THE CONTENT OF SOME CHEMICAL COMPOUNDS IN RED CABBAGE (BRASSICA OLERACEA L.VAR. CAPITATA F. RUBRA) AFTER HARVEST AND LONG-TERM STORAGE

Maria Tendaj, Krzysztof Sawicki, Barbara Mysiak
Department of Vegetable Crops and Medicinal Plants, University of Life Sciences in Lublin

ABSTRACT

The aim of the present study was to evaluate some chemical components in heads of some red cabbage cultivars ('Huzaro F1', 'Kalibos','Langedijker Polana', 'Rodeo F1', 'Roxy F1', 'Zelox F1') immediately after harvest and after 5 months of storage at a temperature of 0–1°C. The study determined the content of total and reducing sugars, crude fibre, anthocyanins, flavonoids expressed as quercetin equivalents, phenolic acids expressed as caffeic acid equivalents,  nitrates (V) and (III), and the level of antioxidant activity using DPPH. The content of individual chemical components greatly varied depending on the cultivar and the time from harvest. Immediately after harvest, heads of the cultivars 'Zelox F1'and 'Langedijker Polana' contained the highest amount of total sugars, while' Rodeo F1' and 'Zelox F1' had the highest content of reducing sugars. Long-term storage of heads had a significant effect on increasing the anthocyanin content and slightly increasing the content of flavonoids and phenolic acids. The study also found a significant decrease in the content of nitrates (V) and an increase in the content of nitrates (III). In spite of an increase in the content of some polyphenolic compounds after 5 months of storage of red cabbage heads, antioxidant activity measured as a percentage of DPPH radical reduction did not increase.

Key words: red cabbage, storage, sugars, crude fibre, anthocyanins, flavonoids, phenolic acids, nitrates.

INTRODUCTION

Red cabbage is a vegetable that is consumed in Poland mainly during the autumn and winter season when it replaces less durable vegetable species – attractive for consumption in spring and summer. Compared to white cabbage, it is characterized by a higher content of health–enhancing components, especially those exhibiting antioxidative activity (Mazza and Miniami, 1993; Bridle and Timberlake, 1997; Leja et al. 2010).

An important advantage of red cabbage is the fact that it is generally consumed raw, which permits the preservation of vitamins sensitive to thermal processing and some polyphenolic compounds. Red cabbage cultivars used for cultivation – usually hybrid ones, need to be evaluated in terms of their usefulness for cultivation, indicating the optimal date of sowing and storage life, as well as in terms of their biological value.

Analysis of the content of nutritional and biologically active components in red cabbage heads immediately after harvest and after long–term storage was an important issue for the evaluation of the quality of this cabbage as a vegetable that is a product available for consumption primarily during the autumn and winter season.

MATERIALS AND METHODS

Material for laboratory analysis (red cabbage heads) was obtained from a field experiment carried out in the period 2006–2008 at the Felin Experimental Farm of the University of Life Sciences in Lublin. Red cabbage was grown from seedlings produced in seedling bed. Preplant fertilization (Azofoska in dose 10 kg 100 m^–2) was introduced one week before seedlings planting. Top dressing fertilization in the amount of 5 kg N  100 m^–2 (in the form of ammonium nitrogen) was applied four weeks after planting date (Tendaj and Sawicki, 2012).

Red cabbage heads were sampled for chemical analysis from marketable yield obtained from this experiment. The determination of chemical components was performed immediately after harvest of cabbage heads – in 2nd decade of October during the successive years of the study (2006, 2007, 2008), and after a 5–month period of their storage, i.e. in the middle of March (2007, 2008, 2009).

The study included the following factors:

• cultivar: ‘Huzaro F1’, ‘Kalibos’, ‘Langedijker Polana ‘, ‘Rodeo F1’, ‘Roxy F1’, ‘Zelox F1’;
• timing of laboratory analysis (immediately after harvest, after 5 months of storage in a cold storage room at a temperature of 0–10C and with approximately 92–95% RH).

Some basic chemical components and biologically active components were determined in red cabbage heads. Dry matter was determined by the oven–dry method (PN–90/A–75101/03); total and reducing sugars by Luff–Schoorl titration (PN–90/A–75101/037); crude fibre by Henneberg and Stohmann’s method modified by Henneberg (Strzelecka et al. 1987); anthocyanins and flavonoids spectrophotometrically according to Christ and Muller (Strzelecka et al. 1987; Polish Pharmacopoeia V, 1999); total phenolic acids expressed as caffeic acid equivalents using Arnov’s method (Polish Pharmacopoeia VI, 2002); nitrates (V) and nitrates (III) reflectometrically using Merck’s RQFlex reflectometer; antioxidant activity (DPPH inhibition, %) following the method described by Yen and Chen (1995), whereas the percentage of inhibition was calculated in accordance with a formula given by Rossi et al. (2003).

RESULTS AND DISCUSSION

Compared to white cabbage, red cabbage is characterized by a higher content of nutritional and biologically active components that determine its high dietetic properties (Singh et al. 2006; Leja et al. 2010; Shama et al. 2012).

Dry matter content. The dry matter content in red cabbage was on average 8.05% and varied significantly depending on the cultivar. Long–term storage of heads did not affect significantly their size (Tab. 1). The cultivar ‘Huzaro F1’ was marked by the significantly highest dry matter content compared to the other cultivars (on average 8.86%), whereas heads of cv. ‘Kalibos’, which have a conical shape, were characterized by the lowest dry matter content (on average 7.18%). After 5 months of storage, some cultivars were found to show a significant increase in dry matter (‘Langendijker Polana’), while some other ones a significant reduction (‘Huzaro F1’). According to the studies of other authors, dry matter of both red and white cabbage can significantly vary depending on the cultivar, cultivation method, and post–harvest treatment (Cebula et al. 2006; Franczuk et al. 2009).

Total and reducing sugars. On average, red cabbage of the studied cultivars contained 5.32% of total sugars and 0.85% of reducing sugars (Tab. 1). The study showed that the cultivar and timing of analysis had a significant effect on the content of these sugars. Freshly harvested heads of cv. ‘Zelox F1’ were characterized by a particularly high content of total sugars, while heads of the cultivars ‘Huzaro F1’ and ‘Roxy F1’ showed the significantly lowest content (on average, it was 7.65 and 7.58% FW). Immediately after harvest, heads of cvs. ‘Rodeo F1’ and ‘Zelox F1’ contained the significantly highest amount of reducing sugars (on average 0.75% FW). Irrespective of the cultivar, after 5 months of storage the study recorded a significant decrease in total sugar content (on average by 5.35% FW) and a significant increase in the content of reducing sugars (on average by 0.54% FW). These results corroborate earlier studies of Lippert and Köhl (2003), Cebula et al. (2006) as well as Jabłońska–Ceglarek et al. (2006). The studies of these authors related to white cabbage in which the content of these sugars was close to that in red cabbage.

Crude fibre. Dietary fibre content in cabbage vegetables varies depending on the species and variety. According toe Elkner and Horbowicz (1996), medium late and late cultivars contain more dietary fibre compared to early varieties. Crude fibre is an essential part of dietary fibre, the content of this component can therefore be an important element of the dietary value of red cabbage. The study showed that the average crude fibre content in the studied cultivars was 1.09% FW and it was significantly dependent on the cultivar. Long–term storage of heads did not have a significant effect on the content of this component. The research of Gyurova et al. (2007) corroborates the results obtained in the present study. These authors report that fibre content in red cabbage ranges 1.24–1.50% FW, depending on the cultivar.

Anthocyanins. Red cabbage belongs to vegetables with a high content of anthocyanins, among which cyanidin is the main pigment (Piccaglia et al. 2002; Grzesiuk et al. 2007; Shama et al. 2012). Because anthocyanins are pigments showing very strong antioxidative properties (Wu et al. 2006; Pliszka et al. 2007, Castaneda – Ovando et al. 2009), therefore red cabbage has a high dietetic and health value.

The content of anthocyanins in the red cabbage cultivars under study significantly varied and averaged 172.39 mg 100 g^–1. The cultivar ‘Huzaro F1’ was characterized by the significantly highest content of this constituent (its average content immediately after harvest was 234.67 mg  100 g^–1 FW, while after storage it was 275.43 mg  100 g^–1 FW). Heads of cv. ‘Kalibos’ contained the lowest amount of anthocyanins – more than twice less compared to the other cultivars.

Long–term storage of heads resulted in a significant increase in the content of this component, except for the cultivar ‘Kalibos’ (Tab. 2). Compared to the results of the research of other authors, the determined anthocyanin content was comparable (Piccaglia et al. 2002) or slightly higher (Pliszka et al. 2007; Biesiada et al. 2010). Other studies show a much higher content of anthocyanins in red cabbage, even reaching a level of 756.0–773.5 mg 100 g^–1 FW  (Scalzo et al. 2008).

Flavonoids. Red cabbage belongs to flavonoid–rich vegetables (Marinova et al. 2005; Olajire and Azees, 2011) and for this reason, among others, it is considered to be an important source of antioxidants ( Leja et al. 2010).

The flavonoid content expressed as quercetin equivalents in the red cabbage cultivars under study was on average 17.8 mg 100 g^–1 FW. Both the cultivar and long–term storage of heads had a significant effect on the content of this component. The highest flavonoid content was found in cv. ‘Huzaro F1’ (on average 21.61 mg 100 g^–1 FW), while the lowest one in cvs. ‘Kalibos’ and ‘Langendijker Polana’ (on average 15.14–16.69 mg 100 g^–1). In the study of red cabbage conducted by Leja et al. (2010), the content of flavonols, which include quercetin, was much higher than in the present study and a significant decrease in their content was found after 4 months of storage. In the cultivars investigated in the present study, a significant decrease in flavonoid content after 5 months of storage of heads was found only in ‘Huzaro F1’ and ‘Zelox F1’ (Tab. 2).

Phenolic acids. The content of phenolic acids in plants depends not only on the species and variety, but also on the stage of maturity as well as on growing and storage conditions (Mattila  and  Hellstron,  2007).

In the red cabbage cultivars studied, the average phenolic acid content expressed as caffeic acid equivalents was 0.063 mg 100 g^–1 FW (Tab. 2). The cultivar ‘Huzaro F1’ was characterized by the significantly highest content of this component, whereas cv. ‘Kalibos’ was marked by the lowest content. According to Singh et al. (2006), red cabbage can contain 18.7 mg kg^–1 FW of phenolic acids expressed as chlorogenic acid equivalents. On the other hand, Malien–Aubert et al. (2001) report that the phenolic acid content in red cabbage can be on average 105.4 mg g^–1 DW. In the study of Lin et al. (2008), the phenolic acid content in red cabbage expressed as gallic acid equivalents was on average 0.2–5.1 mg g^–1 DW.

After a 5–month storage period, the total phenolic acid content significantly increased in the red cabbage cultivars studied. However, this was not demonstrated in all cultivars. The cultivars ‘Huzaro F1’, ‘Kalibos’, and ‘Rodeo F1’ were found to show a decrease in the content of this component. The study of Leja et al. (2010) found a significant decrease in the content of phenolic compounds after 4 months of storage of red cabbage, but this was not found in white cabbage. On this basis it can be concluded that the large variance in the results on the content of phenolic compounds, including phenolic acids, can arise from many factors relating to the genetic properties of a cultivar, cultivation conditions, and the analytical method.

Nitrates. Cabbage grown under Polish conditions does not exhibit a high propensity to accumulate nitrates. This is shown in the research of Biesiada et al. (2010), Gajewski and Radzanowska (2004) as well as Gajewski et al. (2009). Mor et al. (2010) report that the content of nitrates (V) in white cabbage is on average 510 mg NO3ˉ kg^–1 FW and depends on many factors:  growing environment, climate, and cultivar.

The content of nitrates (V) and nitrates (III) in the red cabbage cultivars under study  was on average 305.7 and 3.49 mg NO3^– kg^–1 FW. This is below to level in the official polish standard (PN–92/A–75112). After storage, the content of nitrates (V) decreased significantly, whereas the content of nitrates (III) increased significantly. The following cultivars belonged to those that showed a slightly higher propensity to accumulate nitrates: ‘Huzaro F1’, ‘Roxy F1’, and ‘Zelox F1’ (Tab. 3). Cv. ‘Kalibos’ was characterized by a very low content of nitrates, which is its great advantage.

Antioxidant activity. Antioxidant activity in the red cabbage cultivars under study was evaluated by the method using DPPH; it was on average 20.98% and was significantly dependent on the cultivar and long–term storage. Cv. ‘Kalibos’ showed by far the lowest antioxidant activity (on average a 9.46% reduction of DPPH radicals). This corresponded to the level of reduction shown in freshly harvested and stored white cabbage in the study of Leja et al. (2010). In the other red cabbage cultivars, antioxidant activity was at least twice higher.

Both the present study and the studies of other authors (Pliszka et al. 2007; Biesiada et al. 2010; Leja et al. 2010; Olajire and Azees, 2011) show high antioxidant activity of red cabbage, in particular immediately after harvest.

CONCLUSIONS

1. The content of basic chemical components (sugars, crude fibre, anthocyanins, flavonoids, phenolic acids) in red cabbage heads can greatly vary depending on the cultivar and the time from harvest to the end of long–term storage. Long–term storage has an effect on decreasing the total sugar content, simultaneously increasing the content of reducing sugars and crude fibre. After long–term storage, one can expect a significant increase in the content of anthocyanins and nitrates (III) as well as in the flavonoid content in some cultivars.
2. Red cabbage of the studied cultivars proved to be a vegetable rich in polyphenolic compounds and showing a low propensity to accumulate nitrates. On this basis it can be stated that it is a valuable vegetable both immediately after harvest and after long–term storage.
3. Long–term (five–month) storage of heads can cause in red cabbage an increase in the content of compounds considered to be natural antioxidants (anthocyanins, flavonoids, and phenolic acids), which did not, however, have a significant effect on increasing the level of antioxidant activity measured as the percentage of DPPH inhibition.

REFERENCES

Accepted for print: 12.04.2013

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