Drying is one of the oldest and most important food preservation techniques involving moisture movement from the product to the drying air. The optimum design of drying and aeration and storage systems requires mathematical modelling using basic data on the moisture sorption behaviour of the material to be dehydrated. A large number of empirical, semi-empirical or theoretical models have been reported in the literature for describing moisture sorption isotherms of food materials. The reported work presents a review of literature on equations for fitting moisture sorption isotherms of several vegetables. Variation was shown in equilibrium moisture content values determined for the same product from different isotherm equations. Equilibrium moisture content data obtained from different equations were then used in a mathematical model of vegetable drying to simulate the process. Analysis of the results of simulation showed that the kind of equation of moisture sorption isotherm used in the model of vegetable drying influence the results of simulation. In conclusion it was suggested that an “overall – all” evaluation of this large number of isotherm equations is needed in order to have a more precise (and quantitative) definition of their fitting abilities as applied to different vegetables.
The possibility of differentiation of L.monocytogenes from other Listeria species on the basis of hemolytic activity, the production of phosphatidylinositol-specific phospholipase C (PI-PLC) and the polymerase chain reaction (PCR) for the amplification of a DNA fragment of listeriolysine O (hly A) gene was compared. The screening of Listeria colonies for PI-PLC activity allowed to distinguish the pathogenic for humans L.monocytogenes bacteria from the majority of non-pathogenic Listeria spp. The amplification of DNA from Listeria lysates with two primers selected in area of the hly A gene made possible the differentiation of L.monocytogenes from other Listeria species, including hemolytic L.ivanovii and L.seeligeri bacteria as well as hemolytic or PI-PLC positive L.innocua strains.
The aim of this research was to analyze mechanical and acoustic properties of apples which were dried using different methods. Apple slices were dried using the following methods: convective, fluidal, microwave-convective and the sublimation. The obtained dried apple material was compressed in a Zwick machine with a velocity of 20 mm/min and with a simultaneous recording of the acoustic emission (AE) generated during sample destruction. Bruel&Kjsr accelerometer type 4381 was used for sound recording. Dried fruit porosity was also determined. Analyses conducted proved that drying methods significantly influence mechanical and acoustic properties of dried apples. Mechanical parameters: apparent Young's modulus, work and compression force were the highest for the fluidal dried apples, and the lowest for apples dried by the sublimation method. The latter group of dried apples was also most porous in structure. The obtained dried apple material differed in the number of events, the acoustic energy and in the range of emitted frequencies. There were negative correlations between mechanical and acoustic parameters of dried apples. The porosity of material correlated with the compression force, as well as the acoustic energy and the number of events.
Background. Marination is a good method to enhance attractiveness of chicken wings, which are considered by consumers as least attractive. Sensory value of marinated wings is dependent largely on the flavour of skin, because they contain proportionally more skin than other carcass elements. Moreover, skin constitutes a natural barrier, which may facilitate or hinder the penetration of marinade components, depending on the conformation State of proteins it is composed of primarily collagen. The aim of the study was to investigate the effect of specific marinades on thermal stability of collagen - the main component of skin proteins using differential scanning calorimetry (DSC). Material and methods. Chicken wings were marinated using model marinades, marinades prepared according to original recipes and ready-to-use marinades used in industrial practice. Marinated skin samples were weighted (approx. 10 mg) and analyzed by DSC. Heating rate was 5°C/min, within the range from 20 to 100°C. Results. In analyses using model marinades denaturation temperature (Tmax) of collagen was reduced by approx. 3°C and enthalpy (AH) was lowered by approx. 40%. An even bigger reduction of collagen denaturation temperature (by approx. 7°C) and enthalpy AH (by approx. 48%) was found after the application of marinades prepared following original recipes (W1, W2, W3). In tum, the application of model marinades containing NaCl and organic acids (acetic or citric) resulted in stabilization of collagen, which was manifested by an inerease of enthalpy (AH) by approx. 50% (for marinade containing 2% citric acid). Conclusions. Temperature and enthalpy of collagen denaturation was dependent on type of marinade. The extent of collagen denaturation affects nutritional and sensory value. Considering that time and temperature of intensive heat treatment are important factors in the formation process of carcinogenic compounds i.e. heterocyclic aromatic amines, it bis important to choose these marinades, which reduce the denaturation temperature and enthalpy of proteins.
Food preservation using high pressure is a promising technique in food industry as it offers numerous opportunities for developing new foods with extended shelf-life, high nutritional value and excellent organoleptic characteristics. High pressure is an alternative to thermal processing. The resistance of microorganisms to pressure varies considerably depending on the pressure range applied, temperature and treatment duration, and type of microorganism. Generally, Gram-positive bacteria are more resistant to pressure than Gram-negative bacteria, moulds and yeasts; the most resistant are bacterial spores. The nature of the food is also important, as it may contain substances which protect the microorganism from high pressure. This article presents results of our studies involving the effect of high pressure on survival of some pathogenic bacteria - Listeria monocytogenes, Aeromonas hydrophila and Enterococcus hirae - in artificially contaminated cooked ham, ripening hard cheese and fruit juices. The results indicate that in samples of investigated foods the number of these microorganisms decreased proportionally to the pressure used and the duration of treatment, and the effect of these two factors was statistically significant (level of probability, P ≤ 0.001). Enterococcus hirae is much more resistant to high pressure treatment than L. monocytogenes and A. hydrophila. Mathematical methods were applied, for accurate prediction of the effects of high pressure on microorganisms. The usefulness of high pressure treatment for inactivation of microorganisms and shelf-life extention of meat products was also evaluated. The results obtained show that high pressure treatment extends the shelf-life of cooked pork ham and raw smoked pork loin up to 8 weeks, ensuring good micro-biological and sensory quality of the products.
Inactivation of Campylobacter jejuni (strains No. 6, 19, and 34) was determined in poultry meat pressurised under the following conditions: at 300 MPa for 5, 15, 30, and 60 min, and at 500 MPa for 5, 15, and 30 min, at 20°C. The pressure treatment of 300 MPa applied for 5, 15, and 30 min did not inactivate all cells of the analysed C. jejuni strains. The inactivation of all C. jejuni cells occurred after 60-min pressurisation at 300 MPa. The pressure of 500 MPa resulted in death of all C. jejuni strains, irrespective of the time of pressure treatment. The study demonstrated that the high- pressure technique may be applied for the reduction of C. jejuni cells or their complete inactivation in poultry meat, which in turn, is likely to contribute to the production of more safer poultry products.
W pracy porównano wartość wypiekową mąk pszennych typu 550 i 850, żytniej typu 720 oraz pszenżytniej typu 680, naturalnych i napromienionych promieniami gamma w dawce: 2; 3 i 5 kGy. Napromienienie mąk pszennych w dawce 5 kGy umożliwiło wyizolowanie z nich większej ilości glutenu mokrego oraz znaczne zmniejszenie jego rozpływalności. W miarę zwiększania dawki promieniowania od 2 do 5 kGy następowało zmniejszenie indeksu glutenowego w mąkach pszennych, nie obniżając jednak ich wartości wypiekowej. Zdecydowaną poprawę wartości wypiekowej pod wpływem wszystkich zastosowanych dawek promieni gamma zaobserwowano w badaniach mąki pszenżytniej. Niewielkie zmiany liczby opadania na skutek procesu napromienienia świadczą o zachowaniu aktywności enzymu α-amylazy w badanych mąkach.
The aim of this study was to evaluate the influence of temperature (40, 50, 60, 70°C), flow velocity of the drying air (0,5 i 1 ms-1) and water blanching (3 min) on the specific energy during convective drying of parsley. The total process energy was also evaluated. The results showed that an increase of drying air temperature from 40 to 70 °C caused a decrease of the total process energy by about 43% (1 ms-1s) and 31% (0,5 ms-1) for non-blanching parsley, and about 52% (1 ms-1), and 42% (0,5 ms-1) for blanching material. For each drying temperature the total drying energy was lower in the case of the flow velocity 1.0 ms-1and decreased after blanching. The lowest average total drying energy (10.5 MJkg-1) was obtained for blanched parsley dried at the temperature of 70°C, and for the air flow velocity of 1.0 ms-1.