ORIGINAL ARTICLE Recycling of Bakery Waste as an Alternative Carbon Source for Rhamnolipid Biosurfactant Production Kaustuvmani Patowary 1 · Moonjit Das 2 · Rupshikha Patowary 1 · Mohan Chandra Kalita 3 · Suresh Deka 1 Received: 29 December 2017 / Revised: 9 August 2018 / Accepted: 8 October 2018 © 2018 AOCS Abstract Production of a rhamnolipid biosurfactant (RBS) using discarded mixed bakery waste (BW) employ- ing bacterial strain Pseudomonas aeruginosa strain PG1 (identified by 16 s rDNA sequencing) was investigated for bioconversion of the food waste. Dry and powder form BW was supplemented with mineral salt media (MSM) as a sole carbon source for production of RBS. RBS production was measured based on the drop collapse assay and surface tension (ST) reduction of the culture media. Production of RBS in the culture media was enhanced by optimizing the carbon source (BW) concentration and the proper nitrogen source along with the pH of the MSM. Under optimized culture conditions, 11.56 g L -1 day -1 crude biosurfactant (BS) was achieved. The RBS had the ability to reduce the ST of the optimized MSM from 72.0 to 25.8 mN m -1 dur- ing culture, where the critical micelle concentration (CMC) of the biosurfactant was found to be 100 mg L -1 . Liquid Chromatography Mass Spectroscopy (LC-MS), Fourier Transform Infrared spectroscopy (FTIR), and scanning electron microscopy (SEM)–energy dispersive X-ray spectroscopy (EDS) analyses of the purified BS confirmed that it is of rhamnolipid in nature and it is made up of both monorhamnolipid and dirhamnolipid congeners. Further- more, the RBS did not express any cytotoxic effect on the cell line of mouse L292 fibroblastic cell indicating the bio- safety nature of the high-value biomolecule. Keywords Rhamnolipid  Biosurfactant  Bakery waste  Pseudomonas aeruginosa PG1  Cytotoxicity J Surfact Deterg (2018). Introduction Surfactants are molecules that have surface-active potential to reduce surface tension (ST). The widespread applicabil- ity of surfactants includes the field of petrochemical indus- tries, pharmaceuticals, cosmetic industries, food industry, agrochemicals, and so on. Conventionally, chemical surfac- tants are often used in the areas mentioned above, but such surfactants are persistent in nature due to their poor biode- gradability and extent toxicity toward ecosystem (George and Jayachandran, 2008). As a biosurfactant (BS) possesses appropriate characteristics such as biodegradability, higher selectivity, lower toxicity, environmental compatibility, and particular activity under extreme environmental condi- tions; immense importance has been paid toward the imple- mentation of BS as an alternative for its chemical counterparts (Gautam and Tyagi, 2006). A plethora of microorganism has been reported as BS producers with dif- ferent chemical compositions such as glycolipids, lipopep- tides and lipoproteins, fatty acids, phospholipids, and neutral lipids (Anandaraj and Thivakaran, 2010). Due to its Supporting information Additional supporting information may be found online in the Supporting Information section at the end of the article. * Suresh Deka sureshdeka@iasst.gov.in; sureshdeka@gmail.com 1 Environmental Biotechnology Laboratory, Life Sciences Division, Institute of Advanced Study in Science & Technology (IASST), Paschim Boragaon, Guwahati, Assam, India 2 Centre for Biotechnology & Bioinformatics, Dibrugarh University, Dibrugarh, Assam, India 3 Department of Biotechnology, Gauhati University, Guwahati, Assam, India J Surfact Deterg (2018) J Surfact Deterg (2018) DOI 10.1002/jsde.12242