Vacuum freeze-drying of biological materials is one of the best methods of water removal, with final products of highest quality. The solid state of water during freeze-drying protects the primary structure and the shape of the products with minimal volume reduction. In addition, the lower temperatures in the process allow maximal nutrient and bioactive compound retention. This technique has been successfully applied to diverse biological materials, such as meats, coffee, juices, dairy products, cells, and bacteria, and is standard practice for penicillin, hormones, blood plasma, vitamin preparations, etc. Despite its many advantages, having four to ten times more energy requirements than regular hot air drying, freeze-drying has always been recognized as the most expensive process for manufacturing a dehydrated product. The application of the freeze-drying process to plant-based foods has been traditionally dedicated to the production of space shuttle goods, military or extreme-sport foodstuffs, and specialty foods such as coffee or spices. Recently, the market for ‘natural’ and ‘organic’ products is, however, strongly growing as well as the consumer’s demand for foods with minimal processing and high quality. From this perspective, the market for freeze-dried plant-based foods is not only increasing but also diversifying. Freeze-dried fruits and vegetables chunks, pieces, or slices are nowadays majorly used in a wide range of food products such as confectionaries, morning cereals, soups, bakeries, meal boxes, etc. Instant drinks are prepared out of freeze-dried tea, coffee, or even from maple syrup enriched with polyphenol concentrated extracts from trees. The possibilities are endless. In this review, the application of freeze-drying to transform plant-based foods was analyzed, based on the recent research publications on the subject and personal unpublished data. The review is structured around the following related topics: latest applications of freeze-drying to plant-based foods, specific technological problems that could be found when freeze-drying such products (i.e., presence of cuticle; high sugar or lipid concentration), pretreatments and intensification technologies employed in freeze-drying of plant-based foods, and quality issues of these freeze-dried products.

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There are several factors influencing a fundamental property of a wood species, the limit of hygroscopicity of wood (LH) or fiber saturation point (FSP). The effect of temperature upon the limit of hygroscopicity has been mentioned in literature, but has not been precisely quantified. In this paper we have correlated the LHs with temperature of thermal pretreatment, taking also into account the properties of particular wood species, i.e. density and chemical composition. For our investigation we have selected the most important domestic wood species for industrial processing: oak, beech, poplar, fir and spruce. We have determined the limits of hygroscopicity by method of compression strength parallel to grain, for the following temperature ranges of thermal treatments, in dependence of wood species: for hardwoods from 20° to 80 °C and for softwoods from 20° to 90 °C. Our results demonstrate the general decrease of the limit of hygroscopicity with the increase of temperature of the thermal pretreatment of the examined wood species. Mathematical correlations have been evaluated on the basis of experimental data by polynomial regression statistical method. Wood density is another factor examined as influential upon the limit of hygroscopicity. We have determined the decrease of the LH with the increase of wood density, i.e. denser wood species have lower capacity for water adsorption. The differences obtained for the LHs between the examined wood species have been explained in relation to their chemical compositions. Our results indicate that cellulose is the major wood component determining its capacity for water adsorption.

Scotch pine (P. sylvestris L.) xylem oleoresins from different provenances in central and southern Yugoslavia were studied by means of gas chromatography. The differences in the chemical composition of resin acids and neutral diterpenes compared to samples from other provenances in Europe are in the normal range of variation. The composition of the monoterpene hydrocarbons, however, were variable.Two samples from authochtone stands in western Serbia and southern Makedonia contain levorotatory turpentine oils which are free from 3-carene. A sample from Bosnia yielded a dextrorotatory turpentine oil containing 8.6 per cent 3-carene among the mixture of monoterpenes. Obviously the Bosnian pine stand belongs to the northern Eurasian type of P. sylvestris while the two other provenances are of the Mediterranean entity.

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Xylem oleoresin from P. peuce was analyzed after a Separation into turpentine, resin acid and diterpene neutral fractions using GLC and GCMS. -Pinene was the main component of the turpentine. 7.15-Isopimaradien-18-oic (isopimaric) acid is the main component of the resin acid fraction and is accompanied by 8,15-and 8 (14),15-isopimaradien-18-oic (sandaracopimaric) acids äs well äs by 8 (14),15-pirnaradien-18-oic (pimaric) acid. The second largest component was abietic acid besides of smaller amounts of the other abietane type acids. The high amount of diterpene neutrals contains thunbergol and/or cembrol and palustral and/or levopimaral äs major components.

The procedure is developed for light briquette production from wood and bark materials of different technical origin, regardless of their dimensions and moisture content. Cohesiveness of the light briquette is achieved by the addition of pulp and/or recycled paper waste. The mixture of materials is completely saturated with water and then shaped in molds at low pressure (3 to 5 bars).The briquettes produced by the described procedure are characterized by high porosity and therefore low density (240 to 331 kg/m 3 ).The light briquette structure does not decline upon moisture absorption or water suction, which is the common problem with the wood briquettes produced by conventional methods.The samples of light briquettes were determined to have: low ash content (up to 2.5%), high volatile content (between 70% and 78%), charcoal content (between 15% and 22%) and higher heating value about 20,000 kJ/kg.Combustion characteristics of briquette samples were examined in the furnace. The testing was carried out in the constant temperature conditions. The measurements were repeated in the range between 400°C and 800°C, advancing at constant intervals.The chamber temperature was determined to have the influence upon the volatility of briquettes and the ignition delay time of the volatiles. The influence of the chamber temperature upon combustion time of the volatiles was determined to be insignificant.