Wpływ przechowywania i temperatury suszenia na zawartość steroli w nasionach rzepaku

(1)

Tom XXVII

R

OŚLINY

O

LEISTE

–

O

ILSEED

C

ROPS

2006

Magdalena Rudzińska, Henryk Jeleń, Małgorzata Nogala-Kałucka,

M. Gawrysiak-Witulska

The August Cieszkowski Agricultural University of Poznań, Department of Food Science and Nutrition

The influence of storage time and drying

temperature on sterols content in seeds of rapeseed

Wpływ przechowywania i temperatury suszenia

na zawartość steroli w nasionach rzepaku

Key words: rapeseed, phytosterols, drying, storage

The aim of this work was to monitor changes in phytosterols content in rapeseeds subjected to drying process at various temperatures and stored for one year.

Rapeseeds of Lisek (two localization) and Kronos varieties after harvesting were dried at 60, 80,

100 and 120o_{C. The content of brassicasterol, campesterol, stigmasterol, β-sitosterol and avenasterol}

was determined using gas chromatography. The identity of sterols was confirmed by gas chromatography — mass spectrometry. For all analyzed samples peroxide value and acidity were measured.

Total phytosterols content in rapeseeds samples collected from the field for Lisek I, Lisek II and Kronos varieties was 1681.4, 1811.6 and 1685.1 µg/g seeds respectively. After one-year storage of non-dried seeds total phytosterols content decreased to 1484.6, 1320.4 and 997.7 µg/g seeds respectively. The most significant decrease was noted for stigmasterol and avenasterol for the two

varieties examined. Drying process maintained at temperatures ranging from 60 to 120o_{C resulted in}

a decrease of total phytosterols content. The losses of phytosterols were correlated with drying

temperature and the highest losses were noted for the temperature of 120o_{C. In samples of dried}

rapeseeds, stored for one year, the total content of phytosterols decreased in all analyzed samples. The losses of sterols in dried samples were smaller than in non-dried reference samples.

For all analyzed samples peroxide value after one-year storage decreased, no such trend was observed for acidity of analyzed samples.

These results indicate significant influence of drying temperature and storage time on the content of phytosterols in rapeseed.

Słowa kluczowe: rzepak, fitosterole, suszenie, przechowywanie

Celem prowadzonych badań było określenie zmian zawartości fitosteroli w próbkach nasion rzepaku poddanych procesowi suszenia w zróżnicowanych warunkach temperaturowych i przecho-wywanych przez okres jednego roku.

Badany materiał stanowiły nasiona rzepaku odmiany Lisek (z dwóch lokalizacji) i Kronos, które po zbiorze poddano suszeniu w temperaturach 60, 80, 100 i 120°C. Analizowano zawartość brassika-sterolu, kampebrassika-sterolu, stigmabrassika-sterolu, sitosterolu i awenasterolu za pomocą chromatografii gazowej. Tożsamość steroli potwierdzono za pomocą chromatografii gazowej — spektrometrii mas (GC-MS). Dla analizowanych prób zmierzono także wartości liczby nadtlenkowej i kwasowej.

Całkowita zawartość fitosteroli w próbkach nasion rzepaku zebranych z pola wynosiła dla odmiany Lisek I, Lisek II i Kronos odpowiednio 1681,4, 1811,6 i 1685,1 µg/g nasion. Po rocznym

(2)

Magdalena Rudzińska ... 346

przechowywaniu niesuszonych nasion zawartości te obniżyły się odpowiednio do 1484,6, 1320,4 i 997,7 µg/g nasion. Największe spadki odnotowano dla stigmasterolu i awenasterolu dla obydwu badanych odmian. Proces suszenia nasion w temperaturach 60–120°C powodował spadek zawartości sumy fitosteroli. Straty fitosteroli były proporcjonalne do stosowanej temperatury suszenia, największe ubytki zanotowano dla temperatury suszenia 120°C. W wysuszonych nasionach rzepaku przechowywanych przez okres 1 roku zawartość sumy fitosteroli zmniejszyła się we wszystkich badanych próbkach. Ubytki steroli w wysuszonych próbkach były mniejsze niż w próbkach zebra-nych z pola, niepoddazebra-nych procesowi suszenia.

Dla wszystkich próbek wartość liczby nadtlenkowej po rocznym okresie przechowywania zma-lała, natomiast nie obserwowano takiej zależności dla liczby kwasowej.

Powyższe wyniki świadczą o istotnym wpływie na zawartość fitosteroli nasion rzepaku zarówno temperatury suszenia jak i okresu przechowywania wysuszonych nasion.

Introduction

The storage of oilseed crops, especially rapeseeds, poses a more serious risk of losses than in the case of cereal grains. It is known that the main factor responsible for rapeseeds deterioration during storage is the excessive water content in seeds. Rapeseeds that are mature, sound, with characteristic and natural color and specific for rapeseed odor can be stored with no risk when their water content is 6–7%.

Rapeseed harvested in Poland has usually water content in a range of 7% to 17%, therefore there is a need to decrease water content in them to a level which is regarded as a safe from the storage standpoint (according to Polish Norm – less than 7%). Drying is a process which, when carried out properly, guarantees good quality of dried material. Drying is carried out very often in farms where rapeseeds are stored until November. The applied method of drying can have a substantial influence on the quality of stored rapeseeds and can influence the quality of oil produced from these seeds.

The basic condition, which should be fulfilled to obtain good quality dried rapeseeds is appropriate temperature which should be below 45°C. This temperature can be increased to a certain extent depending on an initial water content in seeds. Rapeseed, which is to be processed immediately, can be dried at higher temperatures; however inappropriate drying conditions can cause losses of fat and its changes. Therefore drying rapeseeds as a preparation step for its further processing has crucial influence on oil obtained from these seeds (Tys, Rybacki 2001).

Plant sterols (phytosterols) form the main part of the non-saponificable fraction of plant lipids. Depending on a kind of plant oil they form from 40 to 80% of this fraction. The most abundant phytosterol is β-sitosterol, which is present in all plant oils. Apart from sitosterol there are also campesterol, stigmasterol avenasterol and brassicasterol present in large quantities, of which the last compound (brassicasterol) is characteristic for the Cruciferae family, to which

(3)

The influence of storage time and drying temperature ... 347

rapeseed is included. In plants phytosterols are the main compounds of cell membranes and take part in lipid transport and detoxification processes.

The ability of phytosterols to decrease the level of cholesterol in blood has been known for almost 50 years (Pollak 1953). The experiments carried out indicate that consumption of approximately 10 g of phytosterols decreases cholesterol level by 10–20%. Nowadays, there is an increasing number of products which have an enriched content of phytosterols, such as margarines, yoghurts, juices and drinks that show anticholesterolemic effect.

Phytosterols exhibit also antioxidative properties, inhibiting autoxidation of fatty acids in oil. Sterols and methylsterols containing ethylidene group at 24 and 28 position of the side chain, such as avenasterol, vernosterol, fucosterol and citrostadienol have especially strong antioxidative properties. Compounds with such a structure cleave proton from position 29 and unactivate free radicals, which in turn do not decompose and are unable to initiate oxidation processes (Gordon, Magos 1983, Pokorny 1987, Małecka 1996).

Rapeseed oil is a rich source of natural phytosterols (Rudzińska et al. 2001). However, the production process of rapeseed oil, especially application of high temperatures in several process stages causes losses of these compounds (Kocchar 1983). The goal of this work was to assess the influence of drying temperature of harvested rapeseed and storage time on the content of phytosterols.

Materials and methods

Samples of rapeseed of Lisek variety originating from two locations (farms, marked as I and II) and Kronos variety were obtained immediately after harvest in 2004. Water content in received samples was approximately 6%. The seed samples were moistened to 12% w.c., then dried at different temperatures (60, 80, 100 and 120ºC). The control samples were rapeseed seeds not subjected to the drying process. The final water content in rapeseed seeds is shown in Table 1. In samples subjected to drying process, as well as in control samples the peroxide value (PV) was determined (according to PN-ISO 3960:1996), acid value (AV, according to PN-ISO 660), and phytosterols content (Rudzińska et al. 2001). All analyses were rerun after a period of twelve months of seeds storage in laboratory conditions (at ambient temperature of 18–22°C).

(4)

Table 1 Water content in rapeseeds after drying at different temperatures

Zawartość wody w nasionach rzepaku po suszeniu w różnych temperaturach Rapeseeds after drying at temperatures

Nasiona po suszeniu w temperaturze

Varieties

Odmiana Próba kontrolna Control sample

60°C 80°C 100°C 120°C

Lisek I 11,3% 6,0% 5,9% 6,0% 5,9%

Lisek II 12,5% 6,0% 5,9% 5,8% 5,8%

Kronos 11,3% 6,0% 5,9% 6,5% 6,1%

To determine the amount of plant sterols GC method described by Rudzińska was applied (2001). According to it 1 gram of ground seeds lipids was extracted using Folch method (Folch et al. 1957). After it, to extracted fat 500 µg of 5-α-cholestane was added as an internal standard. The sample was then saponified using methanolic 1 N KOH at room temperature for 18 hours. The unsaponified fraction was extracted using diethyl ether. Plant sterols were analyzed as TMS derivatives using gas chromatograph Hewlett-Packard 6890 and DB5 column (30 m × 0.32 mm × 0.25 µm, J, W Scientific). Injector and detector temperature was 310°C, samples were injected in a split mode (1 : 25). The analyses were performed at constant temperature of 290°C at a constant helium flow of 1.6 ml/min. Phytosterols were identified based on their retention times, comparing them with standards.

Results and discussion

Rapeseeds after harvest were of good quality, with no damaged or broken seeds. The water content of seeds was 6–7%. To carry out the experiments rapeseeds samples were moistened to achieve water content of 11.3–12.5% (Table 1), followed by drying them in the laboratory dryer to the final water content of approximately 6%. Temperatures applied in laboratory conditions were similar to that used in the drying facilities, only the temperature of 120°C was used as a reference temperature. The analysis of oil obtained from dried rapeseeds did not reveal significant changes in the AV number, which was low for all analyzed samples (Table 2). Only for rapeseed dried at 100ºC (Kronos variety) and 120ºC (Lisek I i II) AV value exceeded 1.

(5)

Tabl e 2 Per oxi de val u e an d aci d val u e i n rapesee d s a ft er dry in g a n d o n e y ear st o re d Li czb a na dt le nk ow a i kw as ow a w n asi onac h rzep aku p o w ysusze ni u or az po pr zech ow yw ani u przez j eden r ok Rapeseeds after dr y ing Nasiona po suszeniu w temp eraturze Rapes eeds aft er dr y ing and s tora g e Nasiona po suszeniu i przechow ywaniu Parameter Wyró żnik

Control sample Próba _kontrolna

60°C 80°C

100°C

120°C

60°C 80°C 100°C 120°C Lisek I var iety — Odmiana Lisek I

Peroxide Value Liczba nadtlenkowa

[eqv O 2 /kg] 5.65 b 9.54 c 10.08 c 11.23 c 13.17 c 3.27 a 4.66 ab 3.64 a 4.68 ab 2.16 a Acid Value — Liczba kwasowa 0.20 a 0.74 cd 0.88 d 0.98 d 1.02 d 0.48 c 0.12 a 0.48 c 0.24 b 0.96 d Lisek II var iety — Odmiana Lisek II

[eqv O 2 /kg] 5.07 b 12.51 c 14.88 c 15.31 cd 16.40 d 2.77 a 4.52 ab 3.50 a 5.52 b 4.30 ab Acid Value — Liczba kwasowa 0.22 a 0.28 a 0.32 a 0.43 b 0.48 b 0.79 c 0.52 b 0.79 c 0.79 c 1.04 d Kronos variety — Odmiana Kronos

[eqv O 2 /kg] 4.75 b 10.67 c 12.03 c 13.31 cd 14.56 d 1.39 a 3.81 b 0.88 a 1.75 a 1.91 a Acid Value — Liczba kwasowa 0.28 a 0.56 b 0.64 bc 1.06 c 1.12 c 0.26 a 0.51 b 0.76 bc 0.52 b 0.52 b

(6)

The peroxide value (PV) in control sample, which was not subjected to drying process ranged from 4.7 to 5.7 meqO2/kg depending on the variety and increased during the drying process for all analyzed varieties (Table 2). The highest PV value was observed for rapeseed sample which was dried at 120ºC and it equaled 13.2– 16.4 meqO2/kg. After one year storage a decrease in PV was noted in control samples as well as in dried seeds. Decomposition of peroxides during storage probably contributes to this effect.

Despite minor changes in the lipid fraction of investigated rapeseed samples changes in phytosterols content during the storage of samples were significant. The results revealed the decrease in total content of phytosterols which was associated with an increase in drying temperature. The total phytosterols content in samples collected from the field at harvest was for Lisek I, Lisek II and Kronos varieties 1681.4, 1811.6 and 1685.1 µg/g seeds respectively. The process of drying seeds at temperatures of 60–120o_{C caused a decrease in total phytosterols content. After} drying the total phytosterols content in Lisek variety from the first location was 1190.6–1500.6 µg/g seeds depending on drying temperature. For Lisek II variety the amount was 982.5–1789.1 µg/g, and for Kronos — 1270.6–1669.65 µg/g of seeds. The losses of phytosterols were proportional to the applied drying temperature — the highest was noted for the drying temperature of 120°C. In rapeseeds dried at 60°C the total phytosterols content was 12–34% lower than in a control sample, whereas in samples dried at 120°C — 32–42% lower than in control (Fig. 1).

After one year storage of seeds that were not subjected to drying total phytosterols decreased to 1484.6, 1320.4 and 997.7 µg/g respectively for the varieties and locations described above. The most pronounced decrease was noted for stigmasterol and avenasterol for both investigated varieties. In dried rapeseeds stored for one year the sum of phytosterols decreased in all samples.

The decrease in phytosterols content in dried samples was less pronounced than in samples which were not subjected to drying after harvest. The sum of sterols in dried seeds stored for 12 months was for Lisek I — 1154.9 to 1305.8 µg/g, for Lisek II — 834.4 to 1653.4 µg/g, and for Kronos — 1106.9 to 1646.9 µg/g seeds. The percent composition of sterols fraction in examined seeds was uniform and characteristic for that in rapeseed oil. The dominating sterol was β-sitosterol, which formed about 40% of total sterols. The content of β-sitosterol ranged from 0.48 to 0.88 mg/g seeds. The content of brassicasterol ranged from 0.15 to 0.24 mg/g seeds — which constituted 20% of total phytosterols fraction. The remaining sterols were present at significantly lower level. The content of stigmasterol ranged from 0.014 to 0.012 mg/g and avenasterol 0.062 to 0.19 mg/g of seeds.

This work summarizes qualitative and quantitative changes in lipid fraction of rapeseed seeds of different varieties collected directly from the field, and subsequently dried at different temperatures and stored for a period of one year.

(7)

The influence of storage time and drying temperature ... 351 LISEK I 0 500 1000 1500 2000 Control sample Próba kontrolna 60ºC 80ºC 100ºC 120ºC LISEK II 0 500 1000 1500 2000 Control sample Próba kontrolna 60ºC 80ºC 100ºC 120º C KRONOS 0 500 1000 1500 2000 Control sample Próba kontrolna 60ºC 80ºC 100ºC 120ºC

dried seeds — nasiona suszone

seeds after storage — nasiona przechowywane

Fig. 1. Total phytosterols content in rapeseed drying at different temperatures and one year stored — Całkowita zawartość fitosteroli w nasionach rzepaku suszonych w różnych

temperaturach i przechowywanych przez jeden rok

drying temperature temperatura suszenia drying temperature temperatura suszenia drying temperature temperatura suszenia content o f ph ytoste rols za wart ość fi tos tero li [µ g /g] content o f ph ytoste rols za wart ość fi tos tero li [µ g /g] content o f ph ytoste rols za wart ość fi tos tero li [µ g /g]

(8)

Tabl e 3 The c o nt ent of phy to st erol s o f ra peseed s Li se k I aft er dry in g at differe n t te m p eratures a n

d one year stora

g e [µg/ g of see d s] Zawarto ść fito stero li w na sion ac h rzepa ku od mi an y Lisek I po wysu szen iu o raz po p rzecho w ywan iu p rzez jed en ro k [µg/g na si on ] Rapeseeds after dr y ing Nasiona po suszeniu w temp eraturze Rapes eeds aft er dr y ing and s tora g e Nasiona po suszeniu i przechow ywaniu Ph y tostero ls Fitos ter ol e

60°C 80°C

100°C

120°C

60°C 80°C 100°C 120°C Bras sicas tero l Brassik aste rol 221.4 ±15.8 218.5 ±18.3 194.9 ±15.2 179.4 ±14.6 148.3 ±10.2 199.9 ±15.2 153.2 ±12.1 154.1 ±11.8 167.6 ±14.9 157.9 ±11.5 Cam p esterol Kampesterol 507.3 ±47.4 552.6 ±45.1 460.7 ±36.2 457.6 ±40.5 440.7 ±32.5 531.0 ±49.1 467.1 ±35.7 408.5 ±30.2 450.6 ±32.5 405.5 ±30.8 Stigm asterol Stigmasterol 125.5 ±9.1 27.0 ±2.2 23.8 ±1.9 14.8 ±0.9 17.3 ±1.1 8.3 _±4.8 25.1 ±1.9 15.8 ±1.1 15.0 ±1.2 14.1 ±0.9 β-Sitosterol β-Sitosterol 638.1 ±30.8 660.2 ±35.2 666.1 ±32.5 581.9 ±50.3 525.1 ±33.2 650.5 ±41.7 582.2 ±38.2 630.3 ±45.7 559.8 ±46.2 520.3 ±40.1 Avenas terol Awenasterol 189.2 ±15.2 72.3 ±5.5 83.4 ±6.6 65.8 ±4.4 59.8 ±4.5 93.9 ±6.4 78.1 ±5.5 82.5 ±6.5 76.3 ±5.6 57.2 ±3.3

(9)

Tabl e 4 The co nt ent o f phy to st er ol s of ra pesee d s Li sek II aft er dry in g at diffe rent tem p eratures a n d one -year stora g e [µ g/g of see d s] Zawarto ść fito stero li w na sion ac h rzepa ku od mi an y Lisek II po wysu szen iu o raz po p rzech ow yw an iu p rzez jed en ro k [µg /g na sion ] Rapeseeds after dr y ing Nasiona po suszeniu w temp eraturze Rapes eeds aft er dr y ing and s tora g e Nasiona po suszeniu i przechow ywaniu Ph y tostero ls Fitos ter ol e

60°C 80°C

100°C

120°C

60°C 80°C 100°C 120°C Bras sicas tero l Brassik aste rol 263.0 ±21.2 258.1 ±20.3 246.5 ±20.3 184.3 ±15.8 142.5 ±11.5 184.1 ±15.4 245.03 ±15.6 195.5 ±15.2 175.5 ±14.2 121.6 ±9.5 Cam p esterol Kampesterol 491.6 ±44.2 485.5 ±40.8 460.1 ±41.8 343.7 ±29.1 281.5 ±23.1 391.4 ±33.5 490.6 ±31.2 448.3 ±30.5 354.7 ±25.6 233.7 ±16.8 Stigm asterol Stigmasterol 52.8 ±4.6 17.9 ±1.1 13.7 ±0.9 13.1 ±0.9 6.6 _±0.5 16.8 ±1.3 18.9 ±1.1 12.5 ±0.8 5.2 _±0.5 6.1 _±0.5 β-Sitosterol β-Sitosterol 868.4 ±31.8 948.1 ±32.5 828.5 ±34.2 585.2 ±28.7 520.2 ±26.3 638.7 ±26.1 837.0 ±38.5 726.2 ±41.5 552.2 ±45.2 388.0 ±25.6 Avenas terol Awenasterol 138.8 ±11.2 79.4 ±5.5 78.4 ±5.9 38.0 ±2.5 31.7 ±2.2 89.4 ±5.5 61.6 ±4.4 56.2 ±3.8 64.7 ±4.1 84.9 ±5.1

(10)

Tabl e 5 The c o nt ent of phy to st erol s o f ra peseed s Kr o nos aft er dry in g at di ffe re nt t em p erat ures a n d o n e y ear st o ra g e [µg/ g of see d s] Zawarto ść fito stero li w na sion ac h rzepa ku od mi an y Krono s po wysu szen iu o ra z po p rzech owyw an iu p rzez jed en ro k [µg /g na sion ] Rapeseeds after dr y ing Nasiona po suszeniu w temp eraturze Rapes eeds aft er dr y ing and s tora g e Nasiona po suszeniu i przechow ywaniu Ph y tostero ls Fitos ter ol e

60°C 80°C

100°C

120°C

60°C 80°C 100°C 120°C Bras sicas tero l Brassik aste rol 244.8 ±20.3 234.1 ±20.4 211.0 ±19.5 216.3 ±18.1 165.4 ±14.5 139.8 ±10.5 282.5 ±21.5 175.9 ±14.3 182.6 ±14.9 165.7 ±14.1 Cam p esterol Kampesterol 521.3 ±45.8 535.2 ±45.6 547.2 ±48.6 538.0 ±50.2 420.3 ±38.1 325.6 ±25.8 527.2 ±45.8 545.2 ±45.2 500.7 ±40.5 410.0 ±35.2 Stigm asterol Stigmasterol 13.4 ±0.9 17.5 ±1.2 18.5 ±1.4 17.9 ±1.3 9.0 _±0.5 1.5 _±0.1 5.7 _±0.3 18.0 ±1.1 14.8 ±1.1 0.0 _±0.0 β-Sitosterol β-Sitosterol 843.4 ±48.2 826.5 ±46.8 734.0 ±45.2 717.0 ±48.3 617.2 ±45.2 495.3 ±38.1 788.1 ±70.2 702.5 ±42.8 617.3 ±42.2 490.4 ±39.0 Avenas terol Awenasterol 62.3 ±4.4 56.4 ±4.6 62.8 ±4.6 63.5 ±5.6 58.8 ±4.2 35.5 ±2.8 43.4 ±3.1 60.7 ±5.2 63.4 ±4.5 40.8 ±3.5

(11)

The influence of storage time and drying temperature ... 355

Phytosterols are the most abundant and important non-glyceride fraction in plant oils (Małecka 1996). These compounds are highly recommended to be included in human diet mainly due to their biological (Hartman 1998), antioxidative (Moreau et al. 1999, Hicks, Moreau 2001) and antipolymerizing properties (Boskou 1998, Blekas, Boskou 1999). Hartmann (1998) described the influence of phytosterols on plant cell membranes, which can be a subject to genetical modification, because their presence influences the stability and thermal resistance of cell membranes. Moreover the properties of phytosterols related to their cholesterol — lowering abilities can induce the breeding experiments to increase the amount of sterols in rapeseed seeds. Phytosterols undergo many changes during various stages of rapeseed oil production, which results in their decreased level in final product (Kochhar 1983). The phytosterols losses are observed mainly in processes which require high temperatures and long term storage of seeds. The experiments described here indicated that storage of rapeseed seeds of higher than normal water content results in higher phytosterols losses than their storage after drying, even at 120ºC. However, the seeds dried at 60ºC were characterized by the lowest phytosterols decrease after one year storage.

In all investigated samples the dominating sterol was β-sitosterol and formed from 37 to 53% of total phytosterols in rapeseed seeds. After one year storage these proportion did not change. Brassicasterol ranged from 11 to 15% of all sterols. These results confirm the literature data. According to Braczko and Jakubowski (1998) β-sitosterol usually states more than 50% of all sterols, whereas brassicasterol and campesterol in rapeseed oil amount to over 90% of all sterols.

Conclusions

1. Storage of rapeseeds at 11–12% water content (higher than normal) results in higher phytosterols losses than their storage after drying at 60, 80, 100 or 120°C.

2. Drying at 60°C results in the lowest phytosterols decrease of all tested drying temperatures (80, 100, 120°C).

Acknowledgements

The authors would like to acknowledge the State Committee for Scientific Research for financing this research under the project No. PBZ-KBN-094/P06/ 2003.

(12)

References

Blekas G., Boskou D. 1999. Phytosterols and stability of frying oils. In: Frying of food oxidation, nutrient and non-nutrient antioxidants biologically active compounds and high temperatures. Technomic Publishing Co. Inc., 205-221.

Boskou D. 1998. Frying temperatures and minor constituents of oils and fats. Grasas Aceites, 49: 326-330.

Braczko M., Jakubowski A. 1998. Sterole w olejach roślinnych i ich znaczenie biologiczne. Tłuszcze Jadalne, 33 (1-2): 82-85.

Folch J., Lees M., Stanley G.H.S. 1957. A simple method for the isolation and purification of total lipids from animal tissue. J. Biol. Chem., 227: 497-509.

Gorgon M.H., Magos P. 1983. The effect of sterols on the oxidation of edible oil. Food Chem., 10: 141-145.

Hartmann M.A. 1998. Plant sterols and the membrane environment. Trends Plant Sci., 3: 170-175. Hicks K.B., Moreau R.A. 2001. Phytosterol and phytostanols: Functional food cholesterol busters.

Food Technol., 55: 63-67.

Kochhar S.P. 1983. Influence of processing on sterols of edible vegetable oils. Prog. Lipid Res., 22: 161-188.

Małecka M. 1996. Przeciwutleniające własności wybranych składników nieglicerydowych olejów roślinnych. Zesz. Nauk. Seria II, Akademia Ekonomiczna w Poznaniu, zeszyt 145.

Moreau R.A., Norton R.A., Hicks K.B. 1999. Phytosterols and phytostanols lower cholesterol. Inform, 10: 572-577.

PN-ISO 3960. Oleje i tłuszcze roślinne oraz zwierzęce. Oznaczanie liczby nadtlenkowej.

Pokorny J. 1987. Major factors affecting the autooxidation of lipids. In: Autooxidation of unsaturated lipids. Ed. H. W.-S. Chan, Academic Press, London, 141-149.

Pollak O.J. 1953. Reduction of blood cholesterol in man. Circulation, 7: 702-706.

Rudzińska M., Kazuś T., Wąsowicz E. 2001. Sterols and their oxidized derivatives in refined and cold pressed seed oils. Rośliny Oleiste – Oilseed Crops, XXII: 477-494.

Tys J., Rybacki R. 2001. Rzepak – Jakość nasion. Procesy zbioru, suszenia, przechowywania. Acta Agrophys., 44: 33-38.