EFFECT OF GERMINATION TIME,TEMPERATURE AND MOISTURE ON MALTING OF SORGHUM

The effect of germination conditions on sorghum malt quality and malting loss was studied by germinating sorghum for different periods of time up to 6 days over a range of temperatures (24 to approximately 36°C) and moisture conditions. The moisture conditions varied from that sufficient to maintain green malt weight to that where surface moisture remained on the malt throughout germination. Germination time, temperature, moisture and the three possible pairwise interactions all had a highly significant effect on malt diastatic power, free α-amino nitrogen and extract. Malting loss was highly significantly affected by germination time and moisture and their pair-wise interaction. However, over the range examined, germination temperature had no significant effect on malting loss. In general diastatic power, free α-amino nitrogen, extract, and malting loss all increased with germination time. Germination temperatures of 24° and 28°C were both equally good for the development of diastatic power, free α-amino nitrogen and extract but higher temperatures were progressively worse. Distatic power, free α-amino nitrogen, extract and malting loss were, in general, all increased by high moisture during germination. However, high moisture and a negative effect on diastatic power towards the end of the germination period.     

A RAPID GUIDE TO ENDOSPERM MALTING POTENTIAL OF BARLEYS USING A SEDIMENTATION PROCEDURE

A rapid (10 minute) procedure is described which appears to differentiate barleys having good potential for malting by traditional methods from those less easy to malt. During controlled milling, barleys of good malting potential release more starch granules and, as a result, a suspension of the milled grain sediments more slowly in 70% ethanol. This probably reflects differences in the nature of the endosperm cell wall and the starch-protein matrix.     

THE USE OF RAPID SCREENING TESTS TO COMPARE CHANGES DURING MALTING IN SORGHUM

Eight sorghum cultivars were malted and samples were taken after steeping and after each of 5 days germination. In genotypes with low levels of grain nitrogen, up to 35% of the nitrogen solubilisation during the malting process occurred in the steeping phase. After 5 days germination, extracts ranged from very low to moderate levels and correlated highly with diastase and half-grain mash results. In addition, genotypes producing higher extracts showed greater reductions in milling energy between 2 and 5 days germination. During malting, there was considerable genotype X day interaction for several quality characters, suggesting variation in rates of development as well as final quantities.     

HEAT SENSITIVITY,OPTIMUM pH AND CHANGES IN ACTIVITY OF SORGHUM PEROXIDASE DURING MALTING AND MASHING

Peroxidase activity was demonstrated in dry and germinating sorghum seeds. The specific activity increased about 14-fold during malting for a 96-hour period. On the average about 41% of peroxidase activity was located in the endosperm, and the remaining 56% in the acrospire and rootlet of sorghum malt. The crude enzyme extract retained 77%, 17.5% and 7.6% of activity after heating at 60°, 70° and 80°C, respectively. More than 50% of the peroxidase activity in the finished malt survived mashing at 65°C. Optimum activity was recorded at pH 5.5 which falls within the observed pH range of sorghum worts. The level of residual peroxidase activity in the wort differed with sorghum species.     

EFFECTS OF AIR REST PERIODS ON MALTING SORGHUM RESPONSE TO FINAL WARM WATER STEEP

The effects off various lengths of air rests on response off malting sorghum main root length, malting loss, diastatic activity, α- and β-amyloytic activity and extract to final warm water steep at 40°C was investigated. Grains were steeped in distilled water for a total of 48 h at 30°C with a 6 h final warm water steep under four different cycles incorporating 1, 2, 3 or 4 h air rest periods. All malt quality properties evaluated were significantly affected by the length of air rest, the cultivar and their pair-wise interactions. Main rootlet length and malting loss reduced progressively as the length of air rest increased. Reducing power, α- and β-amylolytic activity and extract generally increased as the length of air rest was increased for both sorghum cultivars ICSV 400 and KSV 8 examined. The steep cycle incorporating 3 h length of air rest was found by experiment to give the optimum levels of malt quality indices analysed while at the same time causing considerable reduction in average main rootlet length and total malting loss for both grain cultivars.     

EFFECTS OF RAISED TEMPERATURES DURING STEEPING AND GERMINATION ON PROTEOLYSIS DURING MALTING

Raising the temperature from 16°C to 20°C or 25°C for prolonged periods during steeping or germination reduces HWE and TSN and slows down wort separation in laboratory mashes. When the higher temperatures are applied only during the last steep or the first two days of germination the initial rate of modification is accelerated, as is the development of α-amylase and endopeptidase. After four or five days germination the levels of enzyme activity are substantially lower than in the control malt. However, some barleys give malts with acceptable standard analyses after 4 rather than 5 days of germination.     

A NEW MALTING INDEX: PREDICTION OF MALTING QUALITY BY ENDOSPERM HYDRATION

The hydration of barley samples, representing all nine NIAB malting grades, has been measured by determining the levels of a tracer ion using x-ray analysis with a scanning electron microscope. There was a linear relationship between hydration of the ventral endosperm and NIAB malting grade. This relationship was not affected by the total nitrogen level of the barley and can be used as a novel malting index to successfully predict the malting quality of barley on sample sizes too small for micromalting.     

MALTING QUALITY OF SRI LANKAN VARIETIES OF SORGHUM

The malting quality of Sri Lankan sorghum was studied using seventeen varieties. These varieties represented four colour categories (brown, yellow, pink and white) of sorghum found in Sri Lanka. The main criteria used for the assessment of malting quality in this study were the malting loss, diastatic power, liquefying power and the quantity of extract. Malting losses of these varieties were somewhat higher than those encountered in malting barley. However, they appeared to depend partly on the malting conditions. The diastatic powers and liquefying powers observed in this study were inferior to those observed with barley malt. However, with some varieties they appeared to be adequate for the purpose of mashing, as indicated by the high extract values obtained, which were comparable with those of some barley malts. Extract values of the four colour categories varied considerably and the best values were observed with the yellow and pink varieties and some varieties of white. Brown varieties in spite of their comparatively high diastatic powers and liquefying powers gave very little or no extract on mashing.     

CHANGES IN ACTIVITY OF SORGHUM LIPASE DURING MALTING AND MASHING

Lipase activity was monitored during malting and mashing of sorghum grains. All three sorghum varieties contained detectable lipase activity in the ungerminated form. Lipase activity changed only slightly during steeping for 24 hours but increased several fold in the course of germination. Between 24% and 60% of the lipase activity of the green malt was retained after kilning at 48°C but no activity was detected in the wort after mashing at 65°C. About 68% of the lipase activity of 72 hours old malt was detected in the plumule, while 29% and 3% were detected in the endosperm and radicle, respectively. Optimum activity was observed at pH 7.0.     

THE INFLUENCE OF ENDOSPERM STRUCTURE ON THE BEHAVIOUR OF BARLEYS IN THE SEDIMENTATION TEST

Detailed microscopic studies of the relationships between endosperm structures and sedimentation scores show that the sub-cellular organization of the endosperm of barley grains plays a greater part in influencing sedimentation scores than do levels of nitrogen and β-glucans. Differences in sedimentation scores of barleys are directly related to the number of large starch granules which are released from the protein matrix during the milling stage of the sedimentation test. The sedimentation scores of some barleys can be affected by the presence of grains which are visually mealy. The mealy grains selected from a particular sample of barley give higher sedimentation scores than the remaining vitreous grains. However, a high degree of mealiness would be required to cause a significant shift in the usual sedimentation score of a barley sample. The mealy and vitreous grains of the fast-malting barley, Proctor, give higher sedimentation scores than do corresponding grains from Julia, which malts more slowly. The overall structural arrangements of the endosperm cells of Proctor and Julia are similar and can therefore have little effect on the sedimentation scores of these barleys. The central and dorsal cells of the endosperm are smaller and more elongated than are the more laterally placed cheek cells. The latter types of cell thus have a higher ratio of starch to cell wall.     

EFFECTS OF AIR REST PERIOD ON THE MOBILISATION OF SORGHUM RESERVE PROTEINS

The influence of air rest treatment period on the mobilisation of storage proteins of two improved Nigerian sorghum cultivars ICSV 400 and KSV 8 was evaluated. Grains were steeped in distilled water for a total period of 48 h at 30°C with a 6 h final warm steep at 40°C under four different cycles incorporating 1, 2, 3 or 4 h air rest period respectively. Cold water soluble protein, cold water soluble protein modification index, total cold water solubles, total free alpha amino acid nitrogen, carboxy-peptidase and proteinase activities were determined after 6 days malting. All these protein modification indices were highly significantly affected by length of air rest and cultivar, plus their pair-wise interactions. The levels of all these variables were also higher in sorghum cultivar ICSV 400 compared to KSV 8 except for proteinase activity. Significant differences in grain storage protein complexity and structure coupled with probable differences in key proteinase iso-forms are advanced as possible explanation for the higher proteinase activity recorded in KSV 8 malts.     

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.     

羊骨汤不同酶解方式对其成分的影响

将羊骨以1：1的骨水比于0．05MPa高压2．0h后，再以不同的酶、酶浓度和酶解时间酶解骨汤，分析水解度（DH）、肽链长度（PCL）及游离钙含量的变化，并各筛选最优方案。结果表明：①游离钙含量最高：中性蛋白酶，酶浓度1500U／L，酶解6h；②DH最高：胰蛋白酶，酶浓度1：100，酶解6h；③PCL值最低：胰蛋白酶，酶浓度1：125，酶解6h；PCL值最高：碱性蛋白酶，酶浓度1500U／L，酶解8h。     

ENHANCEMENT OF AMYLOLYTIC POTENTIAL OF SORGHUM MALTS BY ALKALINE STEEP TREATMENT

The effect of alkaline steep liquor on sorghum maltability was investigated using three improved Nigeria sorghum cultivara. Germination was for four days at 30°C after steeping under four different regimes. Grain germinability, root length and malting loss were significantly (P < 0.001) repressed by steeping in alkaline liquor for all the cultivars. However, the extent of this repression seemed in all cases significantly dependent on cultivar and steep regime plus their possible interactions. Similarly, the development of diastatic enzymes activities appeared to be highly significantly dependent on steep liquor, steep regime, cultivar, plus their possible pairwise and three way interactions. For ICSV400, highest diastatic power and α-amylase development were attained on steeping grains in alkaline liquor under a continuous steep regime incorporating final warm steep treatment. Conversely, exposure of KSV8 and SK5912 to a regime incorporating air-resting and final warm steep significantly enhanced diastatic power and α-amylase development. β-Amylase activity was in all cases enhanced by alkaline steeping. In fact, β-Amylolytic activity constituted over 70% of total diastatic activity in most alkaline steeped ICSV400 malts. However, SK5912 exhibited relatively low hot water extract in spite of the improved amylolytic activity.     

EFFECT OF MALTING TEMPERATURE AND TIME ON ENZYME DEVELOPMENT AND SORGHUM WORT PROPERTIES

The effect of malting temperature and time on enzyme development and wort properties of an improved Nigerian sorghum cultivar (Ex-Kwara) were investigated. Malting was carried out at two temperature regimes, 20°C and 25°C for eight days. Parameters evaluated included α- and β;-amylase development, hot water extract (HWE), soluble extract, fermentability, fermentable extract, viscosity, filtration rate, reducing sugars, α;-amino nitrogen and total soluble nitrogen (TSN). For virtually all the parameters studied, germination at 25°C produced higher values on the 4th day after which temperature appeared to have little influence. α;-Amylase development continued throughout the germination period while β;-amylase peaked on the 6th day. Optimal values of total soluble nitrogen (TSN) were recorded at both 25°C and 20°C at the 6th and 8th day of germination respectively .     

A REASSESSMENT OF THE PATTERN OF ENDOSPERM HYDROLYSIS (MODIFICATION) IN GERMINATED BARLEY

Microscopic and enzymic studies of germinated barley have confirmed that excised barley embryos can produce α-amylase because the peripheral areas of the scutellar tissue contain aleurone cells. In contrast, the aleurone-free tissue of the scutellum is incapable of producing significant quantities of α-amylase. The potential of excised embryos to develop α-amylase is not correlated with the in vivo elongation of the scutellar epithelial cells in the grain because these cells do not elongate in excised embryos. Detailed anatomical studies revealed that the highly insoluble Intermediate layer of cell wall material, which is located between the embryo and the starchy endosperm, is broken-down asymmetrically, thus confirming that enzymic modification of the endosperm is under aleurone rather than scutellar control, in germinated barley. Other studies which have sited the scutellum of barley as inducing symmetric break-down of the endosperm have not linked structural changes, in vivo, with fluorescent or non-fluorescent staining patterns. Some of these studies have failed to recognise the possibility that grains such as sorghum and rice may have a different pattern of endosperm break-down from that of barley.     

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 .     

THE PROTEIN RESERVES OF THE BARLEY GRAIN AND THEIR DEGRADATION DURING MALTING AND BREWING

The hordeins of barley are the main components of the grain protein, comprising B (sulphur rich), C (sulphur poor) and D (high relative molecular mass) species. A gel fraction can be isolated that consists of the D and part of the B hordein. Other important components of the reserve protein are β-amylase, protein Z and enzyme inhibitors as well as endosperm cell wall protein and protein associated with the starch granules. Degradation of protein is mediated by peptidase enzymes, most important of which are the endopeptidases and the exopeptidases; the latter having specificity for the carboxy- or amino-terminal region of a polypeptide chain. A very high activity of carboxypeptidase develops in the germinating barley grain. Five carboxypeptidases have been identified in malt and three fully characterized. Several endopeptidases have been identified, which have optimum activity close to pH 5.0 (that of the starchy endosperm) and studies with active site inhibitors suggest that sulphydryl dependent species are the most important. However, only limited use has been made of hordein as a substrate in the measurement of peptidase activity in malt. Lack of a complete understanding on the peptidases and their regulation in the germinating barley is a major limiting factor in the knowledge on the mobilization of the protein reserves during malting and mashing. Both de novo synthesis and activation of the peptidases have been demonstrated and the hormones gibberellic acid and abscisic acid appear to have a regulatory role. A controlled modification of the protein reserve is required so that there is an appropriate supply of amino acids for the brewers yeast but retention of proteins important in the desirable foaming component of beer. It is also important that proteins which can interfere in the final stages of brewing, e.g. those with chill haze forming potential, are broken down. An early hydrolysis is required of cell wall proteins and those proteins intimately associated with the starch granules.     

A SIMPLE AND RAPID TEST FOR ASSESSMENT OF ENDOSPERM PROTEIN MODIFICATION DURING MALTING*

A simple test has been developed for the quantitation of endosperm protein modification in malts. Barley meals or ground malts were extracted with a suitable solvent and the clarified hordein extract diluted into an appropriate precipitant. Of a variety of extractants and precipitants investigated, 1M urea-1% (v/v) mercaptoethanol and 1M sodium chloride were respectively found to be most suitable. Under these conditions a turbid suspension forms; the turbidity of extracts decreased progressively during malting. Turbidity was due to selective precipitation of a specific group of “B” hordeins. In an analysis of nine varieties differing in malting qualities, a significant correlation between the reduction in extract turbidity and cell wall modification (Calcofluor staining) was observed at 48 hours' malting. In addition, for each variety examined, protein modification occurred about one day before carbohydrate modification. Analysis of commercial malts and several samples of selected cultivars from regional trials found good correlations between malt turbidities and percent malt extract and Kolbach index. The test is rapid (10–90 mins) and can be used to screen large numbers of samples; since it is simpler than alpha—amino nitrogen or Kolbach index determination, it may be of use in analysis of malts for protein modification.