Stability of the Spray-Dried Pigment of Red Dragon Fruit

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This study evaluated the effect of organic acid additives, temperature and illumination on the color retention of the spray-dried red violet pigment of red dragon ...
PHILIPP AGRIC SCIENTIST Vol. 94 No. 3, 264-269 September 2011

ISSN 0031-7454

Stability of the Spray-Dried Pigment of Red Dragon Fruit [Hylocereus polyrhizus (Weber) Britton and Rose] as a Function of Organic Acid Additives and Storage Conditions K. K. Woo1, *, F. N. Fanny Wong2, H. S. Catherine Chua2 and P. Y. Tang3 1

Department of Chemical Engineering, 2Department of Bioscience and Chemistry, 3Department of Biomedical Engineering, Faculty of Engineering and Science, Universiti Tunku Abdul Rahman, Jalan Genting Kelang, 53300 Setapak, Kuala Lumpur, Malaysia * Author for correspondence; e-mail: [email protected]; Tel: +603 410 79802; Fax: +603 410 79803 This study evaluated the effect of organic acid additives, temperature and illumination on the color retention of the spray-dried red violet pigment of red dragon fruit (Hylocereus polyrhizus [Weber] Britton and Rose) during storage. The pigment was extracted using distilled water at a ratio of 1:1. It was then filtered through a press filter to remove unwanted juice matrix. The collected pigment was subsequently treated with either 0.1% (w/v) ascorbic acid or 0.1% (w/v) citric acid prior to spray-drying procedure. Pigment without additives was used as the control. The resulting spray-dried product was stored at 25 °C and 4 °C, with or without illumination, and at -20 °C without illumination. Quantitative color analysis (L*, C* and h° value) of the spray-dried pigment was carried out within 6 wk. Color regeneration (approximately 20–40% of the initial) was observed at the end of week 5 in all control samples stored in the dark (25 °C, 4 °C and -20 °C). Quantitative determination showed that the h° value shifted from blue (226) to red zone (345) after 6 wk. Increase in C* values was observed in most of the treatments. However, L* did not show significant (P>0.05) changes throughout the storage period. Ascorbic acid and citric acid did not delay color degradation.

Key Words: betalain, betacyanin, natural color, red dragon fruit, spray-dried

INTRODUCTION Synthetic or artificial colorants have been applied to enhance food appearance since the early 20th century (Downham and Collins 2000). About 12 synthetic colorants have been approved for use on food in Japan, 7 in the USA and 16 in the European Union (Shrestha et al. 2006). However, several drawbacks of synthetic colorants such as allergenic and intolerance reactions have been reported (Berzas et al. 1995). Some synthetic food colorants derived from minerals may be hazardous to human health (Bilyk 1979). For example, the use of lead chromate and copper sulphate as pigment in candies and sauerkraut has resulted in fatality due to crosscontamination of some carcinogenic substances such as arsenic and other toxic impurities (Delgado-Vargas and Paredes-Lopez 2002). Thus, natural colorants from plant sources are receiving growing interest from both food manufacturers and consumers in order to replace synthetic colorants (Leathers et al. 1992). However, natural pigments are generally less stable and incur higher production cost compared with synthetic colorants (von Elbe and Goldman 2000).

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Some major categories of plant pigments are betalain, anthocyanins and other flavonoids, carotenoids and chlorophylls. Betalain is one of the five most widely used colorants in the food industry (Jackman and Smith 1996). The pigment is water-soluble and can be classified into two main groups, betacyanin (responsible for the red-violet color) and betaxanthin (responsible for the yellow-orange color) (Stract et al. 2003). Betalains are commercially used as food colorant. Unlike synthetic coloring agents, most of the natural colorants are easily degraded, heat-labile and low in stability due to their natural structure (Jackman and Smith 1996). Besides, betalains possess antioxidation properties which are prone to oxidation (Georgiev et al. 2010). Thus, prevention of oxidation which occurs during extraction and storage is crucial. In general, pH, water activity (aw), temperature, oxygen and light affect the stability of betalains (Herbach et al. 2006a). Therefore, natural colorants will lose their chromatic characteristics during processing, especially during extraction, purification and storage (Escribano et al. 1998; Kanner et al. 2001; Butera et al. 2002; Cai and Corke 2000). Artificial coloring agents are yet to be fully replaced by natural pigments because they have greater resistance and stability (She et al. 1992). Thus, stability improvement by employing The Philippine Agricultural Scientist Vol. 94 No.3 (September 2011)

Color Retention in the Spray-Dried Pigment of Red Dragon Fruit

suitable additives may expand the applicability of natural food colorants (Herbach et al. 2006a). Physical methods in removing moisture from pigment sources or using coating materials may as well provide resistance toward factors that contribute to color changes. For example, freeze-drying and spray-drying procedures that incorporate coating agents may reduce aw and provide safeguard against detrimental environmental factors. Common coating materials such as maltodextrin are used during spray-drying and freeze-drying processes, and are frequently applied as encapsulation agents on pigments to act as a wall barrier to oxidation (Stephane et al. 1997). Freeze-drying is suitable for heat-labile pigments in which color degradation due to heat can be minimized. However, the procedure is far more expensive compared with spray-drying. Microencapsulation using coating material to entrap pigment during spray-drying is an economical method for preventing changes in color (Cai and Corke 2000). Spray-drying method involves a few stages: dispersion, homogenization and atomization (Ré 2006; Desai and Park 2005; Shahidi and Han 1993; Stephane et al. 1997). These procedures are able to produce pigment in the form of particles, granules or agglomerates which are coated with a protective coating agent. Obón et al. (2009) successfully applied spraydrying technique in producing red purple food colorant from Opuntia stricta fruit juice. In the study, glucose syrup (Glucidex 29) was added and a 58% yield was obtained. Spray-dried beet root betacyanin incorporated with maltodextrin had 90% color retention (Azeredo et al. 2007). In this study, the betalain pigment from the red dragon fruit (Hylocereus polyrhizus [Weber] Britton & Rose) was extracted and the effect of spray-drying procedure on the color retention of the pigment under different storage conditions was determined. The effects of various additives, light and temperature on the spraydried product were monitored.

MATERIALS AND METHODS Red dragon fruit (Hylocereus polyrhizus [Weber] Britton & Rose) was purchased from the local wet market. All fruits came from the same batch and were kept at 4 °C before use. All reagents used in the experiment were of analytical grade. The experiment was conducted at the Universiti Tunku Abdul Rahman, Kuala Lumpur, Malaysia between 2008 and 2009. Extraction of Betalain Pigment The red dragon fruits were peeled and the pulp was cut into pieces. The fruits were then blended with a blender and filtered through a filter press (Lotus Scientific, The Philippine Agricultural Scientist Vol. 94 No.3 (September 2011)

K. K. Woo et al.

Malaysia) until turbidity reached 362 NTU; a portable turbidimeter (Eutech Instruments, Singapore) was used to measure turbidity. Distilled water was added to the blended juice at a ratio of 1:1 before filtration. The collected pigment was stored at -20 °C for further analysis. Treatments The pigment was treated with either 0.1% (w/v) ascorbic acid or 0.1% (w/v) citric acid. Pigment without any additive was used as control. The pH of the samples was adjusted to 5.0 using HCl or NaOH prior to spray-drying procedure. Experiment with the same treatment was conducted at the same time. Spray-Drying of Red Dragon Fruit Pigment A total of 48% (w/v) 15 DE maltodextrin was added to the pigment before it was fed into the spray-dryer (LS32042, Lotus Scientific, Malaysia). The inlet temperature was adjusted to 230 °C. The collected samples were then stored with or without illumination at 25 °C and 4 °C, and without illumination at -20 °C. Spectrophotometric Analysis Color retention of betalain was monitored weekly up to 5 wk using UV/Vis spectrophotometer (Genesys 20, Thermo Scientific, USA). A total of 20 mg sample from each storage condition was diluted using 2 mL distilled water. The absorbance values were measured at 538 nm. Quantitative Color Analysis The spectrophotometric measurements were performed with a double beam UV/Vis spectrometer (Lambda 35 UV/Vis Spectrum, Perkin- Elmer, USA) equipped with UV WinLab Version 2.85.04 and color software (Advanced Spectroscopy Software Package). A total of 20 mg spray-dried pigment from each treatment was diluted with 2 mL of distilled water. Subsequently, visible spectra (380–780 nm) were recorded in 1-cm path length cuvettes. Results were expressed as lightness (L*), chroma (C*) and hue (h˚). L* values ranged from 0 to 100 (0 = black to 100 = white). C* represents the saturation or purity of the hue. h˚ is the angle of the 360° color wheel, with 0°, 90°, 180° and 270° corresponding to the red, yellow, green and blue hues, respectively. All samples were measured at 3-wk interval for 6 wk. Statistical Analysis All measurements were carried out in triplicate and statistical analysis was conducted using two-way analysis of variance (ANOVA) (SPSS version 15.0 for Windows R program, SPSS Inc.).

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