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Article

Physico-Chemical and Resistance Characteristics of Rosehip Seeds

by
Alina-Daiana Ionescu
1,
Gheorghe Voicu
1,*,
Elena-Madalina Stefan
1,
Gabriel-Alexandru Constantin
1,
Paula Tudor
2 and
Gheorghe Militaru
2
1
Department of Biotechnical Systems, Faculty of Biotechnical Systems Engineering, National University of Science and Technology POLITEHNICA Bucharest, Splaiul Independentei 313, 060042 Bucharest, Romania
2
Department of Management, Faculty of Entrepreneurship, Business Engineering and Management, National University of Science and Technology POLITEHNICA Bucharest, 060042 Bucharest, Romania
*
Author to whom correspondence should be addressed.
Agriculture 2025, 15(14), 1539; https://doi.org/10.3390/agriculture15141539 (registering DOI)
Submission received: 14 April 2025 / Revised: 11 July 2025 / Accepted: 15 July 2025 / Published: 17 July 2025
(This article belongs to the Section Seed Science and Technology)
Browse Figures
Versions Notes

Abstract

Both the pulp and the seeds of rosehip are important for human health. Rosehip seeds are rich in polyunsaturated fats, which support a healthy skin membrane and protect it from inflammatory factors. In order to be used, the seeds require initial processing, mainly by grinding. This paper first presents a brief review of the physicochemical properties and the content of bioactive compounds in rosehip (Rosa canina) and its seeds. Original research results on the compression behavior of rosehip seeds are presented below, together with the key values of the most important parameters derived from the analysis. For seeds with a thickness ranging from 1.80 to 3.55 mm, the compressive force at the onset of fracture was recorded to be between 94.4 and 156.0 N, while the force required for complete fracture ranged from 114.0 to 495.0 N (with about 12.5% of values considered outside a normal distribution). Additionally, for these forces, the deformation of the seeds ranged between 0.142 and 0.916 mm at the onset of fracture and between 0.248 and 1.878 mm at complete fracture. For these characteristics, the energy consumed ranged between 0.012 and 0.041 J at the onset of fracture and between 0.017 and 0.322 J at complete breaking. The elasticity of the seeds also ranged between 159.9 and 789.1 N/mm, considering the forces and deformations at the onset of fracture. The results of our study contribute to expanding the database on the mechanical characteristics of rosehip seeds, knowledge of which is essential for the initial processing operations used in the pharmaceutical industry aimed at oil extraction.

1. Introduction

The rosehip (Rosa canina) is a plant species found in the flora of Europe, as well as in northwestern Africa and western Asia. It has a stem covered with small thorns and red fruits. In Romania, it is mainly found in wild flora.
Rosehips are pseudofruits of the Rosaceae family, consisting of a fleshy outer layer surrounding a cluster of multiple seeds covered by achenes [1,2], with the pulp of rosehips being a rich source of vitamin C, containing significantly more than citrus fruits [3,4]. Rosehips also differ from other fruits due to their high content of additional compounds, such as vitamin E, phenols, and antioxidants. Ripe rosehip fruits contain 49% water, 21% sugars, 3.6% proteins, 3.5% acids, 23% cellulose, and 2.8% minerals, as well as a wide range of vitamins, such as B1, B2, B3, E, F, K, P, and provitamin A [3,4].
Rosehips contribute to enhancing the resistance of blood capillaries and exhibit astringent, diuretic, and antidiarrheal properties. Moreover, they stimulate appetite and promote digestive function. Regular consumption of rosehip tea may support cardiovascular health and improve digestion and intestinal health, while its content of anti-inflammatory compounds may reduce inflammation within the body [5,6,7].
Information about the morphological characteristics of rosehip fruits, seeds, and seed powder can be found on various links available on the internet powder.
It has been observed that a standardized powder derived from rosehip seeds and pulp may have a significant impact on cellular senescence in human skin wrinkles, moisture retention, and elasticity, thereby improving age-related dermatological conditions [8].
It is considered that rosehip seeds are rich in polyunsaturated fats (linoleic acid, linolenic acid, arachidonic acid, etc.), which support healthy skin membranes and protect the skin from inflammatory factors (UV radiation, cigarette smoke, or pollution) [9,10,11,12], as well as other valuable alcohols and essential oils used in the cosmetic industry.
Studies [9,10,11,12,13,14,15,16,17,18,19,20] show that Rosa canina L. seed powder has considerable potential for applications in multiple sectors, including the food and pharmaceutical industries, as well as in other industrial fields, while studies [21,22,23] provide details on the antioxidant activity of rosehip fruits associated with their contents of antioxidants (39.510–72.673 mmol/kg), total flavonoids (287.80–1686.20 mg quercetin equivalent/kg), and total phenols (38.519–79.080 g gallic acid equivalent/kg).
Cold-pressing is a commonly used method for extracting oil from rosehip seeds, but it is not always preferred, as it exposes the oil to oxidation and results in oil of poor quality.
The methods for extracting fatty acids from rosehip seeds can also vary: traditional solvent extraction, ultrasound-assisted extraction, microwave extraction, and sub- and supercritical fluid extraction are used [19,20,21,22].
Rosehip fruits exhibit highly variable physical characteristics depending on the genotype and species of the shrub [23,24,25,26,27,28,29]. The fruit mass ranged from 3.149 to 4.803 g, the pulp-to-seed ratio was 63.11–71.13%, the ascorbic acid content ranged from 1074 to 2557 mg/100 g, and the total soluble solids content ranged from 31.01% to 36.72%, and the fruits had a total dry mass of 34.82–40% and dimensions of 4.5–7.9 mm in length and 2.8–3.8 mm in diameter [25].
From the presented information, the importance of rosehip fruits and seeds for the pharmaceutical industry and human health is evident, highlighting the necessity of understanding their physical, chemical, and biochemical characteristics, which are crucial in both the initial and final processing stages.
Accurate determination of the mechanics and characteristics of rosehip seeds is essential for the development of theoretical models and the establishment of boundary conditions for simulation and in the design of processing equipment.
Following a review of the specialized literature, a significant gap has been identified regarding scientific studies focused on the physico-mechanical characteristics of rosehip seeds intended for further processing and utilization.
For this reason, we aim to establish correlations with tests conducted on other categories of seeds. For example, in the case of pumpkin seeds, the modulus of elasticity decreases with increasing moisture content as well as with increasing loading rate for the analyzed varieties—both for whole seeds and their kernels [30,31,32,33]. The values of the modulus of elasticity, as well as toughness and maximum deformation, have also been determined from force–deformation curves in the case of gourd seeds [32].
In [31], Khodabakhshian et al. developed a mathematical model to describe the breaking force of sunflower seeds and their kernels, as well as for the absorbed energy and the deformation at the breaking point, as a function of moisture content, variety, and size. References [34,35,36,37,38] present investigations on the relationship between the force and deformation of Jatropha, sunflower, and rapeseed seeds in relation to different volumes of pressed seeds. The authors found that rapeseed seeds showed a lower deformation and a higher deformation energy compared to Jatropha and sunflower seeds, which had higher deformation values for the same levels of deformation energy.
The deformation energy was determined as the area under the force–deformation curve, and the deformation was obtained directly from the compression test [39,40]. Additionally, it was found that the energy and deformation in relation to the volume of pressed Jatropha, sunflower, and rapeseed seeds exhibited an approximately linear relationship [39,40,41,42,43].
The deformation, deformation energy, and energy density, determined from the variation of the force–deformation curves, indicate both an increasing function and a serration effect. It is estimated that understanding the physicochemical and mechanical characteristics of seeds is useful not only for producers but also for the operators of machinery used in the oil extraction process from oilseeds.
From the information presented, it seems to be that there are few tests available in the specialized literature for determining the mechanical characteristics of rosehip fruits and seeds, with most studies focusing on the chemical and biochemical properties.
The compression of rosehip seeds to the point of fracture represents a critical stage in the oil extraction process or in enhancing germination potential. The seeds contained within rosehip fruits (wild rose fruits) are hard and require mechanical compression to break when the aim is to extract oil or other valuable compounds. The overall process involves proper drying to prevent oil degradation, the removal of impurities and plant residues, crushing using a mill, cold-pressing (in cases where preservation of the oil’s therapeutic properties is desired), and filtration.
In nature, rosehip seeds (Rosa canina and related species) are capable of germination without mechanical intervention; however, the process is slow and requires specific natural conditions. Due to their hard and impermeable pericarp, which acts as a physical barrier to germination, rosehip seeds often require mechanical scarification or controlled compression to promote germination, particularly in agricultural or forestry applications. In the context of oil extraction, complete seed crushing is ideal in order to maximize yield efficiency.
Therefore, the objectives of our work are related to the analysis of rosehip seed behavior under compression, estimating the required forces during the process and the cracking energy, as well as assessing the elasticity of the seeds. Additionally, we aim to establish a correlation between the cracking forces and the breaking forces. Prior to the main tests, preliminary measurements of the seeds’ key dimensions were conducted, followed by deformation analysis.

2. Materials and Methods

2.1. Initial Characteristics of Rosehip Fruits and Seeds

The deformation curve of rosehip seeds up to the point of fracture (obtained through a compression test—Figure S1—in Supplimentary File) provides critical insights into their mechanical behavior. Such a curve is particularly valuable in the context of agricultural engineering, especially for seed processing applications such as oil extraction, as well as in the field of plant biomechanics. The maximum breaking force represents the peak value of the applied force before the seed mechanically fails (cracks/fractures) and serves as an indicator of the seed’s mechanical resistance.
The Rosa canina fruits whose seeds were analyzed in our work were collected between August and September 2024 from spontaneous flora located at the edge of a lowland forest in the south-central region of Romania. For the tests carried out in this study, the seeds from fruits that were dried for a period of three months at ambient temperature were used; the seeds were then stored for an additional month in a room with a temperature ranging from 22 to 25 °C.
The pulp mass to seed mass ratio for the fresh, fully ripe fruits examined in this study ranged from 0.70 to 1.35. For the dried fruits, the mass of 100 seeds was 2.02 g, while the mass of 100 dried fruits was 85.44 g. The moisture content of the dried whole powdered Rosa canina (milled) ranged from 4.56% to 4.93%, whereas for the fresh fruits, the moisture content was approximately 27.83% to 32.11%.

2.2. Compression Test of Rosehip Seeds

The seeds were manually separated from the rosehip fruits after drying and were subjected to compression tests in the laboratory.
For testing the breaking resistance of the rosehip seeds, a Hounsfield Tinius Olsen H1-KS (Tinius Olsen, Salfords, UK) testing machine with a two-column setup and a 1000 N load cell was used. The piston speed of the apparatus was set to 1 mm/min.
During compression, the shape and dimensions of the seeds begin to change in response to the applied force, with these deformations depending on several factors: the rate of applied force, the loading position, moisture content, and biochemical composition [41]. The curves resulting from the force–deformation graphs show inflections at the moment of fracture/breaking, so the corresponding values were extracted from these curves for further processing.
During seed pressing, the degree of deformation is influenced by the displacement of the compression device piston (as shown in Figure S1b in Supplementary File), until cracking, respectively complete rupture. This reflects the elasticity and rigidity of the seed up to the point of failure. The elastic modulus (Young’s modulus) is derived from the slope of the initial linear portion of the curve (where the seed exhibits elastic behavior). It quantifies the seed’s rigidity or flexibility and is useful in designing crushing or pressing equipment. Toughness (energy to breaking) (N·mm) is represented by the area under the force–displacement curve up to the breaking point and indicates the energy required to fracture the seed. This parameter is useful for optimizing industrial processes (e.g., pressure setting in presses).
Thus, the moment of the first seed fracture, as well as the moment of the maximum force applied to the seeds during these tests, can be identified. At these moments, both the forces and deformations, as well as the breaking energy and the energy at the maximum applied force, can be determined.
Compressive strength (N/mm2) is refers to the resistance of each seed before it fractures, i.e., the ratio between the force at the moment of fracture and the area of the contact spot of the seed with the piston of the device. However, in our study, this strength can only be estimated, as it cannot be calculated due to the difficulty in estimating the area of the contact spot.
Seed stiffness under compressive load (N/mm) measures the resistance to deformation in response to applied load and can be estimated by the ratio of force to deformation at the moment of breakage. Seed hardness, defined as the ratio of fracture energy to seed volume (J/m3), was determined experimentally using the average seed volume obtained through experimental measurements.
Although information about seed elasticity is obtained from the slope of the regression lines in force–deformation curves (as previously presented), the specialized literature defines the elastic modulus as the stress/strain ratio at the moment of seed fracture [44].
E = σ 0 ε 0
where σ0 is the stress acting on the rosehip seed (MPa) and ε0 is the strain of the rosehip seed.
The deformation stress exhibits the following specific equation:
σ 0 = F 0 A 0
where F0 is the axial force applied to the rosehip seed (N) and A0 is the cross-sectional area of the seed (m2).
The specific deformation (strain) is defined by the following relationship:
ε 0 = Δ L L
where ΔL is the seed dimension in cross section (m) and L is the deformation in the same cross section (m).
Our study primarily presents the profile of the force–deformation curves for a set of seeds subjected to compression tests, along with the values of the energy consumed up to the point of the first fracture and at the point of maximum applied force (complete breaking), as well as the rigidity/elasticity values of the tested seeds. Additionally, it analyzes the mechanical behavior during the second phase of compression from the onset of the first fracture to the point of complete breaking.

3. Results

Accordingly, force–deformation curves were determined for a set of 50 seeds obtained from randomly selected fruits. The distribution curve based on the smallest dimension (seed thickness), which also dictates their orientation during compression testing, is presented in Figure 1.
Figure 1 (left) displays a Gaussian distribution of the smallest dimension of rosehip seeds, specifically their thickness and length, as the second dimension (width) is slightly larger. While we cannot definitively state that the seeds exhibit an equatorial diameter in their cross-sectional area, approximately 80–85% of seeds demonstrated a thickness ranging between 2.2 and 3.3 mm. It is observed, however, that the length of the seeds is almost twice their thickness. Figure 1 (right) presents the distribution of seeds according to their length, from which it can be seen that approximately the same percentage of seeds as in the distribution by thickness have the greatest length (about 5 mm).
The force–strain curves resulting from the QMat program of the testing apparatus are presented in Figure 2, after plotting in the Microsoft Excel 365 program (Version 2506 Build 16.0.18925.20076). In most tested samples, it can be observed that there is a period during which the seed orients with its smallest side vertically, even though the researcher attempted to orient it in this manner from the outset. After this, the force begins to increase proportionally with the deformation. On the corresponding curve, force variations at different moments can be identified, namely the moment of the first fracture, the moment of the second fracture (if present), and the moment of final breaking (at the maximum deformation force), which may occur with or without fluctuations. Finally, the actuator piston of the apparatus retracts.
However, not all seeds exhibit two fractures (breaks), and for some, the moment of breaking coincides with the moment when the maximum force occurs.
There are samples where multiple relatively large fractures are observed during the deformation stroke of the seed piston. The seed’s strength is quite high, as the maximum force can reach values of up to approximately 500 N. Additionally, during the compression stroke, the first significant fracture may occur earlier or later (there is not necessarily a fixed pattern), sometimes with relatively large deformations (0.7–0.9 mm) and with larger or smaller forces, as shown in Figure 2 and Table 1 (summary). It is evident that this phenomenon is influenced by the shape and size of the seed, but the breaking strength may also differ from one seed to another.
The force and displacement corresponding to the onset of the first crack exhibited average values of 119.44 N and 0.387 mm, respectively (Table 1), whereas the force and displacement values at the point of final rupture of the rosehip seeds were 163.06 N and 0.556 mm, respectively (with the deviation percentage as reported in the study). Also, the average energy values associated with the initiation of the first crack and with the complete rupture were 0.018 J and 0.051 J, respectively.
From Figure 2 and Figure 3, one can quickly see differences in both the deformation force and the deformation up to the critical moments that are observable through jumps or inflections of the curves. Moreover, on the horizontal axis, at the beginning of the piston movement, the resulting curves show large deformations and small efforts, which leads to the conclusion that the seeds orient themselves accordingly (with the shortest axis in the direction of pressing) to respond to the stress. Also, the moments when the first cracks appear in the seeds and also the final moment of the final breakage are observable—the shape of the curves strikingly resembling the curve in Figure S1b (taken from the specialized literature). It is understandable that seeds have different sizes, but it is very likely that seeds with the smallest thickness will have higher resistance to deformation compared to larger seeds. It remains for the authors to investigate this aspect in their future works.
Based on the data in Table 1, the rigidity of the seeds, calculated as the ratio between the force and the deformation at the moment of breaking, ranges from 170.3 N/mm to 789.1 N/mm, representing a fairly wide range of values for this parameter. However, if we disregard the highest and lowest values of rigidity, we could say that the typical values of the rigidity of the seeds tested by us fall within a narrower range, specifically 236.7–532.9 N/mm.
Figure 4 shows the linear regression curves, derived from the experimental data, up to the appearance of the first fracture; these curves can be used to estimate the elasticity coefficient of the rosehip seeds.
From the analysis of the data presented in Figure 3 and expressions from relations (1–3), assuming the seed cross section is circular in terms of the contact area with the compression piston and support surface, the resulting average diameter is 2.86 mm, yielding a cross-sectional area of 6.43 mm2. This leads to an average applied stress on the seeds of approximately 25.35 N/mm2 (for a mean applied force of about 163 N), equivalent to 25.35 MPa.
Considering the data in Table 1, which show an average compression piston displacement of 0.556 mm, the resulting mean specific strain is ε0 = 0.194. This yields an average elastic modulus of E = 130.67 MPa.
This value, combined with the aforementioned rigidity and other mechanical characteristics of the seeds, provides critical information for seed processors involved in oil and bioactive compound extraction.
Also, based on a piston speed of 1 mm/min, time values until the appearance of the first fissure ranged from 8.52 s to 54.96 s and within the limits of 11.52–112.76 s until definitive fracture (as shown in Figure S2—in Supplimentary File).
The statistical analysis of the data presented in Table 1, using the Interquartile Range (IQR) and the Python vers. 3.12.5 programming language, revealed that 12.5% of the observations fall into the category of outliers, i.e., values located outside the acceptable limits of the distribution.

4. Discussion

From the analyses carried out in our work on rosehip seeds (Rosa canina), we found that the analyzed seeds were not very large, with seed thicknesses ranging from 1.80 to 3.55 mm, which is quite a wide interval. This led to compression test results within fairly wide limits regarding compression forces and deformations, both until the appearance of cracks and until complete breakage.
Rosehip seeds can be compared to celandine seeds (Chelidonium majus), both having a similar shape and size and being oval and slightly rough to the touch. However, among the seeds of cereal crops, rosehip seeds can be compared to oat and barley seeds without a shell as they have an elongated shape and a brown-beige color; however, the seeds of oats and barley are smoother. Rosehip seeds are much harder, woodier, and more irregular in shape.
In terms of force–strain curves, most biological materials show approximately the same curve shape, with one or more points where the ascending part of the curve shows variations due to the fact that tissue crack/breakage does not occur all at once (microcracks and fissures appear before final rupture).
From the analysis of the force–deformation curves, it is observed that before reaching the maximum force on the device (which corresponds to the complete breaking of the seed), fractures may occur in several stages (one, two, or even more). There may be an initial phase in which the seed reorients itself with its smallest side in the direction of deformation, leading to firm contact with the piston. During this phase, the deformation increases while the force remains close to zero. This self-reorientation of the seed under compression occurs due to irregularities in the seed shape that are visible to the naked eye, despite the small size of the seeds, making it difficult to clearly distinguish between seed width and thickness. There are seeds for which fracture coincides with the point where the force reaches its maximum value, at piston displacements of approximately 0.140–0.293 mm, or where the two points are very close to each other (P4, P7, P9, P14) (Table 1).
Seeds fracturing under a small compression head displacement indicate that rosehip seeds are highly rigid. Consequently, the press or crushing equipment for oil extraction must be precisely calibrated, as excessive force may lead to complete crushing.
There are situations where, although microfractures appear as the piston applies pressure to the seed, the main fracture of the seed occurs very close to the point of maximum force (e.g., P10 sample). Thus, the first minor fractures appear at a deformation of approximately 0.175 mm and a force of 93 N and at a deformation of 0.225 mm and a force of 114 N. The most significant fracture is considered to occur at a deformation of approximately 0.390 mm with a force of 164 N, although the maximum force is recorded at a deformation of 0.474 mm, corresponding to 166.5 N.
According to the data in Table 1, the deformation until breaking falls within the range 0.14–0.91 mm under compressive forces of 140–156 N.
Thus, for the specified deformations, it can be stated that the seeds are not completely brittle but exhibit moderate deformability. This may indicate a semi-ductile structure, featuring an elastic zone—potentially followed by a short plastic region—before fracture initiation.
It must be specified, however, that fractures may occur either earlier or later at different deformation values, with no definite correlation necessarily existing between the seed dimensions and the compressive force. For example, in the case of sample P12, microfractures and fractures appear along the deformation path under the action of the compressive piston. Thus, the first microfracture appears relatively late, at a deformation of 0.47 mm and a force of approximately 119 N, but the main fracture is considered to occur later, at a deformation of about 0.508 mm and a compressive force of 127.6 N. The maximum force is reached even later (138.6 N), at a deformation of approximately 0.563 mm.
Another observed situation shows that several relatively large fractures can occur during the deformation of the seed, with the seed’s strength/rigidity being quite high, as the maximum force reaches values of up to approximately 500 N (Figure 4). During the compression stroke, the first significant fracture appears at relatively large deformations (around 0.940 mm), but the compressive force is not excessively high (approximately 153.7 N).
As shown in Figure 4, most of the analyzed samples exhibit two slopes with linear variation—a steeper slope at the beginning, followed by a more gentle slope. This may indicate the initial rigidity of the seed, with the endocarp being very rigid, after which a fracture/microfracture occurs, leading to a loss of the mechanical integrity of the material. The specialized literature indicates that brittle materials, such as the hard shells of seeds, do not undergo plastic deformation; instead, they fracture abruptly. After fracturing, the material loses its structural integrity and the seed deforms more easily, indicating that the interior is less dense (i.e., it contains a cavity where the actual seed is located).
However, there are seeds that fracture completely at the same time as the initial fissuring occurs and therefore only exhibit a single force–deformation slope, after which the curve exhibits a sudden decrease in force over a very short distance. There are also seeds that develop more than one fracture before completely failing.
From the analysis of the data in Table 1, deformations can be observed within the limits of 0.142–0.916 mm and forces between 91.5 and 156.0 N for the moment of the first significant seed fissures, relative to deformations of 0.248–1.878 mm and forces of 114.0–495.0 N when reaching the moment of definitive fracture (12.5% out of normal data).
Based on the area under the force–deformation curve, the consumed energy (stored in seeds) up to the moment of the first fissures appearing is approximately 0.012–0.041 J, and that when reaching the moment of definitive fracture is between 0.017 and 0.322 J.
Compared to sunflower seeds (which have a maximum energy of 25.608–149.534 mJ in Arabic varieties [36]), by simple calculation, the energy absorbed until rosehip seed breaking is about the same order of magnitude, with the values comparable to the energy consumed when breaking pumpkin seeds [37,38]. Also, according to our calculations, the values are comparable to those for safflower seeds [42] and even lower than those for rapeseed seeds, which have a cracking energy of (0.2–0.4)·10−2 J [42].
Based on the slope of the force–strain curve until the first cracks appear, we estimate an elasticity of rosehip seeds within the limits of 343–780 N/mm (see Table 1); these values are very different from the elasticity values obtained by the authors of [43] for sunflower seeds (40.1–77.5 N/mm), safflower seeds (53.7–114.1 N/mm), and rapeseed seeds (14.7–27.6 N/mm).
Coming back, from Figure 3a, we could say that there is a relatively linear correlation between the maximum breaking force and the force at the appearance of the first crack (but with a very low R2 correlation coefficient). At the same time, the force values at the appearance of the first significant crack in the seeds in relation to the deformation values do not show any correlation, the points on the graph in Figure 3b being dispersed over relatively large intervals. Therefore, we cannot say that there is any correlation between the maximum breaking force and the value of the force at the first crack, just as we cannot say that there is any correlation between the force at the appearance of the first crack and the value of the deformation at that moment, all these factors being relatively random.
Analyzing the curves in Figure 4, a linear correlation for force–deformation curves can be observed, especially up to the moment of the first fissure (included in the figure)—a correlation that presents a coefficient of determination with values above 0.97 in all cases. Therefore, the elasticity coefficient of the seeds could be identified, which, as previously mentioned, ranged between 159.9 and 789.1 N/mm.
It is noteworthy that each rosehip seed behaves relatively similarly under the piston of the compression testing device. However, the parameters determined by the device or calculated based on known relations (deformations, forces, elasticity coefficients, energy consumption), both at the point of the first fracture and at complete rupture, may have different values within the limits presented in this study for seeds with the specified dimensions. It is highly likely that for other rosehip varieties, the values of these parameters may fall within a different range.
The data presented in Table 1 and throughout the study demonstrate a cracking stress comparable to that of hard vegetable materials (e.g., fruit pits, shells), indicating that rosehip seeds are structurally resistant. This justifies the use of specialized pressing equipment, as the mechanical behavior of rosehip seeds is semi-ductile with a short elastic zone. Seeds with hard pericarp/endocarp that are structurally similar to rosehip seeds, including in compression tests, may include cherry pits, peach pits, apricot pits, olive stones, plum stones, or grape seeds.
According to [45,46], the bulk density of rosehip seeds ranged between 0.45 and 0.84 g·cm−3, while the true density showed values of 1.10–1.40 g·cm−3, with porosity values between 40 and 59.1%. Additionally, the average weight of 1000 seeds was 20.2 g, the mean external surface area was 34.5 mm2, and the average seed volume was 0.024 cm3, indicating the relatively low internal capacity of the seeds.
For an average rosehip seed fracture energy of approximately 0.75 N·m, as shown in the data in Table 1, it can be estimated that rosehip seed hardness ranges between 1.85 and 2.05 J/cm3.

5. Conclusions

Knowledge of the physico-mechanical characteristics of cereal seeds is useful for producers and especially operators of the machinery used in their processing (crushing, grinding, mixing, etc.). In the same way, knowledge of the physical and mechanical characteristics of rosehip seeds is necessary to be able to choose and adjust the parameters for the machinery (primarily for grinding).
The data presented throughout this study show significant variation between samples, potentially due to natural seed diversity, moisture differences, force application position, or internal microdefects. The applied mechanical force ranged from 0.007 to 0.041 N·m until initial crack formation, with an estimated rigidity (force/displacement ratio) for the seeds of between 0.17 and 0.789 N/mm.
This information can be used for the design and calibration of presses or crushers, the classification of cultivars based on mechanical resistance, and the optimization of oil extraction processes or seed pre-germination treatments.
To extract essential oils from rosehip seeds, we recommend controlled hot air drying to bring the moisture content to 6–8% and then the use of a staged hammer or disc mills with differentiated stage settings so that the seed embryo remains as intact as possible and the outer woody particles are as large as possible to be properly separated.
Our research shows that there are relatively large differences between the resistance characteristics of rosehip seeds, due both to their irregular external shape and size, but these characteruistics can also vary due to the way the seeds are prepared for processing.
To this end:
(a)
A relatively wide range of seed thickness values was found (1.54–3.72 mm).
(b)
The deformations of the rosehip seeds ranged between 0.142 and 0.916 mm until the first cracks appeared, and the forces at the same moment were within the limits of 94.4–156.0 N. On the other hand, the deformations had values between 0.248 and 1.878 mm at the moment of final breakage, where the maximum forces were 114.0–495.0 N.
(c)
The energy consumed for the deformation of the seeds until the first crack was between 0.012 and 0.041 J and that until final breakage was between 0.017 and 0.322 J.
(d)
The elasticity of the seeds was in the range of 159.9–789.1 N/mm, and the time elapsed from the beginning of the compression of the seeds to the appearance of the first crack was between 8.52 and 36.66 s for a deformation rate of 1 mm/min. The mean elastic modulus, as estimated from the experimental results, was 130.67 MPa.
The statistical analysis performed and presented in the paper shows that about 12.5% of the values of the analyzed parameters are considered outside a normal distribution.
All our experiments and tests were carried out in order to identify the parameters that are important in the first stage of the processing of rosehip seeds and fruits in order to extract valuable components that are important for the pharmaceutical and cosmetic industries.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/agriculture15141539/s1, Figure S1: The Hounsfield/Tinius Olsen model H1 KS device used in our mechanical tests [43] (1. machine table; 2. support and resistance columns; 3. movable traverse with adjustable speed; 4. clamping system of compression device; 5. 1000 N force cell; 6. fixed plate; 7. movable plate; 8. display, adjustment and control panel; 9. emergency stop button; 10. computer with system for data acquisition and processing) and typical force-deformation curves of biological materials during loading: x—bioyield point; y—maximum force point; z—breaking point; m—modulus of elasticity curve [44]; Figure S2: Variation of the time until the first cracks appear, respectively until the final breakage of rosehip seeds.

Author Contributions

Conceptualization, G.V., A.-D.I. and E.-M.S.; methodology, G.V. and A.-D.I.; validation, G.V., G.-A.C. and E.-M.S.; formal analysis, G.V., G.-A.C. and G.M.; investigation, A.-D.I. and G.V.; resources, A.-D.I.; data curation, G.V.; writing—original draft preparation, G.V., P.T. and A.-D.I.; writing—review and editing, G.V.; visualization, E.-M.S. and P.T.; supervision, G.V.; project administration, G.V.; funding acquisition, A.-D.I. and G.M.; All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

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Agriculture 15 01539 g001
Figure 1. The profile of the frequency distribution curve of rosehip seeds as a function of their thickness and length.
Figure 1. The profile of the frequency distribution curve of rosehip seeds as a function of their thickness and length.
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Figure 2. Force–strain curves obtained during compression testing for 15 of the 50 seeds tested.
Figure 2. Force–strain curves obtained during compression testing for 15 of the 50 seeds tested.
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Figure 3. Correlations obtained from the data analysis of experiments: (a) the correlation between the maximum breaking force of seeds and the force at the first fracture; (b) the correlation between the seed fracture force and the deformation at which this force occurs.
Figure 3. Correlations obtained from the data analysis of experiments: (a) the correlation between the maximum breaking force of seeds and the force at the first fracture; (b) the correlation between the seed fracture force and the deformation at which this force occurs.
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Figure 4. Regression analysis of the curves obtained in compression tests with the linear law for the first portion of the curves until the appearance of the fracture (for 15 of the 50 seeds tested (P1–P14)).
Figure 4. Regression analysis of the curves obtained in compression tests with the linear law for the first portion of the curves until the appearance of the fracture (for 15 of the 50 seeds tested (P1–P14)).
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Table 1. Characteristics of rosehip seeds subjected to compression tests.
Table 1. Characteristics of rosehip seeds subjected to compression tests.
No. *Breaking MomentMaximum Force MomentSlope of the Regression LineEnergy Consumption, N·m
Displacement, mmForce, NDisplacement, mmForce, Nat Breakingat Maximum
P10.426140.360.706210.43482.720.0190.067
P20.25999.3850.439139.00365.080.0120.034
P30.293128.9330.293128.933433.620.0220.022
P40.611144.6540.652149.900492.990.0300.035
P50.39294.4300.577129.841377.590.0190.041
P60.506100.5000.608122.125458.480.0120.023
P70.497120.0390.566121.867499.080.0180.026
P80.142112.0550.311153.5823.210.0070.031
P90.202107.6460.248115.5515.660.0130.018
P100.225115.3560.474166.533420.350.0150.052
P110.30691.5420.431114.000343.430.0120.025
P120.508127.6200.562138.567377.000.0250.032
P130.916156.0011.878495.000439.710.0410.322
P140.192146.3330.192146.333779.270.0170.017
P150.212104.450.316129.14472.580.0130.025
P160.499121.7000.645148.233499.470.0160.038
Average0.387119.440.556163.06-0.0180.051
* The samples considered in this study.
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Ionescu, A.-D.; Voicu, G.; Stefan, E.-M.; Constantin, G.-A.; Tudor, P.; Militaru, G. Physico-Chemical and Resistance Characteristics of Rosehip Seeds. Agriculture 2025, 15, 1539. https://doi.org/10.3390/agriculture15141539

AMA Style

Ionescu A-D, Voicu G, Stefan E-M, Constantin G-A, Tudor P, Militaru G. Physico-Chemical and Resistance Characteristics of Rosehip Seeds. Agriculture. 2025; 15(14):1539. https://doi.org/10.3390/agriculture15141539

Chicago/Turabian Style

Ionescu, Alina-Daiana, Gheorghe Voicu, Elena-Madalina Stefan, Gabriel-Alexandru Constantin, Paula Tudor, and Gheorghe Militaru. 2025. "Physico-Chemical and Resistance Characteristics of Rosehip Seeds" Agriculture 15, no. 14: 1539. https://doi.org/10.3390/agriculture15141539

APA Style

Ionescu, A.-D., Voicu, G., Stefan, E.-M., Constantin, G.-A., Tudor, P., & Militaru, G. (2025). Physico-Chemical and Resistance Characteristics of Rosehip Seeds. Agriculture, 15(14), 1539. https://doi.org/10.3390/agriculture15141539

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