Epsilon Archive for Student Projects

Abstract

Kale (Brassica oleracea var. sabellica) side-streams may provide a promising source of leaf protein within a green biorefinery framework, but producing a white protein concentrate (WPC) for food applications remains technically challenging. Valorization of this biomass could support protein diversification and improve the use of underutilized green leafy biomass without requiring additional cropland. This thesis evaluated selected fractionation methods and processing parameters for recovering the white protein fraction from kale leaves. Fresh kale biomass was first mechanically pressed to obtain green juice, followed by thermal treatment, acid precipitation, acid washing, resolubilization, and freeze-drying. Four thermal treatment groups, including water bath heating at 60 °C and steam injection at 40 °C, 50 °C, and 60 °C, were compared. Two non-heated control groups were included to test whether low-temperature acid precipitation and resolubilization improved protein recovery. Protein recovery was assessed using the bicinchoninic acid (BCA) protein assay and mass balance calculations. Final product appearance and color changes during thermal treatment were evaluated by colorimetric analysis in the CIE L*a*b* (CIELAB) color space. Dry matter measurement and chlorophyll determination were used as additional assessments of the methods above.

Thermal treatment changed the color profile of the white juice fraction, especially at higher steam injection temperatures. However, the decolorization in white juice did not result in higher final resolubilized white protein fraction recovery or a brighter freeze-dried product. Final resolubilized protein recovery remained below 9% in all thermally treated groups, while the non-heated controls showed higher recovery but also higher dry mass content. Low-temperature acid precipitation and resolubilization did not significantly improve recovery compared with room-temperature processing under the conditions used. Overall, the results suggest that kale WPC fractionation is limited mainly by acid precipitation, acid washing, and resolubilization rather than thermal treatment alone. Further work should focus on improving protein recovery and characterizing the composition and sensory characteristics of the final WPC product.