Optimization, kinetics, thermodynamics and stability of ultrasound-assisted and high-pressure carbon dioxide extraction of anthocyanins from mangosteen ( Garcinia mangostana Linn.) pericarp

Mangosteen is a genus of Garcinia trees widely grown in Southeast Asia, tropical Africa and South American countries. In the food industry, the mangosteen fruit is often processed into juice, jam and frozen mangosteen’s pulp. However, the pericarp, which accounts for about two-thirds of the whole fruit weight, is often discarded as agricultural waste. This may not only cause environmental pollution but also seriously affect the added value of the mangosteen. Considering the rich anthocyanin content in mangosteen pericarp and the multiple health benefits of anthocyanins such as antioxidant, anti-inflammatory and vision protection, the extraction of anthocyanins from mangosteen pericarp may be an effective strategy to fully utilized mangosteen pericarp. To date, reports on the extraction of anthocyanins from mangosteen pericarp are still very limited. The main objective of this study is to develop an efficient method for the extraction of anthocyanins from mangosteen pericarp and to conduct a preliminary investigation of its mechanism. First, the differences between conventional solvent extraction (CSE), ultrasound-assisted extraction (UAE) and highpressure carbon dioxide extraction (HPCDE) in anthocyanin extraction were compared by analyzing the extraction yield, parameters, kinetic and thermodynamic behaviors. Subsequently, response surface methodology (RSM) was applied to optimize the four main parameters in UAE to further increase anthocyanin yield. Finally, the effects of heating and ultrasound treatment on the stability of the mangosteen anthocyanin extract were also investigated. Singlefactor experiments showed that amplitude, pressure, temperature and liquidsolid ratio significantly affected the anthocyanin yield and produced the maximum anthocyanin yield at 100%, 25 MPa, 80 °C and 60 mL/g, respectively. In the kinetic analysis, both the second-order kinetic model (R2>0.99) and Peleg's model (R2>0.95) were applicable to describe the extraction behavior of anthocyanins. Based on the second-order kinetic model, UAE showed the highest equilibrium concentration with 81.15 mg/100 g, while HPCDE showed the highest rate constant of 0.0149 100 g/mg∙ min, which was nearly two times higher than that of UAE. Thermodynamic analysis showed that enthalpy changes and entropy changes were positive under all extraction methods, and the Gibbs free energy changes were negative, suggesting that the extraction process was endothermic, irreversible and spontaneous. In addition, the highest anthocyanin yield of 92.52 mg/100 g was obtained under the optimal UAE conditions: amplitude 100%, temperature 80 °C, liquid-solid ratio 60 mL/ g for 25 min. There was no significant difference between this result and the predicted value of RSM. In the stability study, heating and ultrasound treatments both accelerated the degradation of anthocyanins, the formation of polymeric colors, the degradation of polyphenols, and the reduction of antioxidant capacity. The concentration of anthocyanin decreased by 6.8%, polymeric color index increased by 24.6%, polyphenol concentration decreased by 9.0%, and DPPH radical scavenging capacity decreased by 17.3% after 30 min of ultrasound treatment at 70 °C. Overall, UAE is a more recommended method for anthocyanin extraction from mangosteen pericarp. Although the high temperature and high amplitude in UAE may lead to degradation of anthocyanins, this amount of degradation is acceptable compared to the increased in yield. The findings of this study will be served as a useful guideline for the application of UAE and HPCDE in mangosteen anthocyanin extraction and help to increase the value of mangosteen.

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