Lipid oxidation and adulteration have a negative impact on functionality and notoriety of foods especially vegetable oils and cause economic losses. The present study investigates the control of two commercial quality aspects of prickly pear seeds oil (PPSO): oxidative stability during storage and detection of adulteration. Peroxide index, specific extinction coefficients K232 and K270, free acidity, and fatty acids composition were evaluated during different periods of incubation (6, 12, and 18 months) at various temperatures (4°C, 25°C, 40°C, and uncontrolled room temperature ranging between 4°C and 40°C) with different packaging (protected and unprotected from sunlight, with and without nitrogen gas bubbling). Based on the physicochemical and biochemical parameters evolution, this study has shown that PPSO stored at 4°C for 18 months preserves the initial quality. However, at 40°C, an intense lipid oxidative process occurred after 6 months of storage. The changes have also affected fatty acids composition, especially rates of linoleic and oleic acids. The shelf-life of oils stored at 25°C and at uncontrolled room temperature can be limited to 6 months. Regarding the impact of light and nitrogen bubbling, sunlight has affected seriously the oxidative stability of oils after 12 months of storage and the bubbling with nitrogen has improved their stability when they have been stored in clear glass bottles. The levels of adulteration detection using fatty acids as markers are relatively high. The detection of oil adulteration can be depicted by fatty acids composition up to 15% of olive and almond oils and up to 20% of rapeseed oil. The iodine value could also be an indicator of the sunflower oil presence in PPSO. Therefore, other minor compounds including sterols and tocopherols should be investigated to depict PPSO adulteration with cheaper oils and to determine lower levels of detection in order to ensure the authenticity of PPSO.
In Morocco, as well as in the Mediterranean countries, prickly pear (
The major tocopherol of PPSO is gamma-tocopherol, representing an average of 90% of total tocopherols, compared with delta-tocopherol (9%) and alpha-tocopherol (1.8%) [
However, there are not many studies concerning the oxidative stability of oils in general and even less for PPOS in particular. It has been reported among the few ones that the stability to oxidation of PPSO is lower than those of olive oil and argan oil, due to the PPSO high level of unsaturated fatty acids [
In addition to the oxidative stability challenge, the detection of oil adulteration especially in cosmetics field is also an important quality aspect to ensure an authentic product especially for oils with high marketing value as is the case with PPSO. The adulteration of PPSO with relatively low-price vegetable oils is common, and, consequently, there is an urgent need to control quality aspects of this oil. Furthermore, there is a need for reliable, rapid, and inexpensive adulteration detection methods in the commercial oil industry [
To the best of our knowledge, this study is the first investigation associating two aspects relating to the PPSO preservation and adulteration which have an immense importance for sanitary and commercial quality, making it possible for the consumer as well as the manufacturer and the authority, to educate the optimal conditions of typicity and authenticity preservation, to raise awareness about potential adulteration, and to pave the way for the establishment of a commercial quality standard of this oil.
In this context, this work aims (i) to study the oxidative stability of PPSO by evaluating its chemical composition changes at different temperatures (4°C, 25°C, 40°C, and uncontrolled room temperature) and conditions of storage (protected and unprotected from sunlight and oxygen) during 18 months and (ii) to detect levels of oil adulteration with comparatively four cheaper vegetables oils (sunflower, rapeseed, olive, and almond oils).
The study was conducted on the variety of prickly pear (
A completely randomized design was used for evaluating the oxidative stability by comparing the quality parameters and fatty acids composition of oil samples (64 oil vials with a capacity of 30 mL) stored at the following conditions: in dark glass bottles at 4°C, 25°C, and 40°C; in dark glass bottles at uncontrolled room temperature ranging between 4°C and 40°C, without nitrogen gas bubbling; in clear glass bottles at uncontrolled room temperature ranging between 4°C and 40°C, without nitrogen gas bubbling; in dark glass bottles, bubbled with nitrogen gas before sealing and placed at uncontrolled room temperature ranging between 4°C and 40°C; and in clear glass bottles, bubbled with nitrogen gas before sealing and placed at uncontrolled room temperature ranging between 4°C and 40°C. Bubbling with nitrogen gas has been made in order to study the impact of the oxygen on oil oxidation. Clear or dark bottles were used with 2 mL headspace volume. Sampling times were at the beginning of the trial (
The determined PPSO quality parameters are peroxide index (meq of O2/kg of oil), specific extinction coefficients K232 and K270, and free acidity (% of oleic acid). The peroxide index was determined according to standard NF 60-220 [
Fatty acids composition was determined by gas chromatography analysis according to the analytical methods described in the IOC standard [
The iodine value (IV), which measures the level of unsaturation in oils and expressed in gram iodine absorbed by 100 g of oil, was calculated from the percentages of fatty acids according to (
In order to detect adulteration of PPSO, four fresh vegetables oils (olive, almond, rapeseed, and sunflower oils) were added to PPSO. These oils, purchased from the market, are characterized by their low commercial values compared to PPSO and the same appearance as PPSO especially olive oil. These oils were mixed with PPSO at different rates ranging between 1% and 50% (vegetable oil/PPSO). The determination of fatty acids profiles of pure oils (as controls) and adulterated oils was carried out by gas chromatography analysis according to the analytical method previously described.
Data are presented in tables and figures as (means ± standard deviations) of three replicates. Analyses of variance especially two-way ANOVA were applied for the oxidative stability tests to assess interaction and main effects of time and temperature and time and packaging conditions for PPSO quality criteria. For the adulteration test, the one-way ANOVA was applied. Student–Newman–Keuls test at level of
The results of the two-way ANOVA, with the objective being the study of the time and temperature interaction effects on the PPSO quality during storage, have shown that all the studied quality parameters (peroxide index, free acidity, and specific extinction coefficients K232 and K270) have experienced very high significance difference (
Evolution of quality parameters of prickly pear seeds oil during storage at various temperatures: 4°C, 25°C, 40°C, and uncontrolled room temperature. (a) Peroxide index. (b) Free acidity. (c) Specific extinction coefficient K232. (d) Specific extinction coefficient K270. The error bars represent the standard deviation of three replicates. Means with the same letter for the same storage time are not significantly different according to Student–Newman–Keuls test at
Fatty acids composition of prickly pear seeds oil as a function of storage time at various temperatures: 4°C, 25°C, 40°C, and uncontrolled room temperature
Temperature (°C) | Time | Fatty acids (%) | ||||||||
---|---|---|---|---|---|---|---|---|---|---|
Myristic | Palmitic | Palmitoleic | Stearic | Oleic | Linoleic | Linolenic | Arachic | Eicosenoic | ||
acid | acid | acid | acid | acid | acid | acid | acid | acid | ||
C14 : 0 | C16 : 0 | C16 : 1 | C18 : 0 | 1 | C18 : 2 | C18 : 3 | C20 : 0 | C20 : 1 | ||
— | 0 | 0.07a ± 0.04 | 12.34a ± 0.01 | 0.74a ± 0.03 | 3.24a ± 0.05 | 21.25a ± 0.10 | 61.44a ± 0.06 | 0.24a ± 0.07 | 0.31a ± 0.01 | 0.29a ± 0.07 |
4 | 6 | 0.06a ± 0.02 | 12.28a ± 0.01 | 0.77a ± 0.02 | 3.25a ± 0.02 | 21.26a ± 0.03 | 61.43b ± 0.09 | 0.22a ± 0.04 | 0.29a ± 0.01 | 0.28a ± 0.06 |
12 | 0.07a ± 0.03 | 12.29a ± 0.06 | 0.73a ± 0.02 | 3.26a ± 0.02 | 21.27a ± 0.03 | 61.44b ± 0.09 | 0.26a ± 0.02 | 0.34a ± 0.06 | 0.25a ± 0.09 | |
18 | 0.05a ± 0.03 | 12.31a ± 0.11 | 0.72a ± 0.01 | 3.26a ± 0.01 | 21.35a ± 0.18 | 61.51b ± 0.01 | 0.25a ± 0.02 | 0.32a ± 0.06 | 0.29a ± 0.00 | |
25 | 6 | 0.07a ± 0.01 | 12.26a ± 0.01 | 0.72a ± 0.01 | 3.32b ± 0.15 | 21.24a ± 0.07 | 61.49b ± 0.09 | 0.24a ± 0.01 | 0.27a ± 0.03 | 0.36a ± 0.05 |
12 | 0.08a ± 0.03 | 12.33a ± 0.10 | 0.75a ± 0.01 | 3.28a ± 0.07 | 21.31a ± 0.07 | 61.47b ± 0.10 | 0.27a ± 0.01 | 0.28a ± 0.01 | 0.25a ± 0.07 | |
18 | 0.06a ± 0.01 | 12.31a ± 0.06 | 0.73a ± 0.02 | 3.28a ± 0.07 | 21.31a ± 0.07 | 61.49b ± 0.08 | 0.25a ± 0.01 | 0.25a ± 0.01 | 0.27a ± 0.04 | |
40 | 6 | 0.08a ± 0.01 | 12.31a ± 0.04 | 0.76a ± 0.00 | 3.28ab ± 0.04 | 21.48b ± 0.03 | 61.02a ± 0.07 | 0.26a ± 0.00 | 0.26a ± 0.00 | 0.34a ± 0.01 |
12 | 0.07a ± 0.01 | 12.40b ± 0.05 | 0.74a ± 0.02 | 3.31a ± 0.01 | 21.49b ± 0.07 | 61.05a ± 0.09 | 0.24a ± 0.01 | 0.26a ± 0.03 | 0.29a ± 0.05 | |
18 | 0.09a ± 0.03 | 12.40a ± 0.05 | 0.71a ± 0.02 | 3.62b ± 0.01 | 22.47b ± 0.07 | 60.10a ± 0.13 | 0.24a ± 0.01 | 0.31a ± 0.00 | 0.28a ± 0.06 | |
RT | 6 | 0.05a ± 0.02 | 12.34a ± 0.01 | 0.75a ± 0.03 | 3.24a ± 0.05 | 21.25a ± 0.10 | 61.42b ± 0.05 | 0.26a ± 0.01 | 0.29a ± 0.00 | 0.33a ± 0.05 |
12 | 0.05a ± 0.02 | 12.29a ± 0.08 | 0.74a ± 0.00 | 3.29a ± 0.06 | 21.27a ± 0.07 | 61.56b ± 0.12 | 0.26a ± 0.03 | 0.29a ± 0.01 | 0.27a ± 0.02 | |
18 | 0.07a ± 0.03 | 12.28a ± 0.04 | 0.75a ± 0.00 | 3.34a ± 0.08 | 21.28a ± 0.03 | 61.42b ± 0.12 | 0.23a ± 0.04 | 0.30a ± 0.01 | 0.28a ± 0.05 |
During 18 months of storage at 4°C, PPSO remained stable without significant changes of free acidity, specific extinction coefficients K232 and K270, and fatty acids composition. Although it is common that, during such long periods of storage, hydroperoxides split into short chain aromatic organic compounds (mainly aldehydes, ketones, alcohols, and short chain fatty acids), which cause the rancidity [
The oxidation of PPSO stored at 25°C was noticeable at 12 months of storage. The production of hydroperoxides and conjugated dienes increased, checked by peroxide index and K232 value (Figures
The storage of PPSO at 40°C impacted seriously the quality of oil. All studied parameters increased from the start of storage, revealing the occurrence of intense oxidative processes. The production of hydroperoxides and conjugated dienes (K232) swiftly increased. The peroxide index and conjugated dienes (K232) varied from 3.40 to 39.48 meq O2/kg of oil and from 1.65 to 5.06, respectively (Figures
Uncontrolled room temperature represents the common temperature of storage in local markets. During the study, the room temperature ranged from 4°C (indoor coldest night) to 40°C (indoor hottest day). The monitoring lipid oxidation of PPSO stored at uncontrolled room temperature showed the intense increase of peroxide index and conjugated dienes (K232) after 6 and 12 months of storage. The values varied from 3.40 to 38.80 meq O2/kg of oil and from 1.65 to 3.93, respectively (Figures
At 18 months of storage, the formation of these secondary oxidation products in PPSO was pronounced but significantly different from that recorded for PPSO stored at 40°C; the K270 values were 0.82 and 0.99, respectively (Figure
The results of the two-way ANOVA, with the objective being the study of the effect of time and packaging interaction on the PPSO quality during storage, have shown, as for time and temperature factors presented above, that all the studied quality parameters (peroxide index, free acidity, and specific extinction coefficients K232 and K270) have showed very high significance difference (
Evolution of quality parameters of prickly pear seeds oil during storage at various packaging conditions: dark glass bottles/clear glass bottles, with nitrogen/without nitrogen. (a) Peroxide index. (b) Free acidity. (c) Specific extinction coefficient K232. (d) Specific extinction coefficient K270. The error bars represent the standard deviation of three replicates. Means with the same letter for the same storage time are not significantly different according to Student–Newman–Keuls test at
Fatty acids composition of prickly pear seeds oil as a function of storage time at different packaging conditions
Packaging conditions | Time | Fatty acids (%) | ||||||||
---|---|---|---|---|---|---|---|---|---|---|
Myristic | Palmitic | Palmitoleic | Stearic | Oleic | Linoleic | Linolenic | Arachic | Eicosenoic | ||
acid | acid | acid | acid | acid | acid | acid | acid | acid | ||
C14 : 0 | C16 : 0 | C16 : 1 | C18 : 0 | C18 : 1 | C18 : 2 | C18 : 3 | C20 : 0 | C20 : 1 | ||
0.07a ± 0.04 | 12.34a ± 0.01 | 0.74a ± 0.03 | 3.24a ± 0.05 | 21.25a ± 0.10 | 61.44a ± 0.06 | 0.24a ± 0.07 | 0.31a ± 0.01 | 0.29a ± 0.07 | ||
Dark glass bottles without nitrogen | 6 | 0.05a ± 0.02 | 12.34a ± 0.01 | 0.75a ± 0.03 | 3.24a ± 0.05 | 21.25a ± 0.10 | 61.42a ± 0.05 | 0.26a ± 0.01 | 0.29a ± 0.02 | 0.33a ± 0.05 |
12 | 0.05a ± 0.02 | 12.29a ± 0.02 | 0.74a ± 0.00 | 3.29a ± 0.06 | 21.27a ± 0.07 | 61.56b ± 0.12 | 0.26a ± 0.03 | 0.29a ± 0.01 | 0.27a ± 0.02 | |
18 | 0.07a ± 0.03 | 12.28a ± 0.04 | 0.75a ± 0.00 | 3.34a ± 0.08 | 21.28a ± 0.03 | 61.42c ± 0.12 | 0.23b ± 0.04 | 0.30a ± 0.01 | 0.28a ± 0.05 | |
Dark glass bottles with nitrogen | 6 | 0.05a ± 0.03 | 12.33a ± 0.02 | 0.76a ± 0.02 | 3.27a ± 0.03 | 21.24a ± 0.14 | 61.45a ± 0.05 | 0.25a ± 0.09 | 0.29a ± 0.01 | 0.32a ± 0.03 |
12 | 0.08a ± 0.03 | 12.27a ± 0.10 | 0.73a ± 0.03 | 3.32a ± 0.02 | 21.26a ± 0.02 | 61.30ab ± 0.05 | 0.27a ± 0.01 | 0.34a ± 0.03 | 0.32a ± 0.00 | |
18 | 0.07a ± 0.01 | 12.25a ± 0.10 | 0.73a ± 0.03 | 3.30a ± 0.01 | 21.30a ± 0.08 | 61.48c ± 0.11 | 0.24b ± 0.06 | 0.27a ± 0.09 | 0.30a ± 0.04 | |
Clear glass bottles without nitrogen | 6 | 0.06a ± 0.04 | 12.36a ± 0.07 | 0.75a ± 0.01 | 3.31a ± 0.05 | 21.29a ± 0.10 | 61.26a ± 0.05 | 0.25a ± 0.04 | 0.32a ± 0.04 | 0.34a ± 0.03 |
12 | 0.08a ± 0.02 | 12.36a ± 0.11 | 0.74a ± 0.04 | 3.30a ± 0.06 | 21.40a ± 0.07 | 61.15a ± 0.02 | 0.24a ± 0.01 | 0.32a ± 0.06 | 0.26a ± 0.05 | |
18 | 0.06a ± 0.04 | 12.35a ± 0.08 | 0.75a ± 0.04 | 3.71b ± 0.02 | 23.57c ± 0.03 | 58.99a ± 0.14 | 0.16a ± 0.06 | 0.26a ± 0.01 | 0.26a ± 0.05 | |
Clear glass bottles with nitrogen | 6 | 0.06a ± 0.02 | 12.32a ± 0.06 | 0.76a ± 0.04 | 3.26a ± 0.05 | 21.17a ± 0.06 | 61.42a ± 0.11 | 0.24a ± 0.02 | 0.31a ± 0.01 | 0.31a ± 0.02 |
12 | 0.06a ± 0.02 | 12.31a ± 0.00 | 0.69a ± 0.03 | 3.31a ± 0.02 | 21.30a ± 0.09 | 61.37ab ± 0.07 | 0.32a ± 0.11 | 0.28a ± 0.05 | 0.24a ± 0.05 | |
18 | 0.04a ± 0.02 | 12.25a ± 0.02 | 0.73a ± 0.02 | 3.51a ± 0.08 | 21.74b ± 0.03 | 61.03b ± 0.01 | 0.27b ± 0.01 | 0.20a ± 0.07 | 0.27a ± 0.01 |
Bubbling oil with nitrogen gas impacted hydroperoxide formation in PPSO especially during 6 and 12 months of storage. The presence of nitrogen, as conditioner gas, contributed to reducing the peroxidation of oils during 6 months both in dark glass and clear glass bottles. The peroxide index increased significantly after 6 months from 3.40 to 26.00 meq O2/kg of oil in the absence of nitrogen and from 3.40 to 19.78 meq O2/kg of oil in the presence of nitrogen (Figure
The protection of PPSO from sunlight was essential to limit hydroperoxides formation in PPSO during 18 months. At 12 months, peroxide index has increased from 3.40 to 45.72 meq O2/kg of oil (for clear glass bottles) and from 3.40 to 38.09 meq O2/kg of oil (for dark glass bottles) (Figure
The combined action of sunlight and oxygen availability affected after 12 months the secondary oxidation rate of oil stored in clear glass bottles without nitrogen. It seems that the contribution of oxygen in PPSO oxidative process is only significant when this oil is exposed to sunlight for a long time (Figures
Concerning the impact of sunlight exposition and oxygen availability on the composition of fatty acids, the changes occurred only for oil stored in clear glass bottles without nitrogen after 12 months. Linoleic acid (C18 : 2) decreased from 61.44% to 58.99% but oleic acid (C18 : 1) increased from 21.25% to 23.57% (Table
As indicated above in the oxidative stability test, the quality parameters of pure PPSO freshly extracted in particular free acidity, peroxide value, and K232 and K270 specific extinction coefficients are (0.24 ± 0.01 % of oleic acid), (3.40 ± 0.20 meq of O2/kg of oil), and (1.64 ± 0.05) and (0.27 ± 0.02), respectively. The
Comparison of fatty acids composition of pure prickly pear seeds oil (PPOS) and PPSO mixed at different rates with (A) olive oil and almond oil.
Fatty acids (%) | Pure oils | Mixture rates (%) | |||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
PPSO | Olive oil | Almond oil | Olive oil/PPSO | Almond oil/PPSO | |||||||
100% | 100% | 100% | 1% | 5% | 10% | 15% | 1% | 5% | 10% | 15% | |
Myristic acid (C14 : 0) | 0.04a ± 0.00 | 0.05a ± 0.00 | 0.00a ± 0.01 | 0.07a ± 0.00 | 0.04a ± 0.00 | 0.05a ± 0.01 | 0.03a ± 0.01 | 0.04a ± 0.00 | 0.00a ± 0.00 | 0.00a ± 0.00 | 0.00a ± 0.01 |
Palmitic acid (C16 : 0) | 12.15e ± 0.04 | 8.80b ± 0.11 | 4.44a ± 0.04 | 12.36e ± 0.24 | 12.18e ± 0.00 | 12.11e ± 0.00 | 11.82d ± 0.07 | 12.15e ± 0.04 | 12.45e ± 0.03 | 11.54d ± 0.20 | 11.02c ± 0.07 |
Palmitoleic acid (C16 : 1) | 0.52a ± 0.06 | 0.40a ± 0.01 | 1.32b ± 0.04 | 0.56a ± 0.02 | 0.52a ± 0.14 | 0.53a ± 0.13 | 0.56a ± 0.00 | 0.52a ± 0.06 | 0.62a ± 0.03 | 0.58a ± 0.01 | 0.50a ± 0.04 |
Stearic acid (C18 : 0) | 3.88d ± 0.06 | 1.85a ± 0.15 | 2.23b ± 1.02 | 3.22c ± 0.34 | 3.26c ± 0.13 | 3.06c ± 0.06 | 3.08c ± 0.12 | 3.80d ± 0.06 | 3.03c ± 0.23 | 3.15c ± 0.11 | 3.09c ± 0.00 |
Oleic acid (C18 : 1) | 20.17a ± 0.11 | 74.11f ± 0.80 | 71.37f ± 0.02 | 21.99b ± 1.82 | 23.61c ± 0.31 | 24.15c ± 0.21 | 30.42e ± 0.03 | 20.17a ± 0.11 | 20.36a ± 0.03 | 25.46c ± 0.87 | 28.66e ± 0.13 |
Linoleic acid (C18 : 2) | 60.21d ± 0.05 | 12.72a ± 0.01 | 20.51b ± 0.10 | 61.05d ± 2.50 | 59.77d ± 0.02 | 59.30d ± 0.02 | 52.74c ± 0.09 | 60.20d ± 0.05 | 61.78e ± 0.64 | 59.17cd ± 0.72 | 55.6c ± 0.22 |
Linolenic acid (C18 : 3) | 0.35a ± 0.03 | 1.00b ± 0.07 | 0.03a ± 0.00 | 0.22a ± 0.04 | 0.15a ± 0.05 | 0.24a ± 0.04 | 0.35a ± 0.05 | 0.35a ± 0.03 | 0.47a ± 0.13 | 0.37a ± 0.06 | 0.21a ± 0.01 |
Arachic acid (C20 : 0) | 0.26b ± 0.01 | 0.27b ± 0.00 | 0.23b ± 0.06 | 0.35b ± 0.02 | 0.34b ± 0.07 | 0.15a ± 0.02 | 0.21b ± 0.03 | 0.26b ± 0.01 | 0.27b ± 0.02 | 0.14a ± 0.03 | 0.34b ± 0.01 |
Eicosenoic acid (C20 : 1) | 0.20a ± 0.04 | 0.28b ± 0.02 | 0.24a ± 0.05 | 0.22a ± 0.02 | 0.32b ± 0.01 | 0.29b ± 0.10 | 0.28b ± 0.01 | 0.20a ± 0.01 | 0.18a ± 0.02 | 0.16a ± 0.01 | 0.29b ± 0.00 |
Iodine value | 129.13e ± 0.80 | 92.90a ± 0.14 | 102.17b ± 0.25 | 131.98g ± 0.12 | 130.79f ± 0.21 | 130.76f ± 0.10 | 124.80c ± 0.19 | 129.12e ± 0.72 | 132.59i ± 0.22 | 132.11h ± 0.36 | 127.98d ± 0.15 |
Comparison of fatty acids composition of pure prickly pear seeds oil (PPOS) and PPSO mixed at different rates with (B) rapeseed oil and sunflower oil
Fatty acids (%) | Pure oils | Mixture rates (%) | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
PPSO | Rapeseed oil | Sunflower oil | Rapeseed oil/PPSO | Sunflower oil/PPSO | ||||||||||
100% | 100% | 100% | 1% | 5% | 10% | 15% | 20% | 1% | 5% | 10% | 20% | 30% | 50% | |
Myristic acid (C14 : 0) | 0.04a ± 0.00 | 0.02a ± 0.00 | 0.04a ± 0.00 | 0.09a ± 0.02 | 0.02a ± 0.00 | 0.02a ± 0.00 | 0.08a ± 0.00 | 0.00a ± 0.00 | 0.09a ± 0.02 | 0.08a ± 0.01 | 0.08a ± 0.02 | 0.06a ± 0.03 | 0.02a ± 0.00 | 0.01a ± 0.01 |
Palmitic acid (C16 : 0) | 12.15f ± 0.04 | 4.80a ± 0.05 | 6.66b ± 0.03 | 12.30f ± 0.20 | 11.46d ± 0.05 | 11.28d ± 0.05 | 11.77e ± 0.23 | 9.84c ± 0.04 | 12.08f ± 0.07 | 11.75e ± 0.24 | 11.37d ± 0.04 | 10.84cd ± 0.45 | 10.11c ± 0.17 | 10.04c ± 0.10 |
Palmitoleic acid (C16 : 1) | 0.52b ± 0.06 | 0.66b ± 0.00 | 0.05a ± 0.01 | 0.50b ± 0.05 | 0.45b ± 0.03 | 0.40b ± 0.01 | 0.48b ± 0.02 | 0.47b ± 0.02 | 0.62b ± 0.01 | 0.60b ± 0.01 | 0.48b ± 0.04 | 0.49b ± 0.07 | 0.58b ± 0.03 | 0.50b ± 0.02 |
Stearic acid (C18 : 0) | 3.88c ± 0.06 | 1.79a ± 0.11 | 3.62c ± 0.16 | 3.27c ± 0.14 | 3.36c ± 0.12 | 3.13bc ± 0.02 | 3.15bc ± 0.02 | 2.79b ± 0.06 | 3.30c ± 0.01 | 3.36c ± 0.07 | 3.33c ± 0.10 | 3.45c ± 0.20 | 3.34c ± 0.07 | 3.14bc ± 0.13 |
Oleic acid (C18 : 1) | 20.17a ± 0.11 | 22.29b ± 0.21 | 26.28e ± 0.03 | 22.30b ± 1.80 | 23.96c ± 0.19 | 21.00a ± 0.14 | 24.36d ± 0.11 | 32.94f ± 0.03 | 20.92a ± 0.16 | 20.21a ± 0.39 | 21.12a ± 0.02 | 21.53a ± 0.71 | 22.00b ± 0.17 | 22.57b ± 0.05 |
Linoleic acid (C18 : 2) | 60.21b ± 0.05 | 59.77b ± 0.71 | 62.28c ± 0.26 | 59.97b ± 2.32 | 58.27b ± 0.04 | 60.88b ± 0.02 | 57.48b ± 0.25 | 49.23a ± 0.46 | 63.00d ± 0.03 | 62.25c ± 0.21 | 62.64c ± 0.13 | 62.57c ± 0.14 | 63.05d ± 0.22 | 62.90d ± 0.13 |
Linolenic acid (C18 : 3) | 0.35b ± 0.03 | 9.13f ± 0.10 | 0.32b ± 0.14 | 0.35b ± 0.08 | 1.50c ± 0.03 | 1.51c ± 0.01 | 1.70d ± 0.01 | 3.98e ± 0.05 | 0.21a ± 0.09 | 0.23a ± 0.03 | 0.24a ± 0.06 | 0.35b ± 0.07 | 0.29ab ± 0.12 | 0.33b ± 0.06 |
Arachic acid (C20 : 0) | 0.26a ± 0.01 | 0.40b ± 0.06 | 0.20a ± 0.10 | 0.22a ± 0.11 | 0.30a ± 0.02 | 0.29a ± 0.02 | 0.29a ± 0.01 | 0.25a ± 0.02 | 0.25a ± 0.03 | 0.20a ± 0.02 | 0.37b ± 0.06 | 0.21a ± 0.03 | 0.20a ± 0.08 | 0.23a ± 0.02 |
Eicosenoic acid (C20 : 1) | 0.20a ± 0.01 | 0.32b ± 0.01 | 0.10a ± 0.04 | 0.40b ± 0.00 | 0.41b ± 0.15 | 0.37b ± 0.01 | 0.37b ± 0.11 | 0.40b ± 0.01 | 0.13a ± 0.02 | 0.14a ± 0.03 | 0.17a ± 0.03 | 0.20a ± 0.02 | 0.20a ± 0.01 | 0.22a ± 0.02 |
Iodine value | 129.13a ± 0.80 | 154.20i ± 0.10 | 137.83h ± 0.10 | 130.59b ± 0.21 | 132.03c ± 0.16 | 134.15d ± 0.11 | 130.58b ± 0.14 | 130.52b ± 0.12 | 134.54e ± 0.52 | 134.63e ± 0.25 | 134.06d ± 0.21 | 134.61e ± 0.80 | 135.84f ± 0.14 | 136.10g ± 0.14 |
For mixtures with olive oil, the identified level to detect PPSO adulteration was 15%. Indeed, the significant increase of oleic acid from 20.17% in pure PPSO to 30.42% in adulterated PPSO at 15% can be considerate as a marker of adulteration (Table
Mixing PPSO with rapeseed oil at different rates (1%, 5%, 10%, 15%, and 20%) showed that linolenic acid, essential fatty acid from the omega 3 family that cannot be synthesized by the body, can be used as a marker to detect the adulteration with this oil (Table
For all mixtures carried out using sunflower oil at different rates including the higher rate of 50%, the occurring changes in fatty acids distribution, even if they were significant (Table
Considering the iodine value (IV) which is an indicator of the oxidative stability of the oil, the pure PPSO showed to be less stable than olive and almond oils by presenting the highest IV (129.13). However, PPSO is more stable than colza and sunflower oils (having 154.20 and 137.83 for IV, respectively). The IV recorded in this study is higher than that reported by De Wit et al. [
In this work, two aspects relating to the PPSO preservation and adulteration of an immense importance for sanitary and commercial quality were studied. It has shown that PPSO stored at 4°C for 18 months preserve the initial quality based on the evolution of quality parameters and fatty acid compositions. However, at 40°C, an intense lipid oxidative process occurred after 6 months of storage. The changes have also affected fatty acids composition especially rates of linoleic and oleic acids. The shelf-life of oils stored at 25°C and at uncontrolled room temperature can be limited to 6 months. The PPSO bubbling with nitrogen has improved its stability when it has been stored in clear glass bottles. Thus, it is recommended to protect PPSO from oxygen and light by using dark glass bottles for a long period of storage even if the use of this packaging material is not easily accepted by some consumers. The levels of adulteration detection using fatty acids as markers are relatively high. The detection of oil adulteration can be depicted up to 15% of olive and almond oils and up to 20% of rapeseed oil. The iodine value could also be an indicator of the presence of sunflower oil detectable in PPSO from 1%. Therefore, other minor compounds including sterols and tocopherols should be investigated to depict the adulteration of PPSO with cheaper oils and to determine lower levels of detection for the authentication of PPSO purity.
The data used to support the findings of this study are available from the first author Fatima Ettalibi (
This research was performed at the Regional Center for Agricultural Research in Marrakesh belonging to the National Institute for Agricultural Research (INRA Morocco) in the framework of the Megaproject: “Preservation and Development of the Cactus Sector” of INRA Medium-Term Research Program (PRMT 2017–2020).
The authors declare that there are no conflicts of interest regarding the publication of this paper.
The authors are grateful to farmers and to the Sebbar Rhamna Cooperative (Skhour Rhamna, Morocco) for their generous assistance during prickly pear fruit harvesting and seeds oil extraction. They would also like to extend their thanks to the technical staff of the Laboratory of Agri-Food Technology and Quality at the Regional Center for Agricultural Research in Marrakesh (INRA Morocco), for providing technical support during the development of this research.