Functional Diversification of Mulberry Leaf Albumins: A Comparative Study of Seven Varieties

The escalating demand for sustainable protein sources necessitates the exploration of underutilized plant-based alternatives. This study evaluated the nutritional composition of seven major mulberry leaf (Morus atropurpurea) varieties consumed in China and characterized the physicochemical, structural, and functional properties of their albumin fractions. Proximate analysis revealed that Yueshen Tang 10 (TS), Yueshen Da 10 (DS), and Caisang No.4 (C4) varieties exhibited high protein (20.72–22.96 g/100 g) and essential amino acid contents, meeting FAO/WHO standards. Ultrasonication-assisted extraction yielded albumin fractions with protein purities exceeding 67 g/100 g. Structural analysis revealed that mulberry leaf albumins exhibited a characteristic lamellar, plate-like structure, with their secondary structures mainly composed of β-turns (38.59%–45.58%), α-helices (21.95%–24.27%), random coils (18.43%–19.96%), and β-sheets (13.45%–18.91%). Functional assessments demonstrated varietal-specific advantages: Albumin of Yueshen Tang 10 (TSP) showed superior in vitro digestibility (90.38%) and foaming capacity (117.15%), while albumin of Caisang No.3 (C3P) exhibited exceptional emulsifying activity (24.07 m²/g) and stability (190.96 min). Albumin of Caisang No.4 (C4P) outperformed soy protein isolate (SPI) in water-holding (8.61 g/g) and oil-absorption capacities (7.96 g/g). Microstructural analysis revealed smoother surfaces in albumin of Yueshen Da 10 (DSP) and TSP, correlating with higher solubility. Notably, all albumins surpassed SPI in emulsifying stability and oil-binding capacity. This study underscores the potential of mulberry leaves as a sustainable protein source, with varietal traits dictating industrial applicability. TSP and DSP are ideal for nutritional supplements, C3P for emulsifiers, and C4P for moisture retention in processed foods. These findings provide actionable insights for optimizing plant protein extraction and advancing functional ingredient development in the food industry.