Biosoftening of arecanut fiber for value added products Akhila Rajan, Jayalakshmi Gopinadha Kurup, Tholath Emilia Abraham ∗ Bioactive Polymer Engineering Section, Regional Research Laboratory (CSIR), Trivandrum 695019, India Abstract The arecanut husk fibers are predominantly composed of cellulose and varying proportions of hemicellulose, lignin, pectin and protopectin. Microbes that selectively remove lignin without loss of appreciable amounts of cellulose and fiber strength properties are extremely attractive for the biosoftening of arecanut fiber. The fungal growth occurs during the first 72 h of incubation and by one week, enzyme production reaches the maximum level, thereby improving color and softness of the fiber. Maximum MnP production of 233.2 IU ml -1 was observed at pH 7.0 for Phanerochaete chrysosporium and a maximum activity of 221.8 IU ml -1 was observed at pH 5.0 for Phanerochaete strain. Maximum improvement of color (brightness) and softness and maximum MnP production of 321.3 IU ml -1 was achieved in a medium lacking both carbon and nitrogen for P. chrysosporium whereas maximum improvement in color and softness and MnP production of 341.2 IU ml -1 was achieved in a medium lacking only carbon for Phanerochaete sp. The fiber treated with P. chrysosporium showed 35.1% and Phanerochaete sp. showed 25.7% increase in strength when compared to the untreated fiber. Elongation of the fiber treated with P. chrysosporium was 5.0% and that treated with Phanerochaete sp. was 4.2% compared to the control fiber which had an elongation of 3.7%. The biosoftened arecanut fibers can be exploited commercially for the production of furnishing fabrics, textiles etc by blending with cotton, viscose and polyester. © 2005 Elsevier B.V. All rights reserved. Keywords: Biosoftening; Lignin; Cellulose; Filamentous fungi; Arecanut fibers 1. Introduction Palm trees are monocot trees grown along the coastal areas and yields commercially important products such as nuts, fiber and oil. Among the palm trees, coconut and are- canut palm are mainly exploited for economic purposes. The advantages of natural lignocellulosic fibers include accept- able specific strength properties, low cost, low density, and biodegradability [1]. Although natural fiber characteristics can vary somewhat with the environmental conditions under which the plants grow, the chemical constitution is mainly of cellulose, hemicellulose, lignins, pectins, waxes, water sol- uble substances and residual ash along with other organic materials [2]. Arecanut, also known as betel nut, is the kernel obtained from the fruit of arecanut palm (Areca catechu Linnaeus). India dominates the world in area (57%), production (53%) and productivity of arecanut (0.379 million tonnes in 2002). ∗ Corresponding author. Tel.: +91 471 2515253; fax: +91 471 2490186. E-mail address: emiliatea@yahoo.com (T.E. Abraham). Arecanut finds place in religious, social and cultural func- tions of India. The presence of the betel nut is a must in the ceremonial plate, as betel nuts are believed to increase pros- perity. The nut is offered to guests, along with a betel leaf, as a mark of respect. The fruit has a fibrous mesocarp, and seeds are with a truncate base, endosperm deeply ruminates with a basalar embryo. The kernel shape is ovate [3]. The husk is about 15–30% of the weight of the raw nut. The arecanut husk fibers are predominantly composed of cellulose and varying proportions of hemicellulose, lignin, pectin and protopectin. The fibers adjoining the inner layers are irregularly lignified group of cells called hard fibers, and the portions of the mid- dle layer below the outermost layer are soft fibers [4]. The total hemicellulose content varies with the devel- opment and maturity, the mature husk containing less hemicellulose than the immature ones. The lignin con- tent proportionately increases with the development until maturity. The polyphenols of ripe Arecanut contain predom- inantly polymerized leucocyanidins, besides minor amounts of (+)-catechin, leucopelargonidin and leucocyanidin. The polyphenols of arecanut are mainly flavonoids, and their