Our project developed a transgenic cell system for anthocyanin biosynthesis by methods of genetic engineering and cell engineering. With the help of a series of experimental verification and data comparison, we found that this anthocyanin biosynthesis system has a short harvest period, a high yield of anthocyanins and produces less waste, and is not affected by changes in external environment. Thus, this anthocyanin biosynthesis system can be amplified for large-scale production of anthocyanins.
The anthocyanins produced in larger quantity and shorter terms by our biosynthetic system can not only meet people's demand for natural food pigments with anti-ageing effects, but also better satisfy people's demand for diversified food colours. At the same time, it can also be used to make food packaging materials with a visual inspection function of food quality.
At present, the industrial production of natural anthocyanins is mainly based on anthocyanin-rich berries of different plants, such as grapes, Blueberry, Blackberry, cherry, Black Currant, etc. Not only do these plants have a long harvest period, they also suffer from climate change and seasonal changes. Therefore, the yield of anthocyanins from these plants is often unstable due to the instability of raw material sources. In addition, since the cultivation and growth of these plants require a large amount of farmland, it is not suitable for large-scale cultivation in countries or regions with a large population but insufficient arable land. Thus, it is difficult to achieve large-scale production of anthocyanins based on raw materials of plants.
The anthocyanin biosynthesis system developed here can be carried out in the production workshop. The anthocyanin-rich carrot hairy roots obtained by transgenic methods can satisfy the conditional requirements for inducing and producing anthocyanins after about 30 days of culture at room temperature and in the dark (Figure 1). As long as the hairy roots are kept being propagated and cultured indoors incessantly, a steady supply chain of raw materials can be obtained, and mass production of anthocyanins can be achieved regardless of the seasons, the climate and cultivated land limit.
Consumers usually have a variety of demands for food colour. Giving food brighter colours adds to its appeal and increases people’s appetite, and sometimes food colours need to be modified for aesthetic reasons. The main type of food colourant used is chemically synthesized, but right now people began to reject its use due to possible health concerns. For example, a common type of artificial red colouring, carmine, is known to cause cancer. Customers now prefer to choose natural food colourants produced from natural sources. However, mass production of natural food colouring is expensive and hard to purify. For instance, people usually use juices of fruits and vegetables to colour desserts, but these colourants cannot be produced in great quantities and are wasteful if produced in greater amounts.
As anthocyanins can present different colours as pH changes in the environment, they can not only provide different colours for different foods, but also give the same food different colours by fine-adjusting the pH value of the food itself.
Below is an experiment to illustrate the colour-changing ability of anthocyanin. The raw juices are watermelon juice, jujube juice, tomato juice and grape juice, were light red, light green, pink and dark green respectively with their pH 5.71, 4.56, 4.48 and 4.24 of each. After 100 mg of dry anthocyanin-rich carrot hairy root powder were added into 1 ml of these juices separately, the juices appeared purple, dark red, red and red of each. Then 40 microliters of white vinegar (pH 2.4) were added separately and the pH of these juices was adjusted. All of the colours became lighter and brighter immediately (Figure 2-4)
As the result, anthocyanins obtained by mass production with this biosynthesis system can not only meet people’s demand for natural food colourings in quantity, but also meet that in quality.
Figure 2 Raw colours of juices
From left: watermelon, jujube, tomato and grape
Figure 3 Colours of juices adding with dry anthocyanin-rich carrot hairy root powder
From left: watermelon, jujube, tomato and grape
Figure 4 Colours of juices adding with dry anthocyanin-rich carrot hairy root powder and white vinegar
From left: watermelon, jujube, tomato and grape
All foods have a certain shelf life. Some substances of the food itself will degrade or undergo other chemical reactions that lead to spoilage over time. In many cases, it is difficult to judge the small changes in food quality with the naked eye, especially in early stages. This causes trouble for the general consumers when selecting the qualified products and avoiding eating spoiled food.
Spoilage often causes irreversible and gradual changes in the pH value of the food. Anthocyanin is extremely sensitive to pH changes in the environment and it is a non-toxic, edible natural pigment. So, can we use anthocyanins as indicators of food spoilage?
In our project, 5 buffer solutions were prepared with pH values of 4, 5, 6, 7, and 8 respectively. The solutions showed purple-red in varying levels after 100 mg of dry anthocyanin-rich carrot hairy root powder. After the buffer was acidified by adding a same amount of HCl solution, the solutions became bright red at varying levels. In the end, they turned purple in varying levels when a same amount of NaOH solution was added respectively. (Figure 5).
It was shown that, on the one hand, anthocyanins can be used to indicate the spoiling of food while it was used as a colouring additive. On the other hand, anthocyanins can be added to produce food packaging materials (such as packaging film) so that people can judge whether the food has deteriorated or not through the colour change on the packaging.