More Scientific Data
slki...@aol.com
A few tidbits from the American Association of
Cereal Chemists. Their site is at
http://www.scisoc.org/aacc/ and their publication
is called "Cereal Chemistry."
--------
> Determination of Yeast Growth in Doughs. Thorn et al.
> CChem 37:415 (1960): Yeast cells were quantitatively
> recovered from dough by a process in which...
Dick had speculated earlier that the scientific data on
microorganism growth in a dough (as opposed to in liquid
or some other medium) might be sparse due to the
difficulties inherent to the medium. Since they have been
doing it with yeast for around 40 years, probably not true.
--------
> Effects of Proteolytic Enzymes on Gluten as Measured
> by a Stretching Test. Kruger. CChem 48:121 (1971):
> The stretching characteristics of gluten are found to
> be changed markedly upon incubation with proteolytic
> enzymes... Increasing concentration of enzyme caused a
> progressive decrease in gluten consistency.
--------
> Effects of Acid-Soluble and Acid-Insoluble Gluten Proteins
> on the Rheological and Baking Properties of Wheat Flours.
> Preston et al. CChem 57:314 (1980): Gluten was fractionated
> into acid-soluble and acid-insoluble protein fractions...
> The dough-strengthening effects obtained when gluten proteins
> were added were mainly due to proteins present in the
> acid-soluble gluten fraction, whereas the acid-insoluble
> gluten proteins at higher levels had a slight dough-
> weakening effect... Addition of increasing levels of
> gluten to the base flours significantly increased loaf
> volume... Similar increases in loaf volume were also obtained
> by addition of the acid-soluble gluten proteins. Addition
> of acid-insoluble gluten proteins significantly reduced
> loaf volumes
This was very interesting, in that it seems to indicate
that the presence of acid can have a marked affect on the
quality of the gluten. This is further supported by the
following article.
> Effect of Strength and Concentration of Acid on the
> Functional Properties of Solubilized Glutens of Good-
> and Poor-Quality Bread Flours. Goforth et al. CChem
> 54:1249 (1977): Acid solubilization was detrimental to
> loaf volume at pH values below 4 for glutens from good-
> quality flours and at pH below about 4.85 for glutens from
> a poor-quality flour. Impaired loaf volume was attributed
> to diminished hydrogen bonding caused by cleavage of
> amide groups from the gluten proteins during solubilization
> in acid.
With respect to sourdough breads, the following study is
relevant to this topic.
> Rheological Dough Properties as Affected by Organic Acids
> and Salt. Galal et al. C Chem 55:683 (1978): A combination
> of organic acids isolated from San Francisco sourdough
> and NaCl profoundly affected dough properties. Mixing time
> and stability of dough were greatly decreased when organic
> acids alone were added. Salt had the opposite effect, however,
> it increased mixing time and dough stability.
--------
Another affect of acid on doughs is the activity of various
Proteases at various pH.
> Rheological Changes in Cracker Sponges During an 18-Hour
> Fermentation. Wu et al. CChem. 66:182 (1989): The pH of
> cracker sponges was the most effective in reducing their
> resistance to extension. The effect was attributed to
> proteolytic enzymes, because the optimum pH of 4.1 coincides
> with the reported optimum pH of indigenous flour protease.
--------
It also looks like proteolytic enzymes are, in fact,
a relatively significant constituent of bread flour.
> The Proteolytic Enzymes of Wheat and Flour and Their
> Effect on Bread Quality in the United Kingdom. Hanford.
> CChem 44:499 (1967)
> The Proteolytic Enzymes in Wheat Flour. Wang et al. CChem
> 46:537 (1969)
> Properties of Wheat Flour Proteinases. McDonald et al.
> CChem 41:443 (1964): Self-digestion of flour showed a
> pH 4.0 optimum... Both dough-mixing and the presence of
> sodium chloride substantially reduced the proteolytic
> activity of flour.
--------
> Influence of Starter Cultures Consisting of Lactic Acid
> Bacteria and Yeasts on the Performance of a Continuous
> Sourdough Fermenter et al. CChem 69:20-27 (1992):
> [Experiment used] eight pure cultures of lactic acid
> bacteria... The performance of the fermenter can be
> improved and stabilized by adding starting cultures of
> yeasts isolated from sourdoughs... Fermenting sourdoughs
> with added yeast showed a significantly higher acid
> formation than did those without (P greater than 95%)
> added yeast. The accelerated acid formation was due
> almost entirely to additional production of acetic acid.
> This effect was independent of the strain of yeast.
This is an interesting insight into output side of
the relationship between bacteria and yeast in a sourdough.
I find it interesting that the presence of yeast increased
acetic acid (which isn't really the kind we want,
is it?).
--------
> Lactic and Volatile (C2-C5) Organic Acids of San
> Francisco Sourdough French Bread. Galal et al.
> CChem 55:461 (1978): Changes were observed in the pH,
> total titratable acidity (TTA), and lactic and volatile
> (C2-C5) organic acid contents of commercially prepared sour
> starter sponges, bread doughs, and fully baked bread.
> The results showed that lactic and acetic acids composed
> most of the total TTA. Gas-liquid chromatography, however,
> showed that six other minor acids (propionic, isobutyric,
> butyric, alpha-methyl n-butyric, isovaleric, and valeric
> acids) contributed to the TTA of the fully fermented starter
> sponge, the fully proofed bread dough, and the baked bread
> (1.19, 0.64, and 0.59%, respectively). Baking increased the
> pH negligibly but decreased the TTA by 9%, mainly due to the
> loss of acetic acid.
> The Acetic Acid Content of Sour French Bread and Dough as
> Determined by Gas Chromatography. Hunter et al. CChem 47:189
> (1970): The total acidity of sour French bread, dough,
> and starter was determined... The results were compared
> conventional bread and dough. There was ten times more acid
> in the sour bread than in the conventional bread. Percentage
> of acetic acid present in the acid fractions was determined by
> gas chromatography. Approximately half of the total acidity
> of sour French bread and three-fourths of the total acidity
> of conventional bread was acetic acid.
--------
Sam Kinsey
slki...@aol.com
-----== Posted via Deja News, The Leader in Internet Discussion ==-----
http://www.dejanews.com/ Now offering spam-free web-based newsreading
Matt
Sam,
Thank you so much for going through all the effort to gather this
information. I found it interesting and very educational. I want to comment
on some of it when I have time. Some of the procedures that we use are
explained by some of this information.
Thanks again,
Matt
Matt
>>Similar increases in loaf volume were also obtained
>> by addition of the acid-soluble gluten proteins. Addition
>> of acid-insoluble gluten proteins significantly reduced
>> loaf volumes
I believe that this explains why we use High-gluten flour for the sourdough
bread. We can use regular bread flour, but that will result in a loaf that
doesn't have the same volume as bread made with the HG.
Thanks again for these posts. I have printed the information and places them
in my personal baking note book for reference purposes.
Matt