Pilot‐plant fractionation of soybean glycinin and β‐conglycinin

Abstract

A laboratory process for separating glycinin and β-conglycinin from soybean flakes was successfully scaled up to the pilot-plant scale (15 kg soy flakes). Average yields of the glycinin and β-conglycinin fractions were both 9.4% on a dry basis (db). The protein contents of glycinin and β-conglycinin fractions were 92.8 and 97.7% db, respectively. The glycinin and β-conglycinin purities were 90.4 and 72.7% of the protein content, respectively, which were very comparable to those of the laboratory-scale process. The total sulfhydryl plus half cystine content of the glycinin fraction was 37.8 mol/mol protein and 14.8 mol/mol protein for the β-conglycinin fraction. The native glycinin structure loss in the glycinin fraction was negligible. The native β-conglycinin loss in the β-conglycinin fraction was 10%, as estimated by rocket immunoelectrophoresis analysis. Hydrophobicity index value showed that hydrophobic properties of the pilot-plant protein fraction were ordered, from high to low: β-conglycinin fraction > glycinin fraction > intermediate mixture fraction.Paper no. J8950 in JAOCS 76, 285-293 (March 1999).KEY WORDS: β-Conglycinin, glycinin, pilot-plant process, protein, protein physicochemical properties, protein yield and purity, soybean proteins, soybeans, soy protein separation.Glycinin and β-conglycinin, the two major soybean storage proteins, apparently play different roles in food and nonfood soy protein products due to their different functional properties such as hydrophobicity, solubility, sulfhydryl cross-linking, gelation, and film formation. Wolf et al. in 1962 (1) first obtained 91-93% ultracentrifugally pure glycinin (11S) by cryoprecipitation followed by fractionation with ammonium sulfate. They reported 25% yield for the purified glycinin. Factors influencing yield and purity of the glycinin fraction, such as extraction ratio, temperature, pH, salt and sugar content, and reducing reagent (2-mercaptoethanol, 2-ME), have been investigated (2). Koshiyama (3) reported a procedure for glycinin and β-conglycinin (7S) fractionation. The glycinin fraction was first cryoprecipitated, and then 0.025 M CaCl 2 was added to remove the residual cold-insoluble proteins. The 7S fraction, which contained mostly β-conglycinin, was precipitated by adjusting the pH of the supernatant to 4.5. After gel filtration, a homogeneous β-conglycinin fraction was obtained as evaluated by ultracentrifugal analysis, which does not differentiate among different proteins of comparable mass. Thanh et al. in 1975 and 1976 (4,5) developed a straightforward process for glycinin and β-conglycinin separation based on differential solubilities of glycinin and β-conglycinin at pH 6.1-6.6. Tris (THAM) buffer (pH 8.0) containing 10 mM 2-mercaptoethanol (ME) was used to extract soy proteins. Glycinin was separated by adjusting the pH to 6.4 and collecting the precipitate after centrifuging at 2-5°C. β-Conglycinin was precipitated at pH 4.8 and purified by redissolving the precipitate in the 0.03 M Tris buffer and adjusting the pH to 6.2. ...

Improved Fractionation of Glycinin and β-Conglycinin and Partitioning of Phytochemicals

“…Glycinin fraction weight was lower at 65°C. These data support the hypothesis of Wu et al (10) that the intermediate fraction is primarily composed of glycinin and -conglycinin proteins that are no longer in their native state. The whey fraction weights were not different, indicating that denatured protein was not being partitioned into whey.…”

“…Wu et al (10) indicated that most of the glycinin and -conglycinin proteins comprising the intermediate fraction were no longer in the native state. It is probable that as the native state was lost and due to protein unfolding, more hydrophobic areas were exposed to interact with the isoflavones.…”

Functional properties of protein ingredients prepared from high‐sucrose/low‐stachyose soybeans

“…Surface hydrophobicity was measured by using the methods of Wu et al (9) with 1-anilino-8-naphthalene sulfonic acid magnesium salt monohydrate (ANS; ICN Biomedicals, Inc., Aurora, OH). Protein dispersions (prepared as in the solubility test) were stirred, adjusted to pH 7.0, and centrifuged at 10,000 × g and 20°C for 10 min.…”

Fate of Phytic Acid in Producing Soy Protein Ingredients

“…The soy protein fractionation procedure utilized as the control in the present study has been reported by Wu et al [17] and was a modification of a procedure first reported by Nagano et al [18]. About 100 g of defatted soy flour was extracted with de-ionized water at 15:1 water-to-flour ratio, the pH was adjusted to 8.5 with 2N NaOH, and the resulting slurry was stirred for 1 h. After centrifuging at 14,300·g and 15°C for 30 min, the protein extract (1st extract) was decanted, and the amount of insoluble fiberrich residue was determined and sampled for proximate composition.…”