Fucoidan is a sulfated polysaccharide derived from brown seaweed, and it has been applied in pharmaceutical fields.Recently, the trend of applying advanced extraction techniques and optimizing extraction conditions has been particularly interested in order to achieve high extraction yield. In this study, response surface methodology (RSM) were employed to optimise the ultrasound-assisted extraction of fucoidan from brown seaweed Tubinaria decurrens. The impacts of three independent variables, including extraction temperatures (X1: 50-80°C), extraction time (X2: 30-60 min), and ultrasound power (X3: 40-100%) was investigated through Box-Behnken experimental design. The results showed that the optimised condition was at extraction temperatures of 70°C, extraction time of 53 min, and ultrasound power of 90%. Under this optimised condition, the extraction yield was 4.28% and close to the predicted yield of 4.34%.
The gravity model was used in this paper to clarify the influencing factors of the export value of non-timber forest products (NTFPs) for Vietnam from 2003 to 2017. The estimates of this model indicate the importance of the size of economies, distance, common borders, exchange rates, average forest area, natural forest closing (NFC) policy of the Vietnamese government, sanitary and phytosanitary measures (SPS), and the interaction of SPS and importers’ GDP (SPS-GDP) as determinants of NTFP export of Vietnam. The main result of this study is the distinct and contradictory effect of NFC policy and SPS measures. While, the NFC policy increase the value of Vietnam's NTFP exports, SPS measures significantly decrease the exportation. Using the SPS-GDP interaction variable yields a noticeable result: the negative impact of SPS on NTFP trade decreases with increasing income of NTFP importers. Furthermore, the NFC needs to continue to implement policies to increase investments in the NTFPs trade, increase the quality of NTFP products from planting, harvesting, to processing, to meet the requirements of future importers. The findings offer several implications both in theory and in practice for trade policies, economic development theory based on Vietnam's forest resources.
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