4.1 Bioactive Compounds
Bioactive compounds comprise a wide variety of natural
compounds which can be found mainly in different colored
FV and offer tremendous storage of food additives,
nutraceuticals, and functional foods. Natural sources of
bioactive compounds are plants, fruits, tea, olive, algae,
bacteria, and fungi. Polyphenols like compounds can be
discovered in the environment at extreme intensity relative
to other compounds. So, to extract sufficient amounts of
bioactive compounds improved and advanced technologies
need to be applied. The common bioactive compound
extraction methods are pressurized liquid extraction, solid–
liquid, or liquid–liquid extraction, ultrasound-assisted and
microwave extractions, enzyme and instant controlled pressure drop‐assisted extractions, and supercritical and subcritical extractions (Gil-Chávez et al. 2013). The FVWs
mainly contain sterols, tocopherols, carotenes, terpenes,
polyphenols, dietary fibers like bioactive compounds which
are value-adding compounds (Kumar et al. 2017). With an
increase in food processing industries by-products and losses
of FV, there is an increase in the amount of FVWs. Thus, the
FVWs can be an alternative source to produce bioactive
compounds which will help to make farmers financially
stronger and cut the problem of managing waste.
4.1.1 Phenolic Compounds
Phenolic compounds are an assembly of diverse molecules
categorized as secondary metabolites widely found in plants.
The most commonly studied bioactive phenolic compounds
from FVWs have health beneficial properties like cardioprotective,
anticarcinogenic,
antioxidant,
and
anti-inflammatory (Haminiuk et al. 2012; Balasundram et al.
2006). The phenolic compounds generally possess an aromatic ring having hydroxy substituents. Of various compounds, tannins, flavonoids, and phenolic acids have dietary
functions. These substances are produced by plants
throughout their ordinary growth and in response to different
situations like biotic stress and UV radiation (Rispail et al.
2005). The type and number of phenolic compounds found
in fruits depend on many factors; types and maturity of
fruits, geographic location, soil composition, climate, storing
conditions, etc. (Robards et al. 1999). Varieties of FVWs
produced as a residue of asparagus, grape, olive, citrus,
apple, onion, pomegranate, potato, mango, carrot, banana,
etc., can be worthy sources of phenolic compounds (Kumar
et al. 2017). The phenolic compounds act as antioxidants and
asa substrate for oxidation reaction. The extraction and
recovery of phenolic compounds are complicated because
these compounds are highly reactive and are unevenly distributed in various forms. The soluble form of phenolic
compounds is mainly located in vacuoles (Rispail et al.
2005). Extraction, as well as recovery of phenolic compounds, are done following submerged or solid-state fermentation methods. However, the most commonly used is
solid-state fermentation due to high efficiency, high yield,
shorter time, and less costly (Martins et al. 2011).
Phenolic acids include hydroxybenzoic acid (syringic,
vanillic, gallic acid) plus caffeic, sinapic, ferulic acid like
hydroxycinnamic acids. Flavonoids are the largest group of
plant phenolics, having few molecular compounds. Tannins
are the third important group of phenolics and have relatively high molecular weight and include hydrolyzable and
condensed tannins (Balasundram et al. 2006).
Flavonols and flavones are commonly found in plants.
One or more hydroxyl groups are bound to a sugar unit
(most commonly glucose) with rhamnose and the disaccharide (Balasundram et al. 2006). Anthocyanins are another
most common and widely found flavonoids which are
accountable for blue, red, and violet colors of some FV,
although red color of orange and tomato is due to carotenoid.
In ripe berries, five classes of phenolic compounds such as
phenolic acid, flavonol, flavones, flavanonols, and anthocyanins are well present. In different types of grapes, different phenolic compounds are found. For example, red
grapes have anthocyanins, whereas white grapes have flavonols. The most common citrus fruits have only rutinosides
that are non-bitter but pummelo and sour oranges have only
flavanone neohesperidosides giving bitter taste. However,
some citrus fruits like grapefruit include both neohesperidosides and flavanone rutinosides. Phenolic compounds like
malvidin glycosides formed during wine maturation are
unaffected by sulfur dioxide bleaching. Cinnamic acid is a
foremost portion of phenolic compounds found in citrus
fruits (Robards et al. 1999). The concentration of phenolics
is different within plant tissues (Balasundram et al. 2006).
Some simple food processing like peeling of FV can abolish
a substantial share of polyphenols. In some fruits such as
grapes, the high concentration of these substances is often
present in the skin than in the pulp. For example, tannin is
complex polyphenols commonly found in the skin and seed
of grape berry. The concentration of tannins is not exactly
the same in wine produced from grapes and in the fresh
harvest fruit. Tannin is lower in wine produced from grapes
compared to fresh grapes due to loss of these compounds
during pressing and fermentation. Conversely, maximum of
the main solutes existing in the grape berry at harvest time
are present in wine composition. Limited digestion process,
physical and thermal processing, and mastication help in the
absorption of the phenolic compounds in the intestine.
Sometimes, nutrients released during digestion may interact
with other food components and form complex and colloidal
structures which may affect in absorption (Parada and
Aguilera 2007). Phenolic compounds are used as dietary
Bioconversion of Fruits and Vegetables Wastes …
149
Bioactive compounds comprise a wide variety of natural
compounds which can be found mainly in different colored
FV and offer tremendous storage of food additives,
nutraceuticals, and functional foods. Natural sources of
bioactive compounds are plants, fruits, tea, olive, algae,
bacteria, and fungi. Polyphenols like compounds can be
discovered in the environment at extreme intensity relative
to other compounds. So, to extract sufficient amounts of
bioactive compounds improved and advanced technologies
need to be applied. The common bioactive compound
extraction methods are pressurized liquid extraction, solid–
liquid, or liquid–liquid extraction, ultrasound-assisted and
microwave extractions, enzyme and instant controlled pressure drop‐assisted extractions, and supercritical and subcritical extractions (Gil-Chávez et al. 2013). The FVWs
mainly contain sterols, tocopherols, carotenes, terpenes,
polyphenols, dietary fibers like bioactive compounds which
are value-adding compounds (Kumar et al. 2017). With an
increase in food processing industries by-products and losses
of FV, there is an increase in the amount of FVWs. Thus, the
FVWs can be an alternative source to produce bioactive
compounds which will help to make farmers financially
stronger and cut the problem of managing waste.
4.1.1 Phenolic Compounds
Phenolic compounds are an assembly of diverse molecules
categorized as secondary metabolites widely found in plants.
The most commonly studied bioactive phenolic compounds
from FVWs have health beneficial properties like cardioprotective,
anticarcinogenic,
antioxidant,
and
anti-inflammatory (Haminiuk et al. 2012; Balasundram et al.
2006). The phenolic compounds generally possess an aromatic ring having hydroxy substituents. Of various compounds, tannins, flavonoids, and phenolic acids have dietary
functions. These substances are produced by plants
throughout their ordinary growth and in response to different
situations like biotic stress and UV radiation (Rispail et al.
2005). The type and number of phenolic compounds found
in fruits depend on many factors; types and maturity of
fruits, geographic location, soil composition, climate, storing
conditions, etc. (Robards et al. 1999). Varieties of FVWs
produced as a residue of asparagus, grape, olive, citrus,
apple, onion, pomegranate, potato, mango, carrot, banana,
etc., can be worthy sources of phenolic compounds (Kumar
et al. 2017). The phenolic compounds act as antioxidants and
asa substrate for oxidation reaction. The extraction and
recovery of phenolic compounds are complicated because
these compounds are highly reactive and are unevenly distributed in various forms. The soluble form of phenolic
compounds is mainly located in vacuoles (Rispail et al.
2005). Extraction, as well as recovery of phenolic compounds, are done following submerged or solid-state fermentation methods. However, the most commonly used is
solid-state fermentation due to high efficiency, high yield,
shorter time, and less costly (Martins et al. 2011).
Phenolic acids include hydroxybenzoic acid (syringic,
vanillic, gallic acid) plus caffeic, sinapic, ferulic acid like
hydroxycinnamic acids. Flavonoids are the largest group of
plant phenolics, having few molecular compounds. Tannins
are the third important group of phenolics and have relatively high molecular weight and include hydrolyzable and
condensed tannins (Balasundram et al. 2006).
Flavonols and flavones are commonly found in plants.
One or more hydroxyl groups are bound to a sugar unit
(most commonly glucose) with rhamnose and the disaccharide (Balasundram et al. 2006). Anthocyanins are another
most common and widely found flavonoids which are
accountable for blue, red, and violet colors of some FV,
although red color of orange and tomato is due to carotenoid.
In ripe berries, five classes of phenolic compounds such as
phenolic acid, flavonol, flavones, flavanonols, and anthocyanins are well present. In different types of grapes, different phenolic compounds are found. For example, red
grapes have anthocyanins, whereas white grapes have flavonols. The most common citrus fruits have only rutinosides
that are non-bitter but pummelo and sour oranges have only
flavanone neohesperidosides giving bitter taste. However,
some citrus fruits like grapefruit include both neohesperidosides and flavanone rutinosides. Phenolic compounds like
malvidin glycosides formed during wine maturation are
unaffected by sulfur dioxide bleaching. Cinnamic acid is a
foremost portion of phenolic compounds found in citrus
fruits (Robards et al. 1999). The concentration of phenolics
is different within plant tissues (Balasundram et al. 2006).
Some simple food processing like peeling of FV can abolish
a substantial share of polyphenols. In some fruits such as
grapes, the high concentration of these substances is often
present in the skin than in the pulp. For example, tannin is
complex polyphenols commonly found in the skin and seed
of grape berry. The concentration of tannins is not exactly
the same in wine produced from grapes and in the fresh
harvest fruit. Tannin is lower in wine produced from grapes
compared to fresh grapes due to loss of these compounds
during pressing and fermentation. Conversely, maximum of
the main solutes existing in the grape berry at harvest time
are present in wine composition. Limited digestion process,
physical and thermal processing, and mastication help in the
absorption of the phenolic compounds in the intestine.
Sometimes, nutrients released during digestion may interact
with other food components and form complex and colloidal
structures which may affect in absorption (Parada and
Aguilera 2007). Phenolic compounds are used as dietary
Bioconversion of Fruits and Vegetables Wastes …
149