Tannic acid: A green crosslinker for biopolymer-based food packaging films

Due to biomaterials' biodegradable, biocompatible, sustainable, and renewable nature, there is growing interest in developing biopolymer-based food packaging films based on green ingredients and strategies. To improve the performance of biopolymer-based food packaging materials, either by modifying the biopolymer molecules or combining them with various additives, including nanomaterials, crosslinkers, bioactive compounds, and other polymers. Among them, green crosslinking technology is considered an effective method to improve the performance of degradable food packaging films. Tannic acid is widely used as a natural green crosslinker in different biopolymer-based films. In this review, after an overview of tannic acid chemistry, different types of biopolymer-based food packaging materials crosslinked by tannic acid have been discussed in detail. In addition, this work summarizes the application of tannic acid crosslinked biopolymer-based food packaging films/coatings for food preservation in recent years. The crosslink of tannic acid could improve the performance of biopolymer-based films comprehensively. The effect of tannic acid on the properties of different films is mainly related to its addition concentration and reaction state, where the crosslinking of tannic acid with polymer molecules increases the cohesion of the polymer network. The crosslinking between tannic acid and polymers occurs, including physical and chemical covalent crosslinking. Importantly, biopolymer-based food packaging films/coatings crosslinked by tannic acid have shown surprising effects in preserving fresh foods.