Abstract

In the present study, the influence of five drying techniques on the structural and biological properties of polysaccharides from lotus leaves (LLPs) was investigated. Results revealed that the yields, contents of basic chemical components, molecular weights, and molar ratios of compositional monosaccharides of LLPs varied by different drying technologies. Low molecular weight distributions were observed in polysaccharides obtained from lotus leaves by hot air drying (LLP-H), microwave drying (LLP-M), and radio frequency drying (LLP-RF), respectively. The high contents of bound polyphenolics were measured in LLP-H and LLP-M, as well as polysaccharides obtained from lotus leaves by vacuum drying (LLP-V). Furthermore, both Fourier transform infrared (FT-IR) and nuclear magnetic resonance (NMR) spectra of LLPs were similar, indicating that drying technologies did not change their basic chemical structures. Besides, all LLPs exhibited obvious biological properties, including in vitro antioxidant capacities, antiglycation activities, and inhibitory effects on α-glucosidase. Indeed, LLP-H exhibited higher 2,2-azidobisphenol (3-ethylbenzothiazoline-6-sulfonic acid) radical scavenging ability (IC50 values, LLP-H, 0.176 ± 0.004 mg/mL; vitamin C, 0.043 ± 0.002 mg/mL) and 2,2-diphenyl-1-(2,4,6-trinitrate phenyl) hydrazine radical scavenging ability (IC50 values, LLP-H, 0.241 ± 0.007 mg/mL; butylated hydroxytoluene, 0.366 ± 0.010 mg/mL) than others, and LLP-M exerted stronger antiglycation (IC50 values, LLP-M, 1.023 ± 0.053 mg/mL; aminoguanidine, 1.744 ± 0.080 mg/mL) and inhibitory effects on α-glucosidase (IC50 values, LLP-M, 1.90 ± 0.02 μg/mL; acarbose, 724.98 ± 16.93 μg/mL) than others. These findings indicate that both hot air drying and microwave drying can be potential drying techniques for the pre-processing of lotus leaves for industrial applications.

Highlights

  • Nelumbo nucifera Gaertn., an aquatically perennial plant, belongs to the family Nelumbonaceae, which is an edible and medicinal plant widely consumed in China [1]

  • Lotus leaf is consumed as a popular tea material, which has a long history, being utilized as a traditional Chinese herb for treating diverse diseases, such as haematemesis, epistaxis, hyperlipidaemia, and obesity [2]. It has attracted increasing attention as a potential functional food due to its diverse health-promoting effects, such as antioxidant, anti-hyperglycemic, anti-proliferative, anti-inflammatory, anti-obesity, and hepatoprotective activities [1,2,3]. These health-promoting effects are correlated with different bioactive compounds that exist in lotus leaves, such as polysaccharides, flavonoids, alkaloids, essential oils, and triterpenoids [1]

  • The results revealed that LLP-M prepared by microwave drying exhibited the highest α-glucosidase inhibitory activity among LLPs, while the weakest α-glucosidase inhibitory effect was observed in LLP-F among LLPs

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Summary

Introduction

Nelumbo nucifera Gaertn. (lotus), an aquatically perennial plant, belongs to the family Nelumbonaceae, which is an edible and medicinal plant widely consumed in China [1]. Lotus leaf is consumed as a popular tea material, which has a long history, being utilized as a traditional Chinese herb for treating diverse diseases, such as haematemesis, epistaxis, hyperlipidaemia, and obesity [2]. It has attracted increasing attention as a potential functional food due to its diverse health-promoting effects, such as antioxidant, anti-hyperglycemic, anti-proliferative, anti-inflammatory, anti-obesity, and hepatoprotective activities [1,2,3]. Polysaccharides from lotus leaves (LLPs) possess potential applications in the pharmaceutical and functional food industries

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