Sugar beet powder production using different drying methods, characterization and influence on sensory quality of cocoa-hazelnut cream

Abstract

The sugar beet powders were produced by oven drying, freeze drying and spray drying methods. Spray-dried powder had spherical particles with smooth surfaces while powders obtained from other methods exhibited flaky shape of particles with irregular surface properties. Freeze drying led to higher porosity, higher phenolic content (466.08 ± 52.71 mmol GAE/g sample) and better flowability (lower angle of repose value) while spray-dried powder depicted better solubility and higher score in overall acceptability in sensory analyses when compared to other powder samples. Oven dried sugar beet powders exhibited the darkest color and lowest score in overall acceptability in sensory analysis. When the sensory attributes and powder properties are considered, spray-dried sugar beet powders might be more appropriate as a functional ingredient to be used in food formulations. On the other hand, more dietary fibre (12.45 ± 2.42 g/100 g powder) and more phenolics containing freeze-dried powders with better color attributes might be better choice in terms of functional properties. This study might be an attractive proposal for developing confectionery products enriched with whole sugar beet powder which have natural bio active substances to fulfill today’s increasingly demanding consumer expectations.

Introduction

Due to growing consumer demand for less calorific and functional ingredients with health–promoting properties, particularly to be used in chocolates, cocoa-hazelnut spreads, confectionery and diary products, researchers have been trying to find alternatives to conventional sweeteners, both caloric and non-caloric (i.e. refined sugar and artificial sweeteners) (Swithers 2016; Rodrigues et al. 2016). While a significant attention has been given to the red beet root vegetable (Beta vulgaris L.) in the recent years (Edziri et al. 2019; Seremet et al. 2020), there is lack of information about sugar beet root extract and its potential use in food formulations. In order to take advantage of the potential health benefits of sugar beet root and add value to the confectionery and sweet products, there is a need to develop functional and natural sugar beet powder which has a good blendability with other powder ingredients.

It has been reported that sugar beet roots have functional ingredients having beneficial effects such as antimicrobial (Chen et al. 2017), antioxidant and anti-mutagenic (Chen et al. 2015). Since sugar is separated from other constituents which are rich in minerals, vitamins, dietary fibre, phenolic components, carotenoids (Turkomp 2019) alkaloids, tannins, terpenoids, steroids (Chen et al. 2015) and saponins (Mikołajczyk-Bator et al. 2016), these valuable components are removed during industrial sugar production process (Rajaeifar et al. 2019).

Drying is reported being one of the most widely used methods to preserve fruits and vegetables and to provide alternative consumption choice during the off-season (Nistor et al. 2017). Drying food materials and converting to powder form has some benefits such as improved shelf life, ease of transportation, ease of dosaging and lower transportation costs (Caparino et al. 2012). Furthermore, smaller spaces are needed for storage. It was reported that the drying method affects some powder properties such as colour, shape, structure, nutritional and nutraceutical properties (Karam et al. 2016). Powder characteristics and behavior (i.e. powder flow) during processing, storage and handling are linked to physical properties of particles as well as bulk powder properties (Fitzpatrick 2013).

Spray drying (SD), freeze drying (FD), and oven drying (OD) are known techniques in the industrial powder production from plant materials (Gardeli et al. 2010; Vardanega et al. 2019). SD technique has been widely used by the food industry in powder production because of its relatively low operation cost and adaptibility to large scale production (Sarabandi et al. 2020). In addition, it is reported as a rapid powder production technique due to the short processing time (Etzbach et al. 2020). However, the heat applied to dry the liquid food material can alter the chemical structure and effect the nutritional quality of the powder product. In FD technique, drying occurs by sublimation under high vacuum. One of the main advantages of this dehydration method is its ability to keep aroma and flavor quality while drying and almost no loss of valuable components (such as vitamins and bioactive substances) due to low operating temperatures (Zhang et al. 2020). Long operation times and high processing costs are the main drawbacks of this method (Sarabandi et al. 2020; Zhang et al. 2020). OD is a conventional drying method applied at temperatures ranging from 45 to 65 °C to dry plant material with some noticable effects on aroma and color properties (Gardeli et al. 2010). When it comes to retention of flavour, heat sensitive compounds and color properties, one can state that FD provides better quality when compared to SD and OD methods (Raja et al. 2019).

In this work, it was aimed to produce powder from sugar beet root using spray drying, freeze drying and oven drying methods and evaluation of powder properties. These three techniques have been selected because they have entirely different performance abilities. The resulting powder materials were used in cocoa-hazelnut spread and sensory analysis has been conducted in order to evaluate consumer acceptability.

Materials and methods

Material

Fresh sugar beet roots having no fungi or damage were obtained from a local market in Istanbul, Turkey. They were washed with tap water, both ends were cut and stored at – 18 °C after placing in plastic bags until being used in powder production. The ingredients used in cocoa-hazelnut spread formulation were purchased from a local market. The chemicals [Folin Ciocalteu reagent, gallic acid (GA), sodium carbonate and 2,2-diphenyl picryl hydrazyl (DPPH)] were obtained from a local distributor of Sigma Chemical Co. (St. Louis, MO, USA).

Methods

Powder production

The skin were peeled from the sugar beet roots before cutting the flesh into small pieces. Three different drying methods (convection drying in the oven, freeze drying and spray drying) have been applied prior to milling in order to obtain dry powder samples. In conventional oven method, the pieces were placed on glass Petri dishes and dried at 65 °C until reaching constant weight. The pieces were kept at − 20 °C for 24 h prior to freeze drying process. Then, the samples were placed on Petri dishes and placed in the drying compartment of a freeze dryer (Teknosem TRS 212 V, Turkey). The samples were freeze-dried at − 66 °C and at around 40 Pa for 62 h. Dried samples were milled using a laboratory scale centrifuge mill (Retsch Zm 200 Ultra, Germany) to obtain powder. The powder material then sieved using a laboratory sieve (Retsch AS100) and powder fractions blow 500 μm was used for the analyses. For spray drying process, a high speed homogenizer (WiseTis HG-15A, witeg Labortechnik GmbH, Wertheim, Germany) was used to prepare sugar beet syrup. 5% (w/v) maltodextrin (MD) was added to help powder formation to the syrup and filtered through a filter before being fed into an atomizer (1 mm) mounted on a Büchi B-290 spray drier (Büchi Labortechnik AG, Flawil, Switzerland). The parameters of spray dryer: inlet air temperature: 140–150 °C, outlet temperature: 75–80 °C, Feed rate: 400–600 mL/h.

Cocoa-hazelnut spread production

The effect of sugar beet powder on sensory attributes of cocoa-hazelnut spread was characterized. For this purpose, 45 g powder samples were added to 55 g of ingredients (Table 1). The sensory attributes were evaluated against control sample to which 45 g of icing sugar was added.

Table 1.

Ingredients used to produce cocoa-hazelnut spread

Ingredients (g/100 g)	HSControl	HSSD-SBP	HSFD-SBP	HSOD-SBP
Vegetable fat	27	27	27	27
Hazelnut paste	8	8	8	8
Cocoa powder	7	7	7	7
Milk powder	5	5	5	5
Whey powder	7.5	7.5	7.5	7.5
Lecithin	0.4	0.4	0.4	0.4
Vanilla	0.1	0.1	0.1	0.1
Icing sugar (sucrose)	45	–	–	–
SD-SBP	–	45	–	–
FD-SBP	–	–	45	–
OD-SBP	–	–	–	45

SD-SBP spray-dried sugar beet powder, FD-SBP freeze-dried sugar beet powder, OD-SBP oven dried sugar beet powder, HS hazelnut spread

Chemical composition analysis

Analyses of moisture, total nitrogen (protein) and fat content were conducted based on the methods as outlined, AOAC 16.006, AOAC 958.48, and AOAC 945.16, respectively (AOAC 2005). The ash content was determined by incineration in an electric muffle furnace at 600 °C.

Bulk and tapped densities of powders

The bulk density (ρb) of SBP samples were calculated by dividing the weight of the powder by corresponding volume (Ermis et al. 2018). The mass of powder filled into 10 mL graduated cylinder was weighed. The bulk density was determined by using Eq. 1.

$${\rho }_{\text{b}}=\text{m}/{\text{V}}_{\text{b}}$$ 1

where b is bulk density, m is the mass of powder and Vb is volume of the powder bed.

The powder sample in glass cylinder manually tapped until there was no further change in volume. The tapped density (ρt) was calculated using Eq. 2 and expressed as kg m⁻³ (Jinapong et al. 2008).

$${\rho }_{\text{t}}=\text{m}/{\text{V}}_{\text{t}}$$ 2

where t is tapped density, m is the mass of powder and Vt is volume of the tapped powder.

Determination of powder flow behavior

Angle of repose approach (Seerangurayar et al. 2017) was used to evaluate the flowability of SBP samples with slight modifications. Powder materials with repose angle up to 35° is a free-flowing material, 35°–45° is fairly cohesive, 45°–55° is cohesive and more than 55° is very cohesive (Carr 1965).

In addition, Hausner Ratio (HR) value (Eq. 4) was also determined (Hausner 1967). This value is dimensionless. According to the HR, the cohesiveness is considered low when HR < 1.2, intermediate when HR is from 1.2 to 1.4 and high when HR > 1.4.

$$\text{HR}={\rho }_{\text{t}}/{\rho }_{\text{b}}$$ 3

Microstructural analysis (SEM images)

The surface characteristics of the particles were examined using a scanning electron microscope (Philips ESEM XL30 FEG, the Netherlands). An ultra thin layer gold coating of particles was performed prior to analysis. The acceleration voltage was set to 5 kV (Salleh vd 2014). The magnification was ranged from 100 × to 20000 ×.

Evaluation of color

The color properties of powder samples were determined using a CFLX 45-2 Model Colorimeter (HunterLab, Reston, VA). The CIELab L* (0 black, 100 white), a* (− green, + red), b* (− blue, + yellow) color components were analysed (Silva et al. 2018).

Evaluation of antioxidant capacity (inhibition of DPPH) and total phenolic content

Folin-Ciocalteu reagent was used in order to determine total phenolic content (Nistor et al. 2017). 0.5 mL sample extract was mixed with 2.5 mL of 10% Folin-Ciocalteu reagent prior to incubation for 2 min at room temperature. Then, 2 mL of 7.5% sodium carbonate was added and vortexed for 1 min. The mixture was left to 50 ± 2 °C for 15 min. The absorbance readings were done at 760 nm against distilled water (blank) using a UV-VIS spectrophotometer (PG Instruments T80, UK) after allowing the mixture to cool at room temperature. Gallic acid was used as a standard, and the results were expressed as milligrams of Gallic Acid equivalent (GAE) per ml of extract.

The DPPH-free radical scavenging capacity was evaluated using a modified method reported by Chen and Ho (1995). 0.2 mL of sample extract was added into 3.8 mL ethanol containing DPPH radicals to get the final concentration of 0.1 mM. The mixture was vortexed for 1 min at room temperature prior to leaving in the darkness for 30 min. A UV-VIS spectrophotometer (PG Instruments T80, UK) was employed to measure the absorbance of the samples at 517 nm against ethanol blank. In addition, a negative control was prepared by adding DPPH solution to 0.2 mL of sample extract and its absorbance was measured. The DPPH inhibition was calculated using Eq. 4 and reported as % inhibition.

$$\%\text{inhibition}=\left[1-\left({\text{A}}_{\text{sample}}/{\text{A}}_{\text{control}}\right)\right]\times 100$$ 4

where A_sample and A_control are absorbance values of the sample and control, respectively.

Total reducing sugar and dietary fibre analises

Reducing sugars consist of glucose and fructose as a result of hydrolysis of sucrose. Lane-Eynon general volumetric method was used to determine the reducing sugar content of the powder samples using AOAC official method 923.09 and total dietary fibre was analysed using AOAC 985.29 method (AOAC 2005).

Solubility

Powder solubility of sugar beet powder samples was analysed by a method used previously (Ermis et al. 2018). 10 mL of distilled water was taken to a glass tube and 1 g of powder sample was transferred into it. The mixture was homogenized using a mechanical homogenizer at 50 Hz for 10 min. The supernatant of the solution was taken and transferred to Eppendorf tube and centrifuged for 10 min at 6000 rpm. The liquid part was taken into an aluminum dish and dried for 24 h at 105 °C. Equation (5) was used to calculate the solubility.

$$\text{Solubility}\left(\%\right)\left(\text{w}/\text{w}\right)=\left[{\text{m}}_{\text{sp}}/{\text{m}}_{\text{tp}}\right]\ast 100$$ 5

where m_sp is the mass of soluble powder and m_tp is the mass of total powder.

FT-IR analysis

The effect of drying methods on chemical structure of powder samples was examined using an ATR-FTIR (Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy). A Schimadzu IR-Tracer100 spectrometer (Kyoto, Japan) equipped with a diamond ATR cell and DLATGS detector was used. LabSolutions IR software was used to analyse the data. The ATR-FTIR spectra SBP samples were recorded with a resolution of 2 cm⁻¹, accumulating 16 scans per spectra. The spectra were recorded from 4000 to 600 cm⁻¹ after background air spectrum was scanned.

Sensory analysis

Sensory evaluation of cocoa-hazelnut spread samples was done using a five-point hedonic scale test with 12 randomly chosen panelists from 4th year students of Food Engineering Program. The list of sensory attributes included descriptors of bitterness, sour taste, sugary taste, mouth feel, color and appearance, and overall acceptability. These attributes were rated on an anchored line scale that provided a 1–5 score range (1-highly undesirable; 5-highly desirable) (Ermiş et. al. 2018).

Statistical analysis

The data obtained from triplicates was expressed as the mean ± standard deviation. One-way analysis of variance (ANOVA) and Tukey’s HSD test for multiple comparisons were used to evaluate the data using Minitab v17 (Minitab Inc, PA, USA) at 95% confidence level (p < 0.05).

Results and discussion

Chemical analyses and nutritional composition

The nutrient composition of raw sugar beet is reported as water content—77.6 ± 1.21 g/100 g of sample, ash—0.80 ± 0.20 g/100 g, protein—0.51 ± 0.18 g/100 g, total lipids—0.15 ± 0.04 g/100 g, carbohydrates—18.54 ± 0.95 g/100 g, and fibers- 2.41 ± 1.20 g/100 g (Turkomp 2019). Results of the chemical and nutritional analysis of SBP samples are presented in Table 2. The moisture contents of the powder samples were in the range of 1.31–5.01%. FD-SBP had significantly higher moisture content than other powder samples. This means that the freeze drying method resulted in higher moisture level than oven and spray drying methods. Similar results were reported in previous studies (Caparino et al. 2012; Seerangurayar et al. 2017). This might be attributed to the variations in drying mechanism of different methods. The ash contents of FD-SBP and SD-SBP were found higher than ash content of OD-SBP which might be associated with varying mineral composition in the samples. However, significantly higher protein and total dietary fibre concentrations were determined from OD-SBP and FD-SBP than SD-SBP (p < 0.05). The reason might be associated with the separation of some protein and fibre fractions during homogenization and filtration steps prior to spray drying process. Similar result was obtained from carrot powder by Santana-Gálvez et al. (2016).

Table 2.

Physico-chemical properties of powder samples

Properties measured	OD-SBP	FD-SBP	SD-SBP
Moisture (g/100 g)	1.40 ± 0.12b	5.01 ± 0.85a	1.31 ± 0.18b
Ash (g/100 g)	0.18 ± 0.04b	0.46 ± 0.09a	0.39 ± 0.08a
Protein (g/100 g)	4.01 ± 0.22a	3.46 ± 0.34a	1.82 ± 0.12b
Total dietary fibre (g/100 g)	14.0 ± 1.51a	12.4 ± 2.42a	5.55 ± 0.65b
Total reducing sugar (g/100 g)	78.9 ± 3.42b	78.5 ± 2.57b	90.2 ± 2.78a
Total phenolic content (mmol GAE/g)	192 ± 26.9b	466 ± 52.7a	236 ± 22.5ab
Antioxidant capacity (% DPPH Inhibition)	98.7 ± 0.38a	98.8 ± 0.07a	98.7 ± 0.01a
Solubility (%)	70.0 ± 2.04bc	75.4 ± 3.45b	93.7 ± 2.65a
L*	54.4 ± 4.44b	83.3 ± 2.70a	78.6 ± 5.57ab
a*	5.35 ± 0.63b	− 3.84 ± 0.24c	7.25 ± 1.32a
b*	22.9 ± 2.61a	14.1 ± 1.30b	13.1 ± 1.72bc
Bulk density	0.39 ± 0.05a	0.35 ± 0.04b	0.39 ± 0.02ab
Tapped density (kg/m3)	0.65 ± 0.07b	0.56 ± 0.07c	0.79 ± 0.06a
Angle of repose	32°	32°	47°
Housner Ratio	1.64 ± 0.08b	1.63 ± 0.09b	2.04 ± 0.06a

SD-SBP spray-dried sugar beet powder, FD-SBP freeze dried sugar beet powder, OD-SBP oven dried sugar beet powder, GAE gallic acid equivalent

L* (0 black, 100 white), a* (− green, + red), b* (− blue, + yellow)

Columns with different letters indicate statistically significant difference (p < 0.05)

Depending on the variety, fresh sugar beet contains 0.05–0.1% of reducing sugars and 12–18% sucrose (Ebrahim et al. 2011). After drying, OD-SBP and FD-SBP samples had similar total reducing sugar concentrations while SD-SBP had significant higher amount of total reducing sugars (p < 0.05) (Table 2).

Phenolic substances are a large group of phytocemicals which are significant for the quality of plant-based foods (Chhikara et al. 2019). Drying method affected total phenolic content of powder samples significantly (p < 0.05) (Table 2). Total phenolic content (TPC) values of SBP samples varied between 192.45 and 466.08 mmol GAE/g sample. FD-SBP had significantly higher amount of phenolic substances when compared to other samples and SD-SBP had slightly higher amount of total phenolics than OD-SBP. These variations might be attributed to the effect of heat applied in OD and SD methods as drying over 60 °C degrade some of the phenolic substances (alternation in the molecular structure of phenolics) (Bazaria and Kumar 2016; Santana-Gálvez et al. 2016). Different drying methods did not cause any significant differences in antioxidant activity (% DPPH Inhibition) of SBP samples (Table 2).

Color properties

Hunter color stimulus values are presented in Table 2. The color difference is also visible and can be visualized from Fig. 1. (noticeable in the electronic version or in color print). Visual investigation showed that OD-SBP had the darkest color (Fig. 1a). There is a color difference between FD-SBP and SD-SBP. When the L*, a*, b* values are examined, one can state that the drying methods affected the color of powders. The sugar beet powder produced by freeze drying had the highest L* value (indicating the lightest color) and lowest a* value (Table 2) while the oven dried powder had the lowest L* value and highest b* value. The dark color formation in oven method might be caused by browning/maillard reactions between sugars and proteins at high temperature (Aydin and Gocmen 2015). The L* (lightness) value for spray-dried powder was observed slightly lower than freeze-dried SBP which might be indicating color change due to high temperature applied during spray drying. No significant difference was noticed in b* value (yellowness) between FD-SBP and SD-SBP while SD-SBP had significantly higher a* (redness) value than FD-SBP (color difference can be seen visually in Fig. 1b, c) (p < 0.05). Minimum color change was obtained for FD-SBP suggesting freeze drying is a promising method to produce high quality powder products in terms of color. These findings agree the data reported in previous studies except some variations (Caparino et al. 2012).

Fig. 1.

Angle of repose of powder samples. a Oven dried sugar beet powder, b freeze-dried sugar beet powder, c spray-dried sugar beet powder

Powder flow properties

Bulk and tapped density values of powder materials can be used as indicators to predict their performance during processes, storage and transportation (Ozdikicierler et al. 2014). They also help to better understand particle properties such as particle size and surface characteristics. The bulk and tapped densities of SBP samples are presented in Table 2. The bulk and tapped densities of sugar beet powders produced by oven drying, freeze drying and spray drying methods varied significantly (from 0.356 to 0.395 and from 0.563 to 0.794 kg/m³ for bulk density and tapped density, respectively). The variations might be linked to the composition of the raw material and the final particle properties such as size, shape, irregularity, porosity and surface structure (Barbosa-Canovas et al. 2005). Therefore, a decrease in inter-particle voids of smaller sized particles with larger contact surface areas per unit volume led to an increase in bulk and tapped density values. Similar observations were reported in previous studies (Caparino et al. 2012; Bazaria and Kumar 2016; Seerangurayar et al. 2017). Raja et al. (2019) reported that the bulk densities of Carica papaya L. leaf powders obtained using different methods varied from 481 to 659 kg/m³. The bulk and tapped density values of FD-SBP were lower when compared to those of OD-SBP and SD-SBP. This could be attributed to the porous structure of particles formed by vaporization of ice under high vacuum conditions with no transfer of liquid while drying (Caparino et al. 2012; Zhang et al. 2020). The tapped density of SD-SBP (with smaller and spherical particles) was significantly higher than OD-SBP and FD-SBP which might be a result of spherical nature of the particles leading to less void between them and hence, more compaction occurred (Fig. 2).

Fig. 2.

SEM images of sugar beet powders with different magnifications. a Freeze-dried sugar beet powder, b spray-dried sugar beet powder, c oven-dried sugar beet powder

The Hausner ratio (HR) and Angle of Repose (AoR) are methods to be used to measure the flowability of powder materials. Poor flowability is considered when the HR is higher than the value of 1.4 and easy flowing when HR is lower than 1.2. The angle of repose can range from 0° to 90°. Over 45° is considered as poor flowing and under 30° is evaluated as free flowing (Beakawi Al-Hashemi and Baghabra Al-Amoudi 2018). SD-SBP showed higher HR and AoR values despite it consisted spherical particles with smooth surfaces. This might be attributed to higher carbohydrate content which affect flowability adversely due to its sticky nature (Table 2). OD-SBP and FD-SBP had relatively better flowability attributes when compared to SD-SBP.

Solubility

Solubility can be used as a useful criterion to evaluate the behavior of powder material in liquid media. Dispersibility, sinkability and wettability are the main properties affecting solubility. There was a slight difference in the solubility between OD-SBP and FD-SBP while both were lower compared to SD-SBP (p < 0.05) (Table 2). The reason to high solubility of spray-dried sugar beet powder might be due to the homogenization and filtration processes applied prior to spray drying and atomization during spray drying. Similarly, Caparino et al. (2012) reported higher solubility of mango powders obtained from spray drying technique. The physical attributes and % amount of fibers present in sugar beet samples used for different drying methods might also affect solubility. Homogenization, filtration and high atomization of the samples prior to spray drying resulted in lower fibre content and smaller size of fibres and hence increased solubility. In addition, adding MD also improved solubility as reported previously (Cano-Chauca et al. 2005). Lower solubility of the powders obtained from oven drying and freeze drying methods might be attributed to the cell structure of beetroot pieces which were not disrupted and therefore smaller portion of the material has undergone dissolution.

Micro structure

SEM images of powder samples FD-SBP, SD-SBP and OD-SBP can be seen in Fig. 2. Bigger and irregular particles with dark brown color (Fig. 1) obtained from oven drying method (OD-SBP) as can be seen in scanning electron micrographic images (Fig. 2c). As can be seen in Fig. 2a, freeze-dried sugar beet powder exhibited a skeletal- and flaky-like structure. This might be a result of the action of direct evaporation of ice preventing shrinkage and collapse of the structure and shape during freeze drying (Ratti 2001). The particle properties of oven-dried sugar beet powder (not shown in Fig. 2) were compact and exhibited irregular particles with sharp edges and considerable indentation as a result of crushing into powder. These findings are in agreement with the findings of Caparino et al. (2012). Spray-dried sugar beet powder contained spherical and smooth surface particles (Fig. 2b). Similar particle properties of hazelnut milk powder produced using spray drying were reported by Ermis et al. (2018). High degree of agglomeration for both FD-SBP and SD-SBP was observed in Fig. 2. This behavior might be attributed to carbohydrate content of sugar beet root leading to sticky structure and the use of low amount of MD (5%) which is generally used to prevent stickiness in food powder systems. When the individual particles of FD-SBP and SD-SBP are examined (Fig. 2), one can state that FD-SBP particles have composite sheets having internal emptied spaces indicating some pore formation during freeze drying. SD-SBP particles exhibited spherical and fine particles having smooth surfaces which depicts the reason why the porosity of particles obtained from freeze drying was always higher when compared to spray drying.

FTIR properties

The FTIR spectra from 400 to 4000 cm⁻¹ for FD-SBP, SD-SBP and OD-SBP samples can be seen in Fig. 3. The spectra revealed that powder samples exhibited similar FTIR spectra profile except some variations in the intensities of the absorbance peaks, especially within 800–1600 cm⁻¹ band. SD-SBP gave smoother spectrum (Fig. 3b) than FD-SBP and even some peaks disappeared in the spectrum (mainly within 800–1000 cm⁻¹ band) obtained from SD-SBP which indicates that the drying method alter the molecular structure of the powder materials. The peaks within 1500–800 cm⁻¹ band region indicate C-O stretching and glycosidic linkage absorption of carbohydrates and this band was reported as carbohydrate fingerprint region (Oldenhof et al. 2005; De Giacomo et al. 2008). There is no detailed information related to peak assignments in this region in literature. The bands around 1500 cm⁻¹ were attributed to bending and/or stretching of amide II groups (Zhao et al. 2013). The band at 1600 cm⁻¹ was assigned to N-H bending of amide I group and COO- and C=O stretching vibrations (De Giacomo et al. 2008). The band around 2900 cm⁻¹ was assigned to C-H stretching from proteins and carbohydrates (Ng et al. 2014). A band region around 3300 cm⁻¹ was attributed to O-H and N-H stretching of hydroxyl groups originating from polysaccharides and protein (Dogan et al. 2007).

Fig. 3.

FTIR spectra of powder samples

Sensory evaluation

Results of sensory evaluation test are presented in Table 3. Some attributes of cocoa-hazelnut spread (HS) samples containing SBP samples obtained using different methods were evaluated significantly lower than the control. Some attributes were scored as undesirable while others were scored as desirable for different powder samples. Cocoa-hazelnut spread containing OD-SBP was scored lower than 3 which corresponds to ‘undesirable’ for bitterness and overall acceptability while FD-SBP was scored lower than 3 for mouth feel, color and appearance and overall acceptability. The attributes which were scored lower than 3 for SD-SBP are bitterness and sour taste. Cocoa-hazelnut spread containing SD-SBP got second highest score from panelists for overall acceptability attribute after control sample containing sucrose. This indicates that spray-dried sugar beet powder seems more appropriate to use in cocoa-hazelnut spread and has a potential to be used in other food product formulations.

Table 3.

Sensory evaluation of cocoa-hazelnut spread samples (n = 12)

Attributes	HSControl	HSOD-SBP	HSFD-SBP	HSSD-SBP
Bitterness	3.41 ± 1.56a	2.91 ± 1.37b	3.50 ± 1.31a	2.83 ± 1.46b
Sour taste	3.58 ± 1.16a	3.58 ± 1.37a	3.25 ± 1.21ab	2.66 ± 1.0abc
Sugary taste	4.08 ± 0.90a	3.00 ± 1.47ab	3.00 ± 1.53ab	3.16 ± 1.11ab
Mouth feel	3.83 ± 0.83a	3.00 ± 1.12b	2.16 ± 0.93c	3.50 ± 1.16ab
Color and appearance	4.08 ± 1.08a	3.91 ± 1.24a	2.50 ± 1.50ab	4.00 ± 1.04a
Overall acceptability	3.83 ± 1.11a	2.50 ± 1.16ab	2.75 ± 1.21ab	3.16 ± 1.26a

SD-SBP spray-dried sugar beet powder, FD-SBP freeze-dried sugar beet powder, OD-SBP oven dried sugar beet powder, HS hazelnut spread

(1-highly undesirable; 5-highly desirable)

Columns with different letters indicate statistically significant difference (p < 0.05)

Conclusion

Some physical properties and micro structures of sugar beet powders obtained using different techniques were investigated in this study. In addition, the powder samples were used in the formulation of cocoa-hazelnut spread and the consumer acceptability was evaluated. Oven dried and spray-dried powders were found to be denser than freeze-dried powder. Spray-dried powders were the most dense which is a result of densely packing behavior of spherical particles having smooth surfaces. There were no significant differences in total reducing sugar contents of OD-SBP and FD-SBP while SD-SBP had remarkably higher amount of total reducing sugar. Significant differences in solubility of three powder samples produced using different drying methods were noticed. The flowability values of oven dried and freeze-dried powders were almost identical while spray-dried powder showed less flowability behavior. The micro structure of particles played an important role in physical properties and powder behavior. Cocoa-hazelnut spread with spray-dried sugar beet powder demonstrated a good overall acceptability. Therefore, sugar beet powder, which has a potential source of bio active compounds, dietary fiber and antioxidants, could be used in food product formulations as a functional ingredient. Further studies should be done to evaluate the formation of rotten fishy smell (especially after prolonged storage) due to some possible changes in its amino acid profile of sugar beet extract powder. In addition, evaluation of the effect of freezing of the beet root pieces at − 18 °C on drying characteristics should be studied. Furthermore, optimization of drying parameters should be studied in detail to obtain powders with better properties.

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.