**3. Solvents used to obtain anthocyanidins**

In this section, literature related to the use of solvents during anthocyanidin extraction process is reviewed. Some differences in the material properties depending on the solvents used during its different chemical processes to obtain viable natural dye are expected. The same situation for anthocyanidins prevails, because different processes are used to obtain anthocyanidins in which it is needed to use different solvents resulting in behavior and property changes.

#### **3.1 Anthocyanidin extraction**

Anthocyanidin-rich extracts can be prepared from fresh, frozen, or dried plant materials. Examples of plants rich in anthocyanidins include blueberry [34], elderberry [35], and purple corn [36], among others. The particle size of source materials is an important factor during extraction; milling or grinding procedures among others are used with the goal of increasing surface area as well as the amount of compound obtained from the extraction process. Liquid nitrogen or lyophilization procedures may be complementary options during the grinding step to reduce anthocyanidin degradation. These are important recommendations given that the compounds involved may be subject to degradation caused by various factors, when carrying out the extraction procedure.

A general classification of extraction procedures is based in its phase used during the procedure such as solid or liquid extraction. Solid extraction is applied to liquid matrices, typically only during purification rather than extraction due to saturation of the absorbents. In the case of liquid extraction, a better recovery yield of anthocyanidins may be expected and for this reason, it is the more commonly used technique to extract these pigments from fruit sources. An important note captured from the literature is that there is a general practice that anthocyanidins are extracted with acidified water and polar organic solvents (methanol, ethanol,

**193**

calculations.

survival.

*Solvent Effects on Dye Sensitizers Derived from Anthocyanidins for Applications in Photocatalysis*

The extraction system can also require subsequent analytical procedures, which is an important consideration. For example, it is noticed that less polar solvents (such as ethanol and acetone) used for the extraction of anthocyanidins from haskap berries compressed the Sephadex LH-20 gel used for extract purification [38]. This step has been considered responsible for favorable results such as longer retention times when the fractions were analyzed by high-performance liquid chromatography and, additionally, the co-extraction of impurities. Less favorable notes that can be mentioned from this study relate to how acetone had a low extraction efficiency and formed anthocyanidin-derived complexes (5-methyl-pyranoantho-

In relation to the techniques, various methods have been developed to increase the efficiency of liquid extractions, decrease the processing time, and minimize the use and exposure to organic solvents. Examples are supercritical fluid extraction [39], pressurized liquid extraction [40], microwave-assisted extraction [41], and

Undoubtedly, solvents may be considered very important in the food, agrochemical, chemical, and biotechnological, among others, process technologies. New streams of scientific research related to solvents are good alternatives for new experimentation. It may be worth mentioning the more relevant advances in this matter during the past two decades where supercritical fluids, ionic liquids, and deep eutectic solvents became the most outstanding subjects actively investigated as potential green solvents [43], in particular for the research associated with food,

Another important perspective is solvents applied in industry, where the value of the products is not only dependent on the production costs themselves but also on the way of production. A critical aspect on the solvent selection for any process including industrial processes is related to safety. An aspect is avoiding the use of chemicals that are potentially dangerous for human health but extends also to have a solvent environmentally friendly including its disposal and also of the waste products containing the solvent. Nowadays, all these aspects need to be considered when real costs of production are calculated. For these reasons and the regulations, green technology is becoming an essential part of process cost and impact estimations. Above all, green technology is a critical aspect for solvent technology and starts as the first action to improve production processes including long and shortterm impact [43] and relates directly on environmental matters and thus on earth

In this section, DFT calculation results from our own research are displayed and analyzed. The first set of results contains ground state data, mainly related to energy results including molecular orbitals, energy gap, and relevant chemical properties. In the second set of results are included excited state data with their corresponding molecular orbital diagrams and absorption spectra based on TDDFT

and acetonitrile) due to their hydrophilic nature [37, 38]. More recently, other solvents have been used (e.g., lactic acid-glucose and choline chloride-malic acid mixtures) in an attempt to increase green alternatives to extract anthocyanidins to

*DOI: http://dx.doi.org/10.5772/intechopen.87151*

cyanin) which were not found in fresh fruits [38].

ultrasound-assisted extraction [42].

**3.2 Solvents used to obtain anthocyanidins**

flavors, fragances, and medicinal plants.

**4. DFT calculations, results, and discussion**

avoid toxic methodologies [37].

*Solvent Effects on Dye Sensitizers Derived from Anthocyanidins for Applications in Photocatalysis DOI: http://dx.doi.org/10.5772/intechopen.87151*

and acetonitrile) due to their hydrophilic nature [37, 38]. More recently, other solvents have been used (e.g., lactic acid-glucose and choline chloride-malic acid mixtures) in an attempt to increase green alternatives to extract anthocyanidins to avoid toxic methodologies [37].

The extraction system can also require subsequent analytical procedures, which is an important consideration. For example, it is noticed that less polar solvents (such as ethanol and acetone) used for the extraction of anthocyanidins from haskap berries compressed the Sephadex LH-20 gel used for extract purification [38]. This step has been considered responsible for favorable results such as longer retention times when the fractions were analyzed by high-performance liquid chromatography and, additionally, the co-extraction of impurities. Less favorable notes that can be mentioned from this study relate to how acetone had a low extraction efficiency and formed anthocyanidin-derived complexes (5-methyl-pyranoanthocyanin) which were not found in fresh fruits [38].

In relation to the techniques, various methods have been developed to increase the efficiency of liquid extractions, decrease the processing time, and minimize the use and exposure to organic solvents. Examples are supercritical fluid extraction [39], pressurized liquid extraction [40], microwave-assisted extraction [41], and ultrasound-assisted extraction [42].

### **3.2 Solvents used to obtain anthocyanidins**

Undoubtedly, solvents may be considered very important in the food, agrochemical, chemical, and biotechnological, among others, process technologies. New streams of scientific research related to solvents are good alternatives for new experimentation. It may be worth mentioning the more relevant advances in this matter during the past two decades where supercritical fluids, ionic liquids, and deep eutectic solvents became the most outstanding subjects actively investigated as potential green solvents [43], in particular for the research associated with food, flavors, fragances, and medicinal plants.

Another important perspective is solvents applied in industry, where the value of the products is not only dependent on the production costs themselves but also on the way of production. A critical aspect on the solvent selection for any process including industrial processes is related to safety. An aspect is avoiding the use of chemicals that are potentially dangerous for human health but extends also to have a solvent environmentally friendly including its disposal and also of the waste products containing the solvent. Nowadays, all these aspects need to be considered when real costs of production are calculated. For these reasons and the regulations, green technology is becoming an essential part of process cost and impact estimations. Above all, green technology is a critical aspect for solvent technology and starts as the first action to improve production processes including long and shortterm impact [43] and relates directly on environmental matters and thus on earth survival.
