Original papers
Ellagitannin and Anthocyanin Retention in Osmotically Dehydrated Blackberries
2017 年 23 巻 6 号 p. 801-810
詳細
2017 年 23 巻 6 号 p. 801-810
The objective of the work was to examine changes in the content of ellagitannins and anthocyanins, which are the main polyphenolic fractions of blackberries, during osmotic dehydration of the fruit in 50 – 65°Bx sucrose solutions. Frozen blackberries were found to be readily dehydrated under mild temperature conditions (30°C), with dry matter content more than doubling after 1 h, and reaching 48% after 3 h in 65°Bx solution. Total ellagitannin retention after 1 h of processing amounted to at least 80%, while after 3 h it ranged from 63.6% to 82.4%. The concentrations of the two main ellagitannins, lambertianin C (a trimer) and sanguiin H-6 (a dimer), revealed similar patterns of variation. The greatest losses, reaching up to 50% after 1 h of dehydration, were recorded for ellagic acid. After the same treatment time, the decrease in anthocyanin concentration was approx. 30 – 40%. The loss of polyphenolic compounds from fruit was attributable to their migration to the syrup. After 3 h of osmotic dehydration, ellagitannin concentration in the syrup amounted to 13.6 – 22.1 mg/100 mL, and that of anthocyanins was 6.7 – 11.2 mg/100 mL.
Osmotic dehydration is a food processing technology consisting of partial water removal as a result of immersing plant tissue in concentrated saccharide or salt solutions. The method is particularly attractive in that it does not involve water phase change, which makes it possible to largely preserve the initial properties of the raw material (Garcia-Martinez et al., 2002). Moreover, any bioactive components of the hypertonic solution (if present) may diffuse to the dehydrated material, enhancing its health benefits (Nambiar et al., 2016). A drawback of the method is the loss of valuable components from the dehydrated fruit or vegetables as a result of migration into the hypertonic solution (syrup) or due to degradation. Therefore, the dehydration conditions should be carefully selected to minimize the losses.
High concentrations of health-promoting polyphenols are found in berries, such as strawberries, blueberries, raspberries, gooseberries, and mulberries. The literature provides examples of their osmotic dehydration (Moreno et al., 2000; Stojanovic and Silva, 2007; Bórquez, 2010; Kucner et al., 2014; Chottamom et al., 2012), but data concerning blackberries are limited and mostly concern dehydration kinetics and sensory properties (Bedoya et al., 2004; Rodriguez-Barona S. et al., 2014; Giraldo G.A.G., 2005), while very little is known about polyphenolic retention. Osorio et al. (2007) provided such information only for monomeric anthocyanins.
Blackberry (Rubus fruticosus) is a shrub characterized by considerable intraspecific variability, belonging to the family Rosaceae. The world production of blackberries is estimated at approx. 155,000 tons annually, with fruit harvested both from commodity plantations and wild-growing plants, especially in North and South Americas, Europe, Asia, and Oceania. The short fruit-bearing period limits the possibility of consuming fresh blackberries, which leads to increased processing and a growing range of products made from them, including frozen foods, jellies, jams, juices, as well as fruit stuffing for dairy products and confectionery (Kaume et al., 2012).
In addition to their palatability and nutritional qualities, blackberries also exhibit therapeutic properties, such as anti-inflammatory, antiviral, and antibacterial activity. Due to the high content of polyphenolic compounds, and especially anthocyanins and ellagitannins, blackberries are also strong antioxidants (Cho et al, 2004; Hassimotto et al., 2008).
Blackberry anthocyanins are a well-characterized polyphenolic group, predominantly consisting of cyanidin glucosides, rutinosides, xylosides, and arabinosides (Kaume et al., 2012; Mertz et al., 2007). The most abundant blackberry anthocyanins are monoglycosides, and, to a lesser extent, diglycosides, in which sugar residues are attached to the flavone carbon backbone at position C3 (Wu et al., 2006). Anthocyanin content in blackberries is variable and depends on such factors as cultivar, environmental conditions, geographic region, ripeness, and, in the case of processed fruit, technological conditions (Kaume et al., 2012). Anthocyanin content typically ranges from 70 to 240 mg/100 g fresh weight (FW) (Cho et al., 2004; Fan-Chiang and Wrolstad 2005).
Ellagitannins, which are hydrolyzable tannins (the other main group in this class of compounds being condensed tannins) are esters of 3,4,5,3′,4′,5′-hexahydroxydiphenic acid (HHDP) and a monosaccharide, usually β-D-glucose, or its oligomers. A fundamental property of ellagitannins is that they release HHDP, which spontaneously lactonizes to ellagic acid. This molecule, which is further metabolized in humans and animals, is thought to be largely responsible for the health-promoting properties of ellagitannins. A diet rich in ellagitannins has a beneficial effect on the fermentation processes occurring in the gastrointestinal system of humans (Battino et al., 2009; Jarosławska et al., 2011; Williams et al., 2004) and animals (Kosmala et al., 2014; Kosmala et al., 2015), and prevents cardiovascular diseases (Mullen et al., 2002) and cancer (Casto et al., 2002; Gonzalez-Sarrias et al., 2010; Seeram et al., 2006; Umesalma and Sudhandiran, 2011). The most abundant blackberry ellagitannins are sanguiin H-6 and lambertianin C (Hager et al., 2010; Mertz et al., 2007).
The objective of the work was to determine the effect of selected osmotic dehydration parameters (time, hypertonic solution concentration) on anthocyanin and ellagitannin retention in blackberries.
Materials Frozen blackberries (Rubus fruticosus) were purchased from Cajdex PPHU (Łódź, Poland).
The following reagents were used: sucrose (Diamant, Pfeifer and Langen Polska S.A., Polska), acetone (Poch S.A., Gliwice, Polska), methanol (J.T.Baker, Deventer, Holland), acetonitrile (LiChrosolv, Darmstadt, Germany), phosphoric acid (purity 85%, J.T. Baker, Deventer, Holland), formic acid (Sigma-Aldrich Chemie, Steinheim, Germany), cyanidin-3-O-glucoside (Extrasynthèse S.A., Genay, France), ellagic acid (Extrasynthèse S.A., Genay, France). Sanguiin H-6 with a purity of 90% and lambertianin C with a purity of 95% (purity was determined by HPLC analysis at a wavelength of 210 nm, as described in the section devoted to polyphenolic determination in fruit) were extracted with acetone from raspberry pomace and isolated by preparative chromatography pursuant to Sójka et al., (2016). The molar masses of lambertianin C and sanguiin H-6 were confirmed using a Q Exactive Orbitrap mass detector (Thermo Fisher Scientific, Walthman, MA) according to the procedure of Sójka et al. (2016).
Osmotic dehydration Dehydration was conducted in tightly sealed plastic containers placed in a water bath shaken at a rate of 150 cycles/min. Frozen blackberries, stored at −18°C, were divided into 13.5 g lots, which were placed in the containers, to which a sucrose solution (50, 57.5 or 65°Bx) was added after approx. 20 min. The amount of the solution was four times the weight of the fruit. Dehydration was conducted at 30°C. Samples were taken after 1 h, 3 h, and 5 h. Each time, three containers were taken from the bath. The fruit was removed from the solution using a sieve (separately from each container). While still in the sieve, the blackberries were immersed in distilled water three times to remove any remaining sucrose solution from the surface of the fruit, which was subsequently dried using filter paper.
Dry matter determination First, 3 g samples of fruit ground in liquid nitrogen in a laboratory mill (IKA A11B) were weighed into weighing dishes containing dried sand (105°C, 1 h). The dishes were then placed in a vacuum dryer set to 70°C and 60 mbar for 20 h. Subsequently, the dishes were cooled in a desiccator for 30 min and weighed. The measurements were made in triplicate.
Determination of polyphenols in fruit Blackberry samples were extracted three times with 70% acetone solution. Approx. 1 g of fruit ground in liquid nitrogen was placed in 7 mL test tubes with stoppers. Then, the samples were immersed in 4 mL 70% acetone, shaken on a vortex mixer, placed in an IS-4 ultrasonic cleaner (Intersonic, Olsztyn, Poland) for 15 min, and finally centrifuged in a MPW-260R laboratory centrifuge (Med Instruments, Warszawa, Poland) at 14,000 rpm for 5 min. Clear extract was decanted into 10 mL volumetric flasks and the sediment remaining in the test tubes was extracted in the same way two times using 3 mL and 2 mL of the extractant. Following the extraction step, the solution in the volumetric flask was made up with 70% acetone. The samples were diluted with methanol as a ratio of 1:1, centrifuged (14,000 rpm), transferred to vials, and analyzed chromatographically using a Knauer chromatograph (Berlin, Germany) equipped with a degasser (Manager 500), two pumps (P1000), stirrer, autosampler (3950), thermostat, and a PDA (2800). Separation was conducted in a 5µ C18 110A 250×4.60 mm Gemini column (Phenomenex, Torrance, CA). The column was thermostated at 35°C. The mobile phase was: A – 0.05% (v/v) phosphoric acid in water; B – 0.05% phosphoric acid in acetonitrile/methanol/water 63/20/17 (v/v/v) mixture. The flow rate was 1.25 mL/min. The gradient program was: 0 – 5 min 5% B; 5 – 30 min 5 – 28% B; 30 – 40 min 28 – 73% B; 40 – 45 min 73% B; 45 – 47 min 73 – 5% B; 47 – 56 min 5% B. The injection volume was 20 µL. The detection conditions were 250 nm for ellagitannins and ellagic acid, and 520 nm for anthocyanins. Quantification of lambertianin C and sanguiin H-6 was conducted based on standard curves in the concentration ranges of 0.5 – 300 and 0.5 – 225 mg/L, respectively. Quantification of anthocyanins was done based on a standard curve for cyanidin-3-O-glucoside in the concentration range of 1.5 – 156 mg/L. Data were recorded using specialized software for chromatographic applications ClarityChrom v. 3.0.5.505 (Knauer, Berlin, Germany). Determinations were made in triplicate.
Determination of polyphenols in hypertonic solutions Following fruit removal, sucrose solutions were diluted: 3-fold with methanol, and then 2-fold with 0.05% (v/v) phosphoric acid for 50°Bx, 4-fold with methanol and 2-fold with 0.05% (v/v) phosphoric acid for 57.5°Bx, or 5-fold with methanol and 2-fold with 0.05% (v/v) phosphoric acid for 65°Bx. The diluted solutions were centrifuged for 5 min in a MPW-260R laboratory centrifuge (Med Instruments, Warsaw, Poland) at 14,000 rpm, transferred to vials, and analyzed chromatographically. Chromatographic separation conditions were identical to those used for fruit analysis. Determinations were made in triplicate.
Identification of ellagitannins and anthocyanins Ellagitannins and anthocyanins were identified using a Dionex 3000 Ultimate high-performance liquid chromatograph (HPLC) coupled to a diode array detector (DAD) and a Q Exacutive Orbitrap mass detector (MS) (Thermo Fisher Scientific, Walthman, MA). Separation was conducted in a Luna C18(2) 100A 250 mm × 4.60 mm; 5 µm column (Phenomenex, Torrance, CA) with a 4 mm × 3 mm guard column (Phenomenex, Torrance, CA). The column was thermostated at 35°C. The mobile phase was: A – 1% (v/v) formic acid in water, B – acetonitrile/methanol/water 63/20/17 (v/v/v) mixture. The flow rate was 1.0 mL/min. The gradient program was: 0 – 6 min 5% B; 6 – 36 min 5 – 28% B; 36 – 48 min 28 – 73% B; 48 – 54 min 73% B; 54 – 60 min 73 – 5% B; 60 – 70 min 5% B. The injection volume was 20 µL. The detection conditions were 250 nm for ellagitannins and ellagic acid, and 520 nm for anthocyanins. Data were recorded using specialized software for chromatographic applications Xcalibur (Thermo). The MS system was equipped with a H-ESI probe used in the negative mode. The source parameters were as follows: vaporizer temperature – 500°C, ion spray voltage – 4 kV, capillary temperature – 400°C; sheath gas and auxiliary gas flow rates – 75 and 20 units, respectively. The full MS (m/z: 200 – 2000) and full MS/dd-MS2 (normalized collision energy – 20) scan modes were used.
Determination of polyphenolic retention in fruit Retention was calculated according to the following formula:
 |
where:
C0 = sample weight prior to dehydration [g] × polyphenolic concentration in the sample prior to dehydration [mg/100 g]
CD = sample weight after dehydration [g] × polyphenolic concentration in the sample after dehydration [mg/100 g]
Due to the fact that the studied material (frozen berries consisting of drupes) was sensitive to processing conditions, a mild dehydration temperature (30°C) was used to minimize adverse effects (Moreno et al., 2000). Analysis of variation in dry matter content (Fig. 1) shows that even at such a low temperature frozen blackberries readily undergo osmotic concentration. The average dry matter content in the starting material was 15.7%, while in dehydrated blackberries it ranged from 33.2% (for 57.5°Bx syrup, 1 h) to 51.3% (for 65°Bx syrup, 5 h). Thus, dry matter content more than doubled after only 1 h. Moreover, the higher the concentration of the sucrose solution, the higher the final dry matter content. For instance, 5 h of blackberry dehydration in a 50°Bx solution led to a dry matter content of 40.8%, while at 57.5°Bx and 65°Bx the dry matter content amounted to 46.5% and 51.3%, respectively. The osmotic pressure gradient increases with solution concentration, which translates into a more rapid tissue dehydration and more intensive dry matter increments (Ahmed et al., 2016).
Dry matter content in blackberries osmotically dehydrated at 30°C in sucrose solutions of various concentrations over different periods of time.
Figs. 2, 3, and 4 show changes in ellagitannin content in dehydrated fruit. The first two charts present data for the main blackberry ellagitannins: lambertianin C (standard, E3; identification data are given in Table 1) and sanguiin H-6 (E4; Table 1). Lambertianin C was the predominant ellagitannin in the fresh material (223.2 mg/100 g). Depending on the process conditions, its content in the dehydrated fruit ranged from 171.2 to 243.9 mg/100 g. Generally speaking, an increase in the concentration of a chemical compound occurs when its concentration increment resulting from loss of water outweighs the compound losses in the course of processing. In the case of blackberries, lambertianin C levels in most samples were lower than in the starting material, decreasing with treatment duration (especially up to 3 h). Lambertianin C retention values (understood as the ratio of the amount of the compound remaining in a given fruit sample after treatment to the amount of that compound present in the sample prior to treatment) indicate losses of 6.4% to almost 35% (Table 2). The lowest decline (less than 20%) occurred after 1 h. No relationship was observed between solution concentration and the retention of this compound. The content of sanguiin H-6 in the starting material amounted to 96.7 mg/100 g, as compared to 71 – 107 mg/100 g in the dehydrated fruit. Retention results were similar to those for lambertianin C. One hour of dehydration decreased sanguiin H-6 concentration by less 20%. Interestingly, an increase in treatment time from 3 h to 5 h did not cause a further drop in retention, which amounted to 67.8 – 73.2% after 5 h. Similar results were obtained for total ellagitannins (including a small fraction of lambertianin C isomers: E1 and E2; Table 1) as can be seen from Fig. 4. Given that after 3 h further dehydration is unproductive due to very small growth in dry matter content, approx. 1/3 of ellagitannin content is lost during the treatment.
Lambertianin C content in blackberries osmotically dehydrated at 30°C in sucrose solutions of various concentrations over different periods of time
Sanguiin H-6 content in blackberries osmotically dehydrated at 30°C in sucrose solutions of various concentrations over different periods of time
Total ellagitannin content in blackberries osmotically dehydrated at 30°C in sucrose solutions of various concentrations over different periods of time
| Compound | tR [min] | MS data | MS/MS value | MS/MS data | Structural assignment (percentage fraction) | Reference |
|---|---|---|---|---|---|---|
| Ellagitannins E1 | 28.67 | [1401.61]−2 [934.07]−3 |
1401 | [1869.14]−1, [1567.14]−1, [1235.07]−1, [935.08] −1, [783.01]−1, [633.07]−1, [301.00]−1 | Lambertianin C isomer (1.6% of d.e.) |
(Gasperotti et al., 2010; Hager et al., 2008) |
| Ellagitannins E2 | 29.57 | [1401.61]−2 [934.07]−3 |
1401 | [1869.15]−1, [1567.14]−1, [1235.07]−1, [935.08]−1, [783.07]−1, [633.07]−1, [301.00]−1 | Lambertianin C isomer (4.9% of d.e.) |
(Gasperotti et al., 2010; Hager et al., 2008) |
| Ellagitannins E3 | 30.42 | [1401.61]−2 [934.07]−3 |
1401 | [1869.16]−1, [1567.15]−1, [1235.07]−1, [935.08]−1, [897.05]−1, [633.07]−1, [301.00]−1 | Lambertianin C (standard) (65.2% of d.e.) |
(Mertz et al., 2007; Gasperotti et al., 2010; Hager et al., 2008) |
| Ellagitannins E4 | 31.98 | [934.07]−2 [1869.16]−1 |
934 | [1567.14]−1, [1235.07]−1, [935.08]−1, [897.05]−1, [633.07]−1, [301.00]−1 | Sanguiin H-6 (standard) (28.3% of d.e.) |
(Mertz et al., 2007; Gasperotti et al., 2010; Hager et al., 2008) |
| Anthocyanins A1 | 24.88 | [447.09]−1 | 447 | [447.09]−1, [285.04]−1 | Cyanidin-3-glucoside (standard) (86.0% of d.a.) |
(Mertz et al., 2007; Jardheim et al., 2011) |
| Anthocyanins A2 | 27.04 | [593.15]−1 | 593 | [593.15]−1, [285.04]−1 | Cyanidin-3-rutinoside (3.6% of d.a.) |
(Mertz et al., 2007) |
| Anthocyanins A3 | 30.06 | [417.08]−1 | 417 | [417.08]−1, [285.04]−1 | Cyanidin-3-xyloside (3.1% of d.a.) |
(Mertz et al., 2007; Jardheim et al., 2011) |
| Anthocyanins A4 | 32.55 | [533.08]−1 | 533 | [285.04]−1 | Cyanidin-3-(6″-malonylglucoside) (7.3% of d.a.) |
(Mertz et al., 2007; Jardheim et al., 2011) |
(standard) - identification based on the standard compound; d.e. - determined ellagitannins; d.a. - determined anthocyanins
| Compound | Dehydration time [h] | Retention [%] | ||
|---|---|---|---|---|
| 50°Bx | 57.5°Bx | 65°Bx | ||
| Lambertianin C | 1 | 79.9 ± 10.2 | 92.5 ± 12.3 | 77.3 ± 3.9 |
| 3 | 62.6 ± 9.5 | 81.7 ± 5.2 | 72.6 ± 11.4 | |
| 5 | 63.1 ± 6.7 | 71.0 ± 24.7 | 73.3 ± 6.2 | |
| Sanguiin H-6 | 1 | 80.0 ± 9.9 | 93.6 ± 7.9 | 80.4 ± 3.6 |
| 3 | 65.1 ± 6.1 | 82.4 ± 4.9 | 66.4 ± 2.5 | |
| 5 | 67.8 ± 3.7 | 73.2 ± 21.4 | 68.4 ± 6.4 | |
| Total ellagitannins | 1 | 79.7 ± 11.2 | 93.8 ± 11.3 | 78.1 ± 2.0 |
| 3 | 63.6 ± 8.5 | 82.4 ± 4.3 | 71.0 ± 9.1 | |
| 5 | 64.2 ± 6.8 | 72.2 ± 24.0 | 72.0 ± 6.3 | |
| Ellagic acid | 1 | 57.1 ± 20.4 | 72.7 ± 17.1 | 50.7 ± 4.9 |
| 3 | 70.5 ± 29.7 | 67.3 ± 7.4 | 44.2 ± 9.3 | |
| 5 | 54.1 ± 14.9 | 64.2 ± 9.3 | 48.2 ± 3.2 | |
| Anthocyanins | 1 | 61.6 ± 3.0 | 60.8 ± 8.7 | 68.6 ± 6.5 |
| 3 | 56.1 ± 8.6 | 50.5 ± 4.4 | 55.9 ± 13.8 | |
| 5 | 51.7 ± 6.7 | 46.8 ± 4.7 | 53.6 ± 6.7 | |
Changes in the content of ellagic acid, a product of ellagitannin hydrolysis, were also analyzed. The concentration of this compound in blackberries (Fig. 5) was much lower (19 mg/100 g) than that of lambertianin C and sanguiin H-6. Osmotic dehydration further reduced ellagic acid levels, especially in the first hour of processing (11.1 – 12.7 mg/100 g). Ellagic acid retention after 1 h, 3 h, and 5 h amounted to 50.7 – 72.7%, 44.1 – 70.4%, and 48.1 – 64.2%, respectively. These results are lower than those for lambertianin C and sanguiin H-6, which may be explained by facilitated migration of ellagic acid molecules, which are much smaller than those of the parent polymers.
Ellagic acid content in blackberries osmotically dehydrated at 30°C in sucrose solutions of various concentrations over different periods of time
The content of lambertianin C and sanguiin H-6 in the studied blackberry fruit is consistent with the data reported by Macierzyński et al. (2014) for 6 blackberry cultivars (32.1 – 163.1 mg/100 g FW for lambertianin C and 21.1 – 162.2 mg/100 g FW for sanguiin H-6). Gasperotti et al. (2010) found lower content of both ellagitannins in 5 blackberry cultivars from three harvest seasons: 306.3 – 665.2 mg/kg FW for lambertianin C and 188.9 – 418.3 mg/kg FW for sanguiin H-6. Also the free ellagic acid levels determined by those authors were lower and amounted to 45.6 – 84.6 mg/kg FW. Those results may be attributable to the application of mild extraction conditions (the fruits were extracted twice for 1 min using a blender).
The available literature does not provide any information on changes in ellagitannin content in osmotically dehydrated fruit. The available data concern other types of tannins and fruits other than blackberries. For instance, Kucner et al. (2013b) studied the content of procyanidins (condensed tannins) in blueberries osmotically dehydrated (65°Bx sucrose, 40°C, 120 min) with a hypertonic solution recycled 15 times; the reported mean retention of those compounds was 77%. The retention of condensed tannins in dehydrated bananas was investigated by Almeida et al. (2014) using 45 – 65% sucrose solutions at 30°C; the obtained results were 98% after 1 h and 79 – 94% after 3 h. Moreno et al. (2016) reported data on catechins, which are components of condensed tannins. Following dehydration in 65°Bx sucrose solution at 30°C for 4 h, catechin content in blueberry dry matter declined by more than 52%. An even greater decrease (over 71%) was found for epicatechin. On the other hand, lower losses were reported by Devic et al. (2010), who dehydrated apples (Gala and Marie Menard) at a higher temperature (45°C), but for a shorter time (3 h), using 60°Bx sucrose solution. In this case, an approx. 27% decrease in catechins and a 15% reduction in procyanidins (polymerized catechins) was found, which provides a good illustration of the relationship between the molecular mass and retention of a substance. Polymerized compounds diffuse into the hypertonic solution more slowly and, as noted by Devic et al. (2010), may more readily interact with cell wall lipopolysaccharides.
More information is available on total or non-tannin polyphenolic compounds. In the study of Araya-Farias et al. (2014), the decrease in polyphenolics in osmotically dehydrated sea buckthorns was approx. 12% (60°Bx sucrose solution, 40°C, 6 h). Kucner et al. (2013b) found that total polyphenolic retention in blueberries depended on the number of dehydration cycles and ranged from 2.4% to 29.4%. Hypertonic solution (65°Bx, 45°C, 4 h) was also recycled in experiments by Germer et al. (2016), who dehydrated guava. Over 15 treatment cycles, total polyphenolic retention varied from 87.5% to 98.5%. Ścibisz and Mitek (2006) reported an 11% decline in polyphenolic content in blueberries (dry weight) after 2 h of dehydration at 20°C and a 19% decrease after 6 h. In turn, after dehydrating mulberries in 60% sucrose solution for 6 h at 35°C, Chottamom et al. (2012) observed an approx. 58% reduction in polyphenolic content in dry matter. In the study of Almeida et al. (2014), bananas dehydrated at 30°C retained 89.8 – 97% of polyphenols after 1 h and 77.7 – 98% after 3 h. Finally, Sette et al. (2015) conducted raspberry dehydration in 61% sucrose solution at ambient temperature for an extremely long period (10 days). Calculations based on the data given in their paper show that polyphenolic content in dry matter decreased to approx. 18% of the initial levels.
As far as the other major group of polyphenols is concerned, the most abundant anthocyanin was cyanidin-3-O-glucoside, which accounted for 86% of total anthocyanins determined (45.8 mg/100 g of fruit). The other major compounds in this class included cyanidin-3-(6″-malonylglucoside) (3.94 mg/100 g), cyanidin-3-O-rutinoside (1.9 mg/100 g), and cyanidin-3-xyloside (1.64 mg/100 g). Fig. 6 shows changes in total anthocyanin content in the dehydrated fruit, which substantially decreased after 1 h of dehydration (from 53.3 to 38.3 – 42.0 mg/100 g). Further dehydration had a less dramatic effect on anthocyanin concentration (31.2 – 38.2 mg/100 g after 3 h and 28.4 – 31.4 mg/100 g after another 2 h), which also translated into retention levels (60.8 – 68.6%, 50.5 – 55.9%, and 46.8 – 53.6% after 1 h, 3 h, and 5 h, respectively).
Anthocyanin content in blackberries osmotically dehydrated at 30°C in sucrose solutions of various concentrations over different periods of time
In the study of Ścibisz and Mitek (2006), anthocyanin losses following 6 h of blueberry dehydration were lower (35%). In turn, Moreno et al. (2016) found that the total content of the three most abundant classes of anthocyanins (delphinidins, cyanidins, and malvidins) in the dry matter of blueberries declined by 48% following treatment in 65°Bx sucrose solution at 30°C for 4 h. Osorio et al. (2007) reported a 86% decrease in anthocyanins (relative to sample weight) in Andes berries following dehydration in 70% sucrose solution at 30°C for 24 h. Moreover, a considerable decline in anthocyanin content (by over 52%) in the dry mass of mulberries was recorded in the work of Chottamom et al. (2012). A 10-day-long raspberry dehydration treatment conducted by Sette et al. (2015) had a very adverse effect on anthocyanins in the dry mass of fruit, with only 5% of their initial content retained (as calculated on the basis of the reported data).
The main cause of reduced polyphenolic content in osmotically dehydrated fruit is the migration into the hypertonic solution (Kucner et al., 2013a). Fig. 7 shows the concentration of ellagitannins (the main compounds and total) in hypertonic solutions. Higher concentrations were recorded for lambertianin C, as after 3 h of dehydration its levels in the solutions ranged from 8.84 to 14.9 mg/100 mL, as compared to 3.97 – 6.20 mg/100 mL for sanguiin H-6. The sum of all ellagitannins determined in the syrup ranged from 13.6 to 22.1 mg/100 g. Some small amounts of free ellagic acid were also recorded (1.40 – 1.90 mg/100 mL after 3 h, see Fig. 8). Finally, the content of anthocyanins ranged from 6.65 to 11.2 mg/100 mL (Fig. 9). Generally, within the studied range, the concentration of the hypertonic solutions did not have a significant effect on their polyphenolic content. In most cases, the lowest content of the substances migrating from the fruit was found for the lowest syrup concentration (50°Bx). However, it should be noted that the final concentration of the compounds migrating from the dehydrated material to the hypertonic solution depends not only on the amount of the transported substance, but also on the volume of water transferred from the fruit to the solution, as well as on the amount of hypertonic solution absorbed by the fruit. This is a complicated system which may lead to major fluctuations in the various substances.
Lambertianin C (top), sanguiin (middle), and total ellagitannin (bottom) content in hypertonic sucrose solutions of various concentrations used for blackberry dehydration over different periods of time
Ellagic acid content in hypertonic sucrose solutions of various concentrations used for blackberry dehydration over different periods of time
Anthocyanin content in hypertonic sucrose solutions of various concentrations used for blackberry dehydration over different periods of time
The fact that migration (not degradation) played a major role in decreasing polyphenol content is confirmed by data presented in Table 3, which shows the balance of individual polyphenols in fruit and hypertonic solution before and after dehydration (in a 65°Bx solution as an example). In the case of lambertianin C, 16.6, 23.8 and 21.4% of the compound present in blackberries before dehydration migrated to syrups after 1, 3, and 5 h of processing, respectively. In the case of sanguiin H-6, the value amounted to 16.3, 23,3 and 20.8%. 30.7, 36.0 and 35.9% of ellagic acid was transferred to the hypertonic solutions. For anthocyanins, it was 51.6, 85.7 and 76.0%. A comparison of polyphenols in the whole system (fruit + syrup) before and after dehydration indicates that blackberry ellagitannins were characterized by a relatively high stability. The possible loss caused by degradation was 11% at the most (sanguiin H-6, after 5 h). The highest loss was noted in the case of ellagic acid (19.9%, after 3 h).
| Compound | Dehydration time [h] | Before dehydration | After dehydration | ||
|---|---|---|---|---|---|
| In fruit [mg] | In fruit [mg] | In solution [mg] | Sum (fruit + solution) [mg] | ||
| Lambertianin C | 1 | 30.55 ± 0.17 | 23.62 ± 1.12 | 5.07 ± 0.66 | 28.69 |
| 3 | 30.85 ± 0.62 | 22.33 ± 3.03 | 7.35 ± 2.60 | 29.69 | |
| 5 | 30.67 ± 0.39 | 22.48 ± 1.81 | 6.56 ± 2.45 | 29.04 | |
| Sanguiin H-6 | 1 | 13.24 ± 0.08 | 10.64 ± 0.53 | 2.21 ± 0.09 | 12.85 |
| 3 | 13.36 ± 0.27 | 8.87 ± 0.18 | 3.16 ± 0.95 | 12.03 | |
| 5 | 13.29 ± 0.17 | 9.09 ± 0.82 | 2.74 ± 1.05 | 11.83 | |
| Total ellagitannins | 1 | 46.82 ± 0.27 | 36.55 ± 0.85 | 7.65 ± 0.71 | 44.21 |
| 3 | 47.28 ± 0.95 | 33.50 ± 3.57 | 11.01 ± 3.67 | 44.51 | |
| 5 | 47.00 ± 0.60 | 33.84 ± 2.85 | 9.76 ± 3.63 | 43.61 | |
| Ellagic acid | 1 | 2.60 ± 0.01 | 1.32 ± 0.13 | 0.80 ± 0.09 | 2.12 |
| 3 | 2.63 ± 0.05 | 1.16 ± 0.24 | 0.95 ± 0.33 | 2.10 | |
| 5 | 2.61 ± 0.03 | 1.26 ± 0.07 | 0.94 ± 0.34 | 2.19 | |
| Anthocyanins | 1 | 7.29 ± 0.04 | 3.89 ± 0.84 | 3.76 ± 0.81 | 7.66 |
| 3 | 7.37 ± 0.15 | 3.47 ± 0.21 | 6.31 ± 1.43 | 9.78 | |
| 5 | 7.32 ± 0.09 | 3.44 ± 0.26 | 5.57 ± 2.26 | 9.01 | |
The available literature data on the migration of the substances found in fruits to the hypertonic solution mostly pertain to anthocyanins or total polyphenols. Considerable resistance to anthocyanin loss was exhibited by blueberries dehydrated at 50°C in 70°Bx sucrose solution reused multiple times in a study by Grabowski et al. (2007), with the maximum anthocyanin concentration in the syrup amounting to approx. 1.3 mg/100 g. In their experiments, Kucner et al. (2013b) obtained much higher polyphenolic levels in 65°Bx syrup reused in 15 cycles of blueberry dehydration at 40°C. In that case, polyphenolic concentration ranged from 4.75 to 34.3 mg/100 g of syrup. Following 10 h dehydration of raspberries, Sette et al. (2015) reported 45 mg of polyphenols (10% of which were anthocyanins) per 100 g of syrup. Similar anthocyanin content in sucrose solution (6.3 g/100 mL) was found following dehydration of Andes berries (Osario et al., 2007).
Polyphenolic migration into the hypertonic solution may be considered from two points of view. On the one hand, limited migration is desirable as a greater proportion of valuable polyphenols remains in the fruit, enabling it to retain more of its antioxidant properties. On the other hand, when polyphenolic migration is significant, the hypertonic solution may be used as a valuable intermediate in the production of foodstuffs fortified with polyphenols from the dehydrated fruit (Chwastek et al., 2016).
Frozen blackberries are readily dehydrated at 30°C. Dry matter content can be more than doubled after 1 h of osmotic dehydration conducted in 50 – 65°Bx sucrose solutions. The process should not be carried out for more than three hours as dry matter gain after that time is minimal. In the presented experiments, the dry matter content of blackberries was significantly affected by syrup concentration (after 3 h, approx. 39% and 48% dry matter was obtained using 50°Bx and 65°Bx solutions, respectively). The retention of ellagitannins depended on dehydration time. The two main compounds in this class, lambertianin C and sanguiin H-6, behaved similarly in this respect as approx. 80 – 90% of them remained the fruit after 1 h and approx. 60 – 80% after 3 h (depending on syrup concentration). A more dramatic decline was noted for ellagic acid (up to 50% after 1 h). Furthermore, as much as 30 – 40% of anthocyanins were lost after 1 h. The reduced content of polyphenols in blackberries was caused by the migration of the compounds into the hypertonic solution, which contained 13.6 – 22.1 mg/100 mL ellagitannins and 6.7 – 11.2 mg/100 mL anthocyanins after 3 h of osmotic processing.
