Determination of amiloride using a ds-DNA-modified pencil graphite electrode based on guanine and adenine signals

A sensitive electrochemical procedure based on ds-DNA interaction with amiloride at a ds-DNA-modified pencil graphite electrode (PGE) was introduced as a promising tool for determination of amiloride. An adsorptive stripping voltammetry was applied for the immobilization of ds-DNA on PGE in acetate buffer (pH 4.8). Differential pulse voltammetry (DPV) was carried out to obtain the change in the oxidation signal intensity of guanine and adenine before and after interaction with amiloride. The decrease in intensity of the guanine and adenine oxidation signals was used as an indicator for the sensitive determination of amiloride. Under the optimum conditions, a linear dependence of the guanine and adenine oxidation signals was observed to the amiloride concentration in the range of 0.75-240 μmol L⁻¹ with a detection limit of 0.5 μmol L⁻¹. The relative standard deviations of 10 replicate measurements of 1.0 and 10.0 μmol L⁻¹ amiloride concentrations were 4.7% and 5.3%, respectively. UV-vis measurements combined with DPV were also carried out to propose the most plausible mechanism for the interaction of amiloride and ds-DNA. The influence of potential interfering substances on the amiloride determination was studied. Finally, the ds-DNA-modified PGE biosensor was applied for the determination of amiloride in tablets and urine samples with satisfactory results.     

Evaluation of nanocomposite packaging containing Ag and ZnO on shelf life of fresh orange juice

Nanocomposite LDPE films containing Ag and ZnO nanoparticles were prepared by melt mixing in a twin-screw extruder. Packages prepared from the films were then filled with fresh orange juice and stored at 4 °C. Microbial stability, ascorbic acid (AA) content, browning index, color value, and sensory attributes of them were evaluated after 7, 28, and 56 days of storage. Packages containing the nanomaterials, expect 1% nano-ZnO, kept the microbial load of fresh juice below the limit of microbial shelf life (6 log cfu/ml) up to 28 days The least degradation of AA (80.50 mg/100 g), development of brown pigments (OD = 0.23) and losing of color (∆E = 6.0) were observed in pouches containing 0.25% nano-ZnO, after the same time. Sensory attributes were also ranked highest for the juice thus packed in the recent packages after 28 days (p < 0.05). Packages containing nanosilver increased shelf life of fresh juice although part of its sensory attributes were lost.

Industrial relevance

Compared with pure packaging materials, antimicrobial nanocomposite packages containing Ag and ZnO as an alternative non-thermal technology can extend the shelf life of fresh orange juice up to 28 days. However, a certain concentration of nano-ZnO in the packages showed less adverse effects on sensory characteristics.     

Enzyme immobilization. Part 4. Immobilization of alkaline phosphatase on Na-sepiolite and modified sepiolite

Alkaline phosphatase from calf intestinal mucous membrane was immobilized on the modified and unmodified Na-sepiolite. The effects of various factors such as concentration of enzyme solution, pH and temperature of immobilization medium, magnetic stirring and various thermodynamic parameters on the immobilization rate of alkaline phosphatase (APh) were evaluated. pH = 10 was optimal for enzyme activity for both the free enzyme and the sepiolite. Sepiolite with bilayer surfactant coverage (SBS) had high ability for immobilization of APh. APh immobilized on SBS showed approximately similar V_max and K_m in comparison with the free enzyme. By immobilization of APh on Na-sepiolite without surfactant (SWS) and sepiolite with monolayer surfactant coverage (SMS), V_max decreased and K_m increased.     

Efficiency of modified skimmed milk base media to achieve high exopolysaccharide/cell ratios by Lactobacillus delbrueckii subsp. bulgaricus SZ2 in optimised conditions defined by the response surface methodology

Exopolysaccharide (EPS) production by Lactobacillus delbrueckii subsp. bulgaricus SZ2 was optimised in modified MRS (M‐MRS) using the response surface methodology (RSM). Maximum EPS production was 74.3 ± 2 mg/L, and the optimised values of the three variables predicted for maximum EPS production included a temperature of 38.7 °C, Bacto‐casitone and glucose concentrations of 24.5 and 29.6 g/L, respectively. To compare EPS production in MRS and skimmed milk (SM), the kinetics of EPS formation and growth were monitored in M‐MRS, SM, skimmed milk plus 2% additional sucrose (Suc‐SM) and skimmed milk containing Bacto‐casitone (20 g/L) and yeast nitrogen base (5 g/L) (BY‐SM). EPS production in all the media tested seemed to be growth‐related. The EPS/cell ratios were determined to be 3.12 × 10^?10, 1.43 × 10^?10, 4.42 × 10^?11 and 3.16 × 10^?11 mg/cell, in Suc‐SM, SM, M‐MRS and BY‐SM, respectively, clearly indicating the greater effect of C/N ratio when cell behaviour in EPS production is considered.     

Microbial and physiochemical changes in yoghurts containing different Lactobacillus delbrueckii subsp. bulgaricus strains in association with Lactobacillus plantarum as an adjunct culture

Two strains of slow and normal acid‐producing Lactobacillus delbrueckii subsp. bulgaricus, mixed separately with Streptococcus thermophilus, were used in the preparation of yoghurt with or without Lactobacillus plantarum A7. Viable cell counts of lactic bacteria, pH, lactic acid and acetic acid concentrations, soluble nitrogen content, spontaneous syneresis, viscosity and firmness were studied at selected points during the refrigerated storage period. Results showed that survival of L. plantarum A7 in yoghurt was independent of the acidification capability of L. delbrueckii subsp. bulgaricus strains which had already been characterised in their pure culture. Thus, in the preparation of probiotic yoghurt, using slow acid‐producing L. delbrueckii subsp. bulgaricus strain in combination with nondairy lactobacilli postfermentation acidification is not restricted but instability in other physicochemical properties of the yoghurt may be expected.     

Effect of heat,nisin and ethylene diamine tetra‐acetate treatments on shelf life extension of liquid whole egg

This study examined the effect of nisin alone or in combination with pasteurisation or ethylene diamine tetra‐acetate (EDTA), on the shelf life of unpasteurised liquid whole egg (LWE) stored at refrigerator temperature for a period of 21 days. The shelf life of samples was determined by counting total mesophilic bacteria, yeast and mould and also pH changes. It was observed that addition of 3 ppm nisin to pasteurised LWE was effective enough to extend the shelf life of this product from about 7 days to at least 21 days. However, for unpasteurised LWE nisin alone had no significant effect on shelf life while treatment of LWE with nisin in combination with EDTA showed a significant antibacterial and antifungal activity leading to extended shelf life of unpasteurised LWE from 1 to 4 days to at least 21 days.     

Biocontrol of Gray Mold Disease on Strawberry Fruit by Integration of Lactobacillus plantarum A7 with Ajwain and Cinnamon Essential Oils

This study was conducted to evaluate the efficacy of the Lactobacillus plantarum A7 (L. Plantarum), ajwain and cinnamon essential oils (AO and CO, respectively) in suppressing gray mold rot in strawberry fruit. AO and CO showed over 90% inhibition of radial mycelia growth with lower concentration of the oils per plate for all tested pathogens. Combined application of L. plantarum with AO and CO was tested to assess the possible synergistic effects of these 3 elements on the control of tested plant pathogens. In this case both combinations of L. plantarum + AO and L. plantarum + CO inhibited the mycelia growth of the pathogens completely. Results showed that the combined treatment of strawberry fruits with L. plantarum + AO (50 μL) and L. plantarum + CO (100 μL) resulted in remarkably improved control of Botrytis infections, in comparison with application of L. plantarum or essential oils alone. Quality attributes (that is pH, acidity, vitamin C, and total soluble solid) of the strawberry fruits did not change significantly (P < 0.01) when combination of Lactobacillus and essential oils was used. To the best of our knowledge, this is the first report on the effects of combination of a Lactobacillus as an antagonist bacterium with essential oils to increase the shelf life of strawberry.     

Effect of nanocomposite packaging containing Ag and ZnO on inactivation of Lactobacillus plantarum in orange juice

Nanocomposite LDPE films containing Ag and ZnO nanoparticles were prepared by melt mixing in a twin-screw extruder. Orange juice was sterilized and was inoculated with 8.5 log cfu/mL of lactobacillus plantarum. Packages prepared from nanocomposite films were then filled with this orange juice and then stored at 4 °C. Microbial stability of the juice was evaluated after 7, 28, 56, 84, and 112 days of storage. The results showed that microbial growth rate significantly reduced as a result of using this nanocomposite packaging material. Reduced numbers of L. plantarum were observed (p < 0.05) in nanocomposite packages of orange juice containing nanosilver and nano-ZnO. Moreover, packaging made from nanocomposite film containing nanosilver showed a more pronounced antimicrobial effects, as compared with nano-ZnO during 112 days storage of inoculated orange juice. However, LDPE + 5% P105 packages, showed a significant antimicrobial activity compared with others.     

Production of microbial exopolysaccharides in the sourdough and its effects on the rheological properties of dough

Exopolysaccharides (EPS) are exogenous microbial metabolites which are secreted mainly by bacteria and microalgae during growth. In addition to natural polysaccharides present in cereal grains flour and dough, microbial flora is usually involved in production of polysaccharide on sourdough fermentation. Total polysaccharides (microbial and flour) were extracted from sourdough and dough samples dehydrated and were added at the rate of 0%, 0.25%, 0.5%, 1%, 1.5%, 2% and 2.5% (w/w flour based) on the dough to investigate its effects on the rheological properties of the dough. Addition of polysaccharides to the dough increased the water absorption and decreased the dough softening after 20 min. Resistance to extension after 45, 90 and 135 min resting time was decreased by increasing the percentage of the added polysaccharides. Longer fermentation time for each level of polysaccharides led to greater stability. No significant differences were observed in the extensibility of dough. The overall effects of different levels of added polysaccharides resulted in a decrease in resistance to extension ratio of the samples. Energy input decreased in all cases. It seems therefore that addition of polysaccharides may be useful when bread is to be made with stronger flour and longer fermentation time is needed.