engleski

Control of mould contamination in industrial hemp seeds by gamma-irradiation: a pilot study

Gamma irradiation is a physical method for materials processing that involves their exposure to high energetic gamma photons emitted by 60Co. Food irradiation up to dose of 10 kGy (and above in some cases) has been considered as an effective technology for microbial decontamination in comparison with traditional pasteurisation methods. Recently, the industrial hemp Cannabis sativa L. subsp. sativa has been grown in Croatia by several individual farmers. Thus, mycobiota of C. sativa was poorly investigated so far in this part of Europe. The aim of this pilot study is to check total mould count and mycobiota composition of two samples of C. sativa prior and after gamma irradiation at doses 1-10 kGy. The irradiation was performed at panoramic source of 60Co in RCDL of RBI. Samples were serially diluted in peptone water and plated in duplicate onto Dichloran Glycerol (DG18) agar and Dichloran Rose Bengal Chloramphenicol (DRBC) agar plates. The number of mould colony-forming unit (CFU) was determined upon incubation 5-7 days at 25°C, and the data were expressed as the number of CFU/g. Upon irradiation at 1, 3, 5, 7 and 10 kGy at dose rate 120 Gy/min and ambient conditions, samples were plated onto DG18 and DRBC and CFU/g was checked on 7th, 14th and 28th day. Total mould count was 7.8×105 CFU/g (DRBC) and 2.5×105 CFU/g (DG18). Fusarium spp. and Cladosporium spp. were dominant natural contaminants which comprised 60% and 20% of hemp mycobiota. All applied irradiation doses suppressed more than 90% of initial mould contamination. Mould count that survived irradiation was between 2000 and 4000 CFU/g which is approximately 0.25 and 0.5 % of initial count. Moulds that survived g-irradiation were Fusarium spp. Cladosporium spp., Aspergillus fumigatus and Phoma spp. In the next experiment hemp samples were sterilized at 25 kGy and inoculated with moulds (2 ml, 102 CFU/ml of water) that survived previous irradiation. Samples were inoculated with single moulds as well as with mixture of all four species, while control was inoculated with 2 ml of water. All samples were incubated 7 days at 25°C and than irradiated with doses of 10, 12 and 15 kGy. After 10 days samples were analysed on DRBC as described previously. All plates remained sterile during 28 days period. In conclusion, gamma irradiation up to 10 kGy can be applied for significant reduction of mould contamination but higher doses are required for complete elimination of particular mould species.

Moulds; Aspergillus; Fusarium; Penicillium; gamma-radiation; hemp

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