Valorization of ghee residue (a dairy industry by-product) through microwave-assisted green extraction of phospholipids: insights from process optimization, extraction kinetics, structural characterization and phospholipid fractions

Ghee residue is a by-product of the ghee (heat clarified cream / butter) processing industry, with limited utilization at present. Even though the industry treats the residue as a waste, channelling it through low value chains in the feed industry is significant, the composition of ghee residue boasts significant amounts fat and protein content. The present study represents a novel approach to valorize ghee residue, as a substrate for extracting phospholipids with microwave-assisted extraction using water as a green solvent. The extracted phospholipids possess techno-functional properties and can be utilized as an emulsifier. The process parameters, namely power, S:S ratio and process time, for the extraction process were obtained based on Taguchi L9 orthogonal array methodology. Optimal process conditions for the maximizing the phospholipids content in the extract were deduced using L₉ Taguchi orthogonal array as combination of power (540 W), time (60 s), S:S ratio of (10 v/w), which resulted in 21.96 % PLs in the extract. However, among the factor’s solvent to S:S ratio significantly contributed in phospholipids extraction. The phospholipid yield in microwave-assisted extract varied from 17.27 to 21.29 %. The kinetics of extraction was described using mathematical models: Peleg’s model reported highest R² of 0.98 which was trailed by Elovich’s model. Scanning electron microscopy images of the microwave-treated ghee residue samples revealed visible surface damage and pole-shaped structures that transformed into blunt edge points. Lipidomic profiling of phospholipids classes revealed 31, 16, 11, 2 and 1 species for phosphatidylcholine, phosphatidylinositol, phosphatidylethanolamine, phosphatidylserine and phosphatidylglycerol, respectively. The study demonstrated the efficacy of microwave-assisted extraction of phospholipids from ghee residue as an effective means of valorizing this dairy by-product.