CHARACTERIZATION AND INHIBITION OF POLYPHENOL OXIDASE FROM PEARS (PYRUS COMMUNIS L. CV. BOSC AND RED)

Red pears had higher PPO activity, total phenolics and chlorogenic acid concentration than Bosc pears. PPO activity and phenolics both decreased in fruits held at room temperature. pH and temperature optima for Bosc and Red pears PPOs were 5.0 and 5.5, and 20 and 23C, respectively. 4-Methylcatechol, catechol and dopamine were good substrates for PPO from both pear cultivars; however, no activity was observed with any of the mono-hydroxy substrates studied. Higher K_m and lower V_max values were observed for Bosc pear PPO. Heating at 75C for 30 min completely inactivated the enzyme from both cultivars. Heating at 55 and 65C for the same duration resulted in partial inactivation (45–60%) of this enzyme. Ascorbic acid, L-cysteine, sodium metabisulfite and thiourea effectively inhibited browning due to pear PPOs.     

SURVIVAL OF VIBRIO VULNIFICUS AT REDUCED TEMPERATURES AND ELEVATED NUTRIENT

Studies were conducted on the survival of the human bacterial pathogen, Vibrio vulnificus, in heart infusion broth held at 5, 10 and 15°C. Culturability was monitored by plate counts on heart infusion agar, and viability by examination of electron transport activity. Whereas V. vulnificus demonstrated growth at 15°C, a rapid loss of culturability for cells held at the lower temperatures was observed. At all temperatures, however, a significant portion of the population was found to remain viable over the 28 day study period. The ability of V. vulnificus cells to metabolize exogenously supplied nutrient at reduced temperatures was also examined as an indicator of viability. Cells were able to rapidly take up and respire mixed amino acids at 9 and 13°C, whereas cells incubated at 2°C showed relatively little metabolism of the labeled substrates. Like the growth and viability study, the radiotracer study indicates survival of V. vulnificus at reduced temperatures, although with reduced rates of activity. The possible implications of these findings for the transport and storage of shellfish is discussed.     

Use of Bicarbonates for Microbial Control and Improved Water-Binding Capacity in Cod Fillets

Dipping cod fillets in ammonium or sodium bicarbonate solutions markedly reduced microbial growth compared to untreated samples after 8 days at 4°C. Total plate counts, proteolytic bacteria and H₂S-producing bacteria were inhibited. Mixing ammonium- and sodium bicarbonates at selected ratios maintained the preservative effect while reducing the ammonia odor. The treated fish had improved texture and moisture retention by both objective and subjective testing but had significantly lower aroma and overall acceptability scores from sensory evaluation.     

EFFECT OF STORAGE CONDITIONS ON THE CHEMICAL, PHYSICAL AND SENSORY CHARACTERISTICS OF STANLEY PLUM PASTES

Stanley plums were processed into purees and then pastes by heat concentration to 25 and 30⁰ Brix. The Brix of these two pastes was increased to 40 and 45⁰, respectively, by sugar addition. Pastes were stored at 4 and 22 ± 2C in the dark for up to 24 weeks. Physical-chemical characteristics and microbiological quality were determined at 4 week intervals. Sensory evaluation was conducted at 0 and 24 weeks. Total solids, water activity, rheological properties and microbiological quality were stable during storage. Total acid, total anthocyanins, total pectin and Hunter ‘L’ and ‘a’ values decreased significantly during storage (P < 0.01). The degradation rate of total anthocyanins was much higher for pastes stored at 22C than those at 4C. Hue angle and Hunter ‘b’ values increased during storage. Sensory evaluation indicated that pastes were still acceptable after 24 weeks of storage.     

Emulsion Stability Studies of Myosin and Exhaustively Washed Muscle from Adult Chicken Breast Muscle

An exhaustively washed chicken breast muscle fraction formed a stable emulsion despite the absence of any soluble material. Measurements of the oil droplet size suggested that about 1 mg of myosin was available per square meter of oil droplet surface. This was less than the amount required to fully cover the surface of the oil droplets and suggested that the classical emulsification theory did not hold for meat “emulsion” products. The formation of a matrix (gel) in the aqueous phase might be a significant contributor towards stabilizing meat sausage-type products.     

ANTIMICROBIAL PROPERTIES OF LAURICIDIN IN MECHANICALLY DEBONED CHICKEN, MINCED FISH AND CHICKEN SAUSAGE

Aerobic plate counts on Plate Count Agar at 25°C were used to determine the time required to reach a microbial spoilage level of 1.0 × 10⁷ C.F.U./g, for mechanically deboned chicken meat, minced fish and chicken sausage stored at 2°C. The storage times were 5, 8 and 9 days, respectively. Addition of citric acid (0.2%), ascorbic acid (0.2%) or lauricidin (250 ppm) alone extended the shelf-life by 0–2 days. The combination of lauricidin and citric acid or lauricidin and ascorbic acid extended the time required to reach a microbial spoilage level for mechanically deboned chicken meat by as much as 7 days, minced fish by as much 4 days and chicken sausage by 8 days.