Papers by Elena Velickova
Food Research International, 2021
Texture and structure of breads have been related to oral processing (FOP) performance and sensor... more Texture and structure of breads have been related to oral processing (FOP) performance and sensory perceptions, but moisture content might play a significant role. To evaluate the real impact of breads texture and structure, eliminating the possible role of moisture content, different toasted breads were investigated. Four commercial toasted sliced breads (white bread -WHB-, whole wheat bread -WWB-, non-added sugar bread -NSU-, non-added salt bread -NSA-) with similar ingredients but different texture and structure were selected. Texture and structure were instrumentally and sensory evaluated, besides FOP (total chewing time, number of chews until swallowing, chewing frequency, and mouthful) and bolus properties (moisture, saliva to bread ratio, hardness, adhesiveness, and cohesiveness). Toasted breads showed significant differences in hardness, cutting strength, and porosity, but panelists did not discriminate among them. FOP results indicated that harder samples (NSU) required longer mastication and a number of chews, and open crumb structures (WWB, WHB) with higher cell areas required less mastication. Also, bolus characteristics were affected by bread types, and bread with lower crumb hardness (WHB) produced more cohesive bolus. Having toasted breads allowed to eliminate possible influence of moisture content differences on sensory perception, mouthful and bolus water incorporation during mastication.
Inulinase immobilisation in PAA/PEG composite for efficient fructooligosaccharides production
Biocatalysis and Biotransformation, 2020
Abstract Inulinase was immobilised by entrapment method in polyacrylamide/polyethylene glycol com... more Abstract Inulinase was immobilised by entrapment method in polyacrylamide/polyethylene glycol composite and evaluated for its efficiency for short-chain fructooligosaccharides (3–6 degrees of polymerisation) production in batch hydrolysis system. Aqueous two-phase polymerisation technique was used to synthesise the composite, where aqueous polyethylene glycol 1000 containing the enzyme was used as dispersant with ammonium persulfate as initiator. The characteristics of free and immobilised inulinase were investigated and compared, and the results showed shift of pH and temperature optimum and change in stability caused by the immobilisation material. The immobilised preparation retained 50% of its initial activity after 20 successive batch cycles of 1 h each. The conversion degree of highly polymerised inulin to fructooligosaccharides (3–6 degrees of polymerisation) was 36% when using 30% PAA/PEG, w/v. Highlights ATPS extracted inulinase was effectively immobilised in PAA/PEG composite. Immobilised enzyme showed good pH and thermal stability. Immobilised catalyst presents good retention of activity after 20 reuses. The entrapped enzyme is effective in producing FOS with the DP from 3 to 6 with proved prebiotic activities. The optimum conditions for batch operating mode were: 2% (w/v) inulin, 30% (w/v) PAA/PEG composite, pH = 4.4 and T = 40ºC.
IOP Conference Series: Earth and Environmental Science, 2019
The aim of this study was to investigate the effect of oregano and chitosan applied as edible coa... more The aim of this study was to investigate the effect of oregano and chitosan applied as edible coatings on the chemical and microbiological properties of different type of meat products. The main focus from the microbiological aspect was on Listeria monocytogenes as a pathogen that can survive for a long period on this type of product and, hence, present a risk for consumers. In vitro testing showed chemical quality after 7 and 14 days’ storage of the three types of products was stable. Promising results were obtained for the microbial analysis, whereby large reductions in L. monocytogenes numbers after 7 and 14 days’ storage at 4°C was measured in the coated products. The results indicated the chitosan and oregano combination can be an effective inhibitor of L. monocytogenes growth in chilled meat products.
Engineering in Life Sciences, 2018
In this study, extracellular inulinase from Bacillus sp. 11/3 was partially purified and concentr... more In this study, extracellular inulinase from Bacillus sp. 11/3 was partially purified and concentrated using aqueous two‐phase system (ATPS). Two different phase forming salts and four types of polyethylene glycol (PEG) were used. Binodal curves and tie‐length lines (TLLs) for eight ATPS were developed. For inulinase purification, concentrations of PEG and salt according to binodal curves (between 17 and 26%) were chosen. All ATPSs for inulinase purification were characterized. An ATPS consisted of 26% PEG1000 and 26% MgSO4 was found to be the most suitable for inulinase purification. This ATPS has 28.47% TLL, 1.03 of volume ratio, purification factor of 4.65 fold and recovery yield of 66.17%. On the SDS‐PAGE electrophoresis two protein bands with molecular weight of around 24 and 56 kDa were observed. The partially purified enzymes had optimal activity at pH 8.0 and 6.5, optimal temperature at 30 and 70°C and kinetic parameters Km = 26.32 mmol and Vmax = 526 mmol/min.
PhD: Non-thermal preservation of fruits and vegetables
The non-thermal preservation methods could be easily combined with the traditional preservation m... more The non-thermal preservation methods could be easily combined with the traditional preservation methods to produce high quality food products. The new mild processing techniques used in this study include: osmotic dehydration, vacuum impregnation, pulse electric field and edible coatings. Five raw materials with different tissue structure such as potato, carrot, Jerusalem artichoke, apple and strawberry were used for the osmotic treatment. The changes in tissue’s density and porosity under different temperatures and concentrations of the osmotic solutions were evaluated. The effect of different parameters on the osmotic dehydration of the different plant tissues in terms of water loss and solid gain, were investigated. The water removal rate was in the range from 0.076 to 0.624 g water /g ѕм ·h, while the solute uptake’s rate was from 0.040 to 1.043 g/g ѕм ·h. The water diffusion coefficient was in the range of 0.8 to 16·10 -11 m 2 /s. Osmotic treatment deactivates the enzymes and it preserves well the aroma and the color, the mechanical and nutritive properties of the fruits and vegetables. The dried apples with well preserved optical and nutritive properties, having the common characteristics of crispy products were transformed in a new product, apple chips. The effect of cryoprotectants on the freezing tolerance of strawberry tissues were evaluated by means of vacuum infusion and pulse electric field. The cryoprotectants used in this study were trehalose and antifreeze protein. They were vacuum infused in the strawberries’ apoplast. The pulse electric field enabled direct impregnation of the plant cells with cryoprotective solutes. The tissue absorbed 9% and 14% of antifreeze protein and trehalose. When the combination of the both solutions was used the tissue absorbed 19%. The combined effect of both cryoprotectants significantly improved the freezing tolerance of the treated strawberries and maintained 90% viability of the plant cells after thawing. The minimal processing of fruits was carried out with edible films. Edible coatings act as moisture and gas barriers and improve the quality and shelf-life of minimally processed fruits and vegetables. For that purpose 10 chitosan-based edible films were prepared. Chitosan films were modified by crosslinking, application of a beeswax coating on both interfaces of the film and preparation of composite films. All edible films were characterized in terms of their optical, mechanical, barrier, sorption and thermal properties. The incorporation of the beeswax into the edible films decreased the water vapour permeability value from 4,15·10 -11 to 1.5·10 -11 mol·m/m 2 ·s·Pa. The edible coatings as a preservation method were tested on strawberries. The coatings modified the respiration rates of the strawberries and slowed down their metabolism extending their shelf-life at 20 oC. The three-layer coatings enabled the best protection of the overall quality of the strawberries, but the chitosan and composite coatings were more preferable for the consumers. The emerging technologies in combination with the already existing methods besides providing microbial stability, fresh look and extended shelf life also gave better preservation of the sensorial and nutritional properties of the fruits and the vegetables.
Cryoprotection of horticultural products has been a matter of concern for the food industry in it... more Cryoprotection of horticultural products has been a matter of concern for the food industry in its search for efficient ways of improving the quality of frozen-thawed products. Research on the cryoprotection of plant tissues should make progress through a better understanding of the natural protective mechanisms of plant tissues during winter survival. The present study reports results on the use of vacuum impregnation (VI) alone or in combination with pulsed electric field (PEF) to obtain cryoprotectant solutions in the tissues. Spinach samples were treated with a combination of PEF and VI prior to freezing in liquid nitrogen and thawing at room temperature. VI was used to impregnate trehalose (40% w/w solution) as cryoprotectant and PEF was used to distribute the cryoprotectant in the extra and intracellular spaces of the tissue. Strawberries were treated with VI prior to freezing in liquid nitrogen ant thawing at room temperature. VI was used to impregnate a combination of trehal...
Foods
The increasing demand for greater utilization of byproducts in the food industry has been driven ... more The increasing demand for greater utilization of byproducts in the food industry has been driven by growing interest in environmental sustainability. This paper examines the market potential and consumer attitudes toward whole-grain and sustainable cookies made with food byproducts and edible films. Additionally, particular attention was given to evaluating levels of sustainability knowledge and nutritional awareness, willingness to purchase environmentally friendly cookies with food byproducts, and to appraise differences in answers between countries and generations. An online questionnaire was used to collect data from Croatian (n = 472), French (n = 166), and North Macedonian consumers (n = 119) aged between 18 and 62, predominantly women (82%) with higher education degrees. Results showed that even if chocolate-coated cookies remain very popular, North Macedonians prefer whole-grain and plain cookies, while the French prefer chocolate-coated cookies and Croats prefer both types ...
Effect of sucrose and salt solution on mass exchange during osmotic pretreatment of carrot and potato
Preservation of Diospyros kaki with edible films
The persimmon, Diospyros kaki, which is also known as kaki, is a very popular fruit. Its widespre... more The persimmon, Diospyros kaki, which is also known as kaki, is a very popular fruit. Its widespread in Europe is now also increasing due to the growing consumption rate. The persimmon is nutritionally important crop since it has increased sugar content and at the same time is good source of biologically active compounds such as ascorbic acid and condensed tannins. Therefore exploring the ways of its preservation is highly important. Persimmon fruits of Macedonian variety were selected according to their ripeness. The fruits before each experiment were washed, peeled and cut in form of discs with a diameter of 18 mm and 2-3 mm thickness. The discs were treated either directly with different edible films or first osmotically dehydrated and then coated, before being air-dried and packed. Textural properties for fresh and coated fruits were measured on texture analyzer using compression/penetration tests. The color parameters of persimmon such as L*, a* and b* values were accessed by co...
Development of a Quince Snack Enriched with Inulin and Stevia
In recent years there is an increased demand for food enriched with physiologically active compon... more In recent years there is an increased demand for food enriched with physiologically active components. Quinces were selected as a raw material in this study. They belong to the same family of fruits such as pears and apples. The quinces that have been examined had around 20% dry mass, 1.7 % fibers, more than 6 mg vitamin C per 100 g fruit, pectin, antioxidants, and other components. Because of the astringent, tart flavour, quinces are commonly processed into marmalades and jellies, with addition of sucrose to improve their taste. Therefore the purpose of this investigation was to develop a new quince snack product which besides functional properties, will also have improved taste due to the infusion of the alternative sweetener, stevia. This study was carried out to evaluate selected quality attributes of a quince snack enriched with prebiotic (inulin) and alternative sweetener (stevia) accompanied with an antibrowning agent by the use of vacuum impregnation. The porosity of the qui...
Biosynthesis of Ethanol with New Immobilized Systems
With an increasing need for renewable fuels, growing attention has been devoted to ethanol, consi... more With an increasing need for renewable fuels, growing attention has been devoted to ethanol, considered as a cleanest liquid fuel alternative to fossil fuels. Ethanol is a renewable, environmentally friendly fuel that is inherently cleaner than gasoline. Recently, significant advances have been made towards the technology of ethanol production. The prospect included is microbiological fermentation with immobilized microorganisms. New biodegradable hydrogels prepared by UV crosslinking were used for immobilization of Saccharomyces cerevisiae cells. These biodegradable hydrogels based on environmentally friendly polymer scaffolds were designed to meet the criteria specified for an immobilized system. Entrapment of yeast cells in a three-dimensional polymer matrix was achieved, and various properties of the polymer matrix as well as the activity of the yeast cells were studied. Ethanol biosynthesis was achieved with PEO and HEC biodegradable hydrogels entrapping S. cerevisiae cell. Thes...
Foods
The aim of this study was to evaluate the effect of different solutions for vacuum impregnation (... more The aim of this study was to evaluate the effect of different solutions for vacuum impregnation (VI) of fresh-cut (FC) apples through an innovative multi-analytical approach. In particular, the individual and synergistic effects of ascorbic acid and calcium lactate on the preservation of freshness of FC apples was assessed through color, texture, microscopy, isothermal calorimetry, and time-domain nuclear magnetic resonance (TD-NMR) evaluations. The analysis was performed immediately after VI and after 24 h of refrigerated storage. The obtained results showed a good preservation of color and higher firmness in the impregnated samples. Concerning the metabolic heat production, a decrease following the VI treatment was observed, especially when the combined solution was used for the impregnation. The TD-NMR studies showed higher changes in terms of signal intensity and transversal relaxation time T2 after 24 h of storage, evidencing the meta-stability of the plant material for its dyn...
Ensuring Sustainability of Baking Industry in North Macedonia
Baking Business Sustainability Through Life Cycle Management
Macedonian Journal of Chemistry and Chemical Engineering
Diffusion models were tested to select the most appropriate model for measuring the diffusion of ... more Diffusion models were tested to select the most appropriate model for measuring the diffusion of glucose and ethanol trough hydroxyethylcellulose (HEC) cryogels. The lag-time model was selected as accurate, rapid and reliable for evaluating the diffusivity of the solutes. The diffusion coefficient of glucose through the HEC cryogel loaded with cells was estimated to be 6.9×10-6 cm2/s, while the diffusion coefficient of ethanol had a value of 2.5×10-5 cm2/s. The cells inside the gel matrix were not a barrier for the transport of the solute molecules. The diffusion properties of the cryogel were also examined in a real system. The parameters characterizing the repeated batch fermentation of glucose to ethanol by entrapped Saccharomyces cerevisiae cells gave evidence of very good diffusion properties of the HEC gel.
Occurrence of meso/micro/nano plastics and plastic additives in food from food packaging
Advances in Food and Nutrition Research
Article Characterization of multilayered and composite edible films from chitosan and beeswax
Chitosan-based edible films were prepared and subjected to cross-linking reactions using sodium t... more Chitosan-based edible films were prepared and subjected to cross-linking reactions using sodium tripolypho-sphate 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 f...
Journal of Food Engineering, 2018
In this study, pulsed electric field (PEF) was coupled with vacuum infusion (VI) to impregnate st... more In this study, pulsed electric field (PEF) was coupled with vacuum infusion (VI) to impregnate strawberries with cryoprotectants. Electroporation of fruits was reached with 5 bi-polar, rectangular pulses of 100 s width with a nominal electric field strength of 850 V/cm. After PEF treatment, the strawberries were vacuum infused with a cryoprotective solution (12 g/100 g trehalose and 0.2 g/100 g acclimated winter wheat extract containing antifreeze proteins) for 14 min. The strawberries were frozen in liquid nitrogen and thawed in air at 20 o C. Cell survival, texture and color were evaluated before and after freezing and thawing cycle. The fruit pre-treated with PEF prior to VI exhibited higher cell viability in epidermal layer and 30% more red color retention compared to just VI samples. However, no further improvement on strawberry quality in terms of drip loss and texture was observed upon the application of PEF.
Macedonian Journal of Chemistry and Chemical Engineering, 2015
The traditional white brined cow cheese was tested as a delivery vehicle for probiotic bacteria. ... more 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 acceptan...
Journal of Food Science and Technology, 2015
A probiotic strain Lactobacillus plantarum PCS26 was used to ferment Jerusalem artichoke juice. G... more A probiotic strain Lactobacillus plantarum PCS26 was used to ferment Jerusalem artichoke juice. Growth kinetics of the bacterial strain was followed during juice fermentation both in flask and in laboratory fermentor. Jerusalem artichoke showed to be an excellent source of nutrients for L. plantarum PCS26 growth. The culture grew very well reaching more than 10 10 cfu/ml in just 12 h. The pH changed from the initial 6.5 to 4.6 at the end of fermentation. The culture hydrolyzed fructooligosaccharides present in the Jerusalem artichoke juice, yielding fructose which was presumably consumed along with the malic acid as energy and carbon source. Lactic acid was the main metabolite produced in concentration of 4.6 g/L. Acetic and succinic acid were also identified. Sensory evaluation of the fermented Jerusalem artichoke juice and its mixtures with blueberry juice showed that the 50/50 % v/v mixture would be very well accepted by the consumers. Above 80 % of the panelists would buy this drink, and over 60 % were willing to pay more for it. Culture survivability in the fermented juices during storage at 4-7°C was assayed by the Weibullian model. The product shelf-life was extended from 19.70 ± 0.50 days of pure Jerusalem artichoke juice to 35.7 ± 6.4 days of the mixture containing 30 % blueberry juice.
Food properties of baked products containing xylitol and sorbitol
Consumers today are well acquainted with the principles of healthy life and proper diet and there... more Consumers today are well acquainted with the principles of healthy life and proper diet and therefore desire food with high quality, balanced nutrient composition, less fat and sucrose and less energy. By popular demand there is now a wide range of products prepared with low energy sweeteners. This study deals with the potential use of xylitol and sorbitol, as low energy sweeteners, in baked products. Cookies containing sucrose, xylitol, combination of sucrose and xylitol and sorbitol were prepared using the sucrose cookies as a reference. The sensory properties were evaluated by discrimination, descriptive and affective test. The storage time of two weeks at room temperature did not show statistically significant influence on the flavor and texture properties of all cookies. Sensory studies were conducted with a consumer panel group of 70 untrained panelists to see whether people find the properties of baked products prepared with polyols acceptable for consumption. Microbiological...
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Papers by Elena Velickova