Functional and rheological properties of lentil protein subfractions

In this thesis study, protein isolate was obtained from red lentils purchased from a local market as an alternative plant-based protein source, and sub-fractions of these isolates were obtained based on Osborne fractions. Lentil protein isolate (LPI) and its sub-fractions—albumin-rich sub-fraction (ALB), globulin-rich sub-fraction (GLO), glutelin-rich sub-fraction (GLUT), and the globulin sub-units legumin-rich sub-fraction (LEG) and vicilin-rich sub-fraction (VIC)—were isolated. The chemical composition, physicochemical properties, functional, and rheological characteristics of these protein fractions were investigated. The protein contents of the ALB, GLO, GLUT, LEG, VIC, and LPI samples were determined as 87.83±0.04%, 79.63±0.04%, 80.33±0.04%, 80.60±0.02%, 91.00±1.41%, and 88.74±0.06%, respectively. The protein samples showed the best solubility at pH 2. Foaming capacity, foam stability, emulsion activity index, and emulsion stability index were examined under pH 2 conditions. Among the protein samples, ALB exhibited the best foaming capacity (300.00±13.33%) and foam stability (172.08±28.78%). Similarly, it showed better emulsion activity (115.41±5.59%) compared to other protein samples. Among the protein samples, GLUT exhibited the best emulsion stability (219.43±25.73%). LEG demonstrated the highest water-holding capacity (231.77±3.87%), while VIC exhibited the best oil-holding capacity (291.87±7.26%). The Amide I and Amide II peaks in the sub-fractions were analyzed using Fourier Transform Infrared Spectroscopy (FTIR). The molecular weight distribution of the protein sub-fractions was examined by sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE). Protein solutions at 10% concentration were prepared with ALB, GLO, GLUT, LEG, and VIC samples, and rheological analyses were conducted. The rheological analysis results were modeled using the Power-law mathematical model. In the flow behavior of the protein samples, as the shear rate increased, the shear stress decreased proportionally. The flow properties indicated that the sub-fraction samples generally exhibited shear-thinning behavior. LEG showed a better gel-forming ability compared to the other samples. In time-dependent temperature sweep tests of the protein samples, the samples were analyzed over a temperature range of 10–90°C for 3 hours, and the G′ and G′′ moduli were recorded to examine time-dependent gelation temperatures. The differences observed in lentil protein sub-fractions compared to total lentil protein were also investigated.