Free Amino Nitrogen Levels Research Articles

The spoilage of lager by draught beer microbiota

Why was the work done: To determine whether the susceptibility of lager to microbiological spoilage is determined by composition, microbiota or both. To assess beer spoilage by a consortium of yeasts and bacteria from draught beer rather than pure laboratory cultures. How was the work done: Four draught beer styles - cask ale and keg lager, ale, and stout – were sampled twice in five different public houses in four different locations. The beers were forced by static incubation at 30°C for four days. ‘Challenge testing’ with an inoculum of heterogeneous microorganisms from the forced samples was used to assess the spoilage of ten commercial lagers by the increase in turbidity at 660 nm. The same approach was used to evaluate the role of nutrients in beer spoilage by forcing with the addition of yeast extract or vitamins (thiamine and riboflavin). What are the main findings: The ten lagers varied in susceptibility to spoilage ranging three-fold from the least to most spoilable. Average spoilage of the beers was comparable for microorganisms from lager, keg ale and stout but ca. 50% greater with microorganisms from cask ale. The ranking of spoilage of the 10 lagers was similar for microbiota from cask ale, keg ale and stout but less so from lager. Spoilage was influenced by beer composition and was inversely related to beer pH and level of free amino nitrogen. The addition of yeast extract stimulated spoilage of the least spoilable lager but the addition of vitamins B1 and B2 had little or no effect. Spoilage was extensive at 30°C, measurable at 12°C but imperceptible at 2°C. Why is the work important: The oft-quoted statement that beer is ‘robust to microbiological spoilage’ is a fallacy. All ten lagers were spoilt by draught beer microorganisms, but some were more spoilable than others. It is suggested that spoilage may be reduced by lowering beer pH and curbing the availability of nutrients for microbial growth. Whilst (as would be expected) beer storage at 2°C suppresses microbial growth, storage at 12°C (as practiced in UK public house cellars) allows spoilage microorganisms to grow in beer. Although the threat of microbial spoilage in the brewing process is managed by good manufacturing practices, draught beer is vulnerable and requires more focus and commitment to hygienic practices to assure quality.

Copper Binding in Sweet Worts Made from Specialty Malts.

Trace levels of copper can impact the flavor stability of beer. The main source of copper is malt, and the wort copper levels are established during mashing and lautering. This study focuses on sweet worts made from experimental roasted and caramel malts. Potentiometric titrations using ion-selective electrodes combined with electron paramagnetic resonance spectroscopy have been used to investigate Cu(II) binding in worts as well as the impact of Cu(II) ions on the wort oxidative stability. High-temperature treatment during malting decreased Cu(II) binding affinities in the worts, with roasted malt worts having lower affinities than caramel malt worts of similar color and pH. Electron paramagnetic resonance spectra indicated dipeptides as the main Cu(II) chelators. A positive correlation between Cu and free amino nitrogen levels in worts is demonstrated. In dark worts with high rates of radical formation, Cu(II) had pronounced antioxidative effects. In contrast, moderate prooxidative effects were observed when adding Cu(II) to pale worts with inherently low rates of oxidation.

Wort Boil Time and Trub Effects on Fermentability

The purpose of this research was to understand and evaluate the effect of high temperature treatment of wort at varying time periods (30, 45, 60, 90, and 120 min) on wort fermentability. The effect of trub was also analyzed. Small-scale fermentations were conducted using a malt (malted from AC Metcalfe) free of premature yeast flocculation tendencies and a standard SMA yeast strain. The turbidity and apparent extract were measured at specific time intervals. The decline in extract was modeled with the ASBC Yeast-14 logistic equation predicting a sigmoidal curve. Turbidity measurements were modeled with a “tilted Gaussian” fit. Heat-treating the wort (at 100 or 121.1 °C) resulted in a significant decline in ADF (p < 0.05). As denoted by the midpoint of the fermentation, all fermentation runs, with and without trub, at lower wort boil durations fermented faster than longer or higher wort-boiling treatments. The decline in wort fermentability was highest upon treatment at wort temperature and pressure levels of 121.1 °C and 3.0 atm. The amount of trub and the wort color formed after each heat treatment showed a gradual increase with heating duration. Free amino nitrogen levels of wort declined significantly with respect to both increase in wort boiling temperature and time intervals (p < 0.001).

Improving Fermentation Rate during Use of Corn Grits in Beverage Alcohol Production

Corn grits are commonly used adjuncts in the brewing industry in the United States, especially for lager beers. The major challenge of using a high amount of adjuncts in the brewing process is reduced levels of nutrients available to yeast during fermentation, which negatively affects the growth and functioning of yeast, and results in sluggish fermentation. The problem is usually addressed by adding external nutrition. The objective of this work was to assess the suitability of corn components other than brewer’s grits to improve the fermentation rates. Water obtained after soaking of corn germ, a vital source of lipids and soluble proteins, was investigated as a source of nutrient during brewing of 40:60 (w/w) corn grits and malt mixture. Performance of water-soluble nutrients from germ of two corn verities, yellow dent corn and flint corn, was investigated. Germ soak water was added during corn grits slurry formation before mashing. The addition of germ water increased the free amino nitrogen levels by 37% and Zn concentrations by 3.6 times in the wort, which resulted in up to a 28% higher fermentation rate (between 48 to 72 h of fermentation) and shortened the fermentation time from 120 to 96 h. The use of water obtained from the soaking of flint corn germ resulted in a similar shortening of fermentation time. In another approach, nutrient-rich concentrated germ soak water was directly added into the wort, which also resulted in similar improvements in the fermentation rate as those from adding germ soak water during slurry formation. Due to leaching of micronutrients and soluble proteins, the oil concentrations in the germ increased by more than 30%, enhancing its economic value.

Effect of the Use of Thermoplastic Extruded Corn or Sorghum Starches on the Brewing Performance of Lager Beers

The use of pregelatinized brewing adjuncts has the potential to reduce mashing times during the manufacturing of beer. In this investigation, pregelatinized corn and sorghum starches extruded with sodium stearoyl lactylate to reduce the formation of resistant starch and working viscosity were mashed to evaluate the brewing performance of resulting worts. Worts and lager beers produced with the double-mashing procedure were compared with traditionally produced counterparts. Sugar and ethanol levels were determined by HPLC with a refractive index detector, and free amino nitrogen was determined with the ninhydrin reagent test method. No statistically significant differences were found in maltose, maltotriose, or free amino nitrogen levels, either before (worts) or after the programmed yeast fermentation (beers). Glucose was less abundant in the control worts (7.3 versus 10 g/L) and depleted after seven days of fermentation. Wort volume adjusted to 12°P obtained per kilogram of dry matter was statistically similar (5.19–5.60 L/kg of raw material) in all cases. Carbohydrate and ethanol yields obtained by mashing with extruded brewing adjuncts were comparable to those obtained by the traditional method. The use of extruded corn or sorghum starches is a technically feasible alternative to double-mashing procedures in the production of lager beers. This alternative technology has the potential of reducing mashing times without compromising wort extract and beer yield.

Optimization of the sorghum malting process forpitoproduction in Ghana

Pito is an alcoholic beverage obtained through a yeast (Saccharomyces cerevisiae) fermentation of wort extracted from sorghum (Sorghum bicolor L. Moench) malt. The malting conditions of sorghum are thought to influence the quality characteristics of the malt, and subsequently the quality of the pito obtained from it. Studies were carried out on a local sorghum cultivar grown in Ghana – chireh, to optimize the conditions for malting conditions for pito production in Ghana. A 33 full factorial experimental design was replicated with steeping times of 12, 16 and 22 h, germination times of 3, 4 and 5 days, and malt drying temperatures of 30, 40 and 50 °C as factors. Diastatic power, extract yield, attenuation limit and free amino nitrogen were determined. Germination duration significantly affected diastatic power and free amino nitrogen (p < 0.001). Extract yield was also significantly influenced by germination duration (p = 0.001). The germination time, steeping time and drying temperature had no significant effect on the attenuation limit. The optimal conditions for malting this specific cultivar grown in Ghana to obtain critical malt quality indices are 12.0–12.5 h steeping, 5 days of germination at 30 °C and drying at 40 °C. Free amino nitrogen levels in all treatments were higher than the minimum requirement for good yeast nutrition and fermentation. Copyright © 2015 The Institute of Brewing & Distilling

Proteolytic Activities of Kiwifruit Actinidin (Actinidia deliciosa cv. Hayward) on Different Fibrous and Globular Proteins: A Comparative Study of Actinidin with Papain

Actinidin, a member of the papain-like family of cysteine proteases, is abundant in kiwifruit. To date, a few studies have been provided to investigate the proteolytic activity and substrate specificity of actinidin on native proteins. Herein, the proteolytic activity of actinidin was compared to papain on several different fibrous and globular proteins under neutral, acidic and basic conditions. The digested samples were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and densitometry to assess the proteolytic effect. Furthermore, the levels of free amino nitrogen (FAN) of the treated samples were determined using the ninhydrin colorimetric method. The findings showed that actinidin has no or limited proteolytic effect on globular proteins such as immunoglobulins including sheep IgG, rabbit IgG, chicken IgY and fish IgM, bovine serum albumin (BSA), lipid transfer protein (LTP), and whey proteins (α-lactalbumin and β-lactoglobulin) compared to papain. In contrast to globular proteins, actinidin could hydrolyze collagen and fibrinogen perfectly at neutral and mild basic pHs. Moreover, this enzyme could digest pure α-casein and major subunits of micellar casein especially in acidic pHs. Taken together, the data indicated that actinidin has narrow substrate specificity with the highest enzymatic activity for the collagen and fibrinogen substrates. The results describe the actinidin as a mild plant protease useful for many special applications such as cell isolation from different tissues and some food industries as a mixture formula with other relevant proteases.

Corn grist adjunct - application and influence on the brewing process and beer quality

In the brewing industry, barley malt is often partially replaced with adjuncts (unmalted barley, wheat, rice, sorghum and corn in different forms). It is crucial, however, to preserve constant quality in the beer to meet the expectations of consumers. In this work, how the addition of corn grist (10 and 20%) influences the quality of wort and beer was examined. The following parameters were analysed: wort colour, dimethyl sulphide (DMS) and protein content, non-fermentable extract, extract drop during fermentation, alcohol content and the attenuation level of the beer, together with filtration performance. The samples (all-malt, and adjunct at 10 and 20% corn grist) were industrial worts and the beers produced in a commercial brewery (3000 hL fermentation tanks). The application of 10 and 20% corn grist had an effect on the wort colour, making it slightly lighter (11.1 and 10.5°EBC, respectively) than the reference barley malt wort (12.2°EBC). The free amino nitrogen level, DMS and non-fermentable extract were significantly lower in the worts produced with the adjunct; the alcohol content and attenuation levels were higher in the beers produced with adjunct. The use of corn grist, at the level of up to 20% of total load, appears to affect some of the technological aspects of wort and beer production, but it does not significantly influence the final product characteristics. Copyright © 2014 The Institute of Brewing & Distilling

Importance of Endosperm Modification for Malt Wort Fermentability1

J. Inst. Brew. 113(2), 228–238, 2007 Malt wort fermentability is dependent on an adequate supply of the essential nutrients required by yeast. The barley and malt factors affecting this supply of nutrients are not well understood. This study used two doubled haploid populations (Arapiles × Franklin, TR251 × HB345), the latter with a hulless barley parent, to investigate effects of barley and malt quality on fermentability. Populations were grown and malted at different locations resulting in a broad range in malt quality with significant differences in extract, modification and enzyme levels. Fermentability, as indicated by apparent attenuation limit and ethanol levels, also showed significant differences among samples. Modification was the most important factor for good fermentability. There appeared to be several different mechanisms by which modification affected fermentability. High viscosities, slow starch release during mashing, increased glucose supply from better -glucan breakdown and increased free amino nitrogen levels all affected fermentability. Effects of starchdegrading enzymes on fermentability became more significant in better modified malts with -amylase showing stronger effects than diastatic power. The poorer fermentability of hulless barley malt was predominately due to low levels of -amylase, although, free amino nitrogen also appeared to be an important factor.

A Study on the Suitability of Unmalted Triticale as a Brewing Adjunct

Although not essential in brewing, adjuncts are used in most countries for cost-reduction purposes. The objective of this study was to evaluate the brewing properties of unmalted triticale—an amphidiploid between wheat and rye—in comparison with those of commercial brewing adjuncts, such as brewers' rice or maize grits. Furthermore, a suitable mashing regime was designed. Laboratory-scale experiments were carried out at adjunct ratios of 0, 30, and 60%, calculated as fermentable substance. We demonstrate that a modest preliquefaction method (64°C for 10 min at pH 5.9) with triticale and 10% malt followed by an infusion process is the most suitable to convert malt–triticale grists. When using this procedure, the carbohydrate composition of triticale worts did not deviate from that of traditional adjunct worts and the triticale worts displayed soluble-nitrogen contents similar to those of all-malt worts. When using triticale, 10–15% higher adjunct ratios could be employed to obtain similar free amino nitrogen levels of wort compared with those of control worts from commercial adjuncts. Compared with 100% malt, 30% triticale increased the wort viscosity by 10% but did not significantly affect filtration rates. We conclude that triticale is highly suitable to serve as a brewing adjunct.

Enzymes Associated with Fusarium Infection of Barley

Infection of barley with species of Fusarium has been reported to decrease malt yield, wort β-glucan, and viscosity and to increase wort soluble nitrogen, free amino nitrogen, and color. These changes are suggestive of the presence of active fungal enzymes, and the objective of this research was to determine whether proteolytic or cell wall degrading enzymes were associated with Fusarium-infected barley. Barley was inoculated with Fusarium graminearum and F. poae in the greenhouse to reduce contamination with other microorganisms. Control samples were inoculated with distilled water only. Mature harvested grain was screened for the presence of endoproteinase, endoxylanase, and β-glucanase. Inoculated barley was found to contain considerable amounts of proteinase and β-glucanase, whereas only a trace of these activities were detected on the control samples. Malts prepared from these samples showed correspondingly elevated free amino nitrogen levels and reduced levels of wort β-glucans. Inoculated barley also displayed significant amounts of endoxylanase, wih no activity being detected in the controls. The results strongly suggest that fungi associated with the Fusarium head blight infection of barley contribute β-glucanase, xylanase, and proteinase activities to the grain. Further, the enzyme levels appear to be such that they may affect the quality of the malt and its consequent wort.

Ripening of Cheddar Cheese with Added Attenuated Adjunct Cultures of Lactobacilli

We made Milled curd Cheddar cheese with Lactococcus starter and an adjunct culture of Lactobacillus helveticus I or Lactobacillus casei T subjected to different attenuation treatments: freeze shocking (FS), heat shocking (HS), or spray drying (SD). Proteolysis during cheese ripening (0 to 6 mo), measured by urea-PAGE and water-soluble nitrogen, indicated only minor differences between control and most adjunct-treated cheeses. However, there were significant differences in the effect of Lactobacillus adjuncts on the level of free amino nitrogen in cheese. Cheeses made with FS or HS Lb. helveticus adjunct exhibited significantly greatest rates of free amino group formation. Lipolysis as measured by total free fatty acids was consistently highest in adjunct-treated cheeses, and FS Lb. casei-treated cheeses showed the highest rate of free fatty acid formation followed by FS Lb. helveticus treated cheeses. Mean flavor and aroma scores were significantly higher for cheeses made with Lb. helveticus strain. Freeze-shocked Lb. helveticus-treated cheeses obtained the highest flavor and aroma scores. Sensory evaluation indicated that most of the adjunct-treated cheeses promoted better texture and body quality.

Comparative development of soluble nitrogen in the malts of barley and sorghum

Sorghum variety (KSV 13) and barley variety (Chariot), at similar levels of total nitrogen, showed different patterns of protein breakdown. Changes in molar concentrations of the sodium acetate buffer, pH 5.4, from 0.05 to 0.2 M in the assay procedure produced similar patterns of endopeptidase activities. The protein and amino acid content of brewers’ worts are mainly derived from malted cereals. Protein solubilisation in sorghum was significantly lower than in barley when both cereals were malted at their optimal temperatures of 30 and 17°C. Although the lower solubilisation of protein in sorghum malt was correlated with lower levels of free amino nitrogen and endopeptidase, the peptide levels of sorghum malts were higher than those in the malts of barley. It is possible that the endopeptidases of sorghum malt may have different specificities from those of barley malt, or that the storage proteins (prolamins) of sorghum may be structurally different from those of barley. Peptides seemed to be transferred from the endosperm to the embryo faster in barley than in sorghum malts.

Rye and Triticale as Feedstock for Fuel Ethanol Production

ABSTRACTNormal gravity rye and triticale mashes, containing 20–21 g of dissolved solids per 100 mL of mash liquid, were fermented with active dry yeast at 27°C. Fermentations were completed within 48 hr for rye, and within 72 hr for triticale. Supplementation of mashes with urea at a concentration of 8 mM accelerated rates of sugar consumption and fermentation, and reduced fermentation time from 48 to 36 hr for rye, and from 72 to 48 hr for triticale. Rye fermented faster than triticale, due to its higher level of free amino nitrogen. Ethanol yields were 356–363 L/tonne of 14% moisture rye grain, and 362–367 L/tonne of 14% moisture triticale. Fermentation efficiencies, which were 90–91% for triticale, and 91–93% for rye, and ethanol yields were comparable to those obtained from wheat and were not affected significantly by urea supplementation. The replacement of wheats by less expensive crops such as rye and triticale would provide good economic opportunities and alternatives for the fuel alcohol industry.

Amylolytic potentials and wort fermenting components of Nigerian sorghums and barley

The diastatic power of four 'improved' Nigerian sorghum cultivars was produced principally by α-amylolytic activity, unlike that of Nigerian Proctor barley which came principally from β-amylolytic activity. Free amino nitrogen levels and extracts of the sorghums were higher than those of barley when the sorghum was mashed in a modified procedure in which the separated active wort was added to the gelatinized (and cooled) sorghum starch of the mash. The percentage fermentability of the sorghum worts ranged from 76 to 79% for the four cultivars as against 83% for Proctor barley. Maltose in the sorghum worts was about 15 mg/ml compared with 50 mg/ml in the barley wort. Maltotriose in the sorghum worts was 14 to 16 mg/ml while in barley it was 11 mg/ml.

Characterisation of grain yield and nitrogen level in relation to flag leaf senescence of wheat varieties

Three wheat cultivars (Triticum aestivum L.), Splendeur, Hobbit and Maris Huntsman grown in pots were compared. Especially when compared to Splendeur, the flag leaf senesced most rapidly in Maris Huntsman, which presented the most rapid loss of moisture, chlorophyll and nitrogen. The uptake of exogenous nitrogen during the post‐anthesis period was lower in the rapidly than in the slowly senescing variety. A higher concentration of free amino nitrogen in the flag leaf at a given sampling date was associated with a lower percentage decrease of soluble proteins at the following date. Acid proteinase activity in the flag leaf was inversely related to moisture percentage and free amino nitrogen level, but unrelated to the nitrogen loss of the flag leaf. Acid proteinase activity in the flag leaf was directly related to grain nitrogen percentage, but inversely related to grain yield. Grain yield was also directly related to the mean soluble protein content of the flag leaf through senescence.

Effect of digestible energy on nitrogen and energy balance in rainbow trout

The utilization by rainbow trout of high protein diets, incorporating 30% of either gelatinized (diet AG) or natural starch (diet AC) was studied. Compared with a commercial diet, both these diets were more efficiently utilized. Food and protein utilization were higher in trout fed the diet AG than in those fed the diet containing the raw starch. Body composition was similar in both groups except for fat content which was elevated in those fed the natural starch. Relative liver weight and post-prandial plasma glucose levels were higher in those fed the diet containing gelatinized starch than in those fed raw starch. Patterns of post-prandial ammonia and total free amino nitrogen levels in the plasma did not differ between the two groups but the levels were consistently higher in those fed diet AC. A bimodal circadian rhythm was found with a maximum at 6 and 9 h and a second peak at 17 and 20 h after the morning meal in trout fed AC and AG diets, respectively. In fasted trout, only one maximum was observed, corresponding to the second peak in fed animals. Nitrogen excretion, following a meal, was much lower in trout fed the AG diet than in those fed either the AC diet or the control diet. Balance studies confirmed the more efficient utilization of protein and energy by trout fed the more digestible starch than by those in the other groups.

Effect of betel-quid chewing on nitrite levels in saliva

A study was made of the effects of chewing betel quid, alone or with tobacco, on salivary levels of nitrite and other factors of importance in the formation of nitrosamines, and the possible relevance of the findings to the development of oral cancer was assessed. When a betel quid was chewed after ingestion of a lunch that was not rich in nitrates, saliva samples taken 1 hr later showed an increase in nitrite level, except in habitual chewers of tobacco. Subsequent studies confirmed that a substantial rise in salivary nitrite followed betel-quid chewing by volunteers who never chewed tobacco, but no such increase occurred when tobacco and betel quid were chewed together. Basal levels of salivary nitrite were also lower in habitual tobacco chewers than in non-chewers. Free amino-nitrogen levels in the saliva were not affected significantly either by habitual tobacco chewing or by the experimental chewing of betel quid or betel with tobacco. However, salivary pH was increased by both types of test chew, and particularly by the betel quid alone, while thiocyanate levels were significantly higher in habitual tobacco chewers than in non-chewers and were further increased after the chewing of betel quid with tobacco.

Further Studies on the Effect of Dietary Carbohydrate and Fat on Protein Metabolism in Rats

A systematic experiment has been carried out in attempting to elucidate the biochemical mechanism underlying “protein sparing” action of dietary carbohydrate and fat. A more simplified experimental condition was employed in the present investigation in comparison with that in our previous experimental design; the effect of dietary carbohydrate and fat on the body protein metabolism was examined in the absence of any protein in the diet. Feeding of either carbohydrate or fat caused a marked decrease in the level of urinary nitrogen and urea. The ingestion of either carbohydrate or fat by rats resulted in a reduction of the rate of ureogenesis in the rat liver with the concomitant decrease in the activities of hepatic amino acid-catabolizing enzymes, e.g., threonine dehydratase, tryptophan pyrrolase, arginase, glutamic-pyruvic transaminase, glutamic-oxalacetic transaminase and glutamic dehydrogenase (except in fat-fed animals). The feeding of either carbohydrate or fat did not result in changes in the level of free amino nitrogen in blood, indicating that the supply of amino acid may not exert an important role in the ureogenesis in liver. The overall results indicate that the reduction of the activities of hepatic amino acid-catabolizing enzymes elicited by the feeding of either carbohydrate or fat may govern protein metabolism in the rat body.

Biochemical Factors Affecting Protein Accumulation in the Rice Grain

Rice grains (Oryza sativa L.) from three varieties and three pairs of lines with different protein content were collected at 4-day intervals from 4 to 32 days after flowering. The samples were analyzed for protein, free amino nitrogen, ribonucleic acid, protease activity, and ribonuclease activity. In addition, the capacity of the intact grain to incorporate amino acids was determined for the three pairs of lines. The maximal level of free amino nitrogen and the capacity of the developing grain to incorporate amino acids were consistently found to be higher in the samples with the high protein content in the mature grain. The ribonucleic acid content of the grain tended to be higher in the high protein samples.