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Charlotte Zuber

FOS 4041 / Th 6:00pm Section


What are the Advantages
of Flavor and Shelf life
in Sourdough Bread Products?


March 22, 2012


Zuber
1


What are the Advantages of Flavor and Shelf Life in Sourdough Bread Products?

Introduction

The process of
making sourdough bread dates back to the roots of civilization. It was
implored as an alternative to the flat, unleavened breads from which many cultures began and is
utilized still because of its advantages over conventional bread. Today, sourdough can be

implemented into many different baked products, including wheat breads, rye breads and even
specialty market breads

(
1
)
. Sourdough begins with the fermentation of a cereal flour and water

(
2
)
. As the mixture sits, fermentation begins by the entrance of e
ffective microorganisms called
yeasts (a fungus) and lactic acid bacteria (LAB)
(
3
)
. Then, the interaction
between
and
byproducts of these microorganisms cause favorable chemical and physical changes to the
mixture.
There are numerous advantageous changes
to consider, but for this investigation, the
focus will be on the consumer interests of sourdough: the
pleasing
flavor enhancements and the
increased shelf life of sourdough bread products.
The byproducts of the LAB are lactic acid and
acetic acid, which p
romote a pleasing sour flavor, hence, the name “sourdough”

(
2
) and

the
contribution of volat
ile and non
-
volatile compounds
contri
bute to flavor, aroma, and acidity. In
addition,

interactions between the yeast and LAB
contribute practical
char
acteristics
in the final
product including

the supplementation of an

antimicrobial environment within the sourdough,
increasing the shelf life of these products

(
3
)
.

The investigation and explanation of the advantages of sourdough will begin in the
following paragrap
hs. Attention will be paid to
both consumer

advantage
s of

sourdough

and to
the processes responsible for achieving these favorable characteristics. However, before the
question of purpose is answered, more information about the key players in sourdough and

different types of sourdough fermentation must be explained.

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2


Understanding the Types of Sourdough and the Microorganisms
I
nvolved

The sourdough fermentation process is utilized today because of these advantages in the
final products. Through the modern d
evelopment of sourdough, researchers have designed
several
types of sourdough starters that enable better control of these advantages. The three
mediums

of sourdough used today are Type I, II, and III. Type one is the most traditional and
emphasizes a long
-
established approach to propagation (reproducing the bacteria) by
“backslopping” weekly or monthly in an industrial environment

(
4
)
.
Backslopping is the process
of starting a new batch with an already used and fermented dough (referred to a sponge, brew o
r
polish)(2). Because it is using already established and thriving colonies of both LAB and yeast
from the sponge, Type I does not require the insertion of baker’s yeast whereas both Type II and
III do. Type II sourdoughs are commonly in liquid form and ar
e inserted into mixtures easily, but
require upkeep because the yeast and bacteria strains are active in the arrangement. Type III are
the favored form of sourdough for large industries because it is in a dry form and microbial life is
stabilized (2). Typ
e II is preferred over Type I because the particular strains and specific
conditions can be selected prior to the inoculation into the flour. Furthermore, current scientific
research is determining which effects are characteristic of certain lactic acid ba
cteria and yeasts,
so that bakers can design and predict the qualities of their bread (5). Similarly, Type III is often
elicited for the addition of favorable flavor (4) and aroma compounds because it contains higher
amounts of acids than both Type I and I
I (6).

Now that the three types of sourdough have been explained, more information is needed
about the microorganisms involved in sourdough that are most responsible for the qualities
sourdough bread represents. These microorganisms are the lactic acid ba
cteria (LAB) and the
yeasts. The most common LAB is the
Lactobacillus plantaru
m
,
followed by
Lactobacillus brevis

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3


and
Lactobacillus sanfranciscenscis

and the most common yeast is
Saccharomyces cerevisiae
,


though hundreds of each microorganism

have been identified (7). LAB far outnumber yeasts,
though

the exact ratio
depends on each individual dough and the p
rocesses involved
(7)
. As far
as the functions of these microorganisms, yeasts are responsible for metabolizing sugars such as
glucose, fru
ctose, sucrose, and maltose whereas the hetero and homo
-
fermentative LAB are
responsible for lactic acid fermentation, proteolysis, and the creation of volatil
e compounds

(
flavor) and
nonvolatile compounds (
aroma and acidity). Studies have also shown that

the Lactic
acid bacteria have antistaling, antimold and antibacterial prevention characteristics (2). Though
they each may separately contribute steps to the overall favorable characteristics of sourdough
bread, the interaction between the two domains of
microorganisms combine to make a true
distinction between sourdough and non
-
sourdough bread.

Answering the Question of Purpose

1.

Flavor enhancement

The flavor of sourdough bread is the most distinguishable characteristic of the bread type
and may also be the most important advantage
considered by consumers
. There are two types
of flavors to discuss in sourdough bread; they are the volatile and non
-
vol
atile compounds.
The volatile compounds contribute most to the “sour” taste of sourdough, made possible
through the alcohols, aldehydes, ketones, esters and sulfur that belong to this group. The non
-
volatile compounds are produced by homo and heteroferment
ative bacteria that acidify and
give aroma to the bread and are present in the organic acids (acetic and lactic acids) (2).
Some studies investigated the actions of the microorganisms

responsible for creating these
compounds
, while others focused on proces
sing and preparation techniques with sourdough
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4


that contributed to taste and aroma enhancement by facilitating additional growth and activity
of the LAB and yeasts.

1.
1

Processing and Preparation of Sourdough on Flavor Enhancement

For example, one
experiment

by Gobbetti

et al

(8
) investigated the creation of volatile
and nonvolatile compounds in sourdough based on different processing parameters like
leavening time, cooking temperature and the addition of fructose and citrate on dough. The aim
was
to determine how each process affected the prosperity and generation of LAB and yeasts,
which would
then

be responsible for the metabolic output

of the vola
tile and nonvolatile
compounds.
Results showed that increased leavening time did not facilitate extr
a generation of
microorganisms but the addition of fructose caused an elevation in LAB cell counts. Increasing
the temperature from 25 to 30 degrees Celsius increased the yeast fermentation, which
influenced the transformation of the nonvolatile compound p
rofile of lactic and acetic acids to
the volatile compounds methyl and butyl alcohols. But, a further temperature increase to 35
degrees Celsius showed a slight decrease in volatile compounds, showing that there is a finite
temperature effect on yeast ferm
entation of sourdough (and therein creation of volatile flavor
compounds) (
8
).


Another article compared the sensory panel of two rye cultivars against 3 different
preparation backgrounds; germinated, sourdough, and milled. The sourdough ryes w
ere found to
have the most intense and sour flavor components compared to germinated and milled. The most
common volatile compounds were furfural, ethyl acetate, 3
-
and 2
-

methylbutanol (
9
). The aim of
this experiment was to conclude which preparation backg
round would be best for lessening the
sour rye taste that some consumers find distasteful. In this case, the sourdough fermented rye
cultivars intensified the flavor of the rye with formation of volatile compounds.

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5


1.2

The affect of Amino Acids on Sourdou
gh flavor

Tho
se articles

focus
ed

on the preparation and processing of bread for the production of
volatile and nonvolatile compounds,
but
another article compared the relationship between the
microorganisms and the addition of specific amino acids. This ex
periment compared the amino
acid content of wheat sourdough rolls, asserting that the higher amino acid content aids
microorganism functioning and decreases pH.

Depending on the content of amino acids,
different volatile and nonvolatile compounds would be

produced

(
10
)
. Moreover, specific amino
acids (ornithine, methionine, phenylalanine, leucine, isoleucine and valine) are very important
for volatile flavor. The study determined the pH and

amino acid counts of each bread sample

and
performed sensory evaluations to test the correlation. Results showed that the

addition of yeasts
and LAB

determine
d

the delectable qualities of sourdough,
and
not simply the amino acids
present, as they prepared separ
ate dough with 10 mmol of the

cla
imed “aromatic” amino acids
and found undesirable taste. However, the presence of the amino acid ornithine, either through
its addition to
L. sanfranciscensis

or broken down through arginine by
L. pontis
, creates a
favorable, roasted flavor.
In addition,
S
. cervisiae

converted amino acids to volatiles

during
proofing and the thermal degradation section of baking and a better taste was produced (1
0
).

1.3

Different Microorganism Combinations and the flavor of their end products

The same study that examined t
he different processes of sourdough in flavor
enhancement also investigated different combinations of specific microoganisms. Researchers
found that a certain subspecies of
L. brevis, L. plantarum
and

S.cervisiae

produced more alcohols
(due to yeast fermen
tation) and a sharper taste. For nonvolatile compounds, researchers found
that a symbiosis between LAB and the yeast
S. exigu
u
s

subspecies M14 gave a well rounded
sensory profile and observed that homo and heterofermentative bacteria produced Ethylacetate
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6


and carbonyl compounds. These findings suggest that the pairing of certain microorganisms
promote different characteristics to the flavor profile of sourdough bread (
8
).

2.

Increased Shelf Life of Sourdough Bread

Aside from taste,

another great concern to consumers of bread products is the shelf life of
their bread. Conventional breads contain many added preservatives that increase the shelf life of
bread for grocery store shelves, whereas sourdough bread develops natural anti
-
stal
ing,
antifungal
and antimicrobial
qualities (1
1
). The increased shelf life includes retaining moisture
with decreased growth of microbes for a longer period of time, as a cue for staling is often seen
as moisture loss (1
2
).
The decreased growth of microbes

has recently been studied with the
interest in foodborne illness, and though little
research
has been conducted with bread,
interesting defensive activity of the LAB

in sourdough

ha
s

been observed (13).

2.1
Anti
-
staling Properties of Sourdough Bread

Inc
reasing shelf life is essentially the attempt at preserving the fresh state of a bread
product. One article focused on many different aspects of freshness in sourdough and tested
their shelf life over eight days. The experiment involved comparing two trad
itionally made wheat
sourdoughs (one with high leavening and one with a lower leavening) with one industrial
prepared sourdough on shelf life qualities such as crumb and crust appearance, moisture content
and water movement, texture, and volatile compounds

for an eight day examination period. The
trial was repeated three times with similar results. Chiavaro
et al

(12)
determined that the water
movement from crust to crumb varied greatly between the three samples. The two traditionally
made sourdoughs had a
much higher water content in their centers and lower on their outer
crusts, whereas the industrially made sourdough had the opposite characteristics. The water
moisture retention also proved to be similar for the two artisan made sourdoughs, both showing
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7


l
ittle moisture loss after the eight days from both crust and crumb, but a significant loss was seen
in the industrial made sourdough. Possible explanations of this phenomenon could be the
increased volume in the artisan sourdoughs that added a cushioning e
ffect to lock in moisture
from the air. Texture findings showed opposite expectations, as the artisan sourdough bread
crusts became significantly harder while the store purchased sourdough became less hard, though
each followed different stages of their tr
ansformations. Volatile compounds for the artisanal
sourdoughs were more numerous than the store purchased sourdough before and after the eight
days (1
2
), suggesting that the acidity of the volatile compounds prevented staling and microbial
interaction (1
1
).

2.2 Anti
-
mold and Anti
-
fungal Properties of Sourdough Bread

Where

air and water loss are the common causes of staling in bread, the fungal enemies
of bread are Aspergillus, Fusarium and Penicillium (1
3
). One experiment set out to determine
which LAB
could prevent these fungi f
rom proliferating in sourdough and
determin
ed

which
homo and heterofermentative bacteria inhibited the fungi of interest. Their results found that
L.
plantarum
CRL 778
and L.brevis CRL 796
inhibited the growth of
A. niger

C
H
101,
and
L.
plantarum

CRL 778 ,
L. brevis

CRL 772 and 796, and
L. reuteri
CRL 1100 inhibited
F.graminearu
m,

but no

LAB inhibited the growth of

Pennicillium

sp. C
H

102

(1
3
)
.


A follow
-
up
experiment used these same LAB strains discovered in the previous
experiment and made real sourdoughs to test the actual anti
-
fungal properties. Each slurry was
used in different proportions in doughs and compared to a sourdough made with yeast and
a
synth
etic pH lowering substance, PCa. The best slurry

was the

40%

SL778. It

proved to have a
five day shelf life, which has similar effects to 0.2% of PCa

(1
4
)
. The
result

for this positive
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8


biopreservation can be explained with its acetic acid
, lactic acid

and

PLA content

that creates a
charged environment
that

inhibits metabolic activities of
outside
microbes.

2.3 Anti
-
bacterial Properties of Sourdough Bread



There are other enemy microorganisms

besides fungi and mold

that can threaten bread
shelf life
,

howe
ver, the
bacteriocins from gram positive
lactic acid
bacteria
can help to protect
the sourdough environment from contaminants
.
Prosperous

research by Gobbetti and
Smacchi
(15)

has found that there are many lactic acid bacteria in sourdough breads that take

on
antagonistic activity when confronting
other LAB as well as microbial contaminants
. In fact, 77
of 232 strains tested produced inhibition zones
against other Lactobacillus strains. Then, these 77
were tested under the pH of 6.5 and the addition of
catalase (to eliminate antimicrobial activity
of organic acids and hydrogen peroxide). The remaining 52 strains were tested under heat and an
environment with hydrolytic enzymes. Proteinases affected

the sensitivity of

L
. sanfrancisco

in a
different fashio
n than any of the other
strains. This determination proved that
L.

sanfrancisco

C57 was the key sourdough starter in demonstrating the most antimicrobial activity

(1
5
)
.

This
research implies
that
L. sanfrancisco

may carry the most responsibility in antibac
terial action of
sourdough because it is possibly the most resilient and defensive LAB.

Nonetheless, other research conducted by Todorov
et al

deemed
Lactobacillus plantarum

ST31 to be a powerful antimicrobial substance with strong bacteriocin qualities t
hat inhibited
other similar strains and Staphylococcus aureus, a foodborne pathogen

(1
6
)
.
It was stable and
active under all constraints including a pH range from 3
-
8 and heat treatment of 100 degrees
Celsius for 10 minutes, but in the presence of urea, a
ctivity ceased. Under a 24 hour time period,
the production activity of the L. palantarum ST31 bacteriocin grew exponentially until reaching a
plateau at 22 hours. This implies that L. plantarum ST31 had control over most environmental
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contaminants and sim
ilar strains because of its unique defense mechanism and structure. If
implemented correctly, it could be a
powerful tool in preventing the onset of bacterial
contaminant activity in sourdough.

Conclusion:
Future Implications to the Field of Dietetics


The advantages of sourdough that consumers may find most interesting are the practical
qualities of flavor enhancement and increased shelf life, but consumers probably do not realize
that sourdough offers additional advantages for their health. As dietitia
ns, we must consider both
practical and health
-
conscious advantages to
better inform the public about sourdough and all of
its facets.


Sourdough not only offers a great taste, but

has been shown to positively facilitate
numerous nutritional reactions. Fo
r example,

a study conducted on 32 Wistar rats demonstrated
the enhanced mineral absorption in sourdough bread compared to other breads. Researchers
found that sourdough had higher absorption in Calcium

and
Magnesium, and significantly higher
absorptions i
n Zinc, Copper, and Iron

(1
7
)
. The reason is assumed to be the decreased levels of
phytates
that are hydrolyzed
in sourdough and th
en

disabled from disrupting the absorption of
trace minerals. With this knowledge, Registered Dietitians have the ability to
inform patients
about this benefit of sourdou
gh, so that they may make a

conscious
decision on

bread

to buy with
the most nutritional density.


Sourdough can also act as a facilitator for
the formation of
bioactive compounds, in this
case, the neurotransm
itter GABA (gamma aminobutyric acid) through the help of
lactobacillus
plantarum

C48 and

Lactococcus

lactics

PU1 in sourdough fermentation. This neurotransmitter is
very important to the Central Nervous System and also has a role in preventing diabetes and

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10


hypertension (1
8
).
The role of sourdough in this situation
may play as nutrition therapy for those
suffering or at risk for these chronic diseases.


Dietitians can explain the unknown health benefits of sourdough to all patients, but it
may only be those

who are be suffering from
or prone to
anemia, and chronic diseases like
diabetes or hypertension

who find it pertains to them
.

However, a basic yet

important nutritional
benefit of s
ourdough pertains to all people: fiber.

Fiber can help in the prevention of many
chronic diseases like heart disease and colorectal cancer while also playing a role in satiety (19).

R
ecent experiments have begun examining the potential of s
ourdough fermentation in modifying
the
bran
of the whea
t kernel
to improve the
common problem of low
loaf volume of whole grain
bread products

(19
)
. This equates to a bread that tastes good and is packed

fu
ll of fiber, a

winning
combination.
Pair that with the enhanced mineral absorption and facilitated creati
on of
neurotransmitters, and sourdough has advantages in all categories of practicality and health.



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11


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