extraction. For instance, the extraction of pectin from mango
peels or tomato wastes was faster than conventional
extraction (Grassino et al. 2016; Wang et al. 2016; He et al.
2016). One of the most important advantages of this
extraction technique is that can be combined with other
advanced extraction methods, such as PLE or MAE, to
improve the recovery of bioactive compounds (Machado
et al. 2017; Sun et al. 2019). Moreover, UAE has been
previously used with a high variety of green solvents such as
water and ethanol, but also with NADES to obtain phenolic
enriched extracts (Espino et al. 2018; Bosiljkov et al. 2017).
UAE has been widely implemented to revalorise several
food wastes such as olive leaves (Vural et al. 2020), fruits
peels (Wang et al. 2016; Van Hung et al. 2020), or winery
by-products (He et al. 2016; Poveda et al. 2018). The great
versatility together with short extraction times provided by
this technology have demonstrated that UAE is an interesting alternative to revalorise food by-products.
In summary, the application of advanced extraction
technologies to obtain functional ingredients from different
agri-food wastes and by-products is a current common
practice which allows isolate bioactive compounds from
agro-industrial wastes to develop added high value products.
4 Agro-Industrial by-Products for Industry
Applications
New opportunities for earning additional income are related
with the sustainable utilisation of agri-food wastes and
by-products. This effective valorisation can efficiently produce high added value products reducing environmental
stress by decreasing unwarranted pollution. In this sense,
by-products of different sources as vegetables, fruits, or
cereals and their main applications are described in Table 2.
4.1 Vegetables
The increase in the use of vegetables in the food industry to
produce processed products (e.g., juices, purees, canning,
salads, etc.) implies a high generation of waste derived from
the vegetables used. This type of waste includes peels,
stems, leaves, stalks, florets, pulps, or the discarding of
vegetables by different criteria such as size, ripeness, and
poor condition, (Sagar et al. 2018; Ben-Othman et al. 2020).
In 2009, Laufenberg et al. estimated the global production
and wasted quantities of vegetables in 865.8 and 70.2 million metric tons, respectively (Laufenberg and Schulze
2009). These horticultural wastes have been used for
bioenergy generation (electricity, biogas, biodiesel) as well
as bio-fertiliser production in order to reduce its environmental impact (Suthar 2009; Singh et al. 2012).
Vegetable peels represent one of the most important
wastes in the processing industry (Akyol et al. 2016). For
example, tomato peels contain a high concentration of
lycopene, which is responsible for the red colour but has also
been attributed beneficial properties for the prevention of
certain pathologies such as chronic diseases (cardiovascular
disorders) or cancer (Jr et al. 2010). Besides these compounds, tomato by-products also contain high amounts of
phenolic compounds, such as caffeic and chlorogenic acids;
fatty acids, pectin, vitamins, and minerals (Mehta et al. 2018;
Ninčević Grassino et al. 2019). On the other hand, potato
and onion peels are also characterised by their high content
of phenolic compounds. In fact, it has been described that
the 50% of potato phenolics are located in the peel (Akyol
et al. 2016). In this sense, potato and onion peels have been
identified for their dietary fibre content as well as bioactive
compounds such as carotenoids and phenolic compounds,
highlighting their high concentration of catechin, quercetin,
and gallic acid (Hallabo et al. 2018). Besides onion peel,
other different onion by-products are generated like roots
which are rich in flavonoids and organo-sulphur compounds
(Lanzotti 2006).
Broccoli is another vegetable that presents different
by-products (i.e., leaves florets, stalk, seed, mix.), which
have been characterised showing the high presence of glucosinolates. Glucoraphanin has been the glucosinolate
detected in highest concentration, which is involved in the
formation of sulforaphane that has been related to beneficial
health properties. In addition, phenolic compounds (i.e.,
chlorogenic and neochlorogenic acids) and flavonoids (i.e.,
kaempferol or quercetin) have been also detected in broccoli
by-products (Thomas et al. 2018). The phytochemical
composition of cauliflower wastes, such as leaves and stems,
has also been explored highlighting the presence of phenolic
acids and flavonoids (Gonzales et al. 2014).
4.2 Fruits
Fruit health benefits are well acknowledged due to the
presence of multitude bioactive compounds (Slavin and
Lloyd 2012). Despite being consumed mainly fresh, fruits
processing entails the production of massive quantities of
by-products such as seeds, stones, stem, peel, skin, pomace,
bagasse, or pulp. Merely the beverages processing industries
produce about 20–60% of fruit by-products (Kowalska et al.
2017). However, precisely in the non-edible fraction is
where major quantities of value health promoting compounds can be found (Ayala-Zavala et al. 2011; Trigo et al.
2020).
As much as 40% of grapes usually end up as by-products
after winemaking and juice processing (Friedman 2014). In
grape pomace (skins and seeds) large amounts of a wide
Revalorisation of Agro-Industrial Wastes into High
235
peels or tomato wastes was faster than conventional
extraction (Grassino et al. 2016; Wang et al. 2016; He et al.
2016). One of the most important advantages of this
extraction technique is that can be combined with other
advanced extraction methods, such as PLE or MAE, to
improve the recovery of bioactive compounds (Machado
et al. 2017; Sun et al. 2019). Moreover, UAE has been
previously used with a high variety of green solvents such as
water and ethanol, but also with NADES to obtain phenolic
enriched extracts (Espino et al. 2018; Bosiljkov et al. 2017).
UAE has been widely implemented to revalorise several
food wastes such as olive leaves (Vural et al. 2020), fruits
peels (Wang et al. 2016; Van Hung et al. 2020), or winery
by-products (He et al. 2016; Poveda et al. 2018). The great
versatility together with short extraction times provided by
this technology have demonstrated that UAE is an interesting alternative to revalorise food by-products.
In summary, the application of advanced extraction
technologies to obtain functional ingredients from different
agri-food wastes and by-products is a current common
practice which allows isolate bioactive compounds from
agro-industrial wastes to develop added high value products.
4 Agro-Industrial by-Products for Industry
Applications
New opportunities for earning additional income are related
with the sustainable utilisation of agri-food wastes and
by-products. This effective valorisation can efficiently produce high added value products reducing environmental
stress by decreasing unwarranted pollution. In this sense,
by-products of different sources as vegetables, fruits, or
cereals and their main applications are described in Table 2.
4.1 Vegetables
The increase in the use of vegetables in the food industry to
produce processed products (e.g., juices, purees, canning,
salads, etc.) implies a high generation of waste derived from
the vegetables used. This type of waste includes peels,
stems, leaves, stalks, florets, pulps, or the discarding of
vegetables by different criteria such as size, ripeness, and
poor condition, (Sagar et al. 2018; Ben-Othman et al. 2020).
In 2009, Laufenberg et al. estimated the global production
and wasted quantities of vegetables in 865.8 and 70.2 million metric tons, respectively (Laufenberg and Schulze
2009). These horticultural wastes have been used for
bioenergy generation (electricity, biogas, biodiesel) as well
as bio-fertiliser production in order to reduce its environmental impact (Suthar 2009; Singh et al. 2012).
Vegetable peels represent one of the most important
wastes in the processing industry (Akyol et al. 2016). For
example, tomato peels contain a high concentration of
lycopene, which is responsible for the red colour but has also
been attributed beneficial properties for the prevention of
certain pathologies such as chronic diseases (cardiovascular
disorders) or cancer (Jr et al. 2010). Besides these compounds, tomato by-products also contain high amounts of
phenolic compounds, such as caffeic and chlorogenic acids;
fatty acids, pectin, vitamins, and minerals (Mehta et al. 2018;
Ninčević Grassino et al. 2019). On the other hand, potato
and onion peels are also characterised by their high content
of phenolic compounds. In fact, it has been described that
the 50% of potato phenolics are located in the peel (Akyol
et al. 2016). In this sense, potato and onion peels have been
identified for their dietary fibre content as well as bioactive
compounds such as carotenoids and phenolic compounds,
highlighting their high concentration of catechin, quercetin,
and gallic acid (Hallabo et al. 2018). Besides onion peel,
other different onion by-products are generated like roots
which are rich in flavonoids and organo-sulphur compounds
(Lanzotti 2006).
Broccoli is another vegetable that presents different
by-products (i.e., leaves florets, stalk, seed, mix.), which
have been characterised showing the high presence of glucosinolates. Glucoraphanin has been the glucosinolate
detected in highest concentration, which is involved in the
formation of sulforaphane that has been related to beneficial
health properties. In addition, phenolic compounds (i.e.,
chlorogenic and neochlorogenic acids) and flavonoids (i.e.,
kaempferol or quercetin) have been also detected in broccoli
by-products (Thomas et al. 2018). The phytochemical
composition of cauliflower wastes, such as leaves and stems,
has also been explored highlighting the presence of phenolic
acids and flavonoids (Gonzales et al. 2014).
4.2 Fruits
Fruit health benefits are well acknowledged due to the
presence of multitude bioactive compounds (Slavin and
Lloyd 2012). Despite being consumed mainly fresh, fruits
processing entails the production of massive quantities of
by-products such as seeds, stones, stem, peel, skin, pomace,
bagasse, or pulp. Merely the beverages processing industries
produce about 20–60% of fruit by-products (Kowalska et al.
2017). However, precisely in the non-edible fraction is
where major quantities of value health promoting compounds can be found (Ayala-Zavala et al. 2011; Trigo et al.
2020).
As much as 40% of grapes usually end up as by-products
after winemaking and juice processing (Friedman 2014). In
grape pomace (skins and seeds) large amounts of a wide
Revalorisation of Agro-Industrial Wastes into High
235