Bread Storage and Preservation

Victoria A Jideani, Department of Food Science and Technology, Cape Peninsula University of Technology, Symphony Way,
Bellville, South Africa
© 2018 Elsevier Inc. All rights reserved.

Abstract 1
Introduction 1
Bread Staling 3
Approaches to Preventing Bread Staling 4
Antimicrobial Spoilage of Bread 5
Storage and Preservation of Bread 5
Reducing or Destroying Mold Spores Contaminating the Bread 6
Physical and Natural Use of Naturally Occurring Compounds 6
Chemical Approaches to Inactivating Microbial Growth and Extend the Shelf Life of Bread 8
Biological Preservation Approach-Use of Lactic Acid Bacteria 8
Effect of Bake-Off Technology on the Storage of Bread 9
Conclusion 10
References 10

Abstract

The limited freshness of bread is consequent to slow chemical or physical changes that result to crumb firmness, referred to as
‘staling’ and microbial attack. Both staling and microbial spoilage limit the sensorial and economic benefits to the baking industry
as well as to the consumer. Published articles from Pubmed database on staling of bread (67 articles) from 1959 to 2018, bread
storage (396 articles) from 1946 to 2018 and bread preservation (198 articles) from 1947 to 2018, were mined to detect the topic
of discussion on bread storage, staling and preservation using KNIME software. The major components of bread such as starch,
gluten and water during storage undergo major modifications resulting to a staled product. The use of fibres (gum Arabic coated
ground flaxseed, b-glycan, hydrated potato and barley flours, fine durum, oat bran, rye bran and wheat bran), enzymes (xylanase,
microbial amylases) and lactic acid sourdough system have potential to reduce bread staling and extend shelf life. Many approaches
to inactivate or delay microbial spoilage in order to extend the shelf life of bakery products include (1) reducing or destroying
mould spores contaminating the bread; (2) physical and natural use of naturally occurring antimicrobial compounds against
food pathogenic and spoilage microorganisms; (3) chemical, use of anti-fungal agents and (4) biological, use of lactic acid bacteria
were discussed.

Introduction

Bread is a yeast-leavened wheat dough baked product with ‘an appealing brownish and crunchy crust, a pleasant aroma, a soft and
elastic crumb texture, a moist mouthfeel’ and fine slicing characteristics (Mondal and Datta, 2008). Sliced bread is a commonly
consumed snack due to its smoothness and compatibility with creamy spreads (Passarinho et al., 2014). Leavening is achieved
when the carbon dioxide produced from the yeast fermentation is trapped in the dough and expands with the dough. Hence, baking
technology is concerned with designing food structures through the formation of correct dough and batter to trap leavening gases
and the fixing of these structures by heat (Mondal and Datta, 2008).
Different types of bread exist across nations and regions as well as variation in speciality bread such as malt loaves, soda, milk
and fruited bread has been reported (Passarinho et al., 2014). One such classification with six criteria, namely (1) type of cereal
(wheat, rye, barley, oat and bran); (2) Sweetened or spiced; (3) preparation method (unsieved, yeast, sourdough and unleavened
bread); (4) shape of the bread (cakes, buns, loaves, rusks, twist biscuits, succaria, hardtack, flatbread); (5) state of the bread (warm,
soft or dry) and (6) faults (collapsed, rock hard, burnt, mouldy and worm eaten) (Carl and Ra, 2017). Another classification
(Table 1) uses five criteria, namely (1) hydration, (2) richness, (3) pre-fermentation, (4) leavener and (5) height (as in flat bread)
(StellaCulinary, 2018; Foedus, 2013; Reinhart, 2001). For the purpose of this review the classification based on processing method
is outlined in Fig. 1. The straight dough method involves the mixing of ingredients in one step. Sponge and dough approach
involves the mixing of ingredients in two steps (1) preparation of the leavening agent where yeast and some flour are mixed
with appropriate quantity of water and allowed to stand for few hours and (2) mixing of the yeast mixture into the rest of the ingre-
dients. In the Chorleywood method all the ingredients are mixed in an ultrahigh mixer for few minutes. Sometimes dried sour-
doughs are used to start the fermentation process requiring cooling the dough to 2
C the day before and automatic warming of
the dough on the day of baking. Pre-fermented frozen dough is fermented prior to freezing. Market concepts related to this

1
2 Bread Storage and Preservation

Table 1 Bread classification

Category Dough Description

Hydration Stiff 50%–57% hydration of liquid to flour e.g. bagels or pretzels. Extremely stiff dough. Chewy, firm,
texture.
Standard 57%–65% hydration of liquid to flour e.g. sandwich bread, rolls, French and other European–style
bread
Rustic Greater than 65% hydration of liquid to flour e.g. ciabatta, pizza, focaccia. A lot of artisan style loaves
including no-knead and high-hydration styles.
Richness Lean Little to no fat or enrichments e.g. French and Italian breads, sourdough hearth and bagels.
Enriched Some fat, dairy, eggs or sugar up to 5%–20% e.g. sandwich bread, soft rolls and challah breads.
Rich Greater than 20% enrichment by weight e.g. brioche, some holiday breads, croissants and Danish
pastry.
Laminate Subcategory of rich doughs with a high percentage of fat that is laminated in layers allowing the
dough to puff when baked to present a flakey crust e.g. puff pastries.
Pre-fermentation Direct or Straight No fermentation, all ingredients in one mixing cycle e.g. Challah, cinnamon buns, English muffins
Indirect or Sponge Pre-fermented or use of starter as in traditional sour dough e.g. Bagels, French and Italian breads,
ciabatta.
Leavener Commercially yeasted Made with commercial yeast (instant, active dry or fresh compressed).
Naturally leavened Made exclusively with wild yeast starter- Sour dough
Chemically leavened Made with a chemical leavening agent (baking powder or baking soda and some other acidic
ingredients) e.g. corn bread, biscotti.
Unyeasted Made without yeast (some can still be chemically leavened) e.g. Matzo crackers.
Mixed Made with both a wild yeast and a commercial yeast (also called “spiking the dough”) e.g. Panettone,
New York deli rye bread, pumpernickel bread.
Height Flat bread Can be enriched or lean, yeasted or unyeasted and are differentiated from other breads by their low
height e.g. pizza (yeasted and enriched), matzo (unyeasted and lean).

Source: Reinhart (2001).

Figure 1 Bread processing technology.

technology is freezer to oven, ready to bake and freezer to bake. Frozen dough bread making procedure involve the dough prepa-
ration, freezing, thawing and baking (Mondal and Datta, 2008).
Water and flour are the most significant ingredients in a bread recipe, with weights on flour (100%) basis and other ingredi-
ents (yeast 2%, sugar 4%, salt 2% and fat 3%) a percent of that amount by weight (Mondal and Datta, 2008; Selomulyo and
Zhou, 2007). A finely textured bread may contain approximately 50% water while 60% to 75% water for most artisan bread
formulas. The higher water content in yeast raised bread results in more carbon dioxide bubbles and a coarser bread crumb
(Mondal and Datta, 2008). Salt initiates fermentation, strengthens the gluten and converts the action of yeast for dough expan-
sion. Shortenings increase the dough machinability. Mechanisation, bread large-scale production and consumer demand for high
quality, convenience and longer shelf life resulted in the use of functional additives such as improvers (include stabilisers, emul-
sifiers, oxidants, gums and enzymes e.g. exogenous alpha-amylases, proteases, hydrolases for non-cellulosic polysaccharides,
lipases, lipoxygenases) and anti-staling agents (Mondal and Datta, 2008; Selomulyo and Zhou, 2007). Emulsifiers increase
 Bread Storage and Preservation 3

dough strength for better machinability, improve the hydration rate, crumb texture, slicing, gas holding capacity and shelf life
extension.
Baking of the dough gives fresh bread characterized by an ‘appealing golden brown and crunchy crust, a pleasant roasted aroma,
fine slicing characteristics, a soft and elastic crumb texture and a moist mouthfeel’ (Mondal and Datta, 2008; Selomulyo and Zhou,
2007). Common characteristics of bread are high moisture (40%) and water activity (0.94 to 0.97; pH ¼ 6), making it susceptible to
mold and consequently a short shelf life (3 to 7 days) (Legan, 1993). The limited freshness of bread is due to (1) slow chemical or
physical changes leading to the crumb firmness, referred to as ‘staling’ (Selomulyo and Zhou, 2007) and (2) microbial attack. Both
staling and microbial spoilage limit the sensorial and economic benefits the baking industry as well as the consumer. This review is
concerned with the storage and preservation of leavened products from a dough of cereal flour and baked, generally recognized as
bread.

Bread Staling

The major components of bread such as starch, gluten and water during storage undergo major changes leading staled product
(Curti et al., 2014). Flour contains starch molecules which have a crystalline or highly organised structure. Fig. 2 outlines the
changes during baking and cooling of bread leading to staling. The starch molecules absorb moisture and swell during baking,
a process known as gelatinisation. Consequently, the starch molecules take on a more disorganised, gel-like arrangement that
gives a soft, fluffy texture setting the structure or crumb of the final loaf. Cooling the loaf below the gelatinisation temperature
makes the starch molecules to reform to their crystallized state as water moves into other parts of the mixture resulting in
progressively harder and dry bread, known as retrogradation or staling. Water migrates from the crumb to crust (Curti
et al., 2014). Recrystallisation occurs faster at cooler temperatures above freezing, hence bread will go stale much faster
when refrigerated. Retrogradation of amylose occurs few hours after baking with that of amylopectin occurring in the long
term and is reported as the major phenomenon involved in bread firming (Ribotta and Le, 2007). The main changes associated
with bread staling include starch retrogradation, reorganisation of polymers within the amorphous region, loss of moisture,
distribution of water between the amorphous and crystalline regions, loss of flavour and crispness, increase in crumb and crust
firmness and reduction in specific volume (Anca et al., 2015; Curti et al., 2014; Mondal and Datta, 2008; Ribotta and Le, 2007;
Gray and Bemiller, 2003). The consequence of bread staling is loss of the characteristic fresh flavour and sensory qualities
resulting in negative perception and low acceptability by the consumers (Curti et al., 2014; Ribotta and Le, 2007; Selomulyo
and Zhou, 2007; Gray and Bemiller, 2003). The preferred parameter for evaluating staling development is crumb firming
(Ribotta and Le, 2007). Starch seems to be responsible for bread staling, however, starch and other ingredients interaction
in the matrix has been reported. The gluten network undergoes some physicochemical changes during storage. Such changes
contributing to bread staling include dehydration leading to loss of plasticity and interaction with starch (Curti et al., 2014).

Figure 2 Changes in bread dough and baked bread during baking and cooling (Node colour by modularity class, node size by betweenness
centrality).
4 Bread Storage and Preservation

The consequence of staling and increasing market demand for bread has resulted to the continuous search for efficient
approaches to prevent staling and extend the shelf life.

Approaches to Preventing Bread Staling

Pubmed database was searched for articles published on staling of bread (67 articles) from 1959 to 2018, bread storage (396 arti-
cles) from 1946 to 2018 and bread preservation (198 articles) from 1947 to 2018. The documents were mined to detect the topic of
discussion on bread storage, staling. and preservation using KNIME software. Co-occurrence is the occurrence of two terms in text
indicating the likelihood relationship. The co-occurrence of terms in the documents were generated using network analysis
approach providing a graphic visualization of potential relationships using Gephi graph visualization and manipulation software.
Fig. 3 indicates the co-occurrence of terms in the articles based on bread staling. The color of the nodes is based on the modularity
class while the size is based on the betweenness centrality of the nodes. Betweenness centrality reflects the ability of a node to affect
other nodes in the network. If a node interacts with another node through an intermediate node, then the role played by this inter-
mediate node is decisive in the association. The more intermediate roles played in associations, the greater the influence of the node
in the network. Similarly, among all nodes in the neighborhood of a specific node, the greater the betweenness centrality of a node,
the more influence it has on that specific node. The staling network has four modular communities. The co-occurrence terms in the
green community with high betweenness centrality are ‘measur’ (140), ‘modifi’ (82.3), and ‘factor’ (50), ‘potato’ (33.8). Popov-
Raljic et al. (2009) reported the application of instrumental measurements of bread crumb colour for measuring bread staling.
The reflectance changes of bread samples packaged in polyethylene could be described by a linear model and the colour of the
different bread categories depends on staling processes and composition of raw material such as flour. They concluded that colour
measurement can be used for screening for bread staling. The ‘modifi’ is related to the modified rice straw (MRS) as a fibre in Fino
bread (Mohamed et al., 2016). The authors reported that 10 or 15% MRS in Fino bread resulted to a higher water retention capacity
compared to the control and consequent improvement of staling rate of the bread. They attributed the increase in water retention to
the high hydrophilic nature of MRS proteins. Curti et al. (2016) studied the ability of potato peel fibre to reduce bread staling over
7 days of storage. The fibre was reported to reduce 1H NMR molecular mobility in bread crumb during storage and consequently
reduces bread staling. Staling kinetics were faster for bread samples baked at higher heating rate based on the first order kinetic
model (Ijah et al., 2014). Bread staling is due to retrogradation of starch with alpha-amylases decreasing the rate of starch gel retro-
gradation by inhibiting the formation of double helices (Palacios et al., 2004). A blend of hydrated potato (Irish or sweet) flour in
wheat bread increased the nutritional value, loaf volume and reduced the rate of staling (Ijah et al., 2014). Replacing 3% wheat flour
with fibre-rich additives (fine durum, oat bran, rye bran and wheat bran) were reported to increase dough stability, with oat bran
giving the higher stability and development time. Oat bran loaves were similar or better than the control for all staling attributes
(Purhagen et al., 2012).
b-glucan and the barley in the purple community relates to anti-staling effects of b-glycan and barley flour in wheat flour chapatti
as reported by Sharma and Gujral (2014). Ground flaxseed incubated at 30
C and heated in a microwave oven to reduce the cyano-
genic glycosides were coated with Arabic gum solution containing ascorbic acid and hydrogenated fat was added to wheat flour to
produce fortified Taftoon bread (Roozegar et al., 2015). The authors reported that increasing coated and uncoated ground flaxseed
decreased water absorption and increased dough stability, development and relaxation time. The highest dough development and
stability occurred with 25% coated ground flaxseed with Arabic gum although with lowest water absorption. The authors concluded
that coated and uncoated ground flaxseed has potential to decrease the staling rate of bread. Roozegar et al. (2015) investigated the
effect of xylanase isolated from Thermomyces languinosus CAU44 in bread making. Xylanase improved the specific bread volume,
with better crumb texture and provided an anti-staling effect.

Figure 3 Network of co-occurrence terms in bread staling (Node colour by modularity class, node size by betweenness centrality).
 Bread Storage and Preservation 5

The blue community relates to the novel sourdough system (Lactobacillus plantarum, and/or Lactobacillus brevis, Saccharomyces cer-
evisiae) prepared from wheat flour supplemented with pulverized date seed (Roozegar et al., 2015). The addition of pulverized date
seed as a dietary fiber in the sourdough reduced bread staling over 7 days of storage. Co-culture of L. plantarum, L. brevis and S. cer-
evisiae gave the highest sourdough acidity and bread specific volume. The drop in pH associated with acid production causes an
increase in the proteases and amylases activity of the flour, consequently resulting in a reduction in staling (Arendt et al., 2007).
The effects of different sourdoughs and additives on bread firmness and staling were studied by Corsetti et al. (2000). Only sour-
dough fermentation delayed starch retrogradation and the effect depends on the level of acidification and on the lactic acid bacteria
strain. The effect of sourdough made of Saccharomyces cerevisiae 141-Lactobacillus sanfranciscensis 57-L. plantarum 13 was improved
with fungal alpha-amylase or amylolytic strains such as L.amylovorus CNBL 1008 or engineered L. sanfranciscensis. A greater delay of
bread firmness and staling was obtained when pentosans or pentosans endoxylanase enzyme and L.hilgardii S32 were added to the
same sourdough. The addition of the bacterial protease to the sourdough increased the bread firmness and staling.
The orange community relates to the effect of tannic acid on bread quality of Chinese wheat (Zhang et al., 2010). Tannic acid
breaks down disulfide bond but also has positive effects on dough properties and bread quality. Disulfide bonds are commonly
considered to be the most important factor affecting changes in the quality of bread, but the authors presented the concept that
other covalent bonds can also improve the quality of flour and bread. The bread adhesiveness and resilience did not change signif-
icantly compared to the control, but changes in hardness and chewiness of the bread made with tannic acid indicated that it could
delay bread staling. The use of fibres (gum Arabic coated ground flaxseed, b-glycan, hydrated potato and barley flours, fine durum,
oat bran, rye bran and wheat bran), enzymes (xylanase, microbial amylases) and lactic acid sourdough system have potential to
reduce bread staling and extend shelf life.

Antimicrobial Spoilage of Bread

Sliced bread, prepacked and wrapped in polyethylene plastic packaging is at high risk of spoilage than unsliced, unwrapped
bread since the cut surfaces can become contaminated and the wrapping allowing moisture condensation due to temperature
fluctuations during transport and storage (Luciana et al., 2009). It is known that more than 90% of bread contamination with
spoilage moulds occurs during the cooling, slicing or wrapping stages. Bread produced without preservatives or with added raw
materials such as bran and seeds results in increased spoilage induced by the microorganisms of Bacillus spp. (Bacillus subtilis
and Bacillus cereus), yeasts and moulds (Anca et al., 2015). Bacterial spoilage of bread results in ropiness mainly caused by
Bacillus subtilis which is reported to originate from the raw materials, the bakery environment and equipment surfaces (Magan
et al., 2012). During baking of bread, the vegetative forms of microorganisms and the bacterial and fungi spores are destroyed.
Hence, for bread to become mouldy it must be contaminated after baking, during the cooling, slicing or wrapping operations.
Furthermore, flour as well as other dry ingredients contain mould spores and the flour dust can spread throughout the bakery
especially where separating different processes is difficult. The airborne distribution of flour dust and mould spores can
contaminate bread (Legan, 1993). Penicillium, Aspergillus, Fusarium and Rhizopus genera are the most common spoiling fungi
isolated from grain products, whereas Zygosaccharomyces, Saccharomycopsis, Pichia, Candida and Debaryomyces genera relate to
the yeast of bakery products and ingredients (Cizeikiene et al., 2013). Other filamentous mould species implicated in spoilage
of bread include Cladosporium, Mucor and Neurospora (Legan, 1993), Monilia, Endomyces (Passarinho et al., 2014). According to
Lega and Voysey (1991) 60% of spoilage of bakery products is attributed to moulds (Penicillium spp and Aspergillus niger)
whereas the yeasts accounted for only 15%. According to Magan et al. (2012) the predominance of Penicillium species may
be due to their ability to grow over a wide temperature ranges and available water in addition to the production of spores
which can become airborne. Bacterial and fungal spoilage is the main cause of economic concern in bakeries and the food
industry (Luciana et al., 2009). The control of contamination of bread with spoilage mould is critical since some of the moulds
contaminating bread are also able to produce toxic secondary metabolites such as mycotoxins (Luciana et al., 2009). Apart
from the uncomfortable sight of visible mould growth on bread, fungi are responsible for off-flavour development, the produc-
tion of mycotoxins as well as allergenic compounds which may be formed even before the mould growth becomes visible
(Nielsen and Rios, 2000).

Storage and Preservation of Bread

Preventing mold spoilage of bakery products can be achieved by restricting the access of spoilage molds to the product; inactivating
the fungal material and inhibiting the growth of the fungus. However, once the mold gains access to the product, the objective is to
control its activity and growth in the product (Magan et al., 2012). Many approaches had been reported in literature to inactivate or
delay microbial spoilage and extend the shelf life of bakery products including (1) reducing or destroying mould spores contam-
inating the bread; (2) physical and natural use of naturally occurring compounds delivering antimicrobial activity against food
pathogenic and spoilage microorganisms (Passarinho et al., 2014)- active packaging; modified atmosphere packaging (MAP), irra-
diation, aseptic packaging; (3) chemical, use of anti-fungal agents-the addition of organic acids such as propionic, benzoic and sor-
bic acids; (4) biological-use of lactic acid bacteria (Magan et al., 2012).
6 Bread Storage and Preservation

Reducing or Destroying Mold Spores Contaminating the Bread

Reducing the number of viable mold spores contaminating bread involves improving bakery hygiene to prevent molds gaining
access (Legan, 1993). Such hygienic approach includes (1) preventing accumulation of debris on machinery such as trays, racks,
travelling belts and slicing machines; (2) laundering prover pockets frequently; (3) keeping walls, floors, ceilings and other surfaces
clean, particularly any surfaces coming into contact with the product; (4) separating flour handling areas from product cooling and
wrapping areas; (5) keeping returned products out of the bakery, especially if already mouldy (Legan, 1993).

Physical and Natural Use of Naturally Occurring Compounds

Packaging is useful in extending the shelf-life and microbiological safety of bread. Commonly used packaging for bread is flexible
plastic or paper with limitations due to the water and oxygen molecules retained in the package headspace and poor barrier prop-
erty. The high level of oxygen in the packaging has a significant contribution to the reduction of shelf life. Hence, oxygen level
control is considered significant for effective packaging of bread. Unfortunately, vacuum packaging is not suitable to extend the shelf
life of bread and bakery products as the products are crushed under the vacuum (Robertson, 2013). Anca et al. (2015) reported that
complex packages made of paper and polypropylene or perforated orientated polypropylene had improved barrier property and
efficiency in bread preservation.
An alternative to chemical preservation is the use of modified atmosphere packaging (MAP) techniques. The principle of MAP
systems is based on molds requiring oxygen to grow and are sensitive to carbon dioxide. Thus, changing the ratio of O2 (low) and
CO2 (high) may retard the germination and growth of molds as well as other microorganisms (Magan et al., 2012). Modified atmo-
sphere packaging (MAP) is widely used to extend the shelf life of baked products with inert gas of 100% carbon dioxide, or a combi-
nation of carbon dioxide and nitrogen (Huang and Miskelly, 2016). Modified atmosphere (60% CO2 and 40% N2) extended the
shelf life of bread to 24 days at 20
C (Fik et al., 2012). Nielsen and Rios (2000) examined the effectiveness of volatiles in MAP
systems for the control of spoilage molds on rye bread and reported that mustard essential oil (ESO) in the volatile phase at
1–10 mg/mL was effective against Penicillium commune, P. roqueforti, Aspergillus flavus and Endomyces fibuliger. High levels of carbon
dioxide retarded growth but not completely.
The consumer demand for high-quality minimally processed and synthetic preservative-free products has resulted in attention
toward preservation techniques using natural compounds. Among such methods, active packaging is the most innovative improved
sensory and shelf life properties while enhancing food quality and safety (Passarinho et al., 2014). Active packaging system (APS)
consist of incorporation of the active agent into the packaging material rather than directly into the food. The compound either
interacts with the food or the atmosphere of the enclosed packaging (Matan et al., 2006). There is a growing interest in the use
of natural plant extracts (essential oils) either alone or as mixtures, or in combination with packaging systems, to extend shelf
life. Essential oils are mostly derived from spices and herbs obtained from different parts of plants including leaves (e.g. rosemary,
sage, thyme), flowers (e.g. clove), bulbs (e.g. garlic, onion) or fruit (e.g. pepper, cardamom) (Deena and Thoppil, 2000). Such natu-
rally occurring compounds which may be extracted from plants essential oils include benzaldehyde, carvacrol, cinnamaldehyde,
cinnamic aldehyde, cymene, eugenol, limonene, menthol, salicylaldehyde, terpineol, thymol and vanillin can deliver antimicrobial
activity against food pathogenic and spoilage microorganisms (Dobre et al., 2011; Passarinho et al., 2014). Oregano (Origanum
vulgare) essential oil (OEO) among plant compounds has been reported to exhibit high contents of phenolic compounds that
are responsible for outstanding antimicrobial properties (Souza et al., 2006). In this regard, OEO-containing sachet innovative
system enabled gradual release of volatile compounds into the packaging atmosphere and have been demonstrated to be effective
in controlling Penicillium sp. and fungal spoilage both on the laboratory media and sliced bread, respectively (Passarinho et al.,
2014). The OEO sachets reduced the growth of yeasts and moulds on sliced bread and allowed the gradual diffusion of volatile
active compound into the bread slices without affecting the bread texture but imparted unpleasant sensory effects when higher
concentration was used. As an alternative to MAP, active packaging (AP) using volatile essential oils (EO) and oleoresins (OL)
from spices and herbs were tested against a range of fungi commonly found on bread. Mustard essential oil showed the strongest
effect, cinnamon, garlic and clove also had high activity, while oregano oleoresin only inhibited growth weakly. Vanilla showed no
inhibitory effect towards the tested microorganisms at the applied concentrations. A. flavus was more resistant than the other micro-
organisms while P. roqueforti was the most sensitive. Mustard essential oil was investigated in greater detail using the active compo-
nent, allyl isothiocyanate (AITC). AITC was fungistatic or fungicidal depending on its concentration, and the concentration of
spores. When the gas phase contained at least 3.5 mg/mL, AITC was fungicidal to all tested fungi. Hot-dog bread was more sensitive
to AITC than rye bread. The minimal recognisable concentration of AITC was 2.4 mg/mL gas phase for rye bread and between 1.8
and 3.5 mg/mL gas phase for hot-dog bread. Hence, the shelf-life of rye bread could be achieved by active packaging with AITC.
Mixtures of cinnamon extract and sodium benzoate were effective in controlling A. flavus (López-Malo et al., 2007). Cinnamon
ESO was incorporated into solid wax paraffin as an active coating and tested for antifungal activity on black bread mould (Rhizopus
stolonifera) (Rodriguez et al., 2008). The authors reported that 6% of the ESO was effective in situ, while 4% was effective in vitro.
The 6% completely inhibited growth on sliced white bread for three days and the extracts of the bread indicated that the active ingre-
dient cinnamaldehyde was present in the bread being responsible for the inhibition effect. The incorporation of ESOs directly as an
ingredient is less effective compared to the expectation from in-vitro studies. Usually ESOs consist of a mixture of esters, aldehydes,
ketones and terpenes and it is thus difficult to know exactly which active component have efficacy for controlling mould growth in
bakery products (Magan et al., 2012).
A problem associated with the MAP for bakery products is the difficulty in reducing the oxygen content within the package to
a very low level due to a large number of pores in the bread matrix which tend to trap oxygen. A reported approach is to use oxygen
 Bread Storage and Preservation 7

absorbers inside the package (Latou et al., 2010). Active packages such as ethanol emitter, oxygen absorber, water absorber, and
oxygen and/or water scavengers have extensively been investigated with promising solutions in food shelf life extension. Use of
1% ethanol released from an adsorbent pad extended the shelf life of packaged white bread to more than 60 days at 22
C, with
chalk molds developing within 10 days (Legan and Voysey, 1991). Ethanol emitters and/or oxygen absorbers have been used to
extend the shelf life of sliced rye bread and durum wheat bread (Latou et al., 2010). The authors reported that a combination of
active packaging with a high barrier packaging material such as PET-SiOx//LDPE could greatly extend the shelf life of sliced bread.
Alternatives to chemical preservation include the use of Ultraviolet (UV), Infrared or microwave irradiation to destroy the mold
spores that gain access to the cut surfaces of bread during cooling and wrapping processes. UV irradiation is not very effective as it
does not penetrate the product and mold spores in crevices within the bread surface are shielded from its effects. Infrared and micro-
wave radiation reheat the bread, thereby pasteurizing it and permitting a very long shelf. However, they can cause moisture conden-
sation requiring a special heat-resistant wrapping material (Legan, 1993). The consumer pressure for minimally processed and
freshly baked bakery goods has limited the use of such procedures (Magan et al., 2012).
The use of nanoparticles and nanotechnology for the slow release of preservatives or alternative antimicrobial agents directly into
the food product over time to enhance shelf-life and mold-free storage time has received attention in the food industry (Magan
et al., 2012). Bread stored in AG/TiO2-based packaging was significantly preserved from the proliferation of yeast/mold, B. cereus
and B. subtilis; degradation of the main nutritional compounds compared to the bread stored in open atmosphere or in common
plastic package (Anca et al., 2015).
Other strategies that have been reported to limit the rate of mould growth in ready-to-eat fresh baked goods such as garlic bread,
tomato and herb-based bread include (1) reformulate recipes by reducing the water availability but without adversely affecting the
eating quality of the product or causing changes in volume, texture or shape; (2) use novel ingredients such as fruit juices (raisin,
prune, apple juice concentrate) that inhibit fungal growth (Sanders, n.d.).
Fig. 4 details the co-occurrence terms network for bread storage. The purple community relates to the work of Giuseppe Rizzello
et al. (2009) on fungal inhibitory activity of water-soluble extract from Amaranthus spp. seeds during storage of gluten-free and
wheat flour breads. Crude water-soluble extract showed inhibition towards a large number of fungal species isolated from bakeries.
When used as an ingredient for the manufacture of gluten-free and wheat flour breads inhibited fungal activities during long-term
shelf-life conditions. Coda et al. (2008) reported the long-term fungal inhibitory activity of water-soluble extracts of Phaseolus vul-
garis cv. Pinto and sourdough fermented with L. brevis AM7 during bread storage. The water-soluble extract is composed of phaseo-
lin alpha-type precursor, phaseolin, and erythroagglutinin phytohemagglutinin precursor and were all inhibitory to a variety of
fungal species isolated from bakeries. The authors identified a mixture of eight peptides from the water-soluble extract of sourdough
L. brevis AM7, and five of these exhibited inhibitory activity. Slices of bread made by sourdough fermentation with L. brevis AM7 and
addition of the water-soluble extract (27%, vol/wt; 5 mg of protein/mL) of P. vulgaris cv. Pinto, packed in polyethylene bags reduced
fungi contamination for 21 days of storage at room temperature, a level of protection comparable to that obtained by 0.3% (wt/wt)
calcium propionate. Purhagen et al. (2012) reported that microencapsulation of L-5-methyltetrahydrofolic acid with ascorbate
improves the stability in baked bread products.
Fig. 5 indicates the terms co-occurrence for bread preservation manuscripts. Denardi-Souza et al. (2018) reported that the extract
from rice bran fermented with Rhizopus oryzae CECT 7560 added to bread at 10 g kg1 extended the shelf life of bread for 3 days.

Figure 4 Network of co-occurrence terms in bread storage. (Node colour by modularity class, node size by betweenness centrality).
8 Bread Storage and Preservation

Figure 5 Network of co-occurrence terms in bread preservation. (Node colour by modularity class, node size by betweenness centrality).

Chemical Approaches to Inactivating Microbial Growth and Extend the Shelf Life of Bread
This is the most common way to prevent or control mold growth by adding chemical compounds to food which prevent or retard
food spoilage molds from growing. Most of these compounds are in practice fungistatic rather than fungicidal as they are effective at
stopping germination and subsequent growth (Magan et al., 2012). Fungicidal compounds though more effective in destroying the
spoilage molds are not approved for use in bread (Magan et al., 2012). Food grade preservatives based on propionic, sorbic and
acetic acids and their salts are used to prevent mold spoilage of bread and bakery products thereby extending their shelf life. These
are aliphatic acids and are quite volatile and corrosive, hence their sodium, potassium or calcium salts are the forms most
commonly used due to their better solubility in water, stability and handling ease. Propionates have little or no effect against yeasts,
making them highly suitable to control mold spoilage in yeast-raised bread products (Magan et al., 2012). These lipophilic weak
acids can penetrate the cell membrane in the undissociated form, thus creating a higher pH environment allowing the molecules to
dissociate, leading to the release of charged anions and protons which cannot cross the plasma membrane. Hence, the high solu-
bility, low taste threshold and low toxicity of the weak organic acids make them suitable for use in bread and baked product preser-
vative systems (Magan et al., 2012.). The pH of the environment and the solubility of the acid determine the foods in which these
weak acids may be effectively used. They have low pKa (4.19–4.87) and are therefore effective in low pH matrices as such conditions
favour the uncharged, undissociated state of the molecule that is permeable across the cell membrane. The maximum pH for activity
is about 6.0–6.5, 5.0–5.5, 4.0–4.5 respectively, for sorbate, propionate and benzoate (Magan et al., 2012).
Phenolic-derived antioxidants (butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), propyl gallate (PG) and tert-
butyl hydroquinone (TBHQ)) have been tested in bread for retarding spoilage through incorporated in bread and challenge testing.
Cladosporium herbarum, Penicillium corylophilum, P. verrucosum and Aspergillus ochraceus were completely inhibited by propyl paraben,
BHA and octyl gallate at 500 ppm (Magan et al., 2012). Kubo et al. (2001) reported that octyl gallate (3, 4, 5-trihydroxybenzoate)
possesses antifungal effect against Saccharomyces cerevisiae and Zygosaccharomyces bailii in addition to its potent antioxidant activity
with catechol moiety as being essential for this activity. The fungicidal activity resulted from its ability to act as a non-ionic surface-
active agent (surfactant). Both parabens and BHA have been reported to significantly inhibit the mycotoxigenic spoilage fungi such
as Fusarium, Penicillium and Aspergillus species (Magan et al., 2012). Parabens are effective over a wider range of pH (3–8) than the
organic acids because of their high pKa value of 8.5. Their antimicrobial activity is related to the length of the ester group of the
molecule. They are applied as alkali solution or as ethanol or propyl glycol solutions in fillings for baked goods, fruit juices, marma-
lades, syrups, preserves and pickled sour vegetables (Magan et al., 2012). The efficacy against mold spoilage of some antioxidants
and essential oils in bread and baked goods indicates that the concentrations required for inhibition of growth were generally higher
than those obtained to be effective in-vitro. This suggests that the active ingredients may be bound to ingredients or dispersion in the
product is not effective enough to enable contact with the spoilage molds to delay growth (Magan et al., 2012).

Biological Preservation Approach-Use of Lactic Acid Bacteria

Consumers’ demand for more natural products have resulted to exploitation of bio-preservation approaches in recent years. Micro-
organisms are already commonly used in the preparation of sourdough breads and lactic acid bacteria (LAB) as starter cultures in
food processing (Magan et al., 2012). Lactic acid bacteria (LAB) are involved in most food fermentations contributing to desired
sensory properties and ensure microbiological safety of final product (Smaoui et al., 2010). Lactic acid bacteria confer antimicrobial
effect due to the production of bioactive molecules including organic acids (lactic-, acetic-, propionic-, sorbic-, benzoic-acids), fatty
acids, hydrogen peroxide, diacetyl, ethanol, phenolic and proteinaceous compounds. In addition, some strains synthesize
 Bread Storage and Preservation 9

antimicrobial substances such as bacteriocins (Cizeikiene et al., 2013; Luciana et al., 2009). Cizeikiene et al. (2013) reported that
LAB producing organic acids and bacteriocins-like-inhibitory substances (BLIS) [Lactobacillus sakei KTU05–6, Pediococcus acidilactici
KTU05–7, Pediococcus pentosaceus KTU05–8, KTU05–9 and KYU05–10 strains] showed fungicidal and fungistatic activities against
fungi and yeast such as Fusarium culmorum, Penicillium chrysogenum, Aspergillus fumigatus, A. versicolor, Penicillium expansum, A. niger,
Debaryomyces hansenii and Candida parapsilosis. P. pentosaceus KTU05–9 (20%) sourdough in a bread recipe artificially contaminated
by Bacillus subtilis spores suppressed the bread ropiness for 6 days at 23
C. Single cell suspension of P. acidilactici KTU05–7,
P. pentosaceus KTU05–8 and KTU05–10 sprayed on the bread surface, inhibited fungi growth for 8 days of storage in polythene
bags. Luciana et al. (2009) reported that L. plantarum CRL 778, Lactobacillus reuteri CRL 1100 and L. brevis CRL 772 and CRL 796
displayed antifungal activity against Aspergillus, Fusarium and Penicillium, the main contaminants in bread. Acetic and phenyl-
lactic acids were the antifungal compounds. The fermentation quotient and the leaven volume of doughs with LAB and yeasts
were higher than doughs without LAB. Furthermore, the inclusion of antifungal LAB strains in the starter culture resulted to
50% reduction in the concentration of calcium propionate [CP], yet with similar shelf life to that of traditional bread containing
0.4% CP. Lavermicocca et al. (2000) reported that using LAB with high and wide antimicrobial activities as starters for sourdough
preparation can protect baked goods from fungal and yeast spoilage by destroying spores which have contaminated the products.
Contamination of moulds can be prevented by irradiating the goods with infrared rays or microwaves, using modified atmospheres
in packaging or adding chemical preservatives such as propionic acid (Luciana et al., 2009). A study investigated the effectiveness of
95 LAB strains against antifungal activity of the most common contaminants in bread indicated that the LAB antifungal activity was
dependent on the LAB strain and the fungus species (Luciana et al., 2009). Lavermicocca et al. (2000) reported that L. plantarum 21B
in sourdough breads offer good protection against a variety of mould spoilage including P. corylophilum, P. expansum, P. roqueforti, E.
fibuliger, A. niger, A. flavus and Fusarium. graminearum. These fungi represent almost all the species commonly isolated from contam-
inated baked goods. The active compound was reported as phenyllactic acid and its corresponding 4-hydroxy derivative (p-hydrox-
yphenyllactic acid). Hence, LABs may produce useful antifungal compounds that could be used to substitute the existing fungistats
with a similar level of effectiveness (Magan et al., 2012).

Effect of Bake-Off Technology on the Storage of Bread

Freezing bake-off technologies are commonly used in the preservation of bread products (Chen et al., 2013). The bake-off tech-
nology (BOT) involves the manufacture of semi-finished products which are then frozen and finished in baking stations at the point
of retail. The bake-off processes most commonly used are the partially baked frozen (PB-F) and unfrozen dough (PB-UF), and the
unfermented frozen dough (U-FD) methods (Le-Bail and Gabric, 2012). For PB-F, partial baking is applied, the bread is then frozen
and stored at freezing condition (20
C). PB-UF is achieved by stopping the baking before crust colouration and stored at room
temperature in modified atmosphere packaging. The bread is baked at a lower temperature than conventional baking (e.g. 180
C
instead of 230
C for a French baguette) and for a shorter time with the objective of baking the bread without crust coloration (Le-
Bail and Gabric, 2012). For U-FD, the dough is prepared, shaped and frozen. The frozen dough has to be thawed, fermented and
then baked. Baking is done after fermentation. Freezing affects dough rheology due to the modification of the free to bound water
ratio. During storage the amount of free water increases with increasing storage resulting in a dehydration of the matrix which loses
its extensibility becoming more elastic (Le-Bail and Gabric, 2012). Fast freezing reduces the gassing power and the number of viable
yeast cells as well as higher sensitivity to storage duration than slow freezing (Selomulyo and Zhou, 2007). A slow freezing rate is
therefore recommended to limit the negative impact of freezing on frozen dough, storage at temperatures lower than the glass tran-
sition temperature of the dough is often preferable. A set point in the freezer (25
C) combined with a final core temperature of
about 12
C followed by packaging and equilibration in frozen storage down to 18
C or lower is considered good practice (Le-
Bail and Gabric, 2012). Such practice is expected to yield optimal bread from frozen dough with minimal energy to freeze the prod-
ucts (Le-bail et al., 2010).
Unbaked dough and baked or part-baked bread could be produced in large quantities during production and then distributed
over an extended period to consumers (Chen et al., 2013). The frozen bread profitability is in the high economic benefits and conve-
nience. Quality deterioration of frozen dough and bread is due to the undesirable physiological changes at the freezing step and
during the frozen storage following the formation and growth of ice crystals that affect the gluten network and starch granules
(Chen et al., 2013). The authors investigated the dynamics of water and ice in wheat bread at 18
C for approximately 4 months.
The frozen bread lost the crumb water, which migrated and formed ice crystals on the bread surface. Within the frozen crumb, the
significant redistribution of water resulted in an elevated crumb heterogeneity of freezable water. Such redistribution of freezable
water accompanied by progressive recrystallization of the ice crystals grew in bulk sizes within days in the frozen crumb. The conse-
quence includes lack of the same appealing quality of unfrozen bread, reduced specific volume, increased crumb firmness, decreased
palatability and degenerated staling tolerance (Selomulyo and Zhou, 2007; Chen et al., 2013). The bread crust has a significant
effect in reducing the effective diffusivity of moisture as the internal water of bread is restricted from escaping outside by the crust
(Chen et al., 2013). Thus, a higher concentration of ice crystals is formed underneath the crust at freezing temperatures.
The bread quality from frozen dough is influenced by dough formation as well as the process parameters including dough mix-
ing time, freezing rate, storage duration and thawing rate. These factors act independently or in synergy to reduce yeast activity which
results in reduced carbon dioxide production or to damage the gluten network which in turn results in poor carbon dioxide reten-
tion and poor baking performance (Rouillé et al., 2000; Lucas et al., 2005). Other problems related to the production of bread from
10 Bread Storage and Preservation

frozen dough include gradual loss of the dough strength, decrease in the retention capacity of CO2 and longer fermentation time,
reduced yeast activity; lower loaf volume and deterioration in the texture of the final product (Selomulyo and Zhou, 2007; Le-Bail
and Gabric, 2012). Loss of dough strength has been attributed to the release of reducing substances such as glutathione from yeast
during freezing, reduction of gluten cross-linking caused by ice recrystallization and the water redistribution due to the modification
in the water binding capacity of dough constituents. Glutathione weakens the dough by cleaving disulfide bonds in the gluten
proteins, an important factor in determining the rheology of gluten (Selomulyo and Zhou, 2007). Loss of water holding capacity
of the dough and the subsequent increase in dough syruping is attributed to the degradation of arabinoxylan, a cell wall polysac-
charide by endogenous xylanases (Gys et al., 2003). During baking, the gluten does not rehydrate and excess water may migrate to
the starch paste, affecting the yield stress of the starch paste thereby compromise the baking performance of the dough. To improve
frozen dough several technical modifications include (1) the isolation of freeze-resistant yeasts; (2) addition of improvers such as
emulsifiers and water-binding agents like hydrocolloids to stabilise the dough network; (3) addition of wheat proteins to increase
shelf life; (4) modification of dough composition; (5) use of heat-stable enzymes to shorten fermentation time, and (6) optimisa-
tion of mixing, freezing and freeze-thaw cycles (Selomulyo and Zhou, 2007). Flour with high gluten content (>12%) is appropriate
for frozen dough, specific flour blends may be used or vital gluten may be added to the flour (Le-Bail and Gabric, 2012). The
amount of yeast for frozen dough can be doubled.
Pre-fermented frozen (PFF) dough, ready-to-bake or oven rise was developed with the objective of having some ready-to-bake
products that may be transferred directly from the freezer to the oven (Le-Bail and Gabric, 2012). The PFF dough is very fragile, the
gas cells may collapse during refrigeration due to gas contraction consequent to (1) a pressure drop caused by refrigeration; (2)
condensation of the humidity contained in the cells and (3) transfer of gaseous CO2 towards the dough due to the increase of solu-
bility of CO2 with decreasing temperature (Le-Bail and Gabric, 2012). Lucas et al. (2010) attributed the decrease in volume of pre-
fermented dough to be related to coalescence of the gas cells during refrigeration. The authors also observed the formation of large
bubbles during freezing due to the compression of gases in a structure that cannot deform globally to the frozen ‘shell’ resulting in
a consecutive rupture of dough film and the coalescence of neighboring bubbles. The freezing tolerance of pre-fermented frozen
dough may be improved by combining chemical leavening and yeast, increasing the protein content of the dough, leavened and
unleavened frozen dough compositions should have over 16%, preferably (17%–18%) wheat protein based on total weight of flour
(Le-Bail and Gabric, 2012).
Hydrocolloids due to their ability to induce structural changes in the main components of wheat flour systems during bread
making and storage have been proposed as a solution to minimize the freezing damage in dough systems (Sharadanant and
Khan, 2006; Le-bail et al., 2010). One of the roles of hydrocolloids is to stabilize water, thereby reducing the free water in the dough
system and to give improved tolerance to frozen storage (Le-Bail and Gabric, 2012). The addition of locust bean gum and gum
Arabic produced dough with better capability to retain the gluten network compared with the frozen control (Sharadanant and
Khan, 2006). The SDS-soluble protein content increased while the residue protein content decreased with frozen storage supporting
the theory of depolymerization of the higher molecular weight polymers (Ribotta et al., 2001; Sharadanant and Khan, 2006). After
each period of frozen storage, the control dough without the hydrocolloid had the highest amount of SDS-soluble protein, while the
k-carrageenan and locust bean gum doughs had the lowest amount. The control dough has the lowest amount of residual protein
relative to the dough treated with hydrocolloids, while the dough treated with k-carrageenan has the largest amount of residual
proteins followed by doughs of locust bean, gum Arabic and carboxymethyl cellulose (CMC) (Sharadanant and Khan, 2006).
Guar gum and DATEM improved the bread volume and texture resulting in a reduced staling rate (Ribotta et al., 2004). The freezing
of dough facilitates the activity of phytase enzymes which degrades phytates. Hence, frozen dough made of wholemeal flour or
those enriched with fiber may have in the presence of phytase higher amount of available minerals which are trapped in phytate
complexes (Rosell et al., 2009).
Mixes of improvers may be made of specific amylases, gluten and ascorbic acid. While amylases facilitate the release of free sugars
for fermentation, gluten and ascorbic acid favor dough rheology and gas retention (Le-Bail and Gabric, 2012). The combination of
shortening and emulsifiers yield higher gas retention during fermentation giving freezing tolerance to the dough.

Conclusion

The Pubmed database contains 67 articles on bread staling, published from 1959 to 2018; 396 articles on bread storage from 1946
to 2018 and 198 articles on bread preservation from 1947 to 2018. Limited freshness of bread is due to staling and microbial attack.
The use of fibres (gum Arabic coated ground flaxseed, b-glycan, hydrated potato and barley flours, fine durum, oat bran, rye bran
and wheat bran), enzymes (xylanase, microbial amylases) and lactic acid sourdough system have potential to reduce bread staling
and extend shelf life.

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