| Micellar casein concentrate (MCC) is a protein spray-dried powder manufactured from skim milk by membrane separation. MCC contains high concentrations of protein and low concentrations of lactose. Compared with the traditional caseinate produced by acid precipitation or rennet coagulation, MCC retains the native structure and shows excellent solubility, foaming and good flavor. MCC has been applied for beverage, ice cream, cheese,yogurt, pastry and functional foods, so it has a wide prospect of application. For the early realization of MCC domestic industrial production, this paper studied the membrane separation process of MCC, and the effect of spray drying temperature and ultrasonic pretreatment on physical and chemical properties and microstructure of casein micelle concentrate.Microfiltration (MF) membrane of 200 nm was used to separate of casein and other components consisting of serum proteins (SP),lactose, ash et al in skim milk. The results showed that: the average flux of ceramic membrane is about 20 Lm-2h-1, which can be used for industrial production. The cumulative removal percentage of ?-Lactalbumin,?-Lactoglobulin, lactose, ash, calcium, was 79.27%, 71.64%, 85.81%, 62.16%, 35.64%.respectively. At the end of the diafiltration process, the mass fraction of 2% NaOH and 0.5%nitric acid solution was used and the membrane flux can be recovered to 99.07% of the initial.The effect of spray drying temperature (130?/65?, 160?/78?, 180?/90?) on the functional properties and microstructure of MCC have been investigated. The results showed that the molecular structure change was insignificant at temperature of 130?/65?. but MCC surface become rough, and associated with depression at 180?/90?. As the increase of spray drying temperature, the D50 of MCC reduced from 14.13 ?m to 10.47?m, the solubility of MCC reduced from 84.14% to 60.44, the moisture content reduced from 4.07% to 3.20%, and the flow index reduced from 4.16 to 1.27.The effect of ultrasonic pretreatment on the functional properties of MCC have been investigated. Microfiltered casein protein retentates were treated with ultrasonic for 0 min,0.5 min, 1 min, 2 min, and 5 min prior to spray drying. The results showed that the conductivity increased from 454.00 ?S.cm-1 to 460.67 ?S.cm-1,the solubility increased from 84.14% to 91.03%, the hydrophobic force increased from 166.32 to 336.96.According to Fourier infrared spectrum, a-helix reduced from 26.39% to 22.82%,?-sheet reduced from 20.30% to 13.94, and ?- fold increase from 31.19% to 31.19%, random coil increased from 22.11% to 27.22%. According to electrophoresis image, there was no significant change in protein sequence. According to electron microscopy, there was significant microstructure changes in protein, and particle size decreased significantly.Moreover, the compressibility and the flow function of MCC decreased significantly after ultrasonic treatment. Additionally, after ultrasonic for 0.5 min, the Basic Flowability Energy(BFE) of MCC attained minimum value 709.31 mJ and after ultrasonic for 1 min, the specific energy (SE) of MCC attained maximum value 15.90 mJ/g.This study successfully realized separation of casein from skim milk through the membrane technology, which provided the reference for the industrialization of the MCC powder. In order to enhance the quality of MCC, spray drying technology and ultrasound modification were done. It can be speculated that these changes in functional properties of MCC would promote its application in food industry. |
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