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Compared to other cultivar lychees, volume density of Feizixiao lychee was higher due to serious shrinkage during freeze-drying (FD). Guiwei lychee and Nuomici lychee were used for comparison in order to illuminate the reason of the aforementioned phenomenon. Lower prefreezing temperature could not improve the volume density of Feizixiao lychee. Microstructure results show that pulp cell of Feizixiao lychee (tail) was smaller and more compact than Guiwei and Nuomici lychee pulp cell. In addition, there is a membrane around the surface of Feizixiao lychee pulp. And the microstructure of Feizixiao lychee tip pulp cell is different from tail pulp cell. Membrane and tip pulp cell are both smaller and more compact than tail pulp cell. These structure differences hinder the moisture removing of Feizixiao lychee during FD. Removing the membrane and tip pulp could not improve the volume density of Feizixiao lychee. Ultrasound treatment for 30 min could significantly enhance the volume density of Feizixiao lychee.

A multi-residue method for determination of pesticide residues in vegetables, using ethyl acetate extraction and determination by means of GC–MSD, is presented. The method includes as many as 27 pesticides such as organophosphorous, organohalogen, organonitrogen and pyrethroids pesticides, which are in common use or forbidden on vegetables in China. After extraction with ethyl acetate, the extract is concentrated and evaporated to dryness and redissolved in ethyl acetate before injection on GC–MSD. The recoveries were obtained in the range 70–100% with 5 exceptions in lettuce and 7 exceptions in cucumber, relative standard deviations between 1.92% and25.39% by means of standard addition to the vegetables blank extracts. The degradation of some pesticides in the 27 was studied by the method developed, the mixture of the pesticides commercial formulations was sparged on the vegetables, then the residues of samples obtained in different time were determined by the developed method. The determination indicated that (all pesticides were used as the instruction): 1.a pesticide, used on different plants, the quantity of the pesticide on the part for people’s dietary differs greatly; 2. some pesticides, degradating slowly and with a large dose, are inappropriate used on vegetables which remain on cropland for a short time. This research does not develop models for pesticides degradation, but provides some data on the safe intervals of the pesticides and a potential method for the study of multi-class pesticides safe intervals on a plant simultaneously.

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