Effects of different factors of ultrasound treatment on the extraction yield of the all-trans-β-carotene from citrus peels
Introduction
Carotenoids are the main dietary sources of Vitamin A and are associated with the reduction in the incidence of cancer [1], age-related macular degeneration (AMD) [2], and cardiovascular diseases [3]. Carotenoids are mainly distributed in plant-derived foods. The largest number of carotenoids found in any fruit are those of citrus fruits, more than 115 different compounds [4]. The carotenoid content in mandarin (Citrus reticulata Blanco) is the highest among all the varieties of citrus fruits in China [5]. The carotenoid content in the peels is higher than the pulp. Bendizao mandarin (Citrus succosa Hort) has the largest carotenoids content among mandarins [5]. Bendizao mandarin (Citrus succosa Hort) and satsuma mandarin (Citrus unshiu Marc) are the main varieties of canned citrus fruits in China [6]. The by-products (peels) of canned citrus fruit occupy 30–40% of the total fruit weight [7]. The peels are an abundant source of natural carotenoids. However, most citrus peels in conventional food processing as by-products are wasted, resulting in certain environmental pollution. It is consequently necessary to effectively extract carotenoids from the citrus peels.
Ultrasound-assisted extraction (UAE) has been widely used for the extraction of nutritional material, such as lipids [8], [9], [10], proteins [11], [12], [13], flavoring, essential oils [14], [15] and bioactive compounds (e.g., flavonoids [16], [17], [18], carotenoids [19], [20], [21], and polysaccharides [22], [23], [24]). Compared with traditional solvent extraction methods, ultrasound extraction can improve extraction efficiency and extraction rate, reduce extraction temperature, and increase the selection ranges of the solvents [25]. In comparison with other extraction methods such as supercritical fluid extraction and microwave-assisted extraction, ultrasound equipment is simpler and economically cheaper.
Ultrasonic cavitation is cited as the major factor leading to the enhancement of extraction. Cavitation can cause locally high temperatures, locally high pressures [26], and free radicals [25], [27], which may accelerate or trigger chemical reactions of extracted compounds. In previous studies, researchers mostly focused on the higher extraction efficiency of UAE. The structure and property change of extracted compounds during extraction using ultrasound have been paid more attention in recent years, especially for some polymers such as protein and polysaccharides. Yang et al. [11] found that the extraction yield of soybean protein isolated from soybean flakes was improved, and simultaneously the properties of isolated soy protein were changed by ultrasound treatment. For instance, the 7S isolated soybean protein aggregated, their emulsification was improved, and the viscosity was decreased. Gülseren et al. [12] found that bovine serum albumin aggregated and the number of free sulfhydryl groups decreased after treatment by high intensity ultrasound. The surface activity, surface hydrophobicity and surface charge were also found to be increased. High intensity ultrasound also caused polysaccharide depolymerization [28], aggregation [24], a viscosity decrease, and an improvement in immunity [24].
Little information is available involving sonochemical studies of the structure and property changes of small molecules such as carotenoids. Zhao et al. [29] found that (all-E)-astaxanthin in a model system degraded to unidentified colorless compounds under ultrasound treatment. The degradation increased by increasing both treatment time and ultrasonic power. Sun et al. [20] extracted lutein from chicken liver by UAE, and found that while the extraction rate of lutein was improved under conditions that led to non-saponification, lutein degradation occurred under conditions where saponification occurred. The literature mentioned above only explored the stability of carotenoids under special conditions of ultrasound treatment. There has been, to our knowledge, no comprehensive study on the stability of any one kind of carotenoids under ultrasound treatment in the literature.
The goal of this study is to determine the effects of different factors of ultrasound treatment on the extraction yield of all-trans-β-carotene (Fig. 1) from citrus peel. This study may help us to effectively control the extraction outcome, reduce degradation, and may establish a better understanding of the mechanism of ultrasound-assisted extraction of carotenoids.
Section snippets
Plant materials
Fresh Bendizao mandarin (Citrus succosa Hort) fruits were kindly offered by the institute of citrus, Huangyan, Zhejiang, China, in December, 2008. The fruits were peeled by hands. The peels were dried for 48 h in an oven with air circulation at 45 °C, and then ground finely in the laboratory with a blade mixer (Wenling linda machine Co., Wenling, Zhejiang, China). The peels powder was separated into five groups according to their particle size through 2, 0.45, 0.36, 0.28, and 0.074 mm sieves
Effect of particle size
The extraction yield increased with decreasing of particle size both by UAE and by CE (p < 0.05) as shown in Fig. 2. The ANOVA statistical analysis results indicated that there were no significant differences between UAE and CE (p > 0.05) on the extraction yields when the particle size was less than or equal to 0.28 mm. However, significant differences in extraction yields between UAE and CE were found when the particle sizes were greater than 0.28 mm. For example, the extraction yield of UAE was
Conclusions
The results of the present study indicate that each factor in the ultrasound treatment had a significant influence on the extraction yield of all-trans-β-carotene from Bendizao mandarin peel under ultrasound-assisted extraction. Ultrasound significantly increased the extraction yield when the particles sizes were greater than 0.28 mm compared to CE extraction. The solvent type influenced the stability and extraction yield of all-trans-β-carotene under ultrasound treatment. Dichloromethane caused
Acknowledgments
This project was supported by the Chinese National Key Technologies R&D Program of 11th Five-year Plan (2006BAD27B06) and the Key Cultural Project of Innovation of Ministry Education (707034).
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