Sourdough and Gluten-Free Products - Sourdough Biotechnology - page 243

Enzymatic processing of GF flours has also been extensively investigated. In
particular, both cross-linking promoting enzymes, such as transglutaminase
(TGase), cyclodextrin glycosyl transferase, glucose oxidase [ 23 , 29 , 30 , 44 ] and
proteases [ 31 ] were shown to improve the viscoelastic properties of batter and the
final bread quality. TGase was proved to be particularly efficient when applied in
GF breads produced with rice and buckwheat flours, used individually or in com-
bination with other ingredients [ 32, 33 ]. In particular, Renzetti et al. [ 33 ] showed
that the mode of action and the effects that TGase exerts on the pseudoplastic
behaviour of the batter and, ultimately, on bread quality vary according to the raw
material used for baking. Glucose oxidase was also used as a bread improver in
rice and oat GF breads [ 23 , 29 ]). Interestingly, protein hydrolysis was shown to
improve the baking quality of rice flour, by decreasing the resistance to deforma-
tion of the batter during the baking process [ 31 ]. Thus, the concept that not only
structure-promoting treatments can improve the bread-making performances of
GF flours brings about new opportunities for GF baking [ 30 , 34 ] .
Overall, even if over the last decade promising improvements in the quality of GF
breads have been obtained, the production of superior quality GF bread still repre-
sents a challenging task. Considering the lack of standardized baking tests, the high
costs of the investigated additives and the great variability of flour-additive interac-
tions, alternative ways to produce high-quality GF breads need to be investigated.
This chapter discusses the recent advances in the application of sourdough in GF
baking as a low-cost, efficient and natural tool to improve the quality of GF bread.

10.2 Sourdough Bread

Sourdough is a mixture of flour and water fermented with lactic acid bacteria (LAB)
and yeasts, which can be added as starter cultures or originate as contaminants in the
fl our [ 35, 36 ]. During sourdough fermentation, the resident LAB are the main factor
responsible for the acidification of the dough and for the synthesis of aroma com-
pounds, exopolysaccharides, enzymes and anti-fungal compounds [ 37- 39 ] . The
addition of sourdough can strongly influence the quality of bread, in terms of
enhanced texture, prolonged shelf life and improved organoleptic and nutritional
pro fi le [ 5, 40 ] . A profound knowledge of the metabolic events and the microbiologi-
cal interactions occurring during sourdough fermentation is of crucial importance for
controlling the fermentation and ensuring constant quality of the sourdough bread.
However, while extensive research has been done on wheat and rye sourdoughs, for
example on their microbial composition and their functional and organoleptic prop-
erties [ 35 ], only little information is available for GF sourdoughs [ 41- 51 ] . Despite
being limited in number, these studies indicate that the GF flours represent a unique
source of novel strains and that GF sourdough can be successfully applied for
modifying the rheological properties of the batters and for producing high-quality
GF breads (Tables 10.1 and 10.2 ). In the next paragraphs we will discuss recent
findings in the application of sourdough fermentation to GF flours.