Commercial Baker Research Articles

Application of yeasts and yeast derivatives for the biological control of toxigenic fungi and their toxic metabolites

Abstract Mycotoxins, the metabolites of toxigenic fungi are important contaminants of food and agriculture industry throughout the world. Among the different strategies to minimize the mycotoxins synthesis and decontamination of food; yeasts and their derivatives are used as efficient biological control agents. In this study, cell walls (CW) of six yeast strains; two commercial baking {Saccharomyces cerevisiae (Sc 1 and Sc2)}, two low-fermenting (Candida intermedia and Lachancea thermotolerans), and two non-fermenting (Cyberlindnera jadinii and Candida friedrichii) were explored to inhibit A. flavus growth, aflatoxin (AF) synthesis and remove mycotoxins from contaminated buffers (at pH 3, 5 and 7) and milk. The volatiles of non-fermenting yeasts showed a significant inhibitory effect on of A. flavus growth (up to 79%) and aflatoxin synthesis potential. The highest mycotoxins binding activities of Sc strains were noted against ochratoxin A (92%), AFB2 (66%), AFG2 (59%) and AFB1 (31%). The highest and lowest binding activities occurred at pH 7 and pH 3, respectively. On the other hand, all yeast CWs significantly (44%–54%) reduced aflatoxin M1 (AFM1) from contaminated milk. These results show clearly that yeasts (particularly Sc) can be used as efficient biocontrol and decontamination agents in food industry or the management of mycotoxin contamination.

Optimised Fractionation of Brewer’s Spent Grain for a Biorefinery Producing Sugars, Oligosaccharides, and Bioethanol

Brewer’s spent grain (BSG) is the main by-product of the beer brewing process. It has a huge potential as a feedstock for bio-based manufacturing processes to produce high-value bio-products, biofuels, and platform chemicals. For the valorisation of BSG in a biorefinery process, efficient fractionation and bio-conversion processes are required. The aim of our study was to develop a novel fractionation of BSG for the production of arabinose, arabino-xylooligomers, xylose, and bioethanol. A fractionation process including two-step acidic and enzymatic hydrolysis steps was investigated and optimised by a response surface methodology and a desirability function approach to fractionate the carbohydrate content of BSG. In the first acidic hydrolysis, high arabinose yield (76%) was achieved under the optimised conditions (90 °C, 1.85 w/w% sulphuric acid, 19.5 min) and an arabinose- and arabino-xylooligomer-rich supernatant was obtained. In the second acidic hydrolysis, the remaining xylan was solubilised (90% xylose yield) resulting in a xylose-rich hydrolysate. The last, enzymatic hydrolysis step resulted in a glucose-rich supernatant (46 g/L) under optimised conditions (15 w/w% solids loading, 0.04 g/g enzyme dosage). The glucose-rich fraction was successfully used for bioethanol production (72% ethanol yield by commercial baker’s yeast). The developed and optimised process offers an efficient way for the value-added utilisation of BSG. Based on the validated models, the amounts of the produced sugars, the composition of the sugar streams and solubilised oligo-saccharides are predictable and variable by changing the reaction conditions of the process.

Validation of brownie baking step for controlling Salmonella and Listeria monocytogenes.

Pathogens, such as Salmonella and Listeria monocytogenes, can survive under the dry environment of flour for extended periods of time and could multiply when flour is hydrated to prepare batter or dough. Therefore, inactivation of these pathogens during the cooking/baking step is vital to ensure the microbiological safety of bakery products such as brownies. The aim of this research was to validate a simulated commercial baking process as a kill‐step for controlling Salmonella and L. monocytogenes in brownies and to determine thermal inactivation parameters of these pathogens in brownie batter. Independent studies were conducted in a completely randomized design for each pathogen. All‐purpose flour was inoculated with a 5‐serovar Salmonella and 3‐strain L. monocytogenes cocktails. For baking validation, brownie batters were prepared from inoculated flour, and cooked in the oven set at 350°F (176.7°C) for 40 min followed by 15 min of ambient air cooling. For calculating D‐values, brownie batter was transferred into thermal‐death‐time disks, sealed, and placed in hot‐water baths. The samples were held for pre‐determined time intervals in hot‐water baths and immediately transferred to cold‐water baths. Microbial populations were enumerated using injury‐recovery media. At the end of baking, Salmonella and L. monocytogenes populations decreased by 6.3 and 5.9 log CFU/g, respectively. D‐values of Salmonella and L. monocytogenes cocktails were 53.4 and 37.5 min at 64°C; 27.2 and 16.9 min at 68°C; 10.7 and 9.1 min at 72°C; and 4.6 and 7.3 min at 76°C; respectively. The z‐values of Salmonella and L. monocytogenes cocktails were 11.1 and 16.4°C, respectively. This study can be used as a supporting document for the validation of similar brownie baking processes to control Salmonella and L. monocytogenes. The data from this study can also be employed for developing basic prediction models for the survival and thermal resistance of these pathogens during brownie baking step.

Optimization of ethanol production using newly isolated ethanologenic yeasts

Yeasts are important microorganisms used for ethanol production; however, they are not equally efficient in the amount of ethanol production under different environmental conditions. It is, therefore, necessary to screen for elite strains to utilize them for commercial production of these commodities. In this study, yeasts were isolated from different Ethiopian traditional fermented alcoholic beverages (teji, tella, shamiata and areqe tinisis), milk and ergo, teff and maize dough, soil and compost, flowers, and fruits to evaluate their potential use for ethanol fermentation process. Isolates were screened for efficient ethanol production and the selected ones were identified using phenotypic and genetic characters using D1/D2 region of LSU rDNA sequence analysis. The yeast isolates were evaluated based on their growth and fermentation of different carbon sources. Response surface methodology (RSM) was applied to optimize temperature, pH and incubation time using central composite design (CCD) in Design-Expert 7.0.0. A total of 211 yeasts colonies were isolated of which 60% were ethanologenic yeasts (ethanol producers) and 40% were non-ethanol producers. The yeast population detected from various sources was in the range of 105CFU from traditional foods and beverages to that of 103CFU from fruits and soil samples. The data also showed that the number of colony types (diversity) did not correlate with population density. The highly fermentative isolates were taxonomically characterized into four genera, of which 65% of the isolates (ETP37, ETP50; ETP53, ETP89, ETP94) were categorized under Saccharomyces cerevisiae, and the remaining were Pichia fermentans ETP22, Kluyveromyces marxianus ETP87, and Candida humilis ETP122. The S. cerevisiae isolates produced ethanol (7.6-9.0 g/L) similar with K. marxianus ETP87 producing 7.97 g/L; comparable to the ethanol produced from commercial baker's yeast (8.43 g/L) from 20 g/L dextrose; whereas C. humilis ETP122 and P. fermentans ETP22 produced 5.37 g/L and 6.43 g/L ethanol, respectively. S. cerevisiae ETP53, K. marxianus ETP87, P. fermentans ETP22 and C. humilis ETP122 tolerated 10% extraneous ethanol but the percentage of ethanol tolerance considerably decreased upon 15%. S. cerevisiae ETP53 produced ethanol optimally at pH 5.0, 60 h, and 34oC. pH 4.8, temperature 36oC, and 65 h of time were optimal growth conditions of ethanol fermentation by K. marxianus ETP87. The ethanol fermentation conditions of P. fermentans ETP22 was similar to S. cerevisiae ETP53 though the ethanol titer of S. cerevisiae ETP53 was higher than P. fermentans ETP22. Therefore, S. cerevisiae ETP53, K. marxianus and P. fermentans ETP22 are good candidates for ethanol production.

Influence of grain quality, semolinas and baker’s yeast on bread made from old landraces and modern genotypes of Sicilian durum wheat

Several studies showed that products made with ancient wheat genotypes have beneficial health properties compared to those obtained with modern wheat varieties, even though the mechanisms responsible for the positive effects are not clear. Ancient durum wheat genotypes are being currently used for the production of pasta, bread and other typical bakery products but the consumption is strictly local. In this work 15 genotypes of Triticum turgidum subsp. durum, including 10 ancient and 5 modern, were characterized for their technological traits through the determination of different parameters: protein content, dry gluten, gluten index, yellow index, ash, P/L, W and G. In addition, the baking aptitude of all genotypes was evaluated. All semolinas were subjected to leavening by commercial baker’s yeast and the experimental breads were subjected to the qualitative characterization (weight loss, height, firmness, colour, volatile organic compounds, image and sensory analysis). The results obtained showed that protein content of grains and semolinas was higher in ancient rather than modern genotypes. Dry gluten ranged from 6.7% of the modern variety Simeto to 13.6% of the ancient genotype Scorsonera. Great differences were found for the yellow index which reached the highest value in Saragolla variety. The P/L and W ratios were significantly higher for the modern genotypes. On average, weight loss was about 14 g, while bread height varied significantly between the trials. Bread consistency varied between 12.6 and 31.3 N. Differences were observed for the yellow of the crumb (higher for modern genotypes) and for the redness of the crust (higher for ancient genotypes). The sensory evaluation displayed a high variability among the breads from the 10 ancient genotypes, while the control breads received scores closed to those of the modern genotypes. This study revealed that the modern durum wheat varieties showed a certain uniformity of behaviour, while the ancient genotypes exhibited a great variability of the final attributes of breads.

History and Domestication of Saccharomyces cerevisiae in Bread Baking.

The yeast Saccharomyces cerevisiae has been instrumental in the fermentation of foods and beverages for millennia. In addition to fermentations like wine, beer, cider, sake, and bread, S. cerevisiae has been isolated from environments ranging from soil and trees, to human clinical isolates. Each of these environments has unique selection pressures that S. cerevisiae must adapt to. Bread dough, for example, requires S. cerevisiae to efficiently utilize the complex sugar maltose; tolerate osmotic stress due to the semi-solid state of dough, high salt, and high sugar content of some doughs; withstand various processing conditions, including freezing and drying; and produce desirable aromas and flavors. In this review, we explore the history of bread that gave rise to modern commercial baking yeast, and the genetic and genomic changes that accompanied this. We illustrate the genetic and phenotypic variation that has been documented in baking strains and wild strains, and how this variation might be used for baking strain improvement. While we continue to improve our understanding of how baking strains have adapted to bread dough, we conclude by highlighting some of the remaining open questions in the field.

Ecology of yeasts associated with kernels of several durum wheat genotypes and their role in co-culture with Saccharomyces cerevisiae during dough leavening

This work was performed to investigate on the yeast ecology of durum wheat to evaluate the interaction between kernel yeasts and the commercial baker's yeast Saccharomyces cerevisiae during dough leavening. Yeast populations were studied in 39 genotypes of durum wheat cultivated in Sicily. The highest level of kernel yeasts was 2.9 Log CFU/g. A total of 413 isolates was collected and subjected to phenotypic and genotypic characterization. Twenty-three yeast species belonging to 11 genera have been identified. Filobasidium oeirense, Sporobolomyces roseus and Aureobasidium pullulans were the species most commonly found in durum wheat kernels. Doughs were co-inoculated with yeasts isolated from wheat kernels and commercial Saccharomyces cerevisiae, in order to evaluate the interactions between yeasts and the leavening performance. Yeast populations of all doughs have been monitored as well as dough volume increase and weight loss (as CO2) measured after 2 h of fermentation. The doughs whose final volume was higher than control dough (inoculated exclusively with S. cerevisiae) were those inoculated with Naganishia albida, Vishniacozyma dimennae (118 mL each), and Candida parapsilosis (102 mL). The weight losses were variable, depending on the co-culture used with S. cerevisiae and the values were in the range of 0.08–1.00 g CO2/100 g. The kernel yeasts species C. parapsilosis, N. albida, P. terrestris, R. mucilaginosa and V. dimennae deserves future attention to be co-inoculated with the commercial starter S. cerevisiae in order to improve the sensory characteristics of bread.

Predominant yeasts in the sourdoughs collected from some parts of Turkey.

In the present study, a total of eight sourdough samples were collected from three different bakeries at two different times in Turkey. Also, laboratory-scale sourdough production was conducted by daily back-slopping for 7 days. Microbiological and chemical properties of the sourdoughs were investigated. Yeast species in the sourdoughs were identified by subjecting all presumptive yeast cultures to internal transcribed spacer region amplification of the 5.8S rRNA gene, restriction fragment length polymorphism analysis using Hae III, Hha I, and Hinf I endonucleases, and sequence analysis of the D1/D2 domain of the 26S rDNA gene. A total of seven profiles were determined according to the restriction fragments. Totally, 148 yeast isolates were identified at the species level (≥400 bp, 99% identity) as Saccharomyces cerevisiae (106), Kazachstania bulderi (11), Pichia fermentans (nine), Pichia membranifaciens (eight), Kazachstania servazzii (seven), Kazachstania unispora (four), and Hanseniaspora valbyensis (three). Although collected sourdoughs were produced without using baker's yeast, S. cerevisiae was the most frequently isolated yeast species. This can be related to the contamination of the bakery environment with commercial baker's yeast during the production of other bakery products. The pH and acidity levels of the collected sourdough samples ranged from 3.71 to 3.96 and 6.78 to 23.93 mL 0.1 N NaOH/10 g dough, respectively. Mean values of the content of maltose + sucrose, glucose, fructose, lactic acid, and acetic acid were 2.43, 1.57, 2.67, 7.30, and 1.40 g/kg, respectively. Due to the artisan and region-dependent handling of the sourdough, different biochemical patterns were observed among the collected samples.

Effect of Commercial Baker’s Yeast Supplementation (Saccharomyces Cerevisiae) in Diet and Drinking Water on Productive Performance, Carcass Traits, Haematology and Microbiological characteristics of Local Quails

Effect of Commercial Baker’s Yeast Supplementation (Saccharomyces Cerevisiae) in Diet and Drinking Water on Productive Performance, Carcass Traits, Haematology and Microbiological characteristics of Local Quails

Fermentative Microbes of Khadi, a Traditional Alcoholic Beverage of Botswana

Khadi is a popular traditional alcoholic beverage in rural households in Botswana. The product is produced by fermentation of ripened sun-dried Grewia flava (Malvaceae) fruits supplemented with brown table sugar. Despite its popularity, its growing consumer acceptance, its potential nutritional value, and its contribution to the socio-economic lifestyle of Botswana, the production process remains non-standardized. Non-standardized production processes lead to discrepancies in product quality and safety as well as varying shelf life. Identification of unknown fermentative microorganisms of khadi is an important step towards standardization of its brewing process for entrance into commercial markets. The aim of this study was to isolate and identify bacteria and yeasts responsible for fermentation of khadi. Yeasts and bacteria harbored in 18 khadi samples from 18 brewers in central and northern Botswana were investigated using classic culture-dependent techniques and DNA sequencing methods. Additionally, we used the same techniques to investigate the presence of bacteria and yeasts on six batches of ripened-dried G. flava fruits used for production of the sampled brews. Our results revealed that Saccharomyces cerevisiae closely related to a commercial baker’s yeast strain sold locally was the most predominant yeast species in khadi suggesting a possible non-spontaneous brewing process. However, we also detected diverse non-Saccharomyces yeasts, which are not available commercially in retail shops in Botswana. This suggests that spontaneous fermentation is partially responsible for fermentation of khadi. This study, presenting the first microbiological characterization of a prominent traditional alcoholic beverage in Botswana, is vital for development of starter cultures for the production of a consistent product towards the commercialization of khadi.

Physicochemical and sensory characterization of bread produced from different dough formulations by Kluyveromyces lactis

This study aimed to investigate the potential of Kluyveromyces lactis to be used as baker's yeast in production of lean bread (100% of wheat flour) and sucrose (10%), lactose (10%), or whey (13.35%) supplemented breads. The pH, total titratable acidity, baking loss, specific volume, color parameters, textural, and sensory properties of breads produced by K. lactis were measured and compared with those of breads produced by commercial baker's yeast. Type of yeast and dough formulation had significant influences on pH, specific volume, baking loss, textural parameters, and color parameters of breads. Commercial baker's yeast presented better results than K. lactis in lean bread. The investigated parameters of K. lactis leavened bread were improved with the addition of each ingredient. Whey and lactose added breads leavened by K. lactis had quality characteristics and sensory scores as good as or better than the breads leavened by commercial baker's yeast. PRACTICAL APPLICATIONS: Several studies have focused on the increase in the nutritional value of wheat based bread. Fortification of dough with whey improves bread protein quality, but also may negatively affect the other quality characteristics of bread. Moreover, breads containing whey powder may not be suitable for people with lactose intolerance due to the high amount of lactose found in it. Kluyveromyces lactis has ability to utilize lactose as a source of carbon. In this study, whey powder fortified bread leavened by K. lactis was judged as acceptable by the sensory panel and received similar scores for odor, taste, and overall acceptability compared to commercial baker's yeast. The results of this study show that K. lactis is feasible yeast for the production of whey powder enriched bread, and thus, may help to use whey powder as a suitable ingredient in bread making.

Potentials of sago fibre hydrolysate (SFH) as a sole fermentation media for bioethanol production

Sago wastewater which contains starchy fibres from sago starch processing mills is commonly discharged directly to nearby stream thus contribute to serious environmental pollution. Sago fibre which is known to be a local agricultural waste mainly contains residual starch of about (50 – 60 %) together with cellulosic component. These contribute to high carbohydrate contents which suitable to be used as substrate for ethanol production. Initially, sago fibre (SF) was converted into sago fibre hydrolysate (SFH) via enzymatic hydrolysis using commercial enzymes; Liquozyme SC DS and Spirizyme Fuel HS. This study emphasized on batch ethanol fermentation by commercial baker’s yeast utilizing 50 g/L and 80 g/L glucose of SFH as the sole fermentation medium. The results indicate that 50 g/L glucose from SFH media is capable of generating maximum ethanol concentration at 20.33 ± 0.15 g/L, with highest glucose consumption efficiency (97.78 %) during 24 hours of fermentation. Similar concentration of bioethanol was obtained in 50 g/L glucose of commercial glucose (CG) media which is at 20.04 ± 0.06 g/L. However, lower ethanol concentration was obtained in both 80 g/L glucose from SFH (13.32 ± 0.12 g/L) and CG (12.98 ± 0. 04 g/L media), respectively. Addition of yeast extract at 3 g/L into 80 g/L SFH as well as CG significantly improve ethanol fermentability (SFH: 41.04 ± 0.04 g/L and CG: 33.96 ± 0.04 g/L). Based on statistical analyses, 50 g/L glucose of SFH media exhibit the highest ethanol yield (0.42 ± 0.003 g/g) and highest fermentation efficiency (81.35 ± 0.572 %) compared to 80 g/L glucose (0.24 ± 0.008 g/g; 46.65 ± 1.50 %). Conclusively, this study demonstrated that glucose in SFH was metabolized efficiently by commercial baker’s yeast during ethanol fermentation, thus suggesting the capability of SFH to be a feasible and alternative substrate with less expensive nitrogen source for the renewable bioethanol production.

Evaluation of the Fermentation Dynamics of Commercial Baker’s Yeast in Presence of Pistachio Powder to Produce Lysine-Enriched Breads

The present work was carried out to evaluate the microbiological, physicochemical, and sensory characteristics of fortified pistachio breads. Pistachio powder (5% w/w) was added to flour or semolina and fermented by a commercial baker’s yeast (Saccharomyces cerevisiae). Pistachio powder did not influence the biological leavening of the doughs. The kinetics of pH and total titratable acidity (TTA) during dough fermentation showed that the leavening process occurred similarly for all trials. The concentration of yeasts increased during fermentation and reached levels of 108 CFU/g after 2 h. Pistachio powder decreased the height and softness of the final breads and increased cell density of the central slices. The amount of lysine after baking increased in pistachio breads and this effect was stronger for semolina rather than flour trials. Sensory evaluation indicated that fortified breads processed from semolina were those more appreciated by the judges. This work clearly indicated that the addition of pistachio powder in bread production represents a promising strategy to increase the availability of lysine in cereal-based fermented products.

Evaluation of enzymatic hydrolysis via alcoholic fermentation of corn flour

Abstract The research was concerned with the enzymatic hydrolysis followed by alcoholic fermentation of corn flour. Commercial corn flour purchased from local market contained starch of 87.25%, moisture 11.86% and ash 0.70%. The kinetics of corn flour hydrolysis was performed at 50°C, 65°C and 80°C using commercial thermos table-∞-amylase and ∞-amyloglucosidase. During hydrolysis the residual starch content was decreased with increasing hydrolysis time. The line weaver- Burk plot for enzyme hydrolysis of corn starch for 2.5%, 5% and 10% flour solution showed a Km value of 2.46, 2.27 and 1.73 mg/ml and Vmax values 1.23, 1.21 and 0.96 U/ml for 50°C, 65°C and 80°C respectively. Thin layer chromatography (TLC) was used to detect the presence of dextrose in the hydrolyzates. The Rf (Retention factors) values showed that the starch was mainly composed of dextrose and depended on carrier solvent use for dextrose assessment. When 100% ethyl alcohol used as carrier solvent the Rf value was 0.72 and ethyl alcohol: ethyl acetate= 1:1 the Rf value was 0.65. Both corn flour solution and its enzymatic hydrolysates were fermented with commercial baker’s yeast. Both the cases starch content was decreased and alcohol content was increased during hydrolysis and alcohol production was 3 times more from hydrolysates. The results obtained here will be useful for further research in the production of other value added products like white vinegar from the produced alcohol from con flour.

Microbial consortia involved in fermented spelt sourdoughs: dynamics and characterization of yeasts and lactic acid bacteria.

This study aims to describe the native microbiota of fermented spelt, taking into consideration both lactic acid bacteria (LAB) and yeasts, for which little data are available. Five samples of commercial spelt flour were subjected to spontaneous fermentation to obtain a type I sourdough. A total of 186 LAB and 174 yeast isolates were selected at different refreshment steps and subjected to further analyses. Within LAB, coccal isolates constituted 78·5% of the total LAB, with the dominance of Pediococcus pentosaceus. Although documented before as a component, this is the first report of a spelt sourdough fermentation dominated by this homofermentative LAB, characterized by a high acidification rate, ability to utilize a wide range of carbon sources and to grow in high osmolarity conditions. Yeast communities resulted in four dominant species, Saccharomyces cerevisiae, Wickerhamomyces anomalus, Pichia fermentans and Clavispora lusitaniae. This study highlights for the first time the biodiversity and dynamics of yeast communities involved in sourdough fermentation of spelt. Compared to commercial baker's yeast, autochthonous W. anomalus, P. fermentans and S. cerevisiae isolates show a good performance, and their use could be an advantage for their acquired adaptation to the environment, providing stability to the fermentation process. SIGNIFICANCE AND IMPACT OF THE STUDY: Nowadays, there is a renewed interest in products based on spelt. This 'ancient grain' is a highly nutritional grain; however, its use is limited to bread-making processes, which are not standardized. The low baking and sensory quality of spelt can be overcome through fermentation processes. However, the autochthonous microbiota of spelt sourdough is poorly known. This study highlights the dynamics of microbial communities involved in sourdough fermentation of spelt and provides the basis for the selection of autochthonous cultures, with the aim of improving the nutritional potential of spelt and its rheology and bread-making properties.

Comparison of survival and heat resistance of Escherichia coli O121 and Salmonella in muffins

This study was conducted to validate a simulated commercial baking process for plain muffins against E. coli O121 (isolated from the recent illness outbreak associated with flour), and compare the thermal inactivation parameters (D- and z-values) of cocktails of four isolates of E. coli O121 and three serovars of Salmonella (Newport, Typhimurium, and Senftenberg) in muffin batter. Flour samples were spray inoculated with the E. coli O121 or Salmonella cocktails, dried back to the pre-inoculation weight to achieve ~7 log10 CFU/g, and used to prepare muffin batter. For the muffin baking validation study using E. coli O121, muffin batter was baked at 375 °F (190.6 °C) oven temperature for 21 min followed by 30 min of ambient cooling. The E. coli O121 population decreased by >7 log10 CFU/g in muffins by 17 min of baking, and was completely eradicated after 21 min of baking and ambient cooling. The D-values of E. coli O121 and Salmonella cocktails in muffin batter at 60, 65 and 70 °C were 42.0 and 38.4, 7.5 and 7.2, and 0.4 and 0.5 min, respectively; whereas the z-values of E. coli O121 and Salmonella were 5.0 and 5.2 °C, respectively.

Comparative Efficacy of Different Brands of Baker’s Yeast Used in Bread Production in Jos Metropolis, Nigeria

Consumption of bread and other baked aerated wheat flour products has spurred the needs to determine the leavening ability of different brands of baker’s yeast used in bread production. In this study we assessed the leaving ability of different brands of baker’s yeast in production of quality bread and the flour used in baking test was Dangote flour. Seven brands of different commercial baker’s yeast were collected from the 13 different brands sold in Jos market. These brands includes: Angel instant active dry yeast (ANGY), Saf-instant active dry yeast (SAFY), Food mont instant active dry yeast (FOMY), Pasha instant active dry yeast (PASY), STK- Royal active dry yeast (ROYA), Vahine active dry yeast (VAHY) and Fermipan active dry yeast (FEMY). The results of the viability tests for the different brands of active dry yeast indicated that six out of the seven brands were 100% viable while one had only one dead cell. Statistical analysis (one-sample-t- test) revealed that there was significant different among the different brands of yeasts used (p<0.05), however ANGY had the highest performance viability (p<0.002) and PASY had the least (p<0.039) as shown in Table 3 in appendix. The result of the pH variation as function of time at 260C shows steady decrease in pH values of all the different brands of yeast suspension. Using regression analysis, pH at 150 minutes contribute 96 percent to the leavening ability of different brands of baker’s yeast used in bread production and 30 minutes contribute the lowest 9.1 percent as shown in the Table 4 in the appendix. It was concluded that all the seven brands of baker’s yeast tested were suitable for use in bread production when compared with the standard.

Yeast Species, Strains, and Growth Media Mediate Attraction of Drosophila suzukii (Diptera: Drosophilidae).

Specific ecological interactions between insects and microbes have potential in the development of targeted pest monitoring or control techniques for the spotted wing drosophilid, Drosophila suzukii (Matsumura), an exotic invasive pest of soft fruit. To evaluate D. suzukii attraction to yeast species from preferred types of fruit, three yeasts were isolated from blackberry fruit and two yeasts from raspberry fruit and used to bait simple plastic bottle traps. Saccharomyces cerevisiae and Hanseniaspora uvarum were identified from blackberries, whereas a different H. uvarum strain was identified from raspberry. Yeast identification was based on sequence analysis of the D1/D2 domain of the large subunit 26S rRNA gene. Commercial baker’s yeast (S. cerevisiae) was similar or more effective for the capture of D. suzukii males and females than yeasts isolated from blackberry or raspberry when grown in sucrose. However, when grown in corn syrup, a strain of S. cerevisiae from blackberry captured the highest number of females and a strain of H. uvarum isolated from raspberry captured high numbers of males and females. Species of Candida, Hanseniaspora, and Pichia from a laboratory yeast collection did not outperform baker’s yeast in pairwise tests when grown in sucrose solution or yeast-peptone-dextrose medium. The raspberry strain of H. uvarum grown in corn syrup outperformed S. cerevisiae grown in sucrose, in terms of captures in baited traps under laboratory conditions. We conclude that yeast species, strain, and growth medium can have a marked influence on D. suzukii attraction to baited traps, a finding that could assist in the development of yeast-related monitoring or control techniques targeted at this pest.

Exploiting heterozygosity in industrial yeasts to create new and improved baker's yeasts.

The main aim of the work was to utilize heterozygosity of industrial yeast strains to construct new baker's yeast strains. Commercial baker's yeast strain ALKO 743, its more ethanol tolerant descendant ALKO 554 selected initially for growth over 300 generations in increasing ethanol concentrations in a glucose medium, and ALKO 3460 from an old domestic sour dough starter were used as starting strains. Isolated meiotic segregants of the strains were characterized genetically for sporulation ability and mating type, and the ploidy was determined physically. Heterozygosity of the segregant strains was estimated by a variety of molecular characterizations and fermentation and growth assays. The results showed wide heterozygosity and that the segregants were clustered into subgroups. This clustering was used for choosing distantly or closely related partners for strain construction crosses. Intrastrain hybrids made with segregants of ALKO 743 showed 16-24% hybrid vigour or heterosis. Interstrain hybrids with segregants of ALKO 743 and ALKO 3460 showed a wide variety of characteristics but also clear heterosis of 27-31% effects as assayed by lean and sugar dough raising. Distiller's yeast ALKO 554 turned out to be a diploid genetic segregant and not just a more ethanol tolerant mutant of the tetraploid parent strain ALKO 743.

An Approach to Measure the Biomass of Bloodworms (Diptera: Chironomidae) in Different Nutrients

Due to their rich nutrient content, late stage Chironomus larvae or bloodworms are considered as the most preferred natural food source of cultured fish. However, it is not popular due to its high cost and low availability. Bloodworm culture is still in its infant stage and mainly therefore harvested from nature. The objective of the study was to achieve a cost-effective culture practice of this insect under laboratory conditions. For this experiment four types of diets were selected, namely, dried potato peel powder (F1), commercial baker’s yeast powder (F2), a mixed culture medium (F3) and commercial fish food powder (F4) along with a control culture medium. The result showed a significant effect of diet on both wet mass [F = 40937.78 > F0.01 (3, 8)] and biomass [F = 13882.84 > F0.01 (3, 8)] of bloodworms. The biomass was almost similar when larvae were fed commercial fish food and mixed diet respectively, but the mixed diet was more cost effective and a rich source of both carbohydrates and protein.