Preparation and characterization of berry anthocyanin-loaded konjac glucomannan emulsion for pH-sensitive active food packaging films

Konjac glucomannan (KGM) is a high-potential biodegradable candidate to replace conventional petroleum-based food packaging films. Nevertheless, pure KGM materials suffer from the absence of antioxidant, antibacterial, and pH-sensing capacities, which severely restricts their practical applications in food preservation. To address these drawbacks, this study fabricated intelligent KGM-based emulsions incorporated with anthocyanins derived from four berry sources, including blueberry, blackcurrant, blue honeysuckle, and black wolfberry (denoted as BBA, BCA, BHA, and BWA, respectively), aiming to expand the application scope of KGM in active food packaging. A total of 13, 4, 5, and 13 unique anthocyanin components were successfully identified in BBA, BCA, BHA, and BWA, respectively, with distinct chemical structures among the four anthocyanin fractions. Specifically, BBA, BCA, and BHA were characterized by glycosylated anthocyanins, whereas BWA exclusively contained acylated anthocyanins. All anthocyanin samples exhibited prominent pH-responsive color-switching behaviors over a wide pH range of 2–13, with BWA showing the most significant color variation. In addition, these berry anthocyanins possessed excellent DPPH and ABTS radical scavenging abilities, as well as effective inhibitory effects against Escherichia coli and Staphylococcus aureus . Fourier transform infrared analysis confirmed that anthocyanins could be firmly incorporated into the KGM matrix through hydrogen-bonding interactions, which effectively endowed the fabricated KGM emulsions with reversible pH-sensitive color variation, superior antioxidant capacity, and prominent antibacterial activity. Moreover, the resultant composite emulsions exhibited moderately reduced swelling capacity and optimized water vapor permeability, achieving desirable physicochemical properties for food packaging films. The fabricated KGM-anthocyanin composite emulsions integrate real-time pH monitoring, antioxidant, and bacteriostatic functions, as well as excellent mechanical performance, thereby can be use to develop for pH-sensitive active food packaging films.