No abstract

No abstract

ACA‐DC 0040 produced an antimicrobial agent, which was named thermophilin T, active against several lactic acid bacteria strains of different species and food spoilage bacteria, such as Clostridium sporogenes C22/10 and Cl. tyrobutyricum NCDO‐1754. The crude antimicrobial compound is sensitive to proteolytic enzymes and α‐amylase, heat‐stable (100 °C for 30 min), resistant to pH exposure at pH 1–12 and demonstrates a bactericidal mode of action against the sensitive strain Lactococcus cremoris CNRZ‐117. The production of bacteriocin was optimized approximately 10‐fold in an aerobic fermenter held at constant pH 5·8 and 6·2. Ultrafiltration experiments with culture supernatant fluids containing the bacteriocin, and further estimation of molecular weight with gel filtration chromatography, revealed that bacteriocin in the native form has a molecular weight in excess of 300 kDa. SDS‐gel electrophoresis of partially purified thermophilin T showed that bacteriocin activity was associated with a protein band of approximately 2·5 kDa molecular mass.

-Thermophilin ST-1 is produced by Streptococcus thermophilus ACA-DC 0001, a "wild" strain isolated from traditional Greek yogurt products. It exerts an inhibitory effect on lactic acid bacteria, several food spoilage and food-borne pathogenic microorganisms, and some Gramnegative phytopathogen bacteria, including Listeria innocua BL 86/20 , Enterococcus faecalis EF1, Staphylococcus aureus ATCC 29996, Xanthomonas campestris BPIC 1660, Pseudomonas syringae BPIC 1549 and Erwinia rubrifasciens BPIC 1710. The crude antimicrobial compound is heat-labile (60°C for 10 min) and sensitive to the proteolytic enzymes pronase and trypsin and high acidic and alkaline conditions, and shows a bactericidal mode of action against the indicator strain Lactococcus lactis ssp. cremoris CNRZ-117. Production of thermophilin ST-1 starts during the early growth of the producer strain and reaches a maximum titer of 2560 AU·mL -1 at the end of the exponential growth. Thermophilin ST-1 was partially purified by ammonium sulfate precipitation, ionexchange and size-exclusion chromatography. SDS-PAGE electrophoresis of purified thermophilin ST-1 showed a single protein band with a molecular mass of 30 kg·mol -1 , classifying this novel bacteriocin with the large heat-labile proteins. Until now, however, the molecular mass of bacteriocins reported in the species of S. thermophilus was less than 10 kg·mol -1 (small, heat-stable peptides). Curing experiments did not result in the loss of bacteriocin production, suggesting that the genetic determinant is probably located on the chromosome. Streptococcus thermophilus

Growth of and bacteriocin production by Streptococcus macedonicus ACA-DC 198 were assessed and modeled under conditions simulating Kasseri cheese production. Controlled fermentations were performed in milk supplemented with yeast extract at different combinations of temperature (25, 40, and 55°C), constant pH (pHs 5 and 6), and added NaCl (at concentrations of 0, 2, and 4%, wt/vol). The data obtained were used to construct two types of predictive models, namely, a modeling approach based on the gamma concept, as well as a model based on artificial neural networks (ANNs). The latter computational methods were used on 36 control fermentations to quantify the complex relationships between the conditions applied (temperature, pH, and NaCl) and population behavior and to calculate the associated biokinetic parameters, i.e., maximum specific growth and cell count decrease rates and specific bacteriocin production. The functions obtained were able to estimate these biokinetic parameters for four validation fermentation experiments and obtained good agreement between modeled and experimental values. Overall, these experiments show that both methods can be successfully used to unravel complex kinetic patterns within biological data of this kind and to predict population kinetics. Whereas ANNs yield a better correlation between experimental and predicted results, the gamma-concept-based model is more suitable for biological interpretation. Also, while the gamma-conceptbased model has not been designed for modeling of other biokinetic parameters than the specific growth rate, ANNs are able to deal with any parameter of relevance, including specific bacteriocin production.

No abstract

Growth conditions that support bacteriocin (thermophilin T) production by Streptococcus thermophilus ACA-DC 0040 were identified. Synthesis of thermophilin T occurred during primary metabolic growth, while its specific rate of synthesis seemed to be optimal at T = 30 degrees C. Thermophilin T activity rapidly decreased in the stationary phase, especially at high growth temperature (i.e. T = 42 degrees C). In media with high content of complex nitrogen sources, high amounts of bacteriocin were detected in the growth environment, while about an 8-fold increase of thermophilin T titer and a 2-fold increase of specific synthesis rate was achieved when a fed-batch fermentation mode was applied.

This study presents, the development of a green method to produce rich in thymol natural zeolite (TO@NZ) nanostructures. This material was used to prepare sodium-alginate/glycerol/xTO@NZ (ALG/G/TO@NZ) nanocomposite active films for the packaging of soft cheese to extend its shelf-life. Differential scanning calorimetry (DSC), X-ray analysis (XRD), scanning electron microscopy (SEM), and Fourier-transform infrared spectroscopy (FTIR) instruments were used for the characterization of such nanostructures and films, to identify the thymol adsorbed amount, to investigate the thermal behaviour, and to confirm the dispersion of nanostructure powder into the polymer matrix. Water vapor transmission rate, oxygen permeation analyzer, tensile measurements, antioxidant measurements, and antimicrobial measurements were used to estimate the film’s water and oxygen barrier, mechanical properties, nanostructure’s nanoreinforcement activity, antioxidant and antimicrobial activity. The findings from the study revealed that ALG/G/TO@NZ nanocomposite film could be used as an active packaging film for foods with enhanced, mechanical properties, oxygen and water barrier, antioxidant and antimicrobial activity, and it is capable of extending food shelf-life.