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Lettuce and spinach inoculated with Escherichia coliO157:H7 were processed and handled in ways that might occur in commercial situations, including variations in holding times before and after product cooling, transportation conditions and temperatures, wash treatments, and product storage temperatures and times. Populations of background microflora and E. coliO157:H7 were enumerated after each step in the system. Data analysis was done to predict response variables with a combination of independent categorical variables. Field temperature, time before cooling, and wash treatment significantly affected E. coliO157:H7 populations on both products. The lowest populations of E. coliO157:H7 were encountered when precool time was minimal, lettuce was washed with chlorine, and storage temperature was 4°C. For lettuce, field and transportation temperature were not important once the storage period started, whereas after 2 days E. coliO157:H7 populations on packaged baby spinach were not affected by field temperature. On chopped iceberg lettuce and whole leaf spinach that was packaged and stored at 4°C, E. coliO157:H7 contamination could still be detected after typical handling practices, although populations decreased from initial levels in many cases by at least 1.5 log units. In abusive cases, where populations increased, the product quality quickly deteriorated. Although E. coliO157:H7 levels decreased on products handled and stored under recommended conditions, survivors persisted. This study highlights practices that may or may not affect the populations of E. coliO157:H7 on the final product.

This study was undertaken to determine the influence of storage time and temperature on the volume, weight, and pH of egg albumen, the physical strength of vitelline membrane, and the fate of SalmonellaEnteritidis artificially inoculated into egg albumen. A fiber-optic probe was used for inoculation with SalmonellaEnteritidis at 102, 104, or 106cells per egg. Both fresh and inoculated eggs were stored at 4, 10, and 22°C for 6 weeks. Five fresh uninoculated eggs from each storage group were collected each week, and the weight, volume, and pH of the egg albumen were measured. The forces, energies, and degrees of membrane deformation required to rupture the vitelline membranes also were determined from either albumen-free yolks or yolks surrounded by albumen. In separate experiments, five inoculated eggs were evaluated each week for populations of SalmonellaEnteritidis. When the eggs were stored at 4°C, the albumen retained significantly more volume and weight and had a relatively lower pH. The vitelline membranes from eggs stored at 4 and 10°C required more force and energy for rupture. Salmonellae flourished at 22°C, even in the albumen with the lowest initial population, 102cells per egg. Storage at 4 and 10°C inhibited the growth of salmonellae in the albumen of eggs with initial populations of 102, 104, or 106cells per egg. In eggs with initial Salmonellapopulations of 106cells per egg that were stored at 22°C, the populations of reached as high as 1010cells per egg after 4 weeks of storage. Storage at 4 and perhaps 10°C postponed the aging process of chicken eggs, preserved the antimicrobial agents of the albumen, and maintained the integrity of vitelline membrane. Low-temperature storage therefore had a significant impact on the safety and overall quality of the eggs.

The effects of hydroxypropylation (molar substitution, MS 0.05, 0.12, and 0.18) and cross-linking (0.03%, 0.1%, and 0.2%) on swelling properties of wheat starch granules at several temperatures and heating times were investigated by laser diffraction particle size analysis. Starch samples were dispersed in water at temperatures ranging from 30 to 90°C, for 1 to 360 min. All starch granules exhibited distinct bimodal size distributions: small B-granules with mean diameter of 2.3 μm and large A-granules with mean diameter of 20.4 μm. As temperature increased, the B-granules swelled more than A-granules. Swelling of A-granules sharply increased at 60°C. Swelling was more pronounced with increasing molar substitution of hydroxypropyl groups, while increased swelling was not observed in cross-linked starches. The dependence of swelling capacity on heating time was different at 60 and 80°C as well as amongst modified starches. As heating time was prolonged, mean granule sizes for native, control, and hydroxypropylated starches at 80°C decreased after reaching maximum size due to loss of granule integrity, while those at 60°C showed no significant change.

A multifactorial design was used to study the role of protein (Pro), polyphenols (PP), sucrose (Suc), pectin (Pec), potassium (K), and pH in the formation of haze in wine. Model wines (32) containing two levels of each factor plus yeast and nutrients were made and allowed to ferment to 0 Brix. Measurements of transmission at 633 nm (%T) following heating showed that PP, Pro, Pro*PP, Pec, and PP*Pec were all significant factors affecting turbidity. Molecular weight and size determinations by size‐exclusion chromatography‐laser light scattering indicated that molecular weight depended on Suc*Pec, Pro*PP*pH, and Pro*Pec*pH while molecular radius depended on PP*Suc*Pec, Pro, PP*Pec, and Suc*pH. Measurement of protein after filtration showed that Pro, PP, Pro*PP, and Pro*PP*pH were all factors. Laser diffraction studies showed three primary peaks in the range 0.05 ‐ 800 μm. The smallest size range had Pro*pH as a significant factor, while the largest had Pec and Pro*K as factors. These results indicate that a variety of factors are important to haze formation and that measurement of particle size, distribution, and interactions depends upon the instrument used to measure it.

The formation of ice during food freezing was examined by magnetic resonance imaging (MRI). Formation of ice was seen as a reduction in spatially located NMR signal intensity. Potatoes, carrots, peas, corn, and chicken legs were studied with an image resolution of 350 μm. Internal structures differentiated by water or fat content were highlighted by MRI. For all but corn, the ice interface advanced uniformly but asymmetrically. Corn kernels froze individually in a process possibly governed by ice nucleation. The time required for the signal to disappear corresponded to that required to reach steady-state enthalpy. MRI could serve to assess freezing times and the importance of food structure to the freezing process.

Magnetic resonance imaging (MRI) techniques have been utilized to experimentally measure velocity profiles and apparent Theological properties of fluid/paniculate mixtures as functions of flow rate, particle loading, and particle size. The experimental velocity profiles were described by apower law model for these systems. A 3% aqueous sodium alginic acid solution was used to form two particle sizes of 2.5 mm and 5.0mm in diameter. The spheres were suspended in a 0.5% carboxymethyl cellulose solution at loadings ofO, 10, 20, and 30% by weight. The average fluid velocity ranged from 2–35 cm/s. The flow behavior index decreased as flow rate, particle loading or particles size increase. Cumulative residence time curves were evaluated based on this modeling procedure. Results of this research have direct application to aseptic processing of fluid/particulate mixtures.

The viscosities of glucose, sucrose, and maltodextrin solutions coexisting with ice were measured by rotational viscometry. Samples were prepared by forming a shell of pure ice in a stainless steel tube immersed in a cooling bath, then introducing aqueous solutions at concentrations corresponding to the ice-melt equilibrium temperature. Temperature dependence of viscosity was analysed in terms of Arrhenius, VTF, WLF, and power-law models. Two glass transition reference temperatures were used with the WLF and power-law models: (1) Tgassociated with the transition from liquid to glass and (2) Tg′ associated with the transition to glass from a maximally freeze-concentrated solution. Plots of Logη vs I/T were fairly linear for each solution, but each displayed a unique slope with EAranging from 168 kJ/K mol to 464 kJ/K mol. WLF and power law models gave a linear fit to all solutions when Tgwas chosen as the reference temperature. Regression analysis gave constants of C1= 16.5 and C2= 37.5 for WLF (Γ = 0.95), and κ = 1018.6and m = 8.5 for power-law (Γ = 0.97) models.

The effect of heating in the absence or presence of oxygen on the enzyme activity and nutritional quality of apple puree were investigated. Using designed equipment, apples were vacuum-ground, packaged, and heated under vacuum (2.67 kPa, 90 °C for 30 min) to limit exposure to oxygen, and compared to those heated in open air. All thermal treatments led to complete inactivation of oxidative enzymes. Heating without oxygen effectively maintained color, antioxidant activity, phenolic compounds, and ascorbic acid, as compared to fresh apples. In contrast, heating with oxygen led to considerable browning and degradation of antioxidant activities, phenolics, and ascorbic acid. The results indicate that thermal processing without oxygen can help preserve the nutritional value and retard changes in phenolic-related quality of fruits and vegetables. This study suggests that browning and nutritional loss during thermal treatment of apple may be attributed to oxidation, which is accelerated by the elevated temperature.

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