Sour Cherry Kernel as an Unexploited Processing Waste: Optimisation of Extraction Conditions for Protein Recovery, Functional Properties and In Vitro Digestibility

Abstract: Kernel of sour cherry (Prunus cerasus L.) is a valuable source of protein generated as byproduct during processing of sour cherries. In this study, optimisation of protein extraction yield from sour cherry kernel was investigated using response surface methodology. Optimum conditions for alkaline solubilisation/isoelectric precipitation extraction were identified as pH 8.5, 1:10 solid-to-solvent ratio, and 1 h extraction time to obtain a protein yield of 63.8% for a protein content of 88.3%. The isoelectric precipitation point of sour cherry kernel protein isolate (SCKPI) was shown to be 4.2 and a high solubility of 85.3% was found at neutral pH. Results showed that SCKPI had a substantially high in vitro protein digestibility (95.7%). Other physicochemical properties such as water- and oil-holding capacities, gelling capacity, emulsion stability, foaming capacity as well as thermal properties were also reported and ensured comparable functionalities indicating a great potential as a valuable plant-based protein source for the food industry. Graphic Abstract: [Figure not available: see fulltext.]