The phenolic contents and antioxidant activities of fruits could be underestimated if the bound phenolic compounds are not considered. In the present study, the extraction efficiencies of various solvents were investigated in terms of the total content of the free and bound phenolic compounds, as well as the phenolic profiles and antioxidant activities of the extracts.

Drying is commonly used for preservation and processing of litchi. However, its polysaccharide structure may be altered by the drying process, resulting in biological activity changes. Polysaccharides from fresh and dried litchi pulp (denoted as LPF and LPD, respectively) were isolated, investigated by GC-MS, GPC and UV/IR spectrum analysis and their antitumor and immunomodulatory activities were evaluated in vitro. LPD, the molecular weight of which was lower than that of LPF, contained more protein, uronic acid, arabinose, galactose and xylose. Compared with LPF, LPD exhibited a higher inhibitory effect on the proliferation of HepG2, Hela and A549 cells from 50–750 μg/mL. LPD was also a better stimulator of spleen lymphocyte proliferation, NK cells cytotoxicity and macrophage phagocytosis from 50–400 μg/mL. In summary, drying could change the physicochemical properties and enhance the bioactivity of polysaccharides from litchi pulp. This finding is supported by the fact that dried litchi pulps are used in Traditional Chinese Medicine.

Dried litchi pulp has been used in traditional remedies in China for many years to treat various diseases, and the therapeutic activity has been, at least partly, attributed to the presence of bioactive polysaccharides. Polysaccharide-protein complexes from vacuum freeze-(VF), vacuum microwave-(VM) and heat pump (HP) dried litchi pulp, which were coded as LP-VF, LP-VM and LP-HP, were comparatively studied on the physicochemical and immunomodulatory properties. LP-HP had a predominance of galactose, while glucose was the major sugar component in LP-VF and LP-VM. Compared with LP-VF and LP-VM, LP-HP contained more aspartate and glutamic in binding protein. LP-HP also exhibited a stronger stimulatory effect on splenocyte proliferation at 200 μg/mL and triggered higher NO, TNF-α and IL-6 secretion from RAW264.7 macrophages. Different drying methods caused the difference in physicochemical properties of polysaccharide-protein complexes from dried litchi pulp, which resulted in significantly different immunomodulatory activity. HP drying appears to be the best method for preparing litchi pulp to improve its immunomodulatory properties.