*Corresponding author Email address: fengrns@ku.ac.th Songklanakarin J. Sci. Technol. 43 (1), 37-44, Jan. - Feb. 2021 Original Article Rambutan (Nephelium lappaceum) peel extract: Antimicrobial and antioxidant activities and its application as a bioactive compound in whey protein isolate film Udomlak Sukatta 1 , Prapassorn Rugthaworn 1 , Nattaporn Khanoonkon 1 , Pariya Anongjanya 1 , Kunat Kongsin 1 , Prakit Sukyai 2, 3 , Nathdanai Harnkarnsujarit 4 , Rungsinee Sothornvit 5* , and Rungsima Chollakup 1 1 Kasetsart Agricultural and Agro-Industrial Product Improvement Institute, Kasetsart University, Chatuchak, Bangkok, 10900 Thailand 2 Biotechnology of Biopolymers and Bioactive Compounds Special Research Unit, Department of Biotechnology, Faculty of Agro-Industry, Kasetsart University, Chatuchak, Bangkok, 10900 Thailand 3 Center for Advanced Studies for Agriculture and Food, Kasetsart University Institute for Advanced Studies, Kasetsart University, Chatuchak, Bangkok, 10900 Thailand 4 Department of Packaging and Materials Technology, Faculty of Agro-Industry, Kasetsart University, Chatuchak, Bangkok, 10900 Thailand 5 Department of Food Engineering, Faculty of Engineering at Kamphaengsaen, Kasetsart University, Kamphaengsaen Campus, Nakhon Pathom, 73140 Thailand Received: 17 January 2019; Revised: 21 October 2019; Accepted: 28 October 2019 Abstract This study focused on assessment of the bioactivities and characterization of rambutan peel extract (RPE) and the feasibility of RPE as a bioactive compound for antimicrobial and antioxidant applications in whey protein isolate (WPI)/cellulose nanocrystal film. The RPE inhibited against nine strains of pathogenic and food spoilage bacteria (Micrococcus luteus, Bacillus sp., Escherichia coli, Pseudomonas fluorescens, Salmonella typhimurium, Staphylococcus aureus, Enterococcus faecalis, Streptococcus sp. and Staphylococcus aureus). The extract also exhibited higher antioxidant activities than those of butylated hydroxytoluene (BHT) (via DPPH, ABTS and FRAP assays), α-tocopherol (via DPPH and ABTS assays) and butylated hydroxyanisole (BHA) (via hydroxyl radical and superoxide anion radical scavenging assays). The WPI/cellulose nanocrystal film containing 3% RPE exhibited moderate antimicrobial activity and strong antioxidant activity, which can be applied as a bioactive film for food packaging application. Keywords: rambutan peel extracts, antimicrobial activity, antioxidant activity, whey protein isolate film, cellulose nanocrystal