ORIGINAL ARTICLE
Optimization of Spray Drying Parameters for White Dragon Fruit (Hylocereus undatus) Juice Powder using Response Surface Methodology (RSM)
*Norzaida Yusof1, Noranizan Mohd Adzahan2 and Kharidah Muhammad2
1Faculty of Bioresources and Food Industry, Universiti Sultan Zainal Abidin, Besut Campus, 22200, Besut, Terengganu, Malaysia
2Faculty of Food Science and Technology, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia
*Corresponding author: [email protected]
Received: 24/10/2020, Accepted: 27/10/2020, Published: 31/10/2020
Abstract
This study was conducted to optimize the production of spray-dried white dragon fruit (Hylocereus undatus) powder using resistant maltodextrin as wall material. The inlet air temperature (140 °C, 150 °C and 160
°C), outlet temperature (75 °C, 80 °C and 85 °C) and resistant maltodextrin concentrations (20%, 25%
and 30%) were tested as independent variables. Process yield, moisture content, water activity, solubility, hygroscopicity and bulk density of the powders were analysed as responses. Process yield significantly (p<0.05) increased with increasing inlet temperature and decreasing resistant maltodextrin concentration.
Outlet temperature and resistant maltodextrin concentration significantly (p<0.05) reduced the moisture content and water activity of the white dragon fruit powder. Powder solubility and hygroscopicity significantly (p<0.05) increased as inlet and outlet temperature increased. Bulk density values decreased as inlet and outlet temperature increased. An optimum conditions for spray dried white dragon fruit powder that would produce high in yield, low moisture content, low water activity, high solubility, low hygroscopicity and high bulk density were found at 153 °C inlet temperature, 82 °C outlet temperature and 20% concentration.
Keywords: Dragon fruit, resistant maltodextrin, powder, response surface methodology, spray drying
Introduction
Dragon fruit (Hylocereus) also known as pitaya is a non-climacteric fruit belongs to the Cactaceae family. There are three varieties of dragon fruit; Hylocereus undatus (red peel with white flesh, Hylocereus polyrhizus (red peel with red flesh) and Hylocereus megalanthus (yellow peel with white flesh). Dragon fruit is native to Central and South America (Le Bellec et al., 2006) and now being cultivated in a large scale in Asian countries such as Vietnam, Taiwan, Philippines and Malaysia. In Malaysia, the most common varieties are the Hylocereus polyrhizus and Hylocereus undatus. Dragon fruit can be considered as an excellent fruit due to its taste, colour and high nutritive value. Previous studies have shown that dragon fruit contain fiber, vitamin C, antioxidants
https://journal.unisza.edu.my/myjas
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and minerals (Jaafar et al., 2009; Mahattanatawee et al., 2006). Dragon fruit juice is popularly consumed as a healthy refreshing drink as it contributes to lower the blood cholesterol level and improves blood circulation in the body (Wu et al., 2006). However, fruit juices have short shelf life and proper storage is costly.
In food industry, spray drying of fruit juice is an established procedure to produce food powder which have numerous benefits such as easier to handle and longer shelf life. The quality attributes of the powder produced in a spray-drying process are dependent on the drying parameters; feed flow rate, inlet and outlet air temperature, atomizer speed and the character of the food material; feed concentration, feed temperature, and inlet air flow rate (Chegini &
Ghobadian, 2005). Liu et al. (2004) reported that feed temperature, inlet, and outlet air temperatures are the main factors that influence the quality of spray dried powder.
Numerous studies have been done on spray drying of fruit juices such as pomegranate juice (Youssefi et al., 2009) sugarcane juice (Nishad et al., 2017) and blackberry juice (Ferrari et al., 2012). The most commonly used as a wall material in spray drying is maltodextrin due to cheaper in cost and commercially available (Kha et al., 2010). Maltodextrin is water-soluble and is added to reduce the stickiness during the spray-drying process as the addition of maltodextrin able to increase the glass transition temperature (Bhandari et al., 1997).
However, use of maltodextrin is limited because it lacks of emulsification properties. Starch hydrolysate containing the indigestible component also termed resistant maltodextrin are shown to have physiological functions similar to dietary fiber (Englyst &Cummings, 1997). In addition, resistant maltodextrin also have the potential to use as wall material due to its properties; viscosity lower than maltodextrin (same DE value), white in colour, clear and stable solution and stable in heat processes (Wakabayashi & Okuma, 2001).
Spray drying of red dragon fruit (H. polyrhizus) juice also has been done by Tze et al.
(2012), but there are still lack of study reported on white dragon fruit (H. undatus) juice. In current study, the use of resistant maltodextrin as wall material to produce white dragon fruit juice powder was conducted to determine the optimal conditions and the effects of spray drying conditions on bulk density, hygroscopicity, water activity, moisture content and yield of the powder produced.
Materials and Methods
Materials
The wall material used was resistant maltodextrin (Fibersol-2), purchased from Castle Chemical Sdn. Bhd., Selangor, Malaysia. All other chemicals and solvents used in this study were of analytical grade and were purchased from Merck.
Preparation of Dragon Fruit Juice
White dragon fruits (WDF) were purchased from a local supplier in Selangor, Malaysia. Fresh dragon fruits were washed and the peels were removed and discarded manually. The pulps were sliced into small pieces, and the juice was extracted using a juice extractor machine (Santos, France). The seeds were separated and removed. The juice (12 °Brix, pH of 5.07) then was stored in the cold chamber maintained at 4°C till further use.
Spray Drying of White Dragon Fruit Juice
The wall material, resistant maltodextrin (RMD) was added to the juice according to the matrix in Table 1. The mixture was homogenized for 10 min at 9500 rpm using a T25 basic lab homogenizer (IKA-WERKE, Germany) until all added RMD had been dissolved. The spray drying process was performed with a pilot-scale spray drier (Model Niro A/S, Gea, Germany) under the following operational conditions: air flow rate, 900 m3/min; rotary atomizer type, 15000 rpm; and peristaltic pump (Model BT300-2J).
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The feed mixtures containing RMD were stirred constantly during spray drying and were given at room temperature (25 °C ± 2 °C). Spray drying was carried out according to the generated experimental design obtained from response surface methodology (RSM) (Table 1). These conditions were chosen after conducting preliminary studies. Spray-dried powders were collected and vacuum sealed in an aluminium bag and stored at room temperature (25 °C) for further analysis.
Table 1: Experimental conditions of the spray drying treatments for white dragon fruit powder with resistant maltodextrin
Run Block
Independent variable
Ti (°C), X1 To (°C), X2 RMD (% w/w), X3
1 1 150 80 25
2 1 140 85 30
3 1 140 75 20
4 1 150 80 25
5 1 160 75 30
6 1 160 85 20
7 3 160 80 25
8 3 140 80 25
9 3 150 80 30
10 3 150 75 25
11 3 150 80 25
12 3 150 85 25
13 3 150 80 25
14 3 150 80 20
15 2 140 75 30
16 2 140 85 20
17 2 150 80 25
18 2 160 75 20
19 2 150 80 25
20 2 160 85 30
RMD: Resistant maltodextrin; Ti: Inlet temperature; To: Outlet temperature.
Experimental Design
Response surface methodology (RSM) was applied in designing the experiments to evaluate the relationships between the three independent variables; inlet air temperature (140 °C to 160 °C, x1), outlet air temperature (75 °C –85 °C, x2), and resistant maltodextrin (DE10) concentration (20–
30% w/w, x3) with dependent variables; yield (Y1), moisture content (Y2), water activity (Y3) solubility (Y4), hygroscopicity (Y5) and bulk density (Y6) of spray-dried WDF juice powder.
The experimental design matrix is shown in Table 1. The experiments were based on a central composite design (CCD), two-level factorial design with three independent variables and 20 experimental runs.
White Dragon Fruit Powder Analysis Yield
The spray drying yield was evaluated according to Obón et al., (2009) and calculated as follow:
48 𝑌𝑖𝑒𝑙𝑑 (%) = 𝑀𝑎𝑠𝑠 𝑜𝑓 𝑝𝑜𝑤𝑑𝑒𝑟 𝑝𝑟𝑜𝑑𝑢𝑐𝑒𝑑 (𝑔)
𝑀𝑎𝑠𝑠 𝑜𝑓 𝑡𝑜𝑡𝑎𝑙 𝑠𝑜𝑙𝑖𝑑 𝑐𝑜𝑛𝑡𝑒𝑛𝑡 𝑜𝑓 𝑓𝑒𝑒𝑑 𝑚𝑖𝑥𝑡𝑢𝑟𝑒 (𝑔)𝑥100 (1)
Moisture Content
The moisture content of the spray dried powders was determined according to Kha et al. (2010) by drying at 105 °C in the oven until constant weight was obtained.
Water Activity
Water activity was determined using a water activity meter (AQUALAB Series 3 TE, USA) by placing the sample in the plastic cup.
Solubility
Solubility was determined according to the method described by Cano-Chauca et al. (2005) with some modification. One gram WDF powder was added into a blender contained 100 mL water and were homogenized for 5 min. The solution was centrifuged (Heraeus Multifuge 3L, Thermo, Germany) at 3000 ×g for 5 min. Twenty-five milliliters (25 mL) of the supernatant was transferred to a pre-weighed Petri dish and dried in an oven at 105 °C for 5 h. The powder solubility (%) was calculated by weight difference.
Hygroscopicity
Hygroscopicity was determined according to Tonon et al. (2008). One gram (1 g) of powder was placed in a desiccator containing NaCl-saturated solution at 25 °C (75.29% relative humidity). The powder was collected after 1 week and weighed. Hygroscopicity was expressed as g of adsorbed moisture per 100 g dry solids (g/100 g).
Bulk Density
The bulk density of WDF powders was determined according to the method described by Cai &
Corke (2000). Three grams (3 g) of the sample was poured through a funnel into a 10 mL graduated cylinder and then tapped 10 times onto a rubber mat from a height of 10 cm. The volume was recorded and was used to calculate the bulk density as g/mL.
Statistical Analysis
Analysis of variance (ANOVA) and regression surface analysis were conducted to define the statistical significance of model terms and fit a regression relationship relating the experimental data to the independent variables. From the initial model, all the terms that were significant (p<0.05) were considered in order to get the final reduced model. However, variables that gave significant effects on quadratic or interaction terms were kept in the reduced model although they were non-significant variables in initial models (Mirhosseini et al., 2009). The generalized polynomial model proposed for predicting the response variables as function of independent variables is given below:
𝑌𝑖 = 𝛽0+ 𝛽1𝑥1+ 𝛽2𝑥2+ 𝛽3𝑥3+ 𝛽11𝑥12+ 𝛽22𝑥22+ 𝛽33𝑥32+ 𝛽12 𝑥1𝑥2+ 𝛽13𝑥1𝑥3+ 𝛽23𝑥2𝑥3 (2)
Where Yi was the response value predicted by the model; β0 was a constant; β1, β2 and β3 were the regression coefficients for linear effect terms; β11, β22 and β33 were quadratic effects; and β12, β13 and β23 were interaction effects. In this model, x1, x2 and x3 were the independent variables.
The experimental design matrix, data analysis, and optimization procedure were performed using the Minitab (Version 14) statistical package (Minitab Inc., PA, USA).
49 Results and Discussion
Response Surface Analysis
Table 2 shows 20 experimental data obtained for 6 response variables studied. Data were expressed as means followed by the standard deviation of three independent measurements. The estimated regression coefficients for the response variables correspond to independent variables are given in Table 3.
Table 2: Experimental data obtained for the response variables studied (Yi) (mean± SD)
Run
Response variable Yield
(Y1, %)
MC (Y2, %)
aw
(Y3)
Sol.
(Y4, %)
HYG (Y5, g/100 g)
BD (Y6, kg/m3) 1 64.46 3.57±0.16 0.21±0.00 95.29±0.11 20.76±0.01 692.2±0.01 2 61.19 2.16±0.04 0.17±0.00 94.88±0.37 22.26±0.28 714.7±0.02 3 64.78 3.78±0.07 0.25±0.02 96.40±0.00 22.56±0.31 750.2±0.00 4 62.68 3.89±0.01 0.24±0.00 95.30±0.07 21.07±0.62 682.9±0.00 5 60.56 3.75±0.11 0.21±0.00 94.72±0.21 21.26±0.10 740.5±0.00 6 70.34 2.30±0.04 0.18±0.02 96.38±1.84 22.59±0.20 730.4±0.01 7 68.09 3.09±0.01 0.22±0.01 95.34±1.05 22.01±0.13 714.9±0.00 8 65.97 2.80±0.22 0.22±0.01 95.46±0.23 21.62±0.19 715.4±0.00 9 72.29 3.09±0.04 0.18±0.01 94.85±0.47 20.34±1.14 715.0±0.02 10 58.03 4.99±0.03 0.26±0.03 94.55±1.26 21.00±0.60 823.6±0.03 11 70.53 3.42±0.05 0.21±0.00 94.85±0.49 20.87±0.01 722.6±0.02 12 70.85 3.08±0.04 0.23±0.02 94.47±1.23 21.67±0.17 790.1±0.00 13 68.31 2.75±0.02 0.21±0.00 94.71±0.75 21.33±0.73 740.2±0.00 14 72.92 2.74±0.10 0.18±0.01 96.26±1.9 21.20±0.70 714.8±0.00 15 65.64 4.01±0.04 0.27±0.00 96.68±0.01 22.23±0.22 714.7±0.03 16 66.88 2.12±0.05 0.19±0.01 94.83±0.07 22.91±0.11 682.7±0.02 17 64.46 3.38±0.05 0.26±0.01 94.71±0.75 21.23±1.52 682.0±0.01 18 60.58 3.89±0.07 0.26±0.01 94.56±1.58 22.32±0.09 715.2±0.00 19 64.68 2.76±0.07 0.26±0.00 94.19±1.05 21.25±1.58 684.4±0.01 20 67.06 2.68±0.19 0.19±0.01 96.04±0.19 23.63±0.05 692.8±0.01
MC: Moisture content; aw: Water activity; Sol.: Solubility; HYG: Hygroscopicity; BD: Bulk density; RMD: Resistant maltodextrin; WDF: White dragon fruit
As seen in Table 3, the significant (p<0.05) response surface models with high R2 values were varied from 0.779-0.961. The values were fitted for all response variables studied and high regression coefficients (R2>0.80) values were achieved for all polynomial regression models exclude solubility.
However, previous study reported that R2>0.75 are relatively adequate for prediction purposes (Seng et al., 2005). Thus, this indicated that more than 78% of the response variation could be explained as a function of the three independent variables studied.
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Table 3: Regression coefficients, R2, adjusted R2, probability values and lack of fit for the final reduced models
Regression Coefficient
Yield (Y1, %)
Moisture content (Y2, %)
Water activity, aw
(Y3)
Solubility (Y4, %)
Hygroscopicity (Y5, g/100 g)
Bulk density (Y6, kg/m3)
b0 -281.9 128.91 4.9305 309.88 423.94 1448.3
b1 -3.702* -1.313* 3.228* -5.88*
b2 -3.359* -0.1379* -2.445* 3.853* -46.46*
b3 -8.911* -1.256* -0.0849* -1.380* -0.751* 3.92*
b12 0.009* -0.02*
b22 -0.152* 0.020* 0.00083* 0.018* 0.29*
b32 0.175* -0.025* 0.00171* 0.027* -0.08*
b12 0.047* 0.016* 0.006*
b13
b23 0.009*
R2 0.817 0.811 0.919 0.779 0.950 0.961
R2 (adj) 0.685 0.723 0.881 0.650 0.904 0.933
Regression p-value
0.006* 0.000* 0.000* 0.002* 0.000* 0.000*
Linear 0.007* 0.028* 0.000* 0.000* 0.000* 0.000*
Square 0.015* 0.032* 0.000* 0.008* 0.000* 0.000*
Interaction 0.016* 0.000* 0.009*
Lack of fit p-value
0.104 0.321 0.172 0.106 0.433 0.425
bi: the estimated regression coefficient for the main linear effects. bii: the estimated regression coefficient for the quadratic effects. bij: the estimated regression coefficient for the interaction effects. 1: Inlet temperature; 2: Outlet temperature; 3: Resistant maltodextrin concentration. *: Significant (p<0.05).
Table 4 shows the probability value of regression coefficients in the final reduced models for each independent variables on 6 response variables studied. The p-values were used as a tool to check the significance of each coefficient. A smaller p-value would indicate a more significant effect on the respective response variables. As shown in Table 4, outlet temperature, X2 seems to be the most significant variables on each response variables studied.
Table 4: The probability value (p-value) of regression coefficients in the final reduced models Variables Yield
(Y1, %)
Moisture content (Y2, %)
Water activity, aw
(Y3)
Solubility (Y4, %)
Hygroscopicity (Y5, g/100 g)
Bulk density (Y6, kg/m3) Linear
X1 0.017 0.0001 0.0001 0.006
X2 0.013 0.0001 0.0001 0.003 0.0001
X3 0.007 0.031 0.004 0.008 0.028 0.006
Quadratic
X12 0.08* 0.0001 0.006
X22 0.01 0.013 0.0001 0.013 0.0001
X32 0.007 0.038 0.005 0.008 0.005
Interaction
X12 0.016 0.0001 0.012
X13
X23 0.049 0.034
*Not significant at (p<0.05)
Powder Yield
The yield of white dragon fruit juice powder varied from 58.03% to 72.92% (Table 2) for 20 experimental runs. This response variable was significantly (p<0.05) influenced by RMD
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concentration, inlet and outlet temperature (Table 3). The highest powder yield was obtained as 72.92 % at 150°Cinlet temperature, 80 °C outlet temperature and 20% (w/w) RMD concentration.
Powder yield decreased with increasing RMD concentration up to 25% (Fig. 1B and 1C), possibly due to increase in mixture viscosity. The increase in feed viscosity caused greater amounts of solids to stick to the chamber wall, thus reducing the product yield (Cai & Corke, 2000). This trend was similar with the results published by Goula & Adamopoulos (2010).
As shown in Table 3, the main linear effect of inlet temperature also exhibited a significant (p<0.05) negative effect on product yield. The 3-D plot (Fig. 1A) showed at fixed 25% RMD concentration, the yield of powder decreased with the increasing inlet temperature, and increased rapidly with increase of outlet temperature. This trend was similar with previous study, who reported that an increase in temperature to 160 and 180 °C will resulted in a lower yield of WDF fruit powder produced with maltodextrin as a wall material (Lee et al., 2013).
Figure 1: Response surface plots showing the significant (p<0.05) interaction effects of independent variables (inlet and outlet temperatures and RMD concentration) on the yield of spray-dried WDF powder.
(A) Hold values concentration at 25%; (B) Hold values outlet temperature at 80 °C and (C) Hold values inlet temperature at 150 °C.
Moisture Content (MC) and Water Activity (aw)
Moisture content of the powder produced were generally lower than 5% (Table 2) and this was consistent with previous study reported on spray dried cactus pear juice (Obón et al., 2009) and
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cagaita fruit extracts (Daza et al., 2016). Water activity of the powder produced exhibited values lower than 0.3 (Table 2), thus considered low and microbiologically stable for general storage (Fontana, 1998). The outlet temperature and RMD concentration significantly (p<0.05) reduced the moisture content and water activity (Table 3 and 4).
Figure 2A and 2B, 3-D plots indicated that at fixed inlet temperature, outlet temperature had a negative impact on the moisture content and water activity. As for RMD concentration, moisture content and water activity increased rapidly with RMD concentration, but beyond 25%
concentration, the value decreased with increasing concentration. This probably due to higher solid concentration in the feed mixtures reduced the water evaporation rate, thereby reducing the moisture content and water activity of the final powders produced (Goula & Adamopoulos, 2008).
Figure 2: Response surface showing the significant (p<0.05) interaction effect of independent variables (inlet and outlet temperatures and RMD concentration) on the (A) moisture content and (B)
water activity of spray-dried WDF powder.
Solubility
The solubility values for the WDF powders obtained at different spray drying conditions are presented in Table 2. The values are varied from 94.19% to 96.68% with the addition of RMD.
The range fell within the typical powder solubility values ranging from 92% to 99% reported by Bhandari et al. (2008), reasonably higher compared with those of other fruit powders, for example, 17.65% to 26.73% for the tomato powder (Santos et al., 2008) and 81.56% for pineapple (Abadio et al., 2004).
The solubility of the WDF powder with RMD was significantly (p<0.05) influenced by all the independent variables (inlet and outlet temperatures and RMD concentration) and the interaction between the inlet and outlet temperatures (Table 3). Results indicated that increased in RMD concentrations increased the powder solubility, given the high solubility of the wall materials used.
RMD is soluble in water up to 70% (w/w) at 20 °C (Matsutani, 1999).
Hygroscopicity
As shown in Table 3, all the independent variables and interactions of independent variables significantly (p<0.05) affected the hygroscopicity of the WDF powders. The inlet temperature exhibited the greatest effect on hygroscopicity of the powders. In Table 2, the highest hygroscopicity values were obtained at 85 °C outlet, 160 °C inlet temperatures and 30% RMD
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concentration because these variables affect the moisture content of the powder produced. The particles of powder with a lower moisture content will easily adsorb ambient moisture, a phenomenon that is related to the greater water concentration gradient between the powder and its surrounding air. These results are in agreement with those of Tonon et al. (2008), who worked on acai powder.
RMD concentrations also influenced the hygroscopicity of the WDF powders.
Hygroscopicity decreased with increasing RMD concentration. A higher amount of total solids in the feed mixture resulted in lesser water to evaporate. Thus, the resulting powders had a lower moisture content and a greater moisture adsorption capacity. This phenomenon was observed also because RMD has a low hygroscopicity, confirming its efficiency as a drying aid. This results are consistent with those of Cai & Corke (2000) and Goula & Adamopoulos (2008).
Bulk Density
The bulk density values of WDF powders ranged from 682.0 kg/m3 to 823.6 kg/m3 (Table 2) and significantly affected by all the independent variables and interactions between the variables (Table 3). These values are higher than those reported by Goula & Adamopoulos (2010) for spray- dried orange juice concentrate, which ranged from 0.14 g/mL to 0.41 g/mL. The outlet temperature had the most significant (p<0.000) effect on the WDF powder (Table 4); the higher the outlet temperature, the lower the bulk density value. These findings are probably because products with higher moisture content will tend to have a higher bulk weight due to the higher water content, becoming considerably denser than the dry solid (Chegini & Ghobadian, 2005).
Optimization of Process Parameters and Verification of the Model
A numerical optimization was carried out by the response optimizer using the Minitab software for determining the exact optimum level of independent variables leading to the overall optimum condition. The numerical optimization results indicated that the overall optimum region to produce spray dried WDF juice powder was achieved at the combined level of 153 °C inlet temperature, 82 °C outlet temperature and 20% RMD concentration. The corresponding response values for process yield, moisture content, water activity, solubility, hygroscopicity and bulk density of WDF powder are given in Table 5. The results indicated that there was no significant difference (p>0.05) between predicted and experimental value for the response variables studied. These observations verified the adequacy of corresponding response surface models relating the experimental data to three independent variables studied; inlet temperature, outlet temperature and materials concentration.
Table 5: Predicted and experimental values for the response variables studied
Variables Predicted value Experimental value
Yield (%) 71.5 71.93
Moisture content (%) 2.28 2.33 ± 0.08
Water activity, aw 0.181 0.177 ± 0.00
Solubility (%) 95.7 96.5 ± 1.16
Hygroscopicity (g/100g) 21.5 23.43 ± 0.44
Bulk density (kg/m3) 714.3 728.6 ± 0.03
Data are mean ± standard deviations of triplicates.
Conclusions
Twenty different runs according to the Central Composite Design (CCD) were used to study the quality parameters of WDF juice powder at various levels of RMD concentration, inlet and outlet temperature. All the variables were highly significant (p<0.05) to the responses studied and outlet temperature exhibited the most influential variable affecting all the responses. Optimum conditions
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for the production of spray-dried white dragon fruit juice powder were established. An inlet temperature of 153 °C, outlet temperature of 82 °C and 20% RMD concentration were shown to be the most optimum conditions to produce encapsulated white dragon fruit juice powder and can be applied in a large scale production.
Acknowledgments
Authors express their gratitude for the financial support granted by Ministry of Higher Education Malaysia (MOHE), UPM-BERNAS and colleagues from Faculty of Food Science and Technology who have assisted and share the information during the progression of this project.
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How to cite this paper: Norzaida Yusof, Noranizan Mohd Adzahan, Kharidah Muhammad (2020). Optimization of Spray Drying Parameters for White Dragon Fruit (Hylocereus undatus) Juice Powder using Response Surface Methodology (RSM). Malaysian Journal of Applied Sciences, 5(2), 45-56.