Wheat Sourdough Breadmaking: A Scoping Review.

Using sourdough in breadmaking can enhance bread's shelf-life and flavor compared to exclusive baker's yeast use and is believed to increase its nutritional quality and healthiness. Previous research established insight into the microbial ecology of sourdough, but the link between leavening agent use, processing, and bread quality remains elusive. However, such knowledge is key for standardization, research on the health benefits, and the definition of sourdough bread. In this systematic scoping review, we analyzed 253 studies and identified large variations in the type and amount of leavening agent, fermentation conditions, and bread quality (specific loaf volume and acidification). The interrelation between these elements and their effect on the extent of fermentation is discussed, together with issues preventing proper comparison of breadmaking procedures. With this review, we want to contribute to the dialogue concerning the definition of sourdough-type bread products and the research into the health benefits attributed to them. Expected final online publication date for the Annual Review of Food Science and Technology, Volume 15 is April 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Industrial production of sourdoughs for the baking branch - An overview.

Sourdoughs are produced both in artisanal and industrial size. Sourdough manufacturers deliver the baking branch either with starters for production of in-house sourdoughs or with fully fermented sourdough products. In the latter case sourdough production is separated in time and space from the bread production. A big part of this convenience products are dried sourdoughs, which are mainly produced from rye and wheat flour, but also from other starch containing plants, like pseudocereals or legumes. The requirements regarding the raw materials used differ from that used for baking bread. The most applied drying techniques for sourdoughs are drum and spray-drying. Compared with other foods, sourdough and sourdough products have only a low risk regarding food safety due to pH < 4.2, however formation of biogenic amines or acrylamide has taken into account. More tools for sourdough authentication are needed but, before developing and validating methods, it would be necessary to include different sourdough products in a clear regulatory framework.

Starter cultures for cereal based foods.

Fermented cereals play a significant role in human nutrition in all parts of the world where cereals grow. These fermentations are started spontaneously or there have been traditional techniques developed in order to keep starter cultures for these processes alive. With the growing impact of industrial microbiology during 20th century this traditional starter culture propagation was replaced often, especially in the dairy industry, by the use of pure, frozen or freeze-dried cultures grown on microbial media. In contrast to the production of ethanol from cereals, in sourdough a pasteurization step before inoculation is avoided due to gelatinization of starch and inactivation of endogenous enzymes. Therefore cultures must be competitive to the relatively high microbial load of the cereal raw materials and well adapted to the specific ecology determined by the kind of cereal and the process conditions. Less adapted cultures could be used, but then the process of back-slopping of cultures is limited. Although cereal fermentations take the biggest volume among fermented foods, only for sourdoughs commercial cultures are available.

Propionic acid production by cofermentation of Lactobacillus buchneri and Lactobacillus diolivorans in sourdough.

Cooperative metabolism of lactobacilli in silage fermentation converts lactate to propionate. This study aimed to determine whether propionate production by Lactobacillus buchneri and Lactobacillus diolivorans can be applied for bread preservation. Propionate formation was observed in cofermentation with L. buchneri and L. diolivorans in modified MRS broth as well as sourdough with low, medium and high ash contents. 48 mM of propionate was formed in sourdough with medium ash content, but only 9 and 28 mM propionate were formed in sourdoughs prepared from white wheat flour or whole wheat flour, respectively. Acetate levels were comparable in all three sourdoughs and ranged from 160 to 175 mM. Sourdough fermented with L. buchneri and L. diolivorans was used in breadmaking and its effect on fungal spoilage was compared to traditional sourdough or propionate addition to straight doughs. Bread slices were inoculated with Aspergillus clavatus, Cladosporium spp., Mortierella spp. or Penicillium roquefortii. The use of 20% experimental sourdough inhibited growth of three of the four moulds for more than 12 days. The use of 10% experimental sourdough deferred growth of two moulds by one day. Bread from traditional sourdough with added acetate had less effect in inhibiting mould growth. In conclusion, cofermentation with L. buchneri and L. diolivorans represents a process to increase antifungal capacities of bread.

Adaptability of lactic acid bacteria and yeasts to sourdoughs prepared from cereals, pseudocereals and cassava and use of competitive strains as starters.

The adaptability of lactic acid bacteria (LAB) and yeasts to sourdoughs prepared from cereals, pseudocereals and cassava was investigated using PCR-DGGE and bacteriological culture combined with rRNA gene sequence analysis. Sourdoughs were prepared either from flours of the cereals wheat, rye, oat, barley, rice, maize, and millet, or from the pseudocereals amaranth, quinoa, and buckwheat, or from cassava, using a starter consisting of various species of LAB and yeasts. Doughs were propagated until a stable microbiota was established. The dominant LAB and yeast species were Lactobacillus fermentum, Lactobacillus helveticus, Lactobacillus paralimentarius, Lactobacillus plantarum, Lactobacillus pontis, Lactobacillus spicheri, Issatchenkia orientalis and Saccharomyces cerevisiae. The proportion of the species within the microbiota varied. L. paralimentarius dominated in the pseudocereal sourdoughs, L. fermentum, L. plantarum and L. spicheri in the cassava sourdough, and L. fermentum, L. helveticus and L. pontis in the cereal sourdoughs. S. cerevisiae constituted the dominating yeast, except for quinoa sourdough, where I. orientalis also reached similar counts, and buckwheat and oat sourdoughs, where no yeasts could be detected. To assess the usefulness of competitive LAB and yeasts as starters, the fermentations were repeated using flours from rice, maize, millet and the pseudocereals, and by starting the dough fermentation with selected dominant strains. At the end of fermentation, most of starter strains belonged to the dominating microbiota. For the rice, millet and quinoa sourdoughs the species composition was similar to that of the prior fermentation, whereas in the other sourdoughs, the composition differed.

Sourdough products for convenient use in baking.

Sourdough fermentations require a specific knowledge on the effects of process parameters, raw materials and micro-organisms in order to obtain a specific, reproducible sourdough and bread quality. This knowledge is not necessarily available in bakeries. Sourdough starter cultures, either active sourdoughs (Reinzuchtsauerteig) or freeze-dried micro-organisms are used to start sourdough fermentation with the required micro-flora. As sourdough fermentation is a labour-intensive and a time-consuming process, a growing demand for convenient products arised early. First organic acids (lactic acid, acetic acid, citric acid) and mixtures thereof came in use. These agents were used directly without or in combination with a sourdough; however, flavour and taste of the resulting breads were unsatisfactory. Based on modified and optimized traditional sourdough processes, dried, pasty and liquid sourdoughs were developed. Companies which produce such ready-to-use products, claim for a convenient, direct production of baked goods in constant quality, in combination with all advantages of a biological sourdough fermentation, e.g. flavour and taste, fresh keeping and prolonged microbial shelf-life. Currently, a broad variety of sourdough products with different fermented cereals is available on the market. In order to obtain a stable product, it is a necessity to inactivate the sourdough micro-biota by e.g. pasteurization, drying or autosterilization.

Monitoring the bacterial population dynamics in sourdough fermentation processes by using PCR-denaturing gradient gel electrophoresis.

Four sourdoughs (A to D) were produced under practical conditions by using a starter mixture of three commercially available sourdough starters and a baker's yeast constitutively containing various species of lactic acid bacteria (LAB). The sourdoughs were continuously propagated until the composition of the LAB flora remained stable. Two LAB-specific PCR-denaturing gradient gel electrophoresis (DGGE) systems were established and used to monitor the development of the microflora. Depending on the prevailing ecological conditions in the different sourdough fermentations, only a few Lactobacillus species were found to be competitive and became dominant. In sourdough A (traditional process with rye flour), Lactobacillus sanfranciscensis and a new species, L. mindensis, were detected. In rye flour sourdoughs B and C, which differed in the process temperature, exclusively L. crispatus and L. pontis became the predominant species in sourdough B and L. crispatus, L. panis, and L. frumenti became the predominant species in sourdough C. On the other hand, in sourdough D (corresponding to sourdough C but produced with rye bran), L. johnsonii and L. reuteri were found. The results of PCR-DGGE were consistent with those obtained by culturing, except for sourdough B, in which L. fermentum was also detected. Isolates of the species L. sanfranciscensis and L. fermentum were shown by randomly amplified polymorphic DNA-PCR analysis to originate from the commercial starters and the baker's yeast, respectively.