Some virulence properties and characterization of motile Aeromonas species from milk and white cheese

Three hundred and thirty-eight samples of milk and milk products in Ankara were screened for the presence of motile Aeromonas species. The overall frequency of aeromonads in these samples was 27%. As expected, raw milk samples were more contaminated with aeromonads than were other products. Sixty-five (49.2%) of the 132 bulk raw milk samples were contaminated with aeromonads. In 35 of these samples, populations of aeromonads from 1.5 × 10² to 3.0 × 10³ cfu/mL were counted in ampicillin dextrin agar (ADA). Ten (40%) of the 25 raw milk samples sold in the street were contaminated with aeromonads. In eight of these samples, 1.2 × 10²−3.0 × 10³ cfu/mL were counted. Five (16%) of the 31 pasteurized milk and 12 (8%) of the 150 white cheese samples were contaminated with Aeromonas spp., but no countable aeromonads population was noted in ADA. The incidence of A. hydrophila, A. sobria and A. caviae in all samples was found to be 90.2%, 4.3% and 5.4%, respectively. The majority of the strains identified as A. hydrophila and A. sobria were able to produce haemolysin, protease and DNase, while strains identified as A. caviae were only positive for DNase. All isolated Aeromonas species ( A. hydrophila, A. sobria and A. caviae ) were positive for uptake of Congo red dye. Nevertheless, only strains identified as A. hydrophila and A. sobria showed a high rate of positive results when tested for the production of the Voges–Proskauer reaction and lysine decarboxylase. The results of this work show that motile Aeromonas spp., especially A. hydrophila , are frequently found in these samples. As these products are usually commonly consumed in Ankara, they can pose a risk especially for children, the elderly and immunocompromised individuals.     

Additives Affect Deoxynivalenol (Vomi toxin) Flour during Breadbaking

The effects of oxidizing (potassium bromate and L-ascorbic acid) and reducing (sodium bisulfite and L-cysteine) agents, and ammonium phosphate, at varying levels, on deoxynivalenol (DON; vomitoxin: 3,7,15-trihydroxy-12,13-epoxytrichothec-9 en-8 one) in whole wheat flour were investigated during breadbaking. Baking of flour containing 3.13 μg/g DON brought about 7.0% toxin reduction in bread. Sodium bisulfite (25 and 50 μg/g) L-cysteine (10, 40, and 90 μg/g and ammonium phosphate (1,000 μg/g) were moderately effective in reducing DON level in bread (38.0 to 46.0%). Potassium bromate (25 and 75 μg/g) and L-ascorbic acid (50 μg/g) had no effect.     

REHYDRATION KINETICS OF MICROWAVE-DRIED OKRAS AS AFFECTED BY DRYING CONDITIONS

The aim of the present work was to understand the effect of drying conditions (microwave output powers and sample amounts) and rehydration temperature on rehydration kinetics of microwave-dried okras. Four different models, Peleg's, Weibull, first order and exponential association, were applied to experimental data, and the corresponding parameters of the models were obtained. In addition, the kinetic parameters of the models were correlated with the ratio of microwave output power to sample amount and temperature. Although all the models applied provided a good agreement with the experimental data with high values of the coefficient of determination of R ², the first-order kinetic model was chosen as the appropriate model because of its simplicity. By using the kinetic parameters of this model, the activation energy for rehydration kinetics was estimated as 1.15 kJ/mol.

PRACTICAL APPLICATIONS

Drying, in general, is a means of removal of water from the material. The purpose of drying food products is to allow longer periods of storage with minimized packaging requirements, reduce shipping weights, and preserve seasonal plants and make them available to consumers during the whole year. Besides these advantages, some important changes take place, as structural and physicochemical modifications, which affect the final product quality during dehydration. Rehydration is a complex process aimed at the restoration of raw material properties when dried material contacted with water, and can be considered as a measure of the injury to the material caused by drying. The objective of rehydration study is to attain as many products in their original characteristics as fast as possible. An improved knowledge of rehydration kinetics would significantly enhance the feasibility of this process.     

IMPROVING THE QUALITY AND SHELF LIFE OF TURKISH ALMOND PASTE

Almond paste is an economically valuable product produced from almonds, sugar and a small amount of water. Oxidative rancidity and oil separation are the major problems that are encountered in the paste products affecting the shelf life. Another problem appears to be drying on the surface of the product resulting in poor consumer acceptability. In this study, the formulation of product was altered by adding a commercial stabilizer, antioxidant mixture and maltose syrup to prevent undesirable quality changes during storage at 4C and 30C. Peroxide value, free fatty acid and Rancimat analysis showed that the addition of antioxidant mixture prevented oxidation effectively and improved sensory scores significantly ( P ≤  0.05). Although stabilizer addition had a detrimental effect on the textural properties, samples that have maltose had high sensory scores. The results showed that incorporation of maltose syrup and antioxidant may improve the texture and shelf life of almond paste.

PRACTICAL APPLICATIONS

The available literature on almond paste is mainly focused on the microbiological quality of the product and the prevention of spoilage reactions by modifying packaging materials. However, there is no report on the optimization of the composition to extend the shelf life of almond paste. Turkish almond paste, a healthy and expensive dessert, is a specialty product that is manufactured by using traditional grinding equipment. However, the limited shelf life of this product decreases its export potential resulting in economical losses. Therefore, improved shelf life and quality of the product is of importance from the economical point of view. In our study, we aimed to improve the quality and shelf life of Turkish almond paste by modifying its formulation in order to minimize the undesirable changes that occur during storage.     

ISOLATION AND PARTIAL CHARACTERIZATION OF A NOVEL BACTERIOCIN PRODUCED BY LACTOCOCCUS LACTIS SSP. LACTIS MC38

This work presents the isolation and partial characterization of a new lactococcal bacteriocin produced by Lactococcus lactis ssp. lactis MC38. The bacteriocin demonstrated broad spectrum of inhibition activity against both pathogenic and food spoilage organisms, and various lactic acid bacteria. This antimicrobial substance appeared to be proteinaceous because its activity was completely inactivated by proteinase K and α‐chymotrypsin. It was heat and pH stable. The apparent molecular mass of the purified bacteriocin, determined by sodium dodecyl sulfate–polyacrylamide gel electrophoresis, was 8.0 kDa. The amino acid composition of the studied bacteriocin was found to be quite different from known lactococcal bacteriocins. The calculation of the number of amino acid residues in the bacteriocin molecule revealed that it contained 62 amino acids.     

MICROBIOLOGICAL QUALITY OF WHEAT STORED UNDER DIFFERENT CONDITIONS IN TURKEY

Four different types of wheat storage systems are widely used in the Marmara region. The existing storage conditions were studied and changes in the microbiological quality of the stored wheat under these conditions were assessed.
Depending on the external conditions, ambient temperatures and relative humidities in the stores were 17–26°C and 50–65% RH during summer and 3–10°C and 62–83% RH during winter, respectively. The low relative humidity level during harvesting and subsequent storage was adequate for obtaining low levels of moisture content and water activity in the produci for safe storage. The increase in relative humidity of the air during winter months did not affect the moisture content of the product considerably and the low temperature prevented mold growth. Therefore, all of the four different storage facilities were suitable for safe storage of grain for a period of one year without significant losses in quality due to microbiological load.     

EFFECT OF HIGH PRESSURE ON LACTOCOCCAL BACTERIOPHAGES

Four different host-specific lactococcal bacteriophages were subjected to high hydrostatic pressure and heat treatments. Pressure treatments were done at room temperature at 300 and 350 MPa for 5–40 min. Complete inactivation of bacteriophages was observed starting at 350 MPa for 20-min treatment at room temperature. The effect of heat on the bacteriophages was analyzed by heat treatment at 71.7C for predetermined lengths of time (1–5 min). Decrease in bacteriophage number was observed after 3 min of heat treatment at 71.7C. Pressure treatment at 350 MPa/5 min and heat treatment at 71.7C/3 min were both found to be effective for the inactivation of lactococcal bacteriophages. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis analysis indicated that protein profiles of pressure-treated (350 MPa, 25 min) bacteriophages were altered.

PRACTICAL APPLICATIONS

Bacteriophages are still a problem for the production of fermented dairy products, as there has not been a process to eliminate them completely from the fermentation environment. Processes such as pasteurization are not adequate to eliminate bacteriophages. However, new food preservation methods have been developed, one of which is high hydrostatic pressure (HHP) processing. HHP has potential application for the inactivation of viruses. Here, we demonstrate the application of HHP to inactivate the bacteriophages of dairy starter culture Lactococcus in comparison with heat treatment.     

A modelling study on kefir grain biomass growth: Influence of various minerals

In this study, the effect of initial kefir grain concentration and various minerals (MgO, MgSO₄.7H₂O, ZnSO₄.7H₂O, CaSO₄.1/2H₂O and Fe₂O₃) on the propagation of kefir grains and the pH evolution of kefir were investigated. The activated kefir grains were inoculated into very low fat (0.1%) cows’ milk under constant temperature (25°C) and impeller speed (100 rpm) for a propagation time of 24 h. Several mathematical models proposed to predict the pH value and kefir grain biomass increase vs propagation time were evaluated by the experimental results for all mineral additions; the Richards equation was found to be the most appropriate one. After evaluation of the experimental data, the most influential mineral addition providing 46.3% increase in kefir grain biomass was found to be MgO with a concentration of 0.30 g Mg²⁺/L. At this optimal condition, a model was derived for the kefir grain biomass concentration representing pH dependence.     

HEAVY METAL LEVELS IN VEGETABLES IN TURKEY ARE WITHIN SAFE LIMITS FOR Cu, Zn, Ni AND EXCEEDED FOR Cd AND Pb

Copper (Cu), cadmium (Cd), nickel (Ni), lead (Pb) and zinc (Zn) contents of various vegetables (cucumber, tomato, green pepper, lettuce, parsley, onion, bean, eggplant, peppermint, pumpkin and okra) produced in Kayseri, Turkey and the soils in which they were grown were determined using Inductively Coupled Plasma–Optical Emission Spectrometry (ICP–OES). These plants are the basis of human nutrition in the study area. The results obtained from the urban area were higher than those of the rural area as a result of pollution. The order of the elements in various vegetables and their concentration ranges in μg/g were Cu (22.19–76.5), Cd (0.24–0.97), Ni (0.44–13.45), Pb (3–10.7) and Zn (3.56–259.2). The concentrations of Cu, Zn and Ni in vegetables studied are within the recommended international standards. The results also show that onion (0.97 μg/g) and peppermint (76.5 μg/g) have the ability to accumulate more Cd and Cu than the other vegetables studied, respectively. Furthermore, there were statistically significant differences (P < 0.05) between the levels of Zn and Pb in all vegetables analyzed from urban and rural areas. Concentrations of metals analyzed in samples could be related to their concentration in the corresponding soils. Enhanced levels of metals observed in some vegetable species could be related to their concentration in the corresponding soils.