P. Kotzekidou

Effect of protective cultures and packaging film permeability on shelf-life of sliced vacuum-packed cooked ham

Cooked ham produced with Lactobacillus alimentarius and Staphylococcus xylosus as protective cultures, and control ham were sliced, vacuum-packed in pouches with oxygen transmission rates (OTR) of 360 and 77 cm(3)/m(2)/24 hr/atm, and stored at 4 °C in the dark. The addition of protective cultures increased (p < 0.05) lactic acid bacteria and micrococci and staphylococci counts in the meats. After cooking, the population of lactic acid bacteria was higher (p < 0.05) in hams produced with L. alimentarius than the other treatments. Protective cultures increased (p < 0.05) the shelf-life of cooked ham. The higher the OTR, the lower the shelf-life. Cooked ham with L. alimentarius was acceptable up to 28 days compared to control ham with a shelf-life of 3 weeks. Micrococci and staphylococci were inhibited in hams with L. alimentarius. Hams with S. xylosus had a better red colour than other treatments. Cooked hams with protective cultures had lower total aerobic bacteria, micrococci and staphylococci and Brochothrix thermosphacta counts than control hams which had higher populations of lactic acid bacteria and lower pseudomonads.

Role of hydrolytic enzymes and oxidative stress in autolysis and morphology of Blakeslea trispora during β-carotene production in submerged fermentation

The role of hydrolytic enzymes (proteases and chitinase) and oxidative stress in the autolysis and morphology of Blakeslea trispora during β-carotene production from a chemically defined medium in shake flask culture was investigated. The process of cellular autolysis was studied by measuring the changes in biomass dry weight, pH, concentration of β-carotene, specific activity of the hydrolytic enzymes and micromorphology of the fungus using a computerized image analysis system. In addition, the phenomenon of autolysis was associated with high concentrations of reactive oxygen species (ROS). The accumulation of ROS produced during fermentation causes oxidative stress in B. trispora. Oxidative stress was examined in terms of the activities of two key defensive enzymes: catalase (CAT) and superoxide dismutase (SOD). The profile of the specific activities of the above enzymes appeared to correlate with the oxidative stress of the fungus. The high activities of CAT and SOD showed that B. trispora is found under oxidative stress during β-carotene production. The culture began to show signs of autolysis nearly in the growth phase and autolysis increased significantly during the production phase. The morphological differentiation of the fungus was a result of the degradation of the cell membrane by hydrolytic enzymes and oxidative stress. Increased β-carotene production is correlated with intense autolysis of clumps, which has as a consequence the increase of the freely dispersed mycelia.

Production of β-Carotene From Beet Molasses by Blakeslea trispora in Stirred-Tank and Bubble Column Reactors Development of a Mathematical Modeling

The effect of aeration rate and agitation speed on β-carotene production from molasses by Blakeslea trispora in a stirred-tank fermentor and optimization of the production of the pigment in a bubble column reactor were investigated. In addition, a central composite design was employed to determine the maximum β-carotene concentration at optimum values for the process variables (aeration rate, sugar concentration, linoleic acid, kerosene). By image analysis of the morphology of the fungus, a quantitative characterization of the hyphae and zygospores formed was obtained. The hyphae were differentiated to intacthyphae, vacuolated hyphae, evacuated cells and degenerated hyphae. An increased proportion of zygospores was correlated to high β-carotene production. In the stirred-tank fermentor, the highest concentration of the carotenoid pigment (92.0 mg/L) was obtained at an aeration rate of 1.5 vvm and agitation speed of 60 rpm. In the bubble column reactor, the aeration rate and concentration of sugars, linoleic acid, kerosene, and antioxidant significantly affected the production of β-carotene. In all cases, the fit of the model was found to be good. Aeration rate, sugar concentration, linoleic acid, and kerosene had a strong positive linear effect on β-carotene concentration. Moreover, the concentration of the pigment was significantly influenced by the negative quadratic effects of the given variables and by their positive or negative interactions. Maximum β-carotene concentration (360.2 mg/L) was obtained in culture grown in molasses solution containing 5% (w/v) sugar supplemented with linoleic acid (37.59 g/L), kerosene (39.11 g/L), and antioxidant (1.0 g/L).

CONTINUOUS PRODUCTION OF LACTIC ACID FROM DEPROTEINIZED WHEY BY COIMMOBILIZED LACTOBACILLUS CASEI AND LACTOCOCCUS LACTIS CELLS IN A PACKED-BED REACTOR

Abstract The continuous production of lactic acid from deproteinized whey by immobilized single and mixed culture of L. casei and L. lactis in Ca‐alginate beads has been investigated. A coimmobilized culture system gave better results than immobilized single cultures regarding lactic acid concentration, productivity, yield, and lactose utilization. Maximum lactic acid productivity of 7 g/lh was obtained at D=0.4 h−1 with a yield of 70% lactic acid and 50% lactose utilization. At a dilution rate of 0.1 h−1, a lactic acid productivity of 2.5 g/lh was obtained with a 55.5% lactic acid yield and 90% lactose utilization. The bioreactor system was operated at a constant dilution rate of 0.1 h−1 for 20 days without loss of original activity. In this case, the average lactic acid productivity, lactic acid yield and lactose utilization were 24 g/lh, 55% and 90%, respectively.

Production of Beta-Carotene from Synthetic Medium by Blakeslea trispora in Fed-batch Culture

Abstract The production of β-carotene from a synthetic medium by Blakeslea trispora in fed-batch culture was investigated. A maximum β-carotene concentration of 85.0 mg L−1 with productivity of 0.16 mg L−1 h−1 and specific β-carotene production rate of 0.01 mg g−1 h−1 was obtained by feeding the cells constantly with olive oil, cottonseed oil, soybean oil, antioxidant, and low concentration of growth factors at feeding rate of 4.2 mL h−1 from the beginning of the fermentation. In this case, the fed-batch culture supported high values of biomass dry weight (11.0 g L−1) and sugar utilization (0.976 g g−1). The morphology of the fungus was studied during growth in fed-batch fermentation system using an image analysis system. Zygospores are the morphological forms, which are responsible for the production of the pigment. The highest percentage of zygospores (11.44%) was correlated with the highest percentage of intracellular β-carotene (0.72%) in the total biomass dry weight. Moreover, high percentages of vacuolated hyphae, evacuated cells, and degenerated hyphae of the microorganism were observed. This was due to the formation of high amount of H2O2 by exposure of the microorganism to high dissolved oxygen concentration.

Fermentation of table olives by oleuropeinolytic starter culture in reduced salt brines and inactivation of Escherichia coli O157:H7 and Listeria monocytogenes.

The effect of an autochthonous starter culture developed by oleuropeinolytic strains belonging to the Lactobacillus plantarum group on the physicochemical and microbiological characteristics and the biophenol content of table olives fermented under reduced salt conditions was studied. Black (cv. Kalamata) and green (cv. Chalkidikis) olives were fermented in two different kinds of brine (Brine A containing 2.3% NaCl, 32.3mM Ca-acetate and 33.9mM Ca-lactate and Brine B containing 4% NaCl, pH5.0 in both brines). The sensory attributes of olives fermented by oleuropeinolytic starter culture assessed by a trained panel did not differ significantly compared with industrial processing. It is possible to carry out significant changes in table olive processing applying a completely microbiological procedure using oleuropeinolytic strains of the L. plantarum group as both the debittering and the fermentation agent in order to achieve improved sensorial and nutritional characteristics of the final product. Table olives processed by the suggested methodology may constitute a good source of biophenols in the diet, especially hydroxytyrosol and tyrosol. The inactivation potential of Escherichia coli O157 EDL-932 and Listeria monocytogenes Scott A in olives fermented by oleuropeinolytic starter culture was evaluated. The population of each pathogen in olive homogenates of both cultivars is inactivated by more than 6logCFU/ml in less than 24h. When whole fermented olives were submerged in peptone/saline (containing 6.7logCFU/ml of the relevant bacterial pathogen) for 30min followed by rinsing in distilled water, the population of viable foodborne pathogens dropped more than 4 logs in olive pulp. During subsequent storage at 22 or 4°C the population of L. monocytogenes Scott A was further eliminated under the detection limit in both olive cultivars whereas the population of E. coli O157 EDL-932 could be detected in olives stored in peptone/saline at 22°C for 7days. The inhibitory effect of olives fermented by oleuropeinolytic starter culture in reduced salt brines on pathogens is due to the antimicrobial activity of the phenolic compounds and the antagonistic action of the associated microflora.

OPTIMIZATION OF β-CAROTENE PRODUCTION FROM SYNTHETIC MEDIUM BY BLAKESLEA TRISPORA IN A STIRRED TANK REACTOR AND RELATIONSHIP BETWEEN MORPHOLOGICAL CHANGES AND PIGMENT FORMATION

ABSTRACT The effect of linoleic acid, kerosene, antioxidant and a mixture of natural oils (olive oil, soybean oil, and cottonseed oil) on the production of β-carotene by Blakeslea trispora and the morphological characteristics of the fungus in a stirred tank reactor were investigated. The mixture of linoleic acid and antioxidant improved slightly the production of β-carotene, while the addition of linoleic acid, kerosene or antioxidant alone to the medium had an inhibiting effect on β-carotene production. The addition to the medium of a mixture of natural oils and antioxidant increased significantly the concentration of the pigment. B. trispora formed hyphae, zygophores and zygospores during β-carotene production. Morphology of the fungus was studied during growth in submerged culture in a stirred tank reactor under different compositions of the production medium using an image analysis system. Zygospores are the morphological forms, which are responsible for pigment production. Maximum β-carotene concentration (1500 mg/L) was obtained in culture grown in medium supplemented with 1% (w/v) each one of olive oil, soybean oil, cottonseed oil and 0.25% (w/v) of antioxidant (butylated hydroxytoluene, BHT). In this case, the morphological characteristics of B. trispora recorded showed intact hyphae, degenerated hyphae and zygospores in percentages of about 30.0%, 2.0% and 51.0% respectively in the biomass dry weight.

Survey of Listeria monocytogenes, Salmonella spp. and Escherichia coli O157:H7 in raw ingredients and ready-to-eat products by commercial real-time PCR kits.

Real-time PCR (RTiPCR) assays including enrichment stage were evaluated for the rapid detection of Listeria monocytogenes, Salmonella spp. and Escherichia coli O157:H7 in raw ingredients and ready-to-eat products using molecular beacon probes available as commercial kits (WARNEX Genevision, Canada & AES Chemunex detection system, France). The accuracy of the assays was evaluated analyzing 1032 naturally contaminated food samples in combination to the conventional cultural methods. Presence/absence testing of the above pathogens was performed in 25 g samples of each product. In case of L. monocytogenes of 39 positive RTiPCR samples, 37 were confirmed by the cultural method (based on McNemars test the difference between the two methods is insignificant). The highest incidence of L. monocytogenes in food products was found in desserts and the second highest in frozen pastries. None of the samples were cultural positive but negative in the RTiPCR test. One among the 343 investigated samples was positive for Salmonella spp. by RTiPCR and the cultural method. Out of 333 samples analyzed for E. coli O157:H7 no positive sample was detected. RTiPCR-based methods proved to be powerful tools for fast, sensitive and accurate pathogen detection in raw food ingredients and ready-to-eat products.

AUTOLYSIS OF Blakeslea trispora DURING CAROTENE PRODUCTION FROM CHEESE WHEY IN AN AIRLIFT REACTOR

The phenomenon of autolysis in Blakeslea trispora during carotene production from deproteinized hydrolyzed whey in an airlift reactor was investigated. The process of cellular autolysis was studied by measuring the changes in carotene concentration, dry biomass, residual sugars, pH, intracellular protein, specific activity of the hydrolytic enzymes (proteases, chitinase), and micromorphology of the fungus using a computerized image analysis system. All these parameters were useful indicators of autolysis, but image analysis was found to be the most useful indicator of the onset and progress of autolysis in the culture. Autolysis of B. trispora began early in the growth phase, continued during the stationary phase, and increased significantly in the decline phase. The morphological differentiation of the fungus was a result of the degradation of the cell membrane by hydrolytic enzymes. The biosynthesis of carotenes was carried out in the exponential phase, where the phenomenon of autolysis was not intense.

Effect of Non-Ionic Surfactants and Beta-Ionone on the Morphology of Blakeslea trispora and Carotenoids Production from Cheese Whey in Submerged Aerobic Growth: A Statistical Approach

The effect of non-ionic surfactants and β-ionone on morphology of Blakeslea trispora and carotenoids production from deproteinized hydrolyzed whey in submerged aerobic growth was investigated. Also, a central composite design was employed to determine the maximum carotenoids concentration at optimum values for the process variables (Tween 80, Span 80, β-ionone). The fit of the model was found to be good. Tween 80 and Span 80 had a strong linear effect on carotenoids production. The concentration of carotenoids was significantly affected by Tween 80 – Span 80 and Span 80 – β-ionone interactions as well as by the negative quadratic effect of β-ionone. The optimum medium composition for the maximum carotenoids production (100.0 ± 5.0 mg/g biomass dry weight) was found in deproteinized hydrolyzed whey supplemented with Tween 80 (33.6 g/L), Span 80 (68.7 g/L), and β-ionone (2.6 g/L). This result indicated that the optimization strategy led to an increase in carotenoids production by 33-fold. The carotenoids content in B. trispora were β-carotene, γ-carotene, and lycopene. The composition of carotenoids depends of the amount of nonionic surfactants and β-ionone added to the cheese whey. The medium composition influenced the morphogenesis of B. trispora and product formation. The addition of surfactants into the medium changed the morphology of the microorganism from solid aggregates to loose aggregates and resulted in a substantial increase in pigment production. B. trispora growing in submerged aerobic growth is able to develop complex morphologies which have been classified into three major groups: freely dispersed hyphae, clumps, and pellets. These parameters are responsible for the production of carotenoids.