| Milk protein concentrate(MPC) is concentrated milk protein powder produced from skim milk by the processing steps of ultrafiltration, diafiltration, evaporating, concentrating and spray drying. Because of the characteristics of high protein, low lactose and some special functional properties, MPC are widely used in food industry. But for another, due to the high protein content, the solubility of MPC decreases significantly during storage, which seriously affects the performance of its functional properties. At the same time, previous studies showed that the sequestration of calcium from MPC could significantly improve the solubility of MPC during storage, which might greatly broaden its application in food industry.This study focused on the usage of the ion exchange resin to effectively remove the exact amount of calcium from MPC system, to suppress the solubility decrease of MPC during storage. It also illustrated the effect of different decalcification ratios on the physicochemical properties of the retentates, the solubility of the MPC during storage and the functionalities of the MPC. This study was devoted to develop new MPC with high storage stability and improved functionalities in order to prolong the shelf life and broaden the applications. The significant conclusions are as follows:(1) Processing of decalcified retentate: The retentate after ultrafiltration had 10.1% total solid and 9% protein. After comparing the ion exchange efficiency of two kinds of ion exchange resins: strong and weak acid types cation exchange resin, including the ion exchange resin dosage, ion exchange time as well as the resin exchange capacity, and the more suitable ion exchange resin chosen for this study was Amberlite SR1 L Na. The static ion exchange time determined was 2 h; and eventually a series of decalcification ratios from 0%to 83.6% for retentates were obtained.(2) Physicochemical properties of decalcified retentates: Regarding the physicochemical properties of the retentates with different decalcification ratios, we did research on the appearance, dissociated protein content, particle size, casein micelle structure and the existing form of colloidal calcium phosphate(CCP) of the retentates. And the results consistently showed that most of the casein micelles dissociated when up to 38.7% of total calcium was removed.(3) Processing of decalcified MPC: 0, 10, 20, 30, 40 g ion exchange resins were added to each 100 g retentate to accomplish 2 h static ion exchange. The obtained milk retention experienced spray drying at inlet temperature of 135 oC and outlet temperature of 75 oC to obtain 0%, 11.1%, 18.6%, 27.0% and 37.1% decalcified MPC.(4) Storage stability of decalcified MPC: The solubility, soluble protein content,dissolution particle size distribution and dissolution microstructure of 0-37.1% decalcified MPC at different storage time were studied. In comparison, fresh non-decalcified MPC was well-dissolved, but its solubility kept decreasing during storage. The storage solubility of fresh 11.1% decalcified MPC was slightly improved. 18.6-37.1% decalcified MPC showed a high level solubility during storage.(5) Functionalities of decalcified MPC: Based on the main applications of MPC in food industry, the functionalities of the study were determined as gelation property, foamability and emulsification. Gelation property of the MPC decreased gradually with the increase of decalcification ratios, but the supplement of calcium could significantly increase the gelation property. Especially, the gelation property of 11.1% decalcified MPC recovered to original value by supplement of calcium. In addition, the foamability and foam stability, the emulsification and emulsion stability were improved with the increase of decalcification ratios.Based on the above analysis, we have the conclusions as follows: 11.1-18.6% decalcified MPC have good physicochemical properties, storage stability, gelation property, and they can be applied into yogurt, cheese and other products as a novel food ingredient. 18.6-37.1%decalcified MPC have improved storage stability, foamability and emulsification, and they can be used in whipped cream, milk foam, ice cream and other food as a new food ingredients.In addition, the solutions of highly decalcified MPC(>37.1%) are clarified, therefore they are expected to be used for processing transparent dairy beverage. |
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