Elsevier

Food Chemistry

Volume 106, Issue 2, 15 January 2008, Pages 685-690
Food Chemistry

Effect of ultrasonic treatment on the recovery and DPPH radical scavenging activity of polysaccharides from longan fruit pericarp

https://doi.org/10.1016/j.foodchem.2007.06.031Get rights and content

Abstract

Ultrasonic technique was employed to extract polysaccharides from longan fruit pericarp (PLFP). The optimal conditions for ultrasonic extraction of PLFP were determined by response surface methodology. Box–Behnken design was applied to evaluate the effects of three independent variables (ultrasonic power, time and temperature) on the recovery and 1,1′-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity of PLFP. The correlation analysis of two mathematical-regression models indicated that quadratic polynomial model could be employed to optimize the ultrasonic extraction of PLFP. From response surface plots, ultrasonic power, time and temperature exhibited independent and interactive effects on the extraction of PLFP. The DPPH radical scavenging activity of PLFP could be improved by application of various ultrasonic power, time and temperature, which was possible due to the degradation of polysaccharides to different extent. The optimal conditions to obtain the highest recovery and the strongest DPPH radical scavenging activity of PLFP were 120 W, 22 min and 60 °C, as well as 241 W, 18 min and 51 °C, respectively. Under these optimal conditions, the experimental values agreed with the predicted ones by analysis of variance. It indicated high fitness of two models used and the success of response surface methodology for optimizing PLFP extraction.

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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