Freezer storage stability

A solution to this dilemma is to place soil samples immediately in a freezer located in the field, the temperature of which is continuously monitored, as described previously. Laboratory-prepared storage study samples can then be used to determine test substance stability under freezer storage conditions that match those used in the field and during transportation and final storage. If a valid laboratory storage stability... 

A second approach to determining freezer storage stability involves the reanalysis of incurred residues found in actual samples that are stored over time. Using this approach, soil from an actual field sample containing residues is periodically analyzed... 

Field fortifications have also been used to measure the storage stability of the analyte in/on exposure matrices during freezer storage prior to analysis. Although use of field fortification samples for freezer storage stability is not the original purpose intended for field fortification samples, this has become an acceptable practice among scientists who work in this scientific discipline. 

The two purified components, component I and component II (the stability and storage of trypsinized component II will be described below), are relatively stable proteins and can be stored in the freezer (at -20 °C) for at least 3 months without loss of their activities, if freezing and thawing are not repeated too frequently. To store them for longer periods, however, it is preferable to freeze-dry and keep them in a deep freezer (-80 °C) in a desiccator both components are stable under the conditions for normal freeze-drying method without any additives. 

The freezer storage stability of PBO within each raw agricultural commodity for up to 12 months was also confirmed. 

The stability of the analyte(s) in matrix during extended freezer storage should be determined by analyzing stored stability QC samples at appropriately selected time intervals and at temperatures that reflect the intended storage conditions and anticipated storage periods for study samples. For many applications, the compound is determined to be stable as long as the calculated concentration of the analyte is within 15 % of the nominal concentration, or the concentration that was established for the same batch of QCs when analyzed immediately after preparation (time zero). Freshly prepared QC samples, or QC samples prepared and stored within an established period of stability, should be used as analytical QCs in the same set that the stability QCs are analyzed to confirm run acceptance. If the analytical QC samples do not meet assay acceptance criteria, the run should be rejected and the stability interval should be repeated. Incurred samples or sample pools may also be analyzed for assessment of stability in a similar manner. 

Shrewsbury et al. (1942) found in studies on the stability of hog fat that the soft fat (peanut-fed, iodine munber 73-80) was consistently less stable than the hard (corn-fed, iodine number 58-60) both fresh and after frozen storage. However, there was more variation in the keeping time of hard fats from different lots of pork than in the keeping time of hard versus soft in any one lot. Peroxide values for fats extracted from the meats after freezer storage for 12 to 16 months were low and showed no significant differences between hard and soft fats. Brady et al. (1946) and Palmer et al. (1953) showed positive correlation between the softness of the fat and the susceptibility to rancidity of bacon and frozen ground pork, respectively. 

Kummerow et al. (1948) found that the feeding of highly unsaturated fatty acids was detrimental to fat stability of eviscerated frozen turkeys, as determined both by peroxide values on the extracted skin fat and also by organoleptic tests on the cooked carcass. Klose et al. (1951) observed fishy flavors in roasted turkeys fed linseed oil as well as fish oils. The fishy flavors in this case were present in the fresh roasted turkeys as well as in those cooked after being stored in the freezer. Peroxide values of birds fed linseed oil increased very rapidly in freezer storage. 

In addition to these inherent characteristics of the fat itself, contact of the fat in meat with an aqueous solution containing surface-active substances, accelerators and inhibitors of rancidity, creates a very different situation from conditions which exist in a container of rendered lard. The author has noted on a number of occasions that the keeping time of fat rendered from pork tissues did not correlate with rancidity development in the ground meat. Schreiber et al. (1947) reported that the stability of fat, as measured by accelerated tests on the extracted fat from fresh birds, was not a good indication of the stability of poultry fat in situ during freezer storage. 

Evidence of the stability and recovery of the seeds and banks should be documented. Storage containers should be hermetically sealed, clearly labelled and kept at an appropriate temperature. An inventory should be meticulously kept. Storage temperature should be recorded continuously for freezers and properly monitored for liquid nitrogen. Any deviation from set limits and any corrective action taken should be recorded. 

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