Influence of the activity of water on the spoilage of foodstuffs

Abstract

An original method for the evaluation of activity of water as a function of water content is described. The effect of temperature on activity, and the effect of the activity of water on drying rate, growth and destruction of micro-organisms, enzyme action, chemical reactions, etc., are determined.

The prediction of moisture sorption isotherms for dairy powders

“…The GAB constants, correlation coefficients and standard error of estimates are given in Table 4. The decrease in moisture content at a given water activity with an increase in temperature, as seen with the data obtained for both the WPI and HMCP at 50 1C, is consistent with the observations of Loncin et al (1968) and Hermansson (1977). MPC powder (Fig.…”

“…This allows the water to become free, which results in an increase in water activity (Jaya, Sughagar, & Das, 2002). This temperature effect has been seen with casein (Loncin, Bimbenet, & Lenges, 1968), whey protein concentrate (Hermansson, 1977), skim milk powder (Berlin, Anderson, & Pallansch, 1970), non-fat milk powder (Heldman, Hall, & Hedrick, 1965), amorphous sucrose (Iglesias et al, 1975), amorphous glucose (Loncin et al, 1968) and sugar beet root (Iglesias et al, 1975). Bronlund and Paterson (2004) found negligible influence of temperature on the isotherm of amorphous lactose over the temperature range of 20-38 1C and at 12 1C, the isotherm deviated downwards above 0.4 water activity.…”

Non-Enzymatic Degradation Pathways of Lactose and Their Significance in Dairy Products

“…It is generally accepted that rates of Maillard reactions are maximal at intermediate a w values (0.5-0.7) (Labuza et al, 1970). In milk powder, browning reactions are maximal at a w values of 0.6-0.7 (Loncin et al, 1968;Ben-Gera and Zimmerman, 1972), whereas in whey powders, the maximum occurs at an a w of 0.44. However, the relative increase in reaction rate with a w is less as temperature is increased (Malec et al, 2002).…”

Enzyme-assisted food processing

“…A reduced A w induces conformational changes, destabilization of enzyme integrity, and loss of catalytic activity. In general, most enzymes require A w ³ 0.85 to have catalytic activity, the exceptions being lipases that may actually remain active and gain activity at A w values as low as 0.3, and even as low as 0.1 (Loncin et al 1968 ) . The unusual behavior of lipases is attributed to an interfacial phenomenon that proceeds better in a reduced moisture environment.…”