Control of the Growth of Coliforms and Moulds in Sorghum Malting by Bacterial and Yeast Cultures

Traditional outdoor floor malted sorghum can be contaminated with high levels of coliform bacteria and moulds that can potentially produce mycotoxins. The effect of steeping with the addition of bacterial and yeast starter cultures on microbial contamination, toxicity and diastatic power (DP) of sorghum malt was investigated. Lactobacillus plantarum, Pedicococcus pentosaceus and Saccharomyces species were selected on the basis of inhibition of fungal species using the disc diffusion assay. Steeping the sorghum with the addition of these cultures at 10⁷‐10⁸ cfu/mL reduced the level of moulds by one to two log cycles, with the Saccharomyces culture appearing to be the more effective and L. plantarum the least effective. Coliforms, where present in significant numbers, were reduced to levels of >10¹‐10² by steeping with the cultures, with the P. pentosaceus culture appearing to be the most effective and Saccharomyces the least effective. There were no detectable amounts of mycotoxins and no significant cytotoxicity in the malts in either the controls or the culture‐steeped malts. Steeping with the cultures did not affect malt DP. The use of such P. pentosaceus and Saccharomyces sp. cultures could be an alternative to chemical treatment for the control of microbial contamination in sorghum malt.     

Effect of steeping temperature on the quality of malt and Pito (an indigenous Ghanaian drink)

Pito is a traditional fermented beverage produced from malted sorghum or millet grains. Steeping is usually performed at 30°C. Limited information exists on the effect of temperature on the characteristics of the malted grains and the Pito. The aim of this work was to study the effect of varying the steeping temperature (30, 35 or 40°C) on the quality of malt and of the Pito brewed from Kadaga sorghum and to specifically determine the diastatic power, extract yield and attenuation limit of the malt. Total soluble solids, pH and alcohol content, as well as the sensory evaluation of the Pito brewed at both 40 and 30°C were assessed. Results from analysis showed that the 40°C malts had the highest diastatic power (88.1 SDU/g), extract yield (96.75% d.m.) and attenuation limit (78.95%). Pito produced from malt steeped at 40°C yielded a significantly higher alcohol content of 3.54 g/100 g, a total soluble solids of 4.34 and a pH of 3.57 and this Pito was preferred over the traditionally prepared Pito at the steeping temperature of 30°C. Therefore steeping sorghum at 40°C yields a quality malt and a quality Pito. This study should aid in the adoption of sorghum for brewing purposes. Copyright © 2015 The Institute of Brewing & Distilling     

The Microbial Contamination,Toxicity and Quality of Turned and Unturned Outdoor Floor Malted Sorghum

Turned and unturned outdoor floor malted sorghum were studied for their total microbial contamination, nature and extent of contamination by moulds, cytotoxicity (IC₅₀) and quality in terms of diastatic power (DP). The presence of aflatoxins, fumonisins, deoxynivalenol and zearalenone were also investigated. Total microbial counts were high (10⁷–10⁸ cfu/g) in both turned and unturned samples. All samples showed contamination by different moulds, with the dominant being Mucor species, Rhizopus oryzae, Fusarium moniliforme and Phoma sorghina as well as Aspergillus flavus and Alternaria alternata. The latter four are known for producing mycotoxins. Malt samples had very low cytotoxicity (IC₅₀ from 62.5 to >1000 kg/kg), though all contained fumonisins, deoxynivalenol and zearalenone at levels of <0.25–2 μg/g, 15–20 and 10–15 μg/kg, respectively. Malt DP was generally lower in turned samples compared to unturned samples probably because the heat conserved in the latter ensured better germination conditions. Overall, turning during germination did not affect the microbial load, mould population and levels of deoxynivalenol and zearalenone in sorghum malt but decreased sorghum malt DP. Thus, alternative methods of controlling the sorghum malt microbial load should be sought.     

Convertibility of IoB,EBC and SABS Methods for Sorghum DP Measurements Using Correlation Coefficients

The convertibility of the methods for Sorghum malt DP measurement using the correlation coefficient (r) was studied using malts of the white sorghum variety (farafara) from malting outlets, which had been steeped for one day and germinated for four days at 30°C. A correlation of 0.97 (p < 0.00001) was obtained between the IoB (Institute of Brewing) and EBC (European Brewing Convention) methods while the correlation dropped to 0.95 (p < 0.001) between the SABS (South African Bureau of Standards) and IoB and 0.94 (p < 0.34) between SABS and EBC methods. The study was extended to include eleven pure varieties (KSV, ICSV and ICSH entries), which had been steeped for one and a half days and germinated for six days at 25°C. A correlation of 0.968 (p < 0.000004) was obtained between the IoB and EBC methods of DP assay. The correlation dropped to 0.90 (p < 0.0002) between SABS and IoB and 0.91 (p < 0.007) between SABS and EBC assay methods. The IoB and EBC methods are considered suitable for sorghum DP measurements as a way of having the DP in one unit when sorghum and barley malts are used in one mash.     

EFFECT OF AMMONIA ON THE MALTING LOSSES OF SOME IMPROVED NIGERIAN SORGHUM VARIETIES

The effect of ammonia treatment as steep liquor on the malting losses and other malting properties of 2 Nigerian sorghum varieties was investigated. Steeping the kernel in 0.1 N ammonia solution for various steeping periods (0 to 18 h) reduced malting losses by suppressing the growth of acrospires. However, mouldiness was not prevented, enzyme development, cold and hot water extracts of the malt were significantly reduced by the application of this chemical. Kernels steeped in 0.3N ammonia solution did not germinate. Malting with ammonia solution may be useful for minimizing malting loss at the expense of optimum development of hydrolytic enzymes, provided the malt produced will only provide malty flavour in beer and external enzymes will be added during processing.     

EFFECT OF ALKALINE STEEPING ON WATER UPTAKE AND MALT QUALITY IN SORGHUM

Condensed tannin-free and high-tannin sorghum grain were steeped in dilute alkali and the effects on water uptake during steeping and final malt quality were determined. With the condensed tannin-free sorghum, steeping in dilute alkali led to increased water uptake during steeping and an improvement in malt quality in terms of diastatic power and free amino nitrogen. These effects are presumed to be due to the alkali opening up the pericarp cell wall structure of the grain, allowing more rapid water uptake. Best results were obtained by application of alkali early in steeping, presumably because the grain is less susceptible to alkali toxicity than later in steeping. Steeping high-tannin sorghum in dilute alkali did not improve malt quality. This appeared to be because water uptake was not increased to the same extent as with condensed tannin-free sorghum, as the alkali reacted with the tannins .     

Sorghum β‐Amylase Production: Relationship With Grain Cultivar,Steep Regime,Steep Liquor Composition and Kilning Temperature

Steep regime, nature of alkaline liquor, and kilning conditions were studied for their effects on sorghum malt β‐amylase development in four Nigerian sorghum cultivars. Malt β‐amylase activity was markedly (p < .001) influenced by all the four factors as well as their various interactions. Overall, malts from KSV 8 variety were the most β‐amylolytic followed in sequence by those from Local Red (LR), SK 5912, and Local white (LW) respectively. The presence or absence of air rests in steep regimes was a significant (p < .001) determinant of sorghum β‐amylase response to final warm steeping, steep liquor and kilning condition. The nature of the alkaline steep liquor was also a major determinant of the pattern of malt β‐amylase response to the kilning condition. Steeping in Ca(OH)₂ enhanced malt β‐amylase activity at the higher temperature of kilning, while KOH produced the opposite effect. Ca(OH)₂ enhancement of β‐amylase development, at a kilning temperature of 50°C, was variety‐dependent suggesting that different sorghum cultivars may employ different biosynthesis models for β‐amylase synthesis. The regime‐dependence of β‐amylase response to kiln temperature suggests that this was an important modulator of sorghum germination physiology.     

Effect of malting regimen on diastatic power,cold and hot water extracts of malts from sorghum

In this study, sorghum grains were malted using different malting regimens and the malt qualities were analysed for cold water extract (CWE), hot water extract (HWE) and diastatic power (DP). Results showed that malting regimen produced sorghum malts with peak CWE, HWE and DP within the pre-determined limits of malting regimen. From this, predictive models of sorghum malt quality were developed and tested. Whilst steeping duration interacts significantly with the germination period to cause variations in CWE and HWE, only the germination period significantly influenced the DP of sorghum malts. However, the kilning temperature showed no significant impact on the parameters studied. Besides CWE, HWE and DP correlating positively with each other, the developed predictive models were significant (P < 0.05) and satisfy the quality of fit (R² > 0.70) of the proposed models. The result demonstrated that wort for different purposes can be obtained by varying the malting operational conditions in the predictive model, thus saving time, resources, preliminary studies and research designs. Besides the promotion of a cheaper local alternative material for industrial wort production and brewing purpose, this research provides valuable insight on the brilliant prospect of variable malting regimen in predicting and adjusting the quality characteristics of sorghum malt and wort. Future studies are required to develop models for wort produced from peak CWE, HWE and DP, for predicting wort quality characteristics.     

INFLUENCE OF CULTIVAR AND GERMINATION CONDITIONS ON PROTEOLYTIC ACTIVITIES IN SORGHUM MALT

The effects of cultivar and germination conditions on proteinase and carboxypeptidase activities in sorghum malt were investigated using enzyme assays based on kafirin, the sorghum prolamin, as substrate. When different sorghum cultivars grown under identical environmental conditions were malted under identical conditions, the proteinase and carboxypeptidase activities of the various malts both differed significantly. This indicates that the activities of these enzymes are cultivar related. Steeping sorghum grain resulted in no significant change in proteinase or carboxypeptidase activity. Proteinase activity increased only moderately with germination time, up to a maximum at 4 days. Neither germination temperature (24–32°C) nor moisture affected proteinase activity. In contrast, there was a large increase in carboxypeptidase activity with germination time up to 4 days and both germination temperature and moisture affected carboxypeptidase activity.     

α-GLUCOSIDASE ACTIVITY OF SORGHUM AND BARLEY MALTS

Sorghum malt α-glucosidase activity was highest at pH 3.75 while that of barley malt was highest at pH 4.6. At pH 5.4 employed in mashing sorghum malt α-glucosidase was more active than the corresponding enzyme of barley malt. α-Glucosidase was partly extracted in water but was readily extracted when L-cysteine was included in the extraction buffer, pH 8. Sorghum malt made at 30°C had higher α-glucosidase activities than the corresponding malts made at 20°C and 25°C. Nevertheless, the sorghum malts made at 20°C and 25°C produced worts which contained more glucose than worts of malt made at 30°C. Although barley malts contained more α-glucosidase activity than sorghum malts, the worts of barley had the lowest levels of glucose. The limitation to maltose production in sorghum worts, produced at 65°C, is due to inadequate gelatinization of starch and not to limitation to β-amylase and α-amylase activities. Gelatinization of the starch granules of sorghum malt in the decantation mashing procedure resulted in the production of sorghum worts which contained high levels of maltose, especially when sorghum malt was produced at 30°C. Although the β-amylase and α-amylase levels of barley malt was significantly higher than those of sorghum malted optimally at 30°C, sorghum worts contained higher levels of glucose and equivalent levels of maltose to those of barley malt. It would appear that the individual activities of α-glucosidase, α-amylase and β-amylase of sorghum malts or barley malts do not correlate with the sugar profile of the corresponding worts. In consequence, specifications for enzymes such as α-amylase and β-amylase in malt is best set at a range of values rather than as single values.     

Current Developments in Malting and Brewing Trials with Sorghum in Nigeria: A Review

Initially, large‐scale lager beer brewing with sorghum malts proved highly intractable due to a number of biochemical problems including: high malting losses estimated at 10–30% as against 8–10% for barley; high gelatinisation temperatures which limited starch solubilisation/ hydrolysis by the amylolytic enzymes during mashing; low extract yield/low diastatic power (DP) due to inadequate hydrolytic enzyme activities especially β‐amylase; low free α‐amino nitrogen (FAN) due to inadequate proteolysis limiting yeast growth during fermentation; high wort viscosities/beer filtration problems due to low endo‐β‐1,3; 1–4‐glucanase activities on the endosperm cell walls causing the release of some β‐glucans. Strident research efforts using improved Nigerian sorghum malt varieties (SK5912, KSV8 and ICSV400) have reported some encouraging results. The knowledge of the biochemical integrity of the endo‐β‐glucanases of the sorghum malt is helping to elucidate their mode of activity in the depolymerisation of the β‐glucans. This is bound to ensure process efficiency in sorghum beer brewing, reduce beer production costs and ultimately, produce a Pilsner‐type of lager beer with 100% sorghum malt.     

Effect of Malting Conditions on Pearl Millet Malt Quality

The effect of malting conditions on pearl millet malt quality in two varieties, SDMV 89004 and SDMV 91018, was investigated. Grain was steeped and germinated at four temperatures, 20°, 25°, 30° and 35°C, over 5 days. Generally, malt quality parameters (percentage of roots and shoots, diastatic power (DP), α‐ and β‐amylase activity, free α‐amino nitrogen (FAN), and malting loss) were significantly affected (P < 0.001) by germination temperature and time, as well as by variety. Malt FAN and malting loss were not affected by variety. A germination temperature of 25–30°C and germination time of 3–5 days were optimal. These conditions resulted in high DP, α‐ and β‐amylase activity, good FAN and moderate malting loss. These malting conditions and the subsequent malt quality of pearl millet are similar to those reported for sorghum. Pearl millet malt can therefore be used for the production of sorghum type beers.     

FACTORS INFLUENCING BETA-AMYLASE ACTIVITY IN SORGHUM MALT

An investigation into factors influencing beta-amylase activity in sorghum malt confirmed that ungerminated sorghum grain exhibited essentially no beta-amylase activity. Malted sorghum had beta-amylase activity less than 25% of the level in barley malt. Neither reducing agents nor papain affected beta-amylase activity in sorghum, indicating that the enzyme is not in a bound form, unlike in barley. Isoelectric focusing indicated that sorghum beta-amylase comprises just one major and one minor isozyme of pl approximately 4.4–4.5, unlike the many isozymes all of higher pl in barley. However, like barley, sorghum beta-amylase was more temperature-labile than its alpha-amylase. Beta-amylase activity in sorghum malt was increased by germination time, high germination moisture and over the germination temperature range investigated (24–32°C), 24°C gave the highest activity. The beta-amylase activity of sorghum malts was significantly correlated with malt diastatic power, despite the fact that alpha-amylase and not beta-amylase is the predominant diastatic enzyme in sorghum malt.     

Relationship between some Sorghum Malt Quality Characteristics and Nature of Alkaline Steep Liquor

Two Nigerian sorghum cultivars, SK5912 and ICSV400 were used to evaluate the relationships between nature of alkaline steep liquor and some malt quality characteristics over a five day germination period. Patterns of development of the malt quality indices examined were significantly influenced by the nature of alkaline steep liquor, cultivar and duration of germination, plus all their possible interactions at p<0.001. Maximum diastatic activity development was attained in ICSV400 and SK5912 when grains were steeped in NaOH and Ca(OH)₂ respectively. Ca(OH)₂ treatment seemed to cause significant enhancement of diastatic enzyme development in SK5912 compared to other treatments presumably due to Ca²⁺ stabilisation of α-amylase. Mean malt cold water extract (CWE) and hot water extract (HWE) were generally similar within both cultivars for the treatments except for ICSV400 where CWE appeared to be remarkably enhanced by NaOH treatment. Data on cold water soluble carbohydrates (CWS-Carbohydrates), CWS — Carbohydrate/CWE and CWS — Carbohydrate/HWE ratios showed that solubilised carbohydrate matter produced during malting constituted significantly higher proportion of total HWE in ICSV400 in contrast to SK5912.     

Lipase Activities During Malting and Fermentation of Sorghum for Burukutu Production

Local red and white, and SK₅₉₁₂ varieties of sorghum grains were malted, and assayed for amylase, diastatic and lipase activities. The 5‐day malts from the red and white varieties were fermented for 48 h to produce burukutu, during which, lipase activities were monitored. Malt values peaked on day 5, and the red malts had the highest diastatic activities while the white variety had the lowest. Lipase activity in the malts peaked on day 4 with the red having the highest activity. The pH of the fermenting gruels decreased from 5.33 and 5.35 and levelled off at 3.88 and 3.85 for the red and white malts respectively. During fermentation, lipase activity peaks were detected at 0 h, 21 h and 45 h for the red malt with the highest peak at 45 h. The peak fermentation times for lipase activity in the white malt was at 0 h, 21 h and 48 h with the highest peak at 48 h. Lipase activity within the first 39 h was higher in the white gruel. Sorghum malt lipase from the red and white varieties may consist of three isoforms, two of which may have activity optima in the acidic pH range.     

STUDIES ON COMPARATIVE MALTING CHARACTERISTICS OF SOME TROPICAL CEREALS AND MILLETS

Malts prepared from some of the tropical cereals and millets were evaluated for their suitability in weaning food formulations. Pearl millet and finger millet malts exhibited high α-amylase activity within 2–3 days of germination, while maize, sorghum, wheat and triticale malts showed high enzyme activity after 4–5 days of germination. Malting drastically lowered the paste viscosity of cereal flours especially millet. Finger millet malt had desirable flavour and taste besides high amylase activity. Wheat and triticale malts also had acceptable flavour. Rice malt was bitter and pearl millet malt developed rancid odour and bitterness within a week after preparation.     

Malt characteristics of sorghum vulgare varieties from ghana

Two local varieties, a white type and a red type, of Sorghum vulgare cultivated in Ghana were malted, using a micro-malting method, and their malt characteristics studied and compared to that of a commercial barley malt. The optimal germination time, at 30°C, to produce a good malt of high diastatic power and extract from local varieties of these varieties was 4-5 days. The local varieties were also found to have high diastatic activities of between 55 and 68% of the commercial barley malt. Hot-water extracts of the well malted sorghum varieties were also found to have higher and sustainable amounts of free amino nitrogen than the commercial malt. The hot-water extracts of sorghum malts were lower than the commercial barley malt, yielding about 66-77% of the barley malt, but contained a higher glucose to malt ratio. In terms of varietal superiority, the white sorghum yielded higher malt extracts than the red type.     

THE EFFECTS OF PROLONGED PERIODS OF TURNING IN SMALL-SCALE DRUM MALTING TRIALS

Steeping grain in continuously turning drums results in a subsequent rapid onset of germination and, in malt germinated in stationary drums, the production of malt with high extracts, compared to controls steeped without agitation, but germinated in a similar fashion. Turning the grain continuously during germination prevents the growth of roots and the attainment of a good hot water extract. If the barley is treated with gibberellic acid, and is turned continuously throughout the germination period, rootlet production is prevented but analytically excellent malt is produced in about 96% yield. Similar results may be obtained if the drums turn for as little as 40% of the total post-steeping germination time, provided turning occurs at intervals throughout this period. The results are in general agreement with the claims of an American patent, and suggest that in full-scale malting, losses may be reduced by deliberately bruising the grain with turners.     

Viscoelastic properties and pasting characteristics of fermented maize: influence of the addition of malted cereals

Investigations were conducted on the viscoelastic properties and pasting characteristics of fermented maize with malted cereals and their suitability for infant feeding. A 3 × 3 × 2 factorial experimental design with malting time, cereal malt concentration and cereal type was used. Maize, millet, and sorghum malts were added to fermented maize to reducing its bulk density. Samples were analysed for their viscoelastic properties and pasting characteristics using Brabender Viscoamylograph. Sorghum malt in comparison to millet and maize malts was not effective in terms of lowering the hot and cold paste viscosities of the fermented maize. Maize and millet malts liquefied the dough considerably during both the hot and cold paste viscosities. The effect of 4‐day malted millet was most pronounced whilst the highest activity of maize malt was observed with the 3‐day malted flours. The addition of maize and millet malts to fermented maize were most effective in lowering the viscoelastic properties of the resulting porridges.     

Kaffircorn malting and brewing studies XIV.—Mashing with kaficorn malt: Factors affecting sugar production

The effects of temperature, time, pH, diastatic power, malt/grain ratio and nature of the substrate on the production of sugar by sorghum malts have been investigated. The optimum temperature for sugar production is 60°. Although sugar production decreases with increasing acidity of the mash, yields are still appreciable. sorghum malt being more active than barley malt under such conditions. With malts of diastatic powers up to 25 K.D.U./g the substrate is in excess; with diastatic powers of 45 K.D.U./g or greater, the amylases are in excess. The use of grain adjuncts permits the control of the enzyme/substrate ratio. The optimum malt/grain ratio lies between 1:3 and 1:2 at pH 6·3 and is a reflection of the ratio of ungelatinised to gelatinised starch and the affinity of the amylases for these two forms of the substrate.