Characterizing polyphenols as protein plasticizers to create edible, sustainable plastic packaging alternatives

Justification 

Plasticizing proteins with phenolic compounds may enable the creation of sustainable food-grade packaging. 

Objective   

We aim to characterize the plasticizing effects of isolated polyphenols on protein films and their interactions.  

Methods 

Protein films were prepared by dissolving gluten, soy, pea, or faba proteins in formic acid containing glycerol (12, 16, or 20% w/w protein) and gallic acid (10% w/w protein). The solutions were cast into Petri dishes (8.5 cm diameter) and dried overnight. After equilibration at 55% relative humidity, the films were analyzed for tensile strength and elongation using a texture analyzer. The film’s water-holding capacity (WHC) and aqueous stability were evaluated at pH 2 and 7. 

Results 

Preliminary testing showed promising elongation properties in films of pea, soy, and faba protein dissolved in formic acid compared to plastic films. Pea, soy, and faba protein films elongated 33-75% as far as sandwich bag and cling wrap films. Moreover, initial data suggest that adding polyphenols to films further enhances flexibility and affects WHC. We found that 10% gallic acid along with 20% glycerol improved elongation in soy and faba films by 24% and 34%, respectively. Thus, gallic acid acted as a plasticizer and improved film flexibility. Faba protein films with 10% gallic acid and 16–20% glycerol exhibited a 17% higher WHC at pH 2 but lower WHC at pH 7. Polyphenols are hypothesized to improve WHC by crosslinking with proteins, giving an increased ability to hold water more efficiently. Future work will explore the effects of various polyphenols on film properties. 

AOCS Significance   

This work expands the knowledge of how proteins could be used to make a sustainable plastic alternative for food and product packaging.