La pasta acida, utilizzata anche per fermentare impasti di farina per la produzione di pane e prodotti secchi da forno, ha numerosi benefici tra cui: la riduzione della presenza ATI e WGA.
La ricerca “Degradation of Wheat Germ Agglutinin during Sourdough Fermentation” Rojas Tovar, Luis E. DOI https://doi.org/10.7939/r3-1474-ec31 evidenzia:
Durante la fermentazione, il pH dell’impasto è sceso a 3,9 ± 0,2, il che ha favorito la degradazione dell’ATI da oligomeri a monomeri; I monomeri ATI sono meno dannosi se consumati. Il WGA viene anche modificato durante la fermentazione del lievito naturale a seconda delle capacità riducenti dei ceppi utilizzati [1].
È stato riportato che il pH è il principale responsabile degli effetti del lievito naturale sulla struttura e sulla bioattività dell’inibitore dell’amilasi-tripsina del grano (ATI). Inoltre, i batteri lattici della pasta madre riducono i legami disolfuro e diminuiscono il potenziale redox dell’impasto. Nello specifico, la glutatione reduttasi del Fructilactobacillus sanfranciscensis riduce il glutatione dimerico ossidato a glutatione, che reagisce ulteriormente per interrompere i legami disolfuro nelle proteine, altera la loro struttura secondaria e promuove la proteolisi delle proteine legate al disolfuro. [2]
Omissis… È stato riportato che i consorzi di lattobacilli e lieviti a lievitazione naturale degradano l’ATI in modo più efficiente rispetto alle colture pure di lattobacilli e quindi possono anche influire sulla degradazione del WGA. [3]
Riferimenti:
[1] “Non Celiac Wheat Sensitivity (NCWS), an intolerance to the ingestion of wheat products, has increased considerably during the past few years. In sensitive individuals, NCWS manifests by intestinal and extra intestinal symptoms in different ways. Two wheat protein fractions have been linked to NCWS, amylase-trypsin inhibitors (ATI) and wheat germ agglutinin (WGA). Physicians recommend that individuals with NCWS adhere to a gluten free diet. However, gluten free diets are often associated with a reduced diversity of products, a higher price and lower sensory and nutritional quality. Thus, it was the objective of this study to explore the possibility of using sourdough fermentation to reduce the bioactivity of these two proteins linked to NCWS in wheat bread. White pastry flour was used to analyze ATI and whole wheat flour for WGA experiments. The analytical techniques used to determine the fate of ATIs and WGA through the fermentation were size exclusion high performance liquid chromatography (SEC-HPLC), and enzyme-linked immunosorbent assay (ELISA). During fermentation, the pH of the dough decreased to 3.9 ± 0.2, which promoted the degradation of ATI from oligomers into monomers; ATI monomers are less harmful when consumed. WGA is also modified during sourdough fermentation depending on the reducing capabilities of the strains used. Initially, commercial whole wheat flour contained 6.6 μg ± 0.7 of WGA per gram. After 24 h fermentation, doughs fermented with Latilactobacillus sakei TMW 1.22 contained 2.7 μg ± 0.4 of WGA per gram of flour, while the doughs fermented with Fructilactobacillus sanfranciscensis DSM20451 and F. sanfranciscensis DSM20451 ΔgshR contained 4.3 μg ± 0.3 and 6.5 ± 1.8 μg, respectively. The WGA-SEC chromatograms show 3 peaks for doughs fermented with F. sanfranciscensis DSM20451 ΔgshR while the chromatograms with the isogenic strain F. sanfranciscensis DSM20451 show a more complex profile with 5 peaks, one of them from a very large molecular size molecule. The concentration of WGA is lower after fermentation with lactobacilli that have high reducing capacity. Clinical studies are required to determine the safety of consumption and the possible reduction in adverse symptoms, but this is a step towards finding new options to incorporate into the diet of NCWS individuals.”
[2] omissis……..Wheat components related to NCWS are fermentable oligo-, di-, and monosaccharides and polyols (FODMAPs), amylase-trypsin inhibitors (ATIs), and wheat germ agglutinins (WGA) [4–7]. NCWS, which is also referred to as gluten sensitivity or gluten intolerance, involves a wide variety of symptoms, including bloating, diarrhea, nausea, and intestinal damage. Extra intestinal symptoms have also been described and may include tiredness, headaches, joint pain and anxiety [5]. Symptoms of NCWS overlap with irritable bowel syndrome (IBS) [6]. Individuals affected by NCWS are normally prescribed a diet which is free of wheat products [8]. Sourdough fermentation does not eliminate gluten proteins that trigger celiac disease but the use of sourdough processes in bread making can be an alternative to gluten free diets to reduce symptoms associated with NCWS. The sourdough process involves longer fermentation times in comparison to straight dough processes, and additionally recruits the metabolic activity of lactic acid bacteria. Sourdough fermentations partially or completely degrade FODMAPs in wheat [9,10] and provide more time and more suitable conditions for wheat aspartic proteases, which are optimally active at low pH, to degrade wheat proteins [11,12]. Wheat flour contains the serine carboxypeptidase D (CPW-II), an exopeptidase with an optimum pH from 4 to 5.5 [13]. The most important proteases in wheat are aspartic proteinases [14] that associate with gluten during mixing and are optimally active at acidic pH [15,16]. Wheat aspartic proteases hydrolyze peptide bonds adjacent to arginine, lysine, phenylalanine, leucine, tyrosine and tryptophan [15,17]. The pH was reported to be primarily responsible for sourdough effects on the structure and bioactivity of the wheat amylase-trypsin inhibitor (ATI) [18]. Moreover, sourdough lactic acid bacteria reduce disulfide bonds and decrease the redox potential of the dough. Specifically, glutathione reductase of Fructilactobacillus sanfranciscensis reduces oxidized, dimeric glutathione to glutathione, which further reacts to disrupt disulfide bonds in proteins, alters their secondary structure and promotes proteolysis of disulfide-bonded proteins [12,19,20].”
[3] This study aimed to determine the fate of WGA and to assess the contribution of thiol-exchange reactions and of proteolysis to WGA modifications during sourdough fermentation. The role of thiol-exchange reactions was assessed by comparing F. sanfrancis- censis DSM20451 with its isogenic glutathione-reductase negative mutant F. sanfranciscensis DSM20451∆gshR [19,20]; the role of proteolytic activity was assessed by protease addition to sourdoughs, and by the use of chemically acidified controls [12]. This study analysed sourdoughs that were fermented with defined strains of lactic acid bacteria. This approach allows an assessment of the contribution of specific metabolic traits—acidification, glu- tathione reductase activity—to the degradation of WGA; however, sourdoughs used in artisanal and industrial practice typically include several species of lactic acid bacteria and additionally include sourdough yeasts or baker’s yeast [37]. Consortia of lactobacilli and sourdough yeasts were reported to degrade ATI more efficiently than pure cultures of lactobacilli [18] and thus may also impact WGA degradation.
Note:
“ WGA is a lectin that is located in the germ of the wheat grain. In the pH-range of 3.5 to 7.4, it forms a dimer with a size of approximately 35 kDa that is relatively heat stable [21–23]. Each monomer is stabilized by 16 intramolecular disulfide bonds [24]. WGA binds N-acetyl glucosamine and its β-(1 → 4)–linked oligomers and has weaker affinity to N- acetyl galactosamine and N-acetyl neuraminic acid [25,26]. WGA’s effects on human health are controversial. Rodent experiments concluded that WGA in doses that substantially exceeded the concentration in wheat decreased growth [27]. In cell culture experiments with Caco2 cells, WGA increased the permeability of the epithelial layer [28] and stimulated synthesis of pro-inflammatory cytokines [29]; WGA also demonstrated toxicity to acute myeloid leukemia cells without significant toxicity to normal cells [30]. The identification of antibodies targeting WGA in human serum indicates its translocation and interaction with the immune system [31]. Owing to the lack of in vivo studies, however, conclusions on the contribution of WGA to NCWS remain speculative [28,32,33].”
Parole chiave: lievito madre; proteolisi; fermentazione; agglutinina di germe di grano; sensibilità al grano; batteri dell’acido lattico