Minimizing sample evaporation in the environmental scanning electron microscope

The ElectroScan environmental scanning electron microscope (ESEM) enables wet samples to be observed by eliminating air but allowing water vapour into the sample chamber. However, evaporation from, and condensation on, the sample may occur during the pumpdown sequence used to reach this state, which means that the sample may not be in its natural state when viewed if due care is not taken. In this paper, the pumping system of the ESEM is described mathematically and expressions are derived for the evaporation and condensation. This treatment is then used to calculate the optimum pumpdown sequence. The importance of using the optimized procedure is illustrated by micrographs of fat emulsions.     

Prediction Equations for Gases in Flexible Modified-Atmosphere Packages of Respiring Produce are Different Than Those for Rigid Packages

Total pressure generally decreases in a sealed rigid package containing respiring produce, whereas total pressure is essentially constant and free volume decreases in a flexible package. We found that predicted O₂, CO₂, and N₂ partial pressures were different for similarly designed (same surface area, thickness, film permeabilities and produce mass) flexible and rigid packages at “quasi steady state” and steady state, respectively. Predicted O₂ and CO₂ partial pressures were slightly higher in a flexible package than in a rigid package and were a function of the film permeability ratio of N₂ to O₂ and of CO₂ to O₂. They also related to the ratio of product CO₂ production rate to O₂ uptake rate, target steady-state O₂ partial pressure, and respiration characteristics. Differences were slight for films such as low-density polyethylene.     

Variation in the Levels of Sodium and Other Minerals of Nutritional Importance in Louisiana Oysters (Crassostrea Virginica)

The concentrations of nine individual minerals were determined in oysters harvested over a 10-month period. Significant (p > 0.01) monthly variations were observed in the levels of all the minerals determined. Salinity of the growing waters was significantly (p > 0.01) correlated to levels of sodium, magnesium, iron, chromium, and nickel in the oysters. Levels of potassium, copper and chromium were related to pH. Zinc and iron levels were correlated (p > 0.05) to water temperature. In this study, variations in the mineral content of oysters were often directly influenced by the growing water. This variation must be taken into consideration, should sodium labeling be required for fresh oysters.     

α-Tocopherol and Ascorbate Delay Oxymyoglobin and Phospholipid Oxidation In Vitro

An oxymyoglobin liposome model was used to study the effects of α-tocopherol and/or ascorbate upon oxymyoglobin and lipid oxidation. Both oxidations were delayed (P<0.05) by increased concentrations of α-tocopherol alone and α-tocopherol/ascorbate relative to controls. The 14 μ Mα-tocopherol/140 μM ascorbate treatment resulted in greatest delay in both oxymyoglobin and lipid oxidation. Ascorbate alone delayed oxymyoglobin oxidation; effectiveness diminished as ascorbate increased. Ascorbate showed a prooxidant effect toward lipid oxidation which was unchanged in the presence of EDTA. Results support the hypothesis that α-tocopherol retards lipid oxidation directly and OxyMb oxidation indirectly.     

VITAMIN E SUPPLEMENTATION EFFECTS ON COLOR AND LIPID STABILITY OF WHOLE AND GROUND LAMB

Crossbred wethers averaging 44.1 kg were fed a diet supplemented with 2000 IU α-tocopheryl acetate/day for 49 days. The controls received the same diet without supplement. Muscles from lambs supplemented with vitamin E contained higher concentrations of a-tocopherol than the controls (P<0.05). There were no differences between control and supplemented animals for myoglobin stabiliry of two muscle slices stored at 4C (P>0.05). Ground semimembranosus (SM)from supplemented animals exhibited higher "a" values and lower Hue angle values (P < 0.05) than meat from control animals at 6 days of storage and longer indicating enhanced color stability due to vitamin E. Vitamin E supplementation decreased lipid oxidation of ground SM at 3, 6, 9, and 12 days of storage at 4C (P < 0.05) and it partially stabilized color of ground lamb. Color stability of whole lamb slices was not affected by vitamin E supplementation.     

MODELING FREQUENCY DISTRIBUTION of STEADY-STATE O2 PARTIAL PRESSURES IN MODIFIED-ATMOSPHERE PACKAGES

A mathematical model was developed to predict the frequency distribution of steady-state O₂ partial pressures in modified-atmosphere packages of fresh and minimally processed fruits and vegetables. Variation in O₂ uptake was predicted to have relatively larger influence on the package O₂ distribution than variation in film permeability to O₂. the model also predicted that the range of O₂ partial pressures in the packages would be larger for the products with lower K_1/2 (a constant in product O₂ uptake equation) values. the percent deviation of package O₂ partial pressures from [O₂]_med increased with [O₂]_med up to about 3 kPa and gradually decreased thereafter. Package O₂ distribution was symmetrical at higher [O₂]_med but became gradually asymmetrical with decreasing [O₂]_med from 6 kPa. the model was used to predict target [O₂]_med for the design of modified-atmosphere packages for different probability levels of having package O₂ being equal to or less than a minimum tolerable level of the product.     

Partial Purification and Thermal Characterization of Pectinmethylesterase from Red Grapefruit Finisher Pulp

Four forms of pectinmethylesterase have been partially purified from red grapefruit finisher pulp by chromatography on Heparin-Sepharose CL-6B. Three forms bound to the heparin-sepharose and could be eluted with a sodium chloride gradient. One form (RGPME3) exhibited high thermal stability retaining 66.7% relative activity after 2 min incubation in an 80°C water bath, and 45.2% of its relative activity after 60 set incubation in a 95°C water bath. RGPME3 had a K_m of 0.106 mg * mL^?1 citrus pectin and a pH optimum between 6 and 7. The most abundant form (RGPMEZ) had a K_m of 0.079 mg * mL^?1 citrus pectin. Denaturing electrophoresis and gel filtration chromatography suggested molecular weights between 20 and 40 kDa for the various forms.     

LIPID COMPOSITION OF BOB AND SPECIAL-FED VEAL

Four muscles were studied to determine the lipid composition of Bob (BV) and Special-fed (SFV) veal. No differences existed for proximate analysis values of muscles from carcasses of different weight classes (P> 0.05). Muscles from SFV were higher in fat (P < 0.05) and generally displayed more protein and less moisture than the BV. BV contained more cholesterol than SFV (P< 0.001); however, there was no difference among the 4 muscles for cholesterol content (P > 0.05). SFV contained more 14:0 and 18:2, and less 16:1, 18:0 and 18:1 fatty acids than BV (P< 0.05). Fatty acid composition on a g per 100 g tissue weight basis was higher in 14:0, 16:0, 17:0, 18:2 and 20:4 (P< 0.05) for SFV. The longissimus contained more 14:0, 16:0, 18:0 and 18:1 than the other muscles studied (P< 0.05). The results indicate that veal is an appropriate low-fat muscle food which meets modern dietary guidelines concerning fat consumption.