Mexican Queso Chihuahua: rheology of fresh cheese†

Rheological properties of fresh Queso Chihuahua made from raw milk (RM) or pasteurized milk (PM) were characterized using texture profile, torsion and small amplitude oscillatory shear analyses. Although the rheological properties varied significantly among the different brands with overlapping ranges for the individual RM and PM cheese brands, overall the PM cheeses were harder, chewier and more cohesive but had lower viscoelastic values than the RM cheeses. Establishing the rheological properties of Mexican Queso Chihuahua increases our understanding of the quality traits of Hispanic‐style cheeses and provides a foundation for maintaining the traditional texture of the cheese.     

COMPARISON OF IN-LINE CONSISTENCY MEASUREMENT OF TOMATO CONCENTRATES USING ULTRASONICS AND CAPILLARY METHODS

This study focuses on the development of a noninvasive, in‐line rheometer using ultrasonics and its comparison with data from a traditional capillary viscometer. The ultrasonic based pointwise viscosity measurement technique combines a measurement of the velocity profile and the pressure drop to determine the shear rate and the shear stress distributions, respectively in a pipe. The experiments were carried out using tomato concentrates at 8.75%, 12.75%, and 17.10% total solids content. The flow system consisted of a 53.2 mm diameter acrylic tube, a positive displacement pump and two pressure transducers. Multiple shear viscosity‐shear rate data were recorded under actual pipeline conditions from a single combined measurement of the velocity profiles using ultrasonics and the pressure gradient, using the pressure transducers. The samples showed shear thinning behavior and a yield stress. Power law and Casson models were used to fit the data and both obtained R² values higher than 0.99. The yield stress was also directly determined from the velocity profiles. Shear viscosity versus shear rate data of the 12.75% total solids sample were obtained by capillary rheometry at four different flow rates. These showed very‐good agreement with those obtained using the velocity profile technique.     

MATURITY STANDARDS FOR PROCESSING CLINGSTONE PEACHES

The flesh color of 5 clingstone peach cultivars was measured (in CIELAB coordinates) by tristimulus colorimeter before and after canning. Before canning, fruit were separated into 3 color classes (1A: green-yellow, 4A: yellow-green, 7A: orange) by visual comparison with a trial maturity chart. After canning, flesh color was measured and visually graded. All samples in color class 1A were rated USDA grade C, while classes 4A and 7A were rated grade A. Flesh color was also measured as a function of time before and after harvest. Fresh flesh L* values were approximately constant, a* values increased steadily, and b* values increased then slightly decreased. Final specifications for a new maturity chart were 7 colors of constant luminance (L*= 76.5) and linearly increasing a* and b* values (?5.0 to 13.0 and 70.1 to 76.4, respectively), corresponding to a time step of 3.5 days between colors.     

Gas Concentrations in Modified Atmosphere Bulk Vegetable Packages as Affected by Package Orientation and Perforation Location

A perforated plexiglass package box was used to study the effects of package orientation and perforation location on gas concentration profiles during modified atmosphere packaging of broccoli (Brassica oleracea) florets. Three package orientations and perforation locations were studied. Two temperature conditions were studied namely: constant temperature at 2°C and variable temperature between 2 and 20°C. Package orientation and perforation location affected gas concentration gradients across the package. Placing the package in a vertical orientation with perforation at the top side, resulted in higher gas concentration gradients in the package. Lower gas concentration gradients were obtained when the package was placed in a vertical orientation with perforation at the lower side. Temperature variation resulted in gas concentration fluctuation in the package.     

THE FOULING AND CLEANING OF ULTRAFILTRATION MEMBRANES DURING THE FILTRATION OF MODEL TEA COMPONENT SOLUTIONS

Proteins and polyphenols are the principal fouling constituents in the ultrafiltration (UF) of black tea liquor. The aim of this study was to determine the relative importance of individual components in the fouling process, to investigate any synergetic interactions that were occurring and to compare the cleaning characteristics of different fouled membranes. A 30‐kD molecular weight cutoff polysulfone UF membrane in dead‐end mode was challenged with model solutions of tea components. Model solutions consisted of tea proteins, theaflavins (TFs), thearubigins and caffeine. Sodium hydroxide was used as a cleaning reagent. Permeate flux decline curves were presented for single components and mixtures. Individual component transfer fluxes and rejections were also presented. An unexpected finding was that protein in a mixture with TFs could permeate the membrane to a degree, while a protein solution in the absence of the polyphenol was completely rejected. The inspection of membranes fouled by different solutions revealed different foulant morphologies. Membrane cleaning with 0.2 wt % sodium hydroxide was generally found to be effective.     

Functional Properties and Shelf Life of Fresh Surimi from Pacific Whiting

Total aerobic plate count (APC), shear stress, shear strain, and color of fresh Pacific whiting surimi stored at 5°C were determined at day 0, 1, 3, 5, and 7. Frozen surimi was prepared with four levels of cryoprotectams (0, 3, 6, and 9%) and was compared with fresh surimi for gelforming ability. Fresh Pacific whiting surimi had a shelf life of 5 days. The gel functionality remained unchanged throughout the storage time. Strain values of fresh surimi were not different from those of frozen surimi with 9% cryoprotectants, but stress values of fresh surimi were almost three times higher than those of frozen surimi.     

Activity Staining of Pacific Whiting (Merluccius products) Protease

An activity staining method using SDS-substrate gel was used to determine Pacific whiting proteolytic activity. The most active protease band was resolved at an apparent M, of 39,500 corresponding to the activity of cathepsin L. The activity was more pronounced for ocean-caught Pacific whiting than Puget Sound Pacific whiting or ocean-caught arrowtooth flounder. Gel electrophoresis activity staining of proteolytic enzymes in Pacific whiting was not as sensitive as the TCA-azocasein assay but provided information on the molecular properties of the enzyme and a semi-quantitative estimation of activity.