How Does Superheated Steam Treatment Affect Nutritional, Functional and Rheological Behavior of Guar Germ Protein Isolates?

Abstract

Superheated steam (SHS) treatment offers a rapid and efficient approach for modifying biopolymers, minimizing oxidation and degradation compared to conventional heating methods. Guar germ protein isolates (GGPI), rich in essential amino acids, remain underexplored despite their nutritional potential. However, GGPI faces limitations in solubility, digestibility, and gelling ability. This study investigates the impact of SHS treatment on the nutritional, structural, functional, and rheological properties of GGPI at temperatures of 120, 130, and 140 °C for 5 and 10 min. SHS treatment significantly increased in-vitro protein digestibility up to 130 °C-10 min (89.08 %). However, prolonged exposure to higher temperatures led to a significant reduction in essential amino acids, accompanied by changes in carbonyl and disulfide content. At lower SHS temperatures, no apparent changes in band intensity of SDS-PAGE patterns were found. Also, non-significant differences in surface hydrophobicity and particle size variation suggested that larger aggregates of GGPI were not formed. Partial unfolding of GGPI was observed at lower SHS temperatures, as indicated by higher random coil structure. On the other hand, at higher SHS temperatures, reorganization of unfolded structure into compact structure occurred, as noted by a significant impact on β-sheet structure (37.34–45.12 %). Furthermore, increasing SHS temperature and time significantly improved the solubility (5.99 %) and emulsifying capacity (4.14 %) of GGPI up to 130 °C-10 min. Broader particle size distribution profiles of GGPI after SHS treatment might have accounted for the non-significant variation in water absorption capacity (1.9–2.11 g/g) and foaming capacity. Simultaneously, GGPI treated at 120 °C for 10 min formed a weaker gel with frequency-dependent behavior. Conclusively, SHS treatment could be more effective for preprocessing GGPI or other plant proteins at temperatures ranging from 120 to 130 °C to enhance solubility, digestibility, and gelling ability. Limited oxidation at higher SHS temperature (140 °C) reduced essential amino acids but did not form larger aggregates, making it suitable for producing low viscous food items.