Effects of thermal and enzymatic treatments and harvesting time on the microbial quality and chemical composition of fibre hemp (Cannabis sativa L.)

The aim of the present study was to examine the effects of pectinase enzyme treatment followed by thermal treatments (steam explosion and dry heating) on the microbial quality and chemical composition of hemp fibres. Before these treatments, the fibres were separated manually from the stems harvested after stand retting in the field before frost, after early frost or in the following spring. The enzymatic treatment of hemp promoted growth of moulds on the fibres (500-fold increase in colony-forming units (cfu)), whereas steam explosion reduced the amount of moulds to a relatively constant level of 102 cfu/g dw. The amount of bacteria was not markedly affected by enzymatic treatment but was reduced tenfold after steam explosion. Steam explosion is thereby a potentially good process for the production of hemp fibres with low fungal contamination, which can be of importance in insulation materials. Dry heating had no effect on mould and bacterial counts at temperatures below 120 °C and durations less than 60 min. The chemical composition was affected by the enzymatic treatment due to extraction and degradation of water-soluble components, pectin and ash. Thus the cellulose content increased by 6% w/w to 67–70% w/w. Steam explosion of the untreated hemp fibres increased the cellulose content to 74% w/w, whereas steam explosion of enzymatically treated hemp increased the cellulose content to 78% w/w.