Ultrafiltration of defatted whey: improving performance by limiting membrane fouling

Optimizing clarified whey ultrafiltration: influence of pH

Whey clarification can be achieved by using a lipid aggregation step followed by microfiltration. The results from using an M5 Carbosep membrane to ultrafilter defatted sweet whey at pH values in the range 8·0–1·5 furnished understanding of the fouling process so that fouling may be minimized. The conventional method of aggregation, allowing the pH to decrease naturally, has been compared with a modified aggregation process in which the pH was maintained constant. These two methods differed significantly in their influence on the subsequent ultrafiltration (UF), with respect to the UF hydraulic characteristics, i.e. reversible, irreversible and overall fouling resistance. Optimal UF performance was obtained at a pH equal to or slightly higher than the aggregation pH (7·5) owing to the limited fouling contribution of proteins and calcium phosphates. The modified process permitted UF at fluxes in the range 50–115 1 h-1 m-2, with moderate transraembrane pressure, even with a protein content two to five times higher than that of regular whey.

Microfiltration performance: physicochemical aspects of whey pretreatment

Clarification of whey by microfiltration (MF) can be achieved after appropriate pretreatment of the feed. A control pretreatment consists of a physicochemical process comprising increased ionic calcium and pH accompanied by heat (50 °C, 15 min) to cause aggregation of complex lipid–calcium phosphate particles, which are then separated by MF. This pretreatment process was modified by increasing the temperature to 55 °C and by maintaining the pH constant during heat treatment. This modification resulted in larger calcium phosphate particles and a lower content of soluble calcium and phosphate ions. As a consequence, a longer period of MF operation, better whey clarification and lower calcium and phosphate content of the filtrate were achieved. This suggests that a loosely structured deposit was formed on the membrane surface which was less resistant to filtration than that resulting from the control pretreatment. During MF, it was necessary to avoid zones of high shear in the retentate compartment that might cause physical alteration of the aggregates.

Fluid dairy product quality and safety: looking to the future

The fiercely competitive nature of the US beverage industry will drive the fluid milk sector of the dairy industry to improve product quality and shelf life to enable dairy beverages to compete with innovative new introductions as well as with currently popular shelf-stable products. The recent substantial growth in the volume of flavored milk sales specifically suggests that attention is needed to improve these products. Further, increasing public awareness and regulatory attention directed toward food safety issues highlight the need for the dairy industry to proactively address and eliminate emerging food safety issues that may negatively impact the image of dairy products. Shelf life and sensory profiles of high temperature short time pasteurized fluid milk products are presented, illustrating the need for greater attention to controlling contaminating microorganisms in processed fluid milk products. Bacterial spoilage patterns of flavored versus unflavored milks are compared, and suggestions are presented for extending flavored product shelf lives. Strategies currently applied to extend shelf life are reviewed. Food safety issues facing the dairy industry are presented within the context of an overview of foodborne illnesses in the United States. The pressing need to determine thermal resistance characteristics of Mycobacterium paratuberculosis is described.

Ultrafiltration performance of heat-treated shamouti orange [Citrus sinensis (L.) Osbeck] juice

During ultrafiltration of orange juice with inorganic membranes, heating of the juice prior to the filtration experiment resulted in a significant increase of the fouling indices. The effect of the irreversible fouling (Rif) was always high, whereas the reversible fouling (Rrf) depended on the treatment. It was clearly seen that fouling was reduced after pectin degradation, but the heat treatment applied to the juice before filtration still resulted in reduced fluxes. It is suggested that pectins and proteins that undergo flocculation/coagulation during the heat treatment tend to interact with the membrane-filtering layer and to cause reduction of permeation flux. To clean the membrane to restore its pure water flux, close to the initial one, a proteolitic enzyme detergent wash was needed.