Hüseyin Bozkurt

Utilization of natural antioxidants: Green tea extract and Thymbra spicata oil in Turkish dry-fermented sausage.

Effect of natural (green tea extract, Thymbra spicata oil) and synthetic antioxidants (buthylatedhydroxytoluene, BHT) on the safety (biogenic amine and TBARS values) and quality (pH, colour and sensory attributes) of sucuk (Turkish dry-fermented sausage) were investigated during the ripening periods. Addition of antioxidants decreased (P<0.05) the TBARS values. It was found that natural antioxidants decreased TBARS formation more than BHT. Antioxidants reduced (P<0.05) putrescine formation in the following order: green tea extract>green tea extract-T. spicata oil>T. spicata oil>BHT, and their mean values were 70.45, 76.05, 83.13, and 95.97mg/kg, respectively. The highest tyramine concentration was observed in control sucuk prepared without any antioxidants, while the lowest was in the recipe with green tea extract as their mean values were about 99.42 and 64.31mg/kg, respectively. The pH, L, b, and overall sensory quality were not significantly different (P>0.05) with the addition of green tea extract, T. spicata oil, green tea extract-T. spicata oil. These results indicated that the most effective antioxidant was found to be green tea extract. This study pointed out that natural antioxidants were more effective than synthetic antioxidants, so they could be easily utilized in sucuk to enhance quality and provide safer products.

Effects of starter cultures and additives on the quality of Turkish style sausage (sucuk)

The effects of starter cultures and additives on the quality of Turkish style sausage (sucuk) were investigated during ripening and storage. Total aerobic plate counts (aerobic bacteria), mould and yeast counts, pH, thiobarbituric acid (TBA) value and biogenic amine formation were followed. Aerobic bacteria increased (P<0.05) during the first 10 days of ripening to 9.26 log CFU/g and they decreased (P<0.05) to 5.70 at the end of the storage. Larger reductions (P<0.05) were observed in sausages made with high levels of potassium sorbate, nitrite and nitrate than in those containing low levels of additives and those without additives at the end of storage. During the first 3 days of ripening, the pH values of all sausages decreased (P<0.05) from 5.98 to about 4.53. Later, the pH values increased slowly, due to decomposition of acids to an approximately constant value of about 5.20. TBA values were higher (P<0.05) in the sausages made without additives than in the others. Sausages prepared using high concentration of additives had lower (P<0.05) concentrations of biogenic amines than the others. Addition of starter culture with high concentration of additives (nitrite, nitrate, α-tocopherol, ascorbic acid, potassium sorbate, potassium pyrophosphate and di-potassium hydrogenphosphate) decreased the formation of biogenic amine.

An eco-friendly process: predictive modelling of copper adsorption from aqueous solution on Spirulina platensis.

The adsorption of copper ions on Spirulina platensis was studied as a function of contact time, initial metal ion concentration, and initial pH regimes. Characterization of this adsorbent was confirmed by FTIR spectrum. Modified Gompertz and Logistic models have not been previously applied for the adsorption of copper. Logistic was the best model to describe experimental kinetic data. This adsorption could be explained by the intra-particle diffusion, which was composed of more than one sorption processes. Langmuir, Freundlich, and Redlich-Peterson were fitted to equilibrium data models. According to values of error functions and correlation coefficient, the Langmuir and Redlich-Peterson models were more appropriate to describe the adsorption of copper ions on S. platensis. The monolayer maximum adsorption capacity of copper ions was determined as 67.93 mg g(-1). Results indicated that this adsorbent had a great potential for removing of copper as an eco-friendly process.

Colour and textural attributes of sucuk during ripening

The sensory (flavour, colour, and ease of cutting scores), colour (Hunter L, a, b, YI, total colour difference, hue angle, chroma, and browning index values) and textural (hardness, adhesiveness, springiness, cohesiveness, gumminess, chewiness, and resilience) attributes of sucuk were followed during the ripening period. Colour scores increased (P<0.05) from score 4 to 6 during the first 3 days of the ripening period and then decreased (P<0.05). The lightness (L values), yellowness (b), and hue angle of sucuk decreased (P<0.05) during the ripening period. The major colour changes occurred between the 5th and 9th days of the ripening period. Pearson correlation test indicates that a positive relationship (P<0.01) exists between a-values and sensory colour scores. The overall sensory scores changed (P<0.05) in parallel to the flavour scores. Hardness, gumminess, and chewiness of sucuk increased (P<0.05) during the ripening period. Strong relationships (P<0.01) were found between hardness and cutting scores. Adhesiveness values of sucuk decreased significantly (P<0.05) about 10 times from -9.3 to -92.6 during the ripening period. Springiness and cohesiveness values decreased during the ripening period, but not significantly (P>0.05). Cutting scores were related (P<0.01) to gumminess (0.921) and chewiness (0.922) values but not to resilience (P>0.05). It was observed that most instrumental colour and textural attributes were in agreement with sensory attributes. These results indicated that instrumental methods could be easily adapted and can be used for evaluation of quality attributes of sucuk during the ripening period.

Prediction of removal efficiency of Lanaset Red G on walnut husk using artificial neural network model

An artificial neural network (ANN) model was used to predict removal efficiency of Lanaset Red (LR) G on walnut husk (WH). This adsorbent was characterized by FTIR-ATR. Effects of particle size, adsorbent dose, initial pH value, dye concentration, and contact time were investigated to optimize sorption process. Operating variables were used as the inputs to the constructed neural network to predict the dye uptake at any time as an output. Commonly used pseudo second-order model was fitted to the experimental data to compare with ANN model. According to error analyses and determination of coefficients, ANN was the more appropriate model to describe this sorption process. Results of ANN indicated that pH was the most efficient parameter (43%), followed by initial dye concentration (40%) for sorption of LR G on WH.

Modeling of biomass production by Spirulina platensis as function of phosphate concentrations and pH regimes

Batch cultivations were performed to evaluate the influence of phosphate concentrations (0.25, 0.5, 0.75, and 1.0 g L(-1)) for pH regimes (9.5, 10.0, and 10.5) on the biomass production by Spirulina platensis. The best condition for cell growth (3.099 g L(-1)) was found at 0.5 g L(-1) phosphate and pH value of 10.0. Cultivation time, phosphate, and pH caused to increase significantly (p<0.01) in biomass production by S. platensis. Lag time was observed up to 4 h. After then, biomass production increased sharply (p<0.01) from 0.020 g L(-1) to 2.063, 2.213, 1.532, and 0.797 g L(-1) at 0.25, 0.5, 0.75, and 1.0 g L(-1) phosphate values, respectively. Modified Gompertz model could be regarded as sufficient to describe the biomass production by S. platensis with high determination coefficients and low sum of square value indicated that. Biological parameters for biomass production were successfully predicted by modified Gompertz model.

Effects of Urtica dioica and Hibiscus sabdariffa on the quality and safety of sucuk (Turkish dry-fermented sausage).

In this study, the effect of Urtica dioica, Hibiscus sabdariffa butylatedhydroxytoluene (BHT) and nitrite/nitrate on the quality (pH, Hunter L-, a- and b-value and sensory attributes) and safety [2-thiobarbituric acid reactive substances (TBARS) value and biogenic amine] were investigated during the ripening periods of sucuk (Turkish dry-fermented sausage). During the first 2 days of ripening, pH values decreased (P<0.05) rapidly from 5.78 to about 4.49. pH values of batters were not significantly (P<0.05) affected by the addition of nitrite/nitrate, BHT, U. dioica, H. sabdariffa. TBARS values increased from 0.52 to about 0.95mg/kg significantly (P<0.05) during the first 4 days in control, and H. sabdariffa added batters. The highest (P<0.05) histamine concentration was determined in the control batter prepared without antioxidant. U. dioica was more effective (P<0.05) on decreasing histamine and putrescine concentration than the other antioxidants. Putrescine concentration in batters increased (P<0.05) from 1.13 to about 15.34mg/kg during the first 4 days. Tyramine concentration increased significantly (P<0.05) during the ripening period from 5.55 to 103.93mg/kg. The control batter had the highest (P<0.05) tyramine concentration about 50.21mg/kg. Hunter L-values were not affected (P>0.05) from ripening time and addition of antioxidants into batter. The Hunter a-value increased (P<0.05) during the ripening periods, however, b-values decreased (P<0.05) from 12.58 to about 10.53. Overall sensory quality evaluated from color, flavor and ease of cutting scores increased (P<0.05) from 3.25 to about 9.00.

Growth of Pseudomonas fluorescens and Candida sake in homogenized mushrooms under modified atmosphere

Abstract Pseudomonas fluorescens and Candida sake were inoculated into mushrooms and stored under different gaseous atmospheres: air, CO 2 :N 2 :O 2 (25:74:1%) and CO 2 :N 2 :O 2 (50:49:1%). The growth of both microorganisms was measured during 18 days of storage at 5 and 10 °C. The percentages of O 2 and CO 2 inside the package and the pH of mushrooms were monitored during the storage. The maximum specific growth rate constant ( μ m ), lag time ( λ ) and maximum population density ( A ) were evaluated from the modified Gompertz model using non-linear regression. The percentage of O 2 in the samples stored in air decreased progressively during an 18-day storage while the percentage of CO 2 increased. The pH of the samples stored under CO 2 decreased whereas the pH of samples stored in air at 10 °C increased during the first 4 days followed by a decrease for the rest of the storage. The lag time increased with an increase in the percentage of CO 2 in the atmosphere. The results suggest that the modified Gompertz model can be used successfully to describe the growth of both C. sake and P. fluorescens in mushrooms. Low CO 2 /high storage temperature combinations were found to favor the growth for both microorganisms.

Use of artificial neural networks and genetic algorithms for prediction of sorption of an azo-metal complex dye onto lentil straw.

Artificial neural network (ANN), pseudo second-order kinetic, and gene expression programming (GEP) models were constructed to predict removal efficiency of Lanaset Red G (LR G) using lentil straw (LS) based on 1152 experimental sets. The sorption process was dependent on adsorbent particle size, pH, initial dye concentration, and contact time. These variables were used as input to construct a neural network for prediction of dye uptake as output. ANN was an excellent model because of the lowest error and the highest coefficient values. ANN indicated that initial dye concentration had the strongest effect on dye uptake, followed by pH. The GEP model successfully described the sorption kinetic process as function of adsorbent particle size, pH, initial dye concentration, and contact time in a single equation. Low cost adsorbent, LS, had a great potential to remove LR G as an eco-friendly process, which was well described by GEP and ANN.

Modelling of Scenedesmus obliquus; function of nutrients with modified Gompertz model

This study attempted to investigate variation in biovolume of Scenedesmus obliquus, in the modified Johnson medium at 20+/-2 degrees C, under 16kergcm(-2)s(-1) continuous illumination. The experiments were carried out at four nitrate (8, 12, 16, and 20mM) and four phosphate (0.1, 0.3, 0.5 and 0.7mM) concentrations at pH 7 and 8. The best response for algal growth was found at 0.3mM phosphate and 12mM nitrate at pH 7, as it was obtained from weight averaging method. Besides, optimum phosphate and nitrate concentrations significantly distinguished (p<0.01) from other concentrations according to Turkeys HSD test. Key features of the growth of S. obliquus under phosphate and nitrate influenced batch culture was successfully predicted by modified Gompertz model. Through the cultivations, specific growth rate (mu) ranged from 0.30 to 1.02 day(-1), while biovolume doubling time (td) varied from 0.68 to 2.30 days. There were important differences (p<0.05) for both mu and td among response variables. Both nutrients displayed noteworthy effect (p<0.01) on the algal biovolume.