Degradation of Tocopherols During Near - ambient Rapeseed Drying

DEGRADATION OF TOCOPHEROLS DURING NEAR-AMBIENT

RAPESEED DRYING

MARZENA GAWRYSIAK-WITULSKA1,3,ALEKSANDER SIGER2and

MALGORZATA NOGALA-KALUCKA2

1Institute of Plant Origin Food Technology

2Department of Food Biochemistry and Analysis

Poznan University of Life Sciences

Wojska Polskiego28,60-637Poznan,Poland

Submitted for Publication July7,2009

Revised Received and Accepted August24,2009

ABSTRACT

Increased interest manifested by consumers in products rich in biologi-cally active components makes it necessary to minimize their loss during drying and storage of raw materials for food production.In this study,the effect of drying conditions and further storage of rapeseed on changes in contents of tocopherols(T)and plastochromanol-8(PC-8)was examined. Seeds of rape cv.Californium,Elektra and Livius,dried after harvest using the near-ambient drying method in a bed of2-m thickness and air heated to a temperature of60,80and100C,were used.Contents of T and PC-8were determined immediately after drying and after6and12months of storage at 10?2C.Quality and quantity of antioxidants in seeds were determined using high-performance liquid chromatography.The near-ambient seed drying method resulted in a decrease in T content by6–11%,while that for hot air drying was4–8%.Seed storage reduced the level of T by a further23–30%. Similar dependences were found for PC-8.The analyzed results demonstrated the effect of varietal differences,drying conditions and storage time on the contents of T and PC-8in rapeseed.

PRACTICAL APLICATIONS

Drying of rapeseed is one of the most energy-intensive stages of its production.At the same time,one needs to consider that these seeds,as 3Corresponding author.TEL:+48-61-848-73-09;FAX:+48-61-848-73-52;EMAIL:wima@ up.poznan.pl

?2009,Wiley Periodicals,Inc.

biological material,are highly sensitive to thermal treatment.Thus,search for best drying conditions with special emphasis on the preservation of bioactive components that affect human health is necessary.The analyses carried out compared the range of loss of natural antioxidants,tocochromanols,during drying and further storage of rapeseed dried using an energy-saving near-ambient drying and dried using hot air.

INTRODUCTION

Worldwide production of rapeseed in recent years has increased to 50million tons,of which 2million tons are produced in Poland (Rosiak 2008).The value of rapeseed for food and industrial purposes depends on the quality of seeds;thus after harvest,seeds should be properly preserved.Because of the morphological structure and chemical composition of rapeseed,its storage poses a much higher risk of quality loss than in the case of storage of cereal grains.The adverse chemical and biochemical changes occurring during storage of rapeseed is ?rst dictated by its excessive moisture content which signi?cantly reduces the time for its safe storage,posing a risk of development of mold fungi (Pronyk et al.2006).Rapeseed harvested in Poland usually has 7–17%moisture and 80–90%of seeds require cleaning and drying to a mois-ture content of approximately 7%(Rybacki et al.2001).High drying tempera-tures cause degradation of seed carotenoids and other bioactives,at the same time losing antioxidant and provitamin activity (Robak and Zachwieja 1998).

The cost of drying constitutes a large proportion of total incurred in rapeseed production;thus,drying at near-ambient temperature in a thick seedbed has gained popularity (Tys and Rybacki 2001;Pagano and Crozza 2002;Ryniecki 2005).In the near-ambient drying process,air with a drying potential,changing stochastically depending on weather conditions,is blown into a thick bed of seeds (Nellist 1998;Ryniecki et al.2006).The thickness of the bed during near-ambient drying may range from around a dozen centime-ters to several meters.In this method,the ?ow of moisture from seeds to air generally occurs only in the layer with a relatively small thickness,called the drying zone (Ryniecki 2005).During that time,seed moisture content in layers above the drying zone remains at a level similar to initial moisture content (Nellist 1998),posing a risk of deterioration of their technological quality and the development of mold fungi.Drying,depending,among other things,on atmospheric conditions,initial seed moisture content and the thickness of the dried layer,lasts from a few to around a dozen days (Ryniecki et al.1993).

A very important group of compounds found in rapeseed is comprised of native antioxidants,including tocochromanols and plastochromanol-8(PC-8).Their presence determines the stability of lipids in stored seeds and an

525

DEGRADATION OF TOCOPHEROLS

526M.GAWRYSIAK-WITULSKA,A.SIGER and M.NOGALA-KALUCKA appropriate nutritive value of produced oils(Ho?us and Sonnewald2003).Four homologues tocopherols(T),alpha-,beta-,gamma-and delta-T,are found in rapeseed with alpha-T and gamma-T amounting to80mg/100g oil,while the other two are found in trace amounts(Ratnayake and Daun2004).In oilseed lipids,there appears to be a direct relationship between the degree of unsatura-tion,as represented by the iodine value,and the total content of T(Shahidi and Shukla1996).In view of new developments in the genetic modi?cation of oilseeds,the content and pro?le of minor components,including those of T, may vary considerably in different varieties.However,the importance of seasonal variation,geographical area of cultivation and degree and type of processing cannot be ignored(Shahidi2002).A primary role of T as antioxi-dants is to quench free radicals in the lipid oxidation reaction(Wang and Quinn 1999).Oilseeds,similar to other plant sources,provide an important reservoir of a myriad of phytochemicals.While some of the phytochemicals present may possess harmful effects when consumed in large amounts,the bene?cial health effects of such components when used in appropriate quantities is well docu-mented(Shahidi2002).Present nutritional recommendations to increase the consumption of food rich in biologically active components enforce the need to minimize their loss during drying and storage of rapeseed.Thus,this study examined the effect of drying conditions and further storage on changes in the content of native T in rapeseed.

MATERIALS AND METHODS

Materials

Experimental material comprised seeds of three cultivars of winter rape Californium,Elektra and Livius freshly harvested from the area of the Wielko-polskie province.Seeds after harvest were dried using the near-ambient and high temperature drying methods.

Near-Ambient Drying

Seeds of cv.Californium were dried using the near-ambient method from initial moisture content of16.2%on a farm belonging to the Agricultural University of Poznan′(at present,renamed to the Poznan′University of Life Sciences).The Experimental Station presented by Gawrysiak-Witulska et al. (2008)was built on the basis of a28-ton metal silo with a diameter of3.2m, equipped with a computer controller(type BIT-04)of the near-ambient drying process with a set of measurement probes,a fan and an electronic air heater. During the experiment,the BIT-04controlled the operation of the air heater so that the air blown into the silo had an adequate drying potential.The experiment

in the silo was run for the seed layer of approximately 2m and was completed after 136h.

Seeds of cv.Elektra and Livius were dried from initial moisture content of 14%,under laboratory conditions,in a specially designed and constructed experimental station to analyze the process of rapeseed drying in a thick bed presented by Ryniecki et al.(2007).The near-ambient drying chamber with a diameter of 0.3m was built from segments with a height of 0.1m.Total height of the seed layer during near-ambient drying was 2m.Moreover,the near-ambient drying stand was equipped with a fan with smooth regulation of rotational speed and a heater with an impulse power regulation,which made it possible to accurately control parameters of the blowing air.Temperature in seed layers was measured using Cu-Konstantan thermoelements,while rela-tive humidity was measured using probes with volume sensors.An electronic humidistat controlled an air heater so that relative humidity of air blown into the seed bulk did not exceed 45%.Every day,individual segments of the near-ambient drying chamber were weighed cyclically in order to determine changes in seed moisture content in individual layers.Near-ambient drying was run until moisture content of 7%was obtained in seeds in the outlet layer for drying air,after 120h from the onset of the process.Relative humidity of atmospheric air during the experiment ranged from 26to 67%,while its temperature ranged from 21to 35C (Fig.1).High Temperature Drying

High temperature drying processes were run in a laboratory drier,con-structed at the Laboratory of Food Industry Engineering and Equipment,the Poznan ′University of Life Sciences.The stand was equipped with two trays made from sieves for thin-layer drying.Seeds of each cultivar were subjected to drying in a thin layer of 0.5cm using air heated to 60,80and 100C.Drying was run until seeds had a moisture content of 7%.Drying time ranged from 12to15min for 100C,15to 20min for 80C and 36to 42min for 60C,respectively.

Samples of seeds harvested from a ?eld were collected,constituting the reference sample (control),seeds immediately after the completion of near-ambient drying from a layer at 0.1m,1.0m,1.5m and 2.0m,and seeds dried using the high temperature method.In samples collected for analyses,the contents of T and PC-8were determined.Analyses were conducted immedi-ately after the completion of drying and after 6and 12months of seed storage at 10?2C.

Determination of Tocochromanols and PC-8

In order to determine tocochromanols and PC-8,collected samples of rapeseed were comminuted in a laboratory mill.For further analyses,2g of a

527

DEGRADATION OF TOCOPHEROLS

sample and 0.5g pyrogallol were weighed and placed in a round-bottomed ?ask,where saponi?cation was performed by adding 20mL anhydrous ethyl alcohol and 2mL of 60%KOH.After 30min heating at the solvent boiling point,50mL of 1%NaCl solution was added to the samples,which were then cooled.Subsequently,50mL n -hexane with a 10%addition of ethyl acetate was added.Tightly sealed ?asks were shaken (at 300rpm)for 30min.Next,approximately 2mL saturated NaCl solution was added.After 15min from the top layer (nonsaponi?ed substances),an amount adequate for high-performance liquid chromatography (HPLC)injection was collected.Recov-ery of T standards,saponi?ed using this method,was 99.9%.T and PC-8were identi?ed qualitatively and quantitatively using an HPLC (Waters 600,Milford,MA)in a system comprising a Waters 600pump,a LiChrosorb Si 60column (200￥4,6mm,5m m,Merck,Darmstadt,Germany)and a ?uorimetric detector.The whole amount was analyzed using the Millenium 32program.The mobile phase comprised a mixture of n -hexane with 1,4-dioxane (97:3,v/v).Flow rate was 1.5mL/min.The ?uorimetric detector (Waters 474)ran at excitation l =290nm and emission l =330nm for T.Concentrations of individual T homologues were calculated from a previously prepared calibra-tion curve (PN-EN-12822/2002;Ryyn?nen et al.2004;PN-EN-ISO 9936/

2006).

222426283032343638400

406080100120T e m p e r a t u r e (C )

Time (h)

Atmospheric air

Drying air

0.1 m

1.0 m

1.5 m

2.0 m

FIG.1.CHANGES IN TEMPERATURE OF ATMOSPHERIC AND DRYING AIR AND IN SEED

LAYERS OF CV .ELEKTRA DURING DRYING AT 0.1M;1.0M;1.5M;2.0M

528M.GAWRYSIAK-WITULSKA,A.SIGER and M.NOGALA-KALUCKA

Statistical Analysis

The results obtained were subjected to statistical analysis.Results are presented as means of three replications ?standard deviation.One-way analysis of variance and post hoc Tukey’s tests for the signi?cance level P <0.05were carried out using a Statistica 7.1(StatSoft,Inc.,Tulsa,OK)statistical package program.

RESULTS AND DISCUSSION

The total T content for cv.Californium,Livius and Elektra in rapeseed harvested from the ?eld was 52.29,54.73and 53.99mg/100g dry matter,respectively (Tables 1–3).According to Abidi et al.(1999)and Dolde et al.(1999),total T content in rapeseed is characterized by high variability and may range from 8to 100mg/100g.The content of these compounds is to a high degree dependent on variable environmental conditions,which makes it very dif?cult to investigate this trait (Dolde et al.1999).According to Marwede et al.(2004),primarily,a -T (35%)and g -T (64%)are found in rapeseed,together with minor amounts of b -T and d -T (approximately 1%).In seeds collected for analyses,the percentage composition of T fractions was uniform and characteristic of rapeseed oil.In all cultivars,the dominant T was g -T at 57–62%of the total T content.For cv.Californium,the content of g -T was 29.99mg/100g dm (57%),while for cv.Livius and Elektra,it was 33.74(62%)and 31.65mg/100g dm (59%)of seeds,respectively (Tables 1–3).Alpha-T accounted for 36–41%of all T,amounting to 21.37mg/100g dm (41%)for cv.Californium;while for Livius,it was 19.90mg/100g dm (36%)and for cv.Elektra,21.23mg/100g dm (39%)(Tables 1–3).The other T were found in much smaller amounts.The content of b -T and d -T in all analyzed cultivars did not exceed 1mg/100g dm.Our investigations also showed that during seed drying,total T content decreased (Tables 1–3).After the comple-tion of drying of rapeseed near-ambient temperature,the total T content in samples decreased by 6–18%,which for cv.Californium amounted to 44.47–47.96mg/100g dm,for cv.Livius,49.64–51.18mg/100g dm,and for cv.Elektra,44.21–47.44mg/100g dm.For each analyzed cultivar,the lowest loss of T during drying was in seeds dried at levels of 0.1and 1m,for Californium,amounting to 8–10%,Elektra,12–13%,and Livius,6–7%,while the biggest loss was in seeds dried at 2m,in cv.Californium amounting to 16%,Elektra,18%,and Livius,9%.Loss of a -T in tested seeds varied from 7to 15%;however,for each analyzed cultivar,the biggest loss was found in seeds dried at a level of 2m:in cv.Californium being 16%,Elektra,14%,and Livius,14%.Statistical analysis of results showed signi?cant differences (P <0.05)of

529

DEGRADATION OF TOCOPHEROLS

T A B L E 1.C H A N G E S O F T H E T A N D P C -8C O N T E N T I N A N A L Y Z E D R A P E S E E D –C A L I F O R N I U M

T i m e C o n t r o l

N e a r -a m b i e n t d r y i n g

H i g h t e m p e r a t u r e d r y i n g

0.1m

1m 1.5m 2m 60C 80C 100C

a -T F r e s h l y h a r v e s t e d s e e d s 21.37?0.05f

18.80?0.04c

18.78?0.02c

18.39?0.18b

18.08?0.07a

19.98?0.12d

20.68?0.06e

20.50?0.02e

A f t e r 6m o n t h s s t o r a g e 21.15?0.21e

18.18?0.03b

17.78?0.07a

18.25?0.09b

17.77?0.19a

19.05?0.02c

20.19?0.12d

19.34?0.07c

A f t e r 12m o n t h s s t o r a g e 20.11?0.04e 16.86?0.16b 16.16?0.09a

17.50?0.01c 16.30?0.06a 17.69?0.33c

18.50?0.04d

17.57?0.12c

g -T F r e s h l y h a r v e s t e d s e e d s 29.99?0.01f

27.48?0.27c

28.46?0.08d

25.36?0.09a

26.37?0.06b

27.71?0.17c

29.04?0.07e

28.73?0.10d ,e

A f t e r 6m o n t h s s t o r a g e 23.56?0.05d

21.47?0.02c

20.90?0.03b

20.59?0.14a

20.71?0.01a ,b

20.47?0.16c

21.60?0.06c

20.58?0.13a

A f t e r 12m o n t h s s t o r a g e

20.21?0.13d 17.88?0.03c

17.22?0.03a ,b

17.66?0.03b ,c 17.50?0.12b ,c 16.71?0.13a

17.90?0.08c

16.90?0.05a

T o t a l -T F r e s h l y h a r v e s t e d s e e d s 52.28?0.04g

46.98?0.29c

47.96?0.05d

45.47?0.14b

44.15?0.13a

48.49?0.32e

50.55?0.05f

50.05?0.16f

A f t e r 6m o n t h s s t o r a g e 45.27?0.28e

40.01?0.04c

39.11?0.04b

39.32?0.24b

38.82?0.15a

39.95?0.18c

42.25?0.06d

40.32?0.10c

A f t e r 12m o n t h s s t o r a g e

40.78?0.39e 35.01?0.13b

33.72?0.13a ,b

35.56?0.04c 34.03?0.15a

34.73?0.09b

36.75?0.03d

34.79?0.15b

P C -8F r e s h l y h a r v e s t e d s e e d s 9.91?0.09c

8.80?0.16b

8.97?0.10b

8.18?0.02a

8.14?0.14a

9.17?0.15b

9.75?0.18c

9.69?0.13c

A f t e r 6m o n t h s s t o r a g e 8.43?0.11c

7.62?0.08a

7.81?0.12a ,b

7.50?0.13a

7.79?0.05a ,b

7.76?0.08a ,b

7.98?0.04b

7.65?0.16a ,b

A f t e r 12m o n t h s s t o r a g e

7.31?0.07e 6.70?0.04a ,b

6.96?0.05b ,c ,d

7.06?0.04c ,d ,e 7.09?0.03d ,e

6.76?0.01b

6.78?0.09b ,c

6.41?0.06a

V a l u e s (m e a n s ?s t a n d a r d d e v i a t i o n )w i t h d i f f e r e n t i n d e x l e t t e r s a r e s t a t i s t i c a l l y s i g n i ?c a n t l y d i f f e r e n t (P <0.05).P C -8,p l a s t o c h r o m a n o l -8;T ,t o c o p h e r o l .

530

M.GAWRYSIAK-WITULSKA,A.SIGER and M.NOGALA-KALUCKA

T A B L E 2.C H A N G E S O F T H E T A N D P C -8C O N T E N T I N A N A L Y Z E D R A P E S E E D –E L E K T R A

T i m e C o n t r o l

N e a r -a m b i e n t d r y i n g

H i g h t e m p e r a t u r e d r y i n g

0.1m

1m 1.5m 2m 60C 80C 100C

a -T F r e s h l y h a r v e s t e d s e e d s 21.23?0.09d

18.41?0.22a

19.14?0.09b ,c

19.42?0.03c

18.28?0.08a

18.70?0.26a ,b

20.58?0.08d

19.64?0.37c

A f t e r 6m o n t h s s t o r a g e 21.10?0.16e

18.19?0.16a ,b

19.03?0.03c

18.88?0.13c

17.85?0.16a

18.32?0.29b

20.09?0.08d

19.18?0.17c

A f t e r 12m o n t h s s t o r a g e 20.27?0.13e 17.70?0.08b 17.92?0.11b ,c

16.54?0.30a 16.15?0.10a 17.84?0.21b ,c

18.81?0.16d

18.22?0.11c

g -T F r e s h l y h a r v e s t e d s e e d s 31.65?0.15g

27.82?0.05d

27.37?0.04c

25.92?0.11b

25.15?0.16a

28.55?0.10e ,f

28.49?0.25e

28.90?0.06f

A f t e r 6m o n t h s s t o r a g e 24.65?0.25d

21.50?0.16b

21.60?0.02b

21.69?0.13b

20.39?0.12a

21.52?0.11b

22.88?0.10c

22.68?0.17c

A f t e r 12m o n t h s s t o r a g e

20.20?0.13c 17.68?0.27a

18.27?0.16a ,b

18.73?0.04b 17.89?0.21a 17.86?0.17a

19.63?0.18c

18.52?0.11b

T o t a l -T F r e s h l y h a r v e s t e d s e e d s 53.99?0.22f

47.19?0.25c

47.44?0.11c

46.17?0.12b

44.21?0.20a

48.66?0.13d

50.08?0.24e

49.51?0.38e

A f t e r 6m o n t h s s t o r a g e 46.43?0.11f

40.28?0.32b

41.25?0.03c

41.21?0.22c

38.82?0.14a

40.56?0.13b

43.73?0.07e

42.53?0.21d

A f t e r 12m o n t h s s t o r a g e

41.01?0.24f 35.82?0.19b

36.65?0.29c ,d

35.76?0.25b 34.48?0.20a

36.19?0.07b ,c

38.97?0.21e

37.27?0.17d

P C -8F r e s h l y h a r v e s t e d s e e d s 10.40?0.01e

9.00?0.10c ,d

8.80?0.14b ,c

8.51?0.26a ,b

8.42?0.26a

9.13?0.09c ,d

9.20?0.17c ,d

9.30?0.07d

A f t e r 6m o n t h s s t o r a g e 8.97?0.21d

7.31?0.08a

7.82?0.17a ,b ,c

7.63?0.27a ,b

7.28?0.22a

7.51?0.25a

8.16?0.13b ,c

8.22?0.10c

A f t e r 12m o n t h s s t o r a g e

7.72?0.18d 6.34?0.07a

7.01?0.01b ,c 7.06?0.03c

6.40?0.15a

6.75?0.09b

7.16?0.14c

7.03?0.02b ,c

531

DEGRADATION OF TOCOPHEROLS

T A B L E 3.C H A N G E S O F T H E T A N D P C -8C O N T E N T I N A N A L Y Z E D R A P E S E E D –L I V I U S

T i m e C o n t r o l

N e a r -a m b i e n t d r y i n g

H i g h t e m p e r a t u r e d r y i n g

0.1m

1m 1.5m 2m 60C 80C 100C

a -T F r e s h l y h a r v e s t e d s e e d s 19.90?0.06d

18.59?0.04c

18.70?0.26a ,b

18.34?0.11c

17.21?0.15a

18.60?0.36c

18.64?0.32c

18.14?0.13b ,c

A f t e r 6m o n t h s s t o r a g e 19.81?0.32c

18.10?0.07b

17.10?0.10a

17.71?0.35b

17.04?0.06a

18.25?0.22b

18.22?0.21b

17.93?0.08b

A f t e r 12m o n t h s s t o r a g e 18.82?0.07d 17.60?0.02c 16.36?0.16a

17.08?0.06b 16.22?0.03a 17.59?0.04c

17.31?0.11b

16.36?0.16a

g -T F r e s h l y h a r v e s t e d s e e d s 33.74?0.39d

32.09?0.23b ,c

32.22?0.33b ,c

31.90?0.15a ,b

31.53?0.32a

32.96?0.10c ,d

32.77?0.36b ,c

31.43?0.14a

A f t e r 6m o n t h s s t o r a g e 27.78?0.21d

25.19?0.18b ,c

24.64?0.28a ,b

25.60?0.17c

24.73?0.23a ,b

25.15?0.12b ,c

25.00?0.15b ,c

24.00?0.13a

A f t e r 12m o n t h s s t o r a g e

23.86?0.01d 21.49?0.12c

20.64?0.06b

21.45?0.20c 20.74?0.24b 21.41?0.14c

20.89?0.07b ,c

19.89?0.25a

T o t a l -T F r e s h l y h a r v e s t e d s e e d s 54.73?0.44e

51.66?0.22c ,d

51.92?0.16b ,c

51.19?0.18b ,c

49.64?0.31a

52.60?0.18d

52.44?0.13d

50.60?0.42a ,b

A f t e r 6m o n t h s s t o r a g e 48.28?0.26c

43.89?0.24b

42.42?0.40a

44.01?0.42b

42.41?0.25a

44.14?0.31b

43.98?0.31b

42.66?0.17a

A f t e r 12m o n t h s s t o r a g e

43.23?0.11d 39.55?0.25c

37.52?0.06a

39.06?0.09b ,c 37.45?0.21a

39.51?0.43c

38.74?0.08b

36.83?0.24a

P C -8F r e s h l y h a r v e s t e d s e e d s 9.50?0.15c

8.73?0.14a ,b

8.76?0.05a ,b

8.50?0.18a

8.32?0.12a

9.03?0.01b

9.01?0.01b

9.15?0.07b ,c

A f t e r 6m o n t h s s t o r a g e 8.64?0.11b

7.60?0.17a

7.88?0.13a ,b

7.81?0.15a ,b

7.49?0.13a

7.85?0.17a ,b

8.07?0.04a ,b

8.32?0.06a ,b

A f t e r 12m o n t h s s t o r a g e

7.63?0.18b 6.79?0.14a

7.13?0.11a ,b 7.29?0.02a ,b 6.68?0.07a

7.24?0.12a ,b

7.10?0.06a ,b

7.24?0.08a ,b

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M.GAWRYSIAK-WITULSKA,A.SIGER and M.NOGALA-KALUCKA

T and PC-8content in cv.Californium,Elektra and Livius seed samples.The higher a given sample was located during the drying process,the bigger were these losses.The highest loss of g -T was during near-ambient drying for all rape cultivars when samples were placed in the drier at the level of 2m,amounting for cv.Californium to 15%,Livius 7%and Elektra 21%,respec-tively.Analysis of PC-8content in dried seeds showed similar dependences as for the loss of g -T.The total decrease in contents of T and PC-8was also recorded in seeds dried using hot air;however,it was signi?cantly lower (at P <0.05)than those determined during near-ambient drying (Tables 1–3).Loss of T in individual samples amounted to 3–7%for cv.Californium,4–8%for cv.Livius and 7–8%for cv.Elektra.The reduction of PC-8content in seeds of cv.Californium and Livius was similar to the decrease of total T content during high temperature drying.In seeds of cv.Elektra,loss of PC-8was higher than those of T amounting to 11–12%.Analyses also showed that the temperature of the drying medium did not have any effect on the degradation of T and PC-8during drying of seeds in cv.Elektra.In case of seed drying for cv.Californium and Livius,conducted analyses showed the effect of tempera-ture of the drying medium on the loss of T.In seeds of cv.Californium,a -T,g -T and PC-8levels,after the completion of drying,were signi?cantly lower (P <0.05)in seeds dried using air at 60C than in seeds dried with air at 80and 100C.Seeds of cv.Livius exhibited a uniform level of a -T and PC-8,irrespective of the applied drying temperature,while the content of g -T was signi?cantly higher in samples dried with air at a temperature of 100C.

Analyses conducted by Nogala-Ka?ucka et al.(2006)showed that the loss of T and PC-8during near-ambient and high temperature drying was compa-rable and amounted to approximately 10%.However,it should be stressed here that those analyses were conducted under laboratory conditions for a seed layer of 1.2m in thickness.During a typical near-ambient drying process in a thick bed,the ?ow of moisture from seeds to air occurs generally only in a relatively thin layer,called the drying zone.It is a slow drying process,lasting from a few to around a dozen days,depending on the drying potential of atmospheric air in the postharvest season in different years (Ryniecki et al.2006).Throughout the entire drying period,the grain layer,being the outlet layer for air,remains wet,waiting for the approach of the drying front.Its moisture content is similar to the initial moisture content of the grain (Gawrysiak-Witulska et al.2008).An increase in the height of the dried seed layer considerably extends the duration of the drying process and enhances the risk of adverse biochemical changes in dried seeds.In the analyses conducted in this study,seeds were dried in a layer with a thickness of approximately 2m (the layer applied during on-farm drying),which considerably extended the process.Figure 2presents changes in seed moisture content of cv.Elektra during near-ambient drying.Changes in moisture content in the layers during

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seed drying of cv.Californium and Livius were similar.The seeds at a level of 0.1m reached a moisture content of 7%after 6h,1m after 48h,1.5m after 78h and 2m after 120h from the onset of the process.At the same time (Fig.1),the temperature of seed bulk in individual layers increased to that of the drying air,while relative humidity in spaces between seeds was reduced.After the completion of drying,moisture content in seeds at a level of 0.1m was 5.5%.This corresponded to equilibrium moisture content of rapeseed calculated from Halsey’s desorption equation (ASAE Standards D245.52000)for a temperature of 30C and relative humidity of 40%.As may be seen from the data presented,during near-ambient drying,the conditions may promote adverse biochemical changes both in the bottom and top layers.If during the drying process atmospheric air is characterized by low humidity (as in the discussed experiments),bottom layers are overdried.Overdrying may reduce seed strength,at the same time increasing its susceptibility to microbial pen-etration.Such seeds are also characterized by excessive brittleness and dusti-ness during processing,which results in an increased residual oil in the meal or it extends extraction time of certain seed batches (poor percolation of the solvent during oil extraction).Moreover,the amount of free fatty acids increases and oxidative processes are intensi?ed (Tys and Rybacki 2001).The results showed that during seed drying by the near-ambient method in a

2-m

6080

100

120

M o i s t u r e c o n t e n t (%)

Time (h)

0.1 m

1.0 m

1.5 m

2.0 m

FIG.2.CHANGES IN RAPESEED MOISTURE CONTENT DURING NEAR-AMBIENT SEED

DRYING OF CV .ELEKTRA AT 0.1M;1.0M;1.5M;2.0M

534M.GAWRYSIAK-WITULSKA,A.SIGER and M.NOGALA-KALUCKA

thick bed,loss of native antioxidants was several percent higher than those dried with hot air.However,it needs to be remembered that hot air drying also results in other adverse changes in the seeds.An increase in the temperature of the drying medium to over 93C causes an increase in the content of peroxides and free fatty acids in oil (Pathak et al.1991;Krygier et al.1995a,b;Gawrysiak-Witulska et al.2005).Moreover,rapeseed drying above 120C has an adverse effect on the color of the produced oil and on the formation of free radicals.Moreover,oil loss results in a considerable loss of carotenoids (Tys et al.2002a,b).High drying temperatures also cause changes in the content of pigments (chlorophyll,b -carotene).Chlorophylls undergo transition to brown pheophytins,which deteriorate oil color and reduce its stability (Krygier et al.2000;Tan ′ska and Rotkiewicz 2003).

Quality traits of seeds are also dependent on the storage time and condi-tions (Tys et al.2000).Rapeseed,due to its morpho-anatomical structure and high fat content,is more sensitive to storage conditions than cereals.Storage of seeds with an elevated moisture content leads to an increase in the activity of lipases,which increases the amount of free fatty acids.Their oxidation and degradation causes a reduction of shelf life of oil (Je ?drychowski et al.1993;Tan ′ska and Rotkiewicz 2003).Postharvest treatments,performed on rapeseed,also have a signi?cant effect on native antioxidants,which to a large extent dictate the stability of lipids in stored seeds (Niewiadomski 1993).In the conducted analyses,after 6months of storage,the total T content in dried seeds decreased by 11–18%,while after 12months,by a further 10–14%.Loss of T was comparable for all the three dried rape cultivars.According to Nogala-Ka?ucka et al.(2006),loss of T during storage of dried seeds at 20C may reach 50%.In our experiments,seeds were stored at 10?2C,which resulted in much smaller loss of T during 1-year of storage (23–30%).During seed storage,the value of a -T/g -T ratio increased,which shows a much faster degradation of homologue g -T than that of a -T.Further analysis of the a -T/g -T ratio also showed that in seeds of cv.Californium and Livius,loss of g -T occurred much faster in these dried at a high temperature than those dried using the near-ambient method.No such dependence was found for seeds of cv.Elektra.Storage of seeds also caused loss of PC-8,which decreased by 4–19%and 11–33%,respectively,after 6and 12months,dried using the near-ambient method.In seeds dried with hot air after 6months storage,the loss of PC-8amounted to 9–21%,while after 1year,it was reduced by a further 13–16%.

It is also important to mention the effect of the re?ning process on individual T homologues.According to the literature data published in the 1970s and 1980s (Morrison 1975;Niewiadomski 1983),loss of T during re?ning may range from 30%to as much as 70%.Technological progress,new technological solutions in recent years,resulted in a much lower loss of T.

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536M.GAWRYSIAK-WITULSKA,A.SIGER and M.NOGALA-KALUCKA According to Bramley et al.(2000),loss of T during re?ning of vegetable oils amounted to15%for olive oil,25%for soy and rapeseed oils,32%for corn oil and35–40%for cottonseed,sun?ower and peanut oils.The reduction of the a-T content in plant oils during a technological process of re?ning results in a deterioration of nutritive value of oils(Eitenmiller and Lee2004).Thus,it is crucial for the raw material,from which edible oil is produced,to be of the highest quality and to reduce as much as possible the loss of native antioxi-dants during postharvest processes,such as seed drying and storage.During drying of seeds by the near-ambient method,loss of T may be higher by several percent than during high temperature drying.However,due to the fact that during seed storage and oil re?ning,loss of T reach a few dozen(20–35%) percent in the?nal product,i.e.,oil,the content of T in oil extracted from seeds dried by the near-ambient method and by high temperature drying will be similar.However,the near-ambient method is more energy ef?cient.Thus, near-ambient drying of seeds may be recommended as a suitable method in the postharvest processing of seeds.

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