Effect of salts on soy storage proteins defatted with supercritical CO₂ and alcohols

Abstract

The primary objective was to determine whether salts will stabilize soy storage proteins against the denaturing effects of alcohols or the heat and pressure used in supercritical CO 2 during the defatting process. Nitrogen solubility index (NSI) and differential scanning calorimetry (DSC) were used to monitor the denaturation of proteins. A variety of salt solutions used to hydrate full-fat soy grits increased the thermal stability of both 7S and 11S storage proteins. DSC was used to monitor their denaturation temperature. Neutral salt hydrations followed the lyotropic series for protein stabilization. Of the salts evaluated, the test results indicate that the reducing salt, sodium sulfite, and the neutral salt, sodium sulfate, when used to steep beans, yielded significantly higher NSI than did the watersteeped controls or other salt treatments after partial defatting with absolute isopropanol or ethanol and supercritical CO 2 . However, these same salt treatments did not as effectively stabilize the proteins against the denaturing effects of ethanol more aqueous than 84% when these alcohols were used as the defatting medium. JAOCS 75, 911-916 (1998).KEY WORDS: Defatting, differential scanning calorimetry, ethanol extraction of oil, heat denaturation, isopropanol extraction of oil, nitrogen solubility index, salt stabilization, soybeans, supercritical CO 2 extraction of oil.For the development of new methodologies to process soy with desired functional properties, the researcher must control the protein denaturation process. It is generally recognized that a high level of solubility reflects a versatile protein with good potential for use in either food or industrial product systems. Denaturing conditions, such as exposure to heat, high pressure, high shear, or organic solvents, tend to lower protein solubility. The denaturation process for soy storage proteins in the heterogeneous cracked bean system is extremely complex, particularly at low to intermediate moisture. Fats, carbohydrates, and nonprotein constituents not only impact the moisture dynamics in the whole bean but also impact the expected protein-solvent and protein-protein interactions during denaturation. Salt stabilization of proteins in solution is an old technology that has already been well researched. However, limited information is available on salt stabilization to protect protein from denaturation during processing under limited-moisture conditions. At high salt concentration (µ > 0.5), the ability of salts to stabilize proteins has been attributed to preferential hydration of the protein molecule as a result of the salt-induced alteration of the water structure in the vicinity of the protein (1). At high concentrations of neutral salts, proteins display decreased solubility, which may result in precipitation due to a salting-out phenomenon. Salting-out reduces solute-solvent contact and enhances solute-solute contact or entanglement by making water a poor solvent for the protein.Here, protein-protein interactions are favored over protein-sol...

Macadamia Oil Extraction With Alcoholic Solvents: Yield and Composition of Macadamia Oil and Production of Protein Concentrates From Defatted Meal

“…The degree of solvent hydration also negatively influences the protein solubility, since with Et6 and IPA12 the lowest NSI values are obtained. [22,31,32,[41][42][43] NSI is a measure of the degree of protein denaturation during processing, thus a low NSI value indicates a greater amount of denatured proteins [41] being the protein solubility influenced by the balance hydrophilicity/hydrophobicity on the surface of proteins. [44] Accordingly, the water-alcohol systems show hydrophilic and hydrophobic characteristics and alcohols destabilize proteins by weakening of the hydrophobic interactions between the non-polar residues and by disturbing the water structure around the protein molecules, which leads to the reduction of the NSI.…”

“…[44] Accordingly, the water-alcohol systems show hydrophilic and hydrophobic characteristics and alcohols destabilize proteins by weakening of the hydrophobic interactions between the non-polar residues and by disturbing the water structure around the protein molecules, which leads to the reduction of the NSI. [42]…”

Estudo da viabilidade técnica da substituição de hexano por etanol no processo de extração de óleo de soja: cinética de extração e índices de qualidade

“…Para o desenvolvimento de novas metodologias de processamento de soja é preciso ter um controle do processo de desnaturação proteica. O processo de desnaturação das proteínas de armazenamento em um sistema heterogêneo é complexo, uma vez que, lipídeos, carboidratos e constituintes não proteicos impactam, não somente na dinâmica da água, mas também nas interações entre proteína-solvente e proteína-proteína durante a desnaturação (Sessa et al, 1998).…”

“…Adicionalmente, é possível observar que ambas as amostras de fase rafinado oriundas de extrações com etanol com 6 e 12% de água, em massa, apresentaram queda dos valores de solubilidade de nitrogênio. Sessa et al (1998) Os resultados obtidos para rendimento de proteína na fase extrato com solvente contendo 6% de água, apresentados na Tabela 5.10, mostraram que na faixa de temperatura de 70 a 90 °C houve uma diminuição quando comparados aos resultados obtidos na faixa de 40 a 65 °C. Estes resultados sugerem que pode ter ocorrido a desnaturação proteica, tanto devido a elevada temperatura quanto a presença de água no solvente, e encontram-se em acordo com os resultados de solubilidade para as fases rafinado obtidos nestas condições.…”

“…As temperaturas de desnaturação (Td) encontradas neste trabalho foram superiores as temperaturas normalmente encontradas na literatura para soja, sendo para fração 7S em torno de 77 °C, e para fração 11S, em torno de 97 °C (Tang et al, 2007;Sobral et al, 2010;Lee et al, 2003;Murray et al, 1985). Sessa et al (1998) explicam que a Td reflete o conteúdo de água presente na amostra, sendo que quanto maior o conteúdo de água, mais baixas serão as temperaturas.…”