At the conclusion of the two-year storage lifetime, vitamin B1 was generally most stable in thermally processed brown rice, less so in split pea soup, and drastically less in BBQ beef brisket, based on NASA’s formulation. Although degradation of B1 was slowest and less influenced by temperature in the thermally processed rice, B1 was more abundant in the split pea soup product at the end of the 2-year storage period at any temperature tested, compared to the more stable brown rice product. B1 in BBQ beef brisket was undetectable at the end of the storage period at 37°C storage and approaching an undetectable limit for the two other storage temperatures.
The process of freeze-drying these foods resulted in unique differences of vitamin B1 stability compared to the non-freeze-dried versions. Freeze-dried brown rice demonstrated better resistance to vitamin B1 degradation at higher temperatures, but a diminished protective effect in refrigeration conditions, comparing the final vitamin B1 concentrations between thermally processed and freeze-dried brown rice. This same trend of decreased temperature dependence on degradation rate was observed in the split pea soup, but not in the BBQ beef brisket, where differences in food matrix composition and chemistry are though to play a role on vitamin B1 degradation differentially. Vitamin B1 was also quantified in brown rice, split pea soup, and BBQ beef brisket that were either thermally processed or freeze-dried, and then stored at either -20°C or -80°C for two years as a quality control measure.
For vitamin C, freeze-drying preserved the vitamin better throughout all foods under all temperatures except 37°C. The degradation rate was the most noticeable difference because in many cases freeze-drying caused the food to approach a zero residual concentration quicker than the thermally processed foods. However, the freeze-drying concentration started with a higher vitamin C amount. As long as the vitamin C was detectable or had a nonzero concentration, freeze-drying still had more vitamin C than the thermally processed foods. This finding stressed how the initial concentration and an elevated storage temperature can influence vitamin C degradation. Sugar snap peas had many bewildering findings for the thermally processed and freeze-dried foods. Specifically for thermally processed sugar snap peas, the vitamin concentration considerably declined for all temperatures and was undetectable for all temperatures before the end of the two-year storage study. The stability was better during freeze-drying, but a sharp drop occurred at 12 months for 20°C freeze-dried sugar snap peas, which seemed valid considering the remaining time points stabilize near that concentration. The cause of the dropped has yet to be determined, and the investigators assume there had to be some form of phenomenon that increased vitamin C dissolved oxygen leading to a more rapid degradation.
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