Microbial re-inoculation reveals differences in the leavening power of sourdough yeast strains

A method based on microbial re-inoculation, or the so-called backslopping and subsequent proofing of rye bread dough simulating commercial one-stage sourdough process, was used for the screening of the leavening capacity of sourdough yeast strains. Two yeast strains were initially tested with seven Lactobacillus strains. Thereafter, 17 yeast strains, mostly of sourdough origin, were tested with a backslopping procedure with heterofermentative Lactobacillus brevis as an acidifying lactic acid bacteria (LAB). The highest leavening capacity was found in sourdoughs containing Candida milleri, in particular when it was accompanied by obligately homofermentative Lactobacillus acidophilus or facultatively heterofermentative Lactobacillus plantarum when it acted homofermentatively. The leavening capacity of the reference strain Saccharomyces cerevisiae was about half that of C. milleri in all sourdoughs tested. The re-inoculation procedure increased the differences found in the leavening capacity of the tested yeast strains during final proofing of rye bread dough. The backslopped sourdoughs containing a heterofermentative Lactobacillus strain were more suppressive than those containing a homofermentative strain. The highest leavening capacity was found in C. milleri strains. The use of one backslopping cycle before assaying the leavening capacity of a laboratory sourdough is recommended since it helps to differentiate between yeast strains to be tested for their leavening power in the final bread dough.     

Chemical leavening and other baker’s yeast substitutes: overview of patents filed between 1833 and 2019

The aim of this study was to review general trends in the patent literature on baker’s yeast substitutes, including chemical leavening and gas injection. Overall, 494 unique inventions were described in patents filed over about 200 years, between 1833 and 2019. About two-thirds of patented inventions targeted acid-reacting materials, and the rest was on non-specific protection of active ingredients (13%), gas injection such as in the aerated bread process (12%), gas-releasing agents like sodium bicarbonate (9%) and miscellaneous dough improvers, including flavouring agents and nutrients (4%). Drawbacks included off-taste and potentially non-healthy residues such as aluminium. Most baker’s yeast substitutes were dry chemical preparations, so-called baking powders, that mainly allowed easy and cheap production of miscellaneous fat- and sugar-rich foods such as cakes, and probably contributed to the popularity of the latter. Applications included ready-to-use dry bakery mixes and refrigerated doughs. Yeast substitutes were originally developed for bread in England and perfected later for fat-rich bakery foods, mainly in the United States. where inventors owned 59% of total patents. Specific aspects of baker’s yeast substitutes will be fully covered in companion articles.     

Gas sources in chemical leavening and other baker’s yeast substitutes: lessons from patents and science

Baker’s yeast produces carbon dioxide during dough fermentation, which gives bakery foods with expanded volume. This review covers gas sources other than baker’s yeast according to information disclosed in patents and supported by scientific literature. Inventors had more interest in gas injection in dough, mainly carbon dioxide, than gas-releasing agents available in chemical leavening, so-called baking powder, with 58 and 43 patented inventions, respectively. For chemical leavening, 20 gas-releasing agents were proposed, including 11 patented and 9 non-patented agents like sodium bicarbonate, the most popular. Other gas-releasing agents included miscellaneous salts of carbonate and bicarbonate (ammonium; calcium; magnesium; potassium) as well as compounds like hydrogen peroxide and, more recently, glutamic acid. Coatings were patented to protect sodium bicarbonate towards moisture and delay its action in dough. Recent trends include aerosol dough and flavourful sodium-free gas-releasing agents.     

Impact of sourdough fermented with Lactobacillus plantarum FST 1.7 on baking and sensory properties of gluten-free breads

Sourdoughs were produced from buckwheat, oat, quinoa, sorghum, teff and wheat flour using the heterofermentative lactic acid bacteria Lactobacillus plantarum FST 1.7 and added to a basic bread formulation of flour from the same grain type (20 % addition level). Dough rheology, textural (crumb hardness, specific volume) and structural bread characteristics (crumb porosity, cell volume, brightness) of sourdough-containing breads were compared to non-sourdough-containing breads (control). Changes in protein profiles as analysed with capillary electrophoresis were observed in all sourdoughs. Furthermore, sourdough addition led to decreased dough strength resulting in softer dough. No influences on specific volume and hardness on day of baking were found for gluten-free sourdough breads. The staling rate was reduced in buckwheat (from 8 ± 2 to 6 ± 2 N/day) and teff sourdough bread (13 ± 1 to 10 ± 4 N/day), however, not significantly in comparison with the control breads. On the contrary, in wheat sourdough bread, the staling rate was significantly reduced (2 ± 1 N/day) in comparison with control bread (5 ± 1 N/day). Sourdough addition increased the cell volume significantly in sorghum (+61 %), teff (+92 %) and wheat sourdough breads (+78 %). Therefore, crumb porosity was significantly increased in all gluten-free and wheat sourdough breads. Shelf life for sourdough breads was one (teff and oat), two (buckwheat, quinoa and sorghum) and 3 days (wheat) and was not prolonged by sourdough addition. The inferior aroma of breads prepared from the gluten-free flours was also not improved by sourdough addition.     

Liquid sourdough fermentation: industrial application perspectives

Sourdough fermentation is considered to play a key role to get improved flavour, texture, nutritional and shelf-life properties of bakery products. Since few years Barilla R&D has been focusing on liquid sourdough fermentation which may deserve several advantages with respect to traditional processes. The results showed that the micro-biota of sourdough markedly influences flavour and texture of bakery products. Particular attention has been paid to lactic acid bacteria and yeasts. Selected lactic acid bacteria and yeasts were tested in sourdough liquid fermentation as single strain or in association. The parameters of fermentations were optimized and standardized to set up a laboratory plant liquid fermentation. Only a few strains of lactic acid bacteria were found to be suitable for liquid fermentation alone or in association with yeasts. Fermentations were carried out at pilot plant and an industrial technology was developed. This work describes the results found for the organoleptic profile of an industrial bread started with liquid sourdough with respect to bakers' yeast bread without sourdough addition.     

From wheat sourdough to gluten‐free sourdough: a non‐conventional process for producing gluten‐free bread

Gluten‐free (GF) sourdough was prepared from wheat sourdough and analysed both in fresh (GFS) and dried forms (DGFS). The gluten content in each GF sourdough sample was <20 mg kg^?1. The dough leavening capacity and the properties of the bread samples were investigated and compared to those of bread prepared using bakery yeast (Saccharomyces cerevisiae). Two commercial rice‐based mixtures (different for the presence/absence of buckwheat flour) were used to prepare bread samples. In GFS, lactic acid bacteria (LAB) and yeasts were found in amounts corresponding to 10⁸ and 10⁷ CFU g^?1, respectively, whereas both LAB and yeasts were detected in lower amounts (about 10⁶ CFU g^?1) in DGFS. When used in bread‐making, both GFS types produced significant dough acidification and exhibited good dough development during proofing, resulting in loaves with specific volume values between 3.00 and 4.12 mL g^?1, values similar to those obtained for reference bread (3.05÷4.15 mL g^?1). The use of GFS was effective in lowering the bread staling rate during storage for up to 7 days.     

Compressed Yeast and Type I Gluten-Free Sourdough in Gluten-Free Breadmaking

The replacement of gluten in cereal-based goods still represents a significant technological challenge, and obtaining high-quality gluten-free (GF) breads brings about the search for ingredients and technologies able to improve the overall features of these products. Even if the use of sourdough has been extensively studied for the traditional baking, thanks to its positive effects on the product associated with the metabolic activities of sourdough-resident microorganisms; only in recent times, similar attempts have been made in GF baking. GF bread, in fact, is more generally produced by a straight-dough process, using compressed yeast as leavening agent. This research aimed to compare the properties of GF doughs and breads obtained using a Type I GF sourdough (GF-SD; in-lab developed), compressed yeast (Saccharomyces cerevisiae; CY), or their mixture (GF-SD + CY) during proofing. There are no studies, in fact, on Type I GF-SD with the stable association between the lactic acid bacterium Lactobacillus sanfranciscensis and the yeast Candida humilis. GF-SD doughs were comparable to CY doughs in terms of height development (adopting a longer fermentation step), and well-developed doughs were obtained in a short time when GF-SD was combined with CY. Despite the lower specific volume and the denser crumb, GF-SD breads were characterized by a more coherent texture, while CY breads were more prone to fracture during storage. Breads leavened with GF-SD + CY showed intermediate features. The promising results coming from the use of the in-lab developed GF-SD thus confirmed the positive effects of adopting the sourdough technology in GF breadmaking, too.     

Emerging fermentation technologies: development of novel sourdoughs

The increasing knowledge of sourdough fermentation generates new opportunities for its use in the bakery field. New fermentation technologies emerged through in depth sourdough research. Dextrans are extracellular bacterial polysaccharides produced mainly by lactic acid bacteria (LAB). These bacteria convert sucrose thanks to an inducible enzyme called dextransucrase into dextran and fructose. The structure of dextran depends on the producing micro-organism and on culture conditions. Depending on its structure, dextran has specific properties which lead to several industrial applications in different domains. The use of dextran is not widely spread in the bakery field even if its impact on bread volume and texture was shown. A new process has been developed to obtain a sourdough rich in dextran using a specific LAB strain able to produce a sufficient amount of HMW dextran assuring a significant impact on bread volume. The sourdough obtained permits to improve freshness, crumb structure, mouthfeel and softness of all kinds of baked good from wheat rich dough products to rye sourdough breads. From fundamental research on dextran technology, a new fermentation process has been developed to produce an innovative functional ingredient for bakery industry.     

响应面法优化自发馒头粉配方

以成品馒头白度、硬度及感官评分为评价指标,在单因素试验的基础上,采用Box-Behnken试验设计对自发馒头粉配方中的酵子、酵母、化学膨松剂（碳酸氢钠和葡萄糖酸内酯）添加量3个因素进行优化,确定适宜的自发馒头粉配方。结果表明,最优的自发馒头粉配方为：酵子添加量0.86%、酵母添加量0.5%、化学膨松剂添加量1.2%（NaHCO3∶葡萄糖酸内酯=42∶89）,采用最优自发馒头粉蒸制的馒头的白度为53.4,硬度为452 g,感官评分为87.5分。     

Investigating the einkorn (Triticum monococcum) and common wheat (Triticum aestivum) bread crumb structure with X‐ray microtomography: effects on rheological and sensory properties

Einkorn wheat (Tm, Triticum monococcum L.) has nutritional characteristics that clearly distinguish it from common wheat (Ta, Triticum aestivum L.) although its rheological dough properties may be less‐performing. Therefore, to better understand the potential of Tm for human consumption and food preparation, we compared the quality of bread baked with ancient einkorn and common wheat leavened with brewer's yeast and sourdough. Results showed that Tm had generally higher firmness (21.6 N vs. 10.5 N), and lower (65.6% vs. 71.2%) and less homogeneous porosity than Ta. These results suggest a minor potential in bread‐making regardless of the Tm high total protein content and underline a weaker gluten ability to expand and retain the fermentation gas. The selection of best‐performing einkorn varieties and leavening agents (e.g. fresh sourdough) can lead to bread products with acceptable texture features, meeting consumer demand for organic, natural and ancient products.     

Inventions on phosphates for chemical leavening

Baking powders contain leavening acids that activate gas-releasing agents such as sodium bicarbonate. This is a review of the patent literature on phosphate-based leavening acids developed between 1856 and 2019. Overall, 174 patented inventions were found on 28 phosphate-based compounds, which corresponded to more than half of the inventions disclosed on leavening acids. Inventors had a strong interest in monocalcium phosphate, sodium acid pyrophosphate and, to a lesser extent, sodium aluminium phosphate and miscellaneous acid phosphates. As cheap alternatives to tartrates, most early phosphate-based leavening acids were difficult to keep because they had a high affinity for moisture and tended to react prematurely with gas-releasing agents in baking powders. The evolution of phosphates in chemical leavening reflected changes in the consumption of bakery foods, especially in the United States where chemical leavening has been very popular for food preparations like prepared flours, ready-to-use bakery mixes and refrigerated doughs. Sodium-free phosphates are solutions to reduce salt intake in food. Alternatives to phosphates are searched due to potential health issues.     

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.     

Spontaneous sourdough processing of Chinese Northern-style steamed breads and their volatile compounds

The effect of amount of flour in the pre-fermented form (10%, 20%, and 30% flour in the pre-fermented form), fermentation time (12, 24, and 36 h), and amount of yeast (0.5%, 1.0%, and 1.5%) on acidity, specific volume, and crumb texture of Chinese Northern-style sourdough steamed breads were studied. Volatile compounds of the sourdough and non-sourdough steamed breads were also determined. The preferments were produced from spontaneous fermentation using all purpose (APF) and whole wheat flours (WWF). Specific volume was the highest at 20% preferment for APF sourdough steamed bread (ASSB) and 30% preferment for WWF sourdough steamed bread (WSSB). The softest texture was obtained with 20% preferment while at 30% preferment there was excessive gluten weakening due to high acidification. A total of 89 volatile compounds were identified in steamed breads with ethanol and 3-methyl-1-butanol being the most abundant compounds.     

Utilization of African grains for sourdough bread making

Abstract: Acha and Iburu flours were singly subjected to sourdough fermentation with previously selected autochthonous starters. Sourdoughs were used (30%, wt/wt) as aroma carriers and acidifiers during short time fermentation with the addition of baker's yeast. Acha and Iburu sourdough breads were compared to wheat sourdough bread started with the same strains and to breads made with the same formula but using baker's yeast alone. During Acha and Iburu sourdough fermentations, starter lactic acid bacteria reached almost the same cell density found in wheat sourdoughs. Acidification was more intense. Iburu sourdough bread had the highest total titratable acidity, the lowest pH, and contained the highest levels of free amino acids and phytase activity. The values of in vitro protein digestibility did not differ between Acha sourdough and wheat sourdough breads, while Iburu sourdough bread showed a slightly lower value. Acha and Iburu sourdough breads showed lower specific volume and higher density with respect to wheat sourdough breads. Nevertheless, Acha and Iburu sourdough breads were preferred for hardness and resilience. As shown by sensory analysis, Acha and especially Iburu sourdough breads were appreciated for color, acid taste and flavor, and overall acceptability. Practical Application: This study was aimed at evaluating the technological and nutritional properties of the African cereals Acha and Iburu. Sourdough fermentation and the use of selected starters increased the nutritional and sensory qualities and the potential application for bakery industry.     

The use of sourdough fermented by antifungal LAB to reduce the amount of calcium propionate in bread

Addition of sourdough is a common practice in the bakery industry to improve, among other quality parameters, the shelf life of bread. In this study, sourdough fermented by antifungal Lactobacillus plantarum strains was investigated for the ability to inhibit growth of common bread spoilage fungi. In both in vitro and sourdough wheat bread system, the antifungal sourdoughs significantly affected the outgrowth of Aspergillus niger, Fusarium culmorum, or Penicillium expansum spores, however on wheat bread outgrowth of Penicillium roqueforti spores was not affected. In an attempt to reduce the amounts of chemical additives in bread, the antifungal sourdoughs were used in combination with calcium propionate (CAP) and possible synergistic effects were evaluated. Presence of 3000 ppm CAP in the bread did not affect the outgrowth of P. roqueforti, whereas outgrowth of the other fungi was retarded. A strong synergistic effect was observed when CAP and antifungal sourdoughs were combined into the bread formulation, and outgrowth of P. roqueforti was affected. The use of reduced CAP amount (1000 ppm) showed significant inhibition only when antifungal sourdough was added. Remarkably, the increase in shelf life achieved was higher than that obtained using 3000 ppm of CAP alone. In conclusion, the results of this study clearly show that the addition of antifungal sourdough has the potential to reduce the levels of chemical additives needed in the bakery industry to ensure the microbiological safety of bread.     

Use of response surface methodology to investigate the effects of processing conditions on sourdough wheat bread quality

Response surface methodology was used to investigate the influence of three factors, sourdough fermentation time, proof time and amount of yeast addition on the quality of sourdough wheat bread. Each predictor variable was tested at five levels. Sourdough fermentation times were 5, 11, 20, 29 and 35 h, yeast addition rates were 0.05, 0.75, 1.77, 2.80 and 3.50% (flour weight basis) and proof times were 16, 40, 75, 110 and 134 min. The performance of two different starter culture types, a mixed strain starter culture called Böcker Reinzucht–Sauerteig Weizen and a single strain starter culture of Lactobacillus brevis, was compared by separately completing the experimental design for each. Independently non-acidified control bread was prepared. A range of loaf quality parameters was determined including pH, total titratable acidity, loaf height, specific volume, crumb mean cell area and crumb hardness. Overall breads with better specific volume values were achieved with the use of sourdough relative to the control. Results indicated that maximum loaf specific volume was achieved when L. brevis sourdough was used particularly when it was used in conjunction with a high rate of yeast. Given a lower rate of yeast addition however, the mixed strain starter culture yielded better bread.     

Emulsifiers: Effects on Quality of Fibre-Enriched Wheat Bread

Resistant starch (RS) is a nutritional ingredient commonly used in bread products as dietary fibre (DF). This ingredient presents similar physiological functions than those imparted by DF, promoting beneficial effects such as the reduction of cholesterol and/or glucose levels on blood. Quality improvement of bread containing RS, with an optimized combination of emulsifiers, will be useful in the development of new and healthy bakery products. The objective of this research was to analyse the effects of different emulsifiers on several quality parameters of dough and bread prepared with wheat flour partially substituted with resistant starch as a dietary fibre. A blend of wheat flour/maize-resistant starch (MRS; 87.5:12.5) with sodium chloride, ascorbic acid, α-amylase, compressed yeast and water was utilized. Emulsifiers were incorporated to formulations in different levels according to a simplex centroid design. The viscoelastic, textural and extensional properties of dough were analysed. Bread quality was evaluated throughout the gelatinization and retrogradation of starch, specific volume of loaves, and texture and firmness of bread crumb. The incorporation of 12.5% (w/w) of MRS to wheat flour caused an increase of 5% in water absorption. Stability decreases markedly (from 9.9 to 2.2 min) and the mixing tolerance index increased (from 79 to 35 UF). The sodium stearoyl lactylate (SSL)–diacetyl tartaric acid esters of monoglycerides (DATEM) mixture increased hardness and resistance to extension on dough, whilst dough containing Polysorbate 80 (PS80) was softer; nevertheless, both types of dough retained less CO₂. An optimized concentration of the three emulsifiers (0.24% SSL, 0.18% PS80, 0.08% DATEM, w/w) was obtained by surface response methodology. The bread prepared with this combination of emulsifiers presented a considerable specific volume with a very soft crumb.     

Overview of Sourdough Technology: from Production to Marketing

Sourdough is a type of dough fermented by yeast and lactic acid bacteria (LAB) used as sponge dough in bread making. Sourdough may have four classifications according to the fermentation type and the technological process used. On sourdough type I, the fermentation of yeasts and LAB present in the flour occurs spontaneously whereas in type II, fermentation occurs after the inoculation of a starter culture. Type III is simply type II sourdough dehydrated and type IV is a mixture of type I and type II sourdough, produced on laboratory scale. With LAB’s growth during fermentation, pH decreases with subsequent hydrolysis of starch and protein, favoring the growth of yeasts. The yeast in turn, releases amino acids during autolysis, contributing to the growth of LAB. Due to this synergistic growth of LAB and yeasts, the products obtained from sourdough show more concentration of flavor, more elastic dough, and a longer shelf life than bread fermented only by yeast. Although, the benefits of this technology, using sourdough, is present just in a few countries, where it is also possible to obtain the dehydrated sourdough starters, for domestic use, in local supermarkets. Due to its fermentative process complexity, this paper presents updated information about the fabrication process of sourdough, main factors affecting this process, benefits of sourdough use for bakery products, and the varieties of dehydrated sourdough commercially available throughout the world.     

Prevalence,Genetic Diversity,and Technological Functions of the Lactobacillus sanfranciscensis in Sourdough: A Review

The use of sourdough as a leavening agent in bread making is a very old method that can be traced back to ancient times. Sourdoughs harbor a complex microbiota that is affected by multiple factors including factors related to cereal plants, grains, and sourdough processing techniques. Lactobacillus sanfranciscensis is the key autochthonous bacterium of the traditional sourdough microbiota and it is said to be “sourdough adapted” species. Despite the great dominance of this bacterium in sourdoughs, the origin of this species still remains unclear. Lactobacillus sanfranciscensis positively influences all aspects of sourdough and fermented foods. However, the positive influence of this species on sourdough is a strain‐dependent characteristic. The first purpose of this review was to discuss factors affecting the microbiota of sourdoughs with particular emphasis on reasons behind the remarkable prevalence of L. sanfranciscensis in this ecological niche. The second objective was to discuss the genotypic and phenotypic classification of L. sanfranciscensis strains and the influence of this species on technological and functional characteristics of sourdough including its influence on rheological properties of dough and bread characteristics, texture, aroma, and shelf‐life through the inhibition of fungal growth.     

Quality attributes and firming kinetics of partially baked frozen wholewheat bread with sourdough

Partially baked frozen (PBF) process prolongs bread shelf life, but diminishes its volume and crumb texture. Therefore, we investigated the possibility of using sourdough for the quality improvement in PBF wholewheat bread. Sourdough was fermented with either Lactobacillus plantarum, Lb. brevis or Leuconostoc mesenteroides mixed with yeast Candida humilis and added at 7.5, 15, 22.5 or 30% on bread dough basis. The choice of sourdough starter significantly affected bread acidity characteristics, flavour, specific volume, shape and crumb firmness. The sourdough amount and acetic acid content of bread inversely correlated to flavour score, specific volume, shape and crumb softness. The overall quality of PBF wholewheat bread was most efficiently improved after adding Lb. plantarum sourdough at 15–22.5%, resulting in retarded firming rate (74–94%) and improved specific volume (25–28%) in comparison with PBF bread without sourdough. Such sourdough has lactic to acetic acid higher than previously recommended for traditional sourbreads.