EFFECT OF SLOW INTRAPARTICLE DIFFUSION ON pH-STABILITY PROFILES OF IMMOBILIZED ENZYME

Stabilities of immobilized enzymes at varying pH under different levels of intraparticle diffusion limitation have been analyzed theoretically and numerically. Unlike pH-activity profiles, which are broadened at high levels of diffusion limitation, pH-stability profiles are narrowest at intermediate levels of limitation. When diffusion limitation is cither absent or very severe, pH-stability profiles are identical in shape, those under severe limitation having half-lives exactly double those free of limitation at all pHs.     

A METHOD FOR MEASURING THE TEXTURE OF MEAT AND THE EFFECT OF NITRITE AND SALT ADDITION ON THE TEXTURE OF CURED MEATS1

An instrumental technique was developed for measuring the texture of canned chopped ham using the 15 cm ² wire extrusion cell of the Ottawa Texture Measuring System. Its measurement efficacy was evaluated by testing enzymatically tenderized ham. This showed that the technique was sensitive to textural changes and that the level of the added enzyme affected the ham's texture exponentially. Nitrite addition to the canned chopped ham product at levels of 0-1000 ppm did not affect its texture. The level of salt used in the curing solution, however, had a marked tenderizing effect. Similarly, compression tests on wieners indicated that nitrite addition did not influence their texture. It was concluded that the characteristic texture of the two products tested cannot be attributed to nitrite addition and that other factors such as the level of salt addition to the canned chopped ham must be responsible.     

Effects of Sodium Tripolyphosphate on Physical and Sensory Properties of Beef and Pork Roasts

Six paired beef round and pork loin roasts were used to determine the effects of sodium tripolyphosphate (STPP) on fresh and reheated roasts. Roasts were pumped 10% of their weight with distilled water (control) or with distilled water containing 4.75% STPP. Roasts were cooked to internal temperatures of 70°C (beef) or 75°C (pork) and evaluated after 0, 1 or 3 days (roasts were reheated to cooked temperatures). This study indicates that phosphate in pork and beef roasts allowed them to be reheated after 1 and 3 days of refrigeration with minimal losses of juiciness, tenderness or flavor intensity, Phosphate injection reduced warmed-over flavor in reheated pork roasts but was not successful in decreasing the incidence of warmedover flavors in reheated beef roasts.     

Oil-in-Water Emulsions Stabilized by Sodium Caseinate or Whey Protein Isolate as influenced by Glycerol Monostearate

Competitive adsorption between glycerol monostearate (GMS) and whey protein isolate (WPI) or sodium caseinate was studied in oil-in-water emulsions (20 wt % soya oil, deionized water, pH 7). Addition of GMS resulted in partial displacement of WPI or sodium caseinate from the emulsion interface. SDS-PAGE showed that GMS altered the adsorbed layer composition in sodium caseinate stabilized emulsions containing < 1.0 wt % protein. Predominance of β-casein at the interface in the absence of surfactant was reduced in the presence of GMS. The distribution of α-lactalbumin and β-lactoglobulin between the aqueous bulk phase and the fat surface in emulsions stabilized with WPI was independent of the concentration of added protein or surfactant.     

ISOLATION OF BDELLOVIBRIOS THAT PREY ON ESCHERICHIA COLI O157:H7 AND SALMONELLA SPECIES AND APPLICATION FOR REMOVAL OF PREY FROM STAINLESS STEEL SURFACES1

Predatory bacteria of the genus Bdellovibrio that prey upon Escherichia coli O157:H7 and Salmonella species were isolated from soil and sewage samples. Bdellovibrio isolates 45k (from soil) and 88e (from sewage) attacked and lysed the E. coli and Salmonella strains tested, with log₁₀ reductions ranging from 2.5 to 7.9 CFU/mL after 7h incubation, using a two-membered culture system. The predators showed activity against the bacteria within the temperature range of 19 to 37C. Bdellovibrio isolate 45k reduced a population of E. coli dried on stainless steel surfaces by 3.6 log₁₀ CFU/cm² following 24 h contact time and at a 10:1 predator to prey ratio and was also effective in reducing the level of biofilm cells. Bdellovibrios can potentially be utilized for removal of bacteria from surfaces of food processing equipment and possibly for controlling the growth of pathogenic and spoilage bacteria in foods.     

INHIBITION OF DIPHENOL OXIDASES: A COMPARATIVE STUDY

The effects of a diverse range of putative inhibitors on o-diphenol oxidases (o-DPOs) from apple, banana and mushroom and a fungal laccase (p-DPO) were compared. The results show that inhibitors varied widely in their effect on DPOs from different sources. In some cases prevention of melanin formation (browning) was due to the direct inhibition of the enzyme catalyzed reaction. In other cases, inhibition was indirect, i.e., due to blocking subsequent melanin-forming reactions of the enzymically formed quinone products.     

PROPERTIES OF FRANKFURTERS PROCESSED WITH POTASSIUM AND SODIUM BICARBONATE

A study was designed to evaluate the use of low levels of sodium (0.25, 0.5, 1%) and potassium (0.25, 0.5%) bicarbonate on the sensory, microbial and functional properties of frankfurters. Both sodium and potassium bicarbonate resulted in higher pH values than control (no bicarbonate) on day 0 but differences diminished after storage at 4°C for 22 days. At the 0.5% level of addition, both sodium and potassium bicarbonate treatments had lower percent free water when compared to controls. The addition of high levels of bicarbonate resulted in diminished sensory properties; however, low levels had sensory characteristics in the acceptable range. No differences were detected between treatments for aerobic plate counts, anaerobic plate counts or yeast and mold counts. Results indicate an acceptable product can be produced using low levels of either sodium or potassium bicarbonate. The use of low levels of bicarbonate also results in beneficial changes of some physical properties.