Effects Of Low Temperature Storage On Properties Of Edible Films Based On Plant Protein And The Elementary Study For Mechanism

The utilization of plant protein films rely highly upon relative humidity and temperatureenvironments. Extreme humidity or temperature can alter the inherent mechanical and barrierproperties of edible protein films. Recently, the application of SPI films at low temperatureshas drawn some research interests since the relative humidity fluctuates much less in thelow-temperature environment. This study was to develop the Soybean Protein Isolate (SPI)and Wheat Gluten (WG) composite edible films, respectively. The differences of Tensilestrength (TS), Elongation at break (EAB), Water vapor permeability (WVP), PermeabilityCoefficient of Oil (PO) and Water Solubility (WS) were determined under low temperatureenvironments and during freezing-microwave defrosting circles, which aimed to evaluate thestability properties of the films. Meanwhile, the color values and the variation of sulfydrylcontent were investigated and Fourier transform infrared spectroscopy was applied to studytransformations of the functional group and secondary structure, which tried to explore thechanges of the film properties from the microscopic structure and aimed to discuss thefeasibility of its application in the cold chain market.After equilibrium, the effects of storage temperatures and times on properties of SPI filmsand WG films were evaluated. The mechanical and barrier properties of the SPI film changedlittle when the cold storage temperature increased. Specially, WG films TS was not affectedsignificantly by the cold storage temperature (p>0.05). However with SPI films, the WVP wasinfluenced significantly. With the decreasing of the frozen storage temperature, EAB of SPIfilms and TS of WG films decreased rapidly. Nevertheless, WVP of SPI films ascendedslightly and PO had no significant change above-20℃.TS of films experienced a slight growth, then descended gradually when the cold andfrozen storage time extended. Similar trend presented to EAB of SPI films but only with coldstorage conditions. EAB of WG films went up gradually along whole period. WVP of SPIfilms transformed more greatly during frozen storage. Both SPI and WG films could keephigh barrier properties of water in the following30days. However, PO of WG films wasinfluenced by storage time significantly.TS and EAB of SPI films plunged steadily with the number of freezing-defrosting timesincreased. WVP of SPI films showed a remarkable difference at the third time offreezing-defrosting circle（p <0.05）. The amplitude of variation of WVP was moderate, but the variation between the first time after defrosting and the control sample was bigger thanSPI films. No matter whether SPI films or WG films, the color was darker than that of theoriginal powder. The amount of dissociate sulfydryl of WG films declined significantly(p<0.05) during the storage. In addition, films could be influenced by frozen temperaturemore significantly than by cold temperature. The mechanical properties of SPI films couldmaintain at original level practically, and even during the first freezing-defrosting circle.However, the appearance of SPI films turned yellowness marginally.