Search

Aspergillus ochraceusas a fungal contaminant and ochratoxin A (OTA) producer plays an important role in coffee quality. Temperature and water activity (aw) significantly influence mycelial growth and OTA production by isolates of A. ochraceuson green coffee beans. Maximum mycelial growth was found at 30°C and 0.95 to 0.99 aw. A marked decrease in growth rate was observed when temperature and awwere reduced. At 0.80 aw, mycelial growth occurred only at 30 and 20°C for one isolate. Maximum OTA production was found at 20°C and 0.99 aw. At 10°C, OTA was not produced, regardless of aw. Similarly, no OTA was detected at 0.80 aw. OTA production ranged from the limit of detection (40 ng g−1of green coffee) to 17,000 ng g−1of green coffee. Significant intraspecific differences in mycelial growth and OTA production were found. Primary data for lag phases prior to mycelial growth under the influence of temperature and awwere modelled by multiple linear regression, and the response surface plots were obtained.

A sponge cake analog was used to study the influence of pH, water activity (aw), and carbon dioxide (CO2) levels on the growth of seven fungal species commonly causing bakery product spoilage (Eurotium amstelodami, Eurotium herbariorum, Eurotium repens, Eurotium rubrum, Aspergillus niger, Aspergillus flavus, and Penicillium corylophilum). A full factorial design was used. Water activity, CO2, and their interaction were the main factors significantly affecting fungal growth. Water activity at levels of 0.80 to 0.90 had a significant influence on fungal growth and determined the concentration of CO2needed to prevent cake analog spoilage. At an awlevel of 0.85, lag phases increased twofold when the level of CO2in the headspace increased from 0 to 70%. In general, no fungal growth was observed for up to 28 days of incubation at 25°C when samples were packaged with 100% CO2, regardless of the awlevel. Partial least squares projection to latent structures regression was used to build a polynomial model to predict sponge cake shelf life on the basis of the lag phases of all seven species tested. The model developed explained quite well (R2= 79%) the growth of almost all species, which responded similarly to changes in tested factors. The results of this study emphasize the importance of combining several hurdles, such as modified atmosphere packaging, aw, and pH, that have synergistic or additive effects on the inhibition of mold growth.

Fusarium verticillioides and F proliferatum isolates were inoculated in mixed cultures with Aspergillus parasiticus on irradiated maize grain at two different inoculum concentrations (2 × 10⁵ and 2 × 10² conidia g^-1 dry maize). The treatments were 0.93-0.98 water activity (a_w) and 15 and 25 °C for 28 days. A complex relationship was found between a_w, temperature, inoculum concentration and the interactions which took place between fumonisin and aflatoxin producers. In general, A parasiticus reduced F verticillioides and F proliferatum populations (by 6-36%) but did not affect fumonisin B₁ production by these species. In contrast, while the Fusarium species were not able to decrease A parasiticus populations, they significantly reduced aflatoxin B₁ accumulation (by 30-93%).
© 2001 Society of Chemical Industry

The effect of water activity (aw, 0·85–0·95), temperature (15–30 °C) and incubation period (2–4 weeks) on growth and calorific losses in relation to colonisation by three mycotoxigenic isolates ofAspergillus ochraceuswas studied on maize-based substrates. The calorific losses (kJ) of maize flour due to fungal growth in relation to temperature andawwere quantified and found to be maximal at 20–30 °C (10·52–16·18%, after 4 weeks at 0·95aw), with only slight losses at 0·85aw(0–7·14%), at both 15 and 20 °C. This suggests that growth of mycotoxigenicAspergillusspp. can significantly contribute to nutritional losses of this staple agricultural food. Calorific values correlated inversely with fungal biomass, with the latter being greatest at 0·95awafter both two and four weeks, and maximal at 30 °C. Most of the single, two-, three- and four-way interactions ofaw, temperature, time and isolate had a statistically significant (p<0·01) influence on calorific losses and fungal biomass.

Mycotoxins are a wide group of fungal toxins that have been associated with severe toxic effects in man and animals. Aflatoxins are the most dangerous of these fungal secondary metabolites. Because there is no definitive way in which complete detoxification of food and feed contaminated with mycotoxins can be achieved, new methods to eliminate mycotoxicosis are sought.

40 Gbit/s transmission using a single optical carrier and electrical time division multiplexing is demonstrated for the first time reusing standard singlemode fibres from the existing fibre infrastructure of Portugal Telecom. Bit error measurements as well as video transmission via STM1 interfaces demonstrate the robustness of dispersion supported transmission under real operating conditions.