Flavour pro®le of idli batter prepared from de®ned microbial starter cultures Renu Agrawal*, E.R. Rati, S.V.N. Vijayendra, M.C. Varadaraj, M.S. Prasad and Krishna Nand Department of Food Microbiology, Central Food Technological Research Institute, Mysore 570 013, India *Author for correspondence: Tel.: +91-821-517539, Fax: +91-821-517233, E-mail: Renu.agrawal@usa.net Received 4 May 2000; accepted 24 October 2000 Keywords: Candida versatilis, fermented food, ¯avour pro®le, idli batter, microbial starters, Pediococcus pentosaceus Summary Idli is a traditional cereal/legume-based naturally fermented steamed product with a soft and spongy texture which is highly popular and widely consumed as a snack food item in India. The predominant fermentation micro¯ora comprises lactic acid bacteria and yeasts and causes an improvement in the nutritional, textural and ¯avour characteristics of the ®nal product. The ¯avour pro®le of idli batter prepared with initial levels of 2 ´ 10 4 c.f.u. g )1 of Candida versatilis CFR 505 and 2 ´ 10 1 c.f.u. g )1 of Pediococcus pentosaceus CFR 2123 in 500 g idli batter, packed in polyester polylaminate pouches and stored at 30  2 °C was periodically analysed by GC-MS. The desirable ¯avour compounds such as ketones, diols and acids were found to be present upto 8 days of storage, whereas undesirable ¯avours like sulphurous and oxazolidone compounds, ethanone and thiazole appeared in the batter subsequent to 6 days of storage. The sensory attributes of idlis (®nal product) prepared from the stored batter related well to the determined ¯avour pro®le. The present study appeared to indicate that the ¯avour pro®le of traditional fermented foods can be a reliable qualitative and quantitative parameter for objective assessment. Introduction Cereal/legume-based foods are a major source of eco- nomical dietary energy and nutrients world-wide. Among the fermented foods of India, idli, a fermented steamed product with a soft and spongy texture is a highly popular and widely consumed snack food in the entire Indian region. Traditionally, the product is made from naturally fermented batter prepared from a mixture of milled rice (Oryza sativa) and dehulled Blackgram dhal (Phaseolus mungo), the proportion of which varies (Desikachar et al. 1960; Radhakrishnamurthy et al. 1961). In general, idli is prepared on a household level and in catering establishments ranging from small to big. Idli batter fermentation has been the subject of many research investigations covering aspects of optimization of ingredients, microbiological, physico-chemical and nutritional (Steinkraus et al. 1967; Ramakrishnan 1979; Venkatasubbaiah et al. 1984; Thyagaraja et al. 1991, 1992). Two signi®cant changes occurring in idli batter fermentation are leavening and acidi®cation. These two parameters have been used as the criteria for judging the progress of fermentation. In recent years, there has been a greater interest in making available the traditional foods as convenience foods to meet the growing demands of changing societal patterns. In this background, protocols were established through the use of optimal cell densities of de®ned microbial starter cultures to achieve in situ fermentation of idli batter in ready-to-use retail packs with reasonable shelf stability at ambient temperature for which a patent has been ®led (Varadaraj et al. 1999). Considering the various aspects involved in idli batter fermentation, the pro®le of ¯avour components desir- able in making the product acceptable has not been studied. The prime objective of this study was to determine the ¯avour components occurring during the storage period of shelf stable idli batter. Materials and Methods All experimental trials were performed in triplicate. Starter cultures and inoculum preparation The cultures included were the native isolates of Pediococcus pentosaceus CFR 2123 and Candida versa- tilis CFR 505 which were available as stock cultures in the culture collection of this department. Strains of P. pentosaceus CFR 2123 and C. versatilis CFR 505 were maintained at 4 °C in Lactobacillus MRS broth and potato dextrose agar (Hi-Media Lab., Mumbai, India) slants, respectively and subcultured at 15 day intervals. For use in the experiment, cultures of P. pentosaceus CFR 2123 and C. versatilis CFR 505 were grown World Journal of Microbiology & Biotechnology 16: 687±690, 2000. 687 Ó 2001 Kluwer Academic Publishers. Printed in the Netherlands.