## 4 Industrial Production of Caroenoid
### Production System and Mechanism in Industrial Scale  
On an industrial scale, there are three different methods of producing carotenes. The first is a physicochemical method, which is the more traditional method of production that involves extracting carotene-containing plant material. Carotenoids are commercially extracted from green plant parts such as roots, flowers, and fruits. Additionally, these pigments are found in vegetable crops such as carrots and tomatoes. Carotene is located in the thylakoid membrane, which is an organelle in chloroplasts. The primary disadvantage of this technology is its high production cost, which is geographically and seasonally dependent on obtaining high-quality raw materials. Chemical synthesis is the second method. Since 1950, researchers have been attempting to chemically synthesize carotenoids [97]. Synthetic carotenoids are now widely used as colors and feed additives. Lycopene, canthaxanthin, astaxanthin, \(\beta\)-carotene, and citranaxathin are the carotenes that have been effectively manufactured on an industrial scale [97]. The third method, known as microbiological biosynthesis. This method takes advantage of microorganisms that can produce carotene naturally. Those microorganisms will be grown and chemically extracted to produce the required pigments. The production process of carotenoids in industry are summarized [97; 98; 99] and visualized in Figure 6. This process has several advantages that compensate for the disadvantages of traditional methods, including low production costs, greater control, a shorter manufacturing time, and a natural end product. Because the use of synthetic carotene is currently restricted in the industrial sector, this approach is regarded as the best choice to replace it [97; 100]. Increasing the efficiency of caroten biosynthesis is one strategy to boost caroten output with this method. The amount of enzyme and its activity level, as well as the amount of carbon or precursors accessible in the external environment, influence caroten biosynthesis [101]. Carotene production in microbes can be increased by providing stimulants and optimizing environmental conditions during the cultivation process. The addition of mevalonic acid as a precursor was found to increase caroten formation by 120% in _R. mucilaginousa_ and 35% in _R. glutinis_[102]. Currently, there are three biosynthetic approaches that can be used to increase carotenoid production, including pathway engineering (metabolic engineering), host genetic modification, and protein engineering for enzyme and pathway optimization [103]. Metabolic engineering is the alteration of metabolic pathways with genetic modifications, such as the introduction of new genes with recombinant DNA technology. The goal of metabolic engineering is to employ molecular biology tools to conduct a systematic investigation of metabolic pathways in order to optimize cell properties through rational genetic modification [72]. Insertion of the _crtE_ gene from the bacteria _P. agglomerans_, chromosome integration of the MVA pathway, and insertion of the _idi_ gene into the _E. coli_ chromosome can increase the production of carotenoids (lutein) [104]. To increase the production yield, it is also necessary to consider the key enzymes, which are the limiting factors in the production of carotenoids. Enzymes with enhanced activity and improved gene expression associated with carotenoid synthesis are necessary for future improvements. For example, in the production of \(\beta\)-carotene, the enzyme resulting from the translation of the _crtYB_ gene becomes a limiting enzyme; thus, it must be produced in higher amounts than other enzymes to obtain higher caroten production [105]. Carotenoid production via operons could also be increased by changing the bioparts i.e., regulatory bioparts used in the genetic circuit [106]. These two concepts create a gap in the need for bioparts that can increase the expression of carotenoid-producing genes and produce higher enzyme activity.