Optimization of spray drying process of Japanese apricot (Prunus mume Sieb. et Zucc.) juice powder using nondigestible maltodextrin by response surface methodology (RSM)

Abstract

The optimal spray-drying conditions for manufacturing Japanese apricot (Prunus mume Sieb. et Zucc.) juice powder (JAJP) using response surface methodology (RSM) were investigated. The optimization was performed using two independent factors, which are inlet air temperature (130–180 °C) and different concentrations of nondigestible maltodextrin (NMD) as a carrier agent (10–30%). Responses such as drying yield, moisture content, water solubility index (WSI), bulk density, color, pH, and antioxidant activities of JAJP were investigated. Moisture content, vitamin C content, color, antioxidant activity, pH and bulk density were greatly influenced by inlet air temperature, but dry yield and WSI were only significantly affected by NMD concentration. The optimum spray drying conditions were determined as 14.7% NMD concentration and 154.5 °C inlet air temperature, respectively. At these optimum conditions, a drying yield of 55.73%, 4.84% moisture content, 90.98% WSI, 0.59 g/mL of bulk density, and 169.87 mg/g vitamin C content in JAJP were measured. Therefore, JAJP with the desirable physicochemical properties could be produced.

Introduction

Japanese apricot (Prunus mume Sieb. Et Zucc.) fruit contains approximately 80% of the fruit flesh, which consists of approximately 85% water and 10% sugar. Japanese Apricot fruit is rich in minerals, vitamins, and organic acids (citric acid, malic acid, succinic acid, and tartaric acid) (Kang et al. 1999). Citric acid stimulates the metabolism of sugars and relieves fatigue, while other organic acids function in the gastrointestinal tract and promote appetite. Japanese apricot is a fruit that cannot be used in its raw form but can be processed. To date, research has been conducted on processed products, such as kimchi (Kim et al. 2010) and red pepper paste (Lee et al. 2011) prepared using processed Japanese apricot juice. These processed products are mostly solid or liquid, and because of their large volume and weight, transportation and storage costs are high. However, if the powdered form of Japanese apricot is used, it will not only reduce the weight but will also lower the transportation cost.

Spray drying is widely used by the food industry to produce dried powder and condensate. Fruit juice powder offers many advantages over its liquid form, such as reduced volume and weight, minimal use of packaging, ease of handling, and product stability even during extended shipping and distribution periods (Goula et al. 2004). The main advantages of spray drying are operational cost effective, minimal product damage, and short spray drying treatment times. (Sagar and Kumar 2010). However, major challenges in the spraydring of fruit juices are stickiness and flowability of powders. Carriers are used to solve this problem. Maltodextrin, gum arabic, and gelatin have been widely used as carriers of spray drying. Among them, maltodextrin can promote drying by changing the surface tackiness of low molecular weight sugars such as glucose, sucrose, fructose, and organic acids, thereby promoting drying and reducing the stickiness of spray-dried products. However, many studies using non-digestible maltodextrin (NMD) have not been conducted. NMD is a soluble dietary fibre obtained by hydrolyzing corn starch and is a recognized functional ingredient in controlling post-dinner blood glucose rise and improving blood triglycerides (Livesey and Tagami, 2009). Currently, NMD sold in the market contains 85% dietary fiber and only provides 2 kilocalories per gram, making its food material rich in dietary fiber and low in calories (Kim 2005). Ohkuma et al. (1990) found that NMD was resistant to digestive system enzymes, while Wakabayashi (1993) experimented on mice by feeding them NMD and reported a significant decrease in the blood glucose of these test subjects. Furthermore, Fujiwara and Matsuoka (1995) reported decreased blood sugar and insulin secretion when NMD was ingested by adults. Thus, the use of NMD is considered to be very beneficial for people with diabetes or obesity and for those who need to lessen their glucose intake. With a growing interest in health, many functional foods are being manufactured with added bioactive ingredients, which affect the process yield and to produce a stable powder with high nutritional and functional values (Igual et al. 2014). In order to obtain a good product with nutritional characteristics and higher process yield, it is important to understand the factors affecting the optimization process of the fruit juice. In this study, the effect of inlet air temperature and NMD concentration on the physical and chemical properties of spray-dried Japanese apricot juice was investigated to improve and optimize the spray drying process.

Materials and methods

Materials

Japanese apricot concentrate was obtained from a local manufacturing company in Gwangyang, Korea, and stored at 4 °C until used. NMD (Corn starch; Daesang, Seoul, Korea) with 20 dextrose equivalents (DE), which was used as a carrier agent, were purchased from a local market in Gwangju, Korea.

Methods

Juice preparation

Before being dehydrated, the juice (an initial of 63° Brix) was diluted with distilled water until a total soluble solid content of 10° Brix was reached. Once the total juice solids were standardized, the following substance was added: nondigestible maltodextrin of range 10–30% (w/v).

Spray drying

Japanese apricot juice was spray-dried using a pilot-scale spray dryer (MH-8, Mehyun Engineering, Gyeonggi-do, Korea) with a rotary disc atomizer. The samples were fed into the main chamber through a 1.5 mm diameter nozzle using a peristaltic pump, and the feed flow rate was controlled with the pump rotation speed. The atomizer speed, feed rate, and compressor air pressure were constant at 9860 rpm, 12 mL/min, and 0.74 MPa, respectively. The inlet air temperature ranged from 130 to 190 °C. The concentration of NMD added to the juice varied from 10 to 34% w/v.

Experimental design

The response surface methodology (RSM) was used to determine the optimal formulation conditions using a 12-level central composite design (CCD), which guided 13 experiments. The independent variables that affect the quality of the final product were different levels of inlet air temperature (IAT) and NMD concentration. The IAT varied between 130 and 190 °C, and the NMD concentration ranged from 10 to 34%. RSM was used to evaluate the effect of the operational parameters on drying yield, moisture content, color, vitamin C content, DPPH radial-scavenging activity, water solubility index (WSI), total flavonoid content (TFC), total phenol content (TPC), and bulk density.

Physicochemical characteristic

Drying yield

Determination of the drying yield was carried out as per the method reported by Laokuldilok and Kanha (2015). The mass of the powder collected was divided by the total solids in the feed mixture in the main chamber of the spray dryer (i.e., the mass of soluble and insoluble solids present in the Japanese apricot juice plus the NMD added to the formulation). The total solid content in the Japanese apricot juice was gravimetrically measured by drying the Japanese apricot juice in a drying oven (FO-600, Jeio Tech, Seoul, Korea), at 105 °C for 24 h.

Moisture content

The moisture content of JAJP (2 g) was determined gravimetrically by drying juice in the oven at 105 °C until a constant weight was achieved (A.O.A.C. 2005).

$$\text{Moisture content}=\frac{\left(\text{W}1-\text{W}2\right)\times 100}{\text{W}1}$$

where,

W1 = weight (g) of sample before drying, W2 = weight (g) of sample after drying.

Color measurement

The color of JAJP (5 g) was determined using a colorimeter (CR-400, Minolta, Tokyo, Japan). The results were expressed as color values of L* (lightness), a* (redness) and b* (yellowness and blueness).

Bulk density

JAJP (2 g) was carefully placed into an empty 10 mL graduated cylinder and vibrated on a vortex vibrator for 1 min. The bulk density (g/mL) was derived from the ratio of the mass of the powder and the volume occupied in the cylinder (Goula and Adamopoulos 2005).

Water solubility index (WSI)

The WSI was determined using the method described by Anderson (1982). A spray-dried powder (2 g) was added to distilled water (25 mL) at 30 °C. The mixture was stirred intermittently for 20 min and centrifuged for 15 min at 2016×g. The supernatant was carefully poured into a Petri dish. Wet solids remaining after centrifugation were dried in an oven (105 °C) overnight. WSI was expressed as a % of total dry solids of the spray-dried sample (2 g).

pH

The pH of JAJP was determined using the method described by Robert (2003). Two grams of JAJP were mixed with 25 mL of distilled water and were homogenized and centrifuged at 2016 × g for 15 min. Then, the pH of the supernatant was measured using a pH meter (EF-7732, Istek, Seoul, Korea).

Vitamin C content

The Vitamin C content in JAJP was measured by analyzing chromaticity measurements using 2,6-dichlorophenolindophenol as previously described by Das and Eun (2018). Briefly, 0.5 mL of diluted Japanese apricot juice powder was added to 0.5 mL of 2,6-dichlorophenolindophenol chloride solution (0.1 mg/mL). The reaction mixture was incubated at room temperature for five minutes, and absorbance was measured at 500 nm using a spectrophotometer. Vitamin C content was calculated using the standard curve of L-ascorbic acid (mg/g).

DPPH radical-scavenging activity

The free radical-scavenging (FRSA) of JAJP solution was analyzed using DPPH (2,2-diphenyl-1-picrylhydrazyl) as described by Das and Eun (2018). Briefly, 50 μL of JAJP solution (1/15 with distilled water) was combined with 950 μL of the 100 μM DPPH reagent ethanol solution. The mixture was allowed to stand for 30 min at room temperature (25 °C). Scavenging activity was measured and quantified by using a spectrophotometer at 517 nm. The results were expressed as a percentage of DPPH radical-scavenging activity. DPPH radical-scavenging activity was calculated using the following equation:

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

Total phenol content (TPC)

The level of TPC in the JAJP solution was determined using the Folin-Ciocalteu reagent (Das and Eun 2018). About 0.25 mL of JAJP diluted solution was combined with 1.75 mL of Folin-Ciocalteu reagent. Afterward, the specimen was treated with 0.5 mL of sodium carbonate (Na₂CO₃) and incubated at room temperature for 30 min in a dark place. The absorbance was measured at a wavelength of 725 nm using a spectrophotometer. Gallic acid was used as the standard, and the results were expressed in μg GAE/100 g.

Total flavonoid content (TFC)

JAJP solution was analyzed for TFC using an aluminum chloride-based colorimetric assay (Das and Eun 2018). An aliquot (1 mL) of JAJP diluted solution (1/10 with distilled water) was mixed with 0.3 mL of 5% sodium nitrite (NaNO₂) and incubated for 5 min. Samples were treated with 0.3 mL of 10% aluminum chloride (AlCl₃), incubated for 6 min, and then 2 mL of 1 M sodium hydroxide (NaOH) was added. The solutions were vortexed, and the absorbance was measured at 510 nm using a spectrophotometer. Catechin was used to construct the calibration curve. The TFC values were expressed as microgram catechin per milliliter of Japanese apricot juice powder (μg CE/100 g).

Results and discussion

Drying yield

Drying yield is a critical factor in the production of spray-dried powder. The drying yield of JAJP varied from 23 to 70% (Table 2). The maximum yield (Table 1) can be obtained under the combination of 30% NMD concentration and IAT 130 °C. As shown in Fig. 1a, the drying yield increased as the NMD concentration increased. In Table 3, NMD concentrations have a significant effect on the drying yield, but the IAT is not considered to have a significant effect (P < 0.05).

$$\text{Drying yield}=+65.14+13.94\ast \text{A}-3.62\ast \text{B}+3.75\ast \text{A}\ast \text{B}-7.83\ast {\text{A}}^2-5.53\ast {\text{B}}^2$$ 1

Table 2.

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

Name	Goal	Minimum limit	Maximum limit
Nondigestible maltodextrin (%)	Is in range	10	30
Inlet air temperature (°C)	Is in range	130	180
Drying Yield (%)	Maximize	23	70
Moisture content (%)	Minimize	1.37	8.12
L*	Maximize	34.14	53.82
a*	Iis in range	5.52	9.4
b*	Is in range	7.13	20.36
Vitamin C content (mg/g)	Maximize	164.21	174.73
DPPH radical-scavenging activity (%)	Maximize	19.11	31.36
pH	Is in range	2.71	2.89
Water solubility index (%)	Maximize	87.71	95.04
Total flavonoid content (μg CE/100g)	Maximize	223.65	565.3
Total phenol content (μg GAE/100g)	Maximize	112.74	271.39
Bulk density	Maximize	0.4	0.8

Table 1.

Experimental data for the optimization of spray-dried Japanese apricot juice powder added with nondigestible maltodextrin. A = nondigestible maltodextrin (%), 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 = pH, response 9 = water solubility index (%), response 10 = total flavonoid content (μg CE/100 g), response 11 = total phenol content (μg GAE/100 g), response 12 = bulk density (g/mL)

STD	RUN	A	B	Response 1	Response 2	Response 3	Response 4	Response 5	Response 6	Response 7	Response 8	Response 9	Remainder 10	Remainder 11	Remainder 12
1	1	10	130	41	8.12	45.27	7.53	16.77	174.73	31.36	2.71	87.71	308.25	214.63	0.8
5	2	10	155	56	5.35	45.08	7.82	16.33	172.73	27.78	2.77	89.41	331.02	254.41	0.44
10	3	20	155	64	4.54	46.96	8.31	16.39	168.28	24.04	2.8	92.16	291.98	167.71	0.6
8	4	20	190	53	1.37	35.17	9.16	7.13	164.21	19.7	2.89	95.04	389.59	199.44	0.4
12	5	20	155	64	4.54	46.96	8.31	16.39	168.28	24.04	2.8	92.16	291.98	167.71	0.6
13	6	20	155	9	4.54	46.96	8.31	16.39	168.28	24.04	2.8	92.16	291.98	167.71	0.6
7	7	20	130	62	5.84	46.79	6.63	18.04	169.9	26.65	2.74	89.41	249.68	151.71	0.8
6	8	34	155	66	2.92	53.8	5.52	18.39	167.07	22	2.85	92.38	285.47	133.3	0.8
2	9	30	130	70	4.8	53.82	1.73	20.36	168.76	25.23	2.78	92.02	223.65	112.74	0.8
9	10	20	155	64	4.54	46.96	8.31	16.39	168.28	24.04	2.8	92.16	291.98	148.58	0.6
11	11	20	155	64	4.54	46.96	8.31	16.39	168.28	24.04	2.8	92.16	291.98	148.58	0.6
3	12	10	180	23	1.82	34.14	9.4	8.99	166.84	23.27	2.79	90.21	565.3	271.39	0.5
4	13	30	180	67	1.68	40.06	8.62	11.46	166.52	19.11	2.88	92.51	288.72	135.98	0.6

^* All the responses are mean values of three replicates

Fig. 1.

Response surface 3D-plot for the effects of inlet air temperature and nondigestible maltodextrin concentration on a drying yield, b moisture content, c bulk density, d water solubility index, and e pH

Table 3.

Significant levels of measured parameters responses values for Japanese apricot juice powder added with nondigestible maltodextrin

P-value	Drying yield	Moisture content	L*	a*	b*	Vitamin C content	DPPH radical-scavenging activity	pH	Water solubility index	Total flavonoid content	Total phenol content	Bulk density
Model	0.007	< 0.0001	< 0.0001	0.0005	< 0.0001	< 0.0001	< 0.0001	< 0.0001	0.0034	0.0013	< 0.0001	0.0003
A	0.0009	< 0.0001	0.0006	0.0022	0.0004	< 0.0001	< 0.0001	< 0.0001	0.0012	0.0046	< 0.0001	0.0140
B	0.1932	< 0.0001	< 0.0001	0.0002	< 0.0001	< 0.0001	< 0.0001	< 0.0001	0.0032	0.0017	0.0017	0.0002
AB	0.2798	0.0011	0.4241	0.0072	0.2874	0.0037	0.0290		0.2619	0.0499	0.1502
A2	0.0323		0.4498	0.0364	0.3906	0.0053	0.0012		0.015		0.0012
B2	0.1022		0.0017	0.0645	< 0.0001	0.2097	0.6705		0.9325		0.7013
R2	0.8584	0.9756	0.9596	0.936	0.9904	0.9643	0.9926	0.9638	0.8857	0.8102	0.9721	0.7998

where,

A = NMD concentration, B = IAT (°C).

Equation (1) shows that drying yield is positively influenced by NMD concentrations of JAJP and that IAT has a negative effect on the drying yield of JAJP. According to the results obtained, the drying yield of JAJP increases as the IAT rises up to 155 °C, but the drying yield decreases when the IAT rises further and reaches 180 °C. This could be the result of the powder melting at higher temperatures. On the other hand, as the NMD concentration increased, the drying yield of JAJP tended to increase, which is considered to be due to the increase in solid content. Similarly, Tonon et al. (2008) reported a significant increase in dry yield as the maltodextrin (MD) concentration of acai juice increased. It is clear that the drying yield of JAJP increases as the NMD concentration increases, but yield increases with IAT increases until 155 °C.

Moisture content

Table 1 shows that moisture content decreased with increasing IAT and NMD concentrations. Table 2 shows the minimum and maximum values that can be obtained when optimizing the spray drying process. As can be seen in Fig. 1b, the moisture content decreases when NMD concentration and IAT increase. In Table 3, NMD concentration and IAT had a significant effect on the moisture content of JAJP (P < 0.05).

$$\text{Moisture content}=+4.30-0.93\ast \text{A}-2.16\ast \text{B}+0.79\ast \text{A}\ast \text{B}$$ 2

The derived Eq. (2) shows that the NMD concentration and the IAT have a negative effect on the moisture content of JAJP. The decrease in moisture content could be caused by the high temperature gradient as the temperature of the hot air increases. As IAT increases, the rate of heat transfer to the particles and moisture evaporation are accelerated, thus reducing the moisture content of JAJP. The moisture content of JAJP decreases as the NMD concentration increases. The total soluble solid content increases by increasing the amount of the carrier, thereby reducing the amount of evaporated water, which is believed to decrease the moisture content of the produced powder.

Using Agaricus blazeri Murill, the same conclusion was found that the powder moisture decreased as the inlet air temperature increased (Hong and Choi 2007). Similarly, for JAJP, the reduction in moisture content was caused by the increase in IAT during spray drying.

Color

In dried foods, color change is considered an important factor because the color of the dried food affects the consumer's preferences. Figure 2a, b show a directly proportional relationship between the increase in L* values and NMD concentration. This relationship can be explained by the increasing amount of solids during the spray drying process. However, as IAT increased, L* values decreased. Similarly, b* values increased with increasing NMD concentration and decreased with increasing IAT. Beyond the IAT of 165 °C, a* does not decrease with increasing NMD concentration.

Fig. 2.

Response surface 3D-plot for the effects of inlet air temperature and nondigestible maltodextrin concentration on a L*, b a* and c b* value

Conversely, a* values increased with increasing IAT, and decreased with increasing NMD concentration. Table 3 shows the probability value (p-value) for NMD concentrations and IAT and using this as reference. The varying levels of NMD concentrations in L* values were found to have no significant effect on JAJP, while IAT had a significant effect (P < 0.05).

$$\text{Color L}\ast =+46.92+3.58\ast \text{A}-5.04\ast \text{B}-0.66\ast \text{A}\ast \text{B}+0.57\ast {\text{A}}^2-3.51\ast {\text{B}}^2$$ 3

$$\text{Color a}\ast =+8.30-1.24\ast \text{A}+1.84\ast \text{B}+1.25\ast \text{A}\ast \text{B}-0.79\ast {\text{A}}^2-0.67\ast {\text{B}}^2$$ 4

$$\text{Color b}\ast =+16.46+1.23\ast \text{A}-3.97\ast \text{B}-0.28\ast \text{A}\ast \text{B}+0.20\ast {\text{A}}^2-2.13\ast {\text{B}}^2$$ 5

Equations (3) and (5) show a negative effect between the L* and b* values of the IAT of JAJP. The changes in L* and b* values as IAT increased can be due to the caramelization process that may have occurred upon the application of high heat during spray drying. Conversely, a positive effect between the L* and b* values on the NMD concentrations of JAJP is observed. The NMD concentration has a positive effect on JAJP in which the white color of NMD lightened the dark color of the Japanese apricot juice. Thus, L* and b* values increased. Likewise, Eq. (4) shows a positive effect between the IAT and a* values of JAJP and has a negative effect between the a * values of NMD concentration of JAJP. The increase in the a* value brought about by the increase in IAT can be explained by the occurrence of non−enzymatic browning reactions. Similarly, Fennema (1976) reported that an increase in sugar concentration also occurred during the spray drying of pineapple juice, which may be the result of some non−enzymatic browning reactions such as caramelization and maillard reactions occurring during the drying process. Lee et al. (2017) also reported that it was affected by caramelization and maillard reaction that occurs when sugar is present at high temperature during drying. Based on these results, it can be concluded that when spray drying Japanese apricot juice, the IAT should be taken into much more consideration than the NMD concentration because IAT can influence the color of JAJP more than the concentration of the carrier agent.

Bulk density

The results for bulk density of the spray-dried JAJP at different NMD concentrations and IAT are shown in Table 1. Figure 1c shows the increasing trend of bulk density of spray-dried JAJP as NMD concentrations increased, and the decreasing trend of bulk density as IAT decreased. Results (Table 3) from varying NMD concentrations show a significant effect on the bulk density of JAJP, whereas IAT did not have a significant effect on the bulk density of JAJP (p < 0.05).

$$\text{Bulk density}=+0.63+0.076\ast \text{A}-0.14\ast \text{B}$$ 6

Equation (6) shows a positive effect between NMD concentrations and the bulk density of JAJP. Similar observations were noted in a study regarding tomato and orange juice powders in which the increase in MD concentrations also led to the increase in bulk density (Goula and Adamopoulos 2010).

Water solubility index (WSI)

Table 1 shows the WSI of the spray−dried JAJP at different NMD concentrations and IAT. Table 2 shows the minimum and maximum values obtained when optimizing the spray drying process. Figure 1d shows the WSI of the spray−dried JAJP. WSI was decreased with increasing IAT and NMD concentration. In Table 3, the obtained WSI of JAJP with varying NMD concentrations and IAT was considered significant (p <0.05).

$$\text{Water solubility index}=+92.07+1.70\ast \text{A}+1.42\ast \text{B}-0.50\ast \text{A}\ast \text{B}-1.21{\text{A}}^2-0.033\ast {\text{B}}^2$$ 7

Equation (7) shows that the IAT and NMD concentrations have a positive effect on with the water solubility index of JAJP. In contrast, bulk density has an opposite effect: the lower the bulk density, the higher the solubility (Fazaeli et al. 2012). Moreover, higher IAT also caused lower bulk density, which in turn could have increased solubility. In a related study, Tonon et al. (2009) also found similar results and explained that MD has a large enthalpy effect on hydrophilic groups, making it easier to absorb water from the surrounding water. From these results, it can be suggested that the WSI of JAJP is greatly influenced by the increase in NMD concentration.

pH

In Fig. 1e, it can be observed that pH tends to increase with increased IAT. In Table 3 as a reference, the pH results of JAJP were found to be affected by IAT and NMD concentrations (p < 0.05).

$$\text{pH}=+2.80+0.037\ast \text{A}+0.053\ast \text{B}$$ 8

Equation (8) shows that IAT has a positive effect on the pH of JAJP. The positive effect was due to the increase in pH with increased IAT, which can be explained by the change in organic acid content in the Japanese apricot juice as temperatures increased. In relation to this, a study by Mahendran (2011) reported that some acids were lost due to evaporation during the spray drying of guava fruit juice, increasing the pH.

Vitamin C content

The effects of NMD concentration and IAT on the vitamin C content of spray−dried JAJP are shown in Fig. 3a. As the IAT and NMD concentration increased, the vitamin C content tended to decrease. Vitamin C content varied from a minimum of 164.21 mg to a maximum of 174.73 mg per 100 g of JAJP (Table 2). The vitamin C content of JAJP has been significantly affected by NMD concentration and IAT (Table 3) (p <0.05).

$$\text{Vitamin C}=+168.34-2.09\ast \text{A}-2.41\ast \text{B}+1.41\ast \text{A}\ast \text{B}+1.21\ast {\text{A}}^2-0.42\ast {\text{B}}^2$$ 9

Fig. 3.

Response surface 3D-plot for the effects of inlet air temperature and nondigestible maltodextrin concentration on a vitamin C content, b DPPH radical-scavenging activity c total phenol content, and d total flavonoid content

Equation (9) shows that IAT and NMD concentrations have a negative effect on the vitamin C content of JAJP. Patil et al. (2014) found that the vitamin C content of spray-dried guava powder was observed to decrease with increased MD concentrations and IAT. Thus, the decrease in vitamin C content appears to be due to the increase in vitamin C oxidation by IAT and NMD concentration increases. It can be seen that as the NMD concentration increases, the vitamin C content decreases. With the same result Lee et al. (2017) reported that high percentage of maltodextrin with high temperature had lower amount of vitamin C. These might be related to oxidize of vitamin C or particle size. Further research is needed to prevent the loss of vitamin C content during spray drying.

DPPH radical-scavenging activity

The DPPH radical−scavenging activity ranged from 19.11 to 31.36% (Table 2). Figure 3b shows the relationship between DPPH radical−scavenging activity of JAJP, in which a decreasing trend in DPPH radical−scavenging activity of JAJP can be observed with increased IAT and NMD concentrations. DPPH radical−scavenging activity of JAJP was found to be significantly affected by NMD and IAT (p <0.05) listed in Table 3.

$$\text{DPPH radical}-\text{scavenging activity}=+24.01-2.64\ast \text{A}-3.27\ast \text{B}+0.49\ast \text{A}\ast B+0.86{\text{A}}^2-0.073\ast {\text{B}}^2$$ 10

Equation (10) shows that the IAT and NMD concentrations have a negative effect on the DPPH radical-scavenging activity of JAJP. There was a significant decrease in DPPH radical-scavenging activity with increased IAT from 130 to 180 °C, which appears to be due to the decreased higher temperatures which adversely affected thestructure of phenolics causing its break down and/or synthesisinto different forms. Similarly, Mishra et al. (2014) reported that DPPH radical-scavenging activity decreased with increased MD concentrations and IAT. In conclusion, the DPPH radical scavenging activity of JAJP decreased with increasing NMD concentration and IAT.

Total phenol content (TPC)

The results for TPC of spray−dried JAJP are shown in Table 1. Figure 3c shows the TPC of the JAJP, and from this, a decreasing trend in TPC can be observed as the temperature increases. The TPC of JAJP is greatly affected by IAT and NMD concentrations (p <0.05) based on the probability value (p−value) listed in Table 3.

$$\text{TPC}=+161.75-59.38\ast \text{A}+20.04\ast \text{B}-8.38\ast \text{A}\ast \text{B}+24.95{\text{A}}^2+1.90\ast {\text{B}}^2$$ 11

Equation (11) shows that the IAT has a positive effect on the TPC of JAJP while NMD concentration has a negative effect on the TPC of JAJP. The effect on NMD concentration is due to the increase in the solid content, leading to a decrease in the amount of phenolic compounds. According to Ahmed et al. (2010), total soluble solid content increases with increasing MD concentration because the resting molecules are located closely which influences the (increased or decreased) phenolic contents.

Total flavonoid content (TFC)

The TFC of spray−dried JAJP at different NMD concentrations and IAT can be seen in Table 1. Figure 3d shows that as the NMD concentration increases, the TFC of JAJP decreases, while as IAT increases, the TFC of JAJP increases. The TFC of JAJP has been significantly affected by NMD concentration and IAT (Table 3) (P <0.05).

$$\text{TFC}=+315.18-60.15\ast \text{A}+70.66\ast \text{B}-48.00\ast \text{A}\ast \text{B}$$ 12

Equation (12) shows that IAT has a positive effect on the TFC of JAJP, and that the NMD concentration has a negative effect on the TFC of JAJP. This inverse trend is thought to be explained by the flavonoid synthesis and polymerizations that take place and affect the total content of these compounds. Similar results are reported by Vidović et al. (2014). Therefore, the TFC of JAJP is significantly affected by IAT rather than by NMD concentrations because the TFC of JAJP increased with increased IAT.

Optimization

Response surface methodology (RSM) is a commonly used tool for analyzing experimental data to optimize processes or products. In order to find out the conditions for producing the optimum powder, a numerical optimization procedure was carried out. The optimum condition for the spray drying of JAJP by using NMD concentration and IAT are as follows: 1) minimum range of moisture content and bulk density, 2) maximum range of drying yield, L *value, vitamin C content, DPPH radical-scavenging activity, WSI, TFC, and TPC, 3) in range of the goal values for a*, b*, and pH. The optimal conditions selected provided by the software was NMD = 14.7%, and IAT = 154.5 °C. With these conditions, it is possible to produce a powder with these properties: 55.73% drying yield, 4.84% moisture content, 45.26 L* value, 8.71 a* value, 15.93 b* value, 169.87 mg/g vitamin C content, 25.74% DPPH radical-scavenging activity, 2.78 pH, 90.78% WSI, 200.07 μg GAE/100 g TPC, 345.40 μg CE/ 100 g TFC, and 0.59 bulk density. Therefore, under this selected model, the spray drying process conditions for JAJP can be optimized.

Conclusion

Japanese apricot juice powder was successfully produced using the spray-drying technique. Effects of spray drying conditions on the physicochemical properties were evaluated using a central composite design. Responses such as drying yield, moisture content, water solubility index (WSI), bulk density, color, pH, and antioxidant activities of JAJP were investigated. Moisture content, vitamin C content, color, antioxidant activity, pH and bulk density were greatly influenced by inlet air temperature, but dry yield and WSI were only significantly affected by NMD concentration. The optimum spray drying conditions were found at 14.7% NMD concentration and 154.5 °C IAT thqnrough RSM. The response surface methodology has been successfully found in determining the optimal process conditions for the production of high-quality spray dried Japanese apricot juice powder with desirable properties for all reactions. Therefore, NMD can be used as a spray drying supplement for Japanese apricot juice. In order to be used for industrial purposes in future studies, a sensory evaluation must be performed to understand the taste of the customer, and the shelf life of the powder must be evaluated and set.