Effects of Carbonic Acid Dips and Packaging Films on the Shelflife of Fresh Fish Fillets

Carbonic acid and semi-permeable packaging materials were investigated for their effect on shelflife of fresh fish. Cod fillets (Gadus morhua) were dipped in carbonic acid and then stored packaged and unpackaged at 2°C. Samples were evaluated for weight loss, surface pH, texture changes, surface microbial growth, headspace gas composition, and sensory characteristics of cooked flavor, odor, and appearance. Carbonic acid was capable of extending shelflife between 7 and 21 days; however, only at a quality level judged as fair to marginal by sensory evaluations. Low permeability packaging slowed bacterial growth and extended shelflife, but retained off-odors and established low oxygen conditions which may present a risk from the growth of pathogenic organisms.     

A New Method to Quantitate the Coagulation Process

A nondestructive method to quantitate the coagulation process has been developed and used to obtain kinetic data on the heat-induced gelation of egg albumen. It involves continuous monitoring of the force exerted by the gel as coagulation takes place and requires only one sample to observe the total process. From the information on the maximum force exerted by the gel, rate constants, Z values, and activation energies were calculated. This approach was applied to evaluate other coagulation processes such as the enzymatic coagulation of milk and the gelation of gelatin by cooling.     

Individual Packaging of Apples for Shelf Life Extension

Red Delicious apples after 2 wk and 4 months of cold storage and after 4 months of CA storage were individually packaged in two heat-shrinkable copolymers. Packaged and control apples were stored at 3°C and 90% RH, 21°C and 30°C and 50% RH, and at 30°C and 50% and 70% RH and the effect of packaging on modification of the microatmosphere inside the fruit and on various chemical and physiological changes were monitored with time. Temperature was the dominant storage factor. At 3°C, packaged and control apples had good eating quality and did not show significant differences (P > 0.05) after 3 months of storage. At 21°C, packaged apples reached a minimum acceptable condition at week 6 of storage which represented a shelf life extension of 3-4 wk over nonpackaged controls. At 30°C, internal quality of packaged apples deteriorated faster than controls. The respiration rate of packaged apples was lower than that of controls.     

Relationship of Water Content to Textural Characteristics, Water Activity, and Thermal Conductivity of Some Commercial Sausages

Mechanical properties from cyclic low strain testing, texture profile parameters and thermal conductivity were evaluated for 7 types of commercial sausage products ranging in moisture content from 27.7% to 62.4% and a_w from 0.857 to 0.993. Hardness, fracturability, the apparent moduli, stress al 20% compression, mechanical hysteresis loss, and strain energy all increased with decreasing moisture level, while springiness and the degree of elasticity decreased. Moisture had no significant effect on cohesiveness. A linear relationship was observed between the a_w and the effective mole fraction of water in the brine, the exact nature of which depended on the thermal process which the product had received. Thermal conductivity decreased with decreasing moisture in a linear manner.     

RESIDENCE TIME DISTRIBUTION (RTD) AND GOODNESS OF MIXING (GM) DURING CO2-INJECTION IN TWIN-SCREW EXTRUSION PART I: RTD STUDIES

The residence-time distribution (RTD) studies are needed to characterize mixing conditions, flow patterns, and the extent of conversions and reactions of the biopolymers in any plasticating or cooking extruder. For the supercritical fluid extrusion process (SCFX), mixing of the fluid and starch-based biopolymers is an important step affecting cell nucleation and growth. RTD was studied in the mixing zone of the extruder, where CO₂ and gelatinized starch are brought together. Three levels of each of the process variables (screw speed and CO₂ injection pressure) were investigated, using specially designed apparatus for color-dye injection, and a die-restrictor to change the pressure profile and hold up volume in the extruder. Control RTD plots were for no CO₂ injection conditions at the same pressure, and the RTD of the full extruder section. Experimental RTDs were evaluated by: (1) the Wolf-White model, (2) a cascade of continuously stirred reactors (CSTR) model and (3) a model based on plug-flow in series with cascade of CSTRs. The last approach was most successful in capturing all aspects of the observed RTD curves including their tails. Injection of CO₂ at the highest pressure (110.3 bar) increased the RTD compared to no CO₂-injection conditions. There were significant differences in the plug flow component of the RTD as well as differences in average residence time as a function of both screw speed and CO₂ injection pressure conditions.     

Moisture Sorption Isotherms of Canola Meals, and Applications to Packaging

Moisture sorption isotherms were determined for defatted canola meal at 16, 22, and 34°C. The isotherms were fitted to the Guggenheim-Anderson-deBoer (GAB) sorption equation. This equation was then used to develop a packaging model that predicted the changes of moisture con-tent of canola meal under stated environmental and packaging conditions. The model was tested using Melinex 813 (12 μm) and Propafilm C (28 μm) packaging films at 86% relative humidity and 23°C. The GAB equation provided a good fit to experimental data (<3% RMS). The monolayer moisture content of the meal was 9.5%. The enthalpy of sorption of the monolayer at 22°C was 84.61 KJ/mol. The model predicted the time required by packaged canola to attain a selected moisture content ± 0.5 days.     

MODELING of TRIGLYCERIDE DISTRIBUTION and YIELD of ANHYDROUS MILK FAT IN A CONTINUOUS SUPERCRITICAL CARBON DIOXIDE EXTRACTION SYSTEM

A mathematical model was developed for continuous extraction of multicomponent mixture anhydrous milk fat (AMF) with supercritical carbon dioxide (SC-CO₂) as its solvent. At a constant temperature and pressure, the triglyceride mixture was separated into vapor and liquid fractions. the composition distribution (indicated by acyl carbon number), mass distribution and yield of AMF were calculated by the model based on thermodynamic equilibrium and material balance. the feed composition and distribution coefficient were required information in this model. the experimental values for the extract were in good agreement with the model used. the results for the raffinate were not as precisely modeled. the main factors which affected the model were temperature, pressure, solvent/feed ratio and extract fraction.