Microbial Growth Estimation in Liquid Media Exposed to Temperature Fluctuations

Comparisons of linear, square root and Arrhenius specific growth rate-temperature models showed no clear overall preference. At low a_w and refrigeration temperature, the linear model was satisfactory for Brochothrix thermosphacta and Pseudomonas fluorescens. A linear relationship between (specific growth rate)^?1 and lag phase was observed for these two psychrotrophs. The R² for B. thermosphacta in 3% (a_w= 0.968), 6% (a_w= 0.950), and 9% NaCl (a_w= 0.943) media was 0.865, 0.946 and 0.994, respectively. In 8% (a_w= 0.973) and 20% (a_w= 0.948) glycerol media, the R² was 0.998 and 0.999, respectively. R² for P. fluorescens growth in NaCl (3 or 4%) or glycerol (10 or 20%) media was >0.99. A cumulative growth adaptation function successfully estimated microbial growth at fluctuating temperatures.     

STABILITY OF WHOLE, FILLETED, AND MINCED TROUT (SALMO IRIDEUS GIBB) DURING FROZEN STORAGE

In order to determine the behavior of trout (Salmo irideus Gibb) muscle in frozen storage, five lots (whole, fillets, and minces obtained by extrusion, “mincer” and “cutter”) were made and stored at -20⁰C for one year. During this period the mince, mainly the one made with “cutter”, was more denaturated than the whole trout and fillets. The highest rate of insolubilization was reached by 255 days of storage (45% of soluble protein in minces and 60% in fillets and whole fish). Also a similar difference was noticed in the cooking drip. The variations of protein solubility do not thoroughly explain the changes in objective texture observed up to 30–75 days of storage. So, other parameters may be connected with these changes. On the other hand, after 165 days, the rancidity increase measured by the TBA value is high, especially in the mince although rancid flavor was detected at 120 days of storage.     

APPLICATION OF A NEW CONTINUOUS FLOW SPECTROPHOTOMETRIC METHOD FOR THE CHARACTERIZATION OF POLYPHENOL OXIDASE NATURALLY IMMOBILIZED ON COCONUT FIBER

The association of continuous flow injection and spectrophotometry affords a simple, novel and rapid way of monitoring continuously the activity of naturally immobilized enzymes in their natural environment, thus eliminating cumbersome purification. The method was applied to determine the activity of polyphenol oxidase (PPO) enzymes naturally immobilized on coconut (Cocus nucifera, L.) fiber tissues. Maximum enzyme activity occurred at a temperature of 25C and at pH 6.0 using catechol as substrate. Thermal stability was assayed in a temperature range of 20 to 75C. The PPO exhibited excellent thermal stability, with only 50% loss in its activity at 75C after 4.3 min exposure. For catechol apparent Michaelis‐Menten constant (apparent Km), apparent Vmax and the apparent activation energy were 9.1 × 10^?3 mol L^?1, 0.20 abs min^?1 and 10.5 kcal mol^?1, respectively. The immobilized PPO showed high activity for o‐diphenols. The reactivity order was caffeic acid > pyrogallol > catechol. Complete inhibition of the enzyme was observed with 1 × 10^?3 mol L^?1 concentration of cyanide, thiourea, L‐cysteine, ascorbic acid, sodium sulfite, nitrates of cadmium, zinc and mercury, individually. Benzoic acid, 3‐hydroxy‐benzoic acid, 4‐acetamidephenol, sodium azide, resorcinol, L‐cystine and EDTA at equal concentrations inhibited PPO partially.     

Traditional and innovative production methods of Fiore Sardo cheese: a comparison of microflora with a PCR‐culture technique

Fiore Sardo is a cheese manufactured on farms in Sardinia from raw ewe’s milk, with Protected Designation of Origin (PDO). The aim of the study was to evaluate the effects of introducing a whey starter culture and specific mechanised cutting operations (innovative) vs traditional manufacture on the microbiological composition of the cheese, as assessed by conventional and molecular (PCR‐Culture Tecnique) methods. Five batches were manufactured by innovative and traditional methods and there was no significant difference between the cheeses.