Tree bark is a versatile source of raw materials for the pharmaceutics, cosmetics and food industries. Finland also produces bark suitable for organic products, as half the country’s forests – close to 12 million hectares – are certified organic.
Tree bark is an exceptionally versatile source of raw materials, its various layers providing different products.
“Bark contains anti-microbial and anti-oxidant compounds which could be used as preservatives, not to mention pharmaceutical compounds and ingredients which enhance the taste of food products”, states Pekka Saranpää, Principal Scientist at Luke, Finland’s Natural Resources Institute.
In addition, bark provides raw materials for adhesives, insulating materials and even water purification, helping in removing impurities.
Despite this versatility bark has been largely neglected as a source of raw materials in comparison with cellulose fibres. Attention to bark’s usability has increased only since the start of the new millennium.
Maximum wood utilisation
Behind the increasing interest in bark is the aim of resource efficient utilisation of forest biomass, in a greater variety of ways.
“The European Union wants to promote the cascading use of wood. Accordingly, the burning of timber and bark for bioenergy is the last alternative when all other possible uses have been exhausted”, says Saranpää. Cascading use of wood is the smartest way to use a natural resource – directing it to high value use before it is reused, recycled and finally burnt for energy. Taking wood straight from the forest and burning it just doesn’t make sense if it can be used for other products first. In this way, the use of forest biomass is maximised, states Saranpää.
According to Saranpää, maximal use of bark products also complies with UN Sustainable Development Goals. Immediate action is demanded to combat climate change and implement sustainable production methods.
“By making use of bark the number of consumer products from renewable raw materials would increase. The tannin-polyphenols from conifer bark, for example, could replace the harmful phenolic compounds from fossil sources which are used in adhesives”, says Saranpää.
Finnish organic bark
One of the advantages of Finnish bark for use in the food and cosmetics industries is that 12 million hectares of the country’s forested areas are already certified organic. These comprise one third of all the world’s certified organic forest areas including other wild collection and bee-keeping.
Finland’s largest certified organic forests lie in the north of the country. The forests there also have another advantage.
“North-grown trees have greater concentrations of stilbenes than those grown in the south. The more extreme the growing conditions, the more the trees contain these antioxidative compounds found in spruce bark”, says Tuula Jyske, Senior Scientist at Luke.
Jyske’s job is to study how the useful compounds found in bark can be utilised by the food industry as additives and aromatics.
She co-ordinates the InnoTrea project, funded by the Academy of Finland, where scientists from various disciplines have studied, for example, whether the tannins extracted from tree bark prevent the oxidization of fats in reindeer meat. This could lead to improved preservation of meat products.
“We also tested whether the tannins might add some exotic flavour to the reindeer meat. Tannins are naturally found in wines for example, affecting their tastes too.”
Jyske’s team has also tested bark tannin extracts in co-operation with an ice-cream producer in northern Finland, the company hoping to find “a new forest-flavour” for its products.
“The results were promising. It seems that these extracts may be capable of improving preservability of certain types of products, add aroma, and replace other preservatives, Jyske summarizes the first development test results.”
Extractives disappear rapidly
Pekka Saranpää points out that extracts from wood and bark can replace almost any oil-based products. But the extraction of bark’s various ingredients and their refinement are a challenge.
“Up to 95 percentages of woody material is wood fibre, but in bark there is a tremendous range. Bark is full of all kinds of cell tissue, which makes its refinement challenging. When you start to break them down and derive extractives, reactions take place which are difficult to control.”
All the phases of the wood procurement chain, as well as environmental conditions, affect the rate at which the various bark extractives are lost. Debarking and chipping are the worst possible scenario in preserving valuable bark extractives-based biochemicals. If bark extractives are desired end-products, wood should not be debarked and chipped beforehand, instead these processes should take place just before feedstock utilization. This adds a new kind of challenge for the material supply chain.
“The bigger the particle size of the stored bark, the better the valuable compounds are preserved in the material. For example, storing bark in piles, all the stilbenes disappear within four weeks”, says Hanna Brännström, Senior Scientist at Luke.
Brännström works on developing new delivery regimes for various types of forest biomass through Biohub – Forest Biobased business hubs – a co-operative project involving Luke and six other partners.
Despite the rapid degradation of some of the valuable components, winter conditions improve the preservation of others, as long as the bark remains on the trunk. Basically, fat-soluble compounds are preserved better than water-soluble ones.
“Raw materials are best stored frozen, or at least as cold as possible”, says Brännström.
Text: Heikki Hamunen