Scale formation of soluble salts is one of the major factors limiting the application of nanofiltration (NF) and reverse osmosis (RO) membranes. This article reviews the scale formation mechanisms in membrane systems, methods to retard scale formation, and a new hybrid system consisting of MF-NF/RO. Two distinct mechanisms in NF/RO fouling by scale formation including surface and bulk crystallization have been identified and investigated. The hydrodynamic operating conditions as well as module geometry determines which fouling mechanism is dominant. An increase in solute concentration at the membrane surface by concentration polarization is responsible for surface crystallization. Conventional methods for scale control only retard the rate of scale formation and their performances are unpredictable. On the other hand, using a MF-NF/RO hybrid system for continuous removal of crystal particles from the retentate stream appears to be effective at high recovery of permeate. When applying the MF-NF/RO hybrid system, substantial improvement in flux is observed in spiral wound module, whereas it is negligible in case of the tubular module. This is because the microfilter could only removes crystals formed in the retentate through the bulk crystallization that is the dominant fouling mechanism in the spiral wound module.

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A novel time-temperature indicator (ITI) using phospholipid-phospholipase was developed to monitor quality change of frozen foods during storage. The 'IT1 was more reliable than the lipase system and monitored quality changes of frozen pork during storage. The TTI was designed for reactions at sub-zero temperatures because the substrate emulsion would be stable at such temperatures. The lT1 contained glycerol and sorbitol as anti-freeze reagents and was designed to show distinctive color changes according to pH by mixing bromothymol blue, neutral red, and methyl red. The 'IT1 had an activation energy of 32.1.2 kcal/mol, suitable for many food reactions.

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