Applications of Prolamin-Based Edible Coatings in Food Preservation: A Review.

Foods are susceptible to deterioration and sour due to external environmental influences during production and storage. Coating can form a layer of physical barrier on the surface of foods to achieve the purpose of food preservation. Because of its good barrier properties and biocompatibility, prolamin-based film has been valued as a new green and environment-friendly material in the application of food preservation. Single prolamin-based film has weaknesses of poor toughness and stability, and it is necessary to select appropriate modification methods to improve the performance of film according to the application requirements. The practical application effect of film is not only affected by the raw materials and the properties of the film itself, but also affected by the selection of preparation methods and processing techniques of film-forming liquid. In this review, the properties and selection of prolamins, the forming mechanisms and processes of prolamin-based coatings, the coating techniques, and the modifications of prolamin-based coatings were systematically introduced from the perspective of food coating applications. Moreover, the defects and deficiencies in the research and development of prolamin-based coatings were also reviewed in order to provide a reference for the follow-up research on the application of prolamin-based coatings in food preservation.

Preparation and structural characterization of epoxidized soybean oils-based pressure sensitive adhesive grafted with tea polyphenol palmitate.

Vegetable oils-based pressure sensitive adhesives (PSAs) are green and sustainable but face unsatisfactory adhesion strengths and are prone to aging during storage and application due to the existence of residual double bonds and massive ester bonds. Nine common antioxidants (tea polyphenol palmitate (TPP), caffeic acid, ferulic acid, gallic acid, butylated hydroxytoluene, tertiary butylhydroquinone, butylated hydroxyanisole, propyl gallate, and tea polyphenols) were grafted into epoxidized soybean oils-PSA (ESO-PSA) system to enhance antiaging properties and adhesion strengths. Results showed ESO-PSAs grafted with caffeic acid, tertiary butylhydroquinone, butylated hydroxyanisole, propyl gallate, tea polyphenols, or TPP didn't occur failure with TPP having best performance. The optimal conditions were ESO reacted with 0.9 % TPP, 70 % rosin ester, and 7.0 % phosphoric acid at 50 °C for 5 min, under which peel strength and loop tack increased to 2.460 N/cm and 1.66 N, respectively, but peel strength residue reduced to 138.09 %, compared with control (0.407 N/cm, 0.43 N, and 1669.99 %). Differential scanning calorimetry and thermogravimetric results showed TPP grafting increased the glass transition temperature of ESO-PSA slightly but improved its thermal stability significantly. Fourier transform infrared spectroscopy and 1H nuclear magnetic resonance results showed TPP, phosphoric acid, and rosin ester all partially participated in the covalently crosslinking polymerization of ESO-PSAs and the rest existed in the network structures in the free form.

Epoxidized Soybean-Oils-Based Pressure-Sensitive Adhesives with Di-Hydroxylated Soybean-Oils Copolymerizing and Antioxidant Grafting.

Vegetable-oils-based pressure-sensitive adhesives (PSAs) are being developed as a substitute for petrochemical-based PSAs for application in daily life. However, vegetable-oils-based PSAs face the problems of unsatisfactory binding strengths and easy aging. In this work, the grafting of antioxidants (tea polyphenol palmitates, caffeic acid, ferulic acid, gallic acid, butylated hydroxytoluene, tertiary butylhydroquinone, butylated hydroxyanisole, propyl gallate (PG), tea polyphenols) was introduced into an epoxidized soybean oils (ESO)/di-hydroxylated soybean oils (DSO)-based PSA system to improve the binding strengths and aging-resistant properties. PG was screened out as the most suitable antioxidant in the ESO/DSO-based PSA system. Under optimal conditions (ESO/DSO mass ratio of 9/3, 0.8% PG, 55% rosin ester (RE), 8% phosphoric acid (PA), 50 °C, and 5 min), the peel adhesion, tack, and shear adhesion of the PG-grafted ESO/DSO-based PSA increased to 1.718 N/cm, 4.62 N, and >99 h, respectively, in comparison with the control (0.879 N/cm, 3.59 N, and 13.88 h), while peel adhesion residue reduced to 12.16% in comparison with the control (484.07%). The thermal stability of the ESO/DSO-based PSA was enhanced after PG grafting. PG, RE, PA, and DSO were partially crosslinked in the PSA system, with the rest being free in the network structures. Thus, antioxidant grafting is a feasible method for improving the binding strengths and aging-resistant properties of vegetable-oils-based PSAs.