Camelina and sophia protein isolates show promise for functional foods

Camelina (Camelina sativa​ (L.) Crantz) and sophia (Descurainis sophia​ L.) belong to the Brassicaceae plant family. 

Camelina meal is the by-product of the oil extraction process from the seeds and defatted camelina meal contains approximately 45% protein, residual crude fat 4.9%, up to 15 % insoluble fiber, 10% carbohydrates, 3% minerals, and approximately 4% phytochemicals, as well as as vitamins. The nutritional quality of camelina protein is similar to that of canola protein. 

Sophia seeds have been used as a traditional medicine to relieve cough and chest discomfort, prevent asthma, and treat cancer. The seed contains 28% protein, 33% oil, and 4% ash. Their amino acids include aspartic acid, threonine, serine, glutamic acid, proline, glycine, alanine, valine, isoleucine, leucine, tyrosine, phenylalanine, histidine, lysine, and arginine. 

Despite these promising profiles, the authors of the current study say there are very few previous studies on extracted proteins and hydrolysates from camelina and sophia seeds, or looking into their functional properties.

Alkaline extraction (AE) has become the most popular technique for the preparation of proteins because of its fairly simple and cost-effective. However, studies have shown ultrasonic-assisted extraction (UAE) to be a more successful extraction method because it provides short extraction time, high extraction yield, low level of solvent use, and the improvement in solubility (Yagoub et al. 2017; Zou et al. 2017). 

Studies have also reported the effects of UAE on structural and functional properties of sunflower protein isolates (Malik and Saini 2018), walnuts (Zhu et al. 2018), faba beans (Martinez-Velasco et al. 2018), and canola protein isolates (Flores-Jimenez et al. 2019). Additionally, the sonicated protein extraction increased gelation capacity while decreasing foaming capacity (Ly et al. 2018). This suggests potentially improved functional and nutritional properties of food proteins developed using UAE. However, according to the current research report, there are no previous studies on the effects of ultrasound treatment on the quality of camelina protein isolate (CPI) and sophia protein isolate (SPI).

The study

In the current study, two researchers from the Memorial University of Newfoundland, Canada, analysed CPI and SPI produced by UAE compared with those produced by AE.

The results indicate the ultrasonic-assisted extraction method was more effective than the traditional method for the extraction of proteins from camelina and sophia seed meals.

The report states: "There were no differences in protein subunit bands for all the samples prepared by ultrasonic-assisted extraction. The surface hydrophobicity of CPI and SPI was higher than that of soybean protein isolates. Ultrasonic-assisted extraction significantly improved water holding capacity and oil absorption capacity, emulsifying capacity, and foaming capacity of the CPI and SPI which indicate the potential use of CPI and SPI as a replacement for soybean protein in food formulations. Further studies on the protein value and digestibility of CPI and SPI are necessary for their application as food ingredients."​

Solubility​

Solubility is one of the most critical characteristics of protein isolates in food formulations as it relates to other functional properties, especially in foams, emulsions, and gels. It also influences the colour, texture, and sensory quality of products. 

This study found  the solubility of UAE protein isolates improved significantly compared with AE. Many factors, including the molecular size and composition of protein, influence protein solubility. The decreased particle size caused by ultrasound is likely to increase protein solubility due to better interaction between protein and water 

Water holding capacity​

Water holding capacity is a measure of the ability of proteins to associate gravity with water and it is closely associated with food products’ texture, mouthfeel, and viscosity (Deng et al. 2019). The WHC of CPI and SPI is significantly higher than that of soy PI. Besides, the WHC of CPI (UAE) increased by 20.3 % compared with that of CPI (AE) while the WHC of SPI prepared UAE was significantly unchanged. This can be explained by the decrease of the particle size and the improvement of protein solubility for samples extracted by UAE (Wang et al. 2020). Therefore, CPI and SPI could be used to possibly replace soy protein isolates in certain foods.

Oil absorption capacity​

In general, the oil absorption capacity of proteins represents their ability to bind to oil. It is closely correlated with flavor retention, shelf life, and emulsifying properties. This characteristic may be influenced by factors such as amino acid composition, the type of oil employed, and hydrophobicity, as well as the method used to extract the protein (Deng et al. 2019; Dong et al. 2011). The results indicate that the oil adsorption ability of CPI and SPI was better than that of soy PI. Compared with AE, the OAC of CPI (UAE) and SPI (UAE) were more enhanced by 29.52 % and 16.95 %, respectively. The improved OAC could be due to the exposure of hydrophobic groups after using UAE. The surface hydrophobicity of CPI and SPI using UAE increased in this analysis, which may make up for the increased OAC of protein isolates.

Foaming properties​

Foaming properties are correlated with the ability to decrease surface tension at the water-air interface and are strongly linked to the protein structure. Also, the foam capacity and foam stability are strongly correlated with protein solubility. The higher protein solubility improves water-protein interactions and helps to unfold the protein structure, therefore enhancing air encapsulation (Mundi and Aluko 2012; Zhang et al. 2018).

With UAE, the FC and FS of SPI were significantly higher than that of AE while they were relatively unchanged in CPI. Ultrasound-assisted alkali extraction could increase foam formation causing changes in protein structure and increase surface hydrophobicity (Wang et al. 2020).

Emulsifying properties​

The emulsifying ability index (EAI) and emulsion stability index (ESI) of CPI at various pH were observed. The UAE method affects the structure of protein isolates by enhancing molecular flexibility and surface hydrophobicity (Wang et al. 2020). The EAI of all samples was higher than that of soy PI at most tested pH values. This suggests the CPI and SPI prepared by UAE emulsifying ability, making it a good candidate emulsifying agent for use in the food industry.

Source: BMC Food Production, Processing and Nutrition​

Ngo, N.T.T., Shahidi, F. 

"Functional properties of protein isolates from camelina (Camelina sativa (L.) Crantz) and flixweed (sophia, Descurainis sophia L.) seed meals"​

https://doi.org/10.1186/s43014-021-00076-8