Growth kinetics and patulin production by Penicillium setosum in pineapple juice under different temperatures and initial pH values

Penicillium setosum, a member of the Penicillium section Lanata-divaricata, is known for its ability to produce high levels of patulin. However, there is a notable lack of information regarding the influence of environmental factors on the growth and patulin production in fruit juice of this species. In this study, we investigated the impacts of temperature (25, 30, 35, or 40 °C), initial pH value (3, 5, or 7), and incubation time (2, 4, or 6 days) on the growth and patulin production in pineapple juice of the selected P. setosum strain HR9-5. The modified Gompertz model was applied to estimate the maximum growth rate and lag time prior to growth. This strain had the highest growth rate with the shortest lag time within the temperature range 30–35 °C, with an initial pH range of 3–5. Furthermore, it had the greatest biomass dry weight and patulin production at 35 °C with an initial pH of 3, and at 25 °C with an initial pH of 7, respectively. The growth rate and lag time prior to growth of P. setosum HR9-5 were significantly influenced by the initial pH, whereas the biomass dry weight was strongly affected by temperature and incubation time. Additionally, all factors and their interactions had a significant impact on patulin production. This study provided the first report on the effect of environmental factors on growth and patulin production by P. setosum in pineapple juice. These findings can contribute to formulating effective prevention strategies to control the growth of P. setosum and subsequent patulin production in pineapple and other fruit juices

Occurrence of Heat-Resistant Mold Ascospores in Pineapple and Sugarcane Field Soils in Thailand

Heat-resistant molds (HRMs) are important spoilage fungi of heat-processed fruit products worldwide. Ascospores of HRMs are widely distributed in the soil in which fruits are grown and are often found associated with raw fruit materials. To date, there is little available information on the distribution of HRMs in the soil and on their heat resistance. Thus, this study determined the presence and characterized the heat resistance of HRMs in soil samples from pineapple and sugarcane fields in Thailand. HRMs were detected in all soil samples, and the most dominant species was Aspergillus with 50–99.2% relative abundance. Other isolates, in descending order of frequency, were Penicillium, Talaromyces, Hamigera, and Paecilomyces. Then, 100 representative HRM isolates were identified based on a combination of morphological characteristics and ITS sequences. They were classified into 5 genera and 24 species. The heat resistance of ascospores aged 30 days produced by selected HRMs was qualitatively determined in a glucose-buffered solution. Based on their log reductions after heat shock at 75°C for 30 min, they were classified as less, moderately, or highly heat-resistant ascospores. HRMs belonging to A. chevalieri, A. denticulatus, A. siamensis, A. laciniosus, A. fennelliae, A. spinosus, Paec. niveus, H. pallida, and T. macrosporus produced high heat-resistant ascospores. In addition, soil physicochemical properties significantly influenced the prevalence of HRMs, depending on the fungal genus. The thermal resistance of ascospores was significantly and positively correlated to available phosphorus, whereas it was negatively correlated to soil pH. The results of this study confirmed the presence of HRMs in soils and potential HRM contamination, especially in fruits growing in acidic or high-nutrient soils, or both

Interactive Inhibition of Aflatoxigenic Aspergillus flavus and Ochratoxigenic Aspergillus carbonarius by Aspergillus oryzae under Fluctuating Temperatures

This study aimed to evaluate the effectiveness of A. oryzae in inhibiting aflatoxin B1 (AFB1) and ochratoxin A (OTA) production by A. flavus and A. carbonarius, respectively, under shifting temperatures. A. oryzae was tested on different agar, namely coconut cream agar (CCA) and chili-based agar to figure out the variation in the effectiveness of A. oryzae on the most appropriate medium for A. flavus and A. carbonarius to produce mycotoxin and under natural condition where they are predominantly found. On CCA, the temperatures applied were 20, 30, 35, 40, 20/30, 20/35, and 20/40 °C, while on chili-based agar, the temperatures imposed were 20, 40, and 20/40 °C, at varied water activity of 0.92 and 0.97aw. The findings indicated that A. oryzae was much more effective in inhibiting the growth of A. flavus rather than A. carbonarius, yet it was able to inhibit higher OTA concentration than AFB1 at fluctuating temperatures on CCA as the most appropriate medium for A. flavus and A. carbonarius. A. oryzae effectively inhibited AFB1 and OTA at static temperature of 20 °C and water activity of 0.97aw on chili-based agar. Under fluctuating temperatures (20/40 °C), A. oryzae was also able to control mycotoxin, particularly OTA at high water activity (0.97aw)