Development of a novel quantitative PCR assay as a measurement for the presence of geosmin-producing fungi

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Abstract

Aims:

To provide an efficient technique for monitoring the off-flavoured fungal compound geosmin.

Methods and Results:

Geosmin-associated gpe1 gene of Penicillium expansum displayed ≥99% similarity to cytochrome P450 gene of geosmin-producing P. restrictum, but ≤40% similarities to geosmin biosynthesis, non-cytochromic gene of Streptomyces avermitilis and cytochrome P450 genes of non-geosmin-producing Neotyphodium lolii, Phoma betae and P. paxilli. Serial 10-fold dilutions of P. expansum's DNA was subjected to a previously reported qPCR assay (Atoui et al. 2007), utilizing gpe1 specific primer pair ‘SNgpe1F/SNgpe1R’. A linear relationship between DNA quantity and Cycle Threshold (Ct), with strong correlative coefficient, was observed. Using the available physico-chemical method, geosmin was quantified in 188 grape samples. Penicillium spp's DNA was quantified in these samples, utilizing the developed qPCR assay. A strong positive correlation (R2 = 0·97) between Penicillium's DNA and geosmin concentration was observed. Furthermore, <50 ng μl−1Penicillium's DNA corresponds to geosmin level below the permitted intensity limit i.e. 4, for ‘Flavour Profile Analysis’.

Conclusions:

Penicillium spp., genomic DNA level can provide an efficient way to quantify geosmin.

Significance and Impact of the Study:

This particular qPCR technique can be utilized in numerous food industries, for the timely detection and monitoring of geosmin contamination.

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