261
The growth period of the plant is an important parameter to consider because
reproducibility in extraction results requires a homogeneous matrix. Yet, plants do
not produce the same type of metabolites depending on the period of their growth.
Moreover, specific stress conditions (temperature, duration and intensity of lighting,
watering, etc.) could be applied to the plants for optimizing the production of
metabolites of interest. This is especially relevant in the case of polyphenols because
the type of produced polyphenols may be different in nature depending on the stress
conditions of the plants. Indeed, polyphenols are generally powerful antioxidants
protecting the plants from external attacks (insects, UV, fungi, etc.) (Naikoo et al.
2019). Their production can therefore be particularly influenced by the living conditions of plants. Our meta-analysis of ca. 100 publications shows that only 24% of
publications dealing with the extraction of polyphenols quote the harvest period of
the raw materials.
A careful selection of the part of the plants (leaves, stems, flowers, roots, etc.) is
equally important for extraction. Feduraev et al. have shown that phenolic compound compositions depend on the part of plants with an accumulation in the leaves,
seeds, and flowers for Rumex crispus and Rumex obtusifolius (Feduraev et al. 2019).
But in some cases, the whole plant (or algae) is chosen.
For the sample preparation before extraction, the plant is usually dried by freezedrying (Jeong et al. 2015; Dai et al. 2016; Cvjetko Bubalo et al. 2016; Radošević
et al. 2016; Bosiljkov et al. 2017; Karageorgou et al. 2017; Fernández et al. 2018a;
Shang et al. 2018; Panić et al. 2019a, b; Saha et al. 2019; Xu et al. 2019) or in an
oven between 30 and 70 °C (Li et al. 2015; Mouratoglou et al. 2016; Tang et al.
2017; Cao et al. 2018a, b; Ozturk et al. 2018; Fraige et al. 2019; Kanberoglu et al.
2019; Panić et al. 2019b; Rajha et al. 2019; Mansur et al. 2019). Phenolic compounds could be sensitive to temperature or light; therefore, plants’ drying is often
performed away from the light or even at room temperature for several days (Wei
et al. 2015a; Yao et al. 2015; Cui et al. 2015, 2018; Peng et al. 2016; Li et al. 2016;
Jancheva et al. 2017; Vieira et al. 2018; Ivanović et al. 2018). However, there is no
standard protocol. For example, Karageorgou et al. chose to wash the Moringa oleifera leaves prior to freeze-drying, while Hamany Djande et al. directly air-dry the
leaves without prior washing (Karageorgou et al. 2017; Hamany Djande et al. 2018).
Then, the raw material is grounded. The grinding can have a strong influence on
the extraction (Komaty et al. 2016). Indeed, intensive grinding can lead to heating
the matter and generate degradation of the compounds. On the other hand, light
grinding can prevent good penetration of the solvent in the matter, thus reducing the
surface contact with the solvent and finally limiting the extraction (Azwanida 2015).
The grinding can be carried out by disintegrator, domestic blender, laboratory mill,
or liquid nitrogen with a mortar and pestle. The goal is to promote cell destruction
and to have a better homogeneity of the mixture, namely, in the case of soft matrix
(succulent leaf, some algae, etc.) (Wan Mahmood et al. 2019). The preparation of
the sample is obviously different depending on the raw material. For instance,
grinding virgin olive oil is not needed because it is a homogeneous liquid, while
Chanioti et al. use a cutting mill to grind the olive pomace (García et al. 2016;
Chanioti and Tzia 2018).
7 Extraction of Plant and Algal Polyphenols Using Eutectic Solvents
The growth period of the plant is an important parameter to consider because
reproducibility in extraction results requires a homogeneous matrix. Yet, plants do
not produce the same type of metabolites depending on the period of their growth.
Moreover, specific stress conditions (temperature, duration and intensity of lighting,
watering, etc.) could be applied to the plants for optimizing the production of
metabolites of interest. This is especially relevant in the case of polyphenols because
the type of produced polyphenols may be different in nature depending on the stress
conditions of the plants. Indeed, polyphenols are generally powerful antioxidants
protecting the plants from external attacks (insects, UV, fungi, etc.) (Naikoo et al.
2019). Their production can therefore be particularly influenced by the living conditions of plants. Our meta-analysis of ca. 100 publications shows that only 24% of
publications dealing with the extraction of polyphenols quote the harvest period of
the raw materials.
A careful selection of the part of the plants (leaves, stems, flowers, roots, etc.) is
equally important for extraction. Feduraev et al. have shown that phenolic compound compositions depend on the part of plants with an accumulation in the leaves,
seeds, and flowers for Rumex crispus and Rumex obtusifolius (Feduraev et al. 2019).
But in some cases, the whole plant (or algae) is chosen.
For the sample preparation before extraction, the plant is usually dried by freezedrying (Jeong et al. 2015; Dai et al. 2016; Cvjetko Bubalo et al. 2016; Radošević
et al. 2016; Bosiljkov et al. 2017; Karageorgou et al. 2017; Fernández et al. 2018a;
Shang et al. 2018; Panić et al. 2019a, b; Saha et al. 2019; Xu et al. 2019) or in an
oven between 30 and 70 °C (Li et al. 2015; Mouratoglou et al. 2016; Tang et al.
2017; Cao et al. 2018a, b; Ozturk et al. 2018; Fraige et al. 2019; Kanberoglu et al.
2019; Panić et al. 2019b; Rajha et al. 2019; Mansur et al. 2019). Phenolic compounds could be sensitive to temperature or light; therefore, plants’ drying is often
performed away from the light or even at room temperature for several days (Wei
et al. 2015a; Yao et al. 2015; Cui et al. 2015, 2018; Peng et al. 2016; Li et al. 2016;
Jancheva et al. 2017; Vieira et al. 2018; Ivanović et al. 2018). However, there is no
standard protocol. For example, Karageorgou et al. chose to wash the Moringa oleifera leaves prior to freeze-drying, while Hamany Djande et al. directly air-dry the
leaves without prior washing (Karageorgou et al. 2017; Hamany Djande et al. 2018).
Then, the raw material is grounded. The grinding can have a strong influence on
the extraction (Komaty et al. 2016). Indeed, intensive grinding can lead to heating
the matter and generate degradation of the compounds. On the other hand, light
grinding can prevent good penetration of the solvent in the matter, thus reducing the
surface contact with the solvent and finally limiting the extraction (Azwanida 2015).
The grinding can be carried out by disintegrator, domestic blender, laboratory mill,
or liquid nitrogen with a mortar and pestle. The goal is to promote cell destruction
and to have a better homogeneity of the mixture, namely, in the case of soft matrix
(succulent leaf, some algae, etc.) (Wan Mahmood et al. 2019). The preparation of
the sample is obviously different depending on the raw material. For instance,
grinding virgin olive oil is not needed because it is a homogeneous liquid, while
Chanioti et al. use a cutting mill to grind the olive pomace (García et al. 2016;
Chanioti and Tzia 2018).
7 Extraction of Plant and Algal Polyphenols Using Eutectic Solvents