Valorisation of date fruit processing waste stream through conjugation and encapsulation of bioactive compounds and their effective utilisation in functional biscuit formulation: A sustainable approach towards a bio-circular economy

In this study, date seed polyphenols were incorporated in biscuits in the forms of conjugates (DSPC) and encapsulates (DSPE). Date seed polyphenol conjugates were prepared with soy protein isolate (SPI) in ratios of 1% SPI solution: polyphenolic extract; 1:20, 1:30, 1:40, and 1:50 (wt:wt). Date seed polyphenol encapsulates were prepared using gum arabic (GA) in ratios of 0.5%, 1%, 1.5%, and 2% (wt/vol). Bioactive properties, in vitro digestion of polyphenols and physical properties of fortified biscuits were analysed. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis and spectroscopic data confirmed the conjugation of date seed polyphenols with SPI along with the quenching of tryptophan fluorescence. Soy protein isolate:polyphenolic extract ratio of 1:40 exhibited the highest polyphenol binding capacity of 53.53%. Encapsulate with 1.5% (wt/vol) GA showed the highest encapsulation efficiency of 62.28% and antioxidant activity increased with increasing GA proportion in encapsulates. The highest 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity of 1.02 mmol trolox equivalents (TE)/g biscuit was observed in 1.5% (wt/vol) DSPE while the highest ferric reducing antioxidant power of 2.75 μmol TE/g biscuit was observed in the DSPC at a ratio of 1:50. Total phenolic content (TPC) of biscuit increased upon incorporation of DSPC and DSPE. The highest TPC of 1.27 mg GAE/g biscuit, after in vitro gastrointestinal digestion, was found in 2% (wt/vol) DSPE. No significant difference (p >. 05) was found in colour of biscuit with fortification of DSPC and DSPE whereas the hardness and the fracturability increased, and the highest values were found in 1.5% (wt/vol) DSPE. Overall, DSPC and DSPE showed promising results in protecting date seed polyphenols during biscuit preparation and in vitro digestion.