Influence of Water Activity

Water availabihty will influence the rate of numerous Maillard pathways thereby influencing the rate of overall flavor formation and possibly flavor character. This is anticipated since some chemical reactions produce water as a byproduct (reaction pathway is inhibited by water) while other chemical reactions consume/require water (reaction pathway is promoted by water). 

Leahy and Reineccius [22] found the influence of water activity on the rate of formation of alkyl pyrazines in a model system to parallel that of classical Maillard reaction. Briefly, the accumulation of pyrazines reached a maximum when heated at an Aw of ca. 0.75 and decreased with either increasing or deCTeasing Aw. This observation suggests that the rate of pyrazine formation is controlled by the initial stages of the Maillard reaction as opposed to an effect on specific pathways of pyrazine formation. 

The accumulation of thiazoles during the heating of a cysteine Dimethylhydroxy-furanone (DMHF) model system decreased with increasing water content while the accumulation of thiophenones and 3,5-dimethyl-l,2,4-trithiolane had an optimum moisture content (ca. 80%) and 2,4-hexanedione and 3-hydroxy-2-pentanone increased with moisture content [23.24], There is little question that the Aw (or moisture content) influences both the rate of the Maillard reaction and influences the sensory properties of a system on heating. 

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Ukhun, M.E. and E.N. Dibie. 1989. Cyanide content of cassava mash and gari flour and influence of water activity (aw) during storage. Bull. Environ. Contam. Toxicol. 42 548-552. 

Leung, H.K. 1987. Influence of water activity on chemical reactivity. In Water Activity Theory and Applications to Food (L.B. Rockland and L.R. Beuchat, eds.) pp. 27-54. Marcel Dekker, New York. 

Describes the physicochemical and biological influences of water activity on food. 

Dalla Rosa, M., Pittia, P., and Nicoli, M.C. 1992. Influence of water activity on headspace concentration of volatiles over model and food systems. Ital. 1 Food Sci. 4 421-432. 

L. S. Malec, A. S. Pereyra Gonzales, G. B. Naranjo, and M. S. Vigo, Influence of water activity and storage temperature on lysine availability of a milk like system, Food Res. Int., 2002, 35, 349-353. 

Rockland, L.B., and S.K. Nishi. 1980. Influence of water activity on food product quality and stability. Food Technol. 34, no. 4 42-51, 59. 

In this work we used an aluminium oxide humidity sensor to measure inline the water vapour pressure. We investigated the partitioning of water between SC-CO2 and the enzyme preparation and we determined the influence of water activity on the initial reaction velocity. 

Allegro C. Oliveira F.A.R. Pocas M.F. 1997. Influence of water activity and oxygen on keeping quality characteristics of ffeeze-dried strawberries. In Proceedings of the Third Main Meeting Process Optimisation and Minimal Processing of Foods, pp. 314-318. 

Zhu H and Grant DJW. Influence of Water Activity in Organic Solvent + Water Mixtures on the Nature of the Crystallizing Drug Phase. 2. Ampicillin. Int J Pharm 1996 139 33-43. 

FIG. 5. Diagrammatic representations of the influence of water activity upon some chemical, enzymatic, and microbiological changes and on overall stability and moisture sorption properties of food products. Source Rockland and Nishi (1980). 

Troller, J. A. (1980). Influence of water activity on microorganisms in foods. Food Technol. 34(5), 76. 

FIGURE 11.14 Influence of water activity on HMF accumulation and brown pigment formation in orange juice concentrate at 45°C for 48 days. 

Zhu, H. Yuen, C. Grant, D.J.W. Influence of water activity in organic solvent plus water mixtures on the nature of the crystallizing drug phase. 1. Theophylline. Int. J. Pharm. 1996, 135, 151-160. 

Sawalha H, den Adel R, Venema P, Bot A, Floter E, van der Linden E. Organogel-emulsions with mixtures of beta-sitosterol and gamma-oryzanol Influence of water activity and type of oil phase on gelling capability. J Agric Eood Chem. 60(13) (2012) 3462-3470. 

Wenqing L, Defa L, Wu Y. (2003). Influence of water activity and temperature on xylanase biosynthsis in pilot-scale sohd-state fermenter by Aspergillus sulphureus. Enzyme Microb Technol, 32, 305-311. 

Cuzzoni, M.T. Stoppini, G. Gazzani, G. Influence of water activity and reaction temperature of ribose-lysine and glucose-lysine Maillard systems on mutagenicity, absorbancy, and content of furfurals. Food Chem. Toxicol. 1988, 26,815-822. 

Chowdary, G. V., and S. G. Prapulla. 2002. The Influence of Water Activity on the Lipase Catalyzed Synthesis of Butyl Butyrate by Transesterification. Process Biochemistry 38 (3) 393-397. 

Figure 11.10 Influence of water activity and temperature on the water vapour barrier properties of wheat gluten-based films. At 5 °C (A), 20 °C ( ) or 50 °C ( ) (from Gontard and co-workers [58])...

The influence of water activity on enzyme activity is shown in Figure 9.4. The reaction rates of all enzymatic reactions slow as water activity becomes limiting. This may be due to reduced enzyme and substrate mobihty at low water activities. If water is needed for the reaction, e.g., a hydrolysis reaction, limited water avail-abiUty will further slow the reaction rate. One should note that in the example, water was added to all samples on day 48 (to increase the aw to 0.75). It is relevant that the enzyme activity of all the lower water activity samples iuCTeased back to their full activity. This has relevance to EM dairy products in that a dry EM product may appear to be stable, i.e., exhibit little change with time, even if it has active enzymes. However, if the active dry product is giveu the opportunity to gain moisture, e.g., added to a high moisture food, the enzymes may continue to attack the dairy product... 

Figure 7.40 Influence of water activity on microorganisms and important reactions in foods r = relative reaction rate, =...

Study of the influence of water activity on the mechanism and kinetics of electrode reactions and their formal potentials in concentrated electrolytes. 

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