Kristina Kljak

Dr. Kristina Kljak

Faculty of Agriculture, University of Zagreb, Svetošimunska 25, 10000 Zagreb, Croatia
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Research Focus & Metrics

Academic Career Length

18Years (2009-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

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29 March 2021 in Foods
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Journal Article
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Kristina KljakKristina Kljak
Kristina Kljak
Klaudija Carović-StankoKlaudija Carović-Stanko
Klaudija Carović-Stanko
Ivica KosIvica Kos
Ivica Kos
ZJZlatko Janječić
Zlatko Janječić
Goran V. KišGoran V. Kiš
Goran V. Kiš
DBDalibor Bedeković
Dalibor Bedeković
The aim of this study was to evaluate the effect of a supplementation diet for hens consisting of dried basil herb and flowers of calendula and dandelion for color, carotenoid content, iron-induced oxidative stability, and sensory properties of egg yolk compared with commercial pigment (control) and marigold flower. The plant parts were supplemented in diets at two levels: 1% and 3%. In response to dietary content, yolks from all diets differed in carotenoid profile (p < 0.001). The 3% supplementation level resulted in a similar total carotenoid content as the control (21.25 vs. 21.79 μg/g), but by 3-fold lower compared to the 3% marigold (66.95 μg/g). The tested plants did not achieve yolk color fan values as the control (13.47) or 3% marigold (11.47), and among them, calendula had the highest values (9.73). Despite the low carotenoid content in diets supplemented with basil herb, iron-induced malondialdehyde (MDA) concentration was low as for marigold (on average 106.83 vs. 92.68 ng/g after 250 min). The treatments differed in sensory color scores for fresh and hard-boiled yolks and flavor while other sensory properties were similar. In conclusion, the supplementation of plants in a hen diet may result in yolks containing carotenoids and other compounds showing a high antioxidant effect.

21 April 2021 in Foods
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MDM. Graça Dias
M. Graça Dias
GBGrethe Iren A. Borge
Grethe Iren A. Borge
Kristina KljakKristina Kljak
Kristina Kljak
AMAnamarija Mandic
Anamarija Mandic
PMPaula Mapelli-Brahm
Paula Mapelli-Brahm
ANTONIO MELÉNDEZ-MARTÍNEZANTONIO MELÉNDEZ-MARTÍNEZ
ANTONIO MELÉNDEZ-MARTÍNEZ
Many studies indicate that diets including carotenoid-rich foods have positive effects on human health. Some of these compounds are precursors of the essential nutrient vitamin A. The present work is aimed at implementing a database of carotenoid contents of foods available in the European market. Factors affecting carotenoid content were also discussed. Analytical data available in peer-reviewed scientific literature from 1990 to 2018 and obtained by HPLC/UHPLC were considered. The database includes foods classified according to the FoodEx2 system and will benefit compilers, nutritionists and other professionals in areas related to food and human health. The results show the importance of food characterization to ensure its intercomparability, as large variations in carotenoid levels are observed between species and among varieties/cultivars/landraces. This highlights the significance of integrating nutritional criteria into agricultural choices and of promoting biodiversity. The uncertainty quantification associated with the measurements of the carotenoid content was very rarely evaluated in the literature consulted. According to the EuroFIR data quality evaluation system for food composition tables, the total data quality index mean was 24 in 35, reflecting efforts by researchers in the analytical methods, and less resources in the sampling plan documentation.

1 January 2015 in Food Chemistry
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Kristina KljakKristina Kljak
Kristina Kljak
DGDarko Grbeša
Darko Grbeša

7 November 2021 in Sustainability
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Kristina KljakKristina Kljak
Kristina Kljak
Marija DuvnjakMarija Duvnjak
Marija Duvnjak
DBDalibor Bedeković
Dalibor Bedeković
Goran V. KišGoran V. Kiš
Goran V. Kiš
ZJZlatko Janječić
Zlatko Janječić
Darko GrbešaDarko Grbeša
Darko Grbeša
Commercial high-yielding corn hybrids have not been evaluated for their ability to pigment egg yolk. Therefore, the objective of this research was to investigate the effects of commercial hybrids with different carotenoid profiles as the only source of pigments in the diets of hens on yolk color and carotenoid content, as well as the carotenoid deposition efficiency into the yolk. Treatment diets, differing only in one of five corn hybrids, were offered in a completely randomized design in six cages per treatment, each with three hens. Treatment diets and yolks differed in carotenoid profile (contents of lutein, zeaxanthin, β-cryptoxanthin and β-carotene, p < 0.001), with total carotenoid contents ranging from 17.13–13.45 µg/g in diet and 25.99–21.97 µg/g in yolk. The treatments differed (p < 0.001) in yolk color, which was determined by yolk color fan (10.8–9.83) and CIE Lab (redness; range 12.47–10.05). The highest yolk color intensity was achieved by a diet with the highest content of zeaxanthin, β-cryptoxanthin and β-carotene. The deposition efficiency of lutein and zeaxanthin (25.52 and 26.05%, respectively) was higher than that of β-cryptoxanthin and β-carotene (8.30 and 5.65%, respectively), and the deposition efficiency of all carotenoids decreased with increasing dietary content. Commercial corn hybrids provided adequate yolk color and could be the only source of carotenoids in the diets of hens, which could reduce the cost of egg production and increase farmers’ income.

24 June 2022 in Agriculture
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Igor BogunovicIgor Bogunovic
Igor Bogunovic
Kristina KljakKristina Kljak
Kristina Kljak
IDIvan Dugan
Ivan Dugan
Darko GrbešaDarko Grbeša
Darko Grbeša
LTLeon Josip Telak
Leon Josip Telak
Paulo PereiraPaulo Pereira
Paulo Pereira
Understanding the importance of grassland management is crucial for predicting the effects on forage production, pasture and ecosystem stability. Studies about the impact of grassland management in temperate humid environments on soil, erosion and aboveground biomass properties are lacking. This study investigates the effect of different grassland managements—no grazing, moderate grazing and heavy grazing—on soil properties, hydrological responses and herbage quality in an organic farm located in Croatia. The results showed that heavy grazing significantly increased soil compaction, structural deterioration, erosion and nutrient transport compared with no grazing. Heavily grazed plots had significantly higher soil organic matter and nutrient concentrations compared with no-grazing plots. Moderately grazed plots had the highest biomass production and the herbage with higher quality compared with other treatments. Significantly higher ash contents on heavily and moderately grazed plots were due to cow trampling. Cow grazing behaviour was a more important factor for plant regrowth and herbage quality than soil properties. Moderate grazing did not induce serious soil erosion problems or reduce soil productivity. Soil conservation measures should focus only on the heavily grazed areas and include the introduction of rotational grazing in combination with various strategies: excluding grazing, reseeding and increasing the diversity of resting areas.

24 June 2021 in Agriculture
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DZDora Zurak
Dora Zurak
Darko GrbešaDarko Grbeša
Darko Grbeša
Marija DuvnjakMarija Duvnjak
Marija Duvnjak
Goran V. KišGoran V. Kiš
Goran V. Kiš
TMTatjana Međimurec
Tatjana Međimurec
Kristina KljakKristina Kljak
Kristina Kljak
The objective of the present study was to determine the content and bioaccessibility of carotenoids in 104 maize hybrids available at the market. Lutein, zeaxanthin, α- and β-cryptoxanthin, and β-carotene were determined in whole grains and micelles produced during standardized INFOGEST digestibility analysis, and their bioaccessibility was calculated as the ratio of micellar and grain carotenoids. Tested hybrids varied in total carotenoid content, with 34% having total carotenoid content in the range of 15–20 µg/g dry matter (DM) and 41% in the range of 20–25 µg/g DM. The amount of bioaccessible carotenoids increased linearly (p < 0.05) with increasing content in the grain, and decreased among determined carotenoidsd in the order: lutein (52%) > zeaxanthin (43%) > β-carotene (43%) > α-cryptoxanthin (27%) > β-cryptoxanthin (26%). Bioaccessibility of lutein, zeaxanthin, and β-carotene decreased with increasing content in the grain (p < 0.05). On average, only 43% of the total carotenoids were bioaccessible in commercial maize hybrids tested, which should be considered when formulating an animal diet.