Chestnut Drying Is Critical in Determining Aspergillus flavus Growth and Aflatoxin Contamination

Abstract

Chestnut drying is used to prevent postharvest losses and microorganism contamination during storage. Several studies reported the contamination by aflatoxins (AFs) produced by Aspergillus spp. in chestnuts. The effect of drying temperatures (from 30 to 50 °C) was evaluated on the growth of A. flavus and the production of aflatoxins in chestnuts. The influence of the treatment on the proximate composition, the total phenol content and antioxidant activity of chestnuts was considered. Fungal colonization was observed on the nuts dried at 30, 35, and 40 °C; the incidence was lower at 40 °C. The highest concentrations of AFB1 and AFB2 were produced at 40 °C. No aflatoxins were detected at 45 or 50 °C. At 40 °C A. flavus was under suboptimal conditions for growth (aw 0.78), but the fungus was able to synthesize aflatoxins. As the temperatures applied increased, the total phenol content increased, while the antioxidant activity decreased. A drying treatment at 45 °C for seven days (aw 0.64) could be a promising method to effectively control both the growth of aflatoxigenic fungi and the production of aflatoxins. This study provides preliminary data useful to improve the current drying conditions used in chestnut mills, to reduce both fungal growth and aflatoxin production.

Adverse Effects, Transformation and Channeling of Aflatoxins Into Food Raw Materials in Livestock

“…A. flavus has an outstandingly high heat tolerance in comparison to other fungi with an upper tolerance limit of 40 • C (Neme and Mohammed, 2017). Prencipe et al (2018) also found that while the growth of A. flavus was suboptimal above 40 • C this relatively high temperature resulted in the most intensive aflatoxin synthesis on chestnut. Hawkins et al (2005) found that 60 • C drying temperature still had no adverse effect on A. flavus thriving on corn kernels but raising the temperature up to 70 • C significantly decreased fungal infection.…”

Effect of Drying Temperatures and Exposure Times on Aspergillus flavus Growth and Aflatoxin Production on Artificially Inoculated Hazelnuts

“…(49) and Turan and Islam (48) suggest to dry hazelnuts with higher temperature (43-49 °C and 45 °C, respectively). For other nuts, the best drying temperatures were found to be above 40 °C: 42 °C for peanuts (18) and 45 °C for chestnuts (36). In this work, hazelnuts were artificially inoculated, while fungal growth and aflatoxin production were promoted by adjusting the moisture content, as a result, high level of aflatoxins were produced especially between 30 °C and 40 °C.…”

“…Mycotoxin production is often promoted under suboptimal growth conditions as an adaptive response (36,39,40). For example, in chestnuts, drying at 40 °C resulted in a significant reduction of fungal growth but also in a higher production of aflatoxins (36).…”

“…The drying experiments were performed in a drying and heating chamber (Binder M115-230V) while, after drying, an environmental testing chamber (Panasonic MLR-352H-PE) was used for storing hazelnuts at 25 °C for 14 days. Moisture content of nuts was determined by weighing samples before and after drying at 103 °C for 14 hours (36). Water activity (aw) was measured by using an electronic hygrometer AquaLab Series 3TE (Decagon Devices Inc., Pullman, WA, USA), which adopted the chilled-mirror technique at 25 •C.…”

HPLC-MS/MS Method for the Detection of Selected Toxic Metabolites Produced by Penicillium spp. in Nuts

“…Among the fatty acids of hazelnut oil, palmitic acid (2.96-7.40%) is the main saturated fatty acid (SFA). The highest share of fatty acids is monounsaturated fatty acids (MUFAs), as oleic acid (73.1%-90.7%), and polyunsaturated fatty acids (PUFAs) as linoleic acid (4.4-16%) [41,42]. Due to the uniqueness of the matrices, the composition of the solvent applied for extraction is a crucial parameter during the development of a multi-mycotoxin method.…”