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The fungal and yeast contaminants cause the spoilage and devaluation of packed bread. The precautions to fungal contaminants include physical treatment, chemical preservative, and packaging system. Nowadays, the active antifungal microorganisms and its metabolites are implemented in the technology of the packing bread to substitute chemical preservatives and approach clean label.
The bread is the staple food represented by many national bread types differing according to production methods and countries of origin. In general, the bread is available for consumers in unpacked and packed form as the loaf or sliced one. In consideration of the fact that the consumption of packed bread increases yearly over Europe and North America, the safety and effective preservation of packed bread against spoilers and contaminants is highly demanded. The right packaging preserves the bread against contamination, prolong the freshness, and consequently limits the bread waste . In spite of sophisticated systems of packaging and application of food preservatives, the fungal spoilage is the main problem of packed bread. This review is focused on possibilities of the protection of the packed bread against fungal spoilage emphasis on alternative methods to approach “clean label.”
The fungi and yeast are widespread eucaryotic organisms present in the environment of bakeries in the form of persistent spores in spite of HAACP concept. The spores are transmitted by air, humans, equipment and input material as the flours, grains, sourdoughs and other raw materials. Although the fungal contaminants are inactivated during the baking process, the new contamination appears during cooling, slicing, wrapping, and storage of the bread. The environmental factors limiting the germination of the spores and development of fungus are moisture, temperature, rate of O2/CO2, the content of permitted preservatives, packaging system including
packaging material. All these factors consequently influence the shelf-life of the packed bread. The fungal contaminants of packed bread are represented mainly by Penicillium commune, P. freii, P. olsoni, P. roquefortii, Aspergillus glaucus, A. niger, Fusarium culmorum, F. graminearum, Mucor mucedo, Cladosporium sp., Alternaria sp., Neurospora crassa, Eurotium repens and many others [2-4].
The bread is exposed to contaminants from the environment during the cooling phase. The physical treatment, such as UV light, is the traditional treatment of the bread surface in most of the bakeries. The characters of UV radiation don’t allow to treat all part of the bread but is an effective support to keep the contaminant-free environment, including packaging process. The use of packaging material concerning the food contact phase, permeability, vapor, and other desired properties is controlled by regulation (2002/72/72/EC) . The modified PE-LD bags are the most frequently used . Modified atmosphere packaging (MAP) with carbon dioxide and nitrogen gas can suppress the mold spoilage depend on packaging technology material used. The MAP, in combination with an antimicrobial agent such as calcium propionate (0.4%), was tested effectively on soy bread by . Similarly, the active packing techniques (APT) based on trapping of oxygen migrating (oxygen absorbers) from bread eliminate the growth of fungi and prolong the shelf-life of the packed bread .
The chemical preservatives represented mainly by short
chain organic acids such as propionic acid, sorbic acid lactic
and phenylacetic acid were tested in many studies as the
effective antifungal agents in bread [9,10]. The weak organic
acids can be applied as protective agents in several ways.
The weak acids can be sprayed on the surface of bakery
products or incorporated as the layer in packaging material
[9,11]. The practical use of a chemical preservative in the
bakery i s l imited b y r egulation [ 12]. A ccording t o l aw, t he
propionate can be added at a maximum of 0.3% and sorbate
0.2% w/w only to packed sliced and rye bread. In the case
of unsliced bread is allowed up only 0.1% w/w of propionate.
The high concentrations of the preservatives can protect
the bread against fungal spoilage, but also influence the
sensory properties. The unsuitable application of chemical
preservatives can develop fungal resistance, fungal growth,
and mycotoxin production.
The limited application of chemical preservatives, emerging
fungal resistance, and the effort to “clean label” encourage the
researchers to test alternative and safety preservatives in
packed bread . The natural products such as ferments with
the effective content of organic acids performing antifungal
effect remain an alternative to approach clean label. The
whole process of fermentation includes essential steps such
as the substrate selection, selection of microorganisms, and
the balance of the technological parameters to obtain optimal
chemical composition of the ferment. Then the ferments
need to be tested against target fungal spoilers in vitro. The
utilization of naturally produced whey ferment with natural
propionate produced by Propionibacterium freudenreichii
was successfully tested in vitro and under semi-pilot
conditions [14, 15]. The practical use of whey ferment with
propionate in the bread dough needs the adjustment of the
bread recipe concerning sensory properties. The antifungal
effect lies in temporary inhibition of spore germination not in
the total elimination of the molds. Thus, the shelf life of packed
bread can be prolonged about two weeks [14,15].
The utilization of lactic acid bacteria (LAB) as the
protective microorganisms in the bakery is based on its
production of active microbial compounds with antifungal
activity during the fermentation process in sourdoughs. LAB
release during fermentation lactate, acetate, and other active
microbial compounds contributed to the production of phenyl
and substituted phenyl derivates of short chain organic acid
[16,17]. T he a ntifungal i nhibitory e ffect i s t he r esult o f t he
synergic action of substrate acidification and low molecular
compounds. The production of active microbial compounds
by LAB is intraspecific characteristics regulated by genes and
environment . The protective LAB cultures are utilized as
the starter culture or/and adjunct in sourdough [16,18,19].
The antifungal activity Lbc. fermentum C14 was successfully
tested against bread molds via spraying LAB suspension
on bread surface by . The strains of LAB belonging to
genera Lactobacillus, Lactococcus, Pediococcus, Weisella,
Leuconostoc are included in Qualified Presumption of Safety
(QPS) for authorized use in the food and feed chain within
European Union . Similarly, in the US, these LAB have the
status as Generally Regarded as Safe (GRAS) under to U. S.
Food and Drug Administration .
The yeast such as Wickerhamomyces anomallus, Pichia
fermentans, Meyerozyma quilliermondii themselves or in
combination with LAB are tested as promising agents with
antifungal properties suitable for sourdough fermentation
with antifungal effect [16,23].
The packed bread is the most widespread commodity of the
bakery industry. The demands of consumers on the quality and
shelf life of bread reflect current nutrition trends and healthy
benefits. The “clean” or “ friendly label” designates the packed
sliced bread without E-numbered additives, enzymes, and
preservatives. The alternative preservatives with antifungal
effects include the ferments with a sufficient content of short
chain organic acid as the product of the fermentation process.
The implementation of the ferment into bread dough or the
application on the bread surface after the baking process are
two main applications needed technological adjustments.
The representatives of LAB remain an effective alternative of
chemical preservatives. Although the principles of antifungal
activity of LAB, yeast, and ferments are known, the fungal
contaminants remain still a severe problem regarding resistant
and adaptive mechanisms fungal organisms to sanitation
chemicals, fungicide, and antibiotics. The antifungal activity
is intraspecific characteristic, so the research is aimed at the
selection and testing new strains of LAB and yeast suitable
for packed bread technology. All the alternative antifungal
treatments postpone the germination of spore or fungus
development but don´t eliminate the fungal contaminants. The
chemical and sensory properties of packed bread are changing
during storage as well as a microbial composition including
yeast and fungi. The healthy packed bread with “clean label”
needs the balance among the nutritious composition, the effect
of natural protective agents, and reasonable shelf life period.
Barman S, Ghosh R, Sengupta S, Mandal NC (2017) Longterm storage of post-packed bread by controlling spoilage pathogens using Lactobacillus plantarum C14 isolated from homemade curd. PLoS ONE 31: 1-17.
EFSA (2012) Scientific Opinion on the maintanence of the list of QPS biological agents intentionally added to food and feed (2012 updated). EFSA J 10: 3020