Identification of lactic acid bacteria isolated from oat sourdoughs and investigation into their potential for the improvement of oat bread quality

The use of sourdough in wheat and rye breads has been extensively studied; however, little is known about its potential effect when baking oat bread. Consequently, the impact of sourdough on oat bread quality was investigated. Two different sourdoughs were prepared from wholegrain oat flour without the addition of starter cultures, by continuous propagation at 28 (SD 28) or 37 °C (SD 37) until the composition of the lactic acid bacteria remained stable. The dominant LAB were identified by sequence analysis of the 16S rDNA isolated from pure cultures. LAB from SD 28 belonged to the species Leuconostoc argentinum, Pedicoccus pentosaceus and Weissella cibaria, while Lactobacillus coryniformis dominated SD 37. The isolated LAB were further used as starter cultures for the production of oat sourdoughs. Fundamental rheology revealed softening of the sourdoughs compared to non-acidified and chemically acidified controls, which could not be attributed to proteolytic activity. Incorporation of oat sourdough into an oat bread recipe resulted in significantly increased loaf-specific volume as well as improved texture, independent of addition level or sourdough type. Overall, the results of this study show that sourdoughs containing lactic acid bacteria isolated from oats have the potential to enhance oat bread quality.     

Dietary exposure assessment of putrescine and cadaverine and derivation of tolerable levels in selected foods consumed in Austria

Biogenic amines (histamine, tyramine, putrescine, cadaverine, agmatine, spermidine and spermine) are nitrogenous compounds. They occur naturally in living organisms and are involved in many biological processes. Nonetheless, high amounts in food may be hazardous to human health. The diamines putrescine and cadaverine in food can potentiate the effects of simultaneously ingested histamine. In protein-rich foods, high concentrations of these diamines are indicative for hygienic deficiencies in the food chain. Even though being formed endogenously and being essential for some physiological metabolic pathways, both diamines are known as precursors for carcinogenic nitrosamines. Putrescine also plays a certain role in tumour growth. Nevertheless, no tolerable levels in foods have been established so far. The present study suggests tolerable levels in cheese, fermented sausages, fish, sauerkraut and seasonings that are based on toxicological threshold levels, occurrence of diamines in foods and food consumption in Austria. Average daily intake of putrescine via fermented food was calculated to be 6.8 (female adults) and 8.8 (male adults) mg per person. Respective numbers for cadaverine were 9.8 and 11.6 mg per person and day. For putrescine, proposed maximum tolerable levels for sauerkraut, fish, cheese, fermented sausages and seasonings are 140, 170, 180, 360 and 510 mg/kg, respectively. Likewise, for cadaverine, in sauerkraut, fish, cheese, fermented sausages and seasonings, maximum tolerable levels are 430, 510, 540, 1,080 and 1,540 mg/kg, respectively. These limits can be met by current manufacturing practices, as ascertained from the results of our own studies and from literature. Admittedly, only few data are published on toxicological threshold levels of these diamines, which mean that these tolerable levels are associated with some uncertainty.     

The application of dextran compared to other hydrocolloids as a novel food ingredient to compensate for low protein in biscuit and wholemeal wheat flour

Wheat is primarily used for bread-making. However, fungal diseases, grain moisture at harvest and low-protein contents strongly influence the quality of the wheat flour, thus creating challenges for traders, millers and commercial bakers who struggle to produce consistently high-quality products. This paper address the replacement of low-protein/wholemeal flour functionality for bread-making purposes. Three hydrocolloids, xanthan gum, dextran and hydroxypropyl methylcellulose, were incorporated into bread recipes based on high-protein flours, low-protein flours and coarse wholemeal flour. Hydrocolloid levels of 0–5 % (flour basis) were used in bread recipes to test the water absorption. The quality parameters of dough (farinograph, extensograph, rheofermentometre) and bread (specific volume, crumb structure and staling profile) were determined. Results showed that xanthan had negative impact on the dough and bread quality characteristics. HPMC and dextran generally improved dough and bread quality and showed dosage dependence. Volume of low-protein flour breads were significantly improved by incorporation of 0.5 % of the latter two hydrocolloids. However, dextran outperformed HPMC regarding initial bread hardness and staling shelf life regardless the flour applied in the formulation.     

Impact of ‘oxidizing’ and ‘reducing’ buckwheat sourdoughs on brown rice and buckwheat batter and bread

The influence of reducing and oxidizing buckwheat sourdoughs on the rheological, protein, and bread properties of buckwheat and brown rice flour was investigated. Batters and breads prepared with chemically acidified doughs, fresh pre-doughs, and fresh pre-doughs containing glutathione (3 mM) were used as controls. No significant differences were observed after the addition of reducing and oxidizing sourdoughs in all trials. Proteolysis was observed after proofing time in buckwheat and brown rice batters, respectively. Acidified doughs increased the elasticity and the gelatinization temperature of buckwheat batters. No notable microstructure changes were detected in brown rice batters. The extension of fermentation time in sourdough caused a slight decrease in bread volumes in all trials. Sourdoughs increased the bread volume and decreased the crumb hardness of buckwheat breads. In trials with brown rice flour, the addition of sourdough did not show relevant volume differences as compared to the controls, except big voids in sourdough bread crumb. Linear correlations between hardness, volume, and cells’ density were observed. However, no clear correlations among rheological parameters and bread characteristics could be detected. These results indicated that the applied strains were responsible for the leavening capacity of the yeast during the proofing time and for crumb structure in trials with buckwheat and brown rice flour. Applied sourdoughs were able to change the molecular, and bread properties of buckwheat and brown rice bread.     

The influence of Fusarium infection and growing location on the quantitative protein composition of (part I) emmer (Triticum dicoccum)

The effect of the fungal infection Fusarium graminearum and Fusarium culmorum on naked barley cultivars (n = 7) with respect to the barley’s total protein content and the content of the protein fractions albumins + globulins, prolamins (hordeins) and glutelins (hordenins) was investigated. A summer barley cultivar (n = 1) was used for comparison. The total protein content of the whole grain flours was very variable, ranging from 125 to 225 g kg⁻¹. The influence of Fusarium infection showed that the content of hordeins and hordenins was slightly reduced, while the albumins and globulins were not affected. In addition, the effect of the two different growing locations on the protein content of the naked barley was also evaluated. It could be shown that the C-hordeins, γ-hordeins and D-hordenins were significantly positively affected by increasing nitrogen supply, whereas the B-hordenin content was significantly negatively influenced. Nitrogen availability seems to be a factor that promotes gene expression for hordeins but reduces the synthesis of the main B-hordenins.     

Factors influencing falling number in winter wheat

The Hagberg falling number (HFN) is one of the most important quality characteristics of wheat. Six winter wheat cultivars from three locations in Germany were analysed to assess the factors influencing the HFN. The cultivars and locations affected significantly the HFN of all the samples. The infection with Fusarium culmorum, determined in another cultivar, also led to an increase in HFN, which suggested that the HFN method is not adequate enough for the true determination of the alpha-amylase activity of fungus-infected, wheat flour. Furthermore, there was no clear correlation between HFN and thousand-kernel weight, starch content or pentosan content. The crude protein content was positively related to the HFN, while the total dietary fibre content depended on the cultivar and location.     

Hydrolysis of glycosidically bound flavour compounds from oak wood by Oenococcus oeni

Malolactic fermentation (MLF), which is conducted by lactic acid bacteria (LAB), has a significant influence on the stability and organoleptic quality of wine. Recent studies have shown that when MLF is carried out in oak wood barrels, LAB were also able to interact with wood and increase volatile compound contents such as vanillin during MLF. The release of these compounds indicates that LAB may convert vanillin precursors present in oak wood. In this work, the effect of commercial glycosidases on the released vanillin was firstly studied. This aldehyde is present in wood extracts in monoglycosidic forms where the major glycones are arabinose and xylose. Other aglycons released during MLF in barrels, syringaldehyde and whisky-lactones, can be considered as other sources of aroma. Secondly, strains selected with high activities toward glycoside substrates could hydrolyse vanillin glycoside precursors from oak wood with the same efficiency as commercial enzymes.     

Heme-dependent and heme-independent nitrite reduction by lactic acid bacteria results in different N-containing products

Seventy strains of lactic acid bacteria were investigated for nitrite reductase activity. Two types of this activity were detected. Type I was found in Lactobacillus plantarum, L. pentosus and Pediococcus pentosaceus. This activity is heme-dependent with ammonia as the sole product. Type II mechanism is heme-independent and reduces nitrite to NO and N₂O.     

Optimization of baking parameters of part-baked and rebaked Irish brown soda bread by evaluation of some quality characteristics

Summary  Part-baked Irish brown soda bread loaves with bicarbonate levels from 0 to 2.8 % were baked, packed and stored for up to 11 days at 5 C then second-baked at 180 or 200 C for various times to give an oven-fresh end product. The quality of the rebaked bread was dependent on characteristics of the part-baked bread, its storage conditions and the processing parameters of the second baking phase. Quality parameters evaluated were bread volume yield, crumb and crust firmness, moisture content and colour. Staling of the part-baked bread during storage at 5 C and the reversion of this process at 59 C was investigated with regard to rebaking time and temperature. Rebaking conditions were optimized by evaluating the core temperature increase in the centre of the bread. Immediately after the second baking phase a post-baking temperature increase was measured which allowed reduction of the in-oven rebaking time. The data were modelled mathematically using least squares analyses.