Comparison of the physical and functional properties of starch/polyvinyl alcohol films containing anthocyanins and/or betacyanins

Highlights

• Food packaging films containing anthocyanins and/or betacyanins were prepared.

• Anthocyanins and betacyanins presented distinct color-responses as a function of pH.

• Betacyanins were more compatible with the film matrix as compared to anthocyanins.

• Films containing both of the pigments were suitable to monitor pork freshness.

Abstract

Anthocyanins and betacyanins are two different types of natural pigments. In this study, active and intelligent packaging were prepared by adding anthocyanins or betacyanins or anthocyanins/betacyanins mixture (in the weight ratios of 3:1, 1:1 and 1:3) into starch/polyvinyl alcohol (PVA) films. The physical and functional properties of developed films were compared. Results showed anthocyanins were more pH-sensitive than betacyanins. However, betacyanins were more beneficial to improve the compactness of the films and had stronger hydrogen bonding interactions with film matrix as compared with anthocyanins. The addition of anthocyanins and/or betacyanins slightly decreased the crystallinity of the films but significantly increased the ultraviolet-visible light barrier, water vapor barrier, antioxidant, antimicrobial, and ammonia-sensitive properties of the films. Moreover, the barrier, antioxidant and antimicrobial properties of the films increased with the increase of betacyanins proportion. Amongst different films, the film containing anthocyanins/betacyanins mixture in the weight ratio of 1:3 presented obvious color changes when the film was utilized to monitor the freshness of pork. Our results suggested betacyanins was more beneficial to enhance the barrier, antioxidant and antimicrobial properties of starch/PVA films. Starch/PVA films simultaneously added with anthocyanins and betacyanins were more suitable to monitor the freshness of pork.

Introduction

Food packaging plays a key role in protecting products from external conditions, making them easy to transport, storage and distribution [1]. In the past, food packaging was emphasized with its appearance, size and completeness [2]. Synthetic polymer films occupy a large proportion in the field of food packaging due to their low cost, durability, good barrier and mechanical properties [3]. However, with increasing demands for environmental protection and the safety of food packaging, the fabrication of food packaging based on biodegradable and natural biopolymers (e.g. proteins, lipids and polysaccharides) has recently received attention [[4], [5], [6]].

Starch, a natural and renewable biopolymer widely distributed in many plants, is frequently selected to fabricate food packaging films due to its low cost, safety, edible and biodegradable properties [7]. However, the films made by starch alone have high water solubility and poor mechanical properties [8]. One solution to overcome the disadvantage of pure starch film is to blend it with other polymers. Polyvinyl alcohol (PVA), the biodegradable and non-toxic synthetic polymer, is one of the candidates for improve the physical properties of starch films [9].

Anthocyanins and betacyanins are two different types of natural pigments, which have many health beneficial effects, such as antioxidant, anti-cancer, anti-inflammatory, antimicrobial and neuro-protective activities [10,11]. In recent years, starch/PVA films have been reinforced with plant extracts rich in anthocyanins (e.g. purple sweet potato, jamun, red cabbage and roselle extracts) or betacyanins (e.g. red pitaya and red beet root extracts) to fabricate active and intelligent packaging [10,[12], [13], [14], [15], [16], [17], [18]]. Both anthocyanins and betacyanins can interact with starch/PVA film matrix with hydrogen bonding interactions, thereby promoting the mechanical and barrier properties of the films. Meanwhile, anthocyanins or betacyanins can improve the antioxidant and antimicrobial activities of the films. Moreover, starch/PVA films containing anthocyanins or betacyanins are pH-sensitive due to the color-response property of the two pigments [[12], [13], [14], [15]]. Therefore, anthocyanins or betacyanins can greatly improve the physical and functional properties of starch/PVA films. However, the physical and functional properties of anthocyanins-rich and betacyanin-rich starch/PVA films have not been compared till now. Moreover, since anthocyanins and betacyanins usually do not coexist in the same plant [19], the fabrication of starch/PVA films containing both anthocyanins and betacyanins has never been reported.

In this study, different starch/PVA films containing anthocyanins-rich Lycium ruthenicum extract (LRE) and/or betacyanins-rich red pitaya peel extract (RPPE) were developed. The aims of this study were: (1) to compare the physical and functional properties of starch/PVA films containing anthocyanins or betacyanins; (2) to investigate the effect of simultaneous addition of anthocyanins and betacyanins (in different weight ratios) on the physical and functional properties of starch/PVA films.