Effect of protein denaturation and lipid removal on rice physicochemical properties

Authors: SIAW, MICHELLE - University Of Arkansas; YANG, YA-JANE - University Of Arkansas; McClung, Anna; MAUROMOUSTAKOS, ANDY - University Of Arkansas

Submitted to: LWT - Food Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/8/2021
Publication Date: 6/26/2021
Citation: Siaw, M.O., Yang, Y., McClung, A.M., Mauromoustakos, A.S. 2021. Effect of protein denaturation and lipid removal on rice physicochemical properties. LWT - Food Science and Technology. https://doi.org/10.1016/j.lwt.2021.112015.
DOI: https://doi.org/10.1016/j.lwt.2021.112015

Interpretive Summary: Rice flour is growing in popularity as a food ingredient due to its hypoallergenicity and bland taste. Cooking properties of rice flour are predominantly governed by starch with amylopectin responsible for starch swelling and pasting properties, whereas amylose is responsible for inhibiting starch swelling. However, proteins and lipids also impact sensory and cooking qualities and thus affect end-use properties. Glutelin accounts for 60-80% of the total protein content in rice and restricts starch swelling properties and starch gel hardness. Prolamin, which constitutes 20-30% of rice protein, causes significant decreases in gel hardness but increases in the breakdown viscosity of starch gel when heated. Although lipids constitute only 1.6-3.1% of the total weight of brown rice, they are are highly concentrated in the outer layer of the grain close to the bran layer found in brown rice. This study was conducted to determine the combined impact of protein denaturation and lipid removal treatments on end-use properties including gelatinization and viscosity, swelling power, and water solubility of brown rice flours. Brown rice of four rice cultivars was evaluated using four protein denaturation (PD) treatments and four lipid removal (LR) treatments, as well as a combination of the two. Protein denaturation and LR exerted contrasting effects on the gelatinization temperatures of treated rice flour, and these effects were enhanced by treatment time. The high temperature applied during the PD treatment promoted protein-protein and protein-starch interactions, leading to increased gelatinization properties, and decreased pasting viscosities and swelling properties. Polar lipids acted as bridges to link starch granules and denatured proteins whereas the removal of non-polar lipids promoted protein-starch interactions and led to decreased pasting and swelling properties. The combined treatments resulted in more significant increases in gelatinization temperatures and decreases in pasting, swelling power and water solubility properties than the individual treatments. These results demonstrate that heat treatment can be employed to produce brown rice flour with improved heat and shear stabilities for specific applications for new food products using rice as an ingredient.

Technical Abstract: The physicochemical properties of rice are influenced by their chemical components and their interactions. It has been demonstrated that the interactions among rice chemical components are enhanced by protein denaturation (PD) via heat treatment and by lipid removal (LR) via solvent extraction. The objective of this study was to investigate the impacts of PD, LR, and their combined treatments on the swelling power, water solubility, and the gelatinization and pasting properties of four brown rice flours. Rice protein was denatured under a vacuum at 100°C and rice lipid was removed via hexane for varying times. The combined treatment was done in two ways; PD followed by LR (PD-LR), and LR followed by PD (LR-PD). The results showed that PD increased gelatinization temperatures while LR decreased gelatinization temperatures. Both PD and LR reduced pasting and swelling properties; however, PD resulted in a greater decrease than LR. Polar lipids are proposed to serve as bridges to link denatured proteins and starch granules in the combined treatments resulting in greater decreases in the gelatinization, pasting, and swelling properties than the individual treatments. The results obtained in this study demonstrate the importance of starch-lipid-protein interactions on the physicochemical properties of brown rice flour.