Synthesis of Silver Nanorods from Food Industrial Waste and Their Application in Improving the Keeping Quality of Milk Padmanaban Sivakumar, † Pandian Sivakumar, † Kamalakannan Anbarasu, ‡ Kannaiyan Pandian, § and Sahadevan Renganathan* ,† † Department of Chemical Engineering, Anna University, Chennai 600025, Tamilnadu, India ‡ Quality Control Department, Tamilnadu Co-operative Milk Producers Federation Limited, Aavin, Sholinganallur, Chennai 600119, Tamilnadu, India § Department of Inorganic Chemistry, University of Madras, Guindy Campus, Chennai 600025, Tamilnadu, India * S Supporting Information ABSTRACT: A novel method for the synthesis of silver nanorods is reported, in which industrial milk waste was utilized, that were then used to extend the stability of milk. During the synthesis, the size of the silver nanorods were affected by pH and temperature. Silver nanorods were formed at alkaline pH in room temperature, whereas nanoparticles were formed in lower pH at elevated temperature. The obtained nanostructures were characterized by UV-visible spectrophotometer, energy dispersive X- ray analysis (EDAX), and transmission electron microscope (TEM). These silver nanorods were used to control coliform and standard plate count (SPC) in milk. This was confirmed by an increase in 4 to 5 folds of methylene blue reduction time as compared to the control. The Hom inactivation model was proposed to express microbial inactivation in milk. The cytotoxic effect of silver nanorods shows that they have been nontoxic to humans even at higher concentration. 1. INTRODUCTION In recent years nanotechnology has been rising as a rapidly growing field with abundant application in science and technology. The active surface area of AgNPs would be significantly large when compared to their compounds, which exhibits remarkable abnormal physiochemical properties and biological activities when exposed to cells of tissues. 1-5 The medicinal properties of silver nanoparticles and their utilization of silver as a drinking agent are not new. Silver compounds act as an effective antimicrobial agent for both aerobic and anaerobic bacteria by precipitating microbial cellular protein and also by blocking the microbial respiratory chain system. 6-8 With advancement of nanotechnology, the interest in the use of the antibacterial potency of silver nanoparticles has been rekindled. The antimicrobial mechanism of AgNPs is similar to that of silver compound. However, because of the larger surface area to volume ratio, AgNPs may have far better efficiency. 4 Nanosize silver has a large surface area for better contact with the micro-organism. The nanoparticles get attached to the cell membrane and react with amino acids containing sulfur that successfully affects bacterial cell viability. 9 AgNPs can also attack the respiratory chain in the mitochondria of micro- organisms and result in their death. 6 A recent study reveals that the antimicrobial activity of AgNPs is solely due to Ag + release even at lower concentrations (released or adsorbed on AgNP coatings). 10 One dimensional metal nanostructures such as wires, rods, and tubes have attracted substantial interest in research because of their unique applications. 11 Silver nanostructures synthesized through chemical methods have adverse chemicals present on the surface of the nanomaterials, which are highly reactive and hazardous. 12 Hence, a green synthesis method employing algae, plants and fungi extracts are used for nanomaterial synthesis. 13 Recently harmless green chemicals like glucose, maltose, lactose, galactose, etc., are also used. 14 Generally two approaches were employed for metal nano- rods synthesis, either by hard template or soft template methods. 15,16 Silver nanorods have been synthesized by using polymers, wet chemicals, sono-chemical, surfactant assistant method, etc. 17,18 When compared to AgNPs, silver nanorods are particularly interesting because of their higher electrical and thermal conductivity and exhibit higher antimicrobial property. In this paper a seedless, cost-effective method was proposed to synthesize silver nanorods by using industrial waste materials. In earlier methods reducing agent, capping agent, and surfactants were used for synthesis. Here the liquid waste which contains lactose and a small quauntity of whey acts as both reducing and capping agent. The only affecting parameters were pH and temperature, which decide both the particle size and shape. The industrial waste material can be reused and the product also will be useful for some other industrial purpose. 19,20 Paneer is a high protein cheese food from South Asian countries, which is produced by curdling of milk. The milk is heated to 70-90 °C and acidified using lemon juice or food grade acids like viniger or citric acid, etc. The coagulated solids settle and the liquid part is separated as waste. At present there is no literature evidence for the synthesis of silver nanorods from these wastes and its application in the keeping quality of Received: March 23, 2013 Revised: July 12, 2013 Accepted: November 19, 2013 Published: November 22, 2013 Research Note pubs.acs.org/IECR © 2013 American Chemical Society 17676 dx.doi.org/10.1021/ie4009327 | Ind. Eng. Chem. Res. 2013, 52, 17676-17681