Johannes Novak

Dr. Johannes Novak

orcid

Research Focus & Metrics

Academic Career Length

24Years (2003-Present)

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

Representative Publications

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24 December 2021 in Frontiers in Plant Science
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Journal Article
Open access
CRCarolina Escobar Rodríguez
Carolina Escobar Rodríguez
JNJohannes Novak
Johannes Novak
FBFranziska Buchholz
Franziska Buchholz
PUPia Uetz
Pia Uetz
LBLaura Bragagna
Laura Bragagna
BMBirgit Mitter
Birgit Mitter
The modes of interactions between plants and plant-associated microbiota are manifold, and secondary metabolites often play a central role in plant-microbe interactions. Abiotic and biotic (including both plant pathogens and endophytes) stress can affect the composition and concentration of secondary plant metabolites, and thus have an influence on chemical compounds that make up for the taste and aroma of fruit. While the role of microbiota in growth and health of plants is widely acknowledged, relatively little is known about the possible effect of microorganisms on the quality of fruit of plants they are colonizing. In this work, tomato (Solanum lycopersicum L.) plants of five different cultivars were grown in soil and in hydroponics to investigate the impact of the cultivation method on the flavor of fruit, and to assess whether variations in their chemical composition are attributable to shifts in bacterial microbiota. Ripe fruit were harvested and used for bacterial community analysis and for the analysis of tomato volatiles, sugars and acids, all contributing to flavor. Fruit grown in soil showed significantly higher sugar content, whereas tomatoes from plants under hydroponic conditions had significantly higher levels of organic acids. In contrast, aroma profiles of fruit were shaped by the tomato cultivars, rather than the cultivation method. In terms of bacterial communities, the cultivation method significantly defined the community composition in all cultivars, with the bacterial communities in hydroponic tomatoes being more variable that those in tomatoes grown in soil. Bacterial indicator species in soil-grown tomatoes correlated with higher concentrations of volatiles described to be perceived as “green” or “pungent.” A soil-grown specific reproducibly occurring ASV (amplicon sequence variants) classified as Bacillus detected solely in “Solarino” tomatoes, which were the sweetest among all cultivars, correlated with the amount of aroma-relevant volatiles as well as of fructose and glucose in the fruit. In contrast, indicator bacterial species in hydroponic-derived tomatoes correlated with aroma compounds with “sweet” and “floral” notes and showed negative correlations with glucose concentrations in fruit. Overall, our results point toward a microbiota-related accumulation of flavor and aroma compounds in tomato fruit, which is strongly dependent on the cultivation substrate and approach.

24 March 2021 in Plants
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BLBrigitte Lukas
Brigitte Lukas
LBLaura Bragagna
Laura Bragagna
KSKatharina Starzyk
Katharina Starzyk
KLKlaudia Labedz
Klaudia Labedz
KSKlaus Stolze
Klaus Stolze
JNJohannes Novak
Johannes Novak
This investigation focused on the qualitative and quantitative composition of polyphenolic compounds of Mediterranean northern shore Cistus creticus and six further, partly sympatric Cistus species (C. albidus, C. crispus, C. ladanifer, C. monspeliensis, C. parviflorus, C. salviifolius). Aqueous extracts of 1153 individual plants from 13 countries were analyzed via high performance liquid chromatography (HPLC). The extracts of C. creticus were primarily composed of two ellagitannins (punicalagin and punicalagin gallate) and nine flavonol glycosides (myricetin and quercetin glycosides, with m-3-O-rhamnoside as the dominant main compound). Differences in the proportions of punicalagin derivatives and flavonol glycosides allowed the classification into two chemovariants. Plants containing punicalagin derivatives and flavonol glycosides were especially abundant in the western and central Mediterranean areas and in Cyprus. From Albania eastwards, punicalagin and punicalagin gallate were of much lesser importance and the predominant chemovariant there was a nearly pure flavonol type. With its two chemovariants, C. creticus takes a central position between the flavonol-rich, purple-flowered clade (besides C. creticus, here represented by C. albidus and C. crispus) and the more ellagitannin-rich, white- or whitish-pink-flowered clade (here represented by C. ladanifer, C. monspeliensis, C. parviflorus and C. salviifolius). The median antioxidative capacity of C. creticus plant material was, with 166 mg Trolox equivalents/g dry wt, about half of the antioxidative capacity of C. ladanifer (301 mg te/g dry wt), the species with the highest antioxidative potential.

12 September 2018 in Porcine Health Management
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IHIsabel Henning-Pauka
Isabel Henning-Pauka
FKFranz-Josef Koch
Franz-Josef Koch
SSSimone Schaumberger
Simone Schaumberger
BWBettina Woechtl
Bettina Woechtl
JNJohannes Novak
Johannes Novak
VNVeronika Nagl
Veronika Nagl
The mycotoxin zearalenone (ZEN) causes functional and morphological alterations in reproductive organs of pigs. In the field, diagnosis of ZEN-induced disorders is often challenging, as relevant feed lots are no longer available, or feed analysis results are not conclusive. Here, we report a field case of hyperestrogenism in newborn piglets. Surprisingly, more than 50 fungal metabolites were detected in hay pellets fed to gestating sows, including ZEN and its modified form zearalenone-14-sulfate (ZEN-14-S). Despite the broad contamination range in this unconventional feed component, a definite diagnosis of mycotoxicosis could not be achieved. In this context, current limitations regarding the confirmation of suspected cases of ZEN-induced disorders are discussed, covering both feed analysis and the biomarker approach. A piglet producer with 200 sows experienced a sudden increase in suckling piglet losses up to 30% by lower vitality and crushing. Predominant clinical signs were splay legs and signs of hyperestrogenism such as swollen and reddened vulvae in newborn piglets. The first differential diagnosis was ZEN mycotoxicosis although feed batches had not been changed for months with the exception of ground hay pellets, which had been included in the diet five months before. Analysis of hay pellets resulted in a sum value of ZEN and its modified forms of more than 1000 μg/kg, with ZEN-14-S alone accounting for 530 μg/kg. Considering the inclusion rate of 7% in the diet for gestating sows, the severe impact of the additional ZEN load due to the contaminated hay pellets seemed unrealistic but could not be completely excluded either. One month after hay pellets had been removed from the diet no further clinical signs were observed. Enrichment materials and other fibre sources can contain significant amounts of mycotoxins and should be therefore included in feed analysis. Adequate methods for broad spectrum mycotoxin determination, including modified mycotoxins, are important. As highlighted by this field case, there is a need to establish reliable biomarkers for ZEN exposure in pigs. Currently, available biomarkers do not allow a solid prediction of the ZEN intake of pigs under field conditions, which limits their application to experimental studies.

1 September 2021 in Food Control
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Journal Article
Open access
FKFilip Knezevic
Filip Knezevic
ANAndreas Nikolai
Andreas Nikolai
RMRudolf Marchart
Rudolf Marchart
SSSilvio Sosa
Silvio Sosa
ATAurelia Tubaro
Aurelia Tubaro
JNJohannes Novak
Johannes Novak

30 December 2015 in SpringerPlus
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AHAvni Hajdari
Avni Hajdari
BMBehxhet Mustafa
Behxhet Mustafa
GAGresa Ahmeti
Gresa Ahmeti
BPBledar Pulaj
Bledar Pulaj
BLBrigitte Lukas
Brigitte Lukas
JNJohannes Novak
Johannes Novak
Pinus mugo Turra, is a native pine species in central and southern Europe, growing in high mountains area (altitudes 1.800–2.300 m.a.s.l.). In Kosovo, it is one of the native pines too, distributed in high altitudes in the Sharri Mountains and Albanian Alps Mountains. Its populations represent an important wealth of essential oil resources available, which make this species very important in terms of economic values. The chemical composition and yields of the essential oils of dwarf pine (Pinus mugo Turra) needles, twigs and cones from six wild populations in Kosovo were investigated with the aim to assess their natural variability. The identity of P. mugo was confirmed by morphology and DNA barcoding. Sixty-two compounds were identified representing 69–95 % of the total identified compounds. The yield ranged from 0.3–0.8 % v/w in needles, 1.0–2.4 % v/w in twigs and 0.1–0.5 % v/w in cones, depending on the origin of plant material and plant organs. α-Pinene (needles: 16.9–24.5 %; twigs: 4.5–8.8 %; cones: 3.1–5.6 %), β-pinene (needles: 1.5–5.4 %; twigs: 2.2–15.4 %; cones: 1.3–14.2 %), δ-3-carene (needles: 15.4–27.8 %; twigs: 24.0–51.6 %; cones: 10.5–31.5 %), limonene + β-phellandrene (needles: 1.9–5.9 %; twigs: 12.6–24.2 %; cones: 2.1–9.3 %), (E)-caryophyllene (needles: 4.4–8.9 %; twigs: 4.0–10.8 %; cones: 10.3–26.9 %) and germacrene D (needles: 4.0–8.3 %; twigs: 0.2–6.19 %; cones: 0.1–12.4 %) were the major components of the essential oil. Principal component analysis (PCA) and hierarchical cluster analyses (HCA) suggests that the population of P. mugo clustering is not related to their geographic location, but rather seemed to be linked to local selective forces acting on chemotype diversity. Low variability related to their geographic location has an economic importance since samples originating from different locations in Kosovo can treated with same standards.

19 March 2013 in Botanical Journal of the Linnean Society
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BLBrigitte Lukas
Brigitte Lukas
RSRosabelle Samuel
Rosabelle Samuel
EMEduard Mader
Eduard Mader
KBKemal Husnu Can Baser
Kemal Husnu Can Baser
HDHayri Duman
Hayri Duman
JNJohannes Novak
Johannes Novak
Origanum (Lamiaceae) comprises a number of essential oil-rich species that have been used by humans for centuries. Today, the four species of section