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- Author or Editor: László Csaba x
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Abstract
The effect of the ionic environment on the adsorption of phenol from aqueous solutions was investigated in a microporous carbon and in an oxidized carbon. It was found that not only the pH of the solution but also the method of its setting affects the adsorption capacity. Thermal desorption of phenol exhibits an even stronger dependence on the method of pH setting than adsorption. The TG response, the position and the corresponding TG steps are also influenced by the surface chemistry. Thermogravimetry is found to be outstandingly useful and informative technique for the studying sorption interactions.
Abstract
Potential functional food bakery products were developed and characterized based on White Lupin (Lupinus albus cv. Nelly) flour. Analytical properties of the seeds resemble to previously described Lupinus species, with significantly high protein content (45%). The high protein and dietetic fiber content of the seeds makes Lupin flour suitable to develop potential functional food products with high nutritional values. Results of the development of sweet biscuits and salty crackers enriched with Lupin flour are presented. Sensory evaluation of the bakery products was carried out by 15 panelists using the nine points hedonic scale. Heat stability of White Lupin proteins were investigated by gel-electrophoretic analysis, White Lupin proteins are quite stable at 140°C, after 35 min heating the biscuits still contain 69% of the original amount of proteins. Baking conditions were optimized also based on gel-electrophoretic experiments, the optimal baking time was 30 min at 140°C. Gluten-free Lupin-based biscuits and crackers were produced by completely omitting wheat flour from the recipes.
Abstract
A simple HPLC-UV procedure is described in our paper which is suitable for the rapid and cost-efficient determination of prochloraz in mushrooms. Prochloraz is the only fungicide in EU which use is allowed in mushroom production. The aim of our work was the development of a simple method that is suitable for the control of this pesticide in everyday analyses during mushroom production. The procedure involves a simple sample preparation method based on solid-liquid extraction (modified QuEChERS extraction method EN 15662) followed by an HPLC-UV determination (recovery: 97–99%; limit of detection LOD: 0.01 mg/kg; limit of quantification LOQ: 0.05 mg/kg).
Biotransformation of l-phenylalanine (l-1a) and five unnatural substrates (rac-1b–f) by phenylalanine ammonia-lyase (PAL) was investigated in a novel microfluidic device (Magne-Chip) that comprises microliter volume reaction cells filled with PAL-coated magnetic nanoparticles (MNPs). Experiments proved the excellent reproducibility of enzymecatalyzed biotransformation in the chip and the excellent reusability of the enzyme layer during 14 h continuous measurement (>98% over 7 repetitive measurements with l-1a). The platform also enabled fully automatic multiparameter measurements with a single biocatalyst loading of about 1 mg PAL-MNP. Computational fluid dynamics (CFD) calculations were used to study the flow field in the chambers and the effect of unintended bubble formation. Optimal flow rate for l-1a reaction and specific activities for rac-1b–f under these conditions were determined.
A Michelson-féle (optikai) interferométer mikrohullámú változatát széles körben használják különböző anyagok dielektromos állandójának meghatározására. Jelen tanulmányban a berendezést talajnedvesség-mérésre alkalmaztuk. A tájékozódó mérések során kiderült, hogy a mintáról visszavert hullám az interferenciaképre és ezáltal a mérésekre zavarólag hat. A visszavert hullám okozta hibát a minta megdöntésével küszöböltük ki. Ferde sugármenetes mérési elrendezést alakítottunk ki, amellyel a mérési eredmények megbízhatóak és reprodukálhatóak lettek. 3,1 mm vastag víztelített homokréteg kiszáradását végig követve, a Topp-féle talaj ε-értékekhez közeli dielektromos állandókat kaptunk. Megállapítottuk, hogy a mikrohullámú hullámhossz-tartományban a vizsgálható talajréteg-vastagság korlátozott. Közvetlen sugármenetes (nem interferometriás) összeállításban a mintán átmenő és az arról reflektálódó hullámenergia meghatározását is elvégeztük. Az eredmények a fizikai elvárásokkal összhangban vannak. A módszer alkalmazása szempontjából bíztató, hogy a mérések szerint a reflektált energia és a víztartalom kapcsolata közel lineáris. Összefoglalóan megállapítható, hogy: az interferometriás mérési elrendezés alkalmas a talaj víztartalmának meghatározására. Alkalmazása azonban kis rétegvastagságokra korlátozódik; a közvetlen sugármenetes reflexiómérés is alkalmasnak látszik a talaj víztartalmának mérésére. Ebben a mérési megoldásban nincsenek talajréteg-vastagsági korlátok. Mindkét mérési eljárás gyakorlati, kiváltképp terepi alkalmazása további kutató-fejlesztő munkát igényel.
Abstract
Minimal processing technologies, like High Hydrostatic Pressure (HHP), heat treatments at low temperatures have an increasing role in food industry. Eggs are considered as functional foods, but for high retention of biological active compounds adequate minimal processing technologies are needed during preservation procedure. In our study, liquid egg yolk (LEY) was examined to meet consumer's expectations.
Combinations of pasteurization (57–63 °C, 5–7 min) and HHP (350–400 MPa, 5 min) were used to provide microbiological stability of LEY. After these treatments samples were examined for mesophyll aerobes and Enterobacteriaceae cell counts (using Nutrient agar an incubation of 30 °C, 48 h) and viscosity attributes (Anton Paar MCR 92).
Our results show that microbiological stability is significantly influenced by the different parameters of heat treatments and HHP. Heat treatment effected at least 3 orders of magnitude decrease in cell count. Viscosity attributes point out that higher pressure of HHP have a stronger effect on viscosity than the temperature of pasteurization.
The results point out a great opportunity for industrial use of minimal processing technologies for LEY. Microbiological safety is strongly influenced by the order of treatments, but viscosity may be independent from the order of the treatments.
Abstract
Starting from mechanical revolution, each day new methods and new equipment have emerged. Today, the Ultra Heat Treatment (UHT) is one of the important technologies that permits to the industry to reduce processing time while maintaining the same quality of the products. Egg and egg products are known as heat-sensitive products, so the UHT enables us to preserve their qualities after a heat treatment.
Our aim is to study the effect of UHT treatment (approximately 67 °C for 190 s) on the Liquid Egg Yolk (LEY). For twenty-one days, the color and the apparent viscosity were measured every seven days, we also studied the damage of protein using DSC (Differential Scanning Calorimetry).
Comparing the two graphs of DSC, the denaturation of protein is distinct. The endothermic peak decreased. This could be seen also on the rheological curves. The apparent viscosity is diminished from 231 mPa.s on the 1st day of storage to 224 mPa.s on 21st day. However, the treated LEY could be stored for longer period than the raw LEY.
Abstract
Eggs are commonly used in the food industry because of their excellent nutrient value and also for their coagulating, foaming, emulsifying, colouring and flavouring properties. Manufacturers substitute shell eggs with processed egg products, such as liquid whole egg, liquid egg yolk or albumin. They have a shelf life of a few weeks, but freezing can increase it to 1 year. However, freezing causes gelation in case of egg yolk. This process is highly dependent on the conditions of freezing and thawing.
In our study, raw liquid egg yolk was frozen and stored for 14 days at −18 °C. On days 1, 7 and 14 samples were thawed by two different methods. Denaturation temperature and enthalpy were investigated by differential scanning calorimetry. Besides, rheological properties were examined at 20 °C, Herschel–Bulkley model was fitted to flow curves of the examined samples. The dry matter content was also recorded during the experiment. Two-way ANOVA was used to analyse data.
The results of the study showed that method of thawing had no significant effect on calorimetric and rheological properties and dry matter content. In contrast, freezing and frozen storage had a significant effect on denaturation enthalpy and rheological properties.
Abstract
Freezing can enhance the storage time of liquid egg products, but egg yolk undergoes an irreversible textural and structural change when it is cooled to –6 °C. In this study, the effects of different salt concentrations on the physical properties of frozen-thawed egg yolk were investigated.
The pasteurised liquid egg yolk (LEY) was treated with 4, 5, and 6% of NaCl before freezing and it was stored at –18 °C for 4 weeks. The colour, pH, and rheological characteristics (firmness, consistency, cohesiveness, and index of viscosity) of yolk samples were evaluated before and after freezing.
Salt treatment resulted in preventing gelation, with decreasing firmness, consistency and viscosity compared to control samples. The pH of all yolk samples increased during frozen storage. The lightness value decreased in treated samples and increased in the control sample after freezing.
The results indicated that the applied salt concentrations could inhibit protein aggregation of LEY induced by freezing during the storage period. At least 5% salt concentration could reduce effectively the changes in rheological properties.
