Mechanical property stability of soy protein isolate films plasticized by a biological glycerol‐based polyester and application in the preservation of fresh‐cut apples

Abstract

Soy protein isolate (SPI) film is a newly developed material used for packaging. However, its application has long been quite limited due to its poor mechanical property stability during storage. In our study, a biological glycerol‐based polyester (bio‐poly glycerol: adipic acid = 1:2 (BGP I), 1:1 (BGP II), and 2:1 (BGP III); w/w) is used as a plasticizer to enhance mechanical properties. These films were evaluated for tensile strength (TS), elongation at break (EB), water vapor permeability (WVP), moisture content (MC), glycerol emigration rate, oxygen permeability (OP), and contact angle (CA) and the morphologies of the films were visualized with a scanning electron microscope (SEM) and an atomic force microscope (AFM) for 60 days at 25°C. The TS of SPI‐BGP I, SPI‐BGP II, and SPI‐BGP III films increased by 12.94%, 18.22%, and 7.93%, respectively, and the EB increased by 23.63%, 37.27%, and 20.33%, respectively, compared to the films plasticized by glycerol. The stability of the WVP, MC, glycerol emigration rate, and OP of the films also increased, and a higher CA indicated a higher hydrophobicity in the films. The SEM and AFM images indicated that the films with BGP could form better cross‐links, so the inner structure of the film was still relatively complete and compact after storing for a period of time. The application experiments showed that the SPI‐BGP films had a good control effect on the browning reaction, effectively prohibiting the growth of microorganisms in fresh‐cut apples and extending the shelf life for at least 23 days compared to the control SPI films. Thus, the addition of a biological glycerol‐based polyester greatly broadens the applications for a SPI film. Practical applications The present study shows the mechanical property stability of SPI films plasticized by a BGP. The study also shows the application of BGP‐SPI films in the preservation of fresh‐cut apples. From the application point of view, this work could facilitate the application of SPI films on fresh‐cut fruits and various foods. Moreover, the study is helpful in understanding the cause and the mechanism of mechanical properties’ decline of SPI films during storage as well as providing help for other researchers in this field.

Synthesis and characterization of eco‐friendly poly(ε‐caprolactone) plasticizer facilitating phthalate‐free polyvinyl chloride with novel star/net‐shaped structures

“…We could evaluate the effect of branching structure on the crystallization behavior of NPCLs‐C4 and SPCLs‐C4 by means of DSC. The degree of crystallinity ( X c , %) of SPCLs as well as NPCLs were determined from the enthalpy of melting using the following equation 32–34 : Where ∆ H m is the enthalpy of samples and ∆ H m 0 is the extrapolated value of enthalpy corresponding to the melting of a 100% linear PCL, which was previously reported to be 139.3 Jg −1 , and W PCL was the weight fraction of PCL in the sample 35 . SPCL3‐C4 and NPCL3‐C4 showed sharp and strong absorption peaks at 47.6 and 42°C, respectively, while NPCL1‐C4, NPCL2‐C4, SPCL1‐C4 and SPCL2‐C4 displayed broad absorption peaks with low absorption peak intensity (Figure 3a).…”

“…Where ΔH m is the enthalpy of samples and ΔH m 0 is the extrapolated value of enthalpy corresponding to the melting of a 100% linear PCL, which was previously reported to be 139.3 Jg À1 , and W PCL was the weight fraction of PCL in the sample. 35 SPCL3-C4 and NPCL3-C4 showed sharp and strong absorption peaks at 47.6 and 42 C, respectively, while NPCL1-C4, NPCL2-C4, SPCL1-C4 and SPCL2-C4 displayed broad absorption peaks with low absorption peak intensity (Figure 3a). Crystallization temperature (T c ) in both NPCLs and SPCLs increased continuously as the molar ratio of alcohol and acid raised (Figure S3).…”

Protein‐based active films: Raw materials, functions, and food applications

“…Food source protein-based active films encapsulate or contain active substances that can inhibit the growth and reproduction of pathogenic microorganisms in the film material and inhibit food spoilage after their release into the microenvironment within the package or by coming into direct contact with the food. Xu, Cao et al (2018) reported that modified SPI films incorporating bioglycerol-based polyesters had good inhibitory effects on the browning of fresh-cut apples and effectively inhibited the growth of microorganisms in apples, extending their shelf life up to 23 days. Lin et al (2020) used natamycin encapsulated in yucca alcohol-soluble protein/carboxymethyl chitosan core-shell nanoparticles to enhance the dispersion of natamycin in water and its stability to light.…”

Storage-induced changes in plasticizer emigration and structural properties of soybean isolate protein-based composite films

“…Soy protein isolate (SPI) as a by-product of edible oil industry, has been valued in the eld of packaging for its inexpensive, biocompatible and renewable advantages [4]. SPI-based lms can be applied to degradable food packaging and coating with moderate mechanical properties and oil barrier properties [5].…”