INFLUENCE OF MALTING CONDITIONS ON QUALITY OF FINGER MILLET MALT

Effect of processing conditions on dry matter loss and quality characteristics of malt from INDAF-6 variety of finger millet was studied. Increasing the temperature of malting from 15 to 35°C caused increased dry matter loss. Germination at 15–20°C gave malts of higher α-amylase activities than those germinated at 30–35°C. Germination at 20°C for 4–5 days gave malt with maximum enzyme activity and acceptable dry matter loss. Drying the malt to 12% moisture and kilning at 70°C for about 45 min resulted in malt of desired aroma, maximum retention of α-amylase and minimum loss of available lysine. The α-amylase in the malted flour caused the slurries to have low hot paste viscosity.     

THE ULTRASTRUCTURE OF GERMINATING SORGHUM AND MILLET GRAINS

The parenchyma tissues of ungerminated and germinated sorghum and millet grains contain abundant fat and protein deposits, which undergo various metabolic changes during germination and seedling growth. The presence of these and other organelles which are characteristic of the mature plant cell was confirmed by a combination of light and electron microscopy. During the early period of the germination process in the millet scutellum, evidence of starch synthesis was apparent, suggesting that fat to starch conversion possibly occurred in the cells of this tissue. In the endosperm of 72 h germinated sorghum and millet grains, starch degradation occurred although such degradation was more extensive in sorghum than in millet.     

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.     

DEVELOPMENT OF AMYLOLYTIC ACTIVITIES IN SORGHUM AND BARLEY MALT

A Nigeria-grown sorghum cultivar was observed to develop more Diastatic Power (DP) and β-amylolytic activity than a previously studied sorghum cultivar grown in Australia. Barley malt produced more Diastatic Power and β-amylolytic activity than the Nigeria-grown sorghum cultivar. In general, the kilned barley malt retained less α-amylolytic activity than kilned sorghum malt. The different diastatic potential of sorghum cultivars may reflect differences in genetic character or growth conditions.     

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.     

COMPARATIVE MALTING PERFORMANCE OF OLD AND NEW BARLEY VARIETIES

A comparison was made of the malting behaviour of eight barley varieties representing a range from ancient to modern types. Plants were grown under controlled conditions in a glasshouse with two different nitrogen treatments and the grain obtained was subjected to a factorial micro-malting analysis. Under the conditions of this experiment there was little evidence of an improvement in malting ability between Plumage Archer and Ark Royal and there is limited scope for further increases in potential hot water extract. It would therefore appear that emphasis should now be given to the production of varieties with good agronomic characteristics which maintain this potential and modify rapidly without the need for abrasion and exogenous GA₃.     

MALTING AND BREWING PROPERTIES OF ABRADED BARLEY*

Pilot scale malting trials confirmed earlier observations that, after gibberellic acid treatment, grain in which the pericarp had been scarified to a small degree malted at a faster rate than the control, which had also been treated with gibberellic acid. The hot water extracts of the abraded grains were correspondingly higher than those of the control while the total processing time was reduced by more than 25%. Abraded malts cured more rapidly than normal gibberellic acid-treated malts and gave worts of higher fermentability, nitrogen content and amino acid content. Beers of good quality were produced from abraded grain.     

EFFECT OF IRRADIATION ON THE MALTING QUALITY OF BARLEY

Two six-row barley cultivars, DL 70 and C 164 were subjected to Co⁶⁰ gamma irradiation in the range of 0 to 250 Krad and malted with and without gibberellic acid treatment. Barley irradiated with doses up to 75 Krad produced normal malts when compared to the controls. Irradiation doses of 125 and 250 Krad significantly increased the malt yields but considerably decreased the α-amylase activity. Gibberellic acid significantly increased the enzyme activity and degree of modification of the irradiated and the control malts.     

ASSESSING MALTING QUALITY BY THE AUTOLYSIS OF BARLEY

There has been prolonged speculation over the past thirty years on the relationship between the properties of aqueous extracts of barley and malting quality. On reviewing the literature on this subject, the concensus of opinion is that the total amount of gum or β-glucan in the barley does not correlate with malting quality. The cytolytic potential of both barley and malt, on the other hand, appears the more important parameter. Present evidence is that measurements made on aqueous extracts, either by viscosity or β-glucan determination, are more indicative of barley cytolytic activity than they are a true measure of gum content. Low β-glucan values in some barleys may therefore be artefacts of enzymic hydrolysis.     

EFFECTS OF THE MYCOTOXINS DIACETOXYSCIRPENOL AND DEOXYNIVALENOL ON MALTING CHARACTERISTICS OF BARLEY

In germination tests, the trichothene diacetoxyscerpanol (DAS) caused reductions in the number and total length of rootlets, and the length of the coleoptile, developing from excised barley embryos, but the effects were less than those of T-2 toxin. Rootlet and coleoptile growth was also inhibited during micromating of barley artificially contaminated with DAS before steeping, whilst α-amylase activity of finished malts were reduced by up to 49%, and α-amino nitrogen levels in worts were also lower than in controls. The effects of deoxynivalenol (DON) were less than those of DAS, e.g. the reduction in α-amylase activity caused by DON applied at the rate of 50 μg g-1 grain was less than one-half of that caused by 20 μg DAS g^?1.     

VARIETAL IDENTIFICATION OF BARLEY AND MALT*

A vertical polyacrylamide — SDS electrophoretic technique, including whole protein extraction and staining steps, was improved with a view to developing it for routine laboratory use with single barley kernels. The pattern consisted of 4 zones: A (albumins-globulins). B and C (hordeins) and D (possibly glutelins) displaying unequal varietal polymorphisms (1, 13, 13 and 4 types respectively). 28% of the barley samples (77 varieties), including most cultivars grown in France, could be unambiguously identified from qualitative differences only, in the B, C and D zones. Adding three other characteristics (hairs and furrow hairiness, peroxidase, zymogram, esterase zymogram), as many as 78% of the varieties could be identified, the other 22% consisting of very closely related barleys. After slight modification of protein extraction conditions, the same methods could be used with malt, based on the same electrophoretic types. A graphic tablet connected to a microcomputer was used for automatic acquisitions of records and comparisons of electrophoretic data.     

IMPROVED MALTING PERFORMANCE OF FRESHLY HARVESTED BARLEY AFTER ABRASION

Abrasion improved the malting performance of dried, freshly-harvested barley and provided an alternative to storage. The maltability of undried, unstored barley was improved by abrasion, but the undried grain was more difficult to abrade than was dried grain. Unabraded barley required storage periods of at least 3 weeks before adequate extracts could be obtained. Although acidulation reduced the malting losses of dried grain, it only improved the yield of extract with barleys stored for at least 9 weeks before malting. The potential of dried freshly-harvested barley to produce α-amylase and endo-β-glucanase, as indicated by the response of endosperm slices to gibberellic acid, was initially low and increased gradually as the barley was stored. It is considered that the dominant factor in the accelerated malting of freshly-harvested barley is the improved distribution of enzymes in the endosperm which results from abrasion.     

A RAPID TEST FOR THE PREDICTION OF MALTING QUALITY OF BARLEY

A grinding energy method developed for the prediction of the nutritional value of grass was adapted and used to differentiate barleys of good malting quality from those difficult to malt. This is a very rapid test (a few minutes per sample) and could be used as an initial step in screening for malting quality.     

PLANT HORMONES IN FUNGI AND BACTERIA FROM MALTING BARLEY

40 Fungi and 16 strains of bacteria, isolated from the grains of three cultivars of matting-grade barley (Kymppi, Pokko and Kustaa, of 1990 harvest), were screened for the production of the plant hormones gibberellic acid (GA₃, abscisic acid (ABA) and indole-3-acetic acid (IAA). Four fungal strains were found capable of GA₃ production and four of ABA production. IAA production was common among both fungi (58% of strains active) and bacteria (88% of strains active). To get an estimate of the physiological significance of the presence of plant hormone producing microbes, the plant hormone production per microbial unit in the liquid growth media of the cultured organisms was weighed against the microbial counts and the endogenous hormone concentrations of barley grains. It was concluded that bacterial IAA production could be of significance in imbibed grains. This presupposes, however, that the conditions be ideal for the propagation of the active species and also, for the production of IAA by those same species and lastly, that similar production occurs in vivo as well as in vitro. Microbial GA3 and ABA production, on the other hand, were estimated to occur in negligent amounts.     

EFFECT OF STORAGE TIME ON THE MALTING QUALITY OF SOME BARLEY VARIETIES

Changes in the malting quality of some barley varieties were monitored at monthly intervals from harvest All the varieties were found to improve after storage for up to one year. Varieties with poorer malting grades improved at a faster rate than good varieties, although ranking consistent with malting grade was maintained.     

DRYING AND STORAGE TREATMENTS FOR OVERCOMING DORMANCY IN MALTING BARLEY

A batch of deeply dormant Triumph barley was stored at ?18°C. The grain was so dormant that its viability, 97–98%, could not be determined using standard tests. Samples were dried to 12% moisture at various rates by varying the temperature and relative humidity of the drying air. Dried samples were stored at three temperatures (15°, 27° and 38°C). At intervals the germination characteristics of subsamples were determined. Germinability improved with storage time, improving faster at the higher temperatures. However some of the samples stored at 27°C and all the samples stored at 38°C suddenly showed a loss of viability, preceded by a loss in vigour. The rate of recovery from dormancy was independent of the drying regime used. Initially the germinability of the barley was 5–10% (1 ml agar test) and 0–4% (3 ml agar test). Recovery from dormancy was extremely slow at 15°C, so that after a year germination values were around 80% (1 ml agar test) and 45% (3 ml agar test). After 27 weeks the viability of grain stored at 27°C began to decline, germinability was 85–90% (1 ml agar test) and 50–60% (3 ml agar test). At 38°C the initial decline in dormancy was rapid, but germinability fell catastrophically at various times between 3 and 30 weeks storage. Other samples of the same lot of Triumph barley were dried to various moisture contents, 9.4%, 10.3%, 11.0%, 13.0% and 14.5%. These were stored at 38°C. The initial rate of recovery from dormancy was rapid, and was unrelated to the moisture content of the grain. The samples dried to 9.4% and 10.3% m.c. achieved germination values close to the viability value, around 95% (1 ml agar test) and 90% 3 ml (agar) tests in 15–18 weeks storage and showed no signs of deterioration in 30 weeks. Grain held at 11% moisture deteriorated after 12 weeks and that stored at 13% and 14.5% deteriorated after 3 weeks. The germinabilities of the samples dried to 9.4% and 10.3% and stored for 15–18 weeks at 38°C were so good, reaching maximal values at 2 days in the germination test, that it is concluded that they could probably not be matched by samples stored cool. The possibility of using higher storage temperature to overcome dormancy and water sensitivity more rapidly, is discussed. Experiments with other grain samples have confirmed that, in most respects, the original barley was typical of deeply dormant Triumph. Samples of Carmargue and Golden Promise matured much more rapidly than Triumph. However water sensitivity was extremely persistent in a sample of Doublet.     

THE MALTING QUALITY OF SOME SPRING BARLEY VARIETIES GROWN IN ENGLAND AND WALES BETWEEN 1880 AND 1980

The malting behaviour of fifteen barley varieties widely grown between 1880 and 1980 has been compared using material grown at two sites in England in 1980. All the varieties examined were considered to be of malting quality at their time of widespread commercial use. Varieties introduced after 1950 gave higher Hot Water Extracts (mean 74·7%) than varieties introduced before 1950 (mean 71·0%), and when the yield data were included to calculate the yield of extract/ha the post-1950 varieties were found to exceed the older varieties by 48·7%. The Kolbach Index of the modern varieties was higher, although there was no evidence of an increase in cold water extract.     

THE RELATIONSHIP BETWEEN BARLEY EXTRACT VISCOSITY CURVES AND MALTING ABILITY

Twelve barley varieties, representing a wide range of malting ability, were examined using the Falling Time technique to determine their raw grain extract viscosities following extraction times ranging from 1 to 6 h. The shape of the viscosity curve was characteristic of each variety and was related to malting ability. A simpler index of potential malting ability was produced by the difference in Falling Time between extraction times of 3 and 4 h. This difference correlated well with the percentage extract obtained after micro-malting, (r = + 0·81, n = 31), and offers a possible method of assessing potential malting ability in barley breeding programmes.     

PREDICTION OF THE MALTING QUALITY OF BARLEY BY A MODIFIED ZELENY SEDIMENTATION TEST

The Zeleny sedimentation test, developed to predict the bread-making quality of wheat flour, has been modified to predict the malting potential of barley samples. The test appears promising for the evaluation of malting potential of unknown varieties.