No description available.

No description available.

published_or_final_version / Biological Sciences / Doctoral / Doctor of Philosophy

Effect of 6.0% polyphosphate treatment on microbial growth and composition of microbial flora of three representative seafoods were investigated. Polyphosphate treatment washed off microorganisms by 1 log in peeled shrimp (10⁷ to 10⁶ and 10⁶ to 10⁵) and cooked crab meat (10⁶ to 10⁵) and by 2 logs in red snapper fillet (10⁶ to 10⁴). Phosphate treatment more readily washed off Pseudomonas sp. and Moraxella sp. and Lactobacillus sp., Corynebacterium sp. and Acinetobacter sp. were the most difficult to wash off. Polyphosphate also raised pH from 7.1 to 7.5 in cooked shrimp, from 7.7 to 8.2 in cooked crab meat and from 6.6 to 7.5 in red snapper fillet. The alkaline pH of up to 9.0, however, had no effect on the growth rates of Pseudomonas I, II and III sp., A. putrifacien sp., Micrococcus sp., Moraxella sp., Flavobacterium- Cytophaga sp., Acinetobacter sp., and Lactobacillus sp. Microbial growth was inhibited immediately following phosphate treatment. The phosphate induced lag period was almost 4 days at 1.1°C for shrimp and crab meat but was not observed in red snapper fillet. The degree of inhibition by phosphate depended on the initial number and kind of bacteria, especially those belonging to genera Pseudomonas, Moraxella, Lactobacillus and Corynebacterium. If still present in phosphate-treated seafoods, Pseudomonas sp. and Moraxella sp. quickly outgrew all others at 1.1°C. Lactobacillus sp. and Corynebacterium sp. became the predominant microorganisms when Pseudomonas sp. and Moraxella sp. were absent. / Graduation date: 1983

Means of improving yield and quality of cooked meat from Dungeness crab (Cancer magister) were investigated. Processing factors of cooking time, cooking medium, and condensed phosphate treatment were evaluated. The effect of condensed phosphate treatment and its interrelationship with cooking time and medium on meat was determined. Meat yield (wet and dry weight) decreased with respect to cooking time according to well defined linear regression functions. Cooking induced solubilization of proteins and reduced water holding capacity. Significant yield losses occurred during the first twelve minutes of cooking. Condensed phosphate treatment significantly increased the yields of meat through steam and water cooking and was directly related to treatment solution concentration and exposure time. Condensed phosphate treatment concentrations between 7 and 10% and treatment times of 90 to 120 minutes provided optimum meat yield. Treatment of crab with a 10% condensed phosphate solution for 120 minutes increased wet weight meat yields over controls ranging from 0.91 to 4.95 percentage points based on raw crab section weight. Action of condensed phosphate produced better meat yields wet weight in water than in steam cooking and was related to a slightly higher retention of moisture. Cooking time and cooking medium did not significantly effect yields of cooked meat. No yield advantage was found for steam over water cooking or for cooking times between 8 and 12 minutes. Phosphorus levels in treated and untreated meat did not vary significantly (p=.05). Levels were not affected by cooking time or medium. A slight increase (NS, P [less than or equal to] .05) in phosphorus levels was observed after condensed phosphate treatment. Sensory evaluation of frozen stored meat showed that steam cooking significantly (P [greater than or equal to] .001) increased overall desirability. This was directly related to a superior (P [greater than or equal to] .05) flavor and a slightly better (NS, P [less than or equal to] .05) texture. Condensed phosphate treatment favorably affected meat quality only after extended storage (406 days). / Graduation date: 1984

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No description available.

No description available.

No description available.

Submitted in complete fulfillment for the Degree of Master of Applied Sciences in Biotechnology, Durban University of Technology, Durban, South Africa, 2016. / A bacterial strain producing an extracellular phytase was identified as Enterobacter sp. ACSS. Optimization of process parameters using statistical methods such as Plackett-Burman design (PBD), the steepest ascent method, and response surface methodology (RSM) significantly improved phytase production by 4.6–fold in shake-flasks. In addition, an overall 1.9-fold increase in phytase production was attained in fed-batch fermentations in a 5 l laboratory fermenter, respectively. The purified 62 kDa phytase from Enterobacter sp. ACSS was active between 40 to 80°C and an acidic pH range of 2.0 to 6.0 with half-life of 693 and 577.5 min at 60°C and pH 2.0, respectively. Additionally, the enzyme is fairly stable with proteolytic enzymes under physiological conditions. It was activated by Ca+2, Mg+2 and Mn+2 while inhibition was caused by Zn+2, Cu+2, Fe+2, Pb+2, Co+2, Ba+2 and surfactants. The Km, Vmax and Kcat observed were 0.21 mM, 131.58 nmol mg-1s-1 and 1.64 × 103 s-1, respectively. The enzyme released inorganic phosphate from animal feed (4.0-6.62 mg/g of diet) and insoluble metal-phytates (45-219 µg/ml) and was effective in improving the characteristics of brown bread. Overall, this study shows that Enterobacter sp. ACSS has the potential to produce significant titres of a thermo- and acid-stable phytase and can be applied in dephytinizing animal feeds, and the baking industry. / M