pubs.acs.org/JAFC Published on Web 12/22/2009 © 2009 American Chemical Society J. Agric. Food Chem. 2010, 58, 981–989 981 DOI:10.1021/jf902907c Comparison of Microencapsulation Properties of Spruce Galactoglucomannans and Arabic Gum Using a Model Hydrophobic Core Compound PIA LAINE,* ,† ANNA-MAIJA LAMPI, ‡ MARKO PEURA, § JARNO KANSIKAS, ) KIRSI MIKKONEN, †,‡ STEFAN WILLFO . R, ^ MAIJA TENKANEN, ‡ AND KIRSI JOUPPILA † † Department of Food Technology, Faculty of Agriculture and Forestry, University of Helsinki, P.O. Box 66, FI-00014 Finland, ‡ Department of Applied Chemistry and Microbiology, Faculty of Agriculture and Forestry, University of Helsinki, P.O. Box 27, FI-00014 Finland, § Department of Physics, Faculty of Science, University of Helsinki, P.O. Box 64, FI-00014 Finland, ) Department of Chemistry, Faculty of Science, University of Helsinki, P.O. Box 55, FI-00014 Finland, and ^ Process Chemistry Centre, A ˚ bo Akademi University, Porthansgatan 3, FI-20500 A ˚ bo, Finland In the present study, microencapsulation and the physical properties of spruce (Picea abies) Ο-acetyl-galactoglucomannans (GGM) were investigated and compared to those of arabic gum (AG). Microcapsules were obtained by freeze-drying oil-in-water emulsions containing 10 wt % capsule materials (AG, GGM, or a 1:1 mixture of GGM-AG) and 2 wt % R-tocopherol (a model hydrophobic core compound that oxidizes easily). Microcapsules were stored at relative humidity (RH) of 0, 33, and 66% at 25 °C for different time periods, and their R-tocopherol content was determined by HPLC. X-ray microtomography analyses showed that the freeze-dried emulsions of GGM had the highest and those of AG the lowest degree of porosity. According to X-ray diffraction patterns, both freeze-dried AG and GGM showed an amorphous nature. The storage test showed that anhydrous AG microcapsules had higher R-tocopherol content than GGM-containing capsules, whereas under 33 and 66% RH conditions GGM was superior in relation to the retention of R-tocopherol. The good protection ability of GGM was related to its ability to form thicker walls to microcapsules and better physical stability compared to AG. The glass transition temperature of AG was close to the storage temperature (25 °C) at RH of 66%, which explains the remarkable losses of R-tocopherol in the microcapsules under those conditions. KEYWORDS: Spruce Ο-acetyl-galactoglucomannans; arabic gum; microencapsulation; R-tocopherol; storage stability INTRODUCTION Wood compounds have been used in the food industry for several years. Phytosterols, xylitol, and carboxymethylcellulose are examples of valuable wood-based compounds, which are widely used in different types of foods all around the world. One potential new wood-based compound for food use is Ο-acetyl-galactoglucomannans (GGM) that is the predominant hemicellulose in spruce (Picea abies)( 1 ). GGM consists of a linear 1f4-linked chain of β-mannopyranosyl and β-glucopyranosyl units to which branches of single R-galactopyranosyl units are attached ( 2 , 3 ). The hydroxyl groups in mannopyranosyl units of GGM are partly substituted by acetyl groups (degree of acetyla- tion ∼ 16%). Compared to common commercial galactoman- nans, for example, locust bean gum, guar gum, or konjac gum, GGM has lower molecular weight and less viscous character in concentrated solutions ( 3 -5 ). GGM can be recovered from the process water of the pulping industry, and methods for effective extraction and recovery have been developed ( 2 , 5 ). GGM has not yet been approved for food use and is not commercially available, but several studies have been done or are ongoing regarding the usage of GGM in different applications including use in edible films ( 6 ) and as emulsion stabilizers in beverages ( 7 ). At its simplest, microcapsules can be produced by preparing emulsions from the capsule material (e.g., polysaccharide and/or protein) and the desired sensitive component which needs protec- tion (e.g., vitamin, flavor or unsaturated lipids) and by drying the achieved emulsions to the amorphous glassy powders ( 8 , 9 ). There are numerous ways for microencapsulation of which, for exam- ple, freeze-drying, spray-drying, and extrusion, produce glassy powders ( 10 ). The ability of the glassy matrix to protect the encapsulated component is based on its very high viscosity, and thus, the molecular mobility and oxygen permeation are extre- mely slow ( 11 ). The state of the capsule matrix may change from glassy to rubbery (= glass transition) if the capsules are stored under such conditions that the glass transition temperature (T g ) of the matrix is lower than the storage temperature. The physical properties of the capsule materials are important to know in order to find the proper storage conditions for microcapsule powders. If the microcapsules are stored under unfavorable conditions, *To whom correspondence should be addressed. Telephone: þ358 9 19158715. Fax: þ358 9 19158460. E-mail: pia.laine@helsinki.fi.