Alginate hydrogel beads containing anthocyanins as a freshness indicator for intelligent food packaging
Abstract
Intelligent food packaging systems are designed to provide dynamic information about products to different stakeholders within the supply chain, including consumers, retailers, and distributors. One such example is the utilization of colorimetric indicators based on anthocyanins in meat and seafood packaging. These indicators undergo noticeable color changes in response to microbial growth, production of volatile amines and changes in the pH of the headspace, attributed to the presence of anthocyanins. These color changes can be directly linked to real-time alterations in product quality. Such interactive packaging systems enable ongoing monitoring of product freshness throughout transportation, distribution, storage, and marketing stages and subsequently reduce food waste.
The present doctoral thesis introduces anthocyanin-loaded alginate hydrogel beads as a novel colorimetric indicator for quality monitoring of meat and seafood products. To this aim, the fundamental features of colorimetric indicator systems applicable in intelligent packaging were investigated. This encompassed the production and characterization of indicators, stability studies, analysis of color response to volatile amines, and evaluation of their effectiveness in packaging two commercial products.
Purple corn extract, renowned for its abundant anthocyanin content, was encapsulated within alginate hydrogel beads using electrostatic extrusion. The optimal conditions for encapsulation were determined, resulting in two types of hydrogel beads with the highest encapsulation efficiency and targeted particle sizes: F1, characterized by maximum encapsulation efficiency and minimum particle size, and F2, featuring maximum encapsulation efficiency with large particle size. The optimal hydrogel beads were characterized in terms of moisture content, encapsulation efficiency, water activity, antioxidant activity, total phenolic content, cyanidin- 3-glucoside content, and color parameters. Morphological studies, along with the Brunauer, Emmett, Teller technique, revealed larger pore volume and pore size, as well as more surface cracks on F2 compared to F1.
The potential of anthocyanin-loaded alginate hydrogel for intelligent packaging applications was assessed by evaluating their storage stability and sensitivity to volatile amines. F1 exhibited higher stability of cyanidine-3-glucoside under light, dark, and 97% relative humidity conditions than F2, thus confirming the results of morphological and pore characteristics. Furthermore, color stability studies conducted in darkness at 4 °C and 97% relative humidity demonstrated that the alginate hydrogels containing anthocyanin retained their color. However, this was not the case under accelerated light conditions. Additionally, the fabricated hydrogel beads responded to different concentrations of ammonia, trimethylamine, and dimethylamine.
The limit of detection for each metabolite was also determined. The application of anthocyanin-loaded alginate hydrogel beads was extended to shrimp and minced chicken packaging. According to shrimp quality parameters such as microbial growth, TVB-N, pH, K-value, H-value, and biogenic amines, both F1 and F2 displayed a transition from pink and reddish hues to pale violet and purple, respectively, on the 5th day of storage, indicating a semi-fresh state. On the 7th day, these colors further shifted to light green and brown, signifying spoilage. The color changes of the indicators in minced chicken were subtle and did not show strong correlations with certain spoilage parameters, suggesting that the effectiveness of the alginate hydrogel beads containing anthocyanin as freshness indicators may be limited to seafood.