Penetration of Sodium Tripolyphosphate into Fresh and Prefrozen Peeled and Deveined Shrimp

The distribution of sodium tripolyphosphate (STP) in peeled and deveined shrimp tails after treatment was investigated using P³² labeled STP. Fresh and frozen brown (Penaeus aztecus) and fresh and frozen white (Penaeus setiferus) shrimp were used in the study. Shrimp were treated in solutions of either 0.5%, 1%, 5%, or 10% STP that had been prepared using P³² labeled STP diluted with “cold” STP. The duration of treatment was either 20 sec, 1 min, 5 min, or 20 min. When shrimp were treated in 0.5% and 1% STP solutions, a phosphate concentration gradient was evident in the shrimp muscle. After such treatments, STP was shown to accumulate on the surface of the muscle preventing further STP uptake. At higher STP concentrations (5% and 10% solutions) prolonged time treatments overcame the concentration gradient as STP became equally distributed through the shrimp muscle (4.8 mm). No difference in the STP penetration mechanism between fresh and prefrozen treated shrimo was evident.     

Phosphorous Levels in Peeled and Deveined Shrimp Treated with Sodium Tripolyphosphate

Using volumetric and spectrophotometric methods for the determination of phosphorous, untreated shrimp were shown to have high and variable phosphorous content. When peeled and deveined shrimp were treated with 0.5% and 1.0% sodium tripolyphosphate (STP) solutions, the STP uptake was shown to be low. At these low treatment concentrations the phosphorous content in the treated shrimp did not exceed the range of natural phosphorous found in untreated shrimp. When higher treatment concentrations were used, treated thrimp could be identified. The stability of STP in treated shrimp during frozen storage was investigated using a P³² STP isotope. After 2 wk of frozen storage at –26°C only 12% of the total activity could be attributed to STP. At the same time, pyrophosphate was present at a level of 25% and orthophosphate at 27%. During further frozen storage, the STP concentration remained at approxinately 12%, pyrophosphate dropped down to as low as 2% while orthophosphate gradually increased reaching 45% of total activity at the end of 10 wk storage period.     

Effect of Treatment, Ice Storage and Freezing on Residual Sulfite in Shrimp

When fresh shell-on tails of penaeid shrimp were treated with sodium bisulfite according to current good manufacturing practices, residual sulfite (SO₂) on the edible portion varied from a high of 92.7 to a low of 60.9 ppm with an average of 80.2 ppm. During freezing and a short period of frozen storage, there was an average loss of 17% in residual sulfite. For shrimp held on ice storage, on the other hand, there was a rapid decrease in residual sulfite to below 10 ppm after six days of storage. The residual levels found on treated shrimp were consistent with action levels set by USFDA for shrimp treated according to good manufacturing practices.     

Extended shelf life milk—advances in technology

This paper describes trends and technological advances in the dairy industry for extended shelf life milk. Demands for longer shelf life and wider distribution of milk and milk products have resulted in the development of processes and packaging concepts to increase the shelf life of these products in cold chain distribution. Factors important for the shelf life of milk are described in detail, and changes necessary from normal pasteurized production are suggested. Various processing methods such as microfiltration, injection and infusion heat treatments are described, and advantages and disadvantages of the different methods explained. In addition, the contamination sources from process to package are discussed, and the prevention of such recontamination in the filling machine is proposed. The paper describes existing and novel methods for sterilization of packaging material in the filling machine and points to possible future developments in this important market segment in the dairy industry.     

SHELF-LIFE STUDIES ON CARBON DIOXIDE PACKAGED FINFISt FROM THE GULF OF MEXICO

Modified atmosphere packaging using CO, was demonstrated to be effective in retarding the growth of microorganisms during storage of fresh fish from the Gulf of Mexico. At 4°C, there was at least a log difference in bacterial counts at 2, 4, and 6 days between fish stored in CO₂ as compared to control fish stored without CO₂. While the CO₂ atmosphere was shown to inhibit the growth of common spoilage types of bacteria such as gram-negative rods (Pseudomonas), stimulation of gram-positive bacteria such asLacto-bacillus was also demonstrated. Fish stored at 4°C for 2–8 days in a modified atmosphere containing CO₂ had lower TVN values than fish stored at the same temperature without CO₂. The results indicate that an extension of the shelf-life of fresh fish can be obtained by packaging and storing the fish in a CO₂ atmosphere.     

The Nature and Importance of Economic Competence

In this paper we define economic competence as the ability toidentify, expand and exploit business opportunities. Economiccompetence constitutes the means through which technologicalpossibilities are converted into economic activity. It consistsof four types of capabilities: (i) selective or strategic; (ii)organizational or coordinating; (iii) technical; and (iv) learningability. The purpose of the paper is (i) to survey the studyof economic competence as it appears in economic literature;(ii) to give a meaningful and operational definition of economiccompetence as one of the factors contributing to macroeconomicgrowth; and (iii) to suggest a methodology to generalize andlink economic competence, as defined at the micro (firm, individual)level, to macroeconomic growth, through simulation on the micro-basedmacroeconomic Model of the Swedish Economic System (MOSES).     

Robustness properties of repetitive controllers

Stability robustness properties of sampled data repetitive control systems are examined. Due to the infinite loop gain at periodic frequencies originating from the included internal model (Internal Model Principle), repetitive systems are, if properly designed, not very sensitive towards possibly time-varying gains. Uncertainty in plant delay is, however, a problem. Controller action timing becomes more or less out of order and may result in severe performance degradation, depending on model type and the number of frequencies included in the design. With a Linear Time-Invariant (LTI) controller comprising the commonly used time delay internal model, the closed loop system is stable for nominal time delay plus/minus at most one sampling interval. A controller based on a reduced order model, perhaps not modelling all harmonics, is utilized lo enhance robustness properties. Simulation runs with different controllers show how different models work in the closed loop, and also that synchronization in time is of utmost importance in order to utilize the delay internal model.     

Effect of Environmental Salinity on Sensory Characteristics of Penaeid Shrimp

White shrimp, Penaeus vannamei, acclimated to 10, 30 and 50 parts per thousand (ppt) salinities were evaluated for flavor by a trained sensory panel. The shrimp were also analyzed for tissue moisture, chloride, free amino acid concentration and free amino acid profile. Results of triangle tests showed a significant flavor difference between shrimp held at 10 and 50 ppt and 30 and 50 ppt but not between 10 and 30 ppt. On a wet weight basis, the free amino acid concentration was 81% higher in shrimp held at 50 ppt than at 10 ppt and 63% higher in shrimp held at 50 as compared to 30 ppt. However, between shrimp held at 30 as compared to 10 ppt the difference was only 11%. The difference in flavor intensity of shrimp held at different salinities appeared to be a direct reflection of the concentration of tissue free amino acids which serve as osmoregulators in shrimp tissue.