Effect of ultrasonic treatment on the recovery and DPPH radical scavenging activity of polysaccharides from longan fruit pericarp
Introduction
Longan (Dimocarpus longan Lour.) is an important fruit in Southeast Asia (Jiang, Zhang, Joyce, & Ketsa, 2002). Longan fruit pericarp contains a significant amount of polysaccharides. A great deal of attention has been paid to polysaccharides for their unique biological, chemical and physical properties in recent years (Schepetkin & Quinn, 2006), and useful applications in developments of therapeutic drugs in modern medicine (Li, Zhou, & Han, 2006).
Ultrasonic treatment has been widely employed to extract polysaccharides from different plant materials (Hromadkova & Ebringerova, 2003), because ultrasonic treatment has mechanical effects that facilitate mass transfer between immiscible phases through a super agitation, especially at low frequency (Vinatoru et al., 1997). However, ultrasonic wave has degradation effects on polysaccharides. The changes in structure and degradation of polysaccharides depend on power and operating parameters (Mislovicova et al., 2000, Zhou and Ma, 2006).
The formation of some diseases, such as cancer, can be directly induced by free radicals, while the radical scavenging activity is one of the important functional properties for bioactive compounds (Athukorala, Kim, & Jeon, 2006). The DPPH radical scavenging activity is often used to evaluate the capacity of antioxidant compounds (Prior & Cao, 1999). Recent studies demonstrated that the antioxidant activity of polysaccharides was related to their degree of polymerization and structure (Chen & Yan, 2005). Under various ultrasonic conditions, the molecular weight and structure of PLFP would be modified, which influenced the DPPH radical scavenging activity.
The objective of this study was to investigate the effect of ultrasonic technique on polysaccharide extraction yield and bioactivity of polysaccharides during the extraction process. Response surface methodology is a statistical method that uses quantitative data from an appropriate experimental design to determine or simultaneously solve multivariate equation (Triveni, Shamala, & Rastogi, 2001). Besides, this experimental methodology can generate a mathematical model (Baş & Boyacı, 2007). In this study, ultrasonic technique was employed to extract polysaccharides from longan fruit pericarp (PLFP). Response surface methodology was used to evaluate the effects of ultrasonic power, time and temperature on the recovery and DPPH radical scavenging activity of PLFP to obtain the optimal extraction conditions.
Section snippets
Materials
Fresh longan fruits (Dimocarpus longan Lour. cv. Shixia) at the commercially mature stage were purchased from a commercial market in Guangzhou, China. Fruits were selected for uniformity of shape and colour.
Chemicals
DPPH was purchased from Sigma chemical company (St. Louis, MO, USA). Glucose, phenol and sulphuric acid were obtained from Guangzhou Reagent Co. (Guangzhou, China). All other chemicals used were of analytical grade.
Extraction and quantification of PLFP
Pericarp tissues (4 g) of longan fruit were immersed into 100 ml of distilled
Effects of ultrasonic power, time and temperature on the recovery of PLFP
The mechanism of ultrasonic extraction involves two processes of physical activity: the dissolution of the extractive substances near the particle surface (rinsing) and the diffusion from the solid particles to the bulk of the liquid extract (slow extraction) (Vinatoru, 2001). The effects of ultrasonic power, time and temperature on the recovery of PLFP as well as their interactions are shown in Fig. 1. The extending ultrasonic time could result in a higher extraction recovery. However, the
Conclusions
The high correlation of two mathematical models indicated that quadratic polynomial model could be employed to optimize ultrasonic extraction process and DPPH radical scavenging activity of PLFP. From response surface plots, three factors (ultrasonic power, time and temperature) significantly influenced the extraction efficiency of PLFP, independently and interactively. The optimal conditions to obtain the highest recovery and strongest DPPH radical scavenging activity of PLFP were determined
Acknowledgements
The financial support provided by National Natural Science Foundation of China (Grant No. 30425040), Eleventh-five-year National Key Technology R&D Program (No. 2006BAD27B03), and Guangzhou Scientific Research Foundation (No. 2004Z1-E0061 and 2005Z2-E0151) was appreciated.
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