Modification of sunnhemp (Crotalaria juncea) protein isolate by high intensity ultrasound: Impact on the molecular structure, amino acid composition and nutritional profiling

Abstract

In the present study, sunnhemp protein isolate (SHPI) was prepared by alkaline extraction followed by acid precipitation method. The prepared sunnhemp protein isolate was subjected to high-intensity ultrasound treatment at 40 and 50% ultrasound amplitude for 10, 20, and 30 min. The effect of ultrasound treatment on molecular flexibility, available lysine content, antioxidant properties, and molecular weight distribution was investigated. The antioxidant activity of ultrasound treated SHPIs was found to be higher than the untreated sample. The optimum ultrasound treatment condition (50% amplitude and 20 min) had the highest molecular flexibility and antioxidant properties among all the sunnhemp protein isolates. The available lysine content of all SHPI samples decreased after ultrasound treatment. SDS-PAGE results demonstrated that there was no change in the electrophoresis patterns of ultrasound treated SHPI samples over the untreated sample, thus indicating the primary structure of the sunnhemp protein isolate was intact. Hydrophobic amino acid content was improved after ultrasound treatment in US5 (50% amplitude for 20 min) sample, thereby resulting in increase in total amino acid content than SHPI without ultrasound treatment. Biological value and essential amino acid index were also improved due to ultrasound treatment in US5 sample. Leucine and isoleucine were the first and second limiting amino acids found in SHPI according to FAO/WHO scoring patterns. Overall, it can be concluded that ultrasound treated SHPI can be a valuable source of plant-based protein with desirable nutritional characteristics at a low cost. The current findings speculated that high-intensity ultrasound treatment can be a valuable technique for the modification of sunnhemp protein isolate with its promising utilization in food supplements.