ORIGINAL PAPER Comparative analysis of solid-state bioprocessing and enzymatic treatment of finger millet for mobilization of bound phenolics Geetanjali Yadav • Anshu Singh • Patrali Bhattacharya • Jude Yuvraj • Rintu Banerjee Received: 6 August 2012 / Accepted: 4 February 2013 Ó Springer-Verlag Berlin Heidelberg 2013 Abstract The present work investigates the probable bioprocessing technique to mobilize the bound phenolics naturally found in finger millet cell wall for enriching it with dietary antioxidants. Comparative study was per- formed between the exogenous enzymatic treatment and solid-state fermentation of grain (SSF) with a food grade organism Rhizopus oryzae. SSF results indicated that at the 6th day of incubation, total phenolic content (18.64 mg gallic acid equivalent/gds) and antioxidant property (DPPH radical scavenging activity of 39.03 %, metal chelating ability of 54 % and better reducing power) of finger millet were drastically enhanced when fermented with GRAS filamentous fungi. During the enzymatic bioprocessing, most of the phenolics released during the hydrolysis, lea- ched out into the liquid portion rather than retaining them within the millet grain, resulting in overall loss of dietary antioxidant. The present study establishes the most effec- tive strategy to enrich the finger millet with phenolic antioxidants. Keywords Solid-state fermentation  b-Glucosidase  Finger millet  Phenolics  Dietary antioxidants Introduction Food quality is defined in terms of its nutritional values and the presence of bioactive compounds exerting positive effects on human health [1]. Cereals grains contain many health promoting components such as vitamins, minerals and phytochemicals including phenolic compounds. Wheat, rice and maize have been highly explored for their phenolic content and the bioactive potential. Apart from these cereals, millets are also of great importance. Finger millet (Eleusine coracana) is one of the staple minor mil- lets in the Indian subcontinent and many of the African countries. These small seeded grains with light brown to brick red colored seed coat possess polyphenol 0.09 to 2.44 mg chlorogenic equivalent/100 mg [2]. Biofunction- ality of finger millets like hypoglycemic [3], hypocholes- terolemic [4] and anti-ulcerative properties is known due to its polyphenol contents [5]. The bioavailability of pheno- lics varies as they exist in bound or in the free form. Bound phenolics are found in cell walls where they are chemically linked to cell wall components, mainly polysaccharides. Free phenolics are located in vacuoles. Phenolic com- pounds occur throughout the millet varieties and are linked to various cell wall components through glycosidic link- ages, such as arabinoxylans and protein. Finger millet seed coat specifically contains bioactive phenolics in wall bound form. From last few decades, filamentous fungi are employed to increase the content of phenolic compounds in various food products, thus enhancing their nutritional profile by solid-state fermentation (SSF). The value addi- tion of finger millet by SSF provides a wide scope for development of functional food. Another emerging technology in the food sector is enzymatic bioprocessing. Microbial enzymes (e.g., pec- tinases, cellulases, a-amylases, xylanase, b-glucosidase, b-xylosidase and b-galactosidase) are attaining significant role in bioprocessing, mainly for release of bioactive phenolic compounds [6]. The enhanced release of the phenolic compounds attached to the cell wall is G. Yadav  A. Singh  P. Bhattacharya  J. Yuvraj  R. Banerjee (&) Microbial Biotechnology and Downstream Processing Laboratory, Agricultural and Food Engineering Department, Indian Institute of Technology, 721302 Kharagpur, India e-mail: rb@iitkgp.ac.in 123 Bioprocess Biosyst Eng DOI 10.1007/s00449-013-0924-4