Abstract
The purpose of this study was to investigate the Maillard reaction between polysaccharides and proteins from longan pulp and the effects of reaction on their in vitro activities. The polysaccharide-protein mixtures of fresh longan pulp (LPPMs) were co-prepared by an alkali extraction–acid precipitation method. They were then dry-heated under controlled conditions for monitoring the characterization of the Maillard reaction by the measurement of the free amino group content, ultraviolet-visible spectrum, Fourier transform infrared spectrum and molecular weight distribution. All the physicochemical analyses indicated the development of the Maillard reaction between polysaccharides and proteins. The in vitro activity evaluation indicated that the Maillard reaction could effectively enhance the antioxidant, antitumor and immunostimulating activities of LPPMs. The enhancement of 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity and ferric reducing antioxidant power displayed both a positive correlation with the reaction time (p < 0.05). LPPMs dry-heated for three days obtained relatively strong inhibitory activity against HepG2 cells and SGC7901 cells, as well as strong immunostimulating effects on the nitric oxide production and tumor necrosis factor α secretion of macrophages. Maillard-type intermacromolecular interaction is suggested to be an effective and controllable method for improving the functional activities of polysaccharides and proteins from longan pulp.
Highlights
Longan (Dimocarpus longan Lour.), a subtropical evergreen tree belonging to Sapindaceae family, is commercially planted in China, Thailand, India and Vietnam [1]
LPPMs dry-heated for three days obtained relatively strong inhibitory activity against HepG2 cells and SGC7901 cells, as well as strong immunostimulating effects on the nitric oxide production and tumor necrosis factor α secretion of macrophages
An alkali extraction–acid precipitation method was used for the co-preparation of polysaccharides and proteins from longan pulp (i.e., LPPMs)
Summary
Longan (Dimocarpus longan Lour.), a subtropical evergreen tree belonging to Sapindaceae family, is commercially planted in China, Thailand, India and Vietnam [1]. Its mature fruits attract great attention due to its desirable flavor and abundant nutrients, and show an increase in production inrecent decades [2]. Several preservation methods, such as canning, freezing and drying, have been implemented to add value to this seasonal fruit because of its highly perishable nature, short storage life and susceptibility to postharvest diseases. Drying is the most common method for the industry to process fresh longan fruits [3]. Polysaccharides and polysaccharide-protein complexes have been confirmed to be the active macromolecules contributing to its antioxidant, antitumor and immunomodulatory activities [2,5,6,7,8], but those from fresh pulp have been rarely reported
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