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KMID : 0380619870190010061
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Korean Journal of Food Science and Technology
1987 Volume.19 No. 1 p.61 ~ p.65
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Effect of Reduction in Sialic acid on Solubility of Non Fat Dry Milk Protein Isolates
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Abstract
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The milk protein portion contains sialic acid which may be used as an index for k-casein. In comparison with non fat dry milk (NFDM) and calcium caseinate, the solubility of NFDM protein isolates at the various pH was inferior. Another consideration for the low solubility relates to the possibility that k-casein may have been extracted or possibly modified by the action of alcohol. The k-casein is the principal stabilizing fraction for casein micelle and any changes which result in its destruction or removal would be expected to have potent results. During solvent treatment, 16.5% of sialic acid was extracted in the first extraction solvent, whereas the second treatment caused only a 4.0% loss, based on sialic acid analysis. A study was conducted on the effect of concentration of methanol on loss of sialic acid. The loss of sialic acid decreased as the concentration of methanol increased to above 62% in both the first and second extracted solvent. It appears that loss of sialic acid is attributed to the water fraction rather than the methanol fraction. The effect of addition of the dried extracted solids on solubility was investigated. Protein solubility of NFDM protein isolates was sharply increased by 10% addition of the extracted solids and, thereafter, decreased. Efforts to restore solubility by feeding-back the extracted material supported the concept that removal of surface k-casein may have been a possible factor.
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