Effects of traditional and advanced drying techniques on the physicochemical properties of Lycium barbarum L. polysaccharides and the formation of Maillard reaction products in its dried berries

•Advanced vacuum-microwave drying was efficient but produced more toxic products.•Heating-involved drying yielded relatively superior nutritional goji berries.•Vacuum freeze-drying produced appearance-fresh but nutrition-less dried berries.•Freeze-thawing caused the loss of polysaccharide and polyphenol.•Goji berries were easy to generate Maillard reaction products in drying process.