Recent trends in methods used to obtain natural food colorants by freeze-drying
Introduction
Food colorants are increasingly used in the food industry(Aberoumand, 2011; Coronel-Aguilera & San Martín-González, 2015; Fernandez, Torres-Giner, & Lagaron, 2009; Houghton & Hendry, 2012; Shipp & Abdel-Aal, 2010). Despite the reported immune suppression or intolerance reactions after consumption of synthetic food colorants (Feketea & Tsabouri, 2017), the usage of natural food colorants has been increasing worldwide (Agrawal, 2013; Low, Tan, Lim, & Chan, 2017; Mahdavi, Jafari, Ghorbani, & Assadpoor, 2014; Obón et al., 2009).
Natural colorants from plant sources enjoy more interest as they impart positive effects on human health (Konczak & Zhang, 2004), and they can also be used as functional additives (Cevallos-Casals, Byrne, Okie, & Cisneros-Zevallos, 2006; Dziki et al., 2015; Moreno, García-Viguera, Gil, & Gil-Izquierdo, 2008; Nontasan, Moongngarm, & Deeseenthum, 2012). However, natural pigments have limited usage due to their lower stability and greater interactions with other food ingredients (Castellar, Obón, Alacid, & Fernández-López, 2003; Idham, Muhamad, & Sarmidi, 2012; Rein & Heinonen, 2004; Sigurdson, Tang, & Giusti, 2017; Wrolstad, Durst, & Lee, 2005); therefore, it is necessary to choose appropriate methods to obtain an effective product.
Much research has been published related to the extraction of natural food colorants (Caldas-Cueva et al., 2016; Gorbunova, Bannikova, Evteev, Evdokimov, & Kasapis, 2018; Ranjan Sarkar, Das, Bhagawati, & Ch Goswami, 2012; Sivakumar, Vijaeeswarri, & Anna, 2011). Conventional technologies of extraction often use high temperatures and toxic solvents (Barba, Galanakis, Esteve, Frigola, & Vorobiev, 2015). However, the extraction step using bio-solvents or organic solvents or novel technique-assisted extraction is very important to obtain high color yield and other qualities such as high levels of phytochemicals and other active compounds (Ngamwonglumlert, Devahastin& Chiewchan, 2017). In recent years, the technique of microencapsulation of colorants by spray-drying has become very popular (García-Lucas et al., 2017; Namazkar & Ahmad, 2013; Priya & Preetha, 2016; Zhang & Zhong, 2013). In this technique, it is also necessary to use different stabilizers (Lacerda et al., 2016; Wiesenborn, Zbikowski, & Nguyen, 1995). However, freeze-drying allows good quality product to be obtained from all or part of the plant without the addition of color stabilizers(Dziki et al., 2018; Nemzer et al., 2011; Rudy et al., 2015). This drying technique is the most suitable for materials sensitive to high temperatures (Dong, Hu, Chu, Zhao, & Tan, 2017; Hua, Liu, & Zhang, 2010; Ray, Raychaudhuri, & Chakraborty, 2016). Ray et al. (2016)only mentioned the freeze-drying technique as the best for drying active compounds.
Review articles by Mortensen (2006) and Sigurdson et al. (2017) describe some of the more commonly used natural food colorants. These reviews summarize major sources of natural colorants. Possible applications of natural pigments and their chemical characteristics are also discussed.
Other reports provide a different approach to the production of currently allowed natural and synthetic food colorants. They describe the historical perspective of those colorants. They also describe the techniques that have been used to improve the attractiveness and stability of color and extend their shelf life. Trends and perspectives of food colorants used in food science are also partially specified (Martins, Roriz, Morales, Barros, & Ferreira, 2016). Carotenoids, anthocyanins, betanins, and chlorophylls have been generally and selectively described in the context of human health, factors affecting their quality, and the type of methods used to obtain them (Rodriguez-Amaya, 2016). Another review describes the potential application of betalains in functional foods (Gengatharan, Dykes, & Choo, 2015).
This review complements recent reports with regard to the points that have not been discussed earlier. It summarizes current research about food colorants obtained by freeze-drying methods. It shows recently used procedures including pretreatments for obtaining colorants. This is the first review to specify measurement of properties of food colorants. It is noteworthy that the abovementioned reviews do not describe methods to assess the quality of food colorants. Therefore, in this review, we discuss the color parameters of recently obtained freeze-dried colorants. We also discuss the changes in color caused by different factors and the use of these natural pigments in food matrices. Finally, we discuss the potential future directions of research with respect to natural food colorants. This is the first review study about freeze-drying techniques to obtain natural food colorants.
Section snippets
Natural sources of freeze-dried colorants
Fruits, vegetables, and flowers are usually the natural sources of pigments (Delgado-Vargas, Jiménez, Paredes-López, & Francis, 2000; Özen, Akbulut, & Artik, 2011; Sinha, Saha, & Datta, 2012; Yoshida, Mori, & Kondo, 2009). In addition, pigments can be obtained from different by-products (Chedea, Kefalas, & Socaciu, 2010; Jing & Giusti, 2005; Morales, Barros, Ramírez-Moreno, Santos-Buelga, & Ferreira, 2015; Schieber, Stintzing, & Carle, 2001). Table 1 shows some of the plant materials recently
Methods used to obtain natural food colorants by freeze-drying
We analyzed some of the recent studies and summarized the different methods applied in the pretreatment and freeze-drying process. Fig. 1 shows the details of various processes used to obtain food colorants from plant material. It was observed that one of the most common methods using freeze-drying consists of extraction, filtration, concentration and freeze-drying.
In the first stage, the natural colorants are very often extracted to obtain an appropriately colored pigment. Table 2, Table 3
Methods of quality measurements of freeze-dried colorants
Fig. 2 presents the methods of quality measurements of freeze-dried colorants.
Many studies have reported the quality of freeze-dried powders, but there are only a few studies that present a comprehensive assessment of the food colorants. For example, Liaotrakoon et al. (2012) measured the dry matter, bulk density, pH, and vitamin C content of colorants extracted from dragon fruits. De Souza et al. (2015) analyzed samples for moisture content, moisture sorption isotherms, water solubility,
Color values of freeze-dried food colorants
Table 4 shows the color parameters of freeze-dried food colorants. The color parameters of freeze-dried red dragon fruit pulp and peel were evaluated by Liaotrakoon et al. (2012). Their results show that, after processing the juice, the L* value of the dried fruit peel slightly decreased, whereas the L* value of the fruit pulp increased. The a* value increased, and b* value decreased the visual color of freeze-dried dragon fruit pulp. The peel showed a red-purple color. The total content of
Color stability in freeze-dried colorants
The inherent instability of pigments is the main problem associated with natural colorants. Studies on the stability of freeze-dried pigments are valuable for the food industry, but still insufficient, because not many authors deal with this issue (Çinar, 2004). Color changes during storage of freeze-dried colorants were evaluated by Duangmal et al. (2008). The authors found that, during storage, there were minor changes in lightness and hue for all samples which was caused by degradation of
Advantages of the freeze-drying technique in the production of natural food colorants
Freeze-drying is a valuable technique for the drying of materials sensitive to high temperatures(Ray et al., 2016). Liaotrakoon et al. (2012) found that freeze-drying resulted in a minor loss of vitamin C content, which was a result of low-temperature and the use of a vacuum. Agudelo, Barros, Santos-Buelga, Martínez-Navarrete, and Ferreira (2017) compared spray-dried samples with those of the freeze-dried grapefruit and found that the freeze-dried samples contained a much higher amount of trace
Conclusion
Future trends in the study of natural colorants should focus on the usage of food industry waste (pomace, peels, flower petals) as the most economical and promising source of food colorants.
For the production of natural colorants by freeze-drying, various extraction methods have been used and to follow new trends it is proposed to use organic solvents or novel techniques using assisted extraction. Due to the advantages of the extraction process, high-yield colorants can be obtained.
The next
Funding sources
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
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