Application of response surface methodology to acidified water extraction of black soybeans for improving anthocyanin content, total phenols content and antioxidant activity
Introduction
Anthocyanins are water-soluble pigments that are responsible for the pink, red, blue and purple colours in plants. Black soybeans have recently drawn more attention due to their high amounts of anthocyanins that have anti-oxidant, anti-diabetic and anti-cancer effects (Xu and Chang, 2008, Mojica et al., 2017, Kim et al., 2008). The majority of the black soybean anthocyanins are found in their seed coat (Xu and Chang, 2008, Choung et al., 2001, Žilic et al., 2013). Choung et al. (2001) found that the anthocyanin content in the seed coats of ten black soybean varieties ranged from 1.58 mg/g to 20.18 mg/g dry weight. The composition of the anthocyanins, which includes malvidin 3-glucoside, petunidin 3-glucoside, delphinidin 3-glucoside and cyanidin 3-glucoside, has been found to vary depending on the black soybean cultivar (Takeoka et al., 1997, Xu and Chang, 2008, Yoshida et al., 1996).
Earlier investigations have developed a method to extract anthocyanins from black soybeans using organic solvents and ultrasound-assisted extraction (Xu and Chang, 2008, Mojica et al., 2017, Lai et al., 2013). The most common solvent is an acidified methanol (Sancho et al., 2015, Choung et al., 2001, Takeoka et al., 1997). However, there is a concern that organic solvents, due to their toxicity, may be left in the extract for functional ingredients and dietary supplements. Fortunately, the anthocyanins found in black soybeans are soluble in water since they are present as glycosylated compounds with glucose (Takeoka et al., 1997, Choung et al., 2001, Yoshida et al., 1996, Xu and Chang, 2008). Many variables, such as extraction temperature, time, pH, solid-liquid ratio, solvent concentration and particle size, influence the extraction yield of anthocyanins (Cacace and Mazza, 2003, Ng et al., 2012). For these reasons, a reliable extraction method that minimizes the use of organic solvents needs to be developed, which ultimately can be used to produce functional ingredients for the food and pharmaceutical industries.
Response surface methodology (RSM) is a statistical and mathematical technique that has been used to evaluate the effects of independent variables as well as their possible interactions. It has several advantages, such as a relatively short time period and lower costs during the optimization process (Bezerra et al., 2008, Said and Amin, 2015). Anthocyanins are susceptible to degradation by pH, temperature, light and the presence of oxygen (Castañeda-Ovando, Pacheco-Hernández, Páez-Hernández, Rodríguez & Galán-Vidal, 2009). The extraction of anthocyanins from black soybeans, therefore, should be optimized to maximize the diffusion of anthocyanins from their matrices while preserving stability during the extraction process.
To the best of our knowledge, this is the first study on the optimization of acidified water extraction from black soybeans for the purpose of improving anthocyanin content and antioxidant activity using RSM. The objectives of this study were i) to establish the optimal extraction conditions of independent variables such as extraction temperature, extraction time, hydrochloric acid (HCl) concentration and solid-liquid ratio; and ii) to compare the experimental and predicted data at the optimal conditions.
Section snippets
Chemicals and materials
Kuromanin chloride, petunidin-3-O-glucoside chloride, Folin-Ciocalteu’s reagent, gallic acid, HCl, potassium chloride, potassium phosphate dibasic, potassium phosphate monobasic, potassium sulfate, sodium acetate, sodium carbonate and 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) were purchased from Sigma-Aldrich (St. Louis, MO, USA). Myrtillin chloride was purchased from Extrasynthese (Lyon, France). Black soybeans (Glycine max (L.) Merr. Cheongja4ho) were provided by the
Results of selection of extraction parameters
The extraction yield of anthocyanins is influenced by various factors, such as extraction time, pH, solid-liquid ratio and extraction temperature (Cacace and Mazza, 2003, Ng et al., 2012). In this study, the effects of HCl concentration (pH), solid-liquid ratio, extraction time and extraction temperature on total anthocyanin extract from black soybeans were preliminarily evaluated to determine the significant parameters. As shown in Fig. 1, all parameters except extraction time had significant
Conclusion
In this study, the optimization of acidified water extraction for total anthocyanin content, total phenol content and ABTS+ scavenging activity from black soybeans was first examined using RSM. The optimum experimental conditions were found to be HCl concentration of 0.359%, solid-liquid ratio of 1/54.2 g/mL and extraction temperature of 56.8 °C. At these conditions, total anthocyanin content, total phenol content and ABTS+ scavenging activity were 136.68 ± 2.76, 1,197.09 ± 33.34 and of
Acknowledgements
This research was supported by the Basic Science Research Program through the National Research Foundation of Korea, South Korea (NRF) funded by the Ministry of Education (2017R1D1A1B03028841).
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