ENZYMIC BREAKDOWN OF ENDOSPERM PROTEINS OF SORGHUM AT DIFFERENT MALTING TEMPERATURES

Enzymic breakdown of endosperm proteins of sorghum was more effective at 20°C than at 25°C and 30°C, as regards total protein solubilization, α-amino nitrogen and peptide production. Although the embryos (axes and scutella), of the three temperature treatments contained similar quantities of protein, it appeared that less proteins, in terms of amino acids and peptides, were transferred to the roots during malting at 30°C than at 25°C and 20°C. During mashing, higher levels of peptides but lower levels of α-amino nitrogen and total soluble nitrogen were released in an infusion mash at 65°C than in a decantation mash where enzymically active wort was decanted and used to mash gelatinized sorghum starch at 65°C. Although more of the maltose-producing enzyme—β—amylase was found in sorghum malts made at 25°C and 30°C than at 20°C, it would seem that, for sorghum, malting temperature of 20°C to 25°C were optimal as regards protein breakdown during malting. The protein breakdown produced when sorghum is malted at 20°C is comparable to that found in barley malt and should support similar levels of adjuncts and yeast growth during brewing.     

Increased Aflatoxin Production by Aspergillus parasiticus Under Conditions of Cycling Temperatures

The effects of cycling temperatures (5°C for 12 hr and 25°C for 12 hr) on aflatoxin production by Aspergillus parasiticus NRRL 2999 in yeast extract sucrose (YES) medium were studied. Cycling temperatures, after preincubation at 25°C for various times, resulted in more aflatoxin B₁, G₁, and total aflatoxin production than did constant incubation at either 25°C, which is generally considered to be the optimum for aflatoxin production, or 15°C, which is the same total thermal input as the 5-25°C temperature cycling. With increased preincubation time at 25°C, toxin production increased and the lag phase of growth was shortened or not evident. Cultures that were preincubated at 25°C for 1, 2, and 3 days prior to onset of temperature cycling showed the greatest increase in maximum aflatoxin production over the 25°C and 15°C constant temperatures. Cultures that were not preincubated at 25°C but subjected to constantly fluctuating temperatures produced maximum amounts of aflatoxin equivalent to cultures incubated at a constant 25°C. The maximum aflatoxin production at all temperatures studied occurred during the late log phase of growth and at pH minimums. Aflatoxins were found in higher concentrations in the broth than the mycelia under temperature cycling conditions, at 15°C, and at 25°C during the first 21 days of incubation, whereas greater amounts of toxin were retained in mycelium at 25°C in the later incubation period (28-42 days).     

Top Pressure and Temperature Control the Fusel Alcohol/Ester Ratio through Yeast Growth in Beer Fermentation

Temperature and top pressure are key factors for maintaining a consistent quality of lager beer. Their influence on yeast growth, CO₂ production, final concentrations of fusel alcohol and ester and production kinetics was analysed under industrial conditions. Fermentations of 12°P lager wort were performed at 10°C or 16°C temperature and 1.05 bars or 1.8 bars top pressure, corresponding to dissolved carbon dioxide concentrations of 1.98 g/litre to 3.65 g/litre. Analysis of variance was performed to test the significance of temperature and dissolved C₂. Results show that temperature increases fermentation rate and the production ratio and final concentration of fusel alcohol, independently of the top pressure applied. Conversely, dissolved carbon dioxide controls the production rate and final concentration of ester by limiting yeast growth. Relationships between initial or maximum ester production rates and maximal growth rates were shown. Considering the metabolic pathways occurring during anaerobic growth of yeast, a limited production of acetyl CoA was expected in cultures with high concentrations of dissolved carbon dioxide. Also, final ester concentration and biomass produced are linearly correlated. Furthermore, whatever the ester considered, its synthesis is not influenced by corresponding fusel alcohol availability. It was demonstrated that fermentations performed with a reasoned combination of temperature and top pressure can result in a beer of distinctive aroma without resorting to modification of the initial wort or yeast strain.     

Effect of temperature and pH on the formation of higher alcohols,fatty acids and esters in the malt whisky fermentation

The levels of higher alcohols, fatty acids and esters in small-scale whisky fermentations which were carried out at different temperatures and initial pH values were investigated. Neither the total higher alcohol content nor the relative abundance of different alcohols was affected by varying the temperature between 20 and 30°C. However, the level of octanoic acid, decanoic acid, ethyl hexanoate and ethyl octanoate were depressed at higher temperatures. The highest level of acetate esters were observed at 25 and 30°C. Altering the initial pH of the wort had little effect on the level of higher alcohols. However, increasing the pH from 4·0 to 7·0 resulted in an increase in the level of octanoic, decanoic and dodecanoic acids. Maximum levels of acetate esters of higher alcohols were obtained when initial pH values of between 5·0 and 6·0 were used.     

Histamine Production in Soy Extended Tuna Salads

Histamine production in tuna salads extended with textured soy protein (TSP) was evaluated. Salads were inoculated with five known histamine-producing bacteria and held at 8°C, 24°C, and 37°C for up to 48 hr. Addition of 30% TSP to tuna salads resulted in higher initial pH and favorable growth conditions for microorganisms and histidine decarboxylase activity. Addition of 15% TSP provided an initial pH for maximal enzyme and histamine production but somewhat slower microbial growth. Tuna salad extended with either 15% or 30% TSP developed toxic levels of histamine (>50 mg/l00 g) when held at either 24° or 37°C for 6 hr. Nonextended tuna salads did not develop toxic levels of histamine even when inoculated with known histamine-producing bacteria and held at 24° or 37°C for 48 hr.     

Comparing the Impact of Environmental Factors During Very High Gravity Brewing Fermentations

The impact of the initial dissolved oxygen, fermentation temperature, wort concentration and yeast pitching rate on the major fermentation process responses were evaluated by full factorial design and statistical analysis by JMP 5.01 (SAS software) software. Fermentation trials were carried out in 2L‐EBC tall tubes using an industrial lager brewing yeast strain. The yeast viability, ethanol production, apparent extract and real degree of fermentation were monitored. The results obtained demonstrate that very high gravity worts at 22°P can be fermented in the same period of time as a 15°P wort, by raising the temperature to 18°C, the oxygen level to about 22 ppm, and increasing the pitching rate to 22 × 10⁶ cell/mL. When diluting to obtain an 11.5°P beer extract, the volumetric brewing capacity increased 91% for the 22°P wort fermentation and 30% using the 15°P wort. After dilution, the fermentation of the 22°P wort resulted in a beer with higher esters levels, primarily the compound ethyl acetate.     

The Selection of a Dried Yeast Strain for Use in the Apparent Attenuation Limit Malt Analysis (AAL) Procedure

This investigation identifies that Mauribrew Lager 497 strain of dried yeast can be used as a standard strain for the determination of malt apparent attenuation limit (AAL). It provides ferment‐ability results for malt quality evaluation laboratories that are comparable to fresh brewery yeast. It was found that the optimal pitching rate in Congress wort (EBC Analytica, 1998, method 4.5.1), was 1 g per 200 mL, pitched at 25°C and fermented for 24 h at 20°C with agitation to complete attenuation. Preliminary trials also indicated that the Mauribrew Lager 497 dry yeast may be useful to brewers for determining the wort batch attenuation characteristics by the limit gravity test. In this case a pitching temperature of 35°C was found to be optimal with all other conditions as above. For the purpose of malt quality evaluation and brewery quality control the advantages of using a standard dry yeast strain include ease and convenience of use, consistency of quality, and uniformity between laboratories when they are located in separate geographic regions.     

Observations on the biology of Oryzaephilus acuminatus Halstead with comparative notes on the common species of Oryzaephilus (Coleoptera; Silvanidae)

The development of Oryzaephilus acuminatus Halstead was investigated over a range of temperatures from 17.5–40°C in combination with humidities from 15–90% r.h. on oatmeal. Development was also studied on groundnuts and copra meal at 30°C, 70% r.h. Eggs failed to hatch at 15°C but eclosion occurred at all other temperatures. The shortes mean egg period was 3 days at 32.5–40°C and the longest 16 days at 17.5°C. Egg mortality was very high outside the range 20–37.5°C but at 25°C, relative humidity had little effect on duration or mortality. Larval periods on oatmeal ranged from 11.2 days at 32.5°C to 110 days at 17.5°C. The highest temperature at which larvae completed development was 37.5°C. Low humidity increased the larval period and at 15% r.h. all larvae died outside the range 25–35°C. The shortest pupal period recorded was 3 days at 32.5°C and the longest mean period was 15.7 days at 20°C. At 17.5°C no pupae survived. Relative humidity had little effect on duration of the pupal period, but over the range 25–35°C mortality increased at lower humidities. Larvae failed to develop on copra meal unless yeast was added and on groundnuts larval mortality was reduced from 59-26% by the addition of yeast. Larvae at 30°C. 70% r.h. passed through 4 instars before pupation, the first being the shortest (3.5 days) and the last the longest (9 days) in duration. At 32.5°C, 70% r.h. oviposition was highest during the first week of laying. The maximum oviposition period lasted 9 weeks and the mean egg production per female was 45 eggs. No eggs were laid at 20°C, 70% r.h.     

Effect of the respiro-fermentative balance during yeast propagation on fermentation and wort attenuation

Breweries use different yeast strains to create beers with different flavours and aromas. Yeast propagation must produce yeast that performs consistently from the first fermentation to harvesting and re-pitching in subsequent fermentations. Breweries propagate yeast in wort leading to low efficiency fermentative growth in Crabtree-positive yeast. There is limited knowledge on the impact on beer production when fermenting with yeast propagated in sugar limited and nutrient supplemented wort. It was hypothesised that propagating yeast in this way would have a positive impact on subsequent fermentation performance. Saccharomyces cerevisiae was propagated at the laboratory scale in standard wort with a high carbon to nitrogen (C:N) ratio (850) or in modified wort supplemented with yeast extract to achieve a low C:N ratio (100) and at varying sugar concentrations. Propagation in low C:N wort with 2°P sugar yielded a 27% decrease in fermentation efficiency and a 46% increase in cell production compared to 2°P high C:N wort. This suggests nitrogen is critical to the respiro-fermentative balance during growth. Yeast propagated in standard wort resulted in slower fermentations and significant under-attenuation compared to yeast grown in the modified wort with low sugar and high nitrogen. The results of this study suggest the nitrogen and sugar content drive the respiro-fermentative balance during yeast propagation. The metabolism of yeast during propagation induces significant downstream impacts on the subsequent fermentation performance and wort attenuation. © 2020 The Institute of Brewing & Distilling     

Changes in Oligosaccharide Content, Enzyme Activities and Dry Matter during Controlled Germination of Cowpeas (Vigna Unguiculata)

Cowpeas were germinated at 25, 30, and 35°C for 12, 24, 48, and 72 hr. Stachyose disappeared after 48 hr germination at 30°C while 85 and 95% reductions occurred at 35°C for 48 and 72 hr. respectively. Total oligosaccharide reduction was significantly greater at 30°C than at 25°C. Protease and amylase activities and rootlet development were minimal after 24 hr germination but increased thereafter. Anerobic incubation was ineffective in furthering reduction of olicosaccharides in seeds germinated at 25 or at 30°C for 12 or 24 hr. Total protein and carbohydrate contents were relatively unaffected.     

Antilisterial Activity of Hops Beta Acids in Broth with or Without Other Antimicrobials

ABSTRACT: Hops beta acids (HBA) are parts of hops flowers used to preserve wort and provide flavor in beer, and are reported as having antimicrobial properties. This study evaluated the antilisterial activity of HBA alone or in combination with other known antimicrobials in a culture broth medium. Listeria monocytogenes (10‐strain mixture) was inoculated (2.6 to 2.8 log CFU/mL) into tryptic soy broth supplemented with 0.6% yeast extract (TSBYE) without (control) or with HBA (0.5 to 5.0 μg/mL), potassium lactate (1.0%), sodium diacetate (0.25%), or acetic acid (0.1%), alone or in combination with HBA (0.5 to 3.0 μg/mL). Survival/growth of the pathogen during storage at 4 °C (35 d), 10 °C (20 d), or 25 °C (2 d) was periodically monitored by spiral plating onto tryptic soy agar plus 0.6% yeast extract. As expected, TSBYE without antimicrobials (control) supported rapid pathogen growth with growth rates of 0.40, 2.88, and 9.58 log CFU/mL/d at 4, 10, and 25 °C, respectively; corresponding Y_end values exceeded 9.0 log CFU/mL at 35, 20, and 2 d storage. HBA used alone (1.0 to 5.0 μg/mL) inhibited growth of L. monocytogenes at all 3 temperatures, with inhibition being more pronounced at higher concentrations and at the lower storage temperature (4 °C). The antilisterial activity of HBA (0.5 to 3.0 μg/mL) was enhanced when combined with sodium diacetate, acetic acid, or potassium lactate, achieving complete inhibition at 4 °C when 3.0 μg/mL HBA were used in combination with each of the above antimicrobials. Overall, HBA exhibited promising antilisterial activity in a broth medium and further studies are needed to investigate its potential antilisterial effects in food products.     

THE EFFECT OF YEAST TREHALOSE CONTENT AT PITCHING ON FERMENTATION PERFORMANCE DURING BREWING FERMENTATIONS

The effect of yeast trehalose content at pitching on the fermentation performance during brewing fermentations was studied using a commercial strain of lager yeast, Saccharomyces cerevisiae (AJL 2155). Pitching yeasts with different trehalose contents were obtained by collecting cells in suspension after 96 h and 144 h of fermentation in EBC tubes in 10.8°P brewers wort at 14°C. The trehalose content of the pitching yeast had no effect on growth, specific gravity and ethanol production during the subsequent fermentation. A high trehalose content of the pitching yeast, however, sustained cell viability during the initial stage of fermentation, increased the carbohydrate utilisation rate and increased the production of isoamyl alcohol and isobutanol. For these aspects of fermentation performance, the trehalose content of the pitching yeast may prove useful in evaluating the vitality of pitching yeasts within the brewery .     

ISOLATION AND CHARACTERISATION OF THE AMYLOTIC SYSTEM OF SCHWANNIOMYCES CASTELLII

The amylolytic system of Schwanniomyces castellii has been isolated and purified by means of ultrafiltration followed by polyacrylamide gel electrophoresis. Both α-amylase and glucoamylase were purified. α-Amylase activity was stable from pH 5·5 to 6·5 and glucoamylase activity was stable at a more acidic range of pH 4·2 to 5·5. The optimal temperature of α-amylase activity was between 30 and 40°C with rapid deactivation at 70°C. The optimal temperature of glucoamylase was 40 to 50°C with rapid decline of activity at 60°C. The K_m of α-amylase with soluble starch as the substrate was 1·15 mg/ml and the K_m of glucoamylase with the same substrate was 10·31 mg/ml. Glucoamylase was able to hydrolyze α-1, 4 and α-1,6 glucosidic linkages, as demonstrated by its ability to hydrolyse maltose and isomaltose respectively, whereas α-amylase could hydrolyse α-1,4 glucosidic linkages only. α-Amylase was shown to be a glycoprotein, whereas no carbohydrates were associated with glucoamylase.     

EFFECT OF ENVIRONMENTAL CONDITIONS ON FLOCCULATION AND IMMOBILISATION OF BREWER'S YEAST DURING PRODUCTION OF ALCOHOL-FREE BEER

A method using immobilised yeasts has been developed and successfully applied for production of alcohol-free beer. The influence of environmental conditions present during alcohol-free beer production on the flocculation and immobilisation of the yeast Saccharomyces cerevisiae var. uvarum was investigated in the present study. In wort, the cells developed flocculation at the end of exponential growth, according to the NewFlo phenotype. In defined medium, the flocculation capacity appeared to be temporary and was lost rapidly during the stationary phase. No increase in cell wall hydrophobicity at the onset of flocculation was observed in either medium. Low growth temperatures increased flocculation capacity approximately four-fold, compared to growth at high temperatures. The optimum temperature for flocculation was at 25°C with cells grown at low or high temperature . A novel method using carboxyfluorescein-stained cells was developed to analyse the initial adhesion of cells to carrier. This method also allowed rapid analysis of the effects of immobilisation to DEAE-cellulose carrier during alcohol-free beer production process. It appeared that a high flocculation capacity stimulated adhesion to the DEAE-carrier .     

Optimum conditions for combined application of Leuconostoc sp. and Saccharomyces sp. to sourdough

Investigation of the optimum conditions for the combined application of Saccharomyces sp. (yeast) and Leuconostoc sp. (lactic acid bacteria, LAB) isolated in a previous study to the development of novel sourdough was carried out by response surface analysis. First, the cell growth conditions were analyzed. LAB showed good proliferation under conditions of 30–35°C, low pH, and high acidity, whereas the growth of yeast was inhibited. The growth of yeast was optimum at 25°C for 24 h. Based on these results, analysis of sourdough was carried out by varying the LAB population, temperature, and time after fixing the number of yeast. It was determined by response surface analysis that the optimal conditions for fermentation are LAB population of 10⁵ CFU/mL, temperature of 25°C, and reaction time of 24 h. From these results, the growth of LAB should be constantly maintained, and an appropriate pH that does not inhibit the growth of yeast due to the presence of generated organic acid is required to allow for the unique properties of sourdough. This study could give useful information for the development of novel sourdough.     

Rehydration of active dried yeast: impact on strength and stiffness of yeast cells measured using microelectromechanical systems

This study investigated the rehydration of active dried yeast and the impact of temperature and wort density on the strength and stiffness of individual cells using a microelectromechanical system. Dried yeast was rehydrated using a variety of methods, including direct pitching into wort (13.6°P) at 12, 22 and 30°C, as well as propagation using YEPD media (4.2°P). Cell viability was found to broadly correlate with measurement of cell strength and stiffness. Both wort density and temperature affected viability and physical characteristics of the cells after 1 h of rehydration. Yeast cells rehydrated at low temperature and high wort density burst at a lower force (0.26 ± 0.02 μN) than cells rehydrated using high temperature and low density media (0.50 ± 0.10 μN). Cells rehydrated at higher temperatures or using low density media showed no significant difference in strength and stiffness when compared with high viability, actively fermenting yeast. Changes in yeast physiology, owing to stress responses, may contribute to the observed differences in mechanical properties. These findings have application in brewery design, as pumping, centrifugation, storage and associated shear impart mechanical stress upon yeast cells. © 2018 The Institute of Brewing & Distilling     

INACTIVATION OF MALT PEPTIDASES DURING MASHING*

Malt contains at least eight different peptidases: three carboxypeptidases (pH optima 4·8, 5·2, 5·7), three aminopeptidases active on aminoacyl-β-naphthylamides (pH optima in hydrolysis of peptides at pH 5·8-6 5), and two (amino)peptidases acting on Leu-Tyr and Ala-Gly at higher pH (pH optima 8·6, 7·8). We have studied the progressive inactivation of these peptidases during mashing with a temperature programme from 45° to 70° C (pH 5·8 → 5·7). All peptidases were stable at 45° C. The five aminopeptidases were inactivated at different rates during a 30-min incubation at 55° C. The carboxypeptidases retained 70–100% of their activities at this temperature, and one of them had 40% residual activity after 60 min at 70° C. Liberation of amino acids continued at a considerable rate during the incubation at 70° C, probably catalysed by the heat-stable carboxypeptidase. Malt carboxypeptidases are therefore more heat-stable in mashing conditions than the aminopeptidases. This property, in combination with their high activities and suitable pH optima, makes them the most important enzymes in the production of free amino acids in mashing.     

THE EFFECTS OF MASHING TEMPERATURE AND MASH THICKNESS ON WORT CARBOHYDRATE COMPOSITION

Temperature and mash thickness are shown to affect both mash performance and enzyme activity. Alpha amylase was found to be considerably more resistant to heat inactivation than was beta amylase. This difference was reflected by changes in wort fermentability that were manifest at temperatures below those which affected levels of extract. Increasing the mashing temperature from 65°C to 80°C had only a slight effect on extract but reduced wort fermentability from over 70% to less than 30%. At 85°C and over, when temperature had a significant effect on alpha amylase, as well as on beta-amylase, extract was lost and starch was present in the wort. Diluting the mash with liquor had a similar effect to that of increasing temperature on both the amylolytic enzymes and on the mash performance. Thin mashes contained more starch and fewer fermentable sugars than did thick mashes at the same temperature. These changes can be related to the stability of the amylolytic enzymes.     

Effects of three temperature regimes on rearing and biological activities of Bracon hebetor (Say) (Hymenoptera: Braconidae)

The body color of Bracon hebetor adults was either black, yellow with black spots, or completely yellow when development from egg to adult took place at 15–18°C, 25 or 35°C, respectively, and the wasps were reared on Ephestia cautella larvae. The longest adult life-span of both sexes occurred when adults reared and emerged at 25°C were held at 15–18°C. Female adults of all colors lived longer than males, especially at 25 and 35°C. The lowest parasitizing efficiency was at 35°C, whereas the highest number of eggs per female occurred at 25°C irrespective of the body color.In general, the parasitoid wasps have somewhat tolerated the three temperature levels and continued to reproduce in spite of their distinct variations in body color. Such variations might be of importance as a mechanism of survival for B. hebetor in date stores during the cold season as well as in the green date palm and cotton fields during warm seasons in Iraq.     

Nutritive Quality of Fermented Sorghum

The relative nutritive value (% RNV) of sorghum fermented at 25°C and at 35°C increased significantly (P < 0.05) over the % RNV of the control. During the consecutive 7-day fermentation at 25°C, time had no effect on the % RNV. The highest % RNV (56.45%) was achieved at the end of 1 day. Fermentation at 35°C was influenced by the time, with the highest % RNV (61.11%) obtained at the end of 7 days. Available lysine and methionine increased substantially (P < 0.01) over the control when sorghum was fermented at 25°C or 35°C for 4 days. Sorghum fermented at 25°C and at 35°C had methionine contents of 25.68 and 26.79 mg/g N, respectively, whereas the control contained only 11.25 mg/g N. Lysine levels were 33.2 and 34.5 mg/g N in sorghum fermented at 25°C and at 35°C, respectively, whereas the control contained 9.1 mg/g N. None of the available B-vitamins studied was altered significantly in the fermented samples.