Impact of hydrothermal treatment on denaturation and aggregation of water-extractable quinoa (Chenopodium quinoa Willd.) protein

A comprehensive review on the recent trends in extractions, pretreatments and modifications of plant-based proteins

Plant-based proteins offer sustainable and nutritious alternatives to animal proteins with their techno-functional attributes influencing product quality and designer food development. Due to the inherent complexities of plant proteins, proper extraction and modifications are vital for their effective utilization. This review highlights the emerging sources of plant-based proteins, and the recent statistics of the techniques employed for pretreatment, extraction, and modifications. The pretreatment, extraction and modification approach to modify plant proteins have been classified, addressed, and the recent applications of such methodologies are duly indicated. Furthermore, this study furnishes novel perspectives regarding the potential impacts of emerging technologies on the intricate dynamics of plant proteins. A thorough review of 100 articles (2018-2024) shows the researchers' keen interest in investigating novel plant proteins and how they can be used; seeds being the main source for protein extraction, followed by legumes. Use of by-products as a protein source is increasing rapidly, which is noteworthy. Protein studies still lack knowledge on protein fraction, antinutrients, and pretreatments. The use of physical methods and their combination with other techniques are increasing for effective and environmentally friendly extraction and modification of plant proteins. Several studies explore the effect of protein changes on their function and nutrition, especially with a goal of replacing ingredients with plant proteins that have improved or enhanced qualities. However, the next step is to investigate the sophisticated modification methods for deeper insights into food safety and toxicity.

Modulation of physico-chemical and technofunctional properties of quinoa protein isolate: Effect of precipitation acid

The typically low solubility and gelation capacity of plant proteins can impose challenges in the design of high-quality plant-based foods. The acid used during the precipitation step of plant protein isolate extraction can influence protein functionality. Here, acetic acid and citric acid were used to extract quinoa protein isolate (QPI) from quinoa flour, as these acids are more kosmotropic than the commonly used HCl, promoting the stabilisation of the native protein structure. While proximate analysis showed that total protein was similar for the three isolates, precipitation with kosmotropic acids increased soluble protein, which correlated positively with gel strength. Microstructure analysis revealed that these gels contained a less porous protein network with lipid droplet inclusions. This study shows that the choice of precipitation acid offers an opportunity to tailor the properties of quinoa protein isolate for application, a strategy that is likely applicable to other plant protein isolates.

Effect of Starch on the Solubility of Quinoa Protein Isolates during Heat Treatment

There is increasing interest in developing quinoa products due to their unique nutritional value. Starch and protein are the primary components in quinoa, and the interaction between them affects the quality of quinoa products. This study extracted the starch and protein from quinoa and simulated the thermal processing of quinoa to investigate the effects of starch on the solubility and structure of quinoa protein isolates during heat treatment. The structure of quinoa protein isolates was characterized by fluorescence spectroscopy, Fourier transform infrared spectroscopy, laser particle size analysis, and scanning electron microscopy. The results showed that starch decreased protein solubility, and the maximum solubility was obtained after heating for 5 min. After starch addition during heat treatment, the surface charge distribution of protein changed, the degree of protein aggregation increased, the particle size of proteins increased, the thermal stability increased, and the β-sheet ratio of the proteins increased, suggesting that the protein structure is more ordered, which is the structural foundation of protein solubility decreasing. The research about the interaction between starch and protein and the effects on the solubility of protein could provide a reference for quinoa products processing.

Structural Properties of Quinoa Protein Isolate: Impact of Neutral to High Alkaline Extraction pH

In this work, we extracted proteins from white quinoa cultivated in the northeast of Qinghai-Tibet plateau using the method of alkaline solubilization and acid precipitation, aiming to decipher how extraction pH (7-11) influenced extractability, purity and recovery rate, composition, multi-length scale structure, and gelling properties of quinoa protein isolate (QPI). The results showed that protein extractability increased from 39 to 58% with the increment of pH from 7 to 11 whereas protein purity decreased from 89 to 82%. At pH 7-11, extraction suspensions and QPI showed the similar major bands in SDS-PAGE with more minor ones (e.g., protein fractions at > 55 or 25-37 kDa) in suspensions. Extraction pH had limited effect on the secondary structure of QPI. In contrast, the higher-order structures of QPI were significantly affected, e.g., (1) emission maximum wavelength of intrinsic fluorescence increased with extraction pH; (2) surface hydrophobicity and the absolute value of zeta-potential increased with increasing extraction pH from 7 to 9, and then markedly decreased; (3) the particle size decreased to the lowest value at pH 9 and then increased to the highest value at pH 11; and (4) denaturation temperature of QPI had a large decrease with increasing extraction pH from 7/8 to 9/10. Besides, heat-set QPI gels were formed by loosely-connected protein aggregates, which were strengthened with increasing extraction pH. This study would provide fundamental data for industrial production of quinoa protein with desired quality.

Effect of Hydrothermal Treatment on the Structure and Functional Properties of Quinoa Protein Isolate

The aim of this study was to investigate the effects of hydrothermal treatment at different temperatures and times on the structure and functional properties of quinoa protein isolate (QPI). The structure of QPI was investigated by analyzing changes in the intrinsic fluorescence spectrum, ultra-violet (UV) spectrum, and Fourier transform infrared spectrum. The solubility, water/oil-holding capacity, emulsifying activity, and emulsion stability of QPI were studied, as were the particle size and the thermogravimetric properties of QPI. The results showed that the average particle size of QPI gradually increased with the increase in hydrothermal treatment time and temperature, and reached a maximum value of 121 °C for 30 min. The surface morphology also became rough and its thermal stability also increased. The endogenous fluorescence and UV spectral intensity at 280 nm decreased gradually with increasing hydrothermal treatment time and temperature, and reduced to the minimum values at 121 °C for 30 min, respectively. After hydrothermal treatment, the secondary structure of QPI tended to be disordered. The functional properties of QPI after treatment were all superior to those of the control. The results of this study might provide a basis for the processing and utilization of QPI.

Heat-induced denaturation and aggregation of protein in quinoa (Chenopodium quinoa Willd.) seeds and whole meal

Physical barriers hinder about 20-25% of the protein from being extracted from whole meal. Heat-induced denaturation and aggregation of protein in quinoa seeds and in whole meal was investigated. Maximally 37% of the protein in seeds covalently aggregate when boiling for 15 min. Although embryonic cell walls surrounding protein bodies remain intact during boiling of seeds, protein aggregation is not hindered. 11S Globulin monomers first dissociate into their acidic and basic subunits which further assemble into large (> 500 kDa) mainly disulfide-linked aggregates. 2S Albumins are not involved in covalent aggregation but partially leach during seed boiling. The presence of disrupted food matrix constituents in whole meal delays denaturation and causes less aggregation of protein in whole meal than in seeds. Globulins still dissociate into their subunits but less and mainly small covalent aggregates (ca. 100-500 kDa) are formed. These novel insights allow developing new quinoa-based food products.