A research group consisting of scientists from the Faculty of Engineering and Technology, Van Hien University, and the Faculty of Chemical Engineering, Ho Chi Minh City University of Technology, has developed an entirely new smart indicator using pectin and betalains extracted from the peel of red dragon fruit (Hylocereus polyrhizus), aiming to monitor beef freshness effectively. What sets this study apart from previous research is the sequential extraction process of betalains and pectin from the same raw material, allowing for maximum utilization of red dragon fruit peel—a common agricultural by-product—while contributing to sustainable and effective environmental waste reduction.
During development, betalains were micro-encapsulated in microcrystalline cellulose—a modification that markedly improved pigment stability against light, oxygen, and heat. Encapsulation preserves the vivid hue of betalains, ensuring a clear visual signal when beef begins to spoil.
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Figure 1. Process of making the freshness indicator from red dragon fruit peel
The smart indicator film is made from a mixture of pectin extracted from dragon fruit peel and polyvinyl alcohol (PVA), with betalains serving as the active indicator compound. Experiments were conducted to optimize the composition, identifying the ideal betalain concentration as 0.08% and the optimal pectin:PVA blending ratio as 4:6 (w/w). With this formula, the indicator film demonstrated several outstanding advantages, including effective UV-blocking capability, high mechanical strength, and especially good water vapor barrier properties, which help protect food during storage and transportation.
Figure 2. Surface morphology of the indicator film
A key highlight of the study is the functional property of the smart indicator film—its color response to specific environmental conditions such as pH and the presence of ammonia gas. Experimental results showed a distinct color change when exposed to solutions of varying pH levels: retaining red in acidic to neutral environments (pH 3 to 7) and gradually shifting to reddish-brown and then yellow in alkaline environments (pH 8 to 12) (Figure 3). This makes it highly useful for monitoring and identifying food quality changes due to pH fluctuations during storage.
Additionally, the indicator film responded quickly and sensitively to ammonia vapor—a key sign of spoilage in protein-rich foods. In ammonia exposure tests, the film changed from red to noticeable brownish-yellow within a few hours and completely turned yellow after 24 hours, demonstrating a highly effective and intuitive indication (Figure 4).
Figure 3. Color response of the indicator film at different pH values
Figure 4. Color response of the indicator film to ammonia over time
One of the significant findings of the study is the film’s ability to clearly change color over the course of beef storage. As spoilage begins, the increase in total volatile basic nitrogen (TVB-N) levels triggers a color change from reddish-pink to brownish-yellow, which can be easily observed with the naked eye. Specifically, in real-world tests, this color change was clearly recorded after 6 days of cold storage at 2–4°C (Figure 5), allowing consumers and retailers to quickly assess food quality without the need for complex analytical methods.
Figure 5. Detection of beef spoilage after 6 days of storage at 4°C
Beyond visual color indication, the film also exhibits other important bioactive properties. Laboratory tests confirmed its strong antibacterial activity, particularly against Escherichia coli. Furthermore, the indicator film shows promising antioxidant capabilities, which can help reduce lipid oxidation and protect food from quality degradation.
These outstanding properties not only demonstrate the practical application potential of the smart indicator film in the food industry but also affirm the economic and environmental value of efficiently utilizing agricultural waste. This innovation paves the way for developing intelligent, safe, and eco-friendly packaging, contributing to sustainable societal development in the future.
This study has been published in the journal Waste and Biomass Valorization.
Reference:
Mang, T.T.X., Dang-Bao, T. & Tran, U.P.N. (2025). A Smart Indicator of Beef Spoilage Using Pectin and Betalains from Red Dragon Fruit (Hylocereus polyrhizus) Peels. Waste Biomass Valor. https://doi.org/10.1007/s12649-025-02900-5