Faculty of Technology and Metallurgy

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Impact of chitosan-beeswax edible coatings on the quality of fresh strawberries (Fragaria ananassa cv Camarosa) under commercial storage conditions
(Elsevier BV, 2013-07)
Velickova, Elena
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Winkelhausen, Eleonora
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Kuzmanova, Slobodanka
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Alves, Vitor D.
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Moldão-Martins, Margarida
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Physical and sensory properties of ready to eat apple chips produced by osmo-convective drying
(Springer Nature, 2014-12)
Velickova, Elena
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Winkelhausen, Eleonora
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Kuzmanova, Slobodanka
The low cost raw material, apple variety Idared, was turned into value-added product, apple chips. The apple chips were produced in a two-step process consisting of osmotic treatment and conventional drying. Osmotic treatment was carried out in 40 % glucose solution at room temperature, followed by convective drying at 105 °C, till reaching water activity of 0.3. Mechanical properties of the apple chips measured by compression and penetration tests were correlated with the sorption properties. The low browning index, 25.5 and high whitening index, 63.7, proved the good retention of the color of the apple chips. The instrumental characteristics of the apple chips were correlated with the sensory characteristics of the product. The new product was accepted by the 95 % of the panelists. The stored apple chips under modified atmosphere showed no significant changes in the quality parameters over 6 month period.
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Characterization of multilayered and composite edible films from chitosan and beeswax
(SAGE Publications, 2015-03)
Velickova, Elena
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Winkelhausen, Eleonora
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Kuzmanova, Slobodanka
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Moldão-Martins, Margarida
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Alves, Vitor D
Chitosan-based edible films were prepared and subjected to cross-linking reactions using sodium tripolyphosphate and/or to beeswax coating on both films interfaces. In addition, chitosan-beeswax emulsion-based films were produced. The goal of these modifications of the chitosan films was the improvement of their barrier to water vapor and to decrease their affinity to liquid water maintaining or improving the mechanical and optical properties of the original chitosan films. The cross-linking with tripolyphosphate decreased both the water vapor permeability and the water absorption capacity to about 55% and 50% of that of the original chitosan films, respectively. However, there was an increase in the films stiffness, revealed by the increased Young modulus from 42 kPa up to 336 kPa. The multilayered wax-chitosan-wax films exhibited a similar improvement of the barrier properties to water vapor, with the advantage of maintaining the mechanical properties of the original chitosan films. However, these wax-coated films showed a higher water absorption capacity, which is believed to be a consequence of water entry into small pores between the film and the wax layers. Regarding the film samples subjected to cross-linking and further coating with beeswax, a similar behavior as the uncoated cross-linked films was observed. The emulsion-based composite films were characterized by a substantial decrease of the water vapor permeability (40%), along with a decrease in their stiffness. Regarding the optical properties, all films presented a yellowish color with similar values of lightness, chroma, and hue.
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Traditional white brined cheese as a delivery vehicle for probiotic bacterium Lactobacillus casei
(Society of Chemists and Technologists of Macedonia, 2015-11-12)
Dabevska-Kostoska, Margita
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Velickova, Elena
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Kuzmanova, Slobodanka
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Winkelhausen, Eleonora
<jats:p>The traditional white brined cow cheese was tested as a delivery vehicle for probiotic bacteria. The cheese was manufactured from pasteurized cow’s milk at an industrial scale, at the same time in three batches, each of 1000 liters milk. Two different initial concentrations of the probiotic bacterium Lactobacillus casei (3.86·107 and 5.81·107cfu g–1) were used. The cheese had relatively short period of ripening (40 days), large percentage of fat (~52% d.m.) and suitable pH values (~4.5) for the survival of probiotics. At the end of the ripening, the probiotic counts were 1.74·108and 3.72·108cfu g–1, respectively. There was no significant difference in most of the quality parameters at the p < 0.05 level between the two probiotic cheeses. Nitrogen fractions and fat content were the key components influencing the overall quality of the cheese samples. The principal component analysis of the sensory attributes demonstrated that the flavor contributed the most to the overall acceptance of all types of cheeses.</jats:p>
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Effect of vacuum infused cryoprotectants on the freezing tolerance of strawberry tissues
(Elsevier BV, 2013-07)
Velickova, Elena
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Tylewicz, Urszula
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Dalla Rosa, Marco
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Winkelhausen, Eleonora
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Kuzmanova, Slobodanka
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Entrapment of Saccharomyces cerevisiae cells in u.v. crosslinked hydroxyethylcellulose/poly(ethylene oxide) double-layered gels
(Elsevier BV, 2010-11)
Velickova, Elena
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Petrov, Petar
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Tsvetanov, Christo
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Kuzmanova, Slobodanka
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Cvetkovska, Maja
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Ethanol production using immobilized Saccharomyces cerevisiae in lyophilized cellulose gel
(Springer Nature, 2010-12)
Winkelhausen, Eleonora
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Velickova, Elena
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Amartey, Samuel A
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Kuzmanova, Slobodanka
A new lyophilization technique was used for immobilization of Saccharomyces cerevisiae cells in hydroxyethylcellulose (HEC) gels. The suitability of the lyophilized HEC gels to serve as immobilization matrices for the yeast cells was assessed by calculating the immobilization efficiency and the cell retention in three consecutive batches, each in duration of 72 h. Throughout the repeated batch fermentation, the immobilization efficiency was almost constant with an average value of 0.92 (12-216 h). The maximum value of cell retention was 0.24 g immobilized cells/g gel. Both parameters indicated that lyophilized gels are stable and capable of retaining the immobilized yeast cells. Showing the yeast cells propagation within the polymeric matrix, the scanning electron microscope images also confirmed that the lyophilization technique for immobilization of S. cerevisiae cells in the HEC gels was successful. The activity of the immobilized yeast cells was demonstrated by their capacity to convert glucose to ethanol. Ethanol yield of 0.40, 0.43 and 0.30 g ethanol/g glucose corresponding to 79%, 84% and 60% of the theoretical yield was attained in the first, second and third batches, respectively. The cell leakage was less than 10% of the average concentration of the immobilized cells.
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Hydroxyethylcellulose cryogels used for entrapment of Saccharomyces cerevisiae cells
(Elsevier BV, 2009-09)
Velickova, Elena
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Winkelhausen, Eleonora
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Kuzmanova, Slobodanka
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Cvetkovska, Maja
;
Tsvetanov, Christo

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