and particle size of spray-dried powder

Based on the results obtained, the structure of microcapsules before and after spray-drying was significantly different, typically as MD with spherical shape but uneven size, but after the spray-drying process, the particles have uniform size, smooth surface. Similar to spray-dried products using MD-GA combination, there is adhesion between particles with finer surfaces (Fig. 1 and 2). This will be similar to the study of Saikia et al. (2015) about micro-material used is MD (DE£20) and the study of Lim et al. (2012) when they used micro-materials MD-GA (DE 10) as a carrier agent.25,36 Moreover, Loksuwan (2007) also showed that the high DE value (DE 24) contains a large amount of low molecular weight sugar, which can act as a plastic, preventing surface shrinkage during spray-drying process and resulting in the formation of finer particles.37 The change in the shape of the particles is due to the spray-drying materials with high sugar content, the product has an amorphous and partially or completely crystallized surface. This indicates that the characteristics of the material depend on the spray-drying conditions and they also depend on the characteristics of the product.38

Figure1.

Microphotographs of MD (a) and MDe (b) at magnification of 1000X.

jkcs-64-259-f001.tif
Figure2.

Microphotographs of MD-GA (a) and MD-GAe (b) at magnification of 1000X.

jkcs-64-259-f002.tif

The particle size of MDe, MD-GAe changes significantly and smaller than MD, MD-GA. The average diameter of MD, MD-GA is 75 μm and 72 μm, respectively. The MDe particle diameter ranges from 3 to 500 μm (dmean=51 μm), while the MD-GAe particle diameter is from 2 to 394 μm (dmean=22 μm) (Fig. 3 and 4). The results showed that the diameter of the particle decreased after the spray-drying process. The special thing is that MDe and MD-GAe have a variety of sizes and they are smaller than the size of the original product. The average particle size after spray-drying of the study is different to that of Ferrari et al. (2012) for blackberry powder (MDe and MD-GAe diameter are 48.89 μm and 28.45 μm, respectively).38 This can be explained that the particle size depends on the type of carrier agent, inlet temperature, inlet flow rate,39 injection pressure, total dry matter content, airflow rate.28 The change in particle size leads to changes in the physical properties of the powder such as wettability, water solubility index (WSI), bulk density, flowability, hygroscopicity of spray-dried powder.

Figure3.

Particle size distribution curve of MD (a) and MDe (b).

jkcs-64-259-f003.tif
Figure4.

Particle size distribution curve of MD-GA (a) and MD-GAe (b).

jkcs-64-259-f004.tif

CONCLUSION

All the powder samples were produced by the spray-drying method with different carrier agents which had low moisture content (2.66–3.31%). This was an advantage for the storage and preservation of spray-dried products. After the spray-drying process, the use of MD-GA combination had the highest bulk density, wettability, TPC and AC values; while the use of MD was reached the highest in the encapsulation yield and flowability values. The color and microstructures of powder products changed completely compared to the initial material. These results showed that the type of carrier agent is a very important factor that strongly affects the physicochemical properties of the dried product. Consequently, depending on the needs of production and the different technology elements that should choose the type of carrier agent appropriately.

Acknowledgements

I am grateful to my co-workers, including Huynh Phat Trien, Tran Thi My Duyen, Le Truong Giang and Le Thi Minh Trang, who supported this study. The publication cost of this paper was supported by the Korean Chemical Society.

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