fertilizer or discarded in rivers or banks causing conservational hazard (Kodagoda and Marapana 2017; Coman et al.
2020; Wadhwa et al. 2013). Thus, lately many researches
have been going and more attentiveness has been given on
the recovery of value-added products like the bioactive
compounds possessing health benefits for humans from
industrial by-products (Coman et al. 2020). Additionally,
FVWs contain high moisture, a good pool of lipids, complex
carbohydrates, nutraceuticals, proteins, and fats. Therefore,
these wastes are recycled to be used as feed resources or can
be commercially utilized as the raw materials for the production of essential metabolites. FVWs are exploited by
certain microbes and transformed into value-added products
adding an economical value of FVWs. This approach of
utilizing resources from wastes creates possibilities in the
development and contributes in the justifiable improvement
of livestock industries (Ravindran and Jaiswal 2016; Wadhwa et al. 2013; Panda et al. 2016). The effective and efficient
utilization of FVWs will increase farmers’ profits, reduce the
cost of animal feeding, generate different profitable products,
aid in waste management, and reduce pollution. Different
FVWs such as cauliflower leaves, corn husk, cabbage leaves,
pea pods, leafy waste of mustard, tomato pomace, citrus
waste, carrot waste, mango peels, bottle gourd pulp, banana
peel, etc., can be directly fed to animals or following drying
or ensiling with crop straws. These dried or ensilaged animal
feeds do not affect nutrient deployment, health, lusciousness,
and functioning of livestock. The FVWs can be utilized in the
production of edible oil, essential oils, pigments, polyphenols, enzymes, bio-methane, bioethanol, bioplastic,
anti-carcinogenic compounds, single-cell proteins, and more
(Wadhwa et al. 2013). The overall simple diagrammatic
representation of converting the FVWs into products adding
value is presented in the Fig. 1.
To fulfill the increasing demand of food for the growing
population, valorization of food supply chain waste should
be studied so that it helps to design different opportunities
for the production of bioactive compounds, biofuels, bioplastics, enzymes, and more. The waste management problem is exaggerated due to ineffective waste management
leading to slow actions on appropriate conduct, treatment,
and disposal of waste (Ravindran and Jaiswal 2016). However, the common and easy waste management strategy is to
prioritize lessening waste production and minimum importance on discarding.
3 Conversion Process
The FVWs and other by-products produced from food
industries can be used in the production of different
value-added products mainly by three processes; thermal
conversion, chemical conversion, and biological conversion
(Singh et al. 2019). The appropriate conversion method
depends on the composition of wastes and by-products and
the aim of the recovery process.
3.1 Thermal Conversion
This process includes incineration, hydrothermal carbonization, pyrolysis, and gasification. Incineration implicates the burning and alteration of waste constituents into
heat and energy and also decreases the volume of solid waste
up to 80–85%. This technique of combusting solid waste is
antiquated, and food waste seems to be unsuitable for
incineration due to moisture content in FVWs. However, this
technique may be beneficial when used after drying of
FVWs with respect to energy loss. The heat generated from
the combustion process is generally consumed by steam
turbines for producing energy or for exchanging heat (Pham
et al. 2015). Thus, the thermal treatment of waste is applied
with the precise aim of generating power (Singh et al. 2019).
Hydrothermal carbonization (HTC) is an aqueous carbonization process performed at a relatively lower temperature (180–350 °C) and autogenous pressure. This process is
suitable for wet or high moisture containing wastes which
alters the food trashes into an energy-rich valuable resource
(Pham et al. 2015). This process has various advantages such
as it is faster than biological processes, removes many
organic impurities and pathogens, and reduces waste volume. HTC process results in the production of highly carbonized and energy-containing material known as hydrochar
which is equivalent to lignite coal. The hydrochars can be
used in removing dyes from polluted water (Singh et al.
2019; Pham et al. 2015).
Gasification and pyrolysis are also thermal processes that
effectively work against food wastes containing carbon.
Gasification is the process in which waste is converted into a
mixture of combustible gas by partial oxidation at temperature
800–900 °C. Similarly, pyrolysis is the process which converts waste into bio-oil, solid biochar, and syngas. The produced combustible gas can be burned directly or can be used as
a feedstock in methanol production (Pham et al. 2015).
3.2 Chemical Conversion
This process is commonly applied in food processing
industries and includes hydrolysis, oxidation for producing
value-added products from food waste (Singh et al. 2019).
The chemicals (acid or alkali) help to disrupt the cell and
extract the compounds. New and alternative solvents with
enhanced physical properties are being used as extraction
solvents such as propane, butane, dimethyl ether for
extraction of natural products like oils, antioxidants, aromas.
Bioconversion of Fruits and Vegetables Wastes …
147
2020; Wadhwa et al. 2013). Thus, lately many researches
have been going and more attentiveness has been given on
the recovery of value-added products like the bioactive
compounds possessing health benefits for humans from
industrial by-products (Coman et al. 2020). Additionally,
FVWs contain high moisture, a good pool of lipids, complex
carbohydrates, nutraceuticals, proteins, and fats. Therefore,
these wastes are recycled to be used as feed resources or can
be commercially utilized as the raw materials for the production of essential metabolites. FVWs are exploited by
certain microbes and transformed into value-added products
adding an economical value of FVWs. This approach of
utilizing resources from wastes creates possibilities in the
development and contributes in the justifiable improvement
of livestock industries (Ravindran and Jaiswal 2016; Wadhwa et al. 2013; Panda et al. 2016). The effective and efficient
utilization of FVWs will increase farmers’ profits, reduce the
cost of animal feeding, generate different profitable products,
aid in waste management, and reduce pollution. Different
FVWs such as cauliflower leaves, corn husk, cabbage leaves,
pea pods, leafy waste of mustard, tomato pomace, citrus
waste, carrot waste, mango peels, bottle gourd pulp, banana
peel, etc., can be directly fed to animals or following drying
or ensiling with crop straws. These dried or ensilaged animal
feeds do not affect nutrient deployment, health, lusciousness,
and functioning of livestock. The FVWs can be utilized in the
production of edible oil, essential oils, pigments, polyphenols, enzymes, bio-methane, bioethanol, bioplastic,
anti-carcinogenic compounds, single-cell proteins, and more
(Wadhwa et al. 2013). The overall simple diagrammatic
representation of converting the FVWs into products adding
value is presented in the Fig. 1.
To fulfill the increasing demand of food for the growing
population, valorization of food supply chain waste should
be studied so that it helps to design different opportunities
for the production of bioactive compounds, biofuels, bioplastics, enzymes, and more. The waste management problem is exaggerated due to ineffective waste management
leading to slow actions on appropriate conduct, treatment,
and disposal of waste (Ravindran and Jaiswal 2016). However, the common and easy waste management strategy is to
prioritize lessening waste production and minimum importance on discarding.
3 Conversion Process
The FVWs and other by-products produced from food
industries can be used in the production of different
value-added products mainly by three processes; thermal
conversion, chemical conversion, and biological conversion
(Singh et al. 2019). The appropriate conversion method
depends on the composition of wastes and by-products and
the aim of the recovery process.
3.1 Thermal Conversion
This process includes incineration, hydrothermal carbonization, pyrolysis, and gasification. Incineration implicates the burning and alteration of waste constituents into
heat and energy and also decreases the volume of solid waste
up to 80–85%. This technique of combusting solid waste is
antiquated, and food waste seems to be unsuitable for
incineration due to moisture content in FVWs. However, this
technique may be beneficial when used after drying of
FVWs with respect to energy loss. The heat generated from
the combustion process is generally consumed by steam
turbines for producing energy or for exchanging heat (Pham
et al. 2015). Thus, the thermal treatment of waste is applied
with the precise aim of generating power (Singh et al. 2019).
Hydrothermal carbonization (HTC) is an aqueous carbonization process performed at a relatively lower temperature (180–350 °C) and autogenous pressure. This process is
suitable for wet or high moisture containing wastes which
alters the food trashes into an energy-rich valuable resource
(Pham et al. 2015). This process has various advantages such
as it is faster than biological processes, removes many
organic impurities and pathogens, and reduces waste volume. HTC process results in the production of highly carbonized and energy-containing material known as hydrochar
which is equivalent to lignite coal. The hydrochars can be
used in removing dyes from polluted water (Singh et al.
2019; Pham et al. 2015).
Gasification and pyrolysis are also thermal processes that
effectively work against food wastes containing carbon.
Gasification is the process in which waste is converted into a
mixture of combustible gas by partial oxidation at temperature
800–900 °C. Similarly, pyrolysis is the process which converts waste into bio-oil, solid biochar, and syngas. The produced combustible gas can be burned directly or can be used as
a feedstock in methanol production (Pham et al. 2015).
3.2 Chemical Conversion
This process is commonly applied in food processing
industries and includes hydrolysis, oxidation for producing
value-added products from food waste (Singh et al. 2019).
The chemicals (acid or alkali) help to disrupt the cell and
extract the compounds. New and alternative solvents with
enhanced physical properties are being used as extraction
solvents such as propane, butane, dimethyl ether for
extraction of natural products like oils, antioxidants, aromas.
Bioconversion of Fruits and Vegetables Wastes …
147