Krastena Nikolova

Krastena Nikolova
Medical University of Varna · Department of Medical Physics and Biophysics

Professor

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104
Publications
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253
Citations

Publications

Publications (104)
Article
Full-text available
The present work aims in exploring the possibilities of fluorescent spectroscopy for quality control of honey, particularly to distinguish types of honey and to distinguish the natural honey from that with artificial additives - sweeteners. 24 samples of the most often encountered sorts of honey in Bulgaria distributed in 7 groups have been studied...
Article
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Melon wine and white cherry wines purchased from the commercial market were studied. The aim of the present work is to evaluate the elemental composition, antioxidant activity and optical properties of these fruit wines. The analysis of certain elements in wines is of interest because the concentrations of some of them are regulated, others because...
Conference Paper
Full-text available
The object of this review article is to follow the current trends in the scientific literature on corrosion in biological fluids of chromium-nickel stainless steels after laser treatment. The paper is organized in three sections. The first section presents the main types of stainless steels according to their microstructure and the application of t...
Article
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The aim of the current study was to investigate some bioactive compounds from Sambucus nigra L. blossoms and to evaluate the antioxidant potential of the obtained extracts. In this study, samples from four different regions of Bulgaria /Rhodopes, Plovdiv, Strandzha and Dobrich region/ from Sambucus nigra L. were collected and analyzed for total phe...
Article
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In this time of COVID-19 pandemic, the strategies for prevention of the infection are a primary concern. Looking more globally on the subject and acknowledging the high degree of misuse of protective face masks from the population, we focused this review on alternative pharmaceutical developments eligible for self-defense against respiratory infect...
Article
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The present study aims to develop recipe compositions and technology for producing sponge cakes from wholemeal flour, partially replaced with a functional plant component dry blossom flour of Sambucus nigra L. Three designs of sponge cakes with 5, 10, and 15% content of flour of Sambucus nigra L. corrected up to 100% with whole-grain oat flour were...
Article
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The composition of grape seeds oil from a mixture of two varieties of red grape (Sangiovese and Pinot noir) from Varna region was investigated. Different analytical techniques have been used to determine the content of biologically active compounds, fatty acids, sterols and elemental compositions. It has been found that the oxidation stability of t...
Article
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Sempervivum tectorum L. is an evergreen plant belonging to a large family of the Crassulaceae. The fresh juice of the plant is used as a folk remedy almost exclusively for external purposes. The combination of several instrumental methods—transmission and fluorescence spectroscopy, ICP-MS spectrometry, and assays for the assessment of antioxidant a...
Article
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The black cumin (Nigella sativa) and coriander (Coriandrum sativum L) are well-known representatives from Ranunculaceae and Apiaceae families, respectively. The aim of the present study is to evaluate the physicochemical properties of oils derived from black cumin and coriander. Their visible and fluorescent spectra have been recorded. The fatty ac...
Article
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Sempervivum tectorum L. is an evergreen plant with fleshy blue-green leaves forming a rosette. The plant is well-known in alternative medicine and has been used for thousands of years. Traditionally for medicinal purposes, the plant is used as a juice obtained by simple squeezing of fresh plants leaves. The total content of Ca, K, Na, Mg, Mn, Fe, Z...
Article
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Sixty-nine samples of red wines, produced in different regions of Bulgaria, Chile and South Africa from the Merlot (42 samples) and Cabernet Sauvignon (27 samples) grape varieties are characterized by 13 physicochemical and optical properties. The physicochemical characteristics (antioxidant activity and anthocyanin content) have been obtained spec...
Article
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Fluorescence spectra and chemical composition of cold-pressed sunflower oleic oils with addition of oils from: 1) basil (Ocimum basilicum), 2) rosemary (Rosmarinus officinalis) and 3) oregano (Origanum vulgare) were studied. The aim of the study is to compare chemical composition of cold pressed oil with and without addition of different plant oils...
Conference Paper
35 red wines from different regions of Bulgaria from the varieties Merlot and Cabernet have been investigated by using an applied photonics method. The quality characteristics such as the antioxidant activity and the anthocyanins have been obtained spectrophotometrically. The integral fluorescence intensity for the 350-360 nm range has been calcula...
Article
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The physicochemical properties of oil extracted from the seeds of Sambucus ebulus, Coriandrum sativum L. and Silybum marianum L. (0.5:1:1) were examined. The fatty acid composition of the oil mixture was found to contain oleic (51.35%) and linoleic acids (35.01%) predominantly. The characteristic peak in infrared spectrum at about 1740 cm-1 was att...
Article
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It is a well-known fact that prior to bottling wine is under permanent changes as a "living organism". While kept in oak wood tuns its physical chemical properties change during the technological processes. In the present research we study two types of red wines from the Varna region, Cabernet Franc and Pinot Noir, year 2017. Samples were picked up...
Article
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In this study, the concentrations of 14 elements in two brands of Bulgarian (three products of each) and a Romanian beer were determined. As a low alcoholic beverage, beer is often consumed in large quantities, therefore the concentration of the elements is compared with the rules for their content in drinking water. The fluorescence spectra for in...
Article
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Main chemical components of chia seeds (imported from Peru) and physicochemical characteristics of their oil were examined. The oil content of the seeds was 30.37% and protein content was 37.96%. The oil was obtained by pressing the chia seeds in Bulgarian factory. The main important physicochemical characteristics of chia seed oil have also been d...
Conference Paper
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The aim of the present work was to measure the content of some biologically active substances, the antioxidant stability and to determine dependencies between them and intensity of fluorescence emission for two excitation wavelengths in UV region - 265 nm and 295 nm, respectively. The juices were prepared from frozen fruits of dogwood (Cornus mas)...
Article
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Thirty – five samples of red wines from different geographic regions have been characterised according to 14 basic optical and chemical characteristics - colour parameters, content of anthocyanins and antioxidant activity. The goals of this study is to compare the tested wines using different statistical methods. Conducting hierarchical cluster ana...
Conference Paper
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This investigation concerns juices obtained from raspberry (Rubus idaeus) by pressing and adding 1 g, 2 g, 3 g of inulin or lactulose with different concentrations-0.5, 1, 1.5 ml. Total content of polyphenols, anthocyanins, β-carotene, color parameters in SIE Lab colorimetric system and antioxidant activity of the samples are determined by using tw...
Conference Paper
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The functional properties of dark, milk and white chocolate with 5% cow butter or sesame oil were improved by addition of 2% or 3% conjugated linoleic acid (CLA). Microbiological, rheological, X-ray diffraction and sensory analysis were carried out. A sensory profile of chocolate with (CLA) was recorded. The acid number in percent of oleic acid was...
Article
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Introduction: The natural woody syrup is a typical product from the Canary Islands and America. It is often used for health food supplement for children, athletes and elderly because it has well-pronounced antioxidant properties. The interest in this syrup is increasing because it is often used in homeopathic medicine and consists of phenolic conte...
Article
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This research is focused on juices of wild berries and more specifically on lingonberry juice. The kinetics of color parameters of the samples with inulin or lactulose during the storage is investigated. The content of anthocyanins, phenolic content, antioxidant activity and fluorescence spectra has been measured. The dependences between chemical p...
Conference Paper
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68 different types of Bulgarian wines were studied in accordance with 9 optical parameters as follows: color parameters in XYZ and SIE Lab color systems, lightness, Hue angle, chroma, fluorescence intensity and emission wavelength. The main objective of this research is using hierarchical cluster analysis to evaluate the similarity and the distance...
Article
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Compositions and technological factors have been developed to obtain a tea drink from Vaccinium vitis-ideae L. according to the vegetative period (April and June). The influence of the technological factors (hydro module, temperature 100 ° C and heating time 5 and 10 min.) was studied by means of discriminative analysis in order to obtain extracts...
Article
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The content of 8 essential and toxic elements (Cr, Mn, Fe, Ni, Cu, As, Cd, Pb) in most famous Bulgarian fruits as strawberry, white cherry, peach, apricot, green apple, pear, blackberry, fig, prune, green and blue-black grapes, melon, watermelon, quince and pumpkin were investigated. The highest content of Fe was found in quince (35.7±0.2 mg kg-1),...
Article
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Fourteen samples from acacia (Robinia pseudoacacia), lime(Tilia sp.), sunflower (Helianthus annuus), thistle (Onopordum acanthium), forest and honeydew honeys have been characterized according to their parameters of mineral and sugar content, color characteristics and refractive index. The samples have been grouped in two clusters–monofloral lime h...
Article
Twenty-two samples from different beers have been investigated in two colour systems-XYZ and SIELab-and have been characterised according to their colour parameters. The goals of the current study were to conduct correlation and discriminant analysis and to find the inner relation between the studied indices. K-means cluster has been used to compar...
Article
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The potential of several physical methods for investigation of the botanical origin of honey has been discussed. Samples from the three most prevalent types of honey in Bulgaria (acacia, linden and honeydew) have been used. They have been examined by laser refractometry, UV, VIS and FTIR spectroscopy, electric conductivity measurement and different...
Article
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The physicochemical characteristics of chia oil from Argentina, which is one of the most efficient omega-3 (n-3) sources for enriching foods, have been studied. The results from analysis show that the chia oil has a relative density of 0.9288, refractive index 1.4810 and yellow color component that dominates over the red one. Its acidity index is 1...
Article
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A total 17 samples of white and red wines have been investigated and characterized with regard to the following optical properties – color coordinates, lightness, Hue angle, chroma and transmission coefficient in visible area. Based on the examined parameters the wines are evaluated in their complexity by hierarchical cluster analysis. The samples...
Article
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TONCHEVA, G., K. NIKOLOVA, D. BOYADZHIEV, I. ALEXIEVA, D. GEORGIEVA, G. ANTOVA, A. ALAD-JADJIYAN and D. BUHALOVA, 2016. Differentiation of Bulgarian wild fruits according to their mineral content. Bulg. J. Agric. Sci., 22: 857–861 The content of 12 essential and toxic elements (V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Mo, Pb) in Bulgarian forest frui...
Conference Paper
Full-text available
Dffirent types of wines according their optical characteristics-color parameters, lightness, brightness, angle of Hue and spectral coefficients of transmissions have been examined by using Single dispersion analysis (one-way ANOVA) and subsequent Duncan's test. For each investigated parameter the samples have been divided according their statistica...
Article
Eleven samples from olive oil have been investigated using four physical methods – refractive index measurement, fluorescence spectra, color parameters and differential scanning colorimetry. In pomace olive oil (POO) and extra virgin olive oil (EVOO) the oleic acid (65.24 %-78.40 %) predominates over palmitic (10.47 %-15.07 %) and linoleic (5.26 %-...
Conference Paper
Eleven samples from olive oil have been investigated using four physical methods – refractive index measurement, fluorescence spectra, color parameters and differential scanning colorimetry. In pomace olive oil (POO) and extra virgin olive oil (EVOO) the oleic acid (65.24 %-78.40 %) predominates over palmitic (10.47 %-15.07 %) and linoleic (5.26 %-...
Conference Paper
In the article it is investigated the potential of honey discrimination by using 3 optical methods - fluorescence spectroscopy, refractometry, color measuring. Samples from three types of honey (acacia, linden, and honeydew) are measured by a fluorescence spectrometer recording emission from 350 to 800?nm with excitation at 370, 395 and 405?nm. Col...
Article
Full-text available
Investigated were four different samples of diseased cows, by means of fluorescence spectroscopy. It was found that the most suitable pumping wavelength fluorescence method to test samples of cows is 245 nm. Selected as low pumping wavelength, because the bacteria that cause diseases and infections in cattle have lower emission wavelengths. Through...
Article
Full-text available
Eleven samples from olive oil have been investigated using four physical methods – refractive index measurement, fluorescence spectra, color parameters and differential scanning colorimetry. In pomace olive oil (POO) and extra virgin olive oil (EVOO) the oleic acid (65.24 %-78.40 %) predominates over palmitic (10.47 %-15.07 %) and linoleic (5.26 %-...
Conference Paper
Full-text available
Abstract:: The physicochemical parameters (refractive index, water content, β-carotene, color parameters and content of glucose, fructose, sucrose and oligosaccharides for 14 types of bee honey have been investigated. They are grouping according the following parameters: 1. Geographic region 1– valley-mountain 2. Geographic region 2 – North or Sou...
Conference Paper
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25 olive oils were studied– different in origin and ways of extraction, in accordance with 17 physico-chemical parameters as follows: color parameters – a and b, light, fluorescence peaks, pigments – chlorophyll and β-carotene, fatty-acid content. The goals of the current study were: Conducting correlation analysis to find the inner relation betwee...
Article
Full-text available
The aim of the article is to investigate the optical properties of Bulgarian honey in regard to the potential of honey discrimination on the base of its botanical origin. Samples from three types of honey (acacia, linden, and honeydew) are measured by a fluorescence spectrometer recording emission from 350 to 800 nm with excitation at 370, 395 and...
Article
Full-text available
The aim of the article is to investigate the potential of honey discrimination (on the base of its botanical origins) by Vis spectroscopy and chemometric analysis. Fifty-five samples from three types of honey (acacia, linden, and honeydew) are measured by a spectrophotometer " Helios Omega " with recorded wavelength range of 380~780 nm for calibrat...
Conference Paper
Full-text available
In this paper we discuss the numerical algorithm of Milev-Tagliani [25] used for pricing of discrete double barrier options. The problem can be reduced to accurate valuation of an n-dimensional path integral with probability density function of a multivariate normal distribution. The efficient solution of this problem with the Milev-Tagliani algori...
Article
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Vaccinium vitis-ideae L.) нараства. Abstract Cranberry (Vaccinium vitis-ideae L.) leaf extracts from the region of Velingrad were tested, collected in April and July. The influence of the duration of the extraction was also studied as well as the content of the hydraulic component and colour parameters. By increasing the time of extraction and modi...
Article
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Agilent Technologies 1220 infinity (САЩ). Установено е нарастване на съдържанието на кверцетин и нарингин в екстрактите от листа в сравнение с тези от плодове, събирани през един и същи месец. С увеличаване-то на вегетационния период съдържанието на нарингин и мирицитин нараства, докато съдържанието на другите флавоноли намалява. В екстрактите от л...
Article
Full-text available
A total of 16 variants, including different water extracts from fruits and leaves of lingonberry, have been investigated and characterized with regards to the trails color parameters, pigments, phenolic acids and flavonoids. The variants have been obtained at different technological parameters – hydromodule, temperature of extraction and different...
Article
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The quality of six bee honey varieties harvested from different locations in South Bulgaria was assessed by several physical and chemical parameters: refractive index, electric conductivity, viscosity, colour, pH, water content, sugar, β-carotene, some essential and toxic trace elements. Obtained results reveal that examined South Bulgarian bee hon...
Article
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We have studied oil extracts form oregano, thyme and pine cone in sunflower oil in 1:5 ratio (herb extract/sunflower oil). The fluorescence spectra have been obtained by using Light emitting diods (LEDs) working at wavelengths of 370 nm, 395 nm, 425 nm and 450 nm have been obtained. The oxidation processes have been studied using UV spectroscopy. T...
Article
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The optical characteristics (color parameters a and b, lightness L), content of chlorophyll and β carotene, fluorescence spectra – of the walnut oils, produced from the one-,two- and three-years old branches during three different vegetation periods – August, September and October were investigated. The fluorescence spectra are obtained for excitat...
Article
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This paper describes a study of the usefulness of some physical methods in the detection of adulteration of extra virgin olive oil with controlled concentration of relatively cheap sunflower oil. We have tested three physical methods measuring refractive indices (RI) and their dispersion curves, fluorescence spectra and color parameters that are re...
Article
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Sunflower oil produced by Pearl Ltd Veliko Tarnovo, with addition of Bulgarian herbs (oregano, thyme and pine cones) has been studied. The starting sunflower oil is a linoleic type containing predominantly linoleic acid (C18: 2 = 521 g.kg-1), followed by oleic (C18: 1 = 344 g.kg-1) and palmitic (C16: 0 = 115 g.kg-1) acid. Upon the examination of fa...
Article
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Tocopherol, carotenoid and chlorophyll content of three pumpkin species (Cucurbita moschata, Cucurbita pepo, Cucurbita maxima) and three melon species (Honeydew, Dessert 5 and Hybrid 1) grown in southern part in Bulgaria were investigated. Highest content of tocopherols was found to be in Cucurbita moschata and in Honeydew glyceride oils-417 mg kg-...
Article
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In this article the possibility to detect adulteration of costly olive oils with cheaper vegetable oils using fluorescence spectroscopy is studied. Total luminescence spectra were recorded by measuring the emission spectra in the range 350 nm to 720 nm for excitation wavelengths from 375 nm to 450 nm. Fluorescence spectra of 12 types of olive oil s...
Article
Full-text available
The objective of this study was to investigate the level of 17 trace ele- ments in wild-harvested fruits (Crataegus monogyna, Cornus mas, Vaccinium vitis-idaea and Vaccinium myrtillus) grown in Plovdiv region in order to define their significance for healthy nutrition. The essential (Mg, Mn, Fe, Zn, Cu, Co and Se), toxic elements (Pb, Cd, Hg, As an...
Article
The objective of this study was to investigate the level of 17 trace elements in wild-harvested fruits (Crataegus monogyna, Cornus mas, Vaccinium vitis-idaea and Vaccinium myrtillus) grown in Plovdiv region in order to define their significance for healthy nutrition. The essential (Mg, Mn, Fe, Zn, Cu, Co and Se), toxic elements (Pb, Cd, Hg, As and...