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Article

Changes in Selected Properties of Cold-Pressed Oils Induced by Natural Plant Additives

by
Marta Krajewska
1 and
Magdalena Kachel
2,*
1
Department of Biological Bases of Food and Feed Technologies, Faculty of Production Engineering, University of Life Sciences in Lublin, 20-612 Lublin, Poland
2
Department of Machinery Exploitation and Management of Production Processes, Faculty of Production Engineering, University of Life Sciences in Lublin, 20-612 Lublin, Poland
*
Author to whom correspondence should be addressed.
Appl. Sci. 2022, 12(7), 3646; https://doi.org/10.3390/app12073646
Submission received: 28 February 2022 / Revised: 29 March 2022 / Accepted: 31 March 2022 / Published: 5 April 2022
(This article belongs to the Topic Future Food Analysis and Detection)
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Abstract

:
Cold-pressed oils are becoming increasingly popular. The stability of these oils is the main concern, as changes occur in their organoleptic characteristics during storage, which could affect their suitability for consumption. Various natural plant components with antioxidant properties are added to cold-pressed oils to preserve their freshness for as long as possible. The present study assessed the effect of addition of garlic and chili pepper on the chemical properties of cold-pressed oil extracted from seeds of flax, hemp, and black cumin. First, the moisture level and the fat and protein content in the seeds were determined, and the oil was then extracted. The oil extraction yield was calculated, and the oil was analyzed to determine its fatty acid composition, acid value, peroxide value, and oxidative stability. Three samples were prepared for further analyses: a control sample with pure oil and two samples supplemented with 1 g/100 g of garlic or chili pepper. Changes in the oil samples stored for 2, 4, and 6 weeks were assessed based on the values of some parameters. The additives were found to exert antioxidant properties, as they caused effective inhibition of oxidative changes occurring during storage of the oils. The additives also extended the induction time.

1. Introduction

Cold-pressed oils are extracted from seeds and fruits of oil-bearing plants with fat content higher than 15%. An exception is oil pressed from amaranth seeds, which contains 4.9–8.1% of fat [1]. According to the Codex Alimentarius, these vegetable oils and edible fats are extracted by mechanical pressing at low temperature. The products can be purified by rinsing with water, sedimentation, filtration, or centrifugation [2]. Cold-pressing oil extraction is a relatively common method based on the use of hydraulic or screw presses equipped with a cooling system. The method is a very simple and ecologically clean technology and does not require significant investment and energy inputs; consequently, it has gained popularity [3]. Given their content of highly active antioxidants (tocopherols, polyphenols, carotenoids, squalene), n-3 and n-6 polyunsaturated fatty acids, and bioactive sterols, cold-pressed oils can be classified as functional foods. Because of their characteristic aroma and flavor, they are most often added to potatoes, cottage cheese, or salad dressings. In addition to their traditional use, they are also applied as an enrichment in some products (e.g., mayonnaise and bread) with various bioactive compounds [4].
An undesirable phenomenon affecting the oils is the decline in their nutritional value during long-term storage. The most substantial changes in the chemical and organoleptic properties of these products are induced by reactions with oxygen [5]. The degradation rate and oil stability depend, for example, on fatty acid composition, oil extraction method, and oxygen concentration, as well as on the presence of free fatty acids, mono- and diacylglycerols, transition metal ions, phospholipids, enzymes, pigments, and antioxidants [6].
One of the methods to prevent unfavorable changes occurring during storage of fats involves combining oils with aromatic ingredients, such as herbs, spices, or seasoning vegetables (e.g., garlic and chili pepper), especially those with high antioxidant potential due to high total phenolic and flavonoid content [7]. This primarily increases the oxidative stability of the mixture [5]. In addition, the content of ingredients, such as vitamin C, provitamin A, carotenoids, capsaicin (chili pepper) [8], phenolic acids, and flavonoids, contributes to the increase in the nutritional value of oils. It improves the parameters beneficial for human health. These additives have been reported to exert a protective role against certain cancers, prevent gastric ulcers, stimulate the immune system, prevent cardiovascular diseases, and protect against age-related macular degeneration and cataract [9,10].
Because the antioxidant activity of these additives (garlic and chili pepper) has not yet been reported in the oils, the present study aimed to determine the effect of addition of garlic and chili pepper (as a source of natural antioxidants that could increase the shelf life and avoid changes in the fatty acid composition of the sample in terms of the degree of lipid oxidation, peroxide value (PV), and oxidative stability) on the chemical properties of cold-pressed oil from selected seeds after 2, 4, and 6 weeks of storage at 10 ± 1 °C.

2. Materials and Methods

The study material consisted of seeds of three plants, namely flax (Linum usitatissimum L.) cv. Luna, hemp (Cannabis sativa L.) cv. Beniko, and black cumin (Nigella sativa L.), and oil extracted from the seeds. The batches of seeds harvested in 2020 were purchased from “MIŁEX” Trade and Service Company in Lublin.

2.1. Determination of Seed Moisture

The seed moisture content was determined with the drying method using a Radwag max 50/l/WH moisture analyzer at 120 °C according to the standard [11].

2.2. Determination of Fat Content

The fat content was determined using a Soxtec 8000 apparatus (ASN 310 applications). The Soxhlet method involved multiple continuous extraction of a fatty substance from a previously dried fragmented product using an organic solvent, removal of the solvent, and determination of the fatty substance with the weight method. The analysis was performed in accordance with the standard [12].

2.3. Determination of Protein Content

The protein content was determined with the Kjeldahl method in accordance with the standard [13]. This method involves conversion of organic nitrogen compounds into ammonium sulfate by mineralization with concentrated sulfuric acid in the presence of a catalyst, alkalization of the solution, distillation with NH3, and titration of ammonia bound to boric acid by using hydrochloric acid.

2.4. Oil Extraction Process

Black cumin and hemp oil. The seeds were pressed using a Farmet DUO screw press (Czech Republic) with a capacity of 18–25 kg/h and engine power of 2.2 kW. Three-kilogram batches of seeds were pressed using a nozzle with a diameter of ten millimeters. Before the beginning of the process, the press was heated up to 50 ± 1 °C. The temperature was measured with an Ama-digit thermometer. After pressing, the oils were set aside for 7 days to allow natural sediment deposition.

2.5. Oil Extraction Yield

The oil extraction yield was calculated based on the weight of the extracted oil, the weight of the seed sample, and the percentage of oil in the seeds. To calculate the extraction yield “W”, the following formula proposed by Rotkiewicz et al. [14] was used:
W = m o l · 100 Z o l · m n · 100   %
where mol—mass of extracted oil (kg), Zol—content of oil in seeds (%), mn—mass of processed seeds (kg).

2.6. Preparation of Samples

After 7 days, samples were collected for quality analyses of the extracted oil without additives. Subsequently, chili pepper and garlic were added to the remaining samples.
To determine the effect of natural plant additives on the properties of the pressed oils, control samples containing pure oil and experimental oil samples supplemented with 1 g/100 g garlic and chili pepper were prepared. All samples were stored in 250 cm3 dark glass bottles at 10 ± 1 °C in a refrigerator.
Determinations of oils in the form of a control sample and with additives were conducted after 2, 4, and 6 weeks.

2.7. Determination of Fatty Acid Composition

The fatty acid composition was determined with the gas chromatography (GC) method (HP 6890 II with a flame ionization detector) according to the standards [15,16,17]. A BPX 70 capillary column (60 m × 0.25 mm, 25 μm) was used for the separation of esters. The following conditions were used: programable column temperature, 140–210 °C; dispenser temperature, 210 °C; detector temperature, 250 °C; carrier gas, nitrogen.

2.8. Determination of Acid Value

The acid value (AV) indicates the amount of free fatty acids contained in the oil. It is expressed as mg of KOH required to neutralize organic acids present in 1 g of oil. The test was conducted with the titration method using a cold solvent in accordance with the standard [18].

2.9. Determination of PV

The PV indicates the content of peroxides and hydroperoxides generated during the initial stages of oil oxidation. It is expressed as millimoles of O2 per kg of oil. The test was performed using the titration method with iodometric determination of the end point in accordance with the standard [19].

2.10. Determination of Oxidative Stability

The oxidative stability of the oils was determined using the Rancimat accelerated oxidation test, which measures the oxidation induction time through the detection of volatile acids generated during this process. The test was performed using a Metrohm 893 Professional Biodiesel Rancimat device in accordance with the standard [20]. Oil samples (2.50 ± 0.01 g) were weighed using the measuring vessel and exposed to air at the flow of 20 l/h at 120 °C. The results were expressed as the oxidation induction time determined automatically from the curve inflection point by using StabNet1.0 software provided by the company.

2.11. Statistical Analysis

The results were analyzed statistically using Statistica 10 statistical package. Analysis of variance (ANOVA) was performed to assess the significance of differences between the values of parameters determined for the individual raw materials. The differences were considered to be significant at the level of 0.05. Detailed analyses of the mean confidence intervals were performed with the Tukey test.

3. Results and Discussion

3.1. Chemical Determinations of Seeds

The results of the determination of the basic chemical composition of the pressed seeds are presented in Table 1.
The analyzed seeds showed a typical and almost similar moisture level ranging from 5.93 (hemp seeds) to 6.64% (flax seeds). The black cumin seeds showed the highest fat content (37.93%), whereas the hemp and flax seeds contained 29.98% and 35.98% fat content, respectively. The protein content varied in the range from 20.21% in the black cumin seeds to 31.05% in the hemp seeds (Table 1).
The analyzed hemp seeds exhibited similar protein content to that reported by other authors (Table 1). In their analysis of the chemical composition of several varieties of hemp, Worobiej et al. [21] and House et al. [22] detected 30.74% and 30.34–38.69% of protein content in shelled seeds, respectively. Significantly lower levels of this component were detected in unshelled seeds (24.16% and 21.32–27.53%, respectively), which indicates that protein is mainly accumulated in the inner parts of the seeds. The fat content in shelled seeds determined by these authors was approximately 10% higher than the level reported in the present study. In unshelled hemp seeds, these values were lower (24.16%) or similar to those detected in the present study (Table 1). Rosik-Dulewska and Dulewski [23] analyzed the chemical composition of flax seeds and showed the protein content of 26.15–29.24% (Table 1). The fat content determined in the present study was 0.09% higher than the value reported by Krajewska et al. [24], who analyzed seeds of the same cultivar harvested in 2014.
In the present study, the fat and protein contents of the black cumin seeds were found to be 37.93% and 20.21%, respectively (Table 1). Similar conclusions were reached by Rashed et al. [25], who reported 38.20% of fat content and 20.85% of protein content in black cumin seeds. A similar fat content of 38.03% was reported by Wolski et al. [26] in a study of commercial seeds of this plant.

3.2. Chemical Determination of Oils

Table 2 summarizes the results of the content of individual fatty acids, their groups, and the n-6 to n-3 acid ratio. The highest content of saturated fatty acids (SFAs) in the total fatty acid pool was observed in the black cumin seed oil (15.94%). The level of SFAs in the other oils was substantially lower, i.e., 7.16% and 9.61% in the hemp and flax seed oil, respectively.
Monounsaturated acids (MUFAs) (Table 2) represented by oleic acid from the n-9 family were present at the level of 13.23% (hemp oil) to 23.98% (black cumin seed oil). The total content of polyunsaturated fatty acids (PUFAs) in the oils was substantially higher than that of MUFAs and ranged from 60.08% to 79.61%. The black cumin seed oil had the lowest amount of these acids, whereas the hemp seed oil showed the highest level; in both cases, these acids were mainly n-6 acids (59.65% and 58.21%, respectively). The flax seed oil was found to have a higher content of n-3 acids (56.94%) and a lower content of n-6 acids (15.96%) (Table 2).
The appropriate ratio of n-6 to n-3 fatty acids in the diet recommended by nutritionists is 4:1 [27]. It is maintained at very high contents of fatty acids from both families. Only the black cumin seed oil among the analyzed samples had a very small amount of n-3 fatty acids (0.43%); therefore, the ratio of n-6 to n-3 fatty acids was unfavorable, i.e., 138.7:1 (Table 2). An excess amount of omega-6 fatty acids in the diet leads to the development of chronic inflammation, which can lead to specific diseases, e.g., malignant neoplasms, skin diseases, or cardiovascular and nervous system diseases [28]. A substantially lower n-6 to n-3 ratio resulting from the higher amounts of both n-6 and n-3 fatty acids was determined in the hemp seed oil (3.2:1). The ratio was 1:3.6 in the flax seed oil.
Wolski et al. also analyzed the fatty acid composition in Nigella damascena depending on the sowing date and seed origin. Their result differed from the fatty acid profile detected in the present study (Table 2). The largest differences were noted in the amounts of SFAs, i.e., their level reported by Wolski et al. [26] was twice as high (31.40% in the oil extracted from commercial seeds and 32.33% in the oil from seeds from the first sowing term). The authors observed lower values of unsaturated fatty acids, with 8.09% and 15.06% differences in MUFAs and PUFAs, respectively. A fatty acid composition in black cumin seed oil similar to that determined in the present study was reported by Obiedzińska and Waszkiewicz-Robak [1] in their analyses of various cold-pressed oils. The contents of SFAs, MUFAs, and PUFAs were 15.76%, 23.99%, and 59.77%, respectively, compared to 15.94%, 23.98%, and 60.08%, respectively, determined in the present study. The same authors also analyzed the composition of flax seed oil. They detected 9.15% of SFAs mainly represented by palmitic acid (5.8%). MUFAs accounted for 17.43% (oleic acid), and PUFAs constituted 72.75% of the content, including 15.82% of linoleic acid and 56.93% of α-linolenic acid. The ratio of n-6 to n-3 acids in their study was 0.3 vs. 0.28 determined in the present study (Table 2).
The fatty acid composition of hemp seed oil was investigated by Caputa and Nikiel-Loranc [29] in terms of its application in cosmetology. No major differences were noted between the results reported by these authors and the present findings (Table 2). The authors reported 7.5% of unsaturated acids, mainly palmitic acid (5%), and a two-fold lower amount of stearic acid. Oleic acid (MUFA) accounted for 13%, and PUFAs constituted 81%, with 4% of γ-linolenic acid, 19% of α-linolenic acid, and 58% of linoleic acid. The authors showed an n-6 to n-3 ratio of 3.3, which was 0.1 higher than the value obtained in the present study (Table 2). Thus, it can be concluded that hemp seed oil almost fulfills the requirements established by nutritionists, where the appropriate ratio of n-6 to n-3 acids in the diet should be 4:1 [27].
The growing interest in the use of natural sources of antioxidants, due to the increasing number of publications on toxicity and carcinogenicity in animals and humans, has limited the use of synthetic antioxidants [30,31]. The results of the oil extraction yield and chemical properties that indicate the quality of the extracted oils immediately after pressing are presented in Table 3. Although the pressing process was performed under comparable conditions, the oil extraction yield from the analyzed seeds differed significantly. The extraction yield of the flax seed oil (81.43%) was substantially higher than that of the black cumin (56.13%) and hemp (72.81%) seed oils. These differences may have resulted from the different structure and chemical composition of the seeds.
The highest yield (81.43%) was obtained in the process of pressing flax seeds with moisture content of 6.64%. The oil yield was within the range of 70.1–85.7% in flax seeds with 6.1–11.6% moisture content reported by Zheng et al. [32]. Similarly, in their study of the effect of the method of flax seed preparation on the parameters of the pressing process, Minkowski et al. [33] showed an extraction yield of 81.6% for the seeds with moisture content of 6.7%. The oil extraction yield for the other seeds analyzed in the present study (Table 3) was similar to the values of 72.54% and 55.49% for hemp seeds and black cumin seeds, respectively, reported by Krajewska et al. [24].
The fatty acid composition and the presence of natural antioxidants are the most important determinants of the durability and quality of oils, which were assessed in the present study based on their AV, PV, and oxidative stability values. The mean AV differed between the analyzed oils (Table 3). The lowest AV was shown by the flax seed oil (0.51 mg KOH/g). A substantially higher AV was exhibited by the hemp seed oil (1.69 mg KOH/g), whereas the black cumin seed oil had the highest AV (2.36 mg KOH/g). As indicated by the PV, the highest amounts of peroxides and hydroperoxides were detected in the black cumin seed oil with a PV of 3.36 mmol O2/kg, while the PV of the flax seed oil was only 0.74 mmol O2/kg. This confirms that the oils met the quality requirements in terms of AV and PV (AV ≤ 4 mg KOH/g, PV ≤ 10 mmol O2/kg) as specified in the Codex Alimentarius [34].
The contents of free fatty acids as well as peroxides and hydroperoxides varied between the analyzed oils (Table 3). The lowest amount of these compounds was detected in the flax seed oil. The AV obtained in the present study differed substantially from the values reported by other researchers. Mińkowski et al. [33] showed an AV of 2.12 mg KOH/g for the oil extracted from flax seeds with moisture content of 6.7% and a PV of 0.72 mmol O2/kg, which was similar to that determined in the present study. Pawłowska et al. [35] analyzed flax and black cumin seed oils and reported AV of 0.07 and 1.62 mg KOH/g, respectively, which were substantially lower than the values determined in the present study. The PV reported by these authors was 2.9 and 34.7 µg O2/kg in flax and black cumin seed oils, respectively, whereas the values in the present study were 0.74 and 3.36 mmol O2/kg, respectively. The AV (Table 3) was similar to the value reported by Krajewska et al. [24], who analyzed oil from seeds of the same variety harvested in 2014. In contrast, a considerably higher PV (8.8 mmol O2/kg) was reported by the authors than that obtained in the present study (1.40 mmol O2/kg).
The antioxidant mechanism of capsaicin present in chili peppers has also been described by Kogure et al. [36], wherein they showed that capsaicin delayed the lipid oxidation of soybean oil during the frying process at 200 °C. Yang et al. [37] showed that the oxidation process takes place at 140 °C, but it is not as effective as that at 100 °C [38].
Oxidative stability is a very important indicator of the quality of cold-pressed oils. The Rancimat accelerated oxidation test is usually applied to determine the oxidative stability and the shelf life of oils [34]. The test results showed that the hemp seed oil was characterized by the lowest value of this parameter (1.75 h), followed by the flax seed oil (2.59 h) (Table 3). The black cumin seed oil was most resistant to oxidation, as its induction time was 5.8 h.
The Rancimat test results showed the lowest stability of the hemp seed oil, slightly higher stability of the flax seed oil, and the highest value of the parameter in the black cumin seed oil (Table 3). The induction time determined by Krajewska et al. [24] was the same for flax seed oil (2.59 h) but shorter by 3.8 h for the black cumin seed oil and by 0.31 h for the hemp seed oil. The study of the effect of flax seed preparation on the quality traits of the extracted oil conducted by Mińkowski et al. [33] demonstrated an induction time range of 4.8–5.0 h for oils extracted from seeds differing in moisture content. These results differed significantly from the values obtained in the present study (Table 3). The differences in the oil induction time might be due to the different content of chlorophyll pigments in the oils, the different composition of fatty acids (the greater the amounts of PUFAs, the shorter the induction time), and the different amounts of peroxides [39].

3.3. Chemical Determinations of Supplemented Oils

Figure 1 shows changes in the values of the quality determinants in the oils supplemented with garlic and chili pepper. The results reveal a significant effect of both storage time and the additives used on the analyzed parameters.
During the storage of the oils at 10 ± 1 °C, an increase in AV and PV was observed in the sample without the additives as compared to those in the freshly pressed oils, with the greatest differences noted after 6 weeks (Figure 1 and Figure 2). The oxidative stability of the oils also changed, i.e., the values decreased with the storage time. The black cumin seed oil exhibited the greatest differences from the freshly pressed oil, as its induction time decreased by 26.7% (Figure 3).
The present study showed that the additives reduced the AV and PV of the oils and extended their induction time. The comparison of the effects of the additives revealed that garlic was more effective than chili pepper. As shown by the statistical analysis, for the flax and hemp seed oils, only the addition of garlic had a significant effect on the AV after 2, 4, and 6 weeks of storage of the samples. A significant effect of both the tested additives on changes in the value of this parameter relative to the control sample was noted in the black cumin seed oil. The addition of garlic to the flax seed oil caused significant changes in PV after 2 and 4 weeks of storage, while significant changes were caused by this additive in the hemp seed oil only after 4 weeks. For the black cumin seed oil, both garlic and chili pepper additives significantly reduced the PV as compared to that for the control sample after 2, 4, and 6 weeks of storage.
The analysis of the changes in the induction time showed that the garlic-supplemented oil had the longest induction time after 6 weeks of storage. The Rancimat test results showed that the addition of garlic to the flax and hemp seed oil produced significant changes in the induction time after 4 weeks and after 4 and 6 weeks of storage, respectively. Statistically significant changes in this parameter were induced in the black cumin seed oil by both additives after each storage period.
Figure 1, Figure 2 and Figure 3 show the effect of the additives used on the chemical parameters that are the determinants of oil quality. The analyses revealed a decrease in the AV and PV and extension of the induction time in the supplemented samples as compared to those for the control sample. A comparison of the effectiveness of the additives showed that garlic had a better effect on the oils than chili pepper. Similar conclusions were reported by Nogala-Kałucka et al. [40] in their study of the effect of substances changing the flavor and aroma of extra virgin olive oil. The authors found an increase in the content of primary oxidation products of approximately 11 and 14 mmol O2/kg in garlic- and chili-pepper-supplemented samples, respectively. The authors also investigated changes in the content of tocopherols, which are natural antioxidants. Their study showed a higher amount of these compounds in garlic oil than in chili pepper oil. As reported by Baiano et al. [41], the addition of a mixture of garlic, bay leaf, and marjoram to olive oil with canned dried tomatoes slowed down the polymerization of triacylglycerols but did not inhibit their oxidation.
The effects of various additives on the quality and stability of cold-pressed oils were also investigated by other scientists. Blicharz-Kania et al. [42] and Krajewska et al. [43] analyzed the effect of turmeric and rosemary supplementation on changes in AV, PV, and induction time in poppy seed oil and the impact of oregano addition on the same parameters in rapeseed oil. The authors showed that the additives exhibited antioxidant properties and effectively reduced oxidative changes occurring during oil storage. They contributed to extension of the induction time of the oils and slowed down the oil hydrolysis process. In both cases, as observed in the present study, the additives reduced the AV and PV in relation to the control.
Zunin et al. [44] investigated the effect of 0.01% and 0.1% addition of carnosic acid (bioactive compound in rosemary) on the oxidative stability of olive oil. The researchers reported an inhibitory effect of the additive on the generation of primary and secondary oxidation products depending on the amount of acid added at 60 °C. In their study of the effect of various flavoring plants (e.g., rosemary, sage, thyme, and basil) on the oxidative stability of olive oil, Ayadi et al. [45] showed the best protective properties of rosemary (at 60 °C), which extended the induction time by 20.5 days as compared to the control. The other plants extended the storage time of oils less efficiently, i.e., by 3.5 and 11.5 days by basil and thyme, respectively. In conclusion, regardless of the type of oils, the addition of natural antioxidants may cause significant changes in the oxidative stability of these products.
The present research was divided into three stages. In the first stage, the seed moisture and the fat and protein contents were determined. The second stage involved the process of oil extraction from the seeds. The oil extraction yield was calculated. Next, the composition of fatty acids was determined, and their quality was assessed through determination of the AV, PV, and oxidative stability.
The final stage of the study involved the evaluation of the effect of supplementation with natural plant additives with antioxidant properties on the quality traits of the analyzed oils after 2, 4, and 6 weeks of storage through analysis of their AV, PV, and oxidative stability. All determinations were performed in triplicate. The arithmetic mean of these repetitions was taken as the result.

4. Conclusions

The addition of garlic and chili pepper to the oils had a positive effect on their quality through extension of the oxidation induction time and inhibition of oxidation to peroxides, which had a positive effect on oil stability. The highest increase in the induction time, i.e., by 4.03 h compared to the control sample, was observed in the garlic-supplemented black cumin seed oil stored for 6 weeks. The additives used in the study exhibited varying antioxidant activities in each of the tested oils, with garlic exhibiting a higher degree of antioxidant activity.
Statistical analysis indicated that both the analyzed additives induced significant changes in AV, PV, and oxidative stability after 2, 4, and 6 weeks of storage only in the black cumin seed oil.
All the tested black cumin and hemp seed oils, both the control samples, and the oils with the addition of natural antioxidants met the requirements for cold-pressed oils in terms of AV and PV throughout the storage period.
The active ingredients contained in chili pepper and garlic improved the oxidative stability of the analyzed oils, and thus, these natural additives can be used to extend their shelf life.

Author Contributions

M.K. (Marta Krajewska) and M.K. (Magdalena Kachel) conceptualization, methodology, formal analysis, data curation, writing—original draft; investigation, resources. 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

All data are contained within the article.

Conflicts of Interest

The authors declare no conflict of interest.

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Applsci 12 03646 g001a 550Applsci 12 03646 g001b 550
Figure 1. Effect of additives on the acid value of stored oils: (a)—flax seed oil; (b)—hemp seed oil; (c)—black cumin seed oil. The values designated by the different small letters are significantly different (α = 0.05).
Figure 1. Effect of additives on the acid value of stored oils: (a)—flax seed oil; (b)—hemp seed oil; (c)—black cumin seed oil. The values designated by the different small letters are significantly different (α = 0.05).
Applsci 12 03646 g001aApplsci 12 03646 g001b
Applsci 12 03646 g002a 550Applsci 12 03646 g002b 550
Figure 2. Effect of additives on the peroxide value of stored oils: (a)—flax seed oil; (b)—hemp seed oil; (c)—black cumin seed oil. The values designated by the different small letters are significantly different (α = 0.05).
Figure 2. Effect of additives on the peroxide value of stored oils: (a)—flax seed oil; (b)—hemp seed oil; (c)—black cumin seed oil. The values designated by the different small letters are significantly different (α = 0.05).
Applsci 12 03646 g002aApplsci 12 03646 g002b
Applsci 12 03646 g003a 550Applsci 12 03646 g003b 550
Figure 3. Effect of additives on the oxidation induction time of stored oils: (a)—flax seed oil; (b)—hemp seed oil; (c)—black cumin seed oil. The values designated by the different small letters are significantly different (α = 0.05).
Figure 3. Effect of additives on the oxidation induction time of stored oils: (a)—flax seed oil; (b)—hemp seed oil; (c)—black cumin seed oil. The values designated by the different small letters are significantly different (α = 0.05).
Applsci 12 03646 g003aApplsci 12 03646 g003b
Table
Table 1. Basic chemical composition of seeds.
Table 1. Basic chemical composition of seeds.
MaterialMoisture (± SD) [%]Fat Content (± SD) [%]Protein Content (± SD) [%]
Flax seeds6.64 ± 0.07 a,*35.98 ± 0.05 a26.35 ± 0.06 a
Hemp seeds5.93 ± 0.06 b29.98 ± 0.04 b31.05 ± 0.06 b
Black cumin seeds6.33 ± 0.05 c37.93 ± 0.06 c20.21 ± 0.05 c
* Values designated by the different small letters in the column are significantly different (α = 0.05).
Table
Table 2. Average fatty acid composition in the analyzed oils.
Table 2. Average fatty acid composition in the analyzed oils.
Fatty AcidFlax Seed Oil
(± SD) [%]		Hemp Seed Oil
(± SD) [%]		Black Cumin Seed Oil
(± SD) [%]
Palmitic (16:0)5.99 ± 0.56 a,*5.02 ± 0.47 b12.91 ± 0.51 c
Stearic (18:0)3.62 ± 0.14 a2.14 ± 0.11 b3.03 ± 0.16 c
Arachidonic (20:0)---
Oleic (18:1)17.49 ± 0.44 a13,23 ± 0.39 b23.98 ± 0.41 c
Linoleic (18:2)15.96 ± 0.83 a58,21 ± 0.78 b59.65 ± 0.81 c
α-linolenic (α-18:3)56.94 ± 0.21 a18.74 ± 0.29 b0.43 ± 0.26 c
γ-linolenic (γ-18:3)-2.66 ± 0.31-
ΣSFA9.617.1615.94
ΣMUFA17.4913.2323.98
ΣPUFA72.9079.6160.08
n-6/n-31/3.63.2/1138.7/1
* Values designated by the different small letters in the row are significantly different (α = 0.05).
Table
Table 3. Extraction yield and chemical properties of fresh cold-pressed oils.
Table 3. Extraction yield and chemical properties of fresh cold-pressed oils.
Type of OilExtraction Yield [%]AV (± SD)
[mg KOH/g]		PV (± SD)
[mmol O2/kg]		Induction Time
(± SD) [h]
Flax seed oil81.43 a,*0.51 ± 0.08 a0.74 ± 0.08 a2.59 ± 0.09 a
Hemp seed oil72.81 b1.69 ± 0.09 b1.40 ± 0.08 b1.75 ± 0.07 b
Black cumin seed oil56.13 c2.36 ± 0.07 c3.36 ± 0.09 c5.80 ± 0.08 c
* Values designated by the different small letters in the column are significantly different (α = 0.05).
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Krajewska, M.; Kachel, M. Changes in Selected Properties of Cold-Pressed Oils Induced by Natural Plant Additives. Appl. Sci. 2022, 12, 3646. https://doi.org/10.3390/app12073646

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Krajewska M, Kachel M. Changes in Selected Properties of Cold-Pressed Oils Induced by Natural Plant Additives. Applied Sciences. 2022; 12(7):3646. https://doi.org/10.3390/app12073646

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Krajewska, Marta, and Magdalena Kachel. 2022. "Changes in Selected Properties of Cold-Pressed Oils Induced by Natural Plant Additives" Applied Sciences 12, no. 7: 3646. https://doi.org/10.3390/app12073646

APA Style

Krajewska, M., & Kachel, M. (2022). Changes in Selected Properties of Cold-Pressed Oils Induced by Natural Plant Additives. Applied Sciences, 12(7), 3646. https://doi.org/10.3390/app12073646

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