Elsevier

Food Chemistry

Volume 229, 15 August 2017, Pages 223-234
Food Chemistry

Floral parts of Gomphrena globosa L. as a novel alternative source of betacyanins: Optimization of the extraction using response surface methodology

https://doi.org/10.1016/j.foodchem.2017.02.073Get rights and content

Highlights

  • Betacyanins extraction from Gomphrena globosa L. was optimized.

  • A novel mechanical process for the pigmented flower parts separation was established.

  • Response surface methodology was used to optimize the extraction variables.

  • Optimal extraction variables were achieved with 165 min, 25 °C, water, 5 g/L S/L.

  • Betacyanins powder production can be an alternative colorant for food industry.

Abstract

The present study describes a novel mechanical process for the pigmented parts of Gomphrena globosa L. The effects of the variables of the maceration extraction of betacyanins have not been properly described. Therefore, this study also aims to optimize the conditions that maximize betacyanins extraction from G. globosa as an alternative source. Assisted by response surface methodology, an experimental design was developed for testing the extraction variables (time, temperature, ethanol-water proportion and solid-liquid ratio). The responses used were betacyanins quantification (by HPLC-PDA-MS/ESI and spectrophotometric analysis), the extraction-yield and the colour intensity of the produced powder. The betacyanins identified were gomphrenin and isogomphrenin II and III. The highest betacyanins content (∼45 mg/g) was obtained by 165 min, 25 °C, 0% of ethanol and 5 g/L of solid-liquid ratio. The betacyanins content from the floral parts of G. globosa is higher than those normally found in other sources highlighting its industrial application.

Introduction

Colour is often the first sensory quality by which we judge all the things that surrounds us including food and food products. Colorants have been used for a long time in the food industry, and the major reason is to improve the attractive and appetizing of foods for the final consumer (Chen, Mou, Hou, Riviello, & Ni, 1998). This kind of additives are also used to compensate the colour loss due to the conditions of manufacturing and storage, enhance natural colour, provide colour to a colourless food, but also to allow the consumers to identify some products by sight (González, Gallego, & Valcárcel, 2002).

Food dyes or colorants can be classified as natural (or nature-identical) or synthetic; natural dyes when compared with the synthetic ones have a lower tinctorial strength, and are more sensitive to environmental conditions such as light, temperature, pH, among others. Due to their potential harmful features, the usage of most synthetic pigments has been restricted, becoming extremely important the application of natural colorants in the food industry (Amchova et al., 2015, Martins et al., 2016). This relates not only to the restrictions in using synthetic dyes, but also to the need to satisfy consumers, which over time become more and more demanding about the quality of the products they are purchasing.

Today, most consumers prefer foods without additives or with natural additives in place of the synthetic ones, which have been associated with some toxic effects (Gengatharan, Dykes, & Choo, 2015). There are many natural dyes used in the food industry, in particular carotenoids, anthocyanins and betalains. The betalains are very similar to the anthocyanins, and include compounds having colours ranging from red-violet (betacyanins) to yellow-orange (betaxanthins) (Carocho, Morales, & Ferreira, 2015). Betacyanin structures have some variations in the acyl groups and sugar moieties; the basic structural unit of most of the betacyanins is betanidin, followed by its C15 epimer, so a considerable number of different betacyanins can be obtained by glycosylation of one of the hydroxyl groups (Delgado-Vargas, Jiménez, & Paredes-López, 2000).

Table 1 shows a bibliographic summary of betalains content from different plant materials. Among the various sources of betalains, the most explored one is red beet (Beta vulgaris L.), due to its very high concentration in these pigments (Nemzer et al., 2011), but there are less explored alternative sources, such as flowers from the amaranthaceae family, Gomphrena globose L. Native to Latin America and commonly known as globe amaranth, this plant contains a variety of compounds with biological activity, being betacyanins one of them. Therefore, this plant is a good candidate as an alternative source to obtain the mentioned pigments (Roriz, Barros, Carvalho, Santos-Buelga, & Ferreira, 2014).

Different solid-liquid systems (maceration, microwave, ultrasound, among many others) are available for the extraction of compounds. There is not a universal approach better than the others, focussing in reducing the time of extraction, amount of solvents, the energy costs and the degradation patterns (Alonso-Salces et al., 2001, Dai and Mumper, 2010, Ince et al., 2013). Betacyanins are generally extracted by maceration extraction technique with water as the main solvent, but aqueous organic solvent mixtures have shown certain improvements in the final extractions yields obtained. Maceration extraction is a conventional method easily transferable to industrial scale and traditionally used in the extraction of bioactive compounds. The main advantage is its simplicity, but if the variables are not properly optimized, very often requires long time periods and high temperatures resulting in high-energy costs and bioactive compounds degradation.

The maceration extraction depends on several process variables whose values cannot be generalized for all matrices due to their specificity in terms of composition and target compounds. Thus, the optimization of the variables involved in the process is needed to select the best conditions to ensure a maximum yield, minimum time, energy and solvent consumption, squeezing the utmost from the maceration system. Traditionally, optimization is achieved by monitoring the influence of one factor at a time. However, by using the response surface methodology (RSM), optimization is done simultaneously and in a more precise manner obtaining polynomial models able to describe within the experimental range tested the optimal conditions that maximize the response criteria used (Bezerra et al., 2008, Ferreira et al., 2007, Kalil and Maugeri, 2000).

Therefore, the aims of the present study were: 1) to develop a process in a pre-industrial form for the isolation of the floral parts (mainly bracts and bracteoles of G. globosa flowers); and 2) optimize the primary variable conditions of the maceration system (time, temperature, ethanol-water proportion and solid-liquid ratio) and maximize betacyanins extraction assisted by the statistical RSM technique, contributing to the understanding of the potential of betacyanins from G. globosa for industrial applications.

Section snippets

Reagents

Acetonitrile of HPLC grade and ethanol p.a. were purchased by Fisher Scientific (Lisbon, Portugal). Water was treated in a Milli-Q water purification system (TGI Pure Water Systems, Greenville, SC, USA). All other chemicals and solvents were of an analytical grade and purchased from common suppliers.

Sample collection

Gomphrena globosa L. plants were purchased by Ervital, a Portuguese company from Castro Daire, established in a mountain region full of diversity. This company markets different certified plant

Producing food colorants from the floral part of G. globosa

The pigmented portion of the plant is only a part of the inflorescence, so to not compromise the effectiveness of the process it is necessary to separate the parts of interest from the remaining plant material. This will increase the effectiveness of the pigment extraction, without the interference of other portions of the plant that are not pigmented. To overcome this problem a mechanical separation process was used for isolating the pigmented parts (bracts and bracteoles) from the flowers

Conclusions

Betacyanins are betalain pigments that display a red-violet colour that have been reported to be three times stronger than the red-purple-blue dye produced by anthocyanins. The applications of betacyanins cover a wide range of matrices, mainly as additives or supplements in the food industry, cosmetics, pharmaceuticals and livestock feed. Although being less commonly used than anthocyanins and carotenoids, betacyanins are stable between pH 3 and 7 and well suited for colouring low acid

Acknowledgements

The authors thank the Foundation for Science and Technology (FCT, Portugal) and FEDER under Programme PT2020 for financial support to CIMO (UID/AGR/00690/2013) and L. Barros (SFRH/BPD/107855/2015) grant. To POCI-01-0145-FEDER-006984 (LA LSRE-LCM) funded by ERDF through POCI-COMPETE2020 and FCT. To Xunta de Galicia for financial support for the post-doctoral researcher of M.A. Prieto. The authors also thank Ana Maria Carvalho for the plant donation and Celestino Santos-Buelga for the preparative

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