355: Ultrasound Assisted Precipitation of Rice Bran Protein to Improve Yield, Functional Properties, and Nutritional Profile

Introduction

Innovative methods in plant protein extraction are advancing the goal of sustainable and high-quality protein production. While ultrasound-assisted extraction (UAE) is known to enhance yields, its role during protein precipitation remains underexplored. This study hypothesizes that applying ultrasound during isoelectric precipitation can disrupt protein-fiber complexes, improving protein properties. The objective of this research is (a) to extract high-quality and purity rice bran protein (RBP) by applying ultrasound during extraction and precipitation and (b) to evaluate the molecular, functional, and nutritional quality of extracted RBPs.

Methods

Defatted rice bran protein was extracted using alkaline extraction (AE) and ultrasound-assisted alkaline extraction (UAE) at pH 9.5 under optimized conditions (400W, 5 minutes). Protein isolates were precipitated at pH 3.5 via isoelectric precipitation (IP) or ultrasound-assisted isoelectric precipitation (UIP). Four combinations (AE-IP, UAE-IP, AE-UIP, and UAE-UIP) were employed, representing varying extraction and precipitation methods. Freeze-dried proteins were analyzed for functional, structural, and digestibility properties using techniques such as FTIR, SDS-PAGE, particle size analysis, and PDCAAS to assess quality and functionality.

Results

Ultrasound-assisted extraction and conventional isoelectric precipitation (UAE-IP) achieved the highest protein yield of 65.7%, compared to 38.9% for conventional extraction. Ultrasound treatment induced significant structural changes; ultrasound-assisted extraction and precipitation (UAE-UIP) increased β-sheets by 96.8% and decreased α-helices by 42.4%. While UAE-IP showed no significant change in surface hydrophobicity, UAE-UIP reduced it by 34.7% compared to the control. Functional properties, including solubility, emulsifying, and foaming capacities, were significantly enhanced. Alkaline extraction with ultrasound-assisted precipitation (AE-UIP) exhibited the highest solubility at pH 7, while UAE-IP showed superior solubility at acidic and alkaline pHs. UAE-UIP demonstrated the best emulsion stability and foaming properties. Ultrasound application also improved protein digestibility, with AE-UIP achieving the highest digestibility of 96.91%. However, excessive ultrasound could negatively impact digestibility. The amino acid profile varied across methods; AE-IP yielded the highest levels of essential amino acids. UAE-IP and UAE-UIP maintained protein digestibility-corrected amino acid scores (PDCAAS), while AE-UIP slightly lowered it to 0.9.

Significance

This research opens up new opportunities that ultrasound-assisted precipitation could be developed to improve the yield, functionality, and nutritional quality of protein.

Authors: Saydul Md Safwa, Nikitha Modupalli, Mahfuzur Rahman*