A Review of the Use of Microscopic Algae as Biological Sensors for Identifying Environmental Pollutants and Smart Packaging of Food Materials

Intelligent food packaging as a new technology can maintain the quality and safety of food during its shelf life. This technology uses indicators and sensors that are used in packaging and detects physiological changes in food (due to microbial and chemical degradation). These indicators usually provide information that can be easily identified by the food distributor and the consumer. However, most of the markers currently used are non-renewable and non-degradable synthetic materials. Microalgae that live in both marine and freshwater are a versatile solution for building new biosensors to detect pollutants such as herbicides or heavy metals. These photosynthetic microorganisms are very sensitive to their environmental changes and allow the detection of pollutants. In the past few years, several studies have been conducted in relation to the development, evaluation and application of biosensors using natural compounds in smart food packaging, and some of them are reported and summarized in Table 2.

In these studies, examples are mainly focused on biosensors related to biopolymers, but some other synthetic polymers that are easily degraded have also been used as examples. In Table 2, it is also specified what the function and application of the sensor is and how it reacts to the loss of freshness of food. Most sensors are sensitive to the change in pH caused by the release of volatile nitrogen compounds, and this change is characterized by a colorimetric response. Sensors are usually placed in the space above the food container, avoiding direct contact with the food, but close enough to detect changes in the environment and respond to changes in food quality. When these biosensors are integrated with biopolymers, they are usually incorporated into the polymer structure, and the color change of the layers (film) indicates changes in food quality in the packed product. The collected information also clearly shows that extracts rich in chemical compounds of pigments that change color with pH and especially anthocyanins have been used in these biosensors. In addition, most studies of biosensors have been conducted on fish, meat, and seafood, which is probably because their quality degradation is an important economic loss and also because the pH of the surrounding environment is changed during the degradation process. , and this change is easily detected through pH-sensitive biosensors. Smart food packaging technology has made it possible to monitor food quality by incorporating markers, sensors and radio frequency identification (RFID) into packaging. The technology also allows producers and consumers to trace the history of a product through important points in the food supply chain.Interestingly, some compounds applied and tested in the sensor not only provide a pH-sensitive dye, but also have other bioactive properties, for example, antimicrobial properties, and its presence in the polymer matrix can also increase the storage activity of packaging materials.

This paper shows that microalgae can be used as biosensors to detect pollutants such as herbicides, heavy metals and volatile organic compounds. These biosensors are very sensitive and reproducible for physical or chemical analysis. One of the main advantages of these microalgal biosensors is that repeated measurements can be performed without extensive sample preparation. They can also be selective, for example chlorophyll fluorescence emitted from photosynthetic activity allows the detection of herbicides, while inhibition of alkaline phosphatase and esterase allows the determination of heavy metals and organophosphate insecticides. Recently, great progress has been made in the identification of genes and related pathways in microalgae, and powerful techniques for genetic engineering have been developed. Collectively, the progress achieved in these areas will rapidly increase our ability to genetically optimize the production of more sensitive microalgae-based biosensors.