Initial concentration of dissolved oxygen

At the beginning of the experiments, the effect of the initial concentration of dissolved oxygen in the liquid phase on the volumetric physical mass transfer coefficient was checked. Results of experiments showed that there was no effect of this kind. Therefore, no effort was made to keep the initial oxygen concentration constant for the rest of the experiments. 

The models developed are adequate to predict the ascorbic acid degradation, browning development and PVG formation in aseptically packed orange juice with initial concentration of dissolved oxygen between 1 and 10 ppm during storage from 4 to 50°C. Errors in the predictions lower than 25% were obtained for most of the cases. 

The Winkler test, or minor variations of it, is the standard wet chemical procedure for measuring the concentration of dissolved oxygen in water samples [24, 28, 29]. It uses a standard 300 mL BOD sample bottle, which is closed with a glass stopper with a polished cone-shaped end. This closure makes it possible to completely fill the bottle with the water sample and avoids any interference from bubbles of air which might otherwise be trapped in the bottle. Initially a white precipitate of manganous hydroxide is prepared in the BOD bottle (Eq. 4.17). 

Fig. 3.41. Oxygen curves. 1 — deoxygenation, 2 — re-aeration, 3 — oxygen sag curve. Do — initial deficiency, Dcr — critical deficiency, Dt — deficiency in the time 1, C — concentration of dissolved oxygen in the time t, K — critical point, F — inflexion point... 

Figure 8 ElTccl of concentration of dissolved oxygen on initial rate of O consumption at constant concentration of thiosulfate (48.4 mmol L ) at 3()°C.

Most of the studies05,20 271 show that a correlation between culture fluorescence and biomass concentration can be obtained mainly in the exponential growth phase. In addition, in order to obtain reproducible correlations, all of the fermentation conditions such as initial substrate concentration, pH, dissolved oxygen level, temperature, and agitation rate have to be the same. However, once the culture is past exponential growth, biomass measurement by following culture fluorescence is no longer accurate. 

The core of the crystalline region of irradiated PE contains residual free radicals. These diffuse slowly to the interface with the amorphous region, where, in the presence of dissolved oxygen, whose equilibrium concentration is maintained by diffusion, they initiate an autooxidative chain of degradation.89 Postirradiation annealing in an inert atmosphere at a temperature above the alpha-transition temperature (85°C) leads to a rapid mutual reactions of the free radicals and eliminates the problem.90... 

At 23.9°C, the 45°Brix concentrate initially exhibited a more rapid loss of ascorbic acid than did the 54°Brix concentrate, but at the end of eight months both had lost about 25% of their starting ascorbic acid. The more rapid loss of ascorbic acid may have been caused by the amount of dissolved oxygen in the 45°Brix concentrate initially. It may have been the result of more rapid diffusion of oxygen into the lower °Brix concentrate once it entered the package along the longitudinal seam and at the comers. Neither factor was measured. 

In conclusion, it is obvious from Fig.s 6-16 to 6-23 that the concentration of dissolved molecular oxygen [(02)aq] during the application of photo-initiated AOPs (and others) must be maintained at a sufficiently high level to guarantee the formation of organic peroxyl radicals (R-O ) on the way to mineralization of organic water contaminants. 

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