Assessing Structural, Thermal, and Functional Characteristics of Marigold Flower Protein as a Sustainable Food Ingredient

The demand for sustainable and alternative protein sources
has
been on the rise, driving interest in the valorization of underutilized
plants. This study evaluated Calendula officinalis (marigold), a common floral waste, as a sustainable alternative
protein source for the food industry. The primary objective of this
study was to investigate the physicochemical properties of protein
fractions from Calendula officinalis flower to evaluate their potential as a novel protein ingredient.
Extraction of the Calendula officinalis flower yielded 92.17% of the crude protein. A sequential extraction
of albumin, globulin, glutelin, and prolamin from marigold flower
revealed albumin as the dominant fraction (65.47%) and exhibited the
highest protein functionality, including water-holding capacity (2.37
g/g), oil-holding capacity (2.49 g/g), and emulsifying capacity (65.22
mL/g). Compared with other protein fractions, glutelin showed a relatively
high emulsifying and foaming capacity (EC: 59.13 mL/g; FC: 16.23%).
Differential scanning calorimetry revealed high thermal stability
for albumin (Tp = 105.28 °C) and
glutelin (Tp = 97.6 °C). Sodium Dodecyl
Sulfate–Polyacrylamide Gel Electrophoresis (SDS-PAGE) and Liquid
Chromatography–Mass Spectrometry (LC-MS) confirmed the presence
of abundant low-molecular-weight polypeptides (<37 kDa), which
enhanced emulsification, while scanning electron microscopy revealed
porous structures aligned with hydration properties. Antioxidant activity
was higher in albumin and glutelin, linked to surface hydrophobicity.
LC-MS/MS identified 33 short-chain proteins, including oxidoreductase
proteins and lipid-transfer proteins. Findings highlight marigold
flower proteins as a sustainable, functional ingredient for a diverse
range of food applications.