Faculty of Food Technology and Biotechnology, University of Zagreb
Abstract
Fruit juices and soft drinks are targets for spoilage yeasts, moulds and bacteria. The aim of this study is to examine the antifungal effect of ethanolic extract of Turkish propolis (EETP) treatments in four nonpasteurized fruit juices including apple, orange, white grape and mandarin against 6 different yeasts isolated from the corresponding spoiled juices. These isolated yeasts include: Candida famata, C. glabrata, C. kefyr, C. pelliculosa, C. parapsilosis and Pichia ohmeri. Minimum Inhibitory Concentration (MIC) ranges were determined responding to the National Committee for Clinical Laboratory Standards (NCCLS) M27-A that were slightly modified with broth microdilution method. In this study, the presence of propolis in apple (pH=3.9), orange (pH=3.7), white grape (pH=3.8) and mandarin (pH=3.4) juices ranging from 0.01 to 0.375 mg/mL inhibited the growth of all spoilage yeasts at 25 °C. MIC ranges of propolis were 0.02–0.375, 0.04–0.375, 0.01–0.185, 0.02–0.185 and 0.04–0.375 mg/mL in mandarin, apple, orange, white grape juices and RPMI medium, respectively. MIC ranges of Na benzoate, which was used as positive control, were 80–320, 80–320, 40–640, 40–80 and 320–1280 μg/mL in mandarin, apple, orange, white grape and RPMI medium as blank control, respectively. In terms of MIC ranges, propolis showed greater antifungal activity than Na benzoate. As a result, propolis had significant antimicrobial activity against the yeast isolates from spoiled fruit juices. It was concluded that propolis is worthy to study further as a natural preservative for foods prone to fungal spoilage.Voćni sokovi i negazirana pića podložni su kvarenju u prisutnosti kvasaca, plijesni i bakterija. Svrha je ovog istraživanja ispitati antifungalni učinak etanolnog ekstrakta turskog propolisa (ETTP) u nepasteriziranom soku jabuke, naranče, bijeloga grožđa i mandarine na 6 različitih sojeva kvasca izoliranih iz pokvarenih sokova. Izolirani su sojevi kvasca Candida famata, C. glabrata, C. kefyr, C. pelliculosa, C. parapsilosis i Pichia omeri. Minimalna inhibicijska koncentracija (MIC) određena je prema standardima nacionalnog odbora za kliničke laboratorije (NCCLS) M27-A, neznatno modificiranih metodom mikrodilucije bujona. Prisutnost propolisa u soku jabuke (pH=3,9), naranče (pH=3,7), bijeloga grožđa (pH=3,8) i mandarine (pH=3,4) u rasponu od 0,01 do 0,375 mg/mL inhibirala je rast svih sojeva kvasca na temperaturi od 25 °C. MIC propolisa u soku mandarine iznosila je 0,02-0,375, u soku jabuke 0,04-0,375, u soku naranče 0,01-0,185, u soku bijeloga grožđa 0,02-0,185 te u RPMI mediju 0,04-0,375 mg/mL. MIC natrijeva benzoata, primijenjenog kao pozitivna kontrola, iznosila je 80-320 u soku mandarine, 80-320 u soku jabuke, 40-640 u soku naranče, 40-80 u soku bijeloga grožđa i 320-1280 μg/mL u RPMI mediju korištenom za slijepu probu. Propolis je imao značajnu antimikrobnu aktivnost na sojeve kvasca izoliranih iz pokvarenih voćnih sokova. Predloženo je daljnje istraživanje propolisa kao prirodnog konzervansa hrane podložne kvarenju u prisutnosti kvasaca
