African Journal of Agricultural Research Vol. 7(47), pp. 6281-6288, 13 November , 2012 Available online at http://www.academicjournals.org/AJAR DOI: 10.5897/AJAR12.1862 ISSN 1991-637X ©2012 Academic Journals Full Length Research Paper Drying of waste grains flour of annatto by using solar energy Dyego da Costa Santos, Alexandre José de Melo Queiroz, Rossana Maria Feitosa de Figueirêdo* and Emanuel Neto Alves de Oliveira Universidade Federal de Campina Grande. Av. Aprígio Veloso, 882, Universitário, Campina Grande, Paraíba, Brazil. Accepted 5 November 2012 This study is aimed at drying annatto seed powders produced from seeds with and without oil used in bixin extraction. Drying was done at night, using a solar energy dryer. The drier consists of a system of solar panels that heat water, which is transferred to a thermal reservoir from where it is used as heat source for drying during the night. The waste grain flour of annatto with initial moisture content of approximately 20% w.b. was dried by approximately 5% w.b. The samples were split into two batches: Exposed to external environment and placed in the drier. The drying kinetic data were fitted by five mathematical models. The drier showed effectiveness in the drying of annatto grains flour at night with difference of more than 10% of moisture content in relation to the samples exposed to external environment. Powders obtained from seeds containing oil took approximately 40% longer to dry than those without oil. The mathematical models assessed satisfactorily represented drying behavior. The highest values of diffusivity were found in dehydrated samples in the drier. Key words: Bixa orellana L., agroindustrial waste, nocturnal drier. INTRODUCTION In accordance with Queiroz et al. (2011), products classified as agricultural waste are often valuable material in the nutritional point of view; this material may also be used in order to increase the yield of the main product. Moreover, its disposal in the environment causes economical and environmental costs, proportional to the exploration volume. The annatto waste grains (Bixa orellana L.) are by- product of the pigment extraction in the dye industry, mainly the bixin. Its gain would represent, in mass or volume, one of the largest returns among agricultural products, since the bixin layer that wraps the grains is very thin, in a manner that during the industrial extraction process there is from 94 to 98% of leftovers (Silva et al., 2006). Rêgo et al. (2010) provided the information that approximately 2,500 t of annatto waste grains are annually obtained in Brazil, almost 97% of it is not used. *Corresponding author. E-mail: rossana@deag.ufcg.edu.br. Tel: +55 83-2101-1547. Currently, most of this waste is disposed; however there is already demand for it by breeders that use it in the composition of animal feed and scientifical works that evidence its practicability for this purpose (Silva et al., 2006; Harder et al., 2007; Rêgo et al., 2010). By exploring its potentiality, these grains can be used in the human nourishment, with differentiated indication for dietary food, due to its high fiber content. Authors such as Pereira et al. (2010) reported the amount of crude fiber in waste grains of annatto of 13.5% d.b. Tonani et al. (2000) found higher amount of crude fiber, corresponding to 15% d.b. The literature contains a number of studies on the drying of agribusiness waste: grape seeds (Roberts et al., 2008); pumpkin seeds (Sacilik, 2007; Jittanit, 2011); guava processing subproduct (Konga et al., 2010); pineapple fiber derived from pineapple waste (Waughon and Pena, 2008); olive oil subproduct (Montero et al., 2011; Milczarek et al., 2011); fermented grape bagasse (Ferreira et al., 2012); orange juice subproduct (Garau et al., 2007); tomato processing subproduct (Celma et al., 2009); among others. Despite the wide diversity of