Sea buckthorn (Hippophaë rhamnoides
L.) belongs to the Elaeagnaceae family and occurs mainly in the northern hemisphere. The high content of flavonols, L-ascorbic acid and lipophilic compounds including carotenoids, tocopherols, fatty acids and phytosterols provides unique health-promoting properties and thus enables a wide range of applications of this plant [1
]. Juices, beverages, jams, oils, teas, pharmaceuticals, cosmetics, dairy and spirits as well as feedstuff are produced from sea buckthorn fruits, leaves, bark and seeds. To date, anti-radical activity, protection against UV radiation, efficacy in dermatological diseases, cardioprotective, hepatoprotective, anti-inflammatory, anti-hyperlipidemic, anti-cholinergic, anti-hypertensive, anti-hyperinsulinemia and antimicrobial properties have been studied [2
]. Due to the high fat content, liquid and semi-liquid products from sea buckthorn separate into two phases and thus are not attractive to consumers. An alternative can therefore be the process of juice encapsulation using drying methods leading to the formation of powders. However, drying pure fruit juices is hindered due to agglomeration of material particles and adhesion to the surface of dryer installations. Fruit juices, including sea buckthorn, contain organic acids and sugars with a low glass transition temperature (Tg). Therefore, the high-molecular weight carrier agents are mixed with the juices before drying to increase the Tg of the product and, as a consequence, avoid a viscoplastic state and caking [4
]. The carrier agents used in the production of powders may be maltodextrin, inulin, gum arabic, carrageenan gum, carboxymethyl cellulose (CMC), starch, pectin, whey protein, gelatin, casein and others; however, each of them affects the physical and chemical properties of products [6
]. The most commonly used techniques are spray drying and freeze drying. However, the potential for vacuum drying, drum drying, reactance window drying, microwave-vacuum and other combined drying is increasing [4
Powders from whole fruits, juice, extract and pomace are produced, depending on the form of the fruit. For instance, powders from mango [10
], apple juice [11
], Roselle extract [8
], orange juice with incorporated lactic acid bacteria [12
], grape skin phenolic extract [13
], purple sweet potato [6
], grape wastes [14
], pomegranate peel phenolics [15
], blackberry phenolics [16
], herb extract [7
] and with probiotics in raspberry juice [9
] have been produced and studied thus far.
Encapsulation involves entrapment of valuable, sensitive or target components or fractions within the coating material. Processing fruit juice into powder can extend its shelf life and thus improve its physical properties and nutritional and pro-healthy value, as in the research by Bąkowska-Barczak and Kołodziejczyk [17
], Aziz et al. [4
] and Çam et al. [15
]. The development of sea buckthorn powders may facilitate the potential use of health benefits of sea buckthorn with their prolonged shelf life and lower transport and storage costs. The encapsulated juice form offers flexibility for innovative formulas and uses as a replacement for juices and concentrates and in new markets, including bakery products, confectionery, sauces, ice cream, dairy and nutritional and functional snacks. Juice powders can fit well with the trend of using natural thickeners and agents that change or enhance the taste, color and health value of products. Additionally, reducing the instability of sea buckthorn bioactive compounds during processing and storage, as well as digestion in the digestive system, may meet the expectations of the cosmetics and pharmaceutical industries [6
]. Thus, the formation of sea buckthorn juice powders can be equally beneficial.
This study aimed to assess the impact of drying methods (spray drying, freeze drying and vacuum drying at 50, 70 and 90 °C) and types of carrier agents (inulin, maltodextrin and mixtures inulin:maltodextrin in the ratio of 1:2 and 2:1) on physical properties (moisture content, water activity, true and bulk density, porosity, color parameters, browning index), chemical components (hydroxymethylfurfural [HMF] and phenolic compounds) and antioxidant capacity of sea buckthorn juice powders before and after six-month storage. To the best of our knowledge, this is the first detailed report on powders from H. rhamnoides juice. It will provide valuable information on the selection of carrier agents and optimal drying conditions, stability of chemical compounds and antioxidant activity of sea buckthorn juice after drying processes and then after storage.
3. Materials and Methods
All standards used for Ultra-Performance Liquid Chromatography Photodiode Array Detector (UPLC-PDA) assays were bought from Extrasynthese (Lyon, France). Ascorbic acid and acetonitrile for ultraperformance liquid chromatography UPLC (gradient grade), carrier agents and the rest of the reagents were procured from Merck (Darmstadt, Germany).
3.2. Material and Sample Preparation
Sea buckthorn berries of cultivar “Józef” were collected from the Experimental Orchard in Dąbrowice of the Research Institute of Horticulture in Skierniewice (Poland). Sea buckthorn juice was squeezed from selected fruits using a laboratory hydraulic press (SRSE, Warsaw, Poland), centrifuged at 5000× g for 10 min (Sigma 6 K15, Shrewsbury, UK) and portioned into four parts. Each portion was mixed with 20% (w/w) commercial inulin (INU), maltodextrin (MALTO) and inulin with maltodextrin in 2:1 (I:M) and 1:2 proportions (I:M), separately. The 20% addition of carrier agents was determined experimentally on the basis of solubility in juice, drying tests and the properties of finished products.
3.3. Drying Methods
Each variant of the juice with carrier agent was divided into five parts (ca. 100 mL each) to undergo various drying methods: spray drying (SD), freeze drying (FD) and vacuum drying (VD) at three different temperatures. The spray drying process of the sea buckthorn juices with different carrier agents was performed using a Bϋchi Mini Spray-Dryer B-290 (Bϋchi AG, Flawil, Switzerland). The initial temperature of the juices was 21 °C. The spray dryer operated at an inlet temperature of 180 °C and the feeding rate was 40 mL min−1
. The freeze-drying process was performed at temperatures from −30 to +30 °C, a pressure of 0.22 mbar and for 24 h using a Christ Alpha 1–4 LSC (Martin Christ GmbH; Osterode am Harz, Germany). The choice of carrier agents and drying parameters was determined experimentally. The drying time was determined on the basis of previous drying tests for juices in the temperature range of 50–90 °C using the determination of water. The water content was determined on the basis of the mass losses of samples during drying in a previous drying test. The process was stopped when the moisture content of samples reached below 5%. The vacuum drying processes at temperatures of 50, 70, and 90 °C were done using a Vacucell ECO line (MMM Medcenter Einrichtungen GmbH, Planegg/München, Germany), at a pressure below 0.1 mbar for 24, 20 and 16 h, respectively. The conditions used in the three drying methods were adequate to ensure complete drying of the samples with a final moisture content below 5%. All drying processes were performed in triplicate. The sea buckthorn juice powders obtained (Figure 1
) were vacuum-sealed in transparent polyamide/polyethylene (PA/PE) moisture-resistant bags and stored at −18 °C for further analyses. Physical analyses and sample extractions for chemical analyses and evaluation of antioxidant activity were performed within 5 days from the production of the powders.
To determine the potential progress of the browning reaction, HMF and phenolic compounds contents, and the antioxidant activity of powders, a storage test was carried out. The second batch of sea buckthorn juice powders was stored in transparent polyamide/polyethylene (PA/PE) bags, for six months, at 20 °C and relative humidity 40%, with access to oxygen, in darkness. A laboratory incubator (ST2, POL-EKO-APARATURA, Wodzisław Śl.; Poland) was used to maintain stable conditions. After this period, the powders were again subjected to selected analyses.
3.5. Physical Properties
Moisture content (%) of the sea buckthorn juice powders was determined by the vacuum-oven method at 70 °C and pressure of 100 Pa for 24 h, using the vacuum dryer from Section 3.3
. Water activity (aw
) was studied at 20 °C using a dedicated device a Novasina (LabMaster-aw, Lachen, Switzerland). True and bulk density (kg m−3
) and porosity (%) were studied and calculated as previously described by Turkiewicz et al. [38
]. Color parameters were measured using a spectrophotometer Minolta Chrome Meter CM-700d (Konica Minolta, Inc.; Osaka, Japan) and expressed in scale of CIE L*a*b* space (10°, D65). Chroma parameter (C), hue angle (h°) and the total color change (dE) were calculated according to Kuck and Noreña [13
] and Šumić et al. [39
]. Browning index was determined in powder extracts (1 g of powder in 100 mL of distilled water). The results were measured at 420 nm using a multi-mode microplate reader SynergyTM
H1 (BioTek, Winooski, VT, USA) and shown in arbitrary units (AU).
3.6. Determination of Phenolic Compounds and Hydroxymethylfurfural (HMF)
Analysis of phenolic compounds and hydroxymethylfurfural (HMF) were performed using an Ultra-Performance Liquid Chromatography with Photodiode Array Detector (UPLC-PDA, Acquity UPLC System, Waters Corp.; Milford, WA, USA). The extraction procedure and analysis conditions of phenolic compounds and HMF were analogous to those given previously by Tkacz et al. [2
] and Turkiewicz et al. [40
], respectively. Quantification was made on the basis of standard curves, using HMF; p
-coumaric and ferulic acids; 3-O
-rutinosides and 3-O
-rhamnosides of isorhamnetin; quercetin; and kaempferol as standards. The other flavonol derivatives were calculated as the corresponding 3-O
-glucoside derivatives. Phenolic acids, flavonols and HMF were detected at wavelengths 320, 360 and 284 nm, respectively. The results were expressed as mg per 100 g of dry matter (DM).
3.7. Determination of Antioxidant Capacity and Antioxidant On-Line Profiling by HPLC-PDA Coupled with Post-Column Derivatization with ABTS·+ Reagent
The antioxidant capacity was tested as free radical-scavenging activity (ABTS·+
). The extraction and assay were conducted as previously described by Tkacz et al. [41
]. The multi-mode microplate reader discussed in Section 3.5
was used. The results of antioxidant effects were calculated as mmol Trolox/100 g DM.
An on-line HPLC system was applied to verify the possible antioxidant capacity of HMF and furosine. The same ABTS·+
reagent was used as in antioxidant capacity assay. Conditions and procedure of the assay were analogous as reported by Tkacz et al. [42
]. The detection wavelengths for HMF and furosine were set at 280 nm, and discoloration of mobile phase after reaction with radical cation was detected as negative peaks at 734 nm. The chromatograms are shown as results.
3.8. Statistical Analysis
One-way analysis of variance (ANOVA) with a significance below 0.05, Duncan’s multiple range test and Pearson’s correlation coefficients (r) were determined to compare the samples. XLSTAT Statistical Software (Addinsoft Inc, New York, NY, USA) integrated with Microsoft Excel 2017 (Microsoft Corp.; Redmond, WA, USA) were used. Drying tests were performed three times and replicates were samples from each trial. Each of the analyses was performed three times and the results were summarized in the form of the mean with standard deviation (SD).
For the first time, research was conducted on the optimization of microencapsulation of sea buckthorn juice using both different drying methods and different carrier agents. The main results of this paper can be summarized as follows:
Inulin caused stronger water retention of powders than maltodextrin. The drying method modulated the water activity more strongly than the type of carrier agents.
Powders with inulin had higher true density values than those with maltodextrin. Bulk density and porosity were significantly differentiated by drying methods, and vacuum drying seems to be a useful technique to obtain powders with high bulk density. The porosity of the spray-dried and freeze-dried powders was higher than after vacuum drying.
In view of the yellow color and its intensity, the use of maltodextrin was competitive compared to inulin. Moreover, spray-, freeze- and vacuum-drying at 50 °C and the addition of maltodextrin were not conducive to browning and HMF formation.
Powders spray- and vacuum-dried at 70 °C had the highest concentrations of phenolic acids and flavonols, respectively. However, in stored freeze-dried powders, phenolic compound losses were the lowest. More phenolic compounds were determined in powders with maltodextrin.
Storage for six months increased antioxidant capacity, but browning compounds, HMF and furosine did not affect this effect.
In conclusion, the results obtained will be useful in the selection of carrier agents and optimization of drying conditions on an industrial scale. Encapsulation technique can be valuable for extending the stability of sea buckthorn juice and for designing innovative and high-quality products, such as attractive functional foods or food ingredients, improving physical and health-promoting properties. The choice of carrier agent and its interaction with the juice should be further investigated to ensure minimal degradation of biologically active compounds and beneficial properties of finished powders. In the future, it will also be valuable to study the stability, bioavailability and kinetics of biologically active compounds released from powders or real food systems by in vitro and in vivo methods.