ABSTRACT
The growth of Aspergillus niger and Zygosaccharomyces rouxii on high moisture prunes and raisins in the presence of preservatives and packed under modified atmospheres was determined. Prunes and raisins adjusted to an aw of 0.84-0.87 in the presence of carbon dioxide atmospheres (40 and 80% CO2) did not support growth of A. niger. However, Z. rouxii spoiled the fruit samples, both in air and under CO2 conditions. Addition of low levels of K-sorbate (186 ppm in prunes and 153 ppm in raisins) or Na-benzoate (176ppm in prunes and 158ppm in raisins) delayed outgrowth of Z. rouxii. The inhibitory effect of preservatives was higher in raisins than in prunes. Modified atmospheres (40% CO2-60% N2 or 80% CO2-20% N2) combined with the addition of 417 and 343 ppm K-sorbate or 383 and 321 ppm Na-benzoate accomplished complete growth inhibition of Z. rouxii and extended the shelf-life of high moisture prunes and raisins at 30 degrees C for at least 6 months.
Subject(s)
Aspergillus niger/growth & development , Food Packaging , Food Preservation , Food Preservatives , Fruit/microbiology , Saccharomycetales/growth & development , Air , Benzoates/administration & dosage , Carbon Dioxide/administration & dosage , Food Preservatives/administration & dosage , Sorbic Acid/administration & dosageABSTRACT
The combined effect of medium water activity (aw) modified atmosphere packaging (MAP) on the conidial germination of Aspergillus niger, Eurotium amstelodami, Penicillium chrysogenum and Fusarium oxysporum was studied by applying response surface methodology (RSM) for 45 days incubation at 20, 30 and 40 degrees C. Oxytetracycline glucose yeast extract (OGYE) agar media were prepared over a wide range of aw (0.80-0.95), controlled by glucose. The headspace atmosphere composition varied from 0-20% for O2 and from 0-80% for CO2 with N2 as balance in the ratio medium/gas mixture of 1/3 (v/v). The results of this experiment were confirmed by repeating some combinations (aw-MAP) in the zone where the inhibition was effective. In contrast to A. niger which germinated and grew better at 30 and 40 degrees C, P. chrysogenum and F. oxysporum were capable of germinating and growing at 20 degrees C but not at 40 degrees C. E. amstelodami was less influenced by the incubation temperature than were the other species. Under anaerobic atmospheres, germination and growth of all tested species were completely inhibited at low aw, while at high aw because of residual O2, conidia germinated but failed to grow. At any aw value between 0.88 and 0.92, conidia failed to germinate when 100% CO2 was applied. Similar results were obtained for E. amstelodami and F. oxysporum in 80% CO2-20% N2 and 60% CO2-40%N2. Under aerobic conditions, at 5% O2 germination and growth occurred only at high aw, while 10 or 20% O2 combined with either 80 or 60% CO2 conidial germination and mould growth were only delayed comparing to the control (air).
Subject(s)
Food Microbiology , Fruit/microbiology , Spores, Fungal/physiology , Culture Media , Fungi/growth & development , Temperature , WaterABSTRACT
The influence of water activity (alpha w), preservatives, modified atmosphere and their combinations on the growth of Z. rouxii was determined by cultivating two strains isolated from raisins and prunes in culture media under different conditions and by counting the colony forming units. Yeast extract glucose broths or agars were adjusted to the desired alpha w by means of glucose. Preservatives added to the media (0-600 ppm) were either K-sorbate, Na-benzoate or their mixture. Modified atmospheres were carried out by packing culture plates or flasks in plastic bags under different CO2-N2 gas mixture. Response surface design was carried out to optimize the growth inhibition of Z. rouxii by the mentioned factors. Although Z. rouxii is osmotolerant, the strains studied could not grow at alpha w 0.79. They also showed a high tolerance to CO2; even 80% CO2 seems to not inhibit growth. However, CO2 atmosphere at high pHs and low preservative concentrations stimulated yeast growth. At pH 4.0 and under modified atmosphere (80% CO2-20% N2), no growth was observed at any alpha w in the range of 0.80-0.90 when using a preservative concentration of 220 ppm Ksorbate or 280 ppm Na-benzoate.
