Evaluation of spray-dried and freeze-dried red pitaya powder as a functional natural colorant in a model juice system

S.W. Chan1*, Y.J. Lee1, P. K. Lim1 and C.P. Tan2

1School of Biosciences, Taylors University, No. 1, Jalan Taylor's, 47500 Subang Jaya Selangor, Malaysia

2Department of Food Technology, Faculty of Food Science and Technology, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia

*Corresponding author:

Dr. Chan Sook Wah

School of Biosciences,

Taylors University,

No. 1, Jalan Taylor's,

47500 Subang Jaya Selangor,

Malaysia.

Tel: +603- 5629 5553

Fax: +603- 5629 5311

E-mail address: sookwah.chan@taylors.edu.my

Abstract

Red pitaya (Hylocereus polyrhizus) is an exotic fruit which belongs to the cactus family of Cactaceae. It is cultivated in many tropical countries such as Thailand, Cambodia, Vietnam, China, Australia and Malaysia. Pitaya fruit has recently drawn considerable attention due to its health beneficial claims such as antioxidant activity and the potential to reduce the risk of hypercholesterolemia and hypertension. Particularly, betacyanin in red pitaya is a potential source of natural colorant as an alternative to synthetic colorant. Consumption of synthetic colorants has been associated with many health problems such as liver and kidney damage. In this work, red pitaya powder was obtained via different processing methods (spray drying and freezing drying). Their physicohemical and antioxidant properties were compared and the stability of red pitaya betacyanin was analyzed by applying into a model juice system. As compared to spray-dried powder, freeze drying produced powder of higher yield with significantly (p < 0.05) lower moisture content, water activity; significantly (p < 0.05) higher bulk density, tapped density and particle size; better flowability and lower cohesiveness. However, betacyanin content and antioxidant activities of both spray-dried and freeze-dried red pitaya powder were comparable. Significant (p < 0.05) changes in betacyanin were observed during 4 weeks storage study. Betacyanin was best preserved in model juice at storage temperature of 4 C, but completely degraded at room temperature and 40 C after one week storage. With these findings, it can be concluded that betacyanin from red pitaya powder could be a potential natural colorant for chilled food products.

Keywords: red pitaya, spray drying, freeze drying, betacyanin, natural colorant

Introduction

Hylocereus polyrhizus or better known as red pitaya fruit is originated from America and belongs to cactus family and plant order of Caryophyllales (Phebe & Chew 2009). This species have its peel and flesh in purple-red color. The flesh contains small black seeds which distributed evenly and its texture is delicate and juicy (Jamilah et al. 2011). Red pitaya fruit is cultivated worldwide in Malaysia, Bangladesh, China, Vietnam, Taiwan, Thailand, Australia, Israel and others (Ee et al. 2014a; Jamilah et al. 2011). In Malaysia, red pitaya fruit is consumed as fresh fruit as well as commercially manufactured to produce juices or jams products. The deep purple color of red pitaya flesh is contributed by the betacyanin pigment. It is reported that betacyanin has antioxidant properties which making it suitable to be used as food colorant and serves as functional ingredient in food product (Lee, Wu & Siow 2013).

One of the factors that affect the customers food choice is color. Synthetic colorant has been applied for ages in order to improve and enhance the food appearance. In Malaysia, 14 synthetic colorants have been permitted to be applied as coloring substance in food (Food Act 1983 (Act 281) & Regulations (as at 1st March 2014). However, due to the reported allergic and intolerance cases after consumption of synthetic colorant and the potential health hazard, natural colorant has recently gained market attention in order to replace synthetic colorant in the food application. According to Food Act 1983 (Act 281) & Regulations (2014), beet red is one of the permitted natural coloring substances to be used in food. Beet red, synonym to beetroot red is a coloring substances extracted from red beets roots. It is composed of mainly betalain pigments, purple-red betacyanins of which account for 75-95% of betanin (FAO 2012). Despite the rich betacyanin content in beet red, red pitaya betalain is more preferable due to the presence of geosmine and pyrazine in beet root which contribute to earthy taste (Chik et al. 2011).

Common methods suitable used to dry heat labile pigment are spray drying and freeze drying. Spray drying converts fluid materials into dry solid particles by atomizing the feed fluid into a hot gas medium to obtain powder instantaneously (Phisut 2012). Spray drying process is commercially used to produce fruit juice powders of good quality and facilitate easier transportation and storage. Freeze-drying refers to lyophilization is a drying process where the water is frozen at very low temperature and subsequently transformed from solid state into the vapor state through sublimation under low pressure. It became one of the best options for the production of heat-sensitive materials because this process does not involve heat (Ciurzyska & Lenart 2011). Spray drying is more commonly used in the production of powder food colorant as it is more economical. However, it might increase loss of antioxidant content as this process involves high temperature. Freeze dried powder often give better properties but it involves high operating cost (Laokuldilok & Kanha 2015; Lee, Wu & Siow 2013). There are various studies reported on the physiochemical properties and antioxidant properties of red pitaya fruit as well as production of spray dried red pitaya powder (Ee et al. 2014a, 2014b; Lee, Wu & Siow 2013; Liaotrakoon et al. 2012; Woo et al. 2011). However, there is limited research on the production of freeze dried red pitaya powder and the comparison of physiochemical properties between spray dried and freeze dried red pitaya powder. Besides, study on the stability of red pitaya betacyanin in the food model system is very scarce. Hence, this research is aimed to compare the physiochemical and antioxidant properties of red pitaya powder produced by spray drying and freeze drying. The effects of temperature and light on the stability of betacyanin of spray dried and freeze dried red pitaya powder in a model juice system were analyzed.

Materials and Methods

Raw materials

All fresh red pitaya fruits used were purchased from fruits shop Eats More Fruits located in Kota Kemuning, Shah Alam, Selangor.

Materials, chemicals, and reagents

Maltodextrin with dextrose equivalent (DE) 10% - 13% was obtained from V.I.S Foodtech Ingredient Supplies Sdn. Bhd., Kepong, Kuala Lumpur. Citric acid anhydrous was purchased from Bake with Yen Sdn. Bhd., Puchong, Selangor. Sugar (coarse sugar) was obtained from Central Sugars Refinery Sdn. Bhd., Shah Alam, Selangor. Methanol, trifluorocetic acid (TFA), acetonitrile, Folin-Ciocalteus (FC) reagent, sodium carbonate anhydrous, denatured ethanol, 1M sodium hydroxide, di-sodium hydrogen phosphate and iron (III) chloride were supplied by Merck, Germany. Sodium nitrite, aluminium chloride-6-hydrate, trichloroacetic acid and potassium ferricyanide were obtained from Bendosen Laboratory Chemicals, Norway. Gallic acid, catechin and betanin (red beet extract diluted with dextrin) were procured from Sigma-Aldrich, USA. Potassium di-hydrogen phosphate was obtained from Hamburg Chemical, Germany. All chemicals and reagents used were of analytical grade or high performance liquid chromatography (HPLC) grade. Distilled water was used throughout the analyses.

Preparation of red pitaya juice

Peel of red pitaya fruits was removed and the flesh was cut into smaller pieces. The flesh was then blended using blender to obtain the puree. The puree was filtered 3 times using muslin cloth to remove seeds before subjected to spray drying and freeze drying.

Spray drying of red pitaya juice

The filtered juice was mixed with distilled water at ratio of 1:2 (150 g of red pitaya juice mixed with 300 g of distilled water). 15% (w/w) of maltodextrin (67.5 g) was added to the red pitaya juice mixture and homogenized using blender. The red pitaya juice mixture was then spray dried using laboratory scale spray dryer (Lab-Plant SD-06, Labplant UK Ltd., UK). The spray drier was equipped with 0.5 mm spray nozzle (215 mm OD 500 mm long). The pump speed of spray dryer was maintained at 11.58 mL/min, inlet temperature at 140 C, fan setting at 4.3 m/s and pressure at 2 bars. The powder obtained was stored in Schott bottle at room temperature until further analysis.

Freeze drying of red pitaya juice

The filtered juice was mixed with same amount of maltodextrin as added into spray dried red pitaya juice (150 g of red pitaya juice mixed with 67.5 g of maltodextrin) and homogenized using blender. The red pitaya juice mixture was then poured into Schott bottle and frozen in ultra-low temperature freezer (Model: DW-86L388, Haier Group, China) at 80 C for overnight. The red pitaya juice mixture was then freeze dried using benchtop freeze dryer (Model: FreeZone 4.5L, Labconco, USA) at 50 C under pressure below 0.110 mBar for 55 hours. The dried red pitaya product was then ground using dry mill. The powder obtained was stored in Schott bottle at room temperature until further analysis.

Yield

The yield of red pitaya powder was calculated using equation below:

Yield (%) =

Solid content of juice is the dry weight of juice.

Moisture content

The moisture content of red pitaya powder was determined using