Gluten-free crispbread with freeze-dried blackberry: quality and mineral composition

ABSTRACT

The aim of the present study is to analyse the effect of freeze-dried blackberry powder (BP) added in the range from 0% to 5% on the physical properties and some nutritional parameters of gluten-free crispbread. Batter added with BP had a significantly lower pH value, while the highest indicator of batter divergence was observed in the batter without the addition of BP. Freeze-dried BP was characterised by the following colour parameters: L* = 42.87, a* = 15.91 and b* = −0.26. Lightness component (L*) of gluten-free crispbread decreased from 75.27 to 42.73, colour (b*) value decreased from 19.91 to 8.27 and redness (a*) value increased from 1.10 to 7.32 with the addition of BP at a range from 0% to 5%. Crispbreads prepared with BP (5%) also had significantly higher minerals including potassium, calcium, magnesium, iron and manganese in comparison to control crispbreads. In addition, BP caused an increase in total flavonoids, phenolics and anthocyanins content.

RESUMEN

El presente estudio se propuso analizar el efecto de la adición de polvo de mora (BP) liofilizado, en el rango de 0% a 5%, sobre las propiedades físicas y algunos parámetros nutricionales del pan crujiente sin gluten. La masa añadida con BP mostró un valor de pH significativamente más bajo, mientras que en la masa a la que no se adicionó BP se constató el indicador de divergencia más alto. El BP liofilizado se caracterizó por los siguientes parámetros de color: L*=42.87, a*=15.91 y b*= −0.26. El componente de luminosidad (L*) del pan crujiente sin gluten disminuyó de 75.27 a 42.73, el valor de color (b*) se redujo de 19.91 a 8.27, mientras que el valor de enrojecimiento (a*) aumentó de 1.10 a 7.32 con la adición de BP en un rango de 0% a 5%. En comparación con los panes crujientes de control, los panes crujientes preparados con BP (5%) presentaron contenidos de minerales significativamente más altos, incluyendo potasio, calcio, magnesio, hierro y manganeso. Además, el BP provocó el aumento del contenido total de flavonoides, fenólicos y antocianinas.

KEYWORDS:

• Blackberry
• gluten-free
• crispbread
• natural colourant

PALABRAS CLAVE:

• zarzamora
• sin gluten
• pan crujiente
• colorante natural

1. Introduction

Consumers are increasingly looking for gluten-free cereal products (Rosell, Barro, Sousa, & Mena, 2014; Różyło et al., 2015; Różyło, Rudy, Krzykowski, & Dziki, 2015). However, only a few studies have focused on gluten-free crispbreads (Dogan, Yildiz, & Meral, 2016; Huber & Schoenlechner, 2017; Mert, Sahin, & Sumnu, 2015). Lyophilised fruits can serve as a good alternative of functional additive in preparing many gluten-free products such as crispbreads. (Drewnowski, Nordensten, & Dwyer, 1998).

Blackberry is worth mentioning as it has a nutrition-rich chemical composition and is a good source of pigments (Clerici & Carvalho-Silva, 2011). As a member of berries, blackberry also contains a high amount of bioactive compounds (Chen, Xu, Zhang, Su, & Zheng, 2016).

In addition, blackberry contains high levels of anthocyanins and other phenolic compounds, mainly flavonols and ellagitannins, which contribute to their notable antioxidant activity (Kaume, Howard, & Devareddy, 2012; Mikulic-Petkovsek, Koron, Zorenc, & Veberic, 2017). Jakobek and Seruga (2012) studied the influence of anthocyanins, flavonols and phenolic acids on the antiradical activity of berries and concluded that anthocyanins and quercetin derivatives have the highest effect.

Phenolic compounds derived from blackberry were found to protect against age-related neurodegenerative diseases and bone loss in vivo (Gilbert et al., 2011). They also reduced the concentration of low-density lipoprotein and inhibited liposomal oxidation in vitro (Kaume et al., 2012).

Anthocyanins present in blackberries, belonging to the flavonoid family, are natural colourant and can therefore be utilised in the food and pharmaceutical industry (Fan-Chiang & Wrolstad, 2005; Jacques & Zambiazi, 2011; Pergola, Rossi, Dugo, Cuzzocrea, & Sautebin, 2006). To improve the extraction of compounds with a high-added value from blackberries, a pulsed electric technology and ultrasound were proposed (Barba, Galanakis, Esteve, Frigola, & Vorobiev, 2015). In another study, gel filtration of ethanolic extracts of blackberries was employed to obtain an anthocyanin-enriched extract (Elisia, Hu, Popovich, & Kitts, 2006).

The conventional technology of extraction very often uses high temperatures and toxic solvents (Barba et al., 2015). Some authors have explained that anthocyanin-rich extracts from blackberries, which are used as natural pigments, are characterised by poor stability, and indicated spray drying as a suitable approach for encapsulating and stabilising these extracts (Weber, Boch, & Schieber, 2017). The effect of different carriers on the physicochemical properties of BP produced by spray drying was evaluated by Ferrari, Germer, Alvim, Vissotto, and de Aguirre (2012). Spray drying technique was also used by Farías Cervantes, Delgado Lincon, Solís Soto, Medrano Roldan, and Andrade González (2016) and Dos Santos, Rodrigues, Da Costa, Bergamasco, and Madrona (2017) to produce BP. Blackberry powders prepared by spray drying and freeze-drying of juice were proposed as a potential colourant (Franceschinis, Salvatori, Sosa, & Schebor, 2013). Freeze-drying of whole fruits could enrich different products with high fibre content. In addition, lyophilisation (freeze-drying) is suggested for drying materials including heat-sensitive antioxidant components (Rudy et al., 2015). Furthermore, freeze-drying can improve the quality of food as it prevents deterioration and microbiological reactions (Ciurzyńska & Lenart, 2011).

So far, there are no reports on the use of freeze-dried BP as a natural additive and colourant in the production of gluten-free crispbreads. Therefore, the objective of this study was to determine the changes in the physical properties including colour and some nutritional parameters of gluten-free crispbread caused by the addition of freeze-dried BP.

2. Materials and methods

2.1. Materials

White rice flour (Melvit, Warsaw, Poland), rapeseed oil, salt and baking soda were used for making gluten-free crispbreads (Table 1). The rice flour was characterised by a protein content of 6.0 ± 0.29%, a carbohydrate content of 78.0 ± 3.7%, a fibre content of 1.4 ± 0.08% and a fat content of 1.0 ± 0.04%. Lyophilised blackberry (Rubus spp) (Elena lyophilisates, Żelazków, Poland) was characterised by a protein content of 8.0 ± 0.14%, a carbohydrate content of 54.0 ± 1.71%, a fibre content of 27.2 ± 0.22% and a fat content of 6.1 ± 0.21%. Rapeseed oil (Kujawski, Kruszwica, Poland), baking soda (Gellwe, Food Care Group, Zabierzów, Poland) and salt were purchased from a local market.

2.2. Particle size distribution of freeze-dried blackberry powder

Blackberry powder was prepared after grinding whole freeze-dried blackberries with a knife grinder (Optimum RK-0150, Expo-service, Warsaw, Poland). The particle size of the prepared freeze-dried BP was analysed using a Mastersizer 3000 (Malvern Instruments Ltd., Great Britain) with a dry powder disperser (Aero S). Averages weighted by volume (D[4;3][μm]) or surface area D [3;2][μm], specific surface area (SSA) [m²ּּ kg⁻¹]. For describing the particle size distributions, D-values (Dv(10), Dv(50) and Dv(90)) were used. Dv(50) is the particle size in microns which indicates that 50% of the sample’s volume is constituted by smaller particles and 50% by larger particles. Similarly, Dv(10) is the size of particles constituting 10% of the sample and Dv(90) is the size of particles constituting 90% of the sample.

2.3. Evaluation of colour parameters of freeze-dried blackberry powder

The colour measurements were performed using a colorimeter (4Wave CR30-16,Planeta, Tychy, Poland). Powders were measured in a layer of 1-cm thickness using a special vessel that was set at the colorimeter probe. The settings of colorimeter were as follows: light: D65; space: LAB; diameter: 16 mm; and style: 8/d. Colour was expressed in CIE-L*a*b*, where L*denotes lightness, a* denotes the red (+)/green (–) value and b* denotes the yellow (+)/blue (–) value.

2.4. Preparation of crispbreads

Gluten-free crispbreads were prepared using rice flour (100%), rapeseed oil (2.5%), salt (0.3%), baking soda (0.5%) and water (170%). The recipe was optimised after trial testing on the basis of our own experience. The control crispbreads were also prepared using rice flour (100%) and other ingredients mentioned above. The amount of flour was taken as 100%, and the ratio of the other components was converted to the weight of flour. The lyophilised BP was added in an amount of 1%, 2%, 3%, 4% and 5% to the control batter. After mixing all the ingredients in a five-speed mixer (Kitchen Aid, St. Joseph, MI, USA) for 1 min, the batters (with an equal mass of 20 g) were immediately transferred to a baking machine (type MD 13211, LifeTec, Germany). Crispbreads (bread discs with a diameter of 80 mm and a thickness of 2 mm) were baked (180–190°C, 4–5 min), dried (40°C, 5 min) and cooled (22°C, 60 min) to room temperature.

Baking tests were done in 16 replicates, and then the gluten-free crispbreads were cooled and wrapped in polyethylene bags.

2.5. Evaluation of pH value of batter

The pH of the gluten-free batter was measured using a pH metre (TESTO 206-ph2, Pruszków, Poland) with a penetration probe used for semi solid substances. The calibration device used buffer solutions at two measuring points. The pH measurements were performed in three replicates.

2.6. Evaluation of batter divergence indicator

Batter divergence was determined by measuring the Zeleny’s sedimentation index (Sadkiewicz Instruments, Bydgoszcz, Poland) (Różyło et al., 2019). A volume of 50 cm³of batter was placed in a cylinder (with a capacity of 100 cm³) on a desktop. The volume of laminated batter was subsequently recorded at 0, 15, 30, 45 and 60 min. Lamination was observed on the batter during measurements (after a certain time, a clear solution was seen on the surface of the batter). Immediately after mixing the batter (t = 0 min), the indicator of divergence was equal to 0%. The indicator of batter divergence (I_d) was calculated and determined as a percentage from the following formula:

(1) $I_d=\left(1-\frac{V_t}{V_0}\right)\cdot 100\mathrm{\%}$(1)

where:

I_d is the indicator of batter divergence,

V_t is the volume of the batter after measurement(at 0, 15, 30, 45 and 60 min) and

V₀ is the starting volume of the batter (50 cm³).

Measurements of batter divergence were performed in triplicate.

2.7. Evaluation of colour parameters of gluten-free batter and crispbread

The colour measurements were performed using a colorimeter (4Wave CR30-16, Planeta, Tychy, Poland)with the help of a liquid measuring device for the batter (immediately after mixing) and a probe applied directly to the whole crispbreads (discs). The settings of colorimeter were as mentioned above, and the colour was recorded using the CIE-L*a*b* uniform colour space. Colour differences(∆L, ∆a, ∆b) were measured, and △E was calculated as follows:

(2) $\mathrm{\Delta }E=\sqrt{{\left(\mathrm{\Delta }L\right)}^2+{(\mathrm{\Delta }a)}^2+{\left(\mathrm{\Delta }b\right)}^2}$(2)

2.8. Mechanical measurements of crispbread

The mechanical test involved breaking a single crispbread disc with a blade. The whole discs (diameter 80 mm, thickness 2 mm) of crispbreads were placed on a base with two parallel arms spaced apart by 35 mm and broken using a strength tester (ZWICK Z020/TN2S). The measuring probe (500 N) was equipped with a blade having a width of 100 mm and a thickness of 3 mm that was positioned parallel and equidistant from the arms of the base. The blade was moving at a speed of 1 mm/s until the sample of crispbreads was broken. The force of crispbread breaking was determined. This test was performed in eight replicates.

2.9. Sensory evaluation of crispbread

The crispbread discs, divided into eight parts, were presented on plastic dishes, coded and served in a randomised order. The panel for sensory evaluation consisted of 52 untrained habitual consumers (22–51 years old, 27 females and 25 males). The consumers evaluated the appearance, taste, texture and overall acceptability of the crispbreads. A 9-point hedonic scale (1: dislike extremely, 5: neither like nor dislike, 9: like extremely) (Lim, Park, Ghafoor, Hwang, & Park, 2011) was used for evaluation.

2.10. Determination of trace elements (FAAS method)

Flame atomic absorption spectrometry (FAAS) was used for the quantitative analysis of elements found in the fruit powders and crispbreads. The content of zinc, copper and iron, as well as sodium and magnesium (Fan, Zhang, Yu, & Ma, 2006) was determined after the previous mineralisation of the sample.

Following the sensory analysis, the best-rated crispbreads prepared with fruits were further analysed for the content of trace elements and flavonoids. These analyses were also performed for control crispbreads and freeze-dried BP.

2.11. Evaluation of flavonoid, phenolics and anthocyanins content

The content of flavonoids in blackberry powder and crispbreads was determined spectrophotometrically following their extraction (Hatcher, 1908).

Extraction was carried out using acetone, hydrochloric acid and methenamine solution. Samples of raw material (1 g) were extracted for 30 min in a boiling water bath with 20 ml of acetone, 2 ml of hydrochloric acid (281 g/l) and 1 ml of methenamine solution (5 g/l). The extracts were separated by decantation, and the residues were extracted two more times. The extracts were filtered and adjusted with acetone. The obtained solution was subjected to liquid–liquid extraction. For this purpose, 20 ml of acetone extract were placed in a separatory funnel, and water (10 ml) was added and extracted with four portions of ethyl acetate, first a volume of 15 ml and then three volumes of 10 ml. The combined ethyl acetate layers were washed with two 40-ml portions of water, filtered into a 50-ml graduated flask and made up to volume with ethyl acetate. The extraction was carried out twice.

To obtain a stock solution of up to 10 ml of the extract, 2 ml of aluminium chloride solution was added and supplemented (1:19) with a mixture of acetic acid and methanol. The comparative solution was made without aluminium chloride solution. The absorbance of the solutions at 425 nm was measured after 45 min using a reference solution. The content of flavonoids based on quercetin was determined according to the formula:

(3) $x=\frac{\mathrm{A}\cdot k}{\mathrm{m}}$(3)

where:

A is the absorbance of the test solution,

k is the conversion factor for quercetin (k = 0.875), m is the weight of raw material (g).

For total phenolics determination, the extraction of powdered sample (1 g) was carried out for 30 min with 5 ml of methanol and water mixture (1:1, v/v). Then, the extracts were separated by decantation in centrifuge for 15 min. The residues were extracted again with 5 ml of methanol and the extracts were combined and stored at −20°C in darkness. The Folin–Ciocalteu method was used for determination Total phenols (Singleton & Rossi, 1965). The total phenols were expressed in mg as gallic acid equivalents (GAE) after measuring the absorbance the mixtures in spectrophotometer (720 nm).

Anthocyanin content was determined after extraction (Fuleki & Francis, 1968) with 95% ethanol and 1.5 N HCl (85:15). The total anthocyanins content was expressed as mg of cyanidin 3-glucoside/100 g of sample (dry basis), after measuring the absorbance of extract in spectrophotometer at 535 nm.

2.12. Statistical analysis

Statistical analysis was done at a significance level (α) of 0.05 using Statistica (Statsoft). Measurement scores were subjected to the analysis of variance (ANOVA). If significant differences were detected in ANOVA, the means were compared using Tukey’s test.

3. Results and discussion

3.1. Particle size distribution of freeze-dried blackberry powder

Results of the analysis of particle size distribution showed that the average particle size of powder weighted by volume was equal to about 247 μm, while the average size weighted by surface was equal to 46.18 μm. It was found that 50% of the sample was constituted by particles smaller than 90.85 μm, 10% by particles smaller than 17.58 μm and 90% by particles smaller than 743.33 μm. A detailed analysis of the results also showed that particles larger than 211 μm and smaller than 743.33 μm accounted for 27% of the sample. It must be considered that BP contained small particles, but there were also large particles present which was due to the difficulty in grinding the seeds. Blackberries have hard seeds that are very difficult to crush, and even long-term grinding does not give satisfactory results. Therefore, we decided to use powder as raw material. In addition, we did not sift the seed particles because we aimed at enriching the nutritional composition of crispbread. Moreover, Van Hoed et al. (2009) showed that berry seeds are a rich source of bioactives and nutrients. In a study on blackberry juices, Hager, Howard, and Prior (2010) observed significant losses of ellagitannin due to the removal of ellagitannin-rich seeds. In another study, ellagitannins were found as the main polyphenolic component of defatted blackberry seeds (Kosmala et al., 2017).

3.2. Colour parameters of freeze-dried blackberry powder

Freeze-dried BP was characterised by an L* value of 42.87, an a* value of 15.91 and a b* value of −0.26 (Table 2). In a study comparing the freeze-dried powders of different fruits (Różyło et al., 2019), freeze-dried BP was found to be significantly lighter than elderberry powder and slightly lighter (not significant) than chokeberry powder. Freeze-dried BP was characterised by a significantly higher redness and less blueness value in comparison with elderberry and chokeberry powder as shown in an earlier study (Różyło et al., 2019). Another study (de Vargas, Jablonski, Flôres, & de Rios, 2017) reported that the peels and seeds of blackberry are rich in pigments and antioxidants, representing a potential source of natural dyes. Blackberries are a great source of anthocyanin pigments (Fan-Chiang & Wrolstad, 2006), and the content of these pigments plays a critical role in determining the colour quality of many fresh and processed fruits (Giusti & Wrolstad, 2005). For example, an anthocyanin-rich extract of a blackberry by-product was obtained through freeze-drying (Yamashita et al., 2017).

Table 1. Formula of crispbreads with blackberry powder addition.

Tabla 1. Fórmula de pan crujiente con polvo de mora añadido.

Amount of freeze-dried blackberry addition(%)	Amount of rice flour addition (%)	Rapeseed oil (%)	Baking soda (%)	Salt (%)	Water (%)
0	100	2.5	0.5	0.3	170
1	99	2.5	0.5	0.3	170
2	98	2.5	0.5	0.3	170
3	97	2.5	0.5	0.3	170
4	96	2.5	0.5	0.3	170
5	95	2.5	0.5	0.3	170

Table 2. Color parameters of freeze-dried blackberry powder in comparison with chokeberry and elderberry powder.

Tabla 2. Parámetros de color del polvo de mora liofilizado en comparación con el polvo de aronia y saúco.

Color parameters	L*	a*	b*
Freeze-dried blackberry	42.87	15.91	−0.26
Freeze-dried chokeberry*	(41.01*)	(12.32*)	(−1.81*)
Freeze-dried elderberry*	(37.61*)	(4.21*)	(−4.53*)
Stand. dev.	0.12	0.03	0.01
	(0.09*)	(0.02*)	(0.09*)
	(0.14*)	(0.04*)	(0.16*)

* Results for freeze-dried chokeberry and elderberry powders already published (Różyło et al., 2019)

* Los resultados correspondientes a los polvos de aronia y de saúco liofilizados ya fueron publicados (Różyło et al., 2019)

3.3. pH value of batter with different amounts of freeze-dried blackberry powder

Significant changes were noted in the pH value of batters with an increase in the content of BP (Figure 1(a)),with the values decreasing significantly as compared to control crispbread. The most significant difference was found between the control batter (6.57) and the batter added with 3% (6.32), 4% (6.22) and 5% (6.18) of BP. This showed that as the content of BP in the batter increased, the pH value decreased. The difference was more noticeable with the increase in the amount of powder from 3% to 5%. Blackberry can cause very high acidity (Milošević, Milošević, & Mladenović, 2016). Fleshy fruit acidity is mainly caused by the organic acids present in most ripe fruits (Etienne, Génard, Lobit, Mbeguié-A-Mbéguié, & Bugaud, 2013). Yamashita et al. (2017) also showed that products obtained after the lyophilisation of blackberries caused high acidity.

Figure 1. pH: value (a) and indicator of batter delamination (b) of gluten-free batter with different amount of freeze-dried blackberry powder.

Figura 1. pH: valor (a) e indicador de la delaminación de la masa (b) de la masa sin gluten con diferentes cantidades de polvo de mora liofilizado.

3.4. Divergence of batter with freeze-dried blackberry powder

Batter with no freeze-dried BP added (control) was characterised by the highest indicator of batter divergence. With an increase in the content of BP, significant changes were noted in the divergence of batter (Figure 1(b)). With the addition of BP in the range from 0% to 3%, the indicator of batter divergence decreased significantly as compared to control. This trend was observed after each time point (15, 30, 45 and 60 min) of examination. With the increase of freeze-dried BP in the range from 3% to 5%, the indicator of batter divergence slightly increased but the value was significantly lower than that of the control. It should be noted that for preparing crispbreads, a lower indicator of batter divergence is desirable. Similar results were obtained in an earlier study by Różyło et al. (2019). The phenomenon of reducing the divergence of batter under the influence of BP could be explained by the presence of pectin which in combination with water is subjected to gelatinisation. Compared to fruits, pectins and arabinogalactans are present in a very small amount in cereals and hence do not contribute substantially to the functionality of noncellulosic polysaccharides (Muralikrishna & Rao, 2007).

3.5. Colour parameters of gluten-free batter and crispbread with freeze-dried blackberry powder

With an increase in the content of BP, significant changes were noted in the colour of the batter (Figure 2(a–c)) (Table 3). The lightness component L* (Figure 2(a)) decreased from 79.5 to 49.3 with the addition of BP in the range from 0% to 5%. Similar values of L* component were obtained with the addition of BP in the range from 4% to 5%. The changes described by ∆L were equal to −14.21 and −30.47, respectively, for the addition of 1% and 5% BP. Control crispbread was obtained from white rice flour, and it was clear that the batter had a bright colour and the addition of BP caused darkening. This is in agreement with another study (Dabash, Burešová, Tokár, Zacharová, & Gál, 2017) where pumpkin flour was used as an additive in rice bread. In this study, colour measurements revealed that lightness decreased with an increase in the amount of pumpkin flour. Parameter a* (Figure 2(b)) increased with the addition of BP in the range from 0% to 5%. The highest redness (a* = 11.53) (Figure 2(c)) was noted in the batter with 5% BP. The changes in redness described by ∆a were equal to 3.89 and 11.57, respectively, for the addition of 1% and 5% BP. The b* value of batter (yellowness+/blueness−) decreased from 7.64 to – 5.06 with an increase in the content (from 0% to 5%) of BP. This means that with an increase in the addition of BP, the batter was turning blue. The control batter was characterised by a considerably higher yellowness. Rice flour is characterised by higher yellowness than fruit powder due to the presence of carotenoids (Lamberts & Delcour, 2008). The changes relating to all the colour parameters described by ∆E (Table 3) were significant and equal to 16.64, 22.64, 27.60, 32.36 and 34.98, respectively, for the addition of 1%, 2%, 3%, 4% and 5% of freeze-dried BP.

Table 3. Color L*a*b* values and changes in color ∆E of batter and crispbreads caused by different amount of freeze-dried blackberry powder.

Tabla 3. Valores de color L*a*b* y cambios en el color ∆E de la masa y de los panes crujientes causados por la adición de diferentes cantidades de polvo de mora liofilizado.

Amount of freeze-dried blackberry addition (%)	L*	a*	b*	∆E
Batter
0	79.54 ± 0.341^i	−0.03 ± 0.001^a	7.64 ± 0.27^f	-
1	65.41 ± 0.765^g	3.85 ± 0.042^d	0.19 ± 0.36^e	16.64 ± 0.670^f
2	59.68 ± 0.503^f	5.39 ± 0.415^f	−1.26 ± 0.19^d	22.64 ± 0.489^e
3	55.43 ± 0.549^e	7.71 ± 0.339^h	−2.78 ± 0.58^c	27.60 ± 0.478^d
4	51.00 ± 0.542^d	9.50 ± 0.547^i	−3.65 ± 0.23^b	32.36 ± 0.517^b
5	49.32 ± 0.922^c	11.53 ± 0.492^j	−5.06 ± 0.53^a	34.98 ± 0.588^a
Crispbread
0	75.27 ± 0.201^h	1.10 ± 0.042^b	19.91 ± 0.601^k	–
1	59.97 ± 0.093^f	3.02 ± 0.243^c	12.52 ± 0.056^j	17.10 ± 0.590^f
2	55.58 ± 0.592^e	4.30 ± 0.119^e	11.71 ± 0.074^i	21.57 ± 0.565^e
3	48.49 ± 0.508^c	6.02 ± 0.306^g	10.64 ± 0.109^h	28.77 ± 0.477^c
4	46.00 ± 0.266^b	6.85 ± 0.524^g	8.42 ± 0.342^g	31.98 ± 0.580^b
5	42.73 ± 0.893^a	7.32 ± 0.286^gh	8.27 ± 0.298^fg	35.12 ± 0.769^a

Means with different letter are significantly different (α < 0.05).

Las medias con letras distintas son significativamente diferentes (α < 0.05).

Figure 2. Force of breaking crispbreads with different amount of freeze-dried blackberry powder.

Figura 2. Fuerza de rotura del pan crujiente con diferentes cantidades de polvo de mora liofilizado.

With an increase in the content of BP, significant changes were noted in the colour of crispbread (Figure 2(d–f)) (Table 3). The lightness component L* (Figure 2(d)) decreased from 75.27 to 42.73 with the addition of BP in the range from 0% to 5%. In comparison with the control batter (Figure 2(a)), the lightness component L* was significantly lower for crispbread, and this change was caused by baking. Parameter a* (Figure 2(e)) increased from 1.10 to 7.32 with the addition of BP in the range from 0% to 5%. The changes in crispbread redness described by ∆a were equal to 1.92 and 6.22, respectively, for the addition of 1% and 5% of BP. Such results could be expected because of the colour of the fruit powder used as an additive. The results were in agreement with other researches related to crispy bakery products, namely biscuits, enriched with anthocyanins (Pasqualone, Bianco, & Paradiso, 2013). Mert et al. (2015) clearly observed the effects of the natural colour of the flours (buckwheat, wheat and rice) in the colour analyses of gluten-free wafers. The changes in a* value were significantly lower than in the case of batter, and this could be due to the heat exposure during baking. For example, the Maillard reaction could cause these changes (Delgado-Andrade, Conde-Aguilera, Haro, Pastoriza de la Cueva, & Rufián-Henares, 2010; Świeca, Gawlik-Dziki, Dziki, Baraniak, & Czyz, 2013). As shown earlier (Mazza & Miniati, 1993), the stability of pigments also depends on temperature. The pigments readily degrade during thermal processing which can have a dramatic impact on the colour quality and may also affect the nutritional properties (Patras, Brunton, O’Donnell, & Tiwari, 2010).

The b* value of gluten-free crispbread (yellowness) decreased from 19.91 to 8.27 with an increase in the content (from 0% to 5%) (Figure 2(f)) of BP. Thus, it is clear that BP contains blue pigments that have an impact on the colour of crispbread.

3.6. Mechanical properties of crispbread with freeze-dried blackberry powder

The force of breaking crispbread changed as a result of the addition of BP (Figure 2). This parameter increased significantly from 4.61N to 6.14N with an increase in the content (from 0% to 5%) of BP. There were no significant differences in the force with the addition of 0%,1%, 2% and 3% of BP in crispbread formulation. The force of breaking crispbreads with fruit added was not determined in this study, but other studies (Quiles et al., 2018) relating to sponge cakes showed the effect of using black currant and Aronia pomace to replace a part of the flour. In these studies, flour replacement led to batters with the lowest viscosity and gave rise to softer cakes with fewer but larger-sized air cells. Among the crispbreads obtained by extrusion cooking, there was no difference noted in hardness in control cereal crispbread and crispbread with apple by-product (Konrade, Klava, & Gramatina, 2017). It is difficult to indicate the reason for the increase in force but it could be due to the presence of fibre in blackberry (Csanádi, Cserjési, Nemestóthy, & Bélafi-Bakó, 2012). As shown by other authors (Aydogdu, Sumnu, & Sahin, 2018; Gularte, de la Hera, Gómez, & Rosell, 2012), fibre-enriched gluten-free cakes had a higher hardness. Our earlier study (Różyło et al., 2019) also showed an increased hardness of wafers prepared with freeze-dried elderberry and chokeberry.

3.7. Sensory evaluation of crispbread with freeze-dried blackberry powder

Sensory evaluation showed that control gluten-free crispbread and crispbread with 3%, 4% and 5% of BP obtained the highest scores for appearance, taste, aroma and overall acceptability (Table 4). The evaluation of appearance showed that crispbread with a lower addition of the freeze-dried fruit powder had a poor appearance. The least acceptable crispbread was the one obtained by the addition of 1–2% of freeze-dried BP. Greater levels of freeze-dried BP (3–5%) led to an acceptable appearance and taste in crispbread. Finally, it was concluded that the most acceptable gluten-free crispbreads can be obtained by adding 4–5% of freeze-dried BP. In the available literature, there are no reports on the addition of freeze-dried blackberry to crispbreads. However, Dos Santos et al. (2017) and Skrovankova, Sumczynski, Mlcek, Jurikova, and Sochor (2015) indicated that the addition of blackberry is highly appreciated to enhance the colour and flavour. In addition, Dogan (2006) explained that the quality of ingredients is very important for obtaining high-quality wafers.

Table 4. Sensory evaluation of gluten-free crispbread with freeze-dried blackberry addition.

Tabla 4. Evaluación sensorial del pan crujiente sin gluten con mora liofilizada añadida.

Amount of blackberry addition (%)	Appearance	Taste	Flavour	Texture	Overall
0	8.7 ± 0.52^a	8.1 ± 0.50^b	8.2 ± 0.48^a	8.5 ± 0.25^a	8.7 ± 0.33^a
1	5.3 ± 0.21^c	6.0 ± 0.33^d	8.3 ± 0.36^a	8.4 ± 0.43^ab	6.2 ± 0.31^c
2	6.3 ± 0.27^b	7.7 ± 0.39^c	8.3 ± 0.41^a	8.3 ± 0.47^ab	6.8 ± 0.39^b
3	8.5 ± 0.49^a	8.3 ± 0.31^b	8.4 ± 0.40^a	8.3 ± 0.39^ab	8.2 ± 0.34^b
4	8.8 ± 0.51^a	8.7 ± 0.21^a	8.4 ± 0.37^a	8.3 ± 0.22^ab	8.6 ± 0.28^a
5	8.9 ± 0.42^a	8.9 ± 0.32^a	8.5 ± 0.23^a	8.2 ± 0.18^b	8.7 ± 0.25^a

Means with different letter are significantly different (α < 0.05).

Las medias con letras distintas son significativamente diferentes (α < 0.05).

3.8. Mineral composition of crispbread

For further analysis, crispbreads with a maximum (5%) amount of BP were selected. These crispbreads had significantly higher minerals (Table 5), including potassium, calcium, magnesium, iron and manganese, in comparison to control crispbreads. The addition of BP to crispbread increased its calcium content by 71%, potassium by 57%, iron by 46%, copper by 19%, magnesium by 16% and manganese by 12%. Blackberries are considered as a rich source of phytochemicals with high nutraceutical value and beneficial health effects (Milosevic, Mratinic, Milosevic, Glisic, & Mladenovic, 2012). These berries are also a good source of essential nutrients such as manganese, magnesium and potassium as reported by Amidžić Klarić, Klarić, Velić, and Vedrina Dragojević (2011). The use of fruits in high-consumption products such as cookies can be beneficial to those countries with a great diversity of fruits having high potential as a source of bioactive compounds, which are not commercially exploited. As mentioned by Pereira, Clerici, and Pastore (2017), blackberries have exceptional sensory quality, gaining attention for their exotic and nutritional appeal, and have an intense bittersweet taste and purplish-red colour due to the high concentration of anthocyanins.

Table 5. Mineral composition of blackberry freeze-dried powder and crispbreads.

Tabla 5. Composición mineral del polvo de moras liofilizado y el pan crujiente.

Kind of material	K (mg/kg)	Na (mg/kg)	Ca (mg/kg)	Mg (mg/kg)	Cu (mg/kg)	Mn (mg/kg)	Fe (mg/kg)	Zn (mg/kg)
Blackberry powder	10800 ± 725^a	41.7 ± 2.1^a	2020 ± 131^a	1230 ± 79^a	8.42 ± 0.43^a	59.2 ± 2.43^a	37.3 ± 2.0^a	14.7 ± 0.7^c
Crispbread with blackberry	1290 ± 83^b	1520 ± 87^b	328 ± 17^b	397 ± 24^b	5.48 ± 0.37^b	10.0 ± 0.7^b	14.5 ± 0.6^b	25.0 ± 1.4^b
Crispbread without fruits (Control)	822 ± 44^c	1450 ± 92^b	192 ± 8^c	342 ± 21^c	4.59 ± 0.25^c	8.96 ± 0.43^c	9.95 ± 0.4^c	33.1 ± 1.8^a

Means with different letter in the same column are significantly different (α < 0.05).

Las medias con letras distintas en la misma columna son significativamente diferentes (α < 0.05).

3.9. Flavonoids, phenolics and anthocyanins content in crispbread

Control crispbreads had a low content of total flavonoids, phenolics and monomeric anthocyanins (Table 6), and the addition of BP caused a certain increase in these substances. Several studies have confirmed that the use of blackberries in high-consumption products such as cookies can bring benefits because they are a source of bioactive compounds (Pereira et al., 2017). The levels of phenolic compounds and anthocyanins were found to increase with an increase in the addition of BP in cookies formulation prepared from whole-wheat grain flour (Pereira, Clerici, Schmiele, & Pastore, 2019). In our study, BP had a significant content of flavonoids, phenolics and monomeric antyhocyanins, which confirmed that the addition of freeze-dried BP caused an increase in these compounds content of crispbreads. Among the phenolic compounds investigated, quercetin and isoquercetin were found to be predominant in blackberries (Schulz et al., 2019). Among the phenolic compounds investigated, quercetin and isoquercetin were found to be predominant in blackberries (Schulz et al., 2019).

Table 6. Total flavonoids content, total phenolics content, and total monomeric anthocyanins in blackberry freeze-dried powder and crispbreads.

Tabla 6. Contenido total de flavonoides, contenido total de fenoles y antocianinas monoméricas totales en el polvo de mora liofilizado y el pan crujiente.

Kind of material	Total Flavonoids (calculated as quertistin) (mg QE/100g)	Total Phenolics (calculated as gallic acid) (mg GAE/100g)	Total Monomeric Anthocyanins (calculated as cyanidin-3 glucoside) (mg/100g)
Blackberry powder	40.0 ± 2.8^a	548 ± 6.35^a	147 ± 9.33^a
Crispbread with blackberry	3.0 ± 0.1^b	16.7 ± 2.12^b	7.2 ± 0.45^b
Crispbread without fruits (Control)	2.3 ± 0.1^c	3.3 ± 0.23^c	2.9 ± 0.13^c

Means with different letter are significantly different (α < 0.05).

Las medias con letras distintas son significativamente diferentes (α < 0.05).

4. Conclusion

The freeze-dried BP, in the amount of 5%, is proposed as a functional additive and natural colourant for preparing gluten-free crispbreads without sugar.

Batters added with 3%, 4% and 5% of BP were characterised by a significantly lower pH value than the batter without fruit powder. A higher indicator of divergence was obtained for control batter in comparison with batters with different amounts of freeze-dried BP. The proposed indicator of divergence helped in differentiating the results and can thus be used for the evaluation of batter and also other liquids.

Freeze-dried BP was characterised by the following colour parameters: L* = 42.87, a* = 15.91 and b* = −0.26. The addition of BP to crispbreads in the range from 0% to 5% caused a considerable decrease in the lightness component (L*), a decrease in the colour (b*) value and an increase in the redness (a*) value, and therefore, BP can be proposed as a valuable natural colourant. Sensory evaluation showed that gluten-free crispbread prepared with 4–5% of BP achieved high scores for appearance, taste and overall acceptability.

Freeze-dried BP with high nutritional potential increased the content of calcium by 71%, potassium by 57%, iron by 46%, copper by 19%, magnesium by 16% and manganese by 12% in crispbreads. Control crispbreads had a low content of flavonoids, phenolics, and monomeric anthocyanins, while the addition of BP caused an increase in these substances.

In conclusion, freeze-dried BP can be proposed as a functional alternative for sugar and a natural colourant for preparing more nutritious crispbreads.

Disclosure statement

No potential conflict of interest was reported by the authors.