ENZYME ACTIVITY OF FUNGI ASSOCIATED WITH STORED MAIZE GRAINS OBTAINED FROM SOME SELECTED FARMS NEAR BENIN CITY, NIGERIA

Global concern about food safety has led to increased interest in the study of food-spoilage fungi. Contaminated food affects human and animal health when such food items are consumed. This study was carried out to determine the fungi associated with stored corn in a bid to establishing their possible role in deterioration of corn. Using standard procedures, these fungi were isolated: Aspergillus, Trichoderma, Penicillium, and Rhizopus species. Results revealed the production of enzymes (protease, amylase, and lipase) by the fungi. The activity of these enzymes could play a role in the spoilage of corn by the fungi. In addition, the isolated fungi are known to be associated with postharvest yield losses in stored produce as well as producing toxins. Therefore, the data presented will help in choosing postharvest practices that will reduce contamination by these fungi. Protease activity values of the isolates ranged from 1.426±0.042 – 1.748±0.023µml-1 (in Aspergillus sp.), 1.599±0.018 – 1.990±0.019µml-1 (in Rhizopus sp.), 1.364±0.018 – 1.679±0.012µml-1 (in Trichoderma sp.) and (1.544±0.017 – 1.714±0.013 μml-1 (in Penicillium sp.). Amylase activity was highest in Rhizopus (1.625±0.054 – 1.790±0.013 μml-1), followed by Penicillium sp and lowest in Aspergillus sp. Lipase activity was highest in Penicillium and lowest in Aspergillus. The detection and identification of fungi are crucial to developing appropriate management strategies for stored corn. Postharvest losses due to these fungi will lead to reduced income for the farmers.

Intermediate thermoresistance in black yeast asexual cells variably increases with culture age, promoting survival and spoilage in thermally processed shelf-stable foods

Black yeasts are a functional group that has caused spoilage in cold-filled and hot-filled beverages as well as other water activity (a w )-controlled food products. We established quantitative thermoresistance parameters for the inactivation of 12 Aureobasidium and Exophiala isolates through isothermal experiments and a challenge study. Culture age (2-day vs. 28-day) variably affected the thermoresisitance among the black yeast strains. Variation in thermoresistance exists within each genus, but the two most resistant strains were the Exophiala isolates. The two most heat resistant isolates were E. phaeomuriformis FSL-E2-0572 with a D 60 -value of 7.69±0.63 min in 28-day culture and E. dermatitidis YB-734 with a D 60 -value of 16.32±2.13 min in 28-day culture. While these thermoresistance levels were, in some cases, greater than those for conidia and vegetative cells from other common food spoilage fungi, they were much more sensitive than the ascospores of heat resistant molds most associated with spoilage of hot-filled products. However, given that black yeasts have caused spoilage in hot-filled products, we hypothesized that this intermediate degree of thermoresistance may support survival following introduction during active cooling before package seals have formed. A challenge study was performed in an acidic (apple cider) and a w -controlled (maple syrup) product to evaluate survival. When apple cider was hot-filled at 82C, black yeast counts were reduced by 4.1-log CFU/ml 24 h after the heat treatment, but the survivors increased up to 6.7-log CFU/ml after two weeks. In comparison, the counts were below the detection limit after both 24 h and 14 days of shelf-life in both products when filled at their boiling points. This suggests that ensuring water microbial quality in cooling tunnels and nozzle sanitation may be essential in mitigating the introduction of these fungi.

Identifikasi komponen dan Uji Potensi Anti Jamur Minyak Atsiri Serai Dapur (Cympobogon citratus) Terhadap Jamur Penghasil Aflatoksin

Aspergillus flavus and A. parasiticus are food spoilage fungi and produce aflatoxin that causes serious food safety problems. The antifungal agent is needed to control these fungi. This study aimed to determine the component of lemongrass essential oil and to test the oil’s ability to inhibit the growth of A. flavus and A. parasiticus. Five variations in the concentration of lemongrass oil were tested separately on A. flavus and A. parasiticus and, fungal growth was observed for 7 days. The results of the identification of the essential oil components using GC-MS showed that lemongrass essential oil has the main components of citral (53.77%) and z-citral (34.05%). Lemongrass essential oil with various concentrations (0.01%; 0.02%; 0.04% and 0.08%) showed the ability to inhibit the growth of A. flavus and A. parasiticus and the concentration of 0.08% indicated that lemongrass oil could inhibit the growth of both fungi for 100% during 7 days of observation. Keywords: antifungal, aflatoxin, citral, essential oil, lemongrass oil ABSTRAK Aspergillus flavus dan A. parasiticus merupakan jamur yang banyak ditemukan mengkontaminasi pangan. Kedua jamur tersebut menghasilkan aflatoksin, yang berbahaya bagi kesehatan manusia, sehingga diperlukan anti-jamur untuk mengendalikan pertumbuhannya. Penelitian ini bertujuan untuk mengetahui komponen minyak atsri serai (Cymbopogon citratus) dan menguji kemampuan minyak tersebut sebagai penghambat pertumbuhan A. flavus dan A. parasiticus. Lima variasi konsentrasi minyak serai diujikan secara terpisah pada A. flavus dan A. parasiticus dan dilakukan pengamatan pertumbuhan jamur selama 7 hari. Hasil identifikasi komponen minyak atsiri menggunakan GC-MS menunjukkan bahwa minyak atsri serai memiliki komponen utama citral (53,77%) dan z-citral (34,05%). Minyak atsiri serai dengan berbagai konsentrasi (0,01%; 0,02%; 0,04% dan 0,08%) menunjukkan kemampuan menghambat pertumbuhan A. flavus dan A. parasiticus dan konsentrasi 0,08 % menunjukkan bahwa minyak serai mampu menghambat pertumbuhan kedua jamur sebesar 100 % selama 7 hari pengamatan Kata kunci: antijamur, aflatoksin, minyak atsiri, minyak serai, sitral

Effect of the Chemical Composition of Free-Terpene Hydrocarbons Essential Oils on Antifungal Activity

In this study, Carum carvi L. essential oil (CEO) and Origanum majorana L. essential oil (MEO) was steam-distillated under reduced pressure. We henceforth obtained three fractions for each essential oil: CF1, CF2, CF3, MF1, MF2, and MF3. Then, these fractions were characterized using the gas chromatography–mass spectrometry (GC-MS) technique. The results indicated that some fractions were rich in oxygenated compounds (i.e., CF2, CF3, MF2, and MF3) with concentrations ranging from 79.21% to 98.56%. Therefore, the influence of the chemical composition of the essential oils on their antifungal activity was studied. For this purpose, three food spoilage fungi were isolated, identified, and inoculated in vitro, in order to measure the antifungal activity of CEO, MEO, and their fractions. The results showed that stronger fungi growth inhibitions (FGI) (above 95%) were found in fractions with higher percentages of oxygenated compounds, especially with (−)-carvone and terpin-4-ol as the major components. Firstly, this work reveals that the free-terpenes hydrocarbons fractions obtained from MEO present higher antifungal activity than the raw essential oil against two families of fungi. Then, it suggests that the isolation of (−)-carvone (97.15 ± 5.97%) from CEO via vacuum distillation can be employed successfully to improve antifungal activity by killing fungi (FGI = 100%). This study highlights that separation under reduced pressure is a simple green method to obtain fractions or to isolate compounds with higher biological activity useful for pharmaceutical products or natural additives in formulations.