CONTENT OF SELECTED ANTIOXIDATIVE COMPOUNDS IN RAW CARROT AND IN FROZEN PRODUCT PREPARED FOR CONSUMPTION

Piotr Gębczyński
Department of Fruit, Vegetable and Mushroom Processing, University of Agriculture in Cracow, Poland

ABSTRACT

The evaluation of the raw material and blanched, cooked and frozen carrot prepared for consumption was carried out after 0, 4, 8 and 12 months of refrigerated storage at –20°C and –30°C. The investigation covered the traditional production method using blanched raw material and a modified method of freezing cooked vegetable; in this case the product merely requires to be defrosted and heated in a microwave oven. Fresh carrot contained 13.02 g dry matter, 8.9 mg vitamin C, 11.6 mg carotenoids, 7.0 mg beta-carotene and 20.9 mg polyphenols/100 g; its antioxidative activity was 19.4% RSA. After 12-months storage carrot prepared for consumption retained 36-45% of vitamin C; 50-77% of carotenoids; 70-80% of beta-carotene; 73-78% of polyphenols while its antioxidative activity was reduced to 30-39% of the initial level, depending on the investigated sample. Frozen carrot produced using the modified technology contained statistically greater amounts of the investigated constituents, apart from polyphenols, after 12 months of storage. The lower storage temperature resulted in better retention of carotenoids, beta-carotene and antioxidative activity. After storage at the lower temperature frozen products prepared for consumption, including those produced using the modified technology, showed a higher sensory quality.

Key words: carrot, freezing, preparing for consumption, antioxidants.

INTRODUCTION

Owing to its nutritive properties, carrot is a highly valued vegetable of the moderate climate [30]. The good storage performance of carrot means it is available as a fresh product all the year round. However, it is also a valuable raw material for processing. It is used in the food industry for the production of highly processed food, such as children’s products, vegetable and vegetable-fruit juices; it is also used in drying and especially in the freezing industry. In the latter, direction of processing carrot is used in single-species frozen products, two-species mixtures, for instance with green pea, or in compound products. It should be stressed that frozen carrot used as an ingredient in or accompaniment to dishes may be used in special diets, being tolerated by older people and patients with serious illnesses of the digestive tract. Hence this vegetable is frequently included in hospital diets [25]. In the traditional method the following procedure is used: blanching – freezing – cooking. Currently, the widespread use of microwave heating in the catering industry and domestic food preparation has prompted modifications in the production and preparation of frozen vegetables, among them carrot, in favour of a modified procedure of: cooking – freezing – defrosting and heating in a microwave oven.

The aim of the work was to determine the quality of frozen carrot prepared for consumption using traditional and modified methods, the latter method giving a product of the ready-to-eat type. The criteria for evaluation were the content of selected constituents having antioxidative properties, and – since new products were obtained – an assessment of sensory quality.

MATERIAL AND METHODS

Material

The investigated material was fresh carrot, carrot prepared for freezing, and frozen carrot after 0, 4, 8 and 12 months of storage at –20°C and –30°C; after each period of refrigerated storage, the product prepared for consumption was analysed.

The cultivar Koral, recommended for processing, was used in the experiment. The harvest and processing were carried out in mid-September. Carrot roots were cleaned and manually peeled. After washing, the roots were cut manually into 10 mm cubes. A mean sample taken for evaluation represented the whole batch of the raw material. The remaining material was divided into two parts, each part being processed using a different technology of preparing the vegetable for freezing and preparing frozen carrot for consumption.

Methods

Production of frozen products
Two variants were used in preparing the raw material for freezing. Using traditional technology (variant I) the raw material was blanched, and after freezing and refrigerated storage the frozen carrot needed traditional cooking. In variant II the raw material was cooked before freezing to a condition approximating to consumption consistency, hence the obtained ready-to-eat product merely required defrosting and heating in a microwave.

In variant I carrot were blanched in a stainless steel vessel in water, the proportion of the blanched material to water being 1:5. The blanching temperature was 95-98°C and the time was 2 min 45 s. These conditions permitted a decrease in the activity of catalase and peroxidase to a level below 5% of the initial value. After blanching the material was immediately cooled in cold water, slightly shaken and left for 30 min on sieves to drain the water remaining on the surface.

In variant II carrot cubes were cooked to a condition approximating to consumption consistency in 2% brine. The cooking was carried out in a stainless steel vessel and the proportion of the raw material to brine was 1:1. The carrot was than placed in boiling water. The time of cooking measured from the moment when the medium began boiling again, to the moment the desired consistency was obtained was 12 min. After cooking the cubes were drained, placed in sieves and cooled in a stream of cold air.

The material from the blanched and cooked samples was divided into two parts, placed on trays and frozen at –40°C in a Feutron blast freezer, type 3626-51. One part was frozen to –20°C, which was obtained inside the frozen product after 90 min. the other part was frozen to –30°C reached after 120 min. After the desired temperature was obtained, 500 g portions of the carrot were packed in polyethylene bags suitable for the storage of refrigerated products. The bags were placed in chamber freezers at –20°C and –30°C respectively.

The preparation of frozen carrot for evaluation
Frozen blanched products were cooked in 2% brine, the proportion in weight of brine to carrot being 1:1. As in the case of cooking, the material was put in boiling water. The time of cooking was 5 min measured from the moment when the brine was boiling again. After cooking the water was immediately drained and the product was cooled to 50°C for sensory evaluation or to 20°C for analyses of chemical composition.

Frozen carrot products cooked before freezing were defrosted and a portion of 500 g in a heat-resisting vessel covered with a lid was heated in a Panasonic microwave type NN-F621. The time of defrosting and heating to 75°C was 7 min 45 s for a product frozen to –20°C and 8 min 15 s for that frozen to –30°C.

Evaluation of the chemical composition and sensory estimate of the products
Dry matter content was determined by gravimetery as the mass loss of a sample at 96-98°C [1]. The content of vitamin C was determined as the sum of ascorbic acid (AA) and dehydroascorbic acid (DHAA) by Zapata and Dufour [37] method adopted by Gil et al. [7]. The analysis was performed by HPLC using Merck-Hitachi system with UV detector. Ascorbic acid and dehydroascorbic acid were quantified with a C18 column with a mobile phase composed of 5% methanol : water solution (v/v) containing 50 mM of potassium dihydrogen phosphate. The detection was made with the UV detector at 348 nm for DHAA after derivatization with 1,2-phenylenediamine (OPDA) and at 261 nm for AA.

Total carotenoids were determined using the Lichtethaler and Buschmann [21] method. The extraction procedures of pigment were carried out under dim light and in glassware wrapped with aluminum foil. The method consisted of repeated acetone extraction, using the mortar and pestle until a colourless residue was obtained, and than filtered over a cotton pad. The extracts were made up to a known volume with acetone. The concentration of carotenoids was measured at 440,5 nm in a Shimadzu UV 160A double-beam spectrophotometer. Beta-carotene analysis [14] consisted of the extraction procedures of pigment, followed by liquid/liquid partitioning with hexane, concentration and column chromatography. The same extracts obtained for carotenoids estimation were used. Hexane extracts were filtered over anhydrous sodium sulphate on filter paper (Whatman No.1 equivalent) and were made up to a known volume. The extract was concentrated ten fold by evaporation and loaded onto the column. Columns (150 x 10 mm) were packed with aluminium oxide to a length of 100 mm and covered with 10 mm of anhydrous sodium sulphate, then washed with hexane containing 1% acetone. The orange coloured eluent containing beta-carotene was collected in a volumetric flask. The concentration of beta-carotene was measured at 450 nm in a Shimadzu UV 160A spectrophotometer and compared with the beta-carotene reference standard.

Total phenolic compounds were determined using the Folin-Ciocalteau reagent according to Singleton, Orthofer and Lamuela-Ravento’s [35]. Two grams of homogenized samples were heated at 80°C for 20 min in an 80% ethanol under reflux. Five millilitres of 10-fold diluted extract and 0.5 ml 2-fold diluted Folin-Ciocalteau reagent was added, and 1 ml of 20% of sodium carbonate was added and the contents were mixed thoroughly. The absorbance was measured at 760 nm in the Shimadzu spectrophotometer after 20 min using chlorogenic acid as a standard. The results were expressed as mg chlorogenic acid equivalents/100 g of fresh weight of product.

The antioxidant activity was measured using DPPH (1.1-diphenyl-2-picrylhydrazyl) radical scavenging method [27]. The radical scavenging activity (RSA) was determined by measuring the absorbance at 516 nm in the above described spectrophotometer and expressed as: RSA (%) = (1 – absorbance at 516 nm after 10 min/absorbance at 516 after 0 min) x 100.

Since part of the frozen samples were prepared using the modified technology, it was deemed appropriate to evaluate the sensory quality of the final products. A team of 5 panellists meeting the requirements of sensory sensitivity [13] conducted the evaluation using 5-point scale, which met the recommendations [12], and using a model card devised by the present authors. The surface appearance, colour, consistency, flavour and taste of products was evaluated. The sum product of sensory evaluation points multiplied by their weight factors was divided by the total weight factors and this was accepted as a total score.

In order to show the differentiation in chemical composition and sensory evaluation a single-factor analysis of variance (ANOVA) was carried out on the basis of the Snedecor F and Student’s T test, the least significant difference (LSD) being calculated for the error probability level of α = 0.01 for the chemical composition and α = 0.05 for sensory evaluation. The computer program Statistica ver.6.1 was used. Determination of the analysed was carried out in four replications.

RESULTS AND DISCUSSION

Research was conducted to ascertain the level of certain compounds with antioxidative properties in fresh carrot, carrot after blanching, cooked carrot, and frozen carrot after 12-month storage period and prepared for consumption, the use of traditional or modified technology of freezing being taken into consideration.

The literature includes a great number of papers reporting the level of antioxidative compounds in fresh fruits and vegetables [11, 16, 28]. The studies usually cover single constituents or a group of them, such as vitamins. Few works deal only with the content of antioxidants in products prepared for consumption, that is, with the effects of culinary or technological processes [11, 26]. Fresh carrot (Table 1) contained small quantities of vitamin C, this confirming earlier studies [4, 10]. However it was a rich source of beta-carotene, as was stressed by Gayathri et al. [5], Hart and Scott [9], Krzesinski and Knaflewski [19] and Lessin et al. [20]. The content of polyphenols and the level of antioxidative activity can be evaluated as an average. Compared with carrot a greater content of polyphenols was found in such vegetables as red beet or onion [15].

Blanching is applied as a treatment which ensures the retention of the natural taste and flavour of frozen vegetable and, by inactivating endogenous enzymes, it also stabilizes a number of constituents in the raw material [2]. After blanching the level of all the indicators analysed in the work was lowered; among them, the content of dry matter by 17%; vitamin C by 40%; carotenoids and beta-carotene by 6%; polyphenols by 11% (Tab. 1). Antioxidative activity was reduced by as much as 43%. In carrot cubes cooked before freezing, the content of dry matter was 5% less than in the raw material, exceeding the value found in blanched carrot; vitamin C was reduced by 51%; carotenoids by 4%; beta-carotene by 3%; polyphenols by 18% and antioxidative activity was 54% lower.

Changes in the level of chemical constituents during thermal treatment in water are due to thermal and enzymatic degradation and solubility in water [29]; changes in weight, absorption or release of water [10, 34]; and also the possible infiltration of sodium chloride into the tissues. This phenomenon was also observed in the investigated carrot. Since the carrots were cooked in salted water before freezing, the loss of dry matter was smaller after cooking than after blanching. A comparison of losses of the analysed constituents during the preparation for freezing shows that the degree of loss did not depend on the length of the thermal treatment. Despite taking longer than blanching, cooking before freezing did not bring about proportionately grater losses. Howard et al. [10] found that prolonged thermal processing, particularly the application of sterilization, brought about depolymerization of some polyphenols and an increase in the content of soluble polyphenols in carrot paste.

The nutritive value of a frozen product depends to a great extent on the retention of chemical constituents during of the preliminary treatment (blanching or cooking), freezing, refrigerated storage and preparation of the product for consumption [36]. The freezing of the investigated material and then its culinary treatment increased the loss of vitamin C, carotenoids and polyphenols and reduced the antioxidative activity (Fig. 1). Minimal changes occurred in the level of beta-carotene. Directly after freezing, different samples of carrot prepared for consumption contained 81-101% dry matter compared with the raw material; 46-48% vitamin C; 84-91% carotenoids; 91-96% beta-carotene and 85-87% polyphenols, while the antioxidative activity was reduced to 43-44%. Differences in comparison with the raw material were significant in the case of all characteristics apart from dry matter in frozen carrot heated in a microwave oven. In the above list small changes were noted in the content of carotenoids and beta-carotene. Some authors have even indicated increases in beta-carotene content in heated vegetables [9, 17]. However, the results reported by Gayrathri et al. [5] show the loss of beta-carotene varying from 16 to 76% in leafy vegetables and in finely chopped carrot and squash.

Decreases in the nutritive value of frozen vegetables during refrigerated storage have been noted by numerous authors: Czarniecka-Skubina [3] in Brussels sprouts; Favell [4] in pea and other vegetables; Lisiewska and Kmiecik [22] and Lisiewska et al. [24] in leafy vegetables. In the present work the refrigerated storage of carrot, irrespective of the method of preliminary processing (blanching or cooking) and the storage temperature applied, brought about gradual decreases in the level of the investigated indicators with the exception of dry matter. The different times of product evaluation, 0, 4, 8 and 12 months, were usually significant in the analogous samples with respect to carotenoids, beta-carotene and antioxidative activity, and after 8 months also in the case of vitamin C and polyphenols. In comparison with the product directly after freezing, after the 12-month period of storage the following decreases were found in the content of the analysed constituents: 22% in vitamin C; 16-41% in carotenoids; 15-25% in beta-carotene; 9-15% in polyphenols and 15-30% in antioxidative activity, depending on the analysed sample. After the longest storage period of 12 months, carrot prepared for consumption retained 36-45% vitamin C; 50-77% carotenoids; 70-80% beta-carotene; 73-78% polyphenols and 30-39% of antioxidative activity, depending on the analysed sample, while the content of dry matter changed within the range of 80-105%.

After 12-months storage, frozen carrot prepared for consumption using the method of freezing cooked carrot and then defrosting it and heating in a microwave oven, when compared with the product obtained using the traditional method, contained on average 29% more dry matter; 17% more vitamin C; 43% more carotenoids; 6% more beta-carotene and its antioxidative activity increased by 14%; the content of polyphenols was 2% less. In the case of dry matter, vitamin C, carotenoids, beta-carotene and antioxidative activity, the differences were statistically significant in the analogous samples.

After 1-year long storage at –20°C and –30°C, an analysis of the average content of the constituents in samples obtained by different methods showed better retention of the analysed constituents at the lower temperature. In frozen carrot stored at –30°C the retention of vitamin C was higher by 7%; of carotenoids and polyphenols by 8% and of beta-carotene and of antioxidative activity by 12%. This difference was significant in the analogous samples at a = 0.01 for carotenoids, beta-carotene and polyphenols and at a = 0.05 for the remaining constituents. A decrease in the storage temperature from –20°C to –25°C prolonged the half-life period of vitamin C in broccoli by almost 40% [18]; and lowering the storage temperature from –15°C to –20°C more than doubled this period in green pea [6]. Also in earlier studies on the refrigerated storage of many vegetable species conducted in the research unit I represent, better retention of nutritive compounds was found at lower temperatures. In some cases these studies revealed such differences only after several months of storage [22, 24].

For consumers the sensory quality of food is no less an important factor than its nutritive value. This is an important consideration for producers who introduce new frozen products since, as Roy et al. [33] observed, the freezing of vegetables could adversely affect such quality traits as flavour and consistency, this not being irrelevant to the commercial value of the products. The sensory evaluation of traditional and modified products concerned frozen carrot after 12 months of refrigerated storage (Table. 2) and after its preparation for consumption (Table 3). Frozen carrot showed good sensory quality and achieved total scores within the range 4.54-4.87 on a scale from 1 to 5. Frozen products stored at –30°C achieved a significantly higher score. Frozen goods produced using the modified method, i.e., from carrot cooked before freezing were of better quality; however, the differences did not exceed 0.2. The above results show that a lowering the storage temperature can also be a means of preserving the sensory qualities of frozen vegetables. Gomez and Sjoholm [8] also observed that the acclimatization of the raw material at a low temperature before processing could improve the consistency of frozen carrot. Frozen carrot prepared for consumption achieved total scores within the range 4.61-4.98, the parameters of evaluation being similar to those presented above in the case of frozen carrot evaluated before defrosting. The better quality of the product stored at –30°C, then defrosted and heated in a microwave oven was above all due to its better consistency and taste. Redmond et al. [32] point to good quality frozen products obtained from cooked carrot and also stress that during 12-months storage the sensory quality of such frozen products did not significantly change.

CONCLUSIONS

100 g of fresh carrot cut in small cubes contained: 13.02 g dry matter; 8.9 mg vitamin C; 11.9 mg carotenoids; 7.0 mg beta-carotene; 20.9 mg polyphenols, its antioxidative activity being 19.4% RSA. Cooking lowered the vitamin C content by 51%; carotenoids by 4%; beta-carotene by 3%; polyphenols by 18% and antioxidative activity by 54%. After 12-months frozen storage and preparation for consumption, all samples showed average decreases of 60% in vitamin C content; 66% in antioxidative activity; 37% in carotenoids content; and relatively small 24% decreases in beta-carotene and polyphenols in comparison with the raw material. Compared with the traditional product, carrot produced using the modified technology and prepared for consumption did not differ in the content of polyphenols; however, it contained significantly more vitamin C, carotenoids, beta-carotene and its antioxidative activity was higher. The lower storage temperature (–30°C) brought about a slightly better (7-12%) retention, of all the investigated traits. However, this difference was not always significant. The product obtained using the modified method and stored at a lower temperature had higher sensory quality, the differences not exceeding 0.2-0.3 on a 5-point scale.

REFERENCES

1. AOAC, (1984). Official methods of analysis. 14th Ed., Association of Official Analytical Chemists, Arlington, Virginia, USA.

2. Bahceci K.S., Serpen A., Gokmen V., Acar J., 2005. Study of lipooxygenase as indicator enzymes in green beans: change of enzyme activity, ascorbic acid and chlorophylls during frozen storage. J. Food Eng., 66, 187-192.

3. Czarniecka-Skubina E., 2002. Effect of the material form, storage and cooking methods on the quality of Brussels sprouts. Pol. J. Food Nutr. Sci., 11, 52, 75-82.

4. Favell D.J., 1998. A comparison of the vitamin C content of fresh and frozen vegetables. Food Chem., 62, 59-64.

5. Gayathri G.N., Platel K., Prakash J., Srinivasan K., 2004. Influence of antioxidant spices on the retention of beta-carotene in vegetables during domestic cooking processes. Food Chem., 84, 35-43.

6. Giannakourou M.C., Taoukis P.S., 2003. Kinetic modelling of vitamin C loss in frozen green vegetables under variable storage conditions. Food Chem., 83, 33-41.

7. Gil M.I., Ferreres F., Tomás-Barberán F.A., 1999. Effect of postharvest storage and processing on the antioxidant constituents (flavonoids and vitamin C) of fresh-cut spinach. J. Agric. Food Chem., 47, 2213-2217.

8. Gomez F.G., Sjoholm I., 2004. Applying biochemical and physiological principles in the industrial freezing of vegetables: a case study on carrots. Trends Food Sci. Technol., 15, 39-43.

9. Hart D.J., Scott K.J., 1995. Development and evaluation of an HPLC method for the analysis of carotenoids in foods, and the measurement of the carotenoid content of vegetables and fruits commonly consumed in the UK. Food Chem., 54, 101-111.

10. Howard L.A., Wong A.D., Perry A.K., Klein B.P., 1999. Beta-carotene and ascorbic acid retention in fresh and processed vegetables. J. Food Sci., 64, 929-936.

11. Ismail A., Lee W.Y., 2004. Influence of cooking practice on antioxidant properties and phenolic content of selected vegetables. Asia Pacific J. Clin. Nutr., 13 (Suppl), S162.

12. ISO 6658, 1985. Sensory analysis – Methodology – General guidance. International Organization for Standardization.

13. ISO 3972. 1991. Sensory analysis – Methodology – Method of investigating sensitivity of taste. International Organization for Standardization.

14. ISO 6558-2, 1992. Fruits, vegetables and derived products – Determination of carotene content – Part 2: Routine methods. International Organization for Standardization.

15. Kahkonen M.P., Hopia A.I., Vuorela H.J., Rauha J.-P., Pihlaja K., Kujala T.S., Heinonen M., 1999. Antioxidant activity of plant extracts containing phenolic compounds. J. Agric. Food Chem., 47, 3954-3962.

16. Kaur C., Kapoor H.C., 2002. Anti-oxidant activity and total phenolic content of some Asian vegetables. Int. J. Food Sci. Technol., 37, 153-161.

17. Khachik F., Goli M.B., Beecher G.R., Holden J., Lusby W.R., Tenorio M.D., Brrera M.R., 1992. Effect of food preparation on qualitative and quantitative distribution of major carotenoid constituents of tomatoes and several green vegetables. J. Agric. Food Chem., 40, 390-398

18. Klimczak J., Irzyniec Z., 2000. Wpływ temperatury na stabilnosc przechowalniczš mrożonych brokułów [Effect of temperature on the storage stability of broccoli]. Chłodnictwo, 10, 38-41 [in Polish].

19. Krzesiński W., Knaflewski M., 2002. The effect of solar radiation on beta-carotene and other carotenoid content in carrot roots. Folia Hort., 14/2, 25-33.

20. Lessin W.J., Catigani G.L., Schwartz S.J., 1997. Quantification of cis-trans isomers of provitamin A carotenoids in fresh and processed fruits and vegetables. J. Agric. Food Chem., 45, 3728-3732.

21. Lichtenthaler H.K., Buschmann C., 2001. Chlorophylls and carotenoids: measurement and characterization by UV-VIS spectroscopy. Curr. Protoc. in Food Anal. Chem., F4.3.1.-F4.3.8.

22. Lisiewska Z., Kmiecik W., 1997. Effects of freezing and storage on quality factors in Hamburg and leafy parsley. Food Chem., 60, 633-637.

23. Lisiewska Z., Słupski J., Zuchowicz E., 2003. Effect of temperature and storage period on the preservation of vitamin C, thiamine and riboflavin in frozen dill (Anethum graveolens L.). Elec. J. Pol. Agric. Univ., Food Sci. Technol. 6, 2; 07: http://www.ejpau.media.pl/series/volume6/issue2/food/art-07.html.

24. Lisiewska Z., Kmiecik W., Słupski J., 2003. Contents of chlorophylls and carotenoids in frozen dill: effect of usable part and pre-treatment on the content of chlorophylls and carotenoids in frozen dill (Anethum graveolens L.), depending on the time and temperature of storage. Food Chem., 84, 511-518.

25. McErlain L., Marson H., Ainsworth P., Burnett S.-A., 2001. Ascorbic acid loss in vegetables: adequacy of a hospital cook-chill system. Int. J. Food Sci. Nutr., 52, 205-211.

26. Nicoli M.C., Anese M., Parpinel M.T., Franceschi S., Lerici C.R., 1997. Loss and/or formation of antioxidants during food processing and storage. Cancer Lett., 114, 71-74.

27. Pekkarinen S.S., Stockman H., Swarz K., Heinonen M.I., Hopia A.I., 1999. Antioxidant activity and partitioning of phenolic acids in bulk and emulsified methyl linoleate. J. Agric. Food Chem., 47, 3036-3043.

28. Pellegrini N., Serafini M., Colombi B., Del Rio D., Salvatore S., Bianchi M., Brighenti F., 2003. Total antioxidant capacity of plant foods, beverages and oils consumed in Italy assessed by three different in vitro assays. J. Nutr., 133, 2812-2819.

29. Petersen M.A., 1993. Influence of sous vide processing, steaming and boiling on vitamin retention and sensory quality in broccoli florets. Z. Lebens.-Unters. Forsch., 197, 375-380.

30. Phillips K.M., Palmer J.K., 1991. Effect of freeze-drying and heating during analysis on dietary fiber in cooked and raw carrots. J. Agric. Food Chem., 39, 1216-1221.

31. Puupponen-Pimiä R., Häkkinen S.T., Aarni M., Suortti T., Lampi A.M., Eurola M., Piironen V., Nuutila A.M., Oksman-Caldentey K.M., 2003. Blanching and long-term freezing affect various bioactive compounds of vegetables in different ways. J. Sci. Food Agric., 83, 1389-1402.

32. Redmond G.A., Gormley T.R., Butler F., 2004. The effect of short- and long-term freeze-chilling on the quality of cooked green beans and carrots. Inn. Food Sci. Emerg. Technol., 5, 65-72.

33. Roy S.S., Taylor T.A., Kramer H.L., 2001. Textural and ultra-structural changes in carrot tissue as affected by blanching and freezing. J. Food Sci., 66, 176-180.

34. Sá da M.C., Rodriguez-Amaya D.B., 2004. Optimization of HPLC quantification of carotenoids in cooked green vegetables – Comparison of analytical and calculated data. J. Food Comp. Anal., 17, 37-51.

35. Singleton V.L., Orthofer R., Lamuela-Raventos R.M., 1999. Analysis of total phenols and other oxidation substrates and antioxidants by means of Folin-Ciocalteu reagent. Met. Enzymol., 299, 152-178.

36. Svanberg S.J.M., Nyman E.M.G.-L., Andersson R., Nilsson T.,1997. Effects of boiling and storage on dietary fiber and digestible carbohydrates in various cultivars of carrots. J. Sci. Food Agric., 73, 245-254.

37. Zapata S., Dufour J.P., 1992. Ascorbic, dehydroascorbic and isoascorbic acid simultaneous determinations by reverse phase ion interaction HPLC. J. Food Sci., 57, 506-511.

Accepted for print: 05.07.2006

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