LWT - Food Science and Technology 173 (2023) 114281
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LWT
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Redistribution of surplus bread particles into the food supply chain
Manuel Gómez a, **, Mario M. Martinez b, *
a
b
Food Technology Area, College of Agricultural Engineering, University of Valladolid, Palencia, Spain
Center for Innovative Food (CiFOOD), Department of Food Science, Aarhus University, AgroFood Park 48, 9200, Aarhus N, Denmark
A R T I C L E I N F O
A B S T R A C T
Keywords:
Stale bread
Food waste
Reuse
Circular economy
Flour
Baked goods are at the top of the food waste categories that most negatively contribute to the environmental
footprint. Fortunately, the distribution scheme of bread favors opportunities for redistribution pathways that are
not always viable for mixed waste or microbiologically contaminated fractions. This review approaches the
redistribution of surplus bread back into the food supply chain as food ingredient. Firstly, safety risks and
existing regulations challenging the use of surplus bread as food ingredient are highlighted. Secondly, this review
emphasizes the functionality of surplus bread flour as edible particles and its suitability as substrate for food
biotechnological applications. According to previous studies performed on fresh bread, most surplus bread
streams generated at production and retail stages should possess a relatively low risk of microbiological and
chemical hazards. However, mycotoxin studies on surplus bread streams are needed. During baking, gluten
denatures, and starch gelatinizes, resulting in surplus bread flour with cold thickening and water retention ca­
pacity, enhanced accessibility for enzymatic amylolysis, but unable to develop a gluten network. Thus, surplus
bread particles possess distinct molecular, supramolecular, and microstructural structure that influence their
successful incorporation into semisolid foods or their suitability as substrate for food biotechnological applica­
tions (e.g., sourdough, alcoholic drinks).
1. Introduction
As much as 30–40% of the food produced globally is wasted, and so
are their valuable nutrients. Food waste is a societal paradox because it
contributes to food insecurity and hinders nutrition in a world where, as
of 2015, almost 800 million people are chronically undernourished
(Gitz, Meybeck, Lipper, Young, & Braatz, 2016). It has been estimated
that the food currently wasted in Europe could feed 200 million people
(Gustavsson, Cederberg, Sonesson, Van Otterdijk, & Meybeck, 2011).
Moreover, food waste represents a dramatic waste of resources,
including land-use, energy, chemicals, materials, and labor force, to be
produced and delivered to the different players involved in the food
supply chain. The inefficiency of food waste also has a negative effect on
consumer incomes and results in roughly EUR 143 billion in economic
losses globally per year across the EU (European Commission, 2020).
Finally, food waste leads to the unavoidable translation into environ­
mental impacts, such as greenhouse gas emissions, eutrophication,
acidification and pressure on water and land (European Commission,
2020; Tonini, Albizzati, & Astrup, 2018).
Baked goods, only preceded by fruit and vegetables, stand out as the
food category most abundantly wasted, representing in some cases 30%
of the waste by mass (Brancoli, Lundin, Bolton, & Eriksson, 2019;
Brancoli, Rousta, & Bolton, 2017). Followed by meat products, baked
goods are situated at the top of the food waste categories that most
negatively contribute to the environmental footprint (Brancoli et al.,
2017, 2019; Eriksson, Strid, & Hansson, 2015). Specifically, Brancoli
et al. (2017, 2019) reported that bread waste in the Swedish super­
markets is the second type of food waste that most negatively contrib­
utes to the environmental footprint. For all the above, the elimination of
bread waste is becoming and indisputable target for those early enthu­
siasts seeking for timely solutions for bread waste and it is a priority in
focus for some funding bodies and local administrations.
Bread waste is mostly generated at household and retail levels,
especially at the supplier-retailer interface (Brancoli et al., 2019). Su­
permarkets often produce 7% more than the expected sales to meet the
consumer demands for freshness and bread types (Stenmarck, Hanssen,
Silvennoinen, Katajajuuri, & Werge, 2011). Efficient solutions for the
elimination of bread waste should follow the food use hierarchy and thus
* Corresponding author.
** Corresponding author.
E-mail addresses: mgpallares@uva.es (M. Gómez), mm@food.au.dk (M.M. Martinez).
https://doi.org/10.1016/j.lwt.2022.114281
Received 6 September 2022; Received in revised form 17 November 2022; Accepted 6 December 2022
Available online 7 December 2022
0023-6438/© 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
M. Gómez and M.M. Martinez
LWT 173 (2023) 114281
prioritize prevention and reduction. This means that the greatest efforts
are to be placed on keeping edible bread edible, which can be achieved
through better logistics and management tools (production and retail
level), reformulation or selection of proper ingredients that extend
shelf-life (production level) or targeting consumer’s education,
behavior, and consumption habits (consumer level) (Garrone, Melacini,
& Perego, 2014; Papargyropoulou, Lozano, Steinberger, Wright, & bin
Ujang, 2014; Teigiserova, Hamelin, & Thomsen, 2020). Notwith­
standing, while the prevention of bread waste should be put as the
highest priority, it is sometimes not economically feasible or techno­
logically possible, and valorization strategies should be then carefully
formulated and implemented.
Fortunatelly, the distribution scheme of bread makes it an ideal
product for redistribution and recovery strategies (Fig. 1), which can
have higher environmental savings together with additional revenue
stream to the bakeries and retailers. Firstly, bread waste generated at
manufacturing and retail stages is not mixed with other food waste and
can, therefore, be managed separately from other waste streams. Sec­
ondly, bread waste, specially that created at the production level, is
generated at large volumes of uniform composition and processability.
Finally, bread distribution is often conducted within a full-service
scheme that involves a take-back agreement between retailer and sup­
plier, which enables a clean flow of bread. All in all, the distribution
scheme of bread favors opportunities for different bread waste redis­
tribution and valorization pathways that are not always viable for a
mixed waste fraction (Brancoli, Bolton, & Eriksson, 2020). This would
support the shift from a linear to a circular economy and meet the global
Sustainable Development Goal (SDG) 12.3 to “halve per capita food
waste at the retail and consumer level, and reducing food losses along
production and supply chains (including post-harvest losses) by 2030”.
The European Union proposed the food waste hierarchy, which provides
a guide to choose the most environmentally efficient end-of-life (EoL)
treatment (European Commission, 2008). Restricting resource use to
more sustainable levels and prioritizing resource efficiency can effec­
tively reduce Greenhouse Gas (GHG) emissions linked to climate
change, as well as offer other benefits of economic and social nature
(Papargyropoulou et al., 2014). However, if prevention is not possible,
the reuse (i.e., redistribution) of waste should be prioritized over recy­
cling (e.g., recycled into animal feed or new bio-based materials), re­
covery (e.g., recovery of energy and single nutrients, for example
through composting), and disposal (European Commission, 2008;
Salemdeeb, Zu Ermgassen, Kim, Balmford, & Al-Tabbaa, 2017; Teigi­
serova et al., 2020).
This review should not be expected to cover all EoL treatments for
surplus bread, such as recycling into feed or biomaterials and recovery
of single components. Instead, our endeavor aims to highlight the gaps
and opportunities for the redistribution of surplus bread as food ingre­
dient into the food supply chain. Although this EoL treatment should be
prioritized in the context of a green transition to a circular economy, the
associated safety risks, the absence of specific regulations for the use of
novel by-products, and the lack of understanding about the colloidal and
structuring properties of surplus bread flour as edible particles, could
challenge most redistribution pathways. In this review, the main safety
and legal requirements that might conflict with redistribution strategies
and exclude certain sources of bread waste to become surplus for human
consumption will be firstly covered. Secondly, we will dive into the new
structure and phase of the main biopolymers present in surplus bread,
gluten and starch, and connect them with the physical properties of
surplus bread particles (i.e., flour). We believe that this section will
provide useful insights for the successful redistribution of surplus bread
not only at the consumption and retail stages (e.g., food banks, catering,
and restaurants), but also at the manufacturing stages as technofunctional ingredient. Finally, the effect of the direct incorporation of
surplus bread flour on the quality of different semisolid foods and bev­
erages, or its use as substrate for food biotechnological applications, will
be discussed, revealing interesting opportunities as food structuring
agents or carbon sources. A literature database search on the topics
“bread”, “by-product”, “surplus”, “waste” and “leftover” was performed,
discarding those papers about the upcycling of bread waste for non-food
purposes as well as those in which bread was used as a system to upcycle
other fruit and vegetable by-products, rather than being the by-product
per se.
Fig. 1. Types of surplus bread generated at the supplier-retailer interface and households and proposed use hierarchy and prioritization according to the most
environmentally efficient end-of-life treatment. 1Long shelf-life bread represents breads with longer shelf-life due to a different formulation typically containing a
relatively higher moisture and fat content than lean, short shelf-life bread (pan bread or buns are some examples).
2
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2. Safety risks challenge redistribution pathways
aromas when used as is (e.g., flour or breadcrumbs), worsening the
quality of any food they are added to. Importantly, increased demand for
preservative-free “clean label” products and the inclusion of whole-grain
flours, in combination with global warming and rising ambient tem­
peratures, may lead to more frequent occurrence of rope-forming bacilli
(Pacher et al., 2022). Bacillus spp. form endospores that are associated
with discoloration and a stringy bread crumb, and characterized by an
unpleasant sweetish odor caused by the release of volatile compounds
(Pacher et al., 2022). It is reasonable to expect that toasting of
higher-moisture surplus bread would extend its shelf life and thus
reduce bread waste. However, rancidity might be a compromise in fatty
breads, and it is unclear whether the environmental impact could be
counteracted by the energy consumption of drying (Svanes, Oes­
tergaard, & Hanssen, 2018). Furthermore, the risk for high acrylamide
content could, by all likelihood, be compromised, as explained in the
next paragraph, and Bacillus endospores could survive baking and
desiccation since they are heat stable (Pacher et al., 2022). As opposed
to higher-moisture surplus bread, lean, short shelf-life bread available in
the supermarket or small bakeries constitute a significant amount of the
total bread waste by weight with negligible microbiological risk, even
without previous steps of drying or freezing. This occurrence is due to
the fact that this category loses its freshness and, hence, it is rejected
within 24–48 h mostly due to staling (or firming). Moreover, it presents
a more rapid decay in water activity than other returned surplus bread
streams, which also confers microbial stability. To the best of our
knowledge, there are no studies reporting the microbial counts or
mycotoxin quantification of surplus bread streams.
The presence of acrylamide is another safety risk that could chal­
lenge redistribution pathways for some types of surplus bread. Acryl­
amide is a rodent carcinogen and a human neurotoxin that is classified
as a probable human carcinogen. Neurotoxicity, adverse effects on male
reproduction, developmental toxicity and carcinogenicity were identi­
fied as possible critical endpoints for acrylamide toxicity from experi­
mental animal studies (EFSA Panel on Contaminants in the Food Chain
(CONTAM), 2015). Acrylamide is formed when certain foods are pre­
pared at temperatures above 120 ◦ C and low moisture, especially in
foods containing asparagine and reducing sugars. Acrylamide has been
found at the highest levels in solid coffee substitutes and coffee, and in
fried potato products, with concentrations above 600 ng/g (Becalski,
Lau, Lewis, & Seaman, 2003; EFSA Panel on Contaminants in the Food
Chain (CONTAM), 2015). In comparison, the content of acrylamide in
bread is 20 times lower, with concentrations of 19–30 ng/g for typical
bread types such as French baguettes (Becalski et al., 2003). Acrylamide
is mainly present in the crust (up to 99%) and not in the crumb (Gökmen
& Şenyuva, 2006; Surdyk, Rosén, Andersson, & Åman, 2004), since the
high moisture of the crumb throughout baking will not allow to reach
the 120 ◦ C required for acrylamide formation. Water activity has also
been reported to play a major role in acrylamide formation in breads,
with acrylamide forming only when the water activity is below 0.8 (De
Vleeschouwer, Plancken, Van Loey, & Hendrickx, 2007). Accordingly,
acrylamide is presumably absent in parbaked bread or dough and very
low in fully baked pan bread from industry and bread from retailers and
households. Presumably, only waste streams of pan bread crust, which is
produced in certain countries as a by-product from the manufacturing of
crustless pan bread, could apparently contribute to the increase of the
daily intake of acrylamide. Steam baking could result in a significant
decrease of acrylamide content in the crust (Ahrné, Andersson, Floberg,
Rosen, & Lingnert, 2007). Reducing the ratio of crust in surplus bread,
for example by making larger breads or separating the crust manually,
could also mitigate the risk for high acrylamide formation. Nevertheless,
it is not clear whether surplus bread, in any of its forms, could represent
an important risk for acrylamide intake unless it is toasted to reduce
water activity and microbial risk, which can increase acrylamide content
dramatically (Streekstra & Livingston, 2020). We believe that this topic
deserves further investigation.
The possible contamination with allergens, such as sesame, dairy or
Ensuring a proper control of microbiological, chemical, and physical
hazards with appropriate facilities and processes, and ensuring trace­
ability steps that cover production and distribution are crucial for pro­
tecting consumers’ life and health. In this scenario, good practices and
regulations aimed to control the quality and safety of surplus bread
foods are necessary to protect human health, even though they might
challenge redistribution strategies.
Only returned bread that has not been contaminated with other
waste fractions is suitable for most of the waste management and
valorization options. Fortunately, bread waste generated at
manufacturing (i.e., baking industry) and retail stages (i.e., supermarket
and small bakeries) is typically not mixed with other food waste and can
therefore be managed separately from other waste streams. Parbaked
bread or dough, fully-baked pan bread and pan bread crust from the
baking industry, together with lean, short shelf-life bread and long shelflife bread produced in the supermarket and small bakeries, generate
large volumes of surplus bread of uniform processability that is noncontaminated with organic matter and can be traced (Fig. 1). In
contrast, household waste is many times mixed with different organic
fractions, exponentially increasing microbiological and chemical risks
and therefore treated as municipal solid waste (Tonini et al., 2018). It is
noteworthy that not all the surplus bread generated at the household
level is contaminated with organic matter, in which case, it can be
redistributed in home recipes as breadcrumbs or flour (e.g., batters and
breadings, pudding, salmorejo, bread salad, semmelknoedel, torrijas),
used as a substrate for home-made alcoholic drinks, such as beer, or used
as feed for domestic animals. Otherwise, non-contaminated household
stale bread is mixed with other municipal solid waste and treated as
such, since collection for other purposes is unfeasible.
Although surplus bread produced at the manufacturing and retailer
stages is not contaminated with organic matter, bacterial and mold
growth cannot always be ruled out and deserves special consideration
particularly in those streams with higher water activity, such as those
from parbaked bread or dough, pan bread and other long shelf-life
breads (Fig. 1). If these surplus bread streams become microbiologi­
cally contaminated, they should not be considered for human or animal
consumption for different reasons. Firstly, although the typical molds
identified as the main sources of potential spoilage microorganisms of
breads can be destroyed with thermal treatments (Axel, Zannini, &
Arendt, 2017; Knight & Menlove, 1961), they can generate mycotoxins
that are resistant to thermal processing and can cause harm in human
health. The mycotoxins trichothecenes produced by the strains of
Fusarium fungi, and specially deoxynivalenol (DON), were reported to
represent the most predominant mycotoxins in different breads in the
German market (Schollenberger et al., 2005), with an incidence of 92%
and median content in positive samples of 134 μg/kg. In another study
performed on Spanish breads, aflatoxin B1, aflatoxin B2 and aflatoxin
G1 were the most abundantly detected mycotoxins with concentrations
ranging from 0.5 to 7.1 μg/kg (Saladino et al., 2017). These discrep­
ancies clearly suggest that different geographical regions or bread types
require different prioritizations. Although these contents did not exceed
their correspondent temporary maximum tolerable daily intake, it is
noteworthy that the disappearance of a mycotoxin during processing
does not necessarily mean detoxification. If the toxin is converted into a
form that escapes detection, it will remain toxic (Karlovsky et al., 2016).
Furthermore, several Fusarium toxins represented by enniatins, beau­
vericin, fusaproliferin and moniliformin, which are neither routinely
determined, nor legislatively regulated, were reported in bread (Vacla­
vikova et al., 2013). Studies are therefore required for better under­
standing the possible toxicity of these mycotoxins (Awuchi et al., 2021).
Special caution should be taken for those surplus bread streams of higher
water activity due to their higher susceptibility for mold growth, which
could potentially raise the levels of mycotoxins. Secondly, microbial
growth can cause an uncontrolled generation of unpleasant flavors and
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LWT 173 (2023) 114281
nuts, of the surplus bread that is going to be reused must also be taken
into account. In the case of reusing these breads, cross-contamination
must be avoided, or the consumer must be alerted to the possible pres­
ence of these allergens.
Any ambition to avoid bread waste through redistribution strategies
can potentially be hindered by the set of regulations and recommen­
dations imposed by the different administrations. Regulations that
define maximum allowed levels for concentrations of hazards that may
be present in food, regulations that list prohibited substances, regula­
tions for novel foods, and regulations specific for food contact materials,
such as packaging, are some examples of the set of regulations and
recommendations for food and feed established by the EU to safeguard
human health that could impede redistribution pathways. Thus, specific
regulations for the use of novel by-products are not in place and
amendments might be needed to reach the sustainability goals for
circularity. Bread redistribution in the food supply chain has been
restricted in certain countries, such as Spain (Real Decreto
BOE-A-2019-6994, 2019), where the sale of milled surplus bread is
restricted. Regulations are however unclear on whether these flours can
be reused internally (in the same company where they were generated).
In other countries, the legislation includes the possibility for some spe­
cific uses of surplus bread. In Austria, the incorporation of up to 10% of
surplus bread in the production of bread is allowed, provided that it does
not contain preservatives and has not been in contact with the potential
buyer (Lebensmittelversuchsanstalt, 2020). In Germany, legislation al­
lows for the addition of surplus bread in the production of sourdough
(Bundesministerium für Ernährung und Landwirtschaft, 2020). None­
theless, the urgent need to reduce surplus bread, together with future
environmental, economic and safety assessments, future research on
circularity, and synergies and trade-offs between these aspects, could
make regulations more permissive provided good hygienic-sanitary
practices are in place. On another note, regulations obliging for all in­
gredients to be listed in food labels could result in an excessive long list
of ingredients in those foods that contain upcycled by-products or waste
streams from different types or locations. It is expected that surplus
bread ingredients could be a mixture of different breads, and different
from day to day and from batch to batch, depending on the type of
surplus bread available at the specific collection point. This would result
in surplus bread-containing foods less appealing for consumers. We
believe that this aspect should also be accounted for by the future reg­
ulations while moving towards a circular biobased economy. These is­
sues and challenges should be approached jointly by the administrations
and the different stakeholders to find common ground for food safety,
consumer trust, and surplus bread redistribution pathways.
aggregates (Cuq, Abecassis, & Guilbert, 2003). Gluten deformation,
entanglement and crosslinking is further enhanced during kneading
because of mechanical stress, resulting in the formation of the gluten
network. On the other hand, only the amorphous part of starch changes
from a glassy state to a rubbery state, leading to an increase in the
molecular mobility of chains and thus enabling water penetration in
crystalline structures (Zeleznak & Hoseney, 1987). However, the crys­
talline regions and the granular morphology of starch remain stable
until the melting temperature (Tm) is reached during the baking step.
During the fermentation step, only the starch granules that were pre­
viously damaged (the so-called damaged starch) becomes a possible
substrate for amylolytic degradation into fermentable sugars that are
subsequently converted into CO2. The rest, which typically represents
more than 90% (starch basis), will remain in a stable, relatively
enzyme-resistant granular form. During the last step, baking, gluten
proteins denature and thermoset, irreversibly losing their ability to form
a gluten network again. Hence, the reuse of thermoset (baked) gluten in
food products that require gluten formation, such as bread, might be
limited. Similarly, starch losses its starch crystalline structure, irre­
versibly swells and some starch chains solubilize (altogether, repre­
senting the so-called gelatinization), which will critically change its
functionality if it is meant to be reused as food ingredient (Cuq et al.,
2003; Varriano-Marston, Ke, Huang, & Ponte, 1980). It is noteworthy
that full starch gelatinization has been reported in crumb by DSC, even
in those breads made with the minimum hydration found in commer­
cially available white bread. On the contrary, only 30–45% of the starch
located in the outer part of the crust fraction was found to gelatinize,
depending on the dough hydration level (Martinez, Roman, & Gomez,
2018). This occurrence is attributed to the fast evaporation of water
from the crust due to the high temperature of the surface. These phase
transitions in both biopolymers affect their water holding capacity and
lead to solid-liquid transitions - denatured gluten does not hold much
water, which is readily absorbed by the gelatinizing starch (Cuq et al.,
2003). The physical changes continue over storage, since the rubbery
state of starch in the crumb makes it sensitive to rapid changes that
occur during storage, a phenomenon called staling. Staling is charac­
terized by an increase in crumb hardness and a loss of cohesiveness,
springiness and resilience over time. Amylopectin and amylose retro­
gradation and moisture migration (moisture loss) are known to be major
contributors (Gray & Bemiller, 2003; Roman, Reguilon, Gomez, &
Martinez, 2020). Thus, gelatinized starch molecules will gradually
re-associate through hydrogen bonding during storage. State diagrams
about these mechanisms have been comprehensively reported by Cuq
et al. (2003). To conclude, together with gluten and starch transitions,
the high temperature reached during bread-making also results in the
inactivation of endogenous enzymes and, if present, non-thermostable
exogenous enzymes, destruction of microorganisms and the partial
reduction of mycotoxin levels. In the crust, Maillard reactions and sugar
caramelization will occur, which bring about its typical dark color and
the potential formation of acrylamide (Gökmen & Şenyuva, 2006; Sur­
dyk et al., 2004).
In summary, surplus bread flour will present almost identical
macronutrient composition to wheat flour, but gluten and starch will
exist in a notably different phase, which will dictate the different
colloidal and structuring behavior of surplus bread particles. Moreover,
the crust to crumb ratio prior to milling into surplus bread flour is
paramount, since the crust will carry additional chemical compounds,
such as dark pigments and acrylamide, and ungelatinized starch, which
might remain fully functional in terms of swelling.
3. Surplus bread particles (bread flours)
Surplus bread can be ground and mechanically fractionated into
flour or breadcrumb that visually resemble that from wheat. Interest­
ingly, most bread types, and particularly lean, short shelf-life surplus
bread, would possess almost identical chemical composition to their
parent wheat flours, except for small additional amounts of salt and
yeast, typically lower than 2% and 10% (flour basis), respectively.
Nevertheless, the main polymers of bread, namely gluten and starch, are
irreversibly and distinctly modified during the different steps of baking.
3.1. Changes occurring during bread baking - from wheat flour to wheat
bread flour
In breadmaking, firstly, wheat flour is hydrated during its mixing
with water, where the plasticizing effect of the latter leads to a marked
decrease in the glass transition temperature (Tg) of gluten and the
amorphous regions of starch below room temperature. On the one hand,
the rubbery state of gluten enhances the relative mobility of molecules
and their high reactivity resulting in the formation of intermolecular
covalent bonds and the consequent formation of three-dimensional
3.2. Behavior of surplus bread flour
The direct milling of surplus bread into flour, and its redistribution as
food ingredient in the food supply chain is one of the cheapest, easiest,
and seemingly most logical strategies to reduce the detrimental envi­
ronmental effects of surplus bread waste. However, successful food4
M. Gómez and M.M. Martinez
LWT 173 (2023) 114281
making requires careful crafting of the mesoscale structure of each food
system. The physicochemical properties of surplus bread flour therefore
need to be understood. Fernandez-Pelaez, Guerra, Gallego, and Gomez
(2021) observed that surplus bread flour presented considerably greater
water retention capacity and swelling (at room temperature), and
resulted in more consistent hydrogels (i.e., with higher viscoelastic
moduli) than traditional wheat flour. Remarkably, small but significant
differences in water retention capacity and swelling were found among
flours originated from different types of surplus bread, including whole
grain bread, classic refined bread, ciabatta, refined dough bread and pan
bread, among others. Flour from those surplus breads richer in compo­
nents different from gluten and starch, such as whole grain and pan
breads, possessed lower water retention capacity and resulted in weaker
hydrogels, compared to the flour from the classic refined bread. This was
expected since the starch component, which is present in higher pro­
portions in the classic refined bread flour, is the main component
responsible for this behavior. Less pronounced differences were found
among breads with similar composition but different bread volume and
morphology, such as low-hydration bread (also known as candeal bread
or refined dough bread) and small breads (pieces of less than 50g).
The same authors found that flours from surplus bread crumb
resulted in weaker gels than the crust counterparts, which could be
explained by the complete starch gelatinization and the subsequent
retrogradation of the former occurring during bread-making. Amyloseamylose interactions would remain relatively intact during hydrogel
formation (at maximum holding temperature of 95 ◦ C) and be less prone
to be dispersed and form new physical junction zones contributing to gel
development (Martinez et al., 2018). Surprisingly, no significant dif­
ferences in water retention capacity were found between surplus bread
flours made from crumb and crust, despite the well-known higher water
retention capacity of gelatinized starch and the fact that ungelatinized
starch is only found in the crust (Martínez, Román, & Gómez, 2018).
Fernandez-Pelaez et al. (2021) could have included crumb in the crust
fractions, harmonizing the amount of gelatinized starch between both
fractions and potentially explaining the lack of significant differences. If
this was the case, it is noted that the separation of the thin layer con­
taining ungelatinized starch within the crust fraction would be techno­
logically impossible at scale. This occurrence could be attributed to the
counterbalancing effect towards water holding capacity of the gluten
present in the crust. The water content in the crust rapidly decreases,
compromising gluten aggregation and hence potentially retaining some
of its water hydration capacity. However, further studies are needed to
confirm this mechanism. Moreover, surplus bread flours from the crust
fraction were significantly darker than the crumb counterparts, which
was attributed to the water-temperature history during baking. This
event enables starch and proteins to get involved in different kinds of
reactions (dextrinization, caramelization, non-enzymatic browning re­
actions, thermal degradation, etc.).
Milling and mechanical fractionation are known factors affecting the
physicochemical properties of wheat flour, both in native (Proto­
notariou, Drakos, Evageliou, Ritzoulis, & Mandala, 2014) or
pre-gelatinized form (Martínez, Rosell, & Gómez, 2014). However, this
was not the case for surplus bread flour. Guerra-Oliveira, Fernandez-­
Peláez, Gallego, and Gomez (2022) did not observe significant differ­
ences in liquid retention capacity and hydrogel hardness among surplus
bread flours of different particle size (<200, <500 and < 1000 μm).
Remarkably, this could lead to a reduction in milling costs, since a fine
particle size would, in principle, not be necessary for optimum func­
tionality. Notwithstanding, the effect of the particle size of surplus bread
flour on its functionality in a final food system is unknown and further
studies are needed.
Thus, the type of bread should be taken into account when aiming for
surplus bread to be of homogenous quality and processability, in which
blending different surplus breads should be benchmarked for specific
parameters of water retention capacity and swelling behavior.
4. Direct redistribution into semisolid food systems
As commented previously, the main biopolymers of bread, namely
gluten and starch, are irreversibly modified during baking, resulting in
surplus bread flour of distinct, but not necessarily worse, physical
behavior compared to its parent wheat flour. In this section, the redis­
tribution of surplus bread flour into semisolid staple foods will be dis­
cussed and related to its functionality (e.g., cold swelling and thickening
behavior). Main findings are summarized in Table 1.
4.1. Surplus bread flour in bread-making
Redistributing surplus bread into bread-making could be seen as one
of the most logical approaches to upcycle surplus bread. However, since
gluten suffered from irreversible transitions during baking, surplus
bread flours in bread-making can be used only in limited percentages.
The overall gluten strength of the dough is gradually reduced with the
amount of surplus bread flour used in the formulation. Furthermore, the
much higher water retention capacity of the gelatinized starch present in
surplus bread flour should be accounted for by readjusting the dough
hydration to higher levels, which also limits its use in large amounts. For
these reasons, deleterious effects in terms of specific volume and crumb
hardness become important from 15%, flour basis (Meral & Karaoglu,
2020). Immonen, Maina, Coda and Katina (2020) reported a decrease in
specific volume and increase in crumb hardness with the use of surplus
bread flour. However, dough hydration was not adjusted by means of a
farinograph or similar device, which could have resulted in under­
hydrated doughs due to the high-water hydration capacity of gelatinized
starch. In another study, Immonen, Maina, Coda, and Katina (2021) still
confirmed a decrease in specific volume and increase in crumb hardness
when incorporating surplus bread at 10% (flour basis) when correcting
the dough hydration with a farinograph. These effects were like those of
the incorporation of pregelatinized starch in different forms (Martínez,
Oliete, & Gómez, 2013; Ortolan et al., 2015). These studies also evi­
denced the significance of gluten denaturation in surplus bread flour and
the dilution of the gluten network in the new breads. The fermentation
of surplus bread flour using exopolysaccharide-producing lactic acid
bacteria reduced the negative effects of its incorporation into bread
(Immonen, Maina, Wang, Coda, & Katina, 2020). The positive effects of
fermentation
were
attributed
to
the
production
of
iso-maltooligosaccharides and, especially, dextrans, the latter resulting
in the best quality of surplus bread flour-containing bread in terms of
specific volume and texture. This explanation agrees with previous
works studying the effect of dextrans in bread-making (Katina et al.,
2009; Wolter, Hager, Zannini, Czerny, & Arendt, 2014).
Enzymatic amylolysis, using α-amylase and amyloglucosidase, of
surplus bread flour has also been reported as another strategy to reduce
the deleterious effect of the use of surplus bread flour in bread-making
(Immonen et al., 2021). Precisely, although the improvement of the
bread specific volume was only moderate, the extensibility of
surplus-bread containing doughs was significantly enhanced. Moreover,
crumb hardness was significantly reduced, especially with those enzy­
matic treatments of longer times and higher enzyme concentration. In
this case, the authors attributed this effect to the generation of
iso-maltooligosaccharides and the degradation of amylopectin, both
contributing to the reduction of the starch retrogradation in the crumb.
It is noted that starch is mostly gelatinized in surplus bread and,
therefore, far easier to be degraded by starch-active enzymes.
Although there are no studies available, we believe that the rheology
of doughs containing surplus bread flour can be improved with the use
of wheat flours of greater strength, with the addition of gluten, and/or
with the incorporation of additives or enzymes that augment dough
strength. These traditional solutions have already been implemented
when using ingredients that reduce gluten strength, such as bran (Teb­
ben, Shen, & Li, 2018), and there is no reason to think that they would
not work with surplus bread flour.
5
Food system
Type of surplus
bread
Level of incorporation
Additional processing
Effects measures instrumentally
Effects measured by a sensory trial
Reference
• White wheat
bread, crumb
• White wheat
bread, crumb and
crust (whole)
• 15% (flour basis)
• 30% (flour basis)
• 45% (flour basis)
N/A
Surplus bread reduced specific volume, cohesiveness and
springiness and increases hardness
No significant differences were observed between crumb and
whole surplus bread flours
Meral, H. & Karaoglu
(2020)
Bread
• White wheat
bread
• 12.5% (flour basis)
Fermentation using:
• Weissella confusa
• Pediococcus claussenii
Bread
• White wheat
bread
• 10% (flour basis)
Enzymatic hydrolysis using:
• α-amylase
• α-amylase and
amyloglucosidase
Bread
• White wheat
bread
• 18% (flour basis)
• 22% (flour basis)
Enzymatic hydrolysis using:
• α-amylase
• amyloglucosidase
• protease
Fermentation using:
• Leuconostoc mesenteroides
• Pediococcus
• Pentosaceus
• Lactobacillus brevis
Fermentation increased the pH, TTA and lactic acid bacteria,
and reduced viscosity, of a surplus bread flour slurry
Bread specific volume was reduced, and crumb hardness
increased, with the addition of non-fermented surplus bread
slurry
The negative effects of the incorporation of surplus bread
slurry were removed, depending on the microorganism used
Slurry without treatment increased dough resistance,
decreased dough extensibility, decreased bread specific
volume and increased hardness
Enzymatically hydrolyzed slurry had the same effects but to a
lesser degree. It also reduced the resistance to extension.
Fermentation reduced pH and increased the content of TTA,
lactic and acetic acids of surplus bread slurries
Surplus bread slurries reduced the microbial development of
breads
Surplus bread reduced overall
acceptability
Bread with 15% surplus bread
presented similar acceptability tan
the control bread
No significant differences were
observed between crumb and
whole surplus bread flours
N/A
• 10% (flour basis)
• 20% (flour basis)
• 30% (flour basis) – only
tested in layer cake
Mechanical fractionation
using 200, 500 and 1000 μm
sieves
• 50% (flour basis)
• 100% (flour basis)
Mechanical fractionation
using 200, 500 and 1000 μm
sieves
Bread
Bread
6
Other baked goods
Sponge and
• White wheat
layer cakes
bread
Cookies
• White wheat
bread
• Whole wheat
bread
Immonen et al. (2020)
Immonen et al. (2021)
N/A
Nionelli et al. (2020)
N/A
Guerra-Oliveira,
Belorio, and Gomez
(2022)
50% increased Overall
acceptability increased with 50%
surplus bread addition, but
decreased with 100%
At 100% addition, surplus whole
wheat bread presented higher
scores than surplus white bread
Guerra-Oliveira et al.
(2021)
(continued on next page)
LWT 173 (2023) 114281
In sponge cakes, surplus bread did not alter batter density and
viscosity, but reduced the specific volume and increased the
hardness of the final product
In layer cakes, surplus bread increased batter viscosity (only
at 30%) and did not alter the specific volume and texture of
the final product
Coarsest particle size (500 and 1000 μm sieves) at 20%
incorporation resulted in sponge cakes that collapsed after
baking
50% surplus bread addition did not modify dough rheology
and texture of cookies, although diameter and spread factor
were slightly reduced
Cookies made with surplus bread as the only starchy
ingredient (
100% addition) increased dough viscoelastic moduli, and the
thickness and hardness of cookies, while reducing their
diameter and spread factor
When using whole wheat surplus bread, coarse flours resulted
in higher dough viscoelastic moduli, cookie diameter and
lower cookie hardness than fine counterparts
M. Gómez and M.M. Martinez
Table 1
Redistribution of surplus bread into the food supply chain as edible flours or substrate for biotechnological applications.
M. Gómez and M.M. Martinez
Table 1 (continued )
Food system
Type of surplus
bread
Other cereal-based systems
Direct expanded
Breadcrumbs
puffed snack
system
7
Direct expanded
puffed snack
system
Breadcrumbs
Food biotechnology
Glucose-rich
• White wheat
paste
bread
Sourdough
• White wheat
bread
• Whole wheat
bread
• Sweet-type bread
Level of incorporation
Additional processing
Effects measures instrumentally
Effects measured by a sensory trial
Reference
Mixtures of pea flour and
surplus bread flour, with
percentages of the latter of:
• 25% (blend basis)
• 50% (blend basis)
• 75% (blend basis)
• 100% (blend basis)
Each blend was extruded as
the sole starchy ingredient
• 100% (flour basis)
N/A
Breadcrumbs reduced density, hardness and crunchiness, and
increased expansion ratio of the final product, depending on
feed moisture content and surplus bread flour percentage in
the blend
N/A
Luo and Koksel (2020)
N/A
In general, the use of surplus bread flour increased the
expansion ratio and reduced the bulk density of the final
product. This effect was strongest at lower feed moisture
content and higher extrusion temperature.
Hardness, crispiness and fiber content were also reduced with
the use of surplus bread flour
N/A
Samray et al. (2019)
• 100% (flour basis)
N/A
N/A
Sigüenza-Andrés et al.
(2022)
• 30% (flour basis)
• 50% (flour basis)
N/A
The slurry produced with the simultaneous amylolysis using
α-amylase and glucoamylase had similar glucose yield at 2 h,
and higher at 4 h, than that obtained by the sequential
amylolysis method of 4 h
Fermentation increased TTA, total microorganism and lactic
acid, and reduced the sugar content similarly to the control
(without surplus bread incorporation)
N/A
Gelinas et al. (1999)
TTA: Total titrable acidity; N/A: Not applicable.
LWT 173 (2023) 114281
M. Gómez and M.M. Martinez
LWT 173 (2023) 114281
4.2. Surplus bread flour in other baked goods
the use of breadcrumbs for making direct expanded extrusion systems
from wheat, which resulted in greater expansion ratio and enhanced
crunchiness. Later, Luo and Koksel (2020) proposed the use of bread­
crumb together with pea flour to obtain extrudates of better nutritional
quality (mostly attributed to the pea components), higher expansion
ratio and crunchiness and lower hardness. These positive effects can be
attributed to the presence of pregelatinized starch, which increases melt
viscosity and facilitates its expansion (Chen & Rizvi, 2006). This event
agrees with the use of pregelatinized rice flour in direct expanded
products (Gat & Ananthanarayan, 2015).
The cold swelling and thickening behaviors of surplus bread flours
can be exploited in certain formulations where this property is desired,
such as sauces (Román, Reguilón, & Gómez, 2018), low fat mayonnaises
(Román, Martínez, & Gómez, 2015; Roman, Walker, Detlor, Best, &
Martinez, 2022) and batters for coatings (Martínez, Sanz, & Gómez,
2015; Román, Pico, Antolín, Martínez, & Gómez, 2018). In the case of
batters for coatings, the use of pregelatinized flours enhanced batter pick
up due to an increased viscosity and stickiness. Understandably, the
direct making of breadcrumbs for breading purposes is easy and popu­
lar, representing one of the best redistribution strategies for surplus
bread at the household level (Fig. 1).
Wheat flour is also the main component of cakes and cookies, thus
they represent plausible food systems for surplus bread redistribution. In
these cases, the development of a gluten network is not necessary, and
the dilution of the gluten network is therefore not troublesome. How­
ever, cake batters are highly hydrated systems where starch gelatiniza­
tion is paramount to set their structure and prevent its collapse after
baking (Donovan, 1977; Guy & Pithawala, 1981). Because of this, and
unlike what occurs in cookies, the quantity of surplus bread flours to be
used is limited, as demonstrated by Guerra-Oliveira, Belorio, and Gomez
(2022). Specifically, the negative effects were more pronounced in
sponge cakes than in layer cakes – the former showing a significant
reduction in specific volume at 10% (flour basis) surplus bread flour
inclusion level, whereas the latter retained its quality even at 20% in­
clusion. The higher propensity of sponge cakes to lose their quality
might be due to the fact that the starch contained in surplus bread flour
does not swell anymore since it has been pregelatinized, which could
negatively affect the thermosetting of the structure and bubble reten­
tion. Likewise, air retention could be negatively affected by the lower
Pickering stabilization of surplus bread flours compared to their parent
wheat flours (Godefroidt, Ooms, Pareyt, Brijs, & Delcour, 2019), the
latter typically possessing a finer particle size (Guerra-Oliveira, Fer­
nandez-Peláez, Gallego, & Gomez, 2022). On the contrary, batter air
entrapment is not as determinant of the final aerated structure in layer
cake systems. The strongest effect of flour particle size in sponge cakes
compared to layer cakes has been observed elsewhere (Dhen et al.,
2016).
Sweet cookie systems, such as sugar snap-cookies, represent the least
challenging scenario for surplus bread redistribution in baked goods.
Gluten formation is not determinant for the final quality of the product.
In fact, the gluten network in sugar snap-cookies is not developed due to
scarce mechanical stress, limited gluten hydration, and the high relative
proportions of sugar and fat. In fact, sugar-snap cookies can easily be
made with 100% gluten-free flour (Mancebo, Picon, & Gomez, 2015).
Moreover, starch gelatinization does not occur during baking mostly due
to the lack of starch hydration and, therefore, it is not a determinant
factor for the final quality of the product either. For these reasons,
higher surplus bread inclusions levels can be attained, and even palat­
able cookies using surplus bread flour as the only starchy ingredient can
be made. However, the water holding capacity of the starchy ingredient
is known to play an important role on cookie quality (Pareyt & Delcour,
2008), which could still limit the incorporation of starchy materials in
pregelatinized form. Thus, the use of pregelatinized flours, with much
higher water retention capacity than their native counterparts, increases
dough consistency and reduces the expansion during baking (Mancebo
et al., 2015; Roman, Sahagun, Gomez, & Martinez, 2019). Nevertheless,
and at the expense of presumably needed more energy to remove more
water, this deleterious effect could be partially corrected by increasing
dough hydration, which reduces dough consistency and enhances its
expansion. Likewise, Guerra-Oliveira, Belorio, and Gomez (2021) re­
ported that the acceptability of cookies made solely with surplus bread
flour was negatively compromised. Remarkably, 50% replacement
levels with surplus bread flour did not result in different dough rheology
or cookie texture. Although these cookies presented slightly lower
diameter than the control, their consumer acceptability was even
improved.
5. Opportunities of surplus bread in food biotechnology
Surplus bread has typically been recovered to produce renewable
energy or fertilizers through anaerobic digestion (Hassan et al., 2021;
Melikoglu, Lin, & Webb, 2015). Nevertheless, opportunities in food
fermentation could open up new EoL circular strategies at the interface
between redistribution and revalorization.
5.1. Sugar syrups and fermented beverages
The starch present in surplus bread is mostly gelatinized and,
therefore, readily accessible for amylolytic degradation. In this way, and
similar to extruded wheat flour (Martínez, Pico, & Gómez, 2015), the
viscosity of a suspension of surplus bread flour can be significantly
reduced with the use of α-amylase, and glucose syrups can be developed
by the joint action of α-amylase and amyloglucosidase and the subse­
quent separation of non-starch components by centrifugation
(Sigüenza-Andrés, Pando, Gómez, & Rodríguez-Nogales, 2022). Making
sugar syrups from bread, however, entail the additional challenge of
removing ionizable compounds, such as inorganic salts or organic acids.
In this regard, the removal of salt, which is typically included at 2%
(flour basis) in bread formulations, should be carefully studied since
salt-containing sugars syrups would possess undesirable flavor charac­
terized as being sweet and salty all at once. Ion exchange-based
desalting would represent one of the few technologies able to separate
salt and sugars (Daza-Serna et al., 2021). This includes the use of ex­
change resins or even chromatographic separation steps. Importantly,
these processes possess an elevated water demand and wastewater
generation. Therefore, alternative solutions are worthy of investigation.
It is noted that the generation of sugar syrups from surplus bread would
leave a relatively starch-free by-product rich in protein and non-starch
polysaccharides, which could be considered for redistribution strate­
gies due to its nutritional value.
There are also other studies about surplus bread flour in which
enzymatic hydrolysis represented a previous step to alcoholic fermen­
tation using Sacharomyces cerevisiae and distillation to produce ethanol
(Ebrahimi, Khanahmadi, Roodpeyma, & Taherzadeh, 2008; Torabi,
Satari, & Hassan-Beygi, 2020). In this process, alongside pH, hydrolysis,
and enzyme concentration, to name a few optimizable parameters, the
hydration level of the flour particles should also be considered during
the conversion of starch into glucose (Demirci, Palabiyik, Gumus, &
Ozalp, 2017). Although many studies propose the use of this alcohol as a
renewable energy, its reuse for human consumption is also possible
provided that all the potential hazards are mitigated, good hygienic
4.3. Other cereal-based food systems
Alongside cakes and cookies, there are other cereal-based food sys­
tems in which gluten development and starch gelatinization do not play
a determinant role on the final quality. Hence, they represent ideal
candidates for successful surplus bread redistribution. Extruded
expanded products such as breakfast cereals and puffed snack systems
are clear examples. Samray, Masatcioglu, and Koksel (2019) proposed
8
M. Gómez and M.M. Martinez
LWT 173 (2023) 114281
sanitary practices are in place, and production processes are adjusted.
Likewise, surplus bread could be reused in beer-making as adjunct,
which is generally considered an alternative to the commonly used
barley malt that contributes fermentable sugars to the brewing wort
(Stewart, 2016). Non-malted cereals and pseudocereals and their
respective starches must be gelatinized prior to being used as adjunct,
but this would not be necessary for surplus bread flour containing all its
starch in gelatinized form. In fact, Martin-Lobera, Aranda,
Lozano-Martinez, Caballero, and Blanco (2022) reported that bread,
used as an adjunct, achieved the same extraction of sugars as malt,
eventually reaching similar alcoholic strength and physicochemical
profile compared to the control malt beer. However, the influence of the
adjunct on the sensory quality of beer (Cadenas, Caballero, Nimubona,
& Blanco, 2021; Yorke, Cook, & Ford, 2021) and on the potential
changes in the processing parameters (Bogdan & Kordialik-Bogacka,
2017) should be carefully considered. Martin-Lobera et al. (2022)
showed that beers made with 50% of the malt replaced by stale surplus
whole bread presented an enhanced physicochemical and flavor profile
than those counterparts made with surplus white bread flour.
Notwithstanding, the different ingredients used in bread-making (e.g.,
type of flour, dough hydration level and the type and content of fat), and
the crust to crumb ratio should be carefully considered since they would
determine the quality of the beer.
Surplus bread flour could also be used to elaborate acidified bever­
ages, with or without probiotics, in a similar manner following the
success of the use of cereals in this type of products (Min, Bunt, Mason, &
Hussain, 2019; Montemurro, Pontonio, Coda, & Rizzello, 2021).
Nevertheless, to the best of our knowledge, there are no studies in this
topic.
bread waste issue. Furthermore, food scientists and technologists will
find a compelling overview of the key and distinct molecular, supra­
molecular and microstructural features of surplus bread particles (flour)
responsible for their food structuring behavior.
Major challenges remain in this area and several important questions
still need to be addressed. Future research should focus on the following
points:
- Establishing specific regulations for the use of novel by-products as
food ingredients to reach sustainability goals for circularity. Any
ambition to reduce bread waste through redistribution strategies can
potentially be hindered by the set of regulations and recommenda­
tions imposed by the different administrations. Hence, they will need
to be amended to account for circular solutions.
- Confirming, with mechanistic studies, that surplus bread waste does
not possess additional risks in terms of mycotoxins and acrylamide
levels compared to fresh bread. Special attention should be paid to
the acrylamide levels of surplus crust, and to the emerging myco­
toxins that are neither routinely determined, nor legislatively
regulated.
- Understanding the conformational changes of gluten, starch, and
other polymeric components of wheat flour during baking and
storage, and how these changes define the behavior of surplus bread
flour as a techno-functional ingredient or substrate for food
applications.
- Understanding the complexity of current and novel food systems so
that alternative ingredients, such as surplus bread flour, can be used
without compromising the final quality of foods.
- Studying the effect of downstream processing on the properties of
surplus bread flour. This could include simple physical steps, such as
mechanical fractionation, or more complex biotechnological path­
ways using enzymes or microorganisms.
- Exploring the possibilities of using surplus bread flour as a substrate
for enzymatic and/or microbial fermentation processes, which could
result in typical products, such as fermented beverages, and new
ones, such as acidified drinks and sourdough containing bioactive
peptides, to name a few examples.
5.2. Sourdough and source of bioactive peptides
The potential of surplus bread can also be exploited for other types of
fermentative processes, such as sourdough production. In fact, extruded
wheat flour derivatives, with relatively similar macrostructure to sur­
plus bread flour, was considered for sourdough development (Juodei­
kiene et al., 2011). The possibility of using surplus bread waste for
sourdough development was contemplated by Gelinas, McKinnon, and
Pelletier (1999). These authors analyzed the behavior of flours from
different sources of surplus bread (refined, wholegrain, and sweet
breads) during fermentation with different starters, reporting a rapid
increase in dough acidity mostly due to the production of lactic acid.
However, the intrinsic microbiota of surplus bread was not investigated,
which could be important considering its potential changes during bread
storage, its variations as a function of the type of bread (Smith, Daifas,
El-Khoury, Koukoutsis, & El-Khoury, 2004), and the potential and
consequent increase of mycotoxins (Schaarschmidt & Fauhl-Hassek,
2018). It is noteworthy that exopolysaccharide-producing lactic acid
bacteria were reported to reduce the negative effects of the incorpora­
tion of surplus bread into bread systems (Immonen et al., 2020), which
was discussed in section 4.1. More recently, Nionelli et al. (2020) pro­
posed the use of surplus bread hydrolysate fermented by Lactobacillus
brevis as antifungal agent, property attributed to the generation of
peptides with antifungal functionality and the significant reduction of
pH. Nevertheless, high doses (18–20%, dough basis) were needed for
successful reduction microbial spoilage.
CRediT authorship contribution statement
Manuel Gómez: Both authors contributed equally in terms of
conceptualization, Visualization, Funding acquisition, Writing – original
draft, and, Writing – review & editing. Mario M. Martinez: Both authors
contributed equally in terms of conceptualization, Visualization, Fund­
ing acquisition, Writing – original draft, and, Writing – review & editing.
Declaration of competing interest
The authors declare no conflict of interest.
Data availability
No data was used for the research described in the article.
Acknowledgements
The authors acknowledge the financial support of Junta de Castilla y
León, Spain (VA177P20) and Independent Research Fund Denmark Danmarks Frie Forskningsfond (project number 1032-00491B).
6. Conclusions and future perspectives
The application of knowledge about the structure and properties of
surplus bread flour is a relatively new and emerging research topic. We
expect that his review will highlight redistribution pathways of surplus
bread into the food supply chain, potentially resulting in environmental
savings together with additional revenue streams for bakeries and re­
tailers. We believe that this review will serve as guidance for all the
different surplus bread stakeholders seeking for timely solutions for the
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