The effect of pH treatment and refrigerated storage on natural colourant preparations (betacyanins) from red pitahaya and their potential application in yoghurt Ashwini Gengatharan, Gary A. Dykes, Wee-Sim Choo * School of Science, Monash University Malaysia, Jalan Lagoon Selatan, 47500 Bandar Sunway, Selangor, Malaysia article info Article history: Received 10 August 2016 Received in revised form 8 March 2017 Accepted 8 March 2017 Available online 11 March 2017 Keywords: Antioxidant Colour Lactic acid bacteria Red beet Red dragon fruit abstract The present study investigated the effects of pH (pH 3, 4, 5 and 6) treatment and refrigerated storage at 4  C on the stability of colourant preparations from red pitahaya and compared to a commercial col- ourant preparations from red beet, E-162. The potential of using colourant preparations from red pit- ahaya in yoghurt and compared to E-162 was also investigated. Immediately after pH treatment, the highest percentage of reduction of betacyanin was observed at pH 3. The loss of betacyanin content in yoghurts containing colourant preparations from red pitahaya and E-162 over 14-days of refrigerated storage was 1.0± 0% and 1.6± 0.1%, respectively. Syneresis in yoghurt containing colourant preparations from red pitahaya and E-162 were lower than that of plain yoghurt. The addition of betacyanins from red pitahaya or E-162 increased the free radical scavenging activity in yoghurts. The total microbial counts of Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus in yoghurts containing colourant preparations from red pitahaya and E-162 were in the 10 8 e10 9 CFU/mL range. The colour acceptability of yoghurt containing colourant preparation from red pitahaya was similar with E-162 and a commercial strawberry flavoured yoghurt suggesting its potential application as a natural functional colourant. © 2017 Elsevier Ltd. All rights reserved. 1. Introduction Colour is an important quality attribute in the food industries whereby it influences consumer's choice and preference. Synthetic colourants such as Tartrazine (E102) and Sudan red were widely used in the past (Ahlstr€ om, Eskilsson, & Bj€ orklund, 2005) but there is an emerging demand for natural pigments to be used as food colourants due to health hazard risks posed by synthetic colour- ants. Betalains specifically betacyanins, are one of the five most widely used colourants in the food industry. However, betacyanins are least studied as compared to the other natural pigment classes such as carotenoids, anthocyanins, chlorophyll and flavonoids. Not only betalains show good tinctorial strength to be used as food colourants but also possess various pharmacological properties (Gengatharan, Dykes, & Choo, 2015). The commercial betalain preparations obtained from red beetroot are listed on food labels as E-162 and is used in a variety of processed foods such as dairy products, frozen desserts and meat (Stintzing & Carle, 2007). However, the typical earthy flavour caused by geosmin (Clydesdale, 1993) may deter the commercial use of E-162 in food application. Furthermore, the risk of carry-over earth bound microorganism from the raw material red beetroot is an important consideration (Chattopadhyay, Chatterjee, & Sen, 2008). Therefore, it is worth- while to search for and develop alternative sources of betacyanins for the potential application as natural colourants. Cactus crops such as red pitahaya or red dragon fruit (Hylocereus polyrhizus) are widely grown across Asia, Israel and Latin America. They are well known for their deep purple colour pulp due to the presence of the red-violet betacyanins (Stintzing & Carle, 2004). They are also devoid of geosmins and the yellow coloured betalains (betaxanthins) which are abundantly present in E-162. Though there are abundant studies on application of anthocyanins as nat- ural colourants in various model food systems, the studies on the use of betalains specifically betacyanins as colourants in model food systems or for food product development are limited. These studies are crucial to demonstrate the potential use of betacyanins as natural food colourants. In a previous study, we demonstrated the effects of temperature treatment on the betacyanin content and colour stability of betacyanins from red pitahaya as well as a * Corresponding author. E-mail address: choo.wee.sim@monash.edu (W.-S. Choo). Contents lists available at ScienceDirect LWT - Food Science and Technology journal homepage: www.elsevier.com/locate/lwt http://dx.doi.org/10.1016/j.lwt.2017.03.014 0023-6438/© 2017 Elsevier Ltd. All rights reserved. LWT - Food Science and Technology 80 (2017) 437e445