k-casein은 유단백질 분획으로 GMP를 포함하고있으떠 GMP는 sialic acid를 포함하고 있으므로 k-casein index로 sialic acid 가 사용될 수 있다. 탈지분유 분리 단백질 용해도는 칼슘카페인 보다 일반적으로 낮으므로 용매처리시 야기되는 k-casein의 손실과 저용해도와의 관계를 규명하고자 하였다. 특히 용매처리시 주요 stabilizing fraction k-casein의 손실 혹은 손상을 고려해야만 한다. 용매처리시 sialic acid 는 제1차 추출용매에 16.5%, 제2차 추출용매에 4.0%손실되어 전체 20.5%가 용매처리시 손실되었다. 또 사용한 메탄올의 농도가 증가할수록 sialic acid손실이 감소하여 sialic acid 손실은 메탄을분획보다 물분획에따라 좌우된 것 같다. 따라서 sialic acid를 함유한 분말 extracted solid의 feed back 실험 결과 10%첨 가시최대 용해도를 나타냈으며 유당은 용해도 변화에 기여하지 못하였다 결론적으로 탈지분유 단백의 저용해도 헌상은 용매처리시 k-casein의 가용성 물질 손실에도 일부 기인한 것으로 사료된다.
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.
