Optimization of Sour Cherry Juice Spray Drying as Affected by Carrier Material and Temperature

Economic and industrial development infl uenced changes in consumer trends, focusing on the consumption of fresh fruits and vegetables as the healthy, nutritive and biologically valuable food, rich in biologically active components. However, fruits and vegetables are highly perishable products, so in order to answer to market demands and ensure their longer period of availability, industry off ers diff erent preservation and processing techniques. The main problem regarding the storage of fruit products is high water content, which makes them susceptible to elevated enzymatic activity and microbial growth, leading to quality degradation and deterioration. The prolongation of fruit product shelf life and stability can be achieved by drying as one of the most commonly used preservation techniques for reduction of the water content of food, and subsequently for reduction of microbial growth as well as enzymatic activity. Furthermore, drying reduces the mass and volume of food products resulting in lower storage and transportation costs and making the product easier to handle (1). Numerous drying methods have been developed aiming to increase productivity, processing control as well as the quality of the fi nal product. Spray drying is a widely spread technique for drying of liquid products, such as fruit juices, into powder form. However, during drying of fruit juices, stickiness on the drier wall, wet, plastic appearance, agglomeration and clumping occur, resulting in operational problems and increased losses (2). Low glass transition temperature of sugars, which make about 90 % of juice dry matt er, is the main cause of the stickiness (3). Common approaches for a solution to this problem involve modifying the sticky characteristics of the material most frequently through the addition of carrier agents and controlling the inlet and outlet temperature of the dryer (4). Advantages of this method mainly include short drying period because of a large heat transfer surface, low product surface temperature, no direct contact of food with heated metal surface, stability and high quality of the fi nal product. As fruit powders have a variety of potential uses in food industry, as semi-products or fi nal products ISSN 1330-9862 original scientifi c paper


Introduction
Economic and industrial development infl uenced changes in consumer trends, focusing on the consumption of fresh fruits and vegetables as the healthy, nutritive and biologically valuable food, rich in biologically active components.However, fruits and vegetables are highly perishable products, so in order to answer to market demands and ensure their longer period of availability, industry off ers diff erent preservation and processing techniques.The main problem regarding the storage of fruit products is high water content, which makes them susceptible to elevated enzymatic activity and microbial growth, leading to quality degradation and deterioration.The prolongation of fruit product shelf life and stability can be achieved by drying as one of the most commonly used preservation techniques for reduction of the water content of food, and subsequently for reduction of microbial growth as well as enzymatic activity.Furthermore, drying reduces the mass and volume of food products resulting in lower storage and transportation costs and making the product easier to handle (1).Numerous drying methods have been developed aiming to increase productivity, processing control as well as the quality of the fi nal product.Spray drying is a widely spread technique for drying of liquid products, such as fruit juices, into powder form.However, during drying of fruit juices, stickiness on the drier wall, wet, plastic appearance, agglomeration and clumping occur, resulting in operational problems and increased losses (2).Low glass transition temperature of sugars, which make about 90 % of juice dry matt er, is the main cause of the stickiness (3).Common approaches for a solution to this problem involve modifying the sticky characteristics of the material most frequently through the addition of carrier agents and controlling the inlet and outlet temperature of the dryer (4).Advantages of this method mainly include short drying period because of a large heat transfer surface, low product surface temperature, no direct contact of food with heated metal surface, stability and high quality of the final product.As fruit powders have a variety of potential uses in food industry, as semi-products or fi nal products with high nutritive and functional benefi ts, optimizing the spray drying process is a worthwhile step.
Sour cherry Marasca (Prunus cerasus var.Marasca) is a cultivar characterized by high content of dry matt er (21.0-27.3%) (5), biologically active compounds (polyphenols, melatonin and vitamin C), dark red colour and inten se sweet-sour aroma (5)(6)(7)(8).Although it is rarely consumed fresh, the possibilities for processing are numerous: jams, juices and concentrated juices, frozen and dried products, among which fruit powders are recognized.Because of its intense colour, fl avour and high dry matt er content, sour cherry Marasca juice is a great material for production of spray-dried fruit powders.However, Marasca juice is a demanding material for spray drying and preservation of its natural att ributes such as colour, aroma and fl avour.Moreover, the characteristics of spray--dried sugar-rich juices, especially the hygroscopicity and thermoplastic behaviour, put additional requirements on the selection of processing parameters.Sour cherry Marasca juice has high content of low-molecular-mass sugars such as glucose and fructose, which cause stickiness and caking during the spray drying and therefore disable the production of free-fl owing dry powder (9).In practice, this problem is solved by the addition of carrier materials, such as polymers and gums, which prevent the stickiness, and by the careful selection of processing parameters such as drying temperature, air fl ow and material fl ow (10).Most frequently used carrier materials are maltodextrins (MD) of diff erent dextrose equivalents (DE).Vardin and Yasar (11) optimized the spray drying process of pomegranate juice with 40 % dry matt er using MDs of 7 and 18 DE added in ratios of juice dry matt er and MD of 1:1, 3:4 and 1:2, at temperatures of 110, 140 and 170 °C.At the ratio 1:2, product yield was over 72 % at temperatures of 110-140 °C and about 67 % at 170 °C.At the ratio 1:1, yield was signifi cantly lower, 25-51 %.Dextrose equivalent was also found to be signifi cant, as maltodextrin with lower dextrose equivalent gave higher yields at higher mass per volume ratios and lower temperatures.Moisture content of the powders decreased with the increased inlet and outlet air temperature, while solubility increased.The hygroscopicity of spray-dried powders increased with increased DE value of MD and slightly decreased with increased inlet air temperature.Solval et al. (12) researched the eff ect of temperature (170, 180 and 190 °C) on the properties of melon juice produced with MD 9-13 DE added in the ratio of juice and MD of 9:1.The increase in temperature caused the reduction of moisture content from 5.39 to 3.81 %.According to these literature reports, it can be concluded that spray drying parameters as well as the carrier addition highly depend on the material that is to be dried and therefore should be carefully optimized.Because of the diff erences between Marasca and other sour cherry cultivars, especially regarding the signifi cantly higher dry matt er content, sour cherry Marasca is a challenging material for spray drying.Therefore, the aim of this research is to optimize the spray drying process of sour cherry Marasca juice in terms of carrier material selection, its concentration and drying temperature and to determine the infl uence of the above-mentioned parameters on physicochemical properties of sour cherry Marasca fruit powders.

Spray drying process
Sour cherry Marasca juice powders were produced on a laboratory scale spray dryer SD 06 (Labplant, North Yorkshire, UK).During the process the following parameters were kept at constant level: air fl ow 3.5 m/s, feed fl ow 485 mL/h and deblocking speed at medium level.Spray drying process was carried out according to the experimental design as follows: three diff erent carriers (MD 4-7 DE, MD 13-17 DE and GA) were added at 20, 30 and 40 % (by mass per volume) to the 100 mL of sour cherry Marasca juice (15 °Brix).The slurry was stirred and preheated to 50 °C on a magnetic stirrer (HSC Ceramic Hot Top-Plate Stirrer, VELP Scientifi ca Srl, Usmate Velate (MB), Italy) for 10 min in order to achieve homogeneous dispersion of carrier material in juice.The slurries were spray dried at three diff erent inlet temperatures, 150, 175 and 200 °C.The corresponding outlet temperatures were 78-80, 87-90 and 99-102 °C, respectively.All powders were produced in duplicate and stored in dark plastic containers in a desiccator at 20 °C until analysis.

Product yield
Product yield was calculated as the ratio of the dry matt er content of the collected powder to the dry matt er content of the slurry according to the following equation: /1/ where m p is the mass (g) of produced spray-dried sour cherry Marasca juice powder, m d is dry matt er content (g) of juice in the slurry and m c is the mass (g) of the carrier in the slurry.

Moisture content
Moisture content (%) of the sour cherry Marasca powders was calculated as the diff erence in the mass before and aft er drying in an oven at 105 °C (FN 500; Nüve, Ankara, Turkey) until the constant mass was obtained (13).

Hygroscopicity
Hygroscopicity of powders was analysed according to Tonon et al. (14).Duplicates of 1 g of each sample were placed in open Petri dishes in a desiccator containing saturated NaCl solution (RH=75.3%) and stored for one week at room temperature.Hygroscopicity was determined by measuring the mass of water adsorbed by the sample, and was expressed in g of adsorbed water per 100 g of powder using the following equation: /2/ where m 7 is the mass (g) of the powder aft er 7 days of storage and m 0 is the mass (g) of the powder before storage.

Solubility
Solubility was determined according to the method described by Anderson et al. (15), with some modifi cations.The mass of 1 g of powder was placed in a glass test tube with 10 mL of distilled water and stirred vigorously at vortex vibrator for 1 min, termostated in a water bath (B-490; Büchi, Flawil, Switzerland) at 37 °C for 30 min and centrifuged at 5500×g for 20 min (Rotafi x 32; Hett ich, Tuttlingen, Germany).Later on, the obtained supernatant was collected and dried in a laboratory oven at 105 °C (FN 500; Nüve) until constant mass was obtained.Solubility was calculated according to the following equation: /3/ where m s is the mass (g) obtained by drying of the supernatant and m p is the mass (g) of the powder taken into analysis.

Bulk density
Bulk density (g/mL) was determined by adding 2 g of sour cherry Marasca powder into an empty 10-mL graduated cylinder and holding the cylinder on a vortex vibrator for 1 min.The ratio of the powder mass and the volume occupied in the cylinder determines the bulk density value (16).

Experimental design and statistical analysis
The experimental design and statistical analysis were done using STATISTICA v. 10 Experimental design (DOE) soft ware (StatSoft Inc., Tulsa, OK, USA).A full factorial design comprising nine experimental trials for each carrier material used was chosen to evaluate the combined effect of two factors, carrier mass per volume ratio and drying temperature, termed X 1 and X 2 , respectively (Table 1), giving in total 27 experimental runs.Experiments were performed in duplicate, starting with the lowest carrier mass per volume ratio and the lowest temperature.The operating variables were considered at three levels, namely low (-1), central (0) and high (1).The values of carrier mass per volume ratio were set at 20 (-1), 30 (0) and 40 % (1) and of temperature at 150 (-1), 175 (0) and 200 °C (1).Repetition experiments were carried out immediately after the corresponding original experiments designed by the program.The responses obtained from the experimental design were product yield (%), moisture content (%), hygroscopicity (g/100 g), solubility (%) and bulk density (g/L).
The design matrix for the experiment and the regression model for each response were calculated as follows (17): where Y is predicted response, β 0 is the fi xed response, β i , β ii and β ĳ are the linear, quadratic and interaction coefficients, and X i and X j are independent factors, respectively.Analysis of variance (ANOVA) was carried out to determine any signifi cant diff erences (p<0.5)among the applied treatments.The model was fi tt ed by multiple linear regressions (MLR).The validity of the quadratic empirical model was tested using the analysis of variance (ANOVA).The confi dence level used was 95 %.
For optimization purposes a prediction and profi ling tool was used.Preferences were set for each response as follows: for product yield, solubility and bulk density preference was high (1.0), while for moisture content and hygroscopicity it was low (0.0).Factors were set at optimum value and were observed at 20 steps for more precise optimization.

Results and Discussion
Fruit juices are one of the most demanding materials for spray drying because of the high content of low-molecular-mass sugars and organic acids.Therefore, it is necessary to optimize the spray drying process in order to obtain the product with good physical and chemical properties, rehydration capacity and with characteristic sensory att ributes.The use of drying aids, specifi cally the carrier materials, is mandatory as they prevent stickiness during the process and also may act as a protection of heat-sensitive compounds because of their role as microencapsulating agents (18).
In sour cherry Marasca juice powders produced according to the experimental design, the following physical and chemical parameters were determined and observed for the optimization: product yield, moisture content, hygroscopicity, solubility and bulk density (Table 1).
Product yield of powders containing MD 4-7 DE ranged from 27.7 to 59.1 %, of powders containing MD 13-17 DE from 6.0 to 60.4 % and of powders containing GA from 34.1 to 54.3 %.According to the previous report by Bhandari et al. (19) the criterion for successful drying is product yield higher than 50 %.Almost all experimental drying conditions with MD 4-7 DE resulted in powders with product yield over 50 %, while with MD 13-17 DE product yield was over 50 % only when using powders with higher carrier mass per volume ratio (30 and 40 %) dried at higher temperatures (175 and 200 °C).On the other hand, GA powders had yield higher than 50 % only at the lowest carrier addition (20 %).
Losses during spray drying can occur as the result of diff erent factors: residue on the dryer walls, fi ne particle loss through the outlet air fi lter and losses due to hand manipulation with powder (20).
Analysis of variance (ANOVA) results for carrier mass per volume ratio and temperature eff ect on the observed physical and chemical parameters are shown in Table 2.Both carrier mass per volume ratio and temperature, as well as combined eff ect of these two factors had signifi cant infl uence on product yield of powders with all three carriers.
With maltodextrin carriers, regardless of dextrose equivalent, the highest carrier mass per volume ratio (40 %) and higher temperatures (175 and 200 °C) resulted in the highest product yield.With 20 % MD 13-17 DE, the stickiness problem occurred, so resulting yields were very low (6.0-19.4%), decreasing with the increase in drying temperature.The cause of the stickiness during drying is the presence of low-molecular-mass sugars, namely sucrose, glucose and fructose, which have low glass transition temperature (19,21) and therefore tend to stick to the dryer walls, leading to low product yield and technical diffi culties during process.Low glass transition temperature, high hygroscopicity, low melting point and high water solubility characterize juice dry matt er and make them highly sticky products.These problems are solved by the addition of carrier materials, polymers and gums, which have the ability to increase the glass transition tempera-ture of juice and consequently decrease or inhibit the stickiness phenomenon (22).Carrier effi ciency primarily depends on its ratio to the juice dry matt er and drying temperature.According to our results, it can be concluded that the use of MD 13-17 DE demands higher carrier ratio as with 20 % carrier addition to the juice with 15 % dry matt er, the stickiness problem occurred, being more expressed with the rise of the drying temperature.
On the other hand, with gum arabic, the highest product yields were obtained with the lowest carrier ratio, regardless of the drying temperature.Vardin and Yasar (11) optimized the spray drying process of pomegranate juice and reported the highest yield at juice to MD ratio 1:2 and temperatures from 110 to 140 °C with decreasing trend at higher temperatures.Dextrose equivalent was also found to be signifi cant as MD with lower DE gave higher yields at higher ratios and lower temperatures.In the present study, both maltodextrins gave similar yields at higher ratios and temperatures, regardless of the dextrose equivalent.Other authors showed compara- Fazaeli et al. (26) reported the eff ect of drying temperature similar to our conclusions.They observed the positive eff ect of temperature increase on spray-dried black mulberry juice yield, explained by more eff ective energy and mass transfer at elevated temperatures (14,27).
Moisture content of sour cherry Marasca powders varied from 1.36-2.49% in those containing MD 4-7 DE, from 1.41-7.69% in those containing MD 13-17 DE and from 3.26-5.71% in those containing GA.This is one of the most important indicators of spray drying eff ectiveness and fi nal product quality (28).
According to the ANOVA results (Table 2) both carrier mass per volume ratio and drying temperature had signifi cant eff ect on moisture content of sour cherry Marasca powders produced with MD carriers, while in powders produced with GA there was no signifi cant eff ect of carrier mass per volume ratio.
Generally, powders produced with MD 4-7 DE had the lowest moisture content, while those with GA had the highest.The exception are powders produced with 20 % of MD 13-17 DE at 175 and 200 °C, which had high moisture residue due to the stickiness that occurred during the process.It can also be observed that increase in MD 13-17 DE carrier mass per volume ratio had evidently positive eff ect on moisture content decrease, which reduced the stickiness problem.These fi ndings are in accordance with other authors' reports.
At higher drying temperatures, the resulting moisture content is lower thanks to more eff ective mass and heat transfer, namely intensive water evaporation (29).Fazaeli et al. (26) also reported the reduction of moisture content in black mulberry juice powder with temperature increase as well as with the increase in carrier concentration.Rodríguez-Hernández et al. (30) observed lower moisture content in Opuntia powders produced with maltodextrins with higher dextrose equivalent, while Fazaeli et al. (26) and Goula and Adamopoulos (27) reported adverse fi ndings for sweet potato and orange juice powders.These authors explained their fi ndings with the structure of maltodextrin with high dextrose equivalent characterized by more short chains and hydrophilic groups which consequently adsorb more water molecules.The results of our research showed that there was no signifi cant difference in the moisture content of powders produced with MD 4-7 DE and MD 13-17 DE at higher mass per volume ratios (30 and 40 %), but results with the addition of 20 % MD are in accordance with the above mentioned studies.
Hygroscopicity of sour cherry Marasca juice powders containing MD 4-7 DE ranged from 18.3 to 26.3 g/100 g, in powders containing MD 13-17 DE from 21.9 to 39.6 g/100 g and in powders containing GA from 20.8 to 34.2 g/100 g.Hygroscopicity is a parameter that describes the fl owability of powders very well, as more hygroscopic powders are less free fl owing due to more adsorbed moisture (31).Both hygroscopicity and fl owability depend on the glass transition temperature.The higher the glass transition temperature, the lower the hygroscopicity and the higher the fl owability (32).
According to the ANOVA results, all observed parameters individually, as well as combined, had a significant infl uence on hygroscopicity of powders with all three carriers used.Powders produced with the MD 4-7 DE had the lowest hygroscopicity, followed by the MD 13-17 DE and the GA with the highest hygroscopicity.Vardin and Yasar (11) also reported higher hygroscopicity of powders produced with maltodextrin with higher dextrose equivalent (18 DE) in comparison with 7 DE.Low--molecular-mass maltodextrins are more susceptible to water adsorption due to more hydrophilic groups (33).Higher mass per volume ratio of carrier material and higher drying temperatures had positive eff ect on hygroscopicity decrease, which is in accordance with previous fi ndings.Moreira et al. (34) reported the decrease in hygroscopicity of acerola powders with an increase in temperature from 170 to 200 °C, explained by the lower moisture content.Tonon et al. (14) observed the infl uence of higher maltodextrin concentration on the decrease of hygroscopicity of acai powders.
The solubility of powders ranged from 81.8 to 96.1 % in those containing MD 4-7 DE, from 81.6 to 97.8 % in those with MD 13-17 DE and from 81.1 to 89.0 % in powders containing GA.It can be observed that regardless of the drying conditions, the powders with GA had significantly lower solubility than the ones with MD, which is related to the diff erent structure and properties of gums and maltodextrins, although the GA is considered as the gum with high water solubility.
Both carrier mass per volume ratio and temperature signifi cantly infl uenced the water solubility of powders with all carriers used (Table 2).General observation is that powders containing 30 % carrier mass per volume ratio have bett er solubility.Fazaeli et al. (26) also observed the positive eff ect of higher maltodextrin mass per volume ratio on the solubility of powders due to the high maltodextrin solubility in water.Contrary to these fi ndings, Selvamuthukumaran and Khanum (35) reported the negative eff ect of higher maltodextrin mass per volume ratios on the solubility of sea buckthorn powder, caused by the higher amount of insoluble residue and more lumps formed during the dissolution.MD 13-17 DE carrier showed opposite behaviour under the infl uence of diff erent temperatures compared to MD 4-7 DE and GA; its solubility decreased at higher drying temperatures.Quek et al. (29) reported the negative eff ect of temperature on the solubility of watermelon powders, similar to the behaviour of powders containing MD 13-17 DE in our study, while temperature increase favoured the solubility of black mulberry and pomegranate powder (11,26).
Bulk density of powders ranged from 0.23 to 0.48 g/ mL in powders containing MD 4-7 DE, from 0.25 to 0.36 g/mL in powders containing MD 13-17 DE and from 0.24 to 0.45 g/mL in powders containing GA.Compared to the sour cherry Marasca juice powders, the bulk density of other powder juices was generally higher (in g/mL): pomegranate powder 0.579-0.687(11), lime powder 0.41-0.69(36), except for pitaya powder, which was lower, 0.29-0.34(37).
Generally, the heavier the powder is, the more easily it fi lls the space between the particles, resulting in higher bulk density.Therefore, the bulk density includes the particles and the space between them and can be related to the powder porosity which includes only the space between the particles (38).
All observed drying parameters had a signifi cant infl uence on bulk density of sour cherry Marasca juice powders regardless of the carrier used.In powders containing maltodextrin, bulk density was higher with lower carrier mass per volume ratio, contrary to powders containing GA. Regarding the drying temperature, powders produced with MD 4-7 DE had higher bulk density when dried at higher temperatures, while powders produced with MD 13-17 DE and GA had higher bulk density at lower temperatures.
The increase in drying temperature also caused lower bulk density of black mulberry powders in the study of Fazaeli et al. (26).Particularly, at higher temperatures the water evaporation rate is faster, dried powder has more porous and fragmented structure, larger particles are formed and therefore the bulk density is lower.Higher temperature usually results in larger particles with more inside cavities (39).The same trend is confi rmed in studies on gac fruit aril powder (2) and pomegranate powder (11).Goula and Adamopouls (40) reported the increase in bulk density of powders with higher dextrose equivalent of maltodextrin while our results show no signifi cant difference between MD 4-7 DE and MD 13-17 DE.
Table 3 shows the equations of regression models for product yield, moisture content, hygroscopicity, solubility and bulk density of sour cherry Marasca juice powders produced with MD 4-7 DE, MD 13-17 DE and GA.In these models, studied spray drying parameters (carrier mass per volume ratio and temperature) are combined in linear, quadratic and interaction coeffi cients, enabling the prediction of response variable values for any desired carrier mass per volume ratio and drying temperature.The adequacy of the model was checked by calculating the coeffi cient of determination, R 2 , which is the proportion of variation in the response att ributed to the model rather than to random error.It has been suggested that a good--fi tt ing model should have R 2 no less than 80 %.As it can be observed, all models had the R 2 higher than 0.9, which implicates the adequacy of the models to predict the physicochemical properties of powders.While R 2 indicates how much of the observed variability in the data was accounted for by the model, R 2 adj modifi es R 2 by taking into account the number of covariates or predictors in the model.An R 2 adj close to the R 2 values insures a satisfactory adjustment of the quadratic models to the experimental data.As it can be observed, all R 2 adj values were close to the R 2 , implying that the models explained the observed powder properties very well.Results of the optimization of spray drying with each carrier are shown in Ta ble 4. Optimization was carried out using the response surface methodology in order to obtain the drying parameters resulting in the powder with high production yield, low moisture content and hygroscopicity, high solubility and high bulk density.Optimal drying conditions are almost similar for powders with MD 4-7 DE and GA, the highest drying temperature of 200 °C, and about 30 % of carrier, twice higher than juice dry matt er content, namely 27 % of MD 4-7 DE and 31 % of GA.For powders produced with MD 13-17 DE, required carrier addition is higher, 40 %, while drying temperature is lower, 150 °C.These diff erences are the result of the infl uence of maltodextrin with higher dextrose equivalent on the powder stickiness at higher temperatures when applied in lower mass per volume ratio.
The optimal conditions for spray drying depend primarily on the material that is to be dried.Therefore, Vardin and Yasar (11) reported the optimal temperature for pomegranate juice drying in the range from 125 to 145 °C, optimal juice dry matt er to carrier ratio of 0.6-0.8 and car-rier MD 7 DE rather than MD 18 DE.Krishnaiah et al. (41) used temperature of 95 °C and maltodextrin to dry matt er ratio of 1.5 for drying of the noni extract, while Selvamuthukumaran and Khanum (35) applied temperature of 162.5 °C and 25 % carrier for optimized spray drying process of sea buckthorn juice.Having in mind the diff erences among the dried materials, all these results are comparable and in accordance with the fi ndings in our study.On the other hand, Karaca et al. (42) researched similar material, sour cherry concentrate, and reported the optimal spray drying conditions to be 150 °C, 25 % sour cherry content with carrier MD 12 DE, resulting in yield higher than 85 %.The temperature eff ect fi ndings are in accordance with our conclusions on higher dextrose equivalent maltodextrins but resulting yields are higher than in our study.These diff erences may derive from the higher carrier mass per volume ratio applied in the reported study as well as from the diff erent spray dryers used, as construction diff erences, especially those regarding the outlet temperature control and outlet fi lters, infl uence the yield losses to a high extent.At defi ned optimal conditions, physicochemical parameters were predicted by the model and confi rmed in experimental trials.Experimental results support the adequacy of the models for prediction of powder properties.It can be observed that powders produced with MD 4-7 DE had the highest product yield, the lowest moisture content and hygroscopicity, and the highest bulk density.On the other hand, powders containing GA had the lowest yield and solubility and the highest moisture content and hygroscopicity.Taking into account the above mentioned, it can be concluded that the MD 4-7 DE is the most suitable carrier for production of the spray-dried sour cherry juice Marasca powder with the best physicochemical properties.

Conclusions
This study confi rmed that carrier material, its mass per volume ratio and drying temperature signifi cantly affect the physical and chemical properties of spray-dried sour cherry Marasca juice powder.Generally, higher maltodextrin carrier amounts caused the increase in product yield, increase of both maltdextrin and gum arabic mass per volume ratio up to 30 % positively aff ected the powder solubility, while bulk density was highest at 40 % carrier addition.High carrier mass per volume ratio decreased the moisture content and hygroscopicity of powders.Higher drying temperature decreased their moisture content and bulk density.Maltodextrin with low dextrose equivalent showed bett er stickiness reduction properties than the one with higher dextrose equivalent, while gum arabic, although with good stickiness reduction properties, produced powders with lower yield and solubility, and with high moisture content and hygroscopicity.
According to the obtained results, it can be concluded that the sour cherry Marasca juice powder with the optimal physicochemical properties is produced with the addition of 27 % of maltodextrin with dextrose equivalent of 4-7 at drying temperature of 200 °C.Further studies have to be done regarding the infl uence of the abovementioned parameters on the phenolic content of the obtained powders in order to design the fi nal product.

Table 1 .
Results of physicochemical parameters of sour cherry Marasca juice powder produced with the addition of 20, 30 and 40 % of maltodextrin (MD) with 4-7 and 13-17 dextrose equivalent (DE) and gum arabic (GA) at diff erent drying temperatures (24)results regarding the carrier ratio, while the ones dealing with the eff ect of drying temperature are diverse.Peng et al.(23)researched the infl uence of MD 20 DE addition on the product yield of spray-dried purple sweet potato.The addition of 30 % MD 20 DE increased product yield from 23.32 to 39.85 %, while further addition gave no eff ect.The importance of carrier use is in the formation of outer layer, the 'wall' surrounding the material and increase of glass transition temperature which results in prevention of stickiness and increase in product yield(24).For eff ective spray drying of concentrated blackcurrant, apricot and raspberry juices, the addition of minimally 35 % of MD 6 DE was necessary (9), while Righett o and Nett o (25) reported the minimum addition of 50 % of MD 25 DE to acerola juice.

Table 2 .
Analysis of variance (ANOVA) for the eff ect of carrier mass per volume ratio (X 1 ) and temperature (X 2 ) on the observed physicochemical parameters of spray-dried sour cherry Marasca juice powder produced with the addition of maltodextrin (MD) of 4-7 and 13-17 dextrose equivalent (DE) and gum arabic (GA) at 95 % confi dence level

Table 3 .
Regression models for the physicochemical parameters of spray-dried sour cherry Marasca juice powder produced with the addition of maltodextrin (MD) with 4-7 and 13-17 dextrose equivalent (DE) and gum arabic (GA), and corresponding values of coeffi cient of determination (R 2 ) and adjusted coeffi cient of determination (R 2 adj )

Table 4 .
Predicted and experimental values of physicochemical parameters of spray-dried sour cherry Marasca juice powder produced with the addition of maltodextrin (MD) with 4-7 and 13-17 dextrose equivalent (DE) and gum arabic (GA) at optimal conditions for each carrier used