Shelf-Life of Meat Loaves Packaged in Vacuum or Nitrogen Gas 2. Effect of Storage Temperature, Light and Time on Physicochemical and Sensory Changes

Effects of temperature, light and time of storage on the physicochemical (gas composition, pH, extract release volume (ERV), exudate and TBA) and sensory (appearance and off-odor) changes of vacuum- or nitrogen-packed meat loaves were examined at intervals during 49 d of storage at -4, 0, 3 and 7°C under dark and lighted display. Meat loaves stored at -4°C did not exhibit significant changes during 49 d of storage, but extending duration and increasing temperature above 0°C had a significant effect on the shelf-life of meat loaves, regardless of treatments. Appearance and off-odor changes were not related to those of ERV, exudate and TBA, but significant relationships were noted between CO₂, pH and sensory changes. Overall, nitrogen packaging significantly improved appearance by retarding the greenish discoloration of meat loaves. Light increased the frequency of green discoloration of vacuum-packed samples after 28 d at 0, 3 and 7°C as compared to nitrogen-packed samples.

Shelf-Life of Meat Loaves Packaged in Vacuum or Nitrogen Gas I. Effect of Storage Temperature, Light and Time on the Microflora Change

The effects of storage temperature, light and time on the microflora of vacuum- or nitrogen-packed meat loaves were examined at intervals during 49 d at -4, 0, 3 and 7°C under dark and lighted displays. Storage of cooked cured meat loaves at -4°C for 49 d produced little increase in lactobacilli numbers (from log₁₀ 5.2 to 6.3) but resulted in significant (P<0.05) increases in psychrotrophs (log₁₀ 3.9 to 5.9) and anaerobes (log₁₀ 5.1 to 6.3 under vacuum). Storage time and temperature above 0°C resulted in a significant (P<0.05) increase in lactobacilli, psychrotroph and anaerobe numbers, regardless of packaging atmospheres, but the times at which counts reached approx. 10⁸/g were deferred, i.e., day 7 at 7°C, day 21 at 3°C and day 28 at 0°C. Apart from a few exceptions in the numbers of psychrotrohs and lactobacilli, there were no significant differences in the numbers of microflora between vacuum- and nitrogen-packed meat loaves. At day 0, the dominant flora in both types of packaged samples was composed of Pseudomonas (32 to 34%), Brochothrix (24 to 38%), Micrococcus (9 to 22%) and Lactobacillus spp. (7 to 20%). By day 49, Lactobacillus spp. became a predominant part (62 to 76%) of the psychrotrophs. Few significant differences in the composition of psychrotrophs were found among different treatments. With an initial level of 10² coliforms per gram, there was no significant (P>0.05) change in coliforms counts between treatments but the numbers of yeasts and molds were lower in nitrogen-packed samples at 3 and 7°C as compared with similarly treated vacuum-packed samples.

Toxicity of deltamethrin and cypermethrin to the larvae of the diamond-back moth, Plutella xylostella L

Two photostable pyrethroids, deltamethrin and cypermethrin, were tested against fourth instar larvae of a susceptible (S) strain and a resistant (R) strain of Plutella xylostella L. by topical application. Both compounds were very effective against the S strain larvae (LD50 for deltamethrin = 0.0014 micrograms/larva, LD50 for cypermethrin = 0.0046 micrograms/larva, at 48 h). However, the R strain collected from the field was greater than 1600-fold resistant to deltamethrin and greater than 30 000-fold resistant to cypermethrin. Deltamethrin was poorly synergised with piperonyl butoxide in the S strain, but much stronger synergism was obtained in the R strain. The possible reasons for such high levels of resistance and the potential use of synergised pyrethroids in Plutella control programmes are discussed.

Effects of Temperature, Light and Storage Time on the Microflora of Vacuum- or Nitrogen-Packed Frankfurters

Frankfurters were vacuum- or nitrogen- packaged and stored at -4, 0, 3 and 7°C for 49 d under light or dark display conditions. Effects of temperature, light and storage duration on microflora in vacuum- and nitrogen-packed sausages were then examined. Differences in number of lactobacilli, psychrotrophic and anaerobic bacteria in vacuum- or nitrogen-packed samples were not statistically significant during storage tests. Lactobacillus development was slightly higher in nitrogen gas compared to vacuum packages, but was also not significantly different. The effectiveness of nitrogen packaging on yeast and mold inhibition was significant, particularly at higher temperatures (3 and 7°C). Nitrogen gas packaging thus offers little advantage over vacuum to promote lactobacillus development, but it is particularly effective against growth of mold and yeast. Initially, the dominant flora of both package samples consisted of Pseudomonas and Microbacterium sp. but Lactobacillus sp. became the predominant psychrotrophs (85.2-96.3%) after 49 d of storage, regardless of different treatments. Temperature was the most important factor which influenced growth of the microflora on frankfurters; freezing temperatures of -4 and 0°C were an effective insurance against development of spoilage microflora in frankfurters for up to 49 d, regardless of packaging atmosphere. With an initial level of 10 to 10³ coliforms per gram, there was no significant change in the number of coliforms during storage. Light had no important influence on microbial growth in frankfurters, irrespective of packaging atmosphere.

Effects of Temperature, Light and Storage Time on the Physicochemical and Sensory Characteristics of Vacuum- or Nitrogen-Packed Frankfurters

Frankfurters prepacked in vacuum or nitrogen gas were stored for 49 d at -4, 0, 3 and 7°C under dark and light conditions. Effects of temperature, light and storage duration on physiocochemical (gas composition, TBA, pH, ERV, nitroso-hematin) and sensory (color and off-odor) characteristics of both package samples were then examined. The relative volume of nitrogen decreased gradually but the change was not significant (P>0.05) during the 49-d study. No significant increases in CO₂ concentration were observed between both package treatments at -4 and 0°C, whereas the largest increase in CO₂ content (4.8-16.8%) occurred at 7°C after 21 d of storage. TBA, pH, ERV and nitroso-hematin values were not differently affected by either modified atmosphere types, regardless of storage temperature and illumination used. With respect to surface discoloration and off-odor, nitrogen-packed frankfurters exhibited a lower incidence of discoloration and off-odor and were of satisfactory appearance, even after 35 d of storage at 7°C. Vacuum-packed samples, however, could not be effectively stored longer than 21 d due to formation of brown and green discolorations. Light generally had a significant effect on surface discoloration of vacuum-packed frankfurters. Data indicate that color and odor changes were not related to the values of TBA, ERV and nitro so-pigment but significant relationships were noted between pH. CO₂ and microflora counts at 7°C.

Distribution of tetracycline in red blood cells

The distribution of tetracycline into human red blood cells was studied in vitro at 37 degrees. The drug was taken up rapidly by the cells, and its distribution equilibrium was reached after approximately 10 min of incubation. The steady-state distribution ratio of the drug between the red cells and extracellular fluid of 0.9% NaCl solution was 2.84, while the distribution ratio between the cells and the plasma solution was 0.9. The reduced cellular uptake in plasma was due to binding of the drug to plasma components. Calcium ions in plasma appeared to reduce tetracycline uptake by the red cells. The red cell distribution of tetracycline in dogs was in close agreement with the in vitro data using the washed human red cells. A dog suffering from severe hypoalbuminemia showed greater uptake of the drug by the erythrocytes, while a normal healthy dog exhibited the red cell-plasma distribution ratio of 0.98. The release rate of tetracycline from the preloaded cells into normal saline solution indicated that the release was directly proportional to the cellular concentration of the drug; the first-order release rate was approximately 1.38 hr-1.

Quantitative GLC determination of pentylenetetrazol in biological fluids

A quantitative, sensitive, and specific GLC method was developed for the determination of pentylenetetrazol in water, plasma, and urine. The assay involves a single extraction of the sample into chloroform followed by centrifugation, evaporation, and chromatography. The method for pentylenetetrazol is reproducible, and the sensitivity limit of the assay is 0.5 mug of pentylenetetrazol/ml of biological fluid using a 2-ml sample. This method has a sensitivty sufficient to detect human plasma levels after therapeutic clinical doses and was successfully applied to monitor complete plasma level profiles of this drug in dogs. The data indicate that this drug is very rapidly absorbed following an oral dose, and the half-life of the drug in plasma is approximately 1 hr.