Agricultural and Food Science, Vol. 14 (2005): 143–153. 143 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 14 (2005): 143–153. © Agricultural and Food Science Manuscript received September 2004 Hygienic quality of stem fractions of mechanically processed fibre hemp and linseed Hanna-Riitta Kymäläinen, Minna Nykter, Mikko Hautala and Anna-Maija Sjöberg Department of Agrotechnology, PO Box 28 (Koetilantie 3), FI-00014 University of Helsinki, e-mail: hanna-riitta.kymalainen@helsinki.fi Bast fibre is the most important fraction of bast fibre plants for technical products, i.e. thermal insulations and packaging materials. The hygienic quality of the various fractions of bast fibre plants is of interest in thermal insulations, because it may affect the quality of indoor air. Packaging materials may be associated e.g. with foodstuffs, which highlights the importance of hygienic quality. The aim of this study was to screen the hygienic quality, determined as microbial content, of mechanically fractionated fibre hemp and linseed plants harvested in the autumn before frost, after early frost and in spring. In addition, the possible correlation between microbes and ash was investigated. Two plant species, fibre hemp and linseed were studied. The plants were cultivated in Siuntio in southern Finland during the years 2002 and 2003, har- vested in autumn or in spring and mechanically fractionated. The microbial contents of the fractions were examined by measuring the total number of microbes using Hygicult® growing slides. The microbial con- tent of fractions of fibre hemp and linseed varied between 103 and 109 cfu/gdw. The fibre of hemp harvested after early frost or in spring had the lowest amount of moulds, but during winter and spring the amounts of bacteria and yeasts increased in hemp. Mechanically separated fibre and shive contained less microbes than the stalk. Ash contents of all examined samples of stems and stem fractions varied between 1% and 14%. The fibre after fractionating had a lower ash content (2.3–3.3%) than that of stems (4.4–6.9%) harvested in the autumn. The ash content of stem and shive decreased to 1.6% during winter, the ash content of fibre being even somewhat lower (0.9%). No correlation was observed between the contents of microbes and ash. Key words: hygienic quality, microbes, ash, bast fibres, linseed, fibre hemp, Linum usitatissimum, Cannabis sativa Introduction Recent research of bast fibre plants has been fo- cused on non-textile applications. Bast fibres may be used for building materials, e.g. thermal insula- tions (Ringleb and Schulz 1996, Koivula et al. 2005), packaging materials (Tavisto et al. 2001) and composites (Hepworth et al. 2000, Hautala et al. 2004). Typical applications for shives as main or secondary component are building materials (e.g. shive-boards, thermal insulations) or horse- 22835_03_Kymalainen.indd 143 12.10.2005 14:09:38 144 A G R I C U L T U R A L A N D F O O D S C I E N C E Kymäläinen, H.-R. et al. Hygienic quality of hemp and linseed stem fractions bedding, but shive has also been used as a compo- nent of packaging materials (Tavisto et al. 2001). Limits for microbial quality of fibre materials have been given e.g. in the legislation of thermal insula- tions (STM 2003). Linseed and hemp are annual bast fibre plants, from which the stem must be retted and bast sepa- rated from woody core using microbial, chemical, thermal or mechanical methods (Sultana 1992). Consideration of microbiological contamination connected e.g. to the retting process has been pre- sented in some previous studies, the focus of which however has been on other aspects. According to the study by Hepworth et al. (2000), the retting process causes microbiological contamination of the fibre as a side effect. If excessive lodging oc- curs in the field due e.g. to too low plant density, fungal infections may occur (Struik et al. 2000). Hobson et al. (2001) suggested low amounts of retting microorganisms to be considered as mar- keting advantages of bast fibres e.g. for health and safety reasons. In addition to their effects on the hygienic quality, microorganisms also affect vari- ous properties of the fibre, such as strength, poros- ity and colour. The inorganic content of a plant is usually characterized by its ash content, which is an ap- proximate measure of the mineral salts and other inorganic matter in the fibre after combustion (Han and Rowell 1997). With development of new har- vesting and processing techniques of fibre plants, contamination with soil and sand has been dis- cussed and found to increase the ash content of plants (Kymäläinen et al. 2002). Due to the micro- bial content of soil, contamination with soil is a potential risk for hygienic quality in products made from plant materials, such as thermal insulations (Koivula et al. 2005) and packaging materials (Sjöberg et al. 2002). Contamination with soil may also cause problems in processing systems (Kymäläinen et al. 2004). The variation of microbial quality of linseed plant during the growing season has been studied earlier by e.g. Saharan and Singh (1985) and Vlou- toglou et al. (1995). In a study by Koivula et al. (2004), changes of microbial quality of linseed and hemp during the growing season were studied. However, there is no published quantitative infor- mation on the hygienic quality of fractionated stems of bast fibre plants. In this study the fibre hemp and linseed plants were cultivated, harvested before and after early frost in autumn and after frost-retting in spring, and fractionated. The aim of the study was to examine the microbial quality de- termined as microbial content of mechanically processed fibre hemp and linseed plant fractions and to investigate correlations between microbial and ash contents of the fractions. In addition, the difference in hygienic quality between the sepa- rated fibre and the stems in the field before harvest was evaluated. Material and methods Cultivation and harvesting of the plants In this study two plant species were investigated: fibre hemp (Cannabis sativa L.), var. Uso and lin- seed (Linum usitatissimum L.), var. Helmi. The plants were cultivated and harvested in Siuntio in southern Finland during the years 2002 and 2003. The plants were cultivated according to common farming practices in Finland (Hakala and Hongisto 1994, Sankari 1998). The growing season of 2002 was relatively cool and moist: average temperature rarely exceeded 20ºC and average relative humid- ity of the air was over 80% most of the time. The climatic conditions and development of microbial quality of the plants during the growing season were reported in detail by Koivula et al. (2004). The winter season 2002–2003 was very cold, with temperatures below –20ºC for some periods. The stalks were harvested by cutting with gar- den shears, threshing or mowing (Table 1) with a mower just before or around noon of the harvest day. Stalks were immediately transported to a dry- ing room (T ~ 50ºC, t = 7 days) with a delay be- tween harvest and drying of approximately three to four hours. The plants and details of harvesting and sampling are presented in Table 1. The dried stems were stored sealed in a plastic foil wrapping 22835_03_Kymalainen.indd 144 12.10.2005 14:09:38 145 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 14 (2005): 143–153. T ab le 1 . I nv es ti ga te d pl an ts , d at e an d m et ho d of h ar ve st , p re tr ea tm en ts a nd s am pl in g. L in se ed L in se ed a ft er t hr es hi ng H em p be fo re e ar ly f ro st H em p af te r ea rl y fr os t S pr in g- ha rv es te d he m p V ar ie ty H el m i H el m i U so U so U so N f er ti li ze r do se , k g ha -1 60 60 92 92 92 D at e of h ar ve st 12 S ep 2 00 2 12 S ep 2 00 2 19 S ep 2 00 2 10 O ct 2 00 2 6 M ay 2 00 3 T em pe ra tu re , º C ; re la ti ve h um id it y of a ir , % a t 9 an d 11 a .m . 9; 9 8 19 ; 56 9 ; 9 8 19 ; 5 6 6; 8 3 9; 7 1 2; 7 7 2; 7 4 10 ; 66 * S te m m at ur it y S te m u nr ip en ed ( se ed m at ur e) S te m u nr ip en ed ( se ed m at ur e) S te m u nr ip en ed S te m s li gh tl y re tt ed S te m o ve rr et te d M oi st ur e co nt en t of s te m s ba se to p 42 17 42 17 62 65 29 22 12 21 H ar ve st m et ho d C ut ti ng P ic ki ng f ro m t he w in dr ow a ft er t re sh in g of t he s ee d M ow in g C ut ti ng M ow in g, r ou nd b al in g S am pl in g of t he s te m s fr om t he fi el d S te m s w er e se le ct ed ev en ly , r an do m ly f ro m th e fi el d. S te m s w er e se le ct ed ev en ly , r an do m ly f ro m th e w in dr ow . T w o 1. 5 x 30 m co lu m ns w er e m ow ed , an d th e sa m pl e w as pi ck ed r an do m ly f ro m th e ha rv es te d st al ks . S te m s w er e se le ct ed ev en ly , r an do m ly f ro m th e fi el d. 2/ 3 of t he fi el d w as ha rv es te d (a ft er t ha t it be ga n to r ai n) a nd ba le d in to 2 r ou nd ba le s, o f w hi ch t he sa m pl e w as l oo se ne d fo r m il li ng . P re li m in ar y tr ea tm en t (t em pe ra tu re o f dr yi ng ~ 5 0 º C ) D ry in g, r ip pl in g, de fo li at in g D ry in g D ry in g, r ip pl in g, de fo li at in g D ry in g, r ip pl in g, de fo li at in g N on e A pp ro xi m at e am ou nt o f sa m pl ed s te m s, l 10 0 10 0 10 0 10 0 20 0 * D at a at 9 a .m . b y th e F in ni sh W ea th er S er vi ce , m ea su re m en t st at io n of S iu nt io . D at a lo gg er w as n ot i n th e fi el d du e to h ar ve st . 22835_03_Kymalainen.indd 145 12.10.2005 14:09:38 146 A G R I C U L T U R A L A N D F O O D S C I E N C E Kymäläinen, H.-R. et al. Hygienic quality of hemp and linseed stem fractions in a storeroom (T ~ 18ºC) for one to three months before fractionation. Fractionation The dried, unprocessed stalk and four fractions (fi- bre, shive, dust, leaves and seeds or seed capsules) of hemp and linseed were studied. The pilot frac- tionating method, introduced and described in de- tail by Kymäläinen et al. (2001), consisted of dry- ing the stalks, milling the stems with a hammer mill, separating particles from an air stream in a cyclone, and separating fibre and shive with a screening drum and a sieve vibrator (Fig. 1). The separated fractions were stored in plastic buckets at room temperature (~ 22ºC) before measure- ments of microbes and ash. Microbial content of the fractions The microbial contents of the fractions were ex- amined by measuring the total number of microbes using Hygicult® Y&F (yeasts and fungi) and TPC (total bacteria) growing slides (Orion Diagnosti- ca). This method was introduced for samples of bast fibre plants by Koivula et al. (2004). The Hy- gicult ® TPC dipslides were validated against swabbing and control plate methods and the results were at the same level (Salo et al. 2000). Samples (Fig. 1) were randomly picked from the fraction container. A separate sample for moisture content measurement was taken at the same time. An amount of 100 ml of saline solution (NaCl 0.9%) was added to a weighed dry sample (5 g, except for the dust samples 1 g because of their limited amount). After 30 minutes of extraction, samples were homogenized for five minutes in a Stomacher 400 Circulator (Merck Eurolab, 230 rpm). An amount of 50 µl of the liquid was pipetted onto one side of a Hygicult® slide. Slides were incubated for 4 days at room temperature (∼ 25°C), after which the colonies were counted and the numbers of mi- crobes were counted as colony forming units per gram of a dry fraction (cfu/gdw). Ash content of the fractions The ash contents of the fractions were measured according to a TAPPI standard (T 211 om-85) with Separating dust and shive residues from the fibre with a sieve vibrator. Harvest of linseed and hemp in the autumn before and after the early frost. Separating fractions from air stream with a cyclone. Collecting dust from the filters of the cyclone. Separating fibre and shive with a drum separator (screening drum). Milling of the stems with an industrial hammer mill (∅ 20 mm). Harvest of hemp in the spring. Drying, deseeding and defoliating stems. Taking a part of the whole stems for examination. FIBRELEAVES AND CAPSULES STEMS SHIVE Sampling for the microbial determination of: 5 replicates except for dust 3 replicates. Sampling for the ash determination: 5 replicates. DUST Fig. 1. Pilot method for fractionation of stems of bast fibre plants and sampling of the fractions for the hygienic measure- ments. 22835_03_Kymalainen.indd 146 12.10.2005 14:09:39 147 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 14 (2005): 143–153. five replicates (the mass of one replicate was 2.5 g) with the minor adjustment of using crucibles with- out lids. Samples (Fig. 1) were randomly picked from the container. The temperature of the furnace while transferring the sample into the muffle fur- nace was 275°C ± 25°C and the ashing tempera- ture 575°C ± 25°C. A temperature of 575°C ± 25ºC is commonly used for combustion (Han and Row- ell 1997), but other temperatures, e.g. 900ºC, are also used (Archibald 1992). Variance analysis (one-way ANOVA, Tukey’s post hoc test of significance) of the SPSS statistical tool was used to examine differences between the mean microbial contents and ash of the fractions harvested at different times. Bivariate correlation analysis (Pearson’s correlation coefficients, two- tailed test of significance) was used to examine the possible correlation between moulds, yeasts and total bacteria, and between ash and microbial con- tents. Results The moisture contents of the dried samples in the microbial and ash determinations, measured from separate samples that were dried in an oven at 103ºC for 24 h, were between 5 and 9% (wet basis; w.b.). Microbial contents of the fractions The microbial contents of fractions of fibre hemp and linseed varied between 103 and 109 cfu/gdw (Fig. 2). The amounts of moulds, yeasts and total bacteria were at the same level in the linseed stems cut before threshing of the seed and in the stems collected from the windrow after threshing (Fig. 2). Therefore only the results of the cut stems are presented in Figure 3. Before early frost, the amounts of the moulds, yeasts and total bacteria were higher in linseed than in hemp (Fig. 3) (P < 0.001, P < 0.05 and P < 0.01, respectively). The fibre of hemp harvested after early frost or in spring had the lowest amount of moulds. The difference between the fractions harvested before and after early frost was statisti- cally significant (P < 0.05). The mould contents of the fibre and shive fractions were lower than that of stem (P < 0.001). The mould content of the hemp stems was highest in spring (Fig. 3a). During winter and spring the amount of yeasts increased in hemp (P < 0.01). There were less yeasts in the fibre and shive than in the stems (P < 0.01) (Fig. 3b). The amounts of bacteria of flax and hemp har- vested at different times differed statistically sig- nificantly from each other (P < 0.05 between all harvesting times). The amount of total bacteria was lower in fibre and shive than in stems of lin- seed and hemp before frost and in hemp after win- ter (P < 0.01). During the winter and spring period there was a clear increase in the amount of bacte- ria, especially in the stems but also in the fibre and shive fractions (Fig. 3c). There was no general correlation between the amounts of moulds, yeasts and total bacteria. How- ever, some of the correlations shown in Table 2 were statistically significant. Ash content of the fractions The seed, capsule and leaf fractions of hemp had the highest (> 10%) ash contents (Fig. 4). The dif- ference between this fraction and all other frac- tions was statistically significant (P < 0.001). The cut stems had the highest ash content of the linseed samples. Threshing, milling and sieving decreased the ash content of linseed from 5.7% (average of stems) to 3.2% (stems from the windrow) and 3.3– 3.4% (fibre and shive). Similarly, the separation decreased the ash content of hemp from 4.4–6.9% (stems before and after frost, respectively) to 2.3– 2.5% (hemp fibre and shive samples before and after frost). Even when the ash contents of the fibre and shive fractions were lower than those of the stems, only the fibre fractions differed statistically significantly (P < 0.05) from stem due to the differ- ences between the two plants. The difference be- tween the fibre and shive samples at one harvest time was negligible (P > 0.05). As shown in Figure 22835_03_Kymalainen.indd 147 12.10.2005 14:09:39 148 A G R I C U L T U R A L A N D F O O D S C I E N C E Kymäläinen, H.-R. et al. Hygienic quality of hemp and linseed stem fractions Fig. 2 c) total bacteria lin se e d , d u st lin se e d s te m s, c u t lin se e d s te m s, w in d ro w lin se e d f ib re lin se e d s h iv e lin se e d c a p s+ se e d h e m p d u st b .f . h e m p s te m s b .f . h e m p f ib re b .f . h e m p s h iv e b .f . h e m p c a p s+ le a v b .f . h e m p d u st a .f . h e m p s te m s a .f . h e m p f ib re a .f . h e m p s h iv e a .f . h e m p c a p s+ le a v a .f . h e m p d u st in s p ri n g h e m p s te m s in s p ri n g h e m p f ib re in s p ri n g h e m p s h iv e in s p ri n g cfu/g (d.w.) a) moulds lin se e d d u st lin se e d s te m s, c u t lin se e d s te m s, w in d ro w lin se e d f ib re lin se e d s h iv e lin se e d c a p s+ se e d h e m p d u st b .f . h e m p s te m s b .f . h e m p f ib re b .f . h e m p s h iv e b .f . h e m p c a p s+ le a v b .f . h e m p d u st a .f . h e m p s te m s a .f . h e m p f ib re a .f . h e m p s h iv e a .f . h e m p c a p s+ le a v a .f . h e m p d u st in s p ri n g h e m p s te m s in s p ri n g h e m p f ib re in s p ri n g h e m p s h iv e in s p ri n g cfu/g (d.w.) b) yeasts lin se e d d u st lin se e d s te m s, c u t lin se e d s te m s, w in d ro w lin se e d f ib re lin se e d s h iv e lin se e d c a p s+ se e d h e m p d u st b .f . h e m p s te m s b .f . h e m p f ib re b .f . h e m p s h iv e b .f . h e m p c a p s+ le a v b .f . h e m p d u st a .f . h e m p s te m s a .f . h e m p f ib re a .f . h e m p s h iv e a .f . h e m p c a p s+ le a v a .f . h e m p d u st in s p ri n g h e m p s te m s in s p ri n g h e m p f ib re in s p ri n g h e m p s h iv e in s p ri n g cfu/g (d.w.) 1.0E+07 1.0E+06 1.0E+05 1.0E+04 1.0E+03 1.0E+08 1.0E+07 1.0E+06 1.0E+05 1.0E+04 1.0E+03 1.0E+09 1.0E+06 1.0E+05 1.0E+07 1.0E+08 Fig. 2. Amounts of microbes (cfu/gdw) in dried and processed fractions at different harvest times: before frost (hemp b.f., linseed), after early frost (hemp a.f.) and in spring (hemp), a) moulds, b) yeasts, c) total bacteria. Columns are means of three (dust samples) or five replicates (other samples), bars in columns are standard errors of means of the replicates (±SE). d.w. = dry weight. 22835_03_Kymalainen.indd 148 12.10.2005 14:09:39 149 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 14 (2005): 143–153. Fig. 3 a) moulds plant in the field* before frost after early frost in spring plant in the field in spring cfu/g(dw) b) yeasts before frost after early frost in spring plant in the field in spring cfu/g(dw) c) total bacteria plant in the field* before frost after early frost in spring plant in the field in spring cfu/g(dw) 100000 1000000 10000000 100000000 1000000000 10000000000 plant in the field* before frost after early frost in spring hemp straw hemp fibre hemp shive hemp capsules & leaves linseed straw linseed fibre linseed shive linseed capsules&leaves 1.0E+07 1.0E+06 1.0E+05 1.0E+04 1.0E+03 1.0E+09 1.0E+08 1.0E+07 1.0E+03 1.0E+04 1.0E+05 1.0E+06 1.0E+10 1.0E+09 1.0E+08 1.0E+07 1.0E+06 1.0E+05 Fig. 3. Amounts of microbes (cfu/gdw) in dried and processed fractions of hemp and linseed at different harvest times: be- fore frost (hemp b.f., linseed), after early frost (hemp a.f.) and in spring (hemp), a) moulds, b) yeasts, c) total bacteria. Results are means of five replicates. * fractions before harvest in the field in autumn (data from Koivula et al. 2004) and in spring Table 2. Pearson’s correlation coefficients between moulds, yeasts, total bacteria and ash (both plant species and all fractions included). Harvest times were analysed separately. Harvest time Ash Moulds Yeasts Total bacteria Ash Before frost 1 0.220 –0.079 0.022 After early frost 1 0.418 0.226 –0.996** Spring 1 0.528 0.601 0.733 Moulds Before frost 0.220 1 0.713* 0.980** After early frost 0.418 1 0.971* –0.487 Spring 0.528 1 0.996 0.965 Yeasts Before frost –0.079 0.713* 1 0.999** After early frost 0.226 0.971* 1 –0.294 Spring 0.601 0.996 1 0.984 Total bacteria Before frost 0.022 0.980** 0.999** 1 After early frost 0.996** –0.487 –0.294 1 Spring 0.733 0.965 0.984 1 * Correlation is significant at the 0.05 level (2-tailed). ** Correlation is significant at the 0.01 level (2-tailed). 4, the ash contents of the spring-harvested samples were the lowest (0.9–1.6%), and the differences between the ash contents of the fractions harvested in spring also differed statistically from those har- vested in autumn (P < 0.01). In most cases there was no significant correlation between the ash and microbial contents of the fractions (Table 2). The only exception was the correlation coefficient of 22835_03_Kymalainen.indd 149 12.10.2005 14:09:39 150 A G R I C U L T U R A L A N D F O O D S C I E N C E Kymäläinen, H.-R. et al. Hygienic quality of hemp and linseed stem fractions Fig. 4 0 2 4 6 8 10 12 14 16 linseed stems linseed stems, w. linseed fibre linseed fibre, w. linseed shive linseed shive, w. linseed caps+leav hemp stems b.f. hemp fibre b.f. hemp shive b.f. hemp caps+leav b.f. hemp stems a.f. hemp fibre a.f. hemp shive a.f. hemp caps+leav a.f. hemp stems in spring hemp fibre in spring hemp shive in spring % (d.b.) Fig. 4. Ash contents of fractions (% dry basis; d.b.). Columns are means of five replicates, bars in columns are standard errors of means of the replicates (±SE). 0.996 between ash and total bacteria (fractions harvested after early frost). Discussion In the present study, the amount of moulds was on the same level in the cut, dry hemp stems (Fig. 3) as in the living plant at the end of the growing sea- son in autumn (Koivula et al. 2004). By processing and mechanical separation, it was possible to pro- duce fibre containing somewhat less moulds and bacteria than the plant in the field (Fig. 2). It is pos- sible that the separation process itself affected this result, but more probably the microbial content is higher in the surface than in the inner parts of the plant. The industrial processes for producing raw material for e.g. packages or loose-fill insulations are similar to the present pilot process. According to the recommendations of the Min- istry of Social Affairs and Health in Finland, the amount of fungal spores should not exceed 104 cfu/g, and the amount of bacteria should be below 105 cfu/g in material samples taken from buildings (STM 2003). However, the focus of these limits is on other building materials than thermal insula- tions, and the information is thus only indicative for the fibre materials of the present study. On the basis of the amount of fungi, the hemp fibre har- vested after early frost or in spring in this study could be accepted, but the amount of bacteria was clearly higher than the recommendation. In our study, the moisture contents of the samples were between 5% and 9% (w.b.) but e.g. in field condi- tions the moisture content of bast fibre plants may be as high as 85% (Koivula et al. 2004). Our re- sults were expressed per dry weight, but if they were converted to fresh weight, the variation range would remain almost the same (based on a mois- ture content 9%) or approximately tenfold lower (moisture content 85%), meaning that the fibre harvested in spring would also be suitable. Frost retting is a method in which seeds are harvested in autumn and the standing stalks are left 22835_03_Kymalainen.indd 150 12.10.2005 14:09:40 151 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 14 (2005): 143–153. to ret in the field for winter. Alternation of thawing and freezing during winter separates fibres from stems (Pasila 2000). The stems of linseed were very short and partly bent or lodged and thus not ideal for frost retting, and therefore only hemp stalks were sampled after early frost and harvested in the spring of the year 2003. In the present study, the early frost decreased the amount of total bacte- ria in those parts of hemp containing tissues of outer layers (stem, capsules), whereas the amount of total bacteria decreased in the inner fractions (fibre and shive). The outer surface of a plant may prevent microbial invasion of the tissues in living plants (Adams and Moss 2002) and it may have affected the lower microbial content of the fibre and shive fractions compared to the whole stalk. Slow freezing or recrystallization of water leads to cellular damage and thus release of cell constitu- ents, causing drip losses during thawing. The drip losses provide substrates for enzyme activity and microbial growth (Fellows 2000), which was seen as changes in the amount of total bacteria in the present study. In kenaf-growing areas, early frost has been found to be a problem because it kills the crop before harvest and the plants develop fungus or mildew. According to the results of this study, threshing of linseed did not affect the microbial content of the stems. In general, all agricultural and process- ing machines are potential contamination sources for the plant materials being processed. Agricul- tural dust consists of inorganic matter, i.e. minerals from rock or soil or silicates from plants, and or- ganic substances, which are biologically more ac- tive than inorganic dusts (Donham 1986). Unlike cellulose and lignin contents, which in- crease with plant age (Struik et al. 2000, Keller et al. 2001), Overbeke and Mazingue (1949) did not find hemicellulose and ash contents to have a sys- tematic progression with age. According to our earlier studies (Kymäläinen et al. 2002), the ash content of mechanically fractionated flax fibre was 2.9–3.8% and that of hemp fibre was 2.2–2.8%, and in most cases the lowest levels were in frost- retted samples. The frost-retted samples also had the lowest ash contents in the present study. This is probably due to changes in the chemical composi- tion (decrease of mineral substances) of the stem during retting. Mineral substances, e.g. K, Na, Ca, Zn and Fe, probably leak out from the stem during retting (Sharma 1992). The ash content of bast fi- bre of linseed produced using a different method than in the present study was 5% and that of hemp 0.8% (Han and Rowell 1997), and that of flax shive was 3.1–5.5% (unretted) and 1.2–2.0% (retted) (Sharma 1992). In the present study, the harvesting and processing was carried out with relatively clean techniques. By contrast, contamination of fibres with soil in various other production meth- ods has been found to increase the ash level much more than was measured in this work (Kymäläinen et al. 2002). Our mechanical pilot process included several steps during which impurities such as dust were removed from fibre and shive. The possible inorganic contaminants were at least partly re- moved from the stem, which in this study resulted in relatively low ash contents of the fibre and shive compared to the ash content of the stem. This may explain why there was no correlation between the contents of microbes and ash in this study. Conclusion The microbial content of the fractions of fibre hemp and linseed varied between 103 and 109 cfu/ gdw. The levels exceeding 10 5 cfu/g may be too high for certain applications such as building ma- terials. The fibre of hemp harvested after early frost or in spring had the lowest amount of moulds, but during winter and spring the amount of bacte- ria and yeasts increased in hemp. Mechanically separated fibre and shive contained less microbes than the stalk. It was shown that the microbial con- tent of fibre cannot be predicted reliably from the microbial content of stems in the field. Fractiona- tion decreased the ash content of stems harvested in the autumn. The ash contents of the frost-retted fractions were the lowest. In this study no correla- tion was observed between the microbial and ash contents. 22835_03_Kymalainen.indd 151 12.10.2005 14:09:40 152 A G R I C U L T U R A L A N D F O O D S C I E N C E Kymäläinen, H.-R. et al. Hygienic quality of hemp and linseed stem fractions Acknowledgements. We are grateful to agroforestry stu- dents Ari Klemola, Janne Pirilä, Jukka Ruunaniemi and Asaye Talibachew in the Flax Team of the Department of Agricultural Engineering and Household Technology for technical assistance and fruitful discussions during the study. We thank the Academy of Finland (SUNARE: Re- search project “Emissions from thermal insulations”) for financial support, and Orion Diagnostica for providing the Hygicult® slides. References Adams, M.R. & Moss, M.O. 2002. Food microbiology. The Royal Society of Chemistry, UK. 479 p. Archibald, L.B. 1992. Quality in flax fibre. In: Sharma, H.S.S. & Sumere, C.F. van (eds.). The biology and processing of flax. Belfast: M Publications. p. 297–309. Donham, K.J. 1986. Hazardous agents in agricultural dusts and methods of evaluation. American Journal of Indus- trial Medicine 10: 205–220. Fellows, P.J. 2000. Food processing technology. 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SELOSTUS Mekaanisesti jakeistetun kuituhampun ja öljypellavan korren hygieeninen laatu Hanna-Riitta Kymäläinen, Minna Nykter, Mikko Hautala ja Anna-Maija Sjöberg Helsingin yliopisto Niinikuitu on tärkein teknisiin sovelluksiin, kuten läm- möneristeisiin ja pakkausmateriaaleihin käytettävä nii- nikuitukasvien jae. Niinikuitukasvien jakeiden hygiee- ninen laatu on tärkeää lämmöneristeissä, jotka voivat vaikuttaa sisäilman laatuun. Pakkausmateriaalit voivat olla yhteydessä esim. ruokaan, mikä korostaa hygieeni- sen laadun merkitystä. Tutkimuksen tavoitteena oli kar- toittaa syksyllä tai keväällä korjatun, mekaanisesti ja- keistetun öljypellavan ja kuituhampun hygieenistä laa- tua, jota kuvattiin mikrobimäärän avulla. Lisäksi tutkit- tiin mikrobimäärien ja tuhkapitoisuuden mahdollista korrelaatiota. Tutkittavana oli kaksi kasvilajia, kuituhamppu ja öl- jypellava. Kasvit viljeltiin ja korjattiin Siuntiossa, Etelä- Suomessa vuosina 2002–2003. Korret korjattiin syksyllä ennen pakkasia, ensimmäisten pakkasten jälkeen tai ke- väällä, minkä jälkeen korret jakeistettiin mekaanisesti. Jakeiden kokonaismikrobimäärät selvitettiin Hygicult®- kastolevyillä. Jakeiden mikrobimäärät vaihtelivat 103 ja 109 välil- lä. Aikaisen pakkasen jälkeen tai keväällä korjatun kui- tuhampun niinikuitu sisälsi vähiten homeita, mutta tal- ven ja kevään aikana bakteerien ja hiivojen määrä kas- voi. Mekaanisesti jakeistettu kuitu ja päistäre sisälsivät vähemmän mikrobeja kuin kokonainen korsi. Multakon- taminaatiota pidetään yleisesti hygieniariskinä. Multa- kontaminaatio lisää korren tuhkapitoisuutta. Jakeiden tuhkapitoisuus vaihteli 1 ja 14 % välillä. Niinikuituja- keen tuhkapitoisuus oli alhaisempi kuin syksyllä korja- tun korren tuhkapitoisuus. Korren ja päistäreen tuhkapi- toisuus laski talven aikana 1,6 %, ja keväällä korjatusta korresta erotetun kuidun tuhkapitoisuus oli niitäkin al- haisempi (0,9 %). Mikrobi- ja tuhkapitoisuuksien välillä ei havaittu korrelaatiota. 22835_03_Kymalainen.indd 153 12.10.2005 14:09:40 Hygienic quality of stem fractions of mechanically processed fibre hemp and linseed Introduction Material and methods Results Discussion Conclusion References SELOSTUS