Vpliv dodatka kinurenske kisline na protimikrobno aktivnost medu

Prašnički, Zala (author), Čanžek Majhenič, Andreja (mentor)

Med je živilo z znanimi protimikrobnimi lastnostmi. V njegovi kemijski sestavi najdemo tudi kinurensko kislino (KK), presnovek triptofana, katere vrednosti se med vrstami medu močno razlikujejo. Največ te kisline je v kostanjevem, precej manj pa v akacijevem medu. Pripisujejo ji nekatere pozitivne lastnosti, med drugim tudi protimikrobno delovanje. Po zaužitju se absorbira v prebavnem traktu in izloči z urinom. Namen te magistrske naloge je bil proučiti protimikrobno aktivnost čiste KK proti 82 različnim sevom mikroorganizmov (MO) in ovrednotiti protimikrobno delovanje 11 različic medov, ki so se razlikovale v botaničnem izvoru (kostanj in akacija) in vsebnosti KK ter mešanice sladkorjev proti naboru 16 sevov. Analize so potekale med majem 2025 in aprilom 2026 v laboratoriju Inštituta za mlekarstvo in probiotike na Oddelku za zootehniko Biotehniške fakultete v Ljubljani. Vzorce medu je zagotovilo podjetje Medex d.o.o, 79 od 82 preizkušanih MO pa Nacionalni laboratorij za zdravje, okolje in hrano (NLZOH) Kranj ter Maribor. Poskusi so bili izvedeni po prilagojeni mikrodilucijski metodi. Minimalna inhibitorna koncentracija (MIK) je bila opredeljena kot najmanjša testirana koncentracija, pri kateri je stopnja rasti seva znašala ≤ 10 % pozitivne kontrole. Čista KK ni proti nobenemu testiranemu sevu v zadostni meri protimikrobno delovala, da bi ji lahko določili MIK. Tudi pri največji testirani koncentraciji (2 mg/ml) stopnja rasti sevov v večini primerov ni znašala manj kot 80 %. V drugem delu analiz smo ugotovili, da kostanjeve različice medov v primerjavi z akacijevimi izkažejo večjo mero protimikrobnega delovanja, pri čemer vsebnost KK nima vpliva. Pomembnejše so druge lastnosti medu, kot npr. velika koncentracija sladkorjev, vsebnost različnih kislin, majhna vodna aktivnost, vsebnost metilglioksala, oligopeptidov, fenolov in tvorba H2O2 v razredčenem medu, na katere pa vpliva botanični izvor medu in zunanji dejavniki (sezona, okolje, regija in način izdelave).

• Language: Slovenian
• Keywords: med, kinurenska kislina, protimikrobno delovanje, mikroorganizmi, urogenitalni trakt, minimalna inhibitorna koncentracija, MIK
• Work type: Master's thesis/paper
• Typology: 2.09 - Master's Thesis
• Organization: BF - Biotechnical Faculty
• Publisher: [Z. Prašnički]
• Year: 2026
• PID: 20.500.12556/RUL-186444
• UDC: 638.16:579.67
• COBISS.SI-ID: 289690627
• Publication date in RUL: 02.09.2026

Secondary language

• Language: English
• Title: The effect of adding kynurenic acid to honey on its antimicrobial activity

Abstract

Honey is a food with well-known antimicrobial properties. Its chemical composition also includes kynurenic acid (KA), a metabolite of tryptophan. The highest concentrations of this acid are found in chestnut honey, while considerably lower concentrations are present in acacia honey. Several beneficial properties have been attributed to KA, including antimicrobial activity. The aim of this master’s thesis was to investigate the antimicrobial activity of pure KA against 82 different strains of microorganisms (MO) and to evaluate the antimicrobial activity of 11 honey variants differing in botanical origin (chestnut and acacia) and KA content, as well as a sugar mixture, against 16 strains. The analyses were carried out between May 2025 and April 2026 in the laboratory of the Institute of Dairy Science and Probiotics at the Department of Animal Science, Biotechnical Faculty, Ljubljana. Honey samples were provided by Medex d.o.o., while 79 of the 82 tested microorganisms were provided by the National Laboratory of Health, Environment and Food (NLZOH) in Kranj and Maribor. The experiments were performed using a modified microdilution method. The minimum inhibitory concentration (MIC) was defined as the lowest tested concentration at which the growth rate of the strain was ≤ 10% of the positive control. Pure KA did not exhibit sufficient antimicrobial activity against any of the tested strains to allow determination of MIC values. Even at the highest tested concentration (2 mg/ml), the growth rate of the strains in most cases did not decrease below 80%. In the second part of the analyses, it was found that chestnut honey variants exhibited greater antimicrobial activity compared to acacia honey variants, whereas KA content had no effect. Other honey characteristics (high sugar concentration, presence of various acids, low water activity, oligopeptides, phenolic compounds and H₂O₂ formation in diluted honey), which are influenced by the botanical origin of the honey as well as by external factors, appear to be more important.

• Keywords: honey, kynurenic acid, antimicrobial activity, microorganisms, urogenital tract, minimum inhibitory concentration, MIC