1. Introduction
Sea buckthorn (Hippophae rhamnoides L.) is a widely cultivated plant in Europe, Asia and Canada. Its unique value is due to its large amounts of both water-soluble (e.g., ascorbic acid, phenolic acids, flavonoids, tannins) and fat-soluble (e.g., carotenoids, tocopherols) antioxidants. Sea buckthorn (SB) berries consist of pulp (55–70% by weight), seeds (10–23% by weight) and peel (5–9% by weight), which are typically rich in oil. However, the proportions are very different due to the genetic diversity of SB, which are also important properties for the processing industry.
Several scientific findings have been published on the high concentration of bioactive compounds in SB berries in connection with their in vivo and in vitro health benefits [
1,
2,
3,
4,
5]. However, the effects of processing and storage on these compounds are less well known.
Due to the bitter, astringent taste and high acid content, the fresh consumption of SB berries is not preferred. It is most commonly consumed in the form of fruit juice and puree, but it is usually mixed with other fruits that soften/mitigate the sour taste or sweeten it [
6].
To preserve the biologically active ingredients, the processing industry prefers modern, gentle preservation methods, e.g., aseptic treatment and filling or high-pressure treatment. In addition to the liquid form, the preservation of berries as a whole is becoming more and more popular, which primarily means dehydration technology, e.g., the lyophilization, vacuum or microwave vacuum drying of whole berries. The processing technology affects the quantity and transformation of the active ingredients of the berries and has effects on the subsequent storability of the product. The suitability of berries for drying (e.g., rate of moisture release, color changes, shape change, puffability, etc.) is greatly influenced by the size of the berries, the seed/berry ratio, the dry matter content and the color. The sensory properties of dried products are significantly determined by the amount and ratio of sugars and acids [
7]. Cultivars with a higher sugar/acid ratio are more prevalent in the processed products [
8]. Using whole SB berries in different products, e.g., mixing dried berries into teas, muesli mixes, slices, and snack products, increases their biological value due to the high content of ascorbic acid, carotenoids, phenolic substances and fatty acids. However, the presence of fatty acids also affects the shelf life of the products.
The specialty of SB is that the whole fruit contains fatty acids. The oil content of the seeds is 100–200 g kg
−1 [
9,
10,
11], while for the flesh and shell parts it is between 20–105 g kg
−1 in the fresh state. SB pulp oil contains approximately 48% saturated and 52% unsaturated fatty acids, while the seed oil contains 12–20% saturated and 80–90% unsaturated fatty acids. The fatty acid profile is essential for evaluating the nutritional value of berries, especially the ratio of polyunsaturated fats.
Nineteen fatty acids have been identified from SB berries, of which eight are saturated and eleven are unsaturated fatty acids. The ratio of saturated fatty acids is between 13.70–42.68%, while monounsaturated fatty acids can be detected between 40.73–60.37% and polyunsaturated fatty acids between 3.70–24.62%. Among the essential fatty acids, linolenic acid and linoleic acid are significant [
12,
13]. Oils from SB seeds and pulp have different fatty acid compositions. Palmitic acid, palmitoleic acid and oleic acid is considerably higher in the flesh, while linoleic acid, linolenic acid and oleic acid predominate in the seed [
14].
Sea buckthorn seed oil contains 7–44% linoleic acid, 27–31% linolenic acid and 17–20% oleic acid. The ratio of omega-6/omega-3 (linoleic acid/linolenic acid) polyunsaturated fatty acids is usually 1:1 [
15]. Additionally, SB oil is the only oil that naturally contains a 1:1 omega-3:omega-6 ratio [
4]. The saturated fatty acid content of the seed oil is approximately 10–13%, with the dominant saturated fatty acids being palmitic acid (7–9%) and stearic acid (2.5–3%) [
9,
10,
16].
Fatty acids play a fundamental role in human health. Many studies have reported on the clinical use of SB oil. The composition of fatty acids found in SB oil is unique and provides many health benefits for the human body, which is why it is highly valued by both the biomedicine and cosmetic industries. They are effective against inflammatory processes, protect epithelial tissues and have a beneficial effect on the digestive organs, respiratory organs, urological organs, female genital organs and the inside of the eye (dry eye syndrome) [
17,
18]. Chand et al. [
19] found that the quality and cholesterol level of egg were significantly improved when laying hens were fed 2 and 3 g/kg SB supplements.
The genetic diversity of SB is enormous, and, accordingly, there can be significant differences in the biologically active ingredient content of individual varieties. However, there are only few data available about the biologically active ingredient content of grown cultivars. To obtain more information about the health-protective value of recent varieties and to clarify the possibilities of their use, a substantial analysis of the individual genotypes is highly important.
The aim of this study was to determine the physical parameters, color characteristics and fatty acid profile of five cultivars and one promising candidate to establish and support the processing of whole berries, e.g., with drying and their storage.
3. Materials and Methods
3.1. Plant Material
In this research, we examined the fruits of five SB cultivars, ‘Askola’, ‘Clara’, ‘Habego’, ‘Leikora’, and ‘Mara’, and a candidate, R-01 (
Figure 2). The research plant materials came from the organic plantation of Superberry Plus Ltd. from Rákóczifalva (47°11′87″ N, 20°21′97″ E), Hungary, in the year 2020. The berries of the studied cultivars were harvested in the full ripening stage (from the beginning of September to the end of October) and after they had reached the characteristic berry color of the cultivar (this parameter was determined visually). Since the peduncle was difficult to separate from the cane, The berries were removed from the pruned fruiting canes one by one with pruning shears. The fruit samples (3 kg/genotypes) were transported to the laboratory immediately after the harvest, where the physicochemical parameters of the samples were determined after arrival. The extracted seeds were stored frozen at −28 °C until determining the fatty acid composition.
3.2. Physical and Physicochemical Parameters
The physical parameters of at least 30 berries per sample were examined. The size parameters of the fruits (height, width, thickness) were determined with millimeter accuracy using a digital caliper (Mitutoyo CD-15DC, Mitutoyo Ltd., Telford, UK) that could be connected to a computer. The weight of the tested fruits and the seed weight were measured on a digital scale (KPZ-2-05-4/6000, Klaus-Peter Zander GmbH, Hamburg, Germany). The flesh/seed ratio was calculated from the berry weight and the seed weight (the weight of the seed/the weight of the berry * 100).
The soluble solid content of the homogeneous, filtered fruit juice was determined in °Brix (g 100 g
−1) with a digital refractometer ((ATAGO Palette PR-10, Atago Co., Ltd., Tokyo, Japan) according to Codex Alimentarius 3-1-558/93 [
38]. The titratable acid content was determined in accordance with the Hungarian standard of MSZ EN 12147:1998 [
39]. The total acid content (m/m%) was given in malic acid equivalents. The sugar/acid ratio was calculated from the ratio of the water-soluble dry matter content to the titratable acid content.
3.3. Determination of Color Coordinates
The color of the fruits (coordinates L*—lightness, a*—redness, b*—yellowness) was determined with a Konica Minolta tristimulus colorimeter (CR-400, Konica Minolta, Inc., Tokyo, Japan) with 20 color readings for all varieties. To calibrate the instrument, we used the calibrating white tile standard produced by the manufacturer. According to the CIE (Commission Internationale de la Éclargie) standard of 1931, which is also accepted in Hungary, color can be described with coordinates (L*, a*, b*) placed in a 3D color space [
40]. L* is the lightness factor in the CIE system; depending on the signs, it characterizes +a* as red, −a* as green, +b* as yellow and −b* as blue. CIELAB uses the color saturation characteristic, where the so-called “chroma” value is interpreted in the a*, b* plane as given in Equation (1), which is the absolute value of the vector, i.e., the distance of the brightness from the axis. The hue angle marked with h indicates the rotation of the direction of the color vector from the direction of the a* axis to the vector C*ab in the color space, so its value can range from 0° to 360° as given in Equation (2). Colors corresponding to hue angle values are red-purple 0°, yellow 90°, bluish-green 180° and blue 270° [
41].
3.4. Determination of Fatty Acid Profile by GC-FID Method
Lyophilized seeds (1 g) of SB cultivars were extracted with petroleum ether (10 mL;15 h) after destruction with 1 M sulfuric acid (5 mL 10%). The fatty acid composition of the fat extracted from the samples was determined in accordance with the ISO 12966-2:2018 standard [
42] with minor modifications by Tormási and Abrankó [
43]. Between 10–15 mg of fat was measured into a 15 mL centrifuge tube, to which 1.8 mL of isooctane and 200 µL of internal standard (1 mg mL
−1 glyceryl trinonadecanoate dissolved in chloroform) were added. After dissolving the fat, the esterified fatty acids in the sample were methylated with 200 µL of potassium hydroxide (stirring for 1 min), and after resting (2 min), 4 mL of saturated sodium chloride solution was added to the sample and homogenized (10 s). Separation of the phases was assisted by centrifugation (3700 g, 10 min). Then, the upper (isooctane) phase was transferred to 0.5 g of sodium sulfate salt for dehydration. The sample prepared in this way was analyzed using the GC-FID method. A FAME mixture was used for the qualitative determination of 37 components, and a 4-point calibration (0, 10, 20, 40 µg mL
−1, supplemented with 100 µg mL
−1 nonadecanoic acid (dissolved in 1 mg mL
−1 isooctane)) was used for quantitative determination.
To determine the fatty acids, an Agilent (Santa Clara, CA, USA) 6890 GC-FID system equipped with an Agilent 7683 autosampler was used. For separation, a Phenomenex (Torrance, CA, USA) Zebron ZB-FAME (60 m, 0.25 mm, 0.20 μm) column with a cyanopropyl stationary phase and a hydrogen gas (1.2 mL/min) mobile phase was used. The inlet temperature was 250 °C, and the detector temperature was 260 °C. A split ratio of 50:1 and a 1 μL injection volume were used. The temperature program started from 100 °C, which was kept constant for 3 min. Then, the column was heated at 20 °C/min to reach 166 °C, where it was kept for 5 min. Then, it was heated to 180 °C at 1 C/min, and finally it was heated to 240 °C at 10 °C/min, where it was kept for 3 min.
The following fatty acids were determined: myristic acid (C14:0; R
t min: 9.94), pentadecanoic acid (C15:0; R
t min: 11.05), palmitic acid (C16:0; R
t min: 12.43), palmitoleic acid (C16:1n-7c; R
t min: 13.24), stearic acid (C18:0; R
t min: 16.30), oleic acid (C18:1n-9c; R
t min: 17.20), linoleic acid (C18:2n-6c; R
t min: 19.04), α-linolenic acid (C18:3n-3c; R
t min: 21.56), arachidic acid (C20:0; R
t min: 21.59), gondoic acid (C20:1n-9c; R
t min: 23.00), dihomo-γ-linolenic acid (C20:3n-6c; R
t min: 26.63), behenic acid (C22:0; R
t min: 27.91) and cis-15-tetracosenoic acid (C24:1n-9c; R
t min: 31.02) (
Supplementary Materials (Figure S1 and Table S1)).
3.5. Statistical Analysis
The data were evaluated using the SPSS 27.0 program (SPSS Inc., Chicago, IL, USA) using the MANOVA test. The separation of homogeneous groups was checked with the univariate Tukey test, and the RSD value was 5% (n = 30).
Principal component analysis (PCA) (SPSS software v. 27) was used to compare multiple independent groups in the case of the fatty acid profile. The variance eigenvalue was greater than 1. The loadings (or factor scores) corresponding to the principal components were calculated from the correlation matrix.
4. Conclusions
The examination of the physical, biochemical and sensory properties of SB cultivars as well as the effect of processing technologies on individual cultivars requires continuous research. The spread of mild processing procedures provides an opportunity to preserve the bioactive active ingredient as much as possible; therefore, mapping their applicability is of particular importance. Until now, the processing industry has concentrated only on the production of juice, pulp and dietary supplements in the case of SB berries. The great advantage of drying whole berries is that the flesh, skin and seed are processed together. Therefore, these are consumed together as well. However, it is crucial to approach and examine the properties of the berries from this point of view, i.e., the examination of the physical parameters, color characteristics, sugar/acid ratio and fatty acid profile of the berries. The physical parameters determine the processability, the setting of the drying parameters and the sugar/acid ratio determine the sensory properties, and the fatty acid profile characterizes the effect on human health and the rancidity and shelf life of the dried products. Based on the tested parameters, ‘Mara’, ‘Clara’ and ‘Ascola’ were promising cultivars concerning their sugar/acid ratio. Regarding the fatty acid profile, ‘Mara’ also stood out with its high proportion of unsaturated fatty acids. From the point of view of functionality, the candidate R-01 was essential to highlight because of its outstanding palmitoleic acid content and favorable omega 6/omega 3 ratio.
The results indicated that it is worth using the SB seed alone or in the form of a whole berry for the production of functional or enriched foods, especially in their dried form, where the biologically valuable components are present in a concentrated form. They can be used to improve the dietary omega 6/omega 3 ratio, e.g., in bakery products, muesli bars or food supplements. Therefore, in the future it is worth studying the effect of drying methods on the fatty acid composition and their changes.