PROPERTIES OF SOY PROTEIN ISOLATE ANTIMICROBIAL FILMS AND ITS APPLICATION IN PRESERVATION OF MEAT
Recently, increasing interest to improve food safety and extend their shelf-life has led to the development and testing of the edible films with antimicrobial properties. The soy protein isolate (SPI) antimicrobial films were made with Nisin (N), sodium lactate (NaL), EDTA (E) and their optical combination (C). The C film showed a significant (p<0.05) antimicrobial effect on three food pathogens, E.coli, Salmonella and Bacillus cereus, which inhibitory zone is 32mm, 33.33mm and 32.33mm, respectively. The addition of N and NaL to SPI film reduced its mechanical properties, that is, the tensile strength (TS) was reduced from 10.8716MPa to 8.1405MPa (N1) and 3.2715MPa (NaL3) and the elongation at break (E) was increased from 3.03% to 4.73% (N3, N4) and 11.21 % (NaL4). While the addition of EDTA and combination increased TS from 10.8716MPa to 17.0600MPa (E4) and reduced E from 3.03% to 2.36% (E1). The water vapor permeability (WVP), oxygen permeability (OP) and total color difference (ΔE) of films had changed with the addition of antimicrobial agents. The FTIR analysis showed no specific interaction between active groups of Nisin with functional group of control film. However, the intensity of peaks in the spectrum of NaL and EDTA increased, indicating interactions between NaL, EDTA and SPI.
The application experiments showed the total bacterial count and TVB-N value of sample wrapped by ordinary wraps, SPI film and SPI antimicrobial film were incresed as storage time extended. On the 6th day, the sample wrapped by SPI film has been metamorphism, which total bacterial count and TVB-N value were 8.922 lg cfu/g and 21.340 mg/100g. On the 9th day, the sample wrapped by ordinary wraps has been metamorphism, which total bacterial count and TVB-N value were 7.866 lg cfu/g and 21.150 mg/100g. And the sample wrapped by SPI antimicrobial film had been metamorphism on the 12th day, indicating that the SPI antimicrobial film had a bacteriostatic preservation effect on the meat antibacterial preservation and extend the shelf life to 3-6 days compared with SPI film and ordinary wraps. The SPI antimicrobial film broadens the application of SPI film.