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Isolation and functional properties of protein from the whey of acid-modified gluten Dosanjh, Bakhshish S.


Insolubility of gluten in water and salt solutions limits its utilization in the food industry. To overcome this difficulty, gluten can be solubilized by mild acid treatment (47). Gluten in 0.02 N HCl was heated at 120°C for 30 minutes and water soluble protein fraction was precipitated at pH 4.7. The remaining whey possessed about 9% of the original protein in the gluten. Experiments were carried out to isolate the protein from whey and to assess its functional properties. Upon adjusting the whey to pH 1.0, about 44% of total N was precipitated, but the yield was increased to 74% by heating the acidified whey to 90°C for 10 minutes. The addition of ferric chloride (45 mg FeCl₃·6H₂0 per litre of whey with 0.4% protein) to the acidified whey before heating increased the yield to about 84%. Hexametaphosphate (HMP) (128 mg sodium hexametaphosphate per litre of whey) reduced the brown colour of the Fe-containing precipitate. Elution of HMP-Fe-protein through Sephadex G-200 column using 0.1 M phosphate buffer revealed four distinct peaks. Molecular weights of peaks were calculated to be (I) > 100,000, (II) 62,000, (III) 29,000 and (IV) < 10,000. Ash content of final product was high (8.8%) due to use of sodium hydroxide for neutralization. /Amino acid analysis showed significantly lower amount of lysine in HMP-Fe-protein compared to unhydrolyzed gluten. Ninety-nine point two percent N in HMP-Fe-protein was water soluble and had excellent emulsifying capacity. Foamability was poor but improved greatly when lowered to pH 5.0 before whipping. Isoelectric precipitates at pH 6.2 and pH 8.2 were also collected from the whey. Another sample was prepared by ultrafiltration of the supernatant after precipitation at pH 8.2. These three samples were compared with HMP-Fe-protein complex. The yield of all the three samples was lower but functional properties were equal to or better as compared to HMP-Fe-protein. The amino acid balance was significantly better in these samples.

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