Mobility and Stability Characterization of Model Food Systems Using NMR, DSC, and Conidia Germination Techniques

Water usability as a descriptive parameter of thermodynamic properties and water mobility in food solids

A classic problem in preservation is the microbes can grow in low-moisture foods. In this paper, the water sorption, and thermodynamic properties of glucose/WPI solid matrices were measured, while their molecular mobility was analyzed and associated with the microbial growth of D. Hansenii at various a_w and 30 °C. Although the sorption isotherms, T_g, and relaxation processes of studied matrices were affected by a_w and WPI, the microbial growth showed highly dependent on water mobility rather than a_w. Hence, we introduced water usability (U_w), derived from the mobility difference between system-involved water and liquid pure water explicating from the classical thermodynamic viewpoint, to describe the dynamic changes of water mobility in glucose/WPI matrices. Despite to a_w, the yeast growth rate was enhanced at high U_w matrices concomitantly with a rapid cell doubling time. Therefore, the proposed U_w provides a better understanding of the water relationships of microorganisms in food preservation.

Investigating the moisture sorption behavior of amorphous sucrose using a dynamic humidity generating instrument

The moisture sorption behavior of freeze-dried amorphous sucrose was investigated using a dynamic humidity generating instrument, the Dynamic Vapor Sorption (DVS) instrument. The kinetic moisture sorption profiles of freeze-dried amorphous sucrose samples with 29% crystalline content were obtained using the DVS instrument at 9 relative humidity (RH) values, ranging from 10% to 90%, at 25 degrees C. Moisture-induced crystallization was observed for %RH values between 40% and 80%, where the crystallization onset time decreased as %RH increased. The moisture sorption behavior of freeze-dried amorphous sucrose with 3 crystalline contents, 23%, 29%, and 80%, was also compared, revealing that the crystalline content had a significant impact on the pseudo-sorption isotherm of freeze-dried amorphous sucrose. In general, for %RH values below 90%, samples that had a lower percent crystalline content had a higher pseudo-equilibrium moisture content, with the difference becoming most pronounced for the 60% to 80% RH values. The moisture-induced crystallization results as a function of %RH obtained in this study were compared to those previously reported in the literature, leading to an extensive discussion of both the experimental protocols used and the hypothesized mechanisms governing the long-term stability of amorphous materials. The hypothesized mechanisms discussed included the glass transition temperature boundary, the zero mobility temperature, and the hydration limit. Based on the dissimilarity in these hypothesized mechanisms, additional theoretical and experimental exploration is still merited in order to adequately predict the conditions (for example, moisture content, %RH, and temperature) required to ensure long-term stability of amorphous solids.

Determination of the bulk moisture diffusion coefficient for corn starch using an automated water sorption instrument

The bulk moisture diffusion coefficient (Db) is an important physical parameter of food ingredients and systems. However, the traditional method of measuring Db using saturated salt solutions is very time-consuming and cumbersome. New automated water sorption instruments, which can be used to conveniently and precisely control both relative humidity and temperature, provide a faster, more robust method for collecting the data needed for determining Db. Thus, the objectives of this study were to (1) investigate the use of the DVS instrument for collecting the data needed for determining the adsorption (Dba) and desorption (Dbd) bulk moisture diffusion coefficients for dent corn starch as a function of relative humidity and (2) determine the effect of temperature on Dba for dent corn starch at a constant relative humidity. Kinetic water sorption profiles of dent corn starch were obtained at eight relative humidity values ranging from 10 to 80% at 10% intervals at 25 degrees C and at five temperatures, 15, 20, 25, 30, and 35 degrees C, at 50% relative humidity using a DVS instrument. Db was calculated from the kinetic water sorption profiles using the full solution of Fick's second law for the thin slab model, as well as the slope method, a simplification of the full model. The Dba of dent corn starch at 25 degrees C reached a maximum at intermediate relative humidity values, after which Dba decreased due to a change in the moisture diffusion mechanism from vapor to liquid diffusion. The Dbd of dent corn starch at 25 degrees C remained nearly constant as a function of relative humidity. The Dba for dent corn starch increased as temperature increased from 15 to 35 degrees C, with an activation energy of 38.85 +/- 0.433 kJ/mol.

The influence of additives on beer stability investigated by EPR spectroscopy

In thermally-accelerated aging followed by EPR spectroscopy of beer samples of various stabilities, free radical 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPOL) was shown to be an effective indicator of the breakdown of a sample's stability, comparable to the commonly used spin trapping agent alpha-phenyl-N-tert-butylnitrone (PBN). Both indicators were then employed to investigate the influence of additives on beer stability. The addition of L-ascorbic acid (ASC) to the beer samples accelerated the radical processes and a lower stability was found. DL-alpha-tocopherol (alpha-TOC) did not influence beer stability significantly (probably due to its limited solubility). Na2SO3, described as a very effective stabilizer in experiments with the PBN spin trap, was found not to be effective using the TEMPOL indicator. This is probably due to inhibition in the formation of spin adducts or their degradation by Na2SO3.