Optimization of spray drying process parameters for production of Japanese apricot (Prunus mume Sieb. et Zucc.) juice powder

Abstract

Optimization of spray drying conditions namely inlet air temperature (IAT) and maltodextrin (MD) concentration was utilized by response surface methodology for Japanese apricot (Prunus mume Sieb. et Zucc.) juice powder (JAJP) manufacture. Drying yield, moisture content, water solubility index (WSI), bulk density, color, pH, total phenol content (TPC), total flavonoid content (TFC), vitamin C content, and DPPH radical-scavenging activity of juice powder were measured. Moisture content, vitamin C content, color, DPPH radical-scavenging activity, pH, and bulk density were greatly influenced by IAT, but drying yield, WSI, TPC, and TFC were only significantly affected by MD concentration. The spray drying condition was optimum at 10% MD concentration and 165.8 °C IAT. The properties of juice powder were 37.50% drying yield, 4.81% moisture content, 134.25 mg/g vitamin C content, 27.52% DPPH radical-scavenging activity, 2.78 pH, 89.15% WSI, 232.856 μg GAE/100 g TPC, 404.66 μg CE/100 g TFC, and 0.49 bulk density.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-021-00950-8.

Introduction

Japanese apricot (Prunus mume Sieb. Et Zucc.) is comprised of 85% water, 10% sugar, and 5% organic acid. It is often used for commercial purposes such as syrup extract, vinegar, jam, wine, and pickled vegetables. A high respiration rate causes a rapid change in the quality of Japanese apricot during storage, resulting in color changes in fruit softening (Shin, 1995). Among these processed products, Japanese apricot juice is the most popular material that can be further processed into other value-added products. However, fruit juice should be stored at low temperatures, and its use has disadvantages such as expensive transportation and storage costs. In contrast, the powdered form is lighter in weight and cheaper in transportation costs. Therefore, it is more advantageous to develop Japanese apricot juice in a powdered form.

Different drying techniques, namely hot air drying, freeze drying, and spray drying, have been used in the food industry to enhance productivity and product quality. Spray drying is one of the most widely used processing methods powder production in liquid foods due to its low cost and quick drying speed (Tamime, 2009). Spray drying can convert juice into dehydrated powder to extend shelf-life during storage. It is used in industrial applications to process beverages, soup, ice cream. The quality of the powder produced by spray drying depends on the dry air characteristic, type of carrier agent, the interaction between hot air and droplets in the chamber, and the scale of the spray dry used (Nguyen et al., 2020). The most widely used carrier agent in fruit juice powder production is MD (Gabas et al., 2007). MD is a starch hydrolysis product mainly composed of D-glucose units connected by α (1 → 4) glycosidic bonds. It has a molecular weight of 180 g/mol and a dextrose equivalency of 20 (Whistler et al., 2012). MD is widely used as a carrier in spray drying because it is cheaper than other carriers and can increase the powder recovery rate by reducing the stickiness of spray-dried products. Also, MD is widely used as a carrier agent not only because it reduces the oxidation of the cell wall matrix, but also because it is useful in bulking and film formation. Peng et al. (2013) found that the retention of some food properties, such as nutrients, pigments, and flavorings, during spray drying is due to MD. It can protect the feed material against chemical and enzymatic reactions and also reduce the moisture of the feed material (Wang et al., 2009). MD is also highly soluble in water. As this property may significantly reduce the viscosity of the feed, MD is considered adequate for spray drying (Pierucci et al., 2007).

This study aims to determine the optimal spray-drying conditions of JAJP juice using regression analysis and the response surface methodology (RSM). RSM is a statistical and mathematical technique that analyzes and optimizes processes that involve several variables (Poodi et al., 2018).

The aim of this research is (1) to investigate the effects of different IAT and MD concentrations on the physicochemical properties of JAJP and (2) to find the optimal conditions of the spray drying process.

Materials

Japanese apricot juice was acquired from a local juice production company in Gwangyang, Korea, and kept at 4 °C until use. The maltodextrin (starch; Daesang, Seoul, Korea) with 20 dextrose equivalents (DE) was purchased from a local market in Gwangju, Korea. Gallic acid, 2,2–diphenyl–1–picrylhydrazyl (DPPH), L-ascorbic acid, ( −)-catechin, Folin-Ciocalteu reagent, sucrose, and D fructose were purchased from Sigma Aldrich (St. Louis, MO, USA). Sodium carbonate, sodium hydroxide, and aluminum chloride were acquired from Daejung Chemicals and Metals (Siheung, Gyeonggido, S. Korea).

Methods

Juice preparation

Initially, Japanese apricot juice was at 63° Brix. Using distilled water, the juice was diluted until 10° Brix. Once 10° Brix was reached, the total juice solids were added with MD of range of 10% to 30% (w/v).

Spray drying

Similar to the process by Kim et al. (2021), spray drying of Japanese apricot juice was performed using a pilot-scale spray dryer (MH-8, Mehyun Engineering, Gyeonggi-do, Korea) with a rotary disc atomizer (Fig. S1). Using a peristaltic pump, 1.5 mm diameter nozzle was used to feed the samples into the main chamber. Pump rotation speed controlled the feed flow rate. The atomizer speed was constant at 9860 rpm, feed rate at 12 mL/min, and compressor air pressure at 0.74 MPa. The inlet air temperature was manipulated at a range from 130 to 180 °C.

Experimental design

RSM is used to analyze experimental data to optimize process parameters. 13 experiments were conducted with RSM using a twelve-level central composite design (CCD). In this experiment, two independent variables that were manipulated were MD concentration and IAT. MD concentration was manipulated between the range of 10% and 30%, and IAT was manipulated between the range of 130 °C and 180 °C. For analysis, each of these two independent variables (i.e., MD concentration (X1) and IAT (X2)) were coded into four levels: − 1, 0, 1, and + α. The value for alpha (1.414) was derived for the purpose of enabling rotatability in the design (Table S1). Drying yield, moisture content, color, vitamin C content, DPPH radial-scavenging activity, pH, WSI, TFC, TPC, and bulk density were used as the parameters for determining the quality properties of Japanese apricot juice powder. All of these parameters were optimized using RSM.

Physicochemical characteristic

Drying yield

The drying yield of Japanese apricot juice was calculated as follows:

$$\text{Drying yield}=\frac{M}{\mathit{TS}}\times 100$$

where M is the mass of dry powder, which was collected from the spray-dryer collection chamber, and TS is the mass of total solids, including both soluble and insoluble solids after MD was added to the juice.

Moisture content

The moisture content was measured by placing the sample in the oven at 105 °C until a constant dried weight was achieved (A.O.A.C, 2016).

Color measurement

Sample color was measured by using a colorimeter (CR-400, Minolta, Tokyo, Japan). In this study, three color values that were obtained are L* (brightness), a* (red), and b* (yellow and blue) (Chang et al., 2020).

Bulk density

Each sample of 2 g of JAJP was placed in a 10 mL graduated cylinder in a vortex vibrator and was vibrated for 1 min. After the process, the mass and volume of the JAJP were measured. Based on the measurements, the bulk density (g/mL) is calculated as the ratio of the mass and the volume of the JAJP (Rajam & Anandharamakrishnan, 2015).

Water solubility index (WSI)

Each sample of 2 g of JAJP was added to distilled water (25 mL) at 30 °C. The sample solution was intermittently mixed for 20 min and centrifuged at 2016 × g for 15 min. The supernatant was transferred into a Petri dish and the precipitate was dried overnight at 105 °C. Then, the weight was measured. As a result, WSI represents the percentage of total dry solid of the spray dried samples (Anderson, 1982).

pH

To each sample of 2 g of JAJP, distilled water (25 mL) was mixed, homogenized, and centrifuged at 2016 × g for 15 min. Then, a pH meter (EF-7732, Istek, Seoul, Korea) was used to measure the pH of the supernatant (Robert, 2003).

Vitamin C content

Vitamin C content was measured using the technique by Das and Eun (2018). 0.5 mL of diluted JAJP was added to 0.5 mL of 2,6–dichlorophenol indophenol chloride solution (0.1 mg/mL). The mixed reactant was incubated for 5 min at 21 °C and absorbance was measured at 500 nm using a spectrophotometer. Vitamin C content was determined based on a standard curve of L-ascorbic acid (mg/g).

DPPH radical-scavenging activity

DPPH radical-scavenging activity was analyzed using the method by Das and Eun (2018). 950 μL of 100 μM DPPH reagent ethanol solution was combined with 50 μL of powder solution (1/15 in distilled water). The mixture was incubated at 21 C for 30 min. The scavenging activity of JAJP was measured using a spectrophotometer at 517 nm. Distilled water was used as a control. The percentage of DPPH radical-scavenging activity was calculated based on a equation listed below:

$$\text{DPPH free radical - scavenging activity(\% )}=\frac{\text{Abs}\text{.of control - Abs}\text{.of sample}}{\text{Abs}\text{.of control}}\times 100$$

Total phenol content (TPC)

TPC was measured using the Folin-Ciocalteu reagent by the method of Das and Eun (2018). 1.75 mL of Folin-Ciocalteu reagent was combined with approximately 0.25 mL of a dilute powder solution. Then, the JAJP was mixed with 0.5 mL of sodium carbonate (Na₂CO₃) and incubated at 21 °C for 30 min in a dark place. Absorbance was measured using a spectrophotometer at a wavelength of 725 nm. Using gallic acid was used as the standard, the results were expressed as μg GAE/100 g.

Total flavonoid content (TFC)

The TFC was analyzed using the aluminum chloride-based colorimetric analysis by Das and Eun (2018). 0.3 mL of 5% sodium nitrite (NaNO₂) was mixed with 1 mL solution (1/10 with distilled water) and left to stand for 5 min. The sample was treated with 0.3 mL of 10% aluminum chloride (AlCl₃) and incubated for 6 min, then 2 mL of 1 M sodium hydroxide (NaOH) was added. After vortexing, the absorbance of mixed solution was measured at 510 nm using a spectrophotometer. The calibration curve was constructed using Catechin. TFC values are shown as micrograms of catechin per milliliter of JAJP (μg CE/100 g).

Results and discussion

Drying yield

For production of spray-dried powders, drying yield is considered an important parameter. Under the combination of 30% MD concentration and IAT 130 °C, a maximum yield of 67% was found (Table 1). The powder yield for JAJP varied from 23 to 67% (Table 2). Figure 1(A) demonstrates the drying yield increased as the MD concentration increased. According to Table 3, drying yield is significantly affected by MD concentration (P < 0.05).

$$\text{Drying yield}=51.82+14.00A-0.74B$$ 1

where A = MD concentration, B = inlet air temperature (°C).

Table 1.

Experimental data for the optimization of spray-dried Japanese apricot juice powder added with maltodextrin

STD	RUN	A	B	Response 1	Response 2	Response 3	Response 4	Response 5	Response 6	Response 7	Response 8	Response 9	Response 10	Response 11	Response 12
1	1	10	130	23	7.37	44.27	8.65	15.59	148.24	35.86	178.88	2.69	376.58	86.44	0.8
5	2	10	155	47	6.39	44.08	9.09	14.46	136.86	28.52	200.33	2.77	379.18	88.41	0.4
10	3	20	155	56	4.97	41.03	8.17	16.79	135.72	27	135.98	2.8	347.05	90.7	0.5
8	4	20	190	54	1.59	32.18	9.46	8.43	124.53	19.84	164.13	2.9	392.85	94.21	0.36
12	5	20	155	56	4.97	41.03	8.17	16.79	135.72	27	135.98	2.8	347.05	90.7	0.5
13	6	20	155	56	4.97	41.03	8.17	16.79	135.72	27	135.98	2.8	347.05	90.7	0.5
7	7	20	130	60	6.4	45.79	7.67	17.46	137.38	28.96	134.19	2.74	304.99	87.13	0.8
6	8	34	155	58	3.87	53	7.68	18.77	128.53	26.07	121.33	2.85	317.05	94.65	0.8
2	9	30	130	67	5.16	52.82	6.45	19.48	134.3	28.71	112.74	2.78	275.71	91.61	0.8
9	10	20	155	56	4.97	41.03	8.17	16.79	135.72	27	135.98	2.8	347.05	90.7	0.5
11	11	20	155	56	4.97	41.03	8.17	16.79	135.72	27	135.98	2.8	347.05	90.7	0.5
3	12	10	180	25	2.88	39.06	9.49	9.83	128.23	26	279.39	2.79	438.4	90.24	0.57
4	13	30	180	65	2.64	33.14	9.29	13.38	125.41	14.21	143.58	2.88	347.29	91.61	0.6

*All the responses are mean values of three replicates

A = maltodextrin concentration (%, B = inlet air temperature (°C), response 1 = drying yield (%), response 2 = moisture content (%), response 3 = color L* value, response 4 = color a* value, response 5 = color b* value, response 6 = vitamin C content (mg/g), response 7 = DPPH radical-scavenging activity (%), response 8 = total phenol content (μg GAE/100 g), response 9 = pH, response 10 = total flavonoid content (μg CE/100 g), response 11 = water solubility index (%), response 12 = bulk density (g/mL)

Table 2.

Criteria and limits of the optimized spray drying of Japanese apricot juice powder added with maltodextrin

Name	Goal	Minimum	Maximum
		Limit	Limit
Maltodextrin (%)	is in range	10	30
Inlet air temperature (°C)	is in range	130	180
Drying Yield (%)	Maximize	23	67
Moisture content (%)	Minimize	1.59	7.37
L*	Maximize	32.18	53
a*	is in range	6.45	9.49
b*	is in range	8.43	19.48
Vitamin C content (mg/g)	Maximize	124.53	148.24
DPPH radical-scavenging activity (%)	Maximize	14.21	35.86
Total phenol content (μg GAE/100 g)	maximize	112.74	279.39
pH	is in range	2.69	2.9
Total flavonoid content (μg CE/100 g)	Maximize	275.71	438.4
Water solubility index (%)	Maximize	86.44	94.65
Bulk density (g/mL)	Maximize	0.36	0.8

Fig. 1.

Response surface plots representing the effects of IAT and MD concentration on (A) drying yield, (B) moisture content, (C) bulk density, and (D) water solubility index and (E) pH

Table 3.

Regression coefficients for the prediction of response variables and their significance levels

Source	Response 1					Response 2					Response 3					Response 4
	Sum of Squares	df	Mean Square	F Value	p-value Prob > F	Sum of Squares	df	Mean Square	F Value	p-value Prob > F	Sum of Squares	df	Mean Square	F Value	p-value Prob > F	Sum of Squares	df	Mean Square	F Value	p-value Prob > F
Model	1366.64	2	683.32	8.48	0.007	30.90	5	6.18	93.04	< 0.0001	430.73	5	86.15	32.54	0.0001	8.64	5	1.73	126.36	< 0.0001
A	1362.61	1	1362.61	16.91	0.0021	4.08	1	4.08	61.38	0.0001	11.80	1	11.80	4.46	0.0727	2.53	1	2.53	184.77	< 0.0001
B	3.77	1	3.77	0.05	0.833	20.18	1	20.18	303.79	< 0.0001	206.19	1	206.19	77.88	< 0.0001	4.52	1	4.52	330.22	< 0.0001
AB	–	–	–	–	–	0.97	1	0.97	14.61	0.0065	52.35	1	52.35	19.77	0.003	1.00	1	1.00	73.12	< 0.0001
A2	–	–	–	–	–	0.01	1	0.01	0.19	0.675	74.16	1	74.16	28.01	0.0011	0.17	1	0.17	12.57	0.0094
B2	–	–	–	–	–	1.28	1	1.28	19.23	0.0032	12.17	1	12.17	4.60	0.0693	0.04	1	0.04	2.91	0.1317
Residual	805.67	10	80.57	–	–	0.46	7	0.07	–	–	18.53	7	2.65	–	–	0.10	7	0.01	–	–
Lack of Fit	805.67	6	134.28	–	–	0.46	3	0.15	–	–	18.53	3	6.18	–	–	0.10	3	0.03	–	–
Pure Error	0.00	4	0.00	–		0.00	4	0.00	–	–	0.00	4	0.00	–	–	0.00	4	0.00	–	–
Cor Total	2172.31	12	–	–	–	31.37	12	–	–	–	449.26	12	–	–	–	8.74	12	–	–	–

	Response 5					Response 6						Response 7						Response 8
Model	126.24	5	25.25	1043.84	< 0.0001	437.17	3	145.72		48.99	< 0.0001	254.67	2	127.333		28.3547	< 0.0001	22,195.2	5	4439.04		24.32	0.0003
A	22.45	1	22.45	928.00	< 0.0001	107.75	1	107.75		36.22	0.0002	67.06	1	67.0604		14.9331	0.0031	15,295.1	1	15,295.10		83.78	< 0.0001
B	56.81	1	56.81	2348.75	< 0.0001	299.14	1	299.14		100.56	< 0.0001	188.00	1	188.004		41.8648	< 0.0001	3397.96	1	3397.96		18.61	0.0035
AB	0.03	1	0.03	1.19	0.3105	30.91	1	30.91		10.39	0.0104	–	–	–		–	–	1213.48	1	1213.48		6.65	0.0366
A2	0.26	1	0.26	10.62	0.0139	–	–	–		–	–	–	–	–		–	–	4158.15	1	4158.15		22.78	0.002
B2	20.14	1	20.14	832.79	< 0.0001	–	–	–		–	–	–	–	–		–	–	267.078	1	267.08		1.46	0.2657
Residual	0.17	7	0.02	–	–	26.77	9	2.97		–	–	44.9073	10	4.49073		–	–	1277.92	7	182.56		–	–
Lack of Fit	0.17	3	0.06	–	–	26.77	5	5.35		–	–	44.9073	6	7.48456		–	–	1277.92	3	425.97		–	–
Pure Error	0.00	4	0.00	–	–	0.00	4	0.00		–	–	0.00	4	0.00		–	–	0.00	4	0.00		–	–
Cor Total	126.41	12	–	–	–	463.95	12	–		–	–	299.57	12	–		–	–	23,473.1	12	–		–	–

	Response 9					Response 10					Response 11					Response 12
Model	0.03	2	0.02	105.48	< 0.0001	18,435.55	2	9217.77	64.39	< 0.0001	65.61	2	32.81	50.53	< 0.0001	0.26	5	0.05	7.10	0.01
A	0.01	1	0.01	69.61	< 0.0001	10,291.69	1	10,291.69	71.89	< 0.0001	37.36	1	37.36	57.55	< 0.0001	0.02	1	0.02	2.63	0.15
B	0.02	1	0.02	141.70	< 0.0001	8111.43	1	8111.43	56.66	< 0.0001	28.37	1	28.37	43.69	< 0.0001	0.15	1	0.15	20.92	0.00
AB	–	–	–	–	–	–	–	–	–	–	–	–	–	–	–	0.00	1	0.00	0.03	0.86
A2	–	–	–	–	–	–	–	–	–	–	–	–	–	–	–	0.05	1	0.05	6.69	0.04
B2	–	–	–	–	–	–	–	–	–	–	–	–	–	–	–	0.03	1	0.03	4.19	0.08
Residual	0.00	10	0.00	–	–	1431.54	10	143.15	–	–	6.49	10	0.65	–	–	0.05	7	0.01	–	–
Lack of Fit	0.00	6	0.00	–	–	1431.54	6	238.59	–	–	6.49	6	1.08	–	–	0.05	3	0.02	–	–
Pure Error	0.00	4	0.00	–	–	0.00	4	0.00	–	–	0.00	4	0.00	–	–	0.00	4	0.00	–	–
Cor Total	0.04	12	–	–	–	19,867.092	12	–	–	–	72.11	12	–	–	–	0.31	12	–	–	–

*P < 0.05

A = maltodextrin concentration (%), B = inlet air temperature (°C), response 1 = drying yield (%), response 2 = moisture content (%), response 3 = color L* value, response 4 = color a* value

*P < 0.05

A = maltodextrin concentration (%), B = inlet air temperature (°C), response 5 = color b* value, response 6 = vitamin C content (mg/g) response 7 = DPPH radical-scavenging activity (%), response 8 = total phenol content (μg GAE/100 g)

*P < 0.05

A = maltodextrin concentration (%), B = inlet air temperature (°C), response 9 = pH, response 10 = total flavonoid content (μg CE/100 g), response 11 = water solubility index (%), response 12 = bulk density (g/mL)

Equation (1) demonstrates the relationship of MD concentration and IAT on the drying yield of JAJP. Drying yield is positively impacted by the MD concentration of JAJP and negatively influenced by IAT. Based on the results, the drying yield decreased at a drying temperature of 155 °C or higher. This trend can happen because the powder particles do not reach the drying chamber walls when the temperature is very high, and the IAT negatively affects the drying yield. Similar results have been reported in other studies (Aragüez‐Fortes et al., 2019). MD concentration, on the other hand, positively affects the drying yield of JAJP. This effect is likely to have occurred from the increase in solid content. A similar study (Tan et al., 2015) found that the dry yield increases in proportion to the MD concentration.

Moisture content

The moisture content of JAJP is shown in Table 1. The lowest moisture content was recorded at 1.59% when 20% MD concentration was used at 190 °C. Table 2 shows the minimum and maximum values of moisture content. As shown in Fig. 1(B), a decrease in moisture content was shown by increasing MD concentration and IAT. Table 3 indicates that the moisture content of JAJP had a considerable impact on MD concentration and IAT (P < 0.05).

$$\text{Moisture content = 5}.03-0\text{.79A}-1\text{.77B}+0\text{.49AB}+0{\text{.052A}}^2-0{\text{.52B}}^2$$ 2

The derived Eq. (2) indicates that MD concentration and IAT negatively affect the moisture content of JAJP. IAT increases the evaporation of water molecules and decreases the moisture content as a result. As Fazaeli et al. (2012) reported, high IAT promoted the heat to transfer to the particles leading to the evaporation of water and reduction in moisture content. This effect of IAT on the moisture content was reported in other studies using pink guava powder and acai juice power (Patil et al., 2014; Tonon et al., 2011). On the other hand, the moisture content of JAJP was observed to decrease as MD concentration increased, showing a negative effect between them, which can be explained by the increase in total solid content. Another study showed a similar result that MD decreased moisture content and increased the total solid content of the tested samples (Caliskan and Dirim, 2013). In the present study, a major variable affecting the moisture content of JAJP is high inlet air temperature.

Color

Color is an important sensory attribute that helps determine the quality of a powdered product. Different MD concentrations and IAT affecting the color of JAJP are shown in Tables 1, 2 shows the minimum and maximum values of color. Figure 2(A) shows a directly proportional relationship between L* values and MD concentration due to the increasing number of solids during spray drying. In contrast, this darkening in color was likely due to the high temperature in the air. IAT positively influenced while MD negatively affected the a* values. Conversely, for b* values, both IAT and MD concentration had a negative effect (Table 3). Based on Table 3, the different levels of MD concentrations had no statistically significant effect on L* values of JAJP, Whereas IAT significantly decreased the L* values (P < 0.05).

$$\text{Color L* = 41}.14+1.\text{35A}-5.\text{65B}-3.\text{62AB}+3.{\text{95A}}^{\text{2}}-1.{\text{60B}}^{\text{2}}$$ 3

$$\text{Color a* = 8}.20-0\text{.62A}+0\text{.84B}+0\text{.50AB}+0{\text{.19A}}^{\text{2}}+0{\text{.092B}}^{\text{2}}$$ 4

$$\text{Color b* = 16}.75+1\text{.86A}-2\text{.96B}-0\text{.085AB}-0{\text{.23A}}^{\text{2}}-2{\text{.06B}}^{\text{2}}$$ 5

Equations (3, 5) indicates the negative effect of IAT on the L* and b* values of JAJP and the positive effect of MD concentration on the L* and b* values of JAJP. In contrast, Eq. (4) shows the positive effect of IAT with the a* values of JAJP and the negative effect of MD concentration with the a* values of JAJP. The negative effect between IAT and L* and b* values can be attributed to the non−enzymatic browning process when high heat is introduced during the spray−drying process. On the other hand, as IAT increases, the a* value increases, which may explain that non−enzymatic browning reactions may occur during spray drying. Likewise, Nishad et al. (2017) reported that juice contents and carrier concentrations affected color. In addition, the color changes caused by hot air temperature increases may result from caramelization and Maillard reactions. Between the two factors associated with the change in L*, a*, and b* colors, IAT showed a greater effect compared to MD concentration, which means that the color of the product greatly depends on the drying temperature. Therefore, it is important to carefully design the IAT to obtain the desired color of the spray−dried powder.

Fig. 2.

Response surface plots representing the effects of IAT and MD concentration on (A) L*, (B)a*, and (C) b*value

Bulk density

The results for bulk density of the spray-dried JAJP at different MD concentrations and IAT are shown in Tables 1 and 2 shows the minimum and maximum values of bulk density. Figure 1(C) shows a tendency that the bulk density of JAJP increases with increasing MD concentration and decreases with increasing IAT. The results show that the bulk density of JAJP has a significant effect on MD concentration, whereas IAT has no significant effect (P < 0.05) (Table 3).

$${\text{Bulk density =}\text{0.49}\text{+}\text{0.054A}\text{-}\text{0.15B}\text{+}\text{7.500E}\text{-}\text{003 AB}\text{+}\text{0.10A}}^2{\text{+}\text{0.080B}}^2$$ 6

Equation (6) demonstrates the negative relationship between IAT with the bulk density of JAJP. Comparable results from Singh and Hathan (2017) were reported, namely that bulk density decreased with increasing inlet temperature. An increase in IAT often leads to dried layers forming on the droplet surface. However, at higher temperatures, a vapor-impermeable film is formed on the droplet surface due to thinning or case hardening. Then, vapor bubbles are generated and expand the droplets (Chegini and Ghobadian, 2005; Finney et al., 2002; Tonon et al., 2008, 2011). As a result, the density of JAJP decreases with increasing IAT.

Water solubility index (WSI)

Table 1 indicates the results for WSI of the spray−dried JAJP at different MD concentrations and IAT. Table 2 shows the minimum and maximum values of WSI. Figure 1(D) represents the WSI of the spray−dried JAJP. WSI was found to decrease at higher levels of IAT and MD concentration. The obtained WSI of JAJP was significantly affected by varying MD concentration and IAT (P < 0.05)(Table 3).

$$\text{Water solubility index = 90}.61+2\text{.32A}+2\text{.02B}$$ 7

Equation (7) demonstrates that IAT and MD concentration have a positive effect on the WSI of JAJP. This is due to the increased WSI with increasing IAT and MD concentration. As the inlet air temperature becomes higher, the density of the produced powder becomes lower, while its solubility becomes higher. It can be seen that bulk density was oppositely affected since the bulk density became lower as the solubility increased (Fazaeli et al., 2012). In addition, increasing the IAT led to the decrease in the bulk density and increase in the water solubility. Phisut (2012) reported that MD has a chemical structure that absorbs moisture more easily from ambient water. Similar observations were reported by Pires and da Silva Pena (2017). Therefore, increasing IAT and MD concentration during spray drying increases the WSI of the JAJP.

pH

Table 2 shows the minimum and maximum values of pH. Figure 1(E) indicates the tendency of pH to rise with increasing IAT. It is found that IAT had a more marked effect on the pH of JAJP than MD concentration did (P < 0.05) (Table 3).

$$\text{pH = 2}.80+0\text{.037A}+0\text{.053B}$$ 8

Equation (8) demonstrates that IAT positively affected the pH of JAJP. This outcome can be elucidated by the change in the organic acid content of Japanese apricot juice with increasing temperature. Lee et al. (2017) also presented that the pH change is directly affected by the organic acid content. Therefore, IAT is the main factor affecting the pH of JAJP, not the MD concentration^.

Vitamin C content

The effects of the IAT and MD concentration on the vitamin C content of spray−dried JAJP are shown in Fig. 3(A). As both the IAT and MD concentrations increased, the vitamin C content decreased. The observed Vitamin C content in JAJP varied between the ranges of 124.53 mg per 100 g and 148.24 mg per 100 g (Table 2). The lowest value of vitamin C content at 124.53 mg per 100 g was obtained at 190 °C IAT and 20% MD concentration, while the highest value of vitamin C at 148.24 mg per 100 g at 130 °C IAT and 10% MD concentration. From this, the trend in which vitamin C decreases as IAT increases could be observed (Table 1). The vitamin C content of JAJP was significantly influenced by MD concentration and IAT (Table 3) (P < 0.05).

$$\text{Vitamin C = 134}.33-3\text{.94A}-6\text{.56B}+2\text{.78AB}$$ 9

Equation (9) demonstrates that the IAT and MD concentration is negatively affected by the vitamin C content of JAJP. The vitamin C content decreased due to the reduction of particle size and faster decomposition of compounds as the IAT and MD concentration increased. The high IAT of the spray-drying process contributes to a significant decrease of vitamin C content because vitamin C is highly sensitive to heat (Shishir et al., 2017). Another study on spray-dried mandarin beverage powder presented that vitamin C content tended to decrease with increasing MD concentration and IAT (Lee et al., 2017). Thus, the reduction in vitamin C content could be caused by the increase in oxidation of vitamin C as affected by hot air, and by the increase in MD concentration. Further research is needed to determine other parameters and techniques that can minimize vitamin C content loss.

Fig. 3.

Response surface plots representing the effects of IAT and MD concentration on (A) vitamin C content, (B) DPPH radical-scavenging activity, (C) total phenol content, and (D) total flavonoid content

DPPH radical-scavenging activity

Table 1 indicates the DPPH radical−scavenging activity of spray−dried JAJP at varying levels of MD concentrations and IAT. The DPPH radical−scavenging activity ranged from 14.21% to 35.86% (Table 2). Figure 3(B) reveals the relationship between DPPH radical−scavenging activity and drying conditions of JAJP, Both IAT and MD concentration had a negative effect on the DPPH radical−scavenging activity of JAJP. DPPH radical−scavenging activity of JAJP markedly impacted by MD concentration and IAT (P < 0.05) in Table 3.

$$\text{DPPH radical}-\text{scavenging activity = 26}.65-3\text{.11A}-5\text{.20B}$$ 10

Equation (10) demonstrates that IAT and MD concentrations negatively influence the DPPH radical-scavenging activity of JAJP. DPPH radical-scavenging activity decreased significantly as IAT increased from 130 to 180 °C, and this result appears to be due to the high drying temperature. Mishra et al. (2014) explained that this phenomenon was caused by the decrease in DPPH radical-scavenging activity as MD concentration and IAT increased. Thus, the DPPH radical-scavenging activity of JAJP is affected more by IAT than by the MD concentration.

Total phenol content (TPC)

Table 1 displayed the results for TPC of spray−dried JAJP, which range from 112.74 to 279.39 μg GAE/100 g JAJP (Table 2). Figure 3(C) shows an increasing trend in the TPC of JAJP as the temperature increases. The TPC is significantly affected by the IAT and MD concentration (P < 0.05) (Table 3).

$$\text{TPC}=135.88-48.62\text{A}+22.92\text{B}-17.42\text{AB}+29.61{\text{A}}^2+7.50{\text{B}}^2$$ 11

Equation (11) demonstrates that the IAT positively influenced TPC of JAJP, whereas MD concentration negatively affected these factors. This trend of MD concentration is predicted to be due to the solid content increase, which decreases the amount of phenolic compounds. Similarity was found by Mishra et al. (2014), that the increase in the MD concentration from 5 to 9% led to a significant decrease in the TPC content of the powder. Also, it is found that IAT positively affects the TPC of JAJP. This positive relationship is due to the increase in polyphenol synthesis with higher IAT. A study by Hwang (2006) reported a similar result using pears. Hwang (2006) reported that antioxidants are more heat resistant than vitamin C and that most of the plant's phenolic components are in the form of glycosides or esters in a more stable conjugated form.

Total flavonoid content (TFC)

Table 1 indicates the TFC of spray−dried JAJP at varying MD concentrations and IAT. Table 2 shows the minimum and maximum values of TFC. Figure 3(D) illustrates the increase in the MD concentration predicts a decrease in the TFC of JAJP, while an increase in the IAT predicts an increase in the TFC. Based on the p−value found in Table 3, IAT and MD concentration were found to have a significant effect on the TFC in JAJP (P < 0.05).

$$\text{TFC}=351.46-38.\text{49A}+34.\text{17B}$$ 12

As shown in Eq. (12), the TFC of JAJP is positively affected by the IAT and negatively affected by the MD concentration. An explanation for this trend in the TFC is due to flavonoid synthesis and polymerization, which these processes affect the total content of the compounds. Comparable results have been presented using orange juice that the increase in TFC is due to the increase in TFC due to the reaction or structural decomposition of various phenolic compounds occurring at high temperatures (185 °C) upon spray drying (Saikia et al., 2015). Ioannou et al. (2012) reported that drying process generally results in the breakdown of flavonoids. However, the present study indicated that spray drying is a less aggressive technique that preserves flavonoids.

Optimization

Thirteen different experimental treatments based on the CCD were utilized to investigate the quality attributes of JAJP on the different levels of IAT and MD concentration. Results from the spray-drying process show that all these variables have significant effects on the physicochemical properties of JAJP. Optimum conditions for the spray drying of JAJP with MD as a drying aid were determined to obtain the specific values for each variable as summarized in Table 2. The overlay plot shown in Fig. S2 indicates the optimized parameters proposed by expert software design to obtain the required range of responses. Therefore, the conditions for spray drying of JAJP can be optimized using this selected model. Developing spray-dried JAJP with maltodextrin not only reduces shipping cost but also increases shelf life. In order to further promote the commercial expansion of JAJP, research on the shelf-life and sensory attributes of spray-dried JAJP are recommended in the future.

Supplementary Information

Below is the link to the electronic supplementary material.