Electrospun soy protein isolate-based fiber fortified with anthocyanin-rich red raspberry (Rubus strigosus) extracts

In this study, electrospun soy protein isolate (SPI) nanocomposite fiber mats were developed utilizing the lowest concentration possible of poly(ethylene oxide) (PEO) containing the highest levels of anthocyanin-rich red raspberry (Rubus strigosus) extract [ARRE; 20% raspberry powder in 95% ethyl alcohol/water/85% lactic acid (80:19:1; v/v/v)]. Variations in the physicochemical attributes of SPI nanofiber mats were investigated as a function of adding ARRE before and after protein denaturation. The electrical conductivity of fiber-forming solutions significantly decreased with increasing ARRE. Scanning electron microscopy (SEM) imaging did not reveal noticeable overall microstructural morphological differences (seen as beads-on-fiber structures) but slightly altered the density of beads in the electrospun SPI fibers. Fourier transform infrared (FUR) spectroscopy provided insights into the hydrogen bonding interactions between ARRE and SPI in relations to the processing methods used. Specifically, the addition of ARRE after denaturation of SPI caused the amide I bond at 1656 cm(-1) of SPI to dramatically increase, which indicates ARRE induced C 0 stretching vibration of soy protein, possibly due to the attachment of polyphenols in ARRE to the hydrophobic pockets of the soy protein side-chains. Simultaneously, the addition of ARRE after SPI denaturation imparts fiber forming solutions with a significant higher level of bioactive anthocyanins and a greater antibacterial activity against Staphylococcus epidermidis, this illustrates that anthocyanin-rich plant extracts could serve as new biological ingredients to create novel active/functionalized SPI-based nanomaterial in food systems. (C) 2013 Elsevier Ltd. All rights reserved.