Effects of enzymatic modification of starch, proteins and pentosans on dough and
tortilla properties were determined to establish the role of these wheat components in
tortilla staling. Starch, protein and pentosans were respectively modified with a-amylase,
protease and transglutaminase (TG), and xylanase. Tortillas were stored at 22oC and
evaluated for at least three weeks.
Amylase improved shelf-stability of tortillas, produced a significant amount of
dextrins and sugars, retarded decrease in amylose solubility, and weakened starch
granules. However, control and treated tortillas had similar degrees of amylopectin
crystallinity. Staling of tortillas appears to involve starch that reassociates into an
amorphous structure.
Micrographs of control dough had thin protein strands forming a continuous
matrix. Protease-treated dough had pieces of proteins in place of the continuous matrix,
while TG-treated dough had thicker protein strands that were heterogeneously
distributed. Both treatments resulted in shorter shelf-stability of tortillas. The
organization of protein in dough is important for dough structure and appears to impact
tortilla flexibility.
Protein solubility and SDS-PAGE results did not differentiate control and treated
dough or tortillas. The fractions or molecular weight distribution are not significant
determinants of protein functionality. Tertiary and quaternary protein structures of gluten
may be more related to tortilla shelf-stability. The 75 ppm xylanase treatment resulted in weaker tortilla structure and
significantly higher amounts of low molecular weight saccharides and sugars. Control
and the 25 ppm treatment sample had a similar shelf-stability and texture profile.
Pentosans may affect staling indirectly through the effect on gluten development.
Fresh tortillas have amylopectin in an amorphous state, while amylose is mostly
retrograded. The gluten matrix provides additional structure and flexibility to the tortilla.
Pentosans may or may not be attached to the gluten network. Upon storage, amylopectin
retrogrades and recrystallizes, firming the starch granules, resulting in firmer tortillas.
Starch hydrolysis decreased the rigid structure and plasticized polymers during storage.
It also reduced the restriction imposed by retrograded starch on gluten and allowed it
more flexibility. Thus, the flexibility of tortillas results from the combined
functionalities of amylose gel, amylopectin solidifying the starch granules during storage,
and the changed functionality of gluten after baking.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-1306 |
| Date | 15 May 2009 |
| Creators | Alviola, Juma Novie Ayap |
| Contributors | Rooney, Lloyd W., Waniska, Ralph D. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | electronic, application/pdf, born digital |
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