A RAPID METHOD FOR THE DETERMINATION OF DIASTATIC POWER

A rapid method for the determination of diastatic power is described. The enzyme extraction and starch hydrolysis steps have been shortened to 10 min each and a colorimetric method involving the use of p-hydroxybenzoic acid hydrazide has been used for the determination of reducing sugars. The method avoids some sources of error associated with previous methods. The sensitivity of the method allows the use of small samples making it suitable for the measurement of diastatic power in barley breeding.     

霉菌对麦芽品质影响的研究

麦芽是啤酒酿造的主要原料,其表面附着了各类微生物,尤其是受霉菌侵染的麦芽可能引起β-葡聚糖、可溶氮和麦汁黏度升高等问题。本文研究了三种大麦在制麦过程中添加已筛选的大麦自身携带的四种霉菌对麦芽质量的影响,发现链格孢霉和镰孢霉对大麦细胞壁降解和细胞内基质溶解有明显的负作用,导致β-葡聚糖酶活力降低,β-葡聚糖含量增加,麦汁的浊度升高;其中镰孢霉对Gairdner的麦汁浊度影响最大,增加220%;添加镰孢霉的三种麦芽中蛋白酶活力和库值都有所降低,其中国产内蒙麦芽库值下降最多,下降了7.2%。      

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.     

Brewing Beer with Sorghum

Research reports on extracts, proteins, total nitrogen and free amino nitrogen content of sorghum malt and worts obtained from mashes indicate that sorghum is potentially an alternative substrate for conventional beer brewing in the tropics. Remarkable variations in biochemical characteristics among different sorghum cultivars affect their optimal malting conditions. Factors such as temperature and time of steeping and germinating of grains with their intrinsic enzymic activities, and kilning temperature determine the quality of malt. Further works on mashing, viscosity and fermentability of worts as well as the character of the resulting beers, such as alcoholic content, colour, taste and specific gravity tend to confirm the status of sorghum as a credible substitute for barley in beer brewing. This review reports on progress made in the use of sorghum for brewing beer.     

EFFECTS OF FINAL WARM WATER STEEP AND AIR REST CYCLES ON MALT PROPERTIES OF THREE IMPROVED NIGERIAN SORGHUM CULTIVARS

The effects of final warm steeping at 40°C and air-rest cycles on malting loss and other malt quality parameters of three improved Nigerian sorghum cultivars were investigated. Grains were steeped for 48 h under four different steep regimes then germinated for 4 days at 30°C. The effect of final warm steeping on kernel growth, malting loss, diastatic power, α and β-amylase and extracts of the malts was significantly affected by air-resting, cultivar and the pair-wise interactions of cultivar and steep regime. Generally, malting loss and kernel growth reduced significantly (p< 0.001) when the steep cycle was a combination of air-resting and final warm water steep at 40°C. Diastatic power, α-amylase, β-amylase and extract also improved significantly in both ICSV 400 and KSV 8 when these grains were malted by a steep regime which combined both air-rest cycles and final warm water steep. However steeping these grains under a final warm water steep without air-resting led to a decrease in extract recovery and enzyme activity. Conversely steeping SK 5912 by a combination of air-resting and final warm water steep generally, inhibited rather than enhanced extract and enzyme development.     

温水浸麦方法探讨

选用合理的浸麦方法,用温水进行浸麦,不但对麦芽质量没有大的影响,而且还能大幅度缩短浸麦时间,节约浸麦用水。     

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.     

USE OF NITROGEN DIOXIDE AFTER STEEPING TO INHIBIT FORMATION OF NITROSAMINES IN MALT

Application of nitrogen dioxide (NO₂) to barley at the start of the germination phase of malting inhibits the formation of NDMA in subsequent kilning, even when high NO_x conditions are used. Malts produced using these treatments contained reduced levels of nitrosamines and other analytical values were normal. Beer of sound flavour and other properties was brewed from these malts. However, it has yet to be established whether other nitroso compounds are formed during NO₂ treatment. Consequently a recommendation that this treatment can be adopted as an industrial protocol awaits further investigation .     

ALKALINE STEEPING AND THE STABILITY OF BEER

On the basis of the experimental evidence gathered in the course of this investigation, it is concluded that the alkaline steeping of barley leads to better colloidal (physical, non-biological) stability of the beer without significantly affecting its flavour or any of its standard characteristics. Since the alkaline steeping invariably lowers the tanninogen contents of malt (both anthocyanogens and catechins decrease), whereas its other principal analyses do not change in any predictable manner, it should follow that the tanninogen decrease is mainly responsible for better stability of the beer. It is also apparent that no malt characteristics, except tanninogen and protein contents, have a definite effect on the colloidal stability of the beer. A relationship between the tanninogen and protein contents of malt has also been established.     

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.     

MEASUREMENT OF DIASTATIC POWER

Modifications to the method of estimating the diastatic power of malt using starch hydrolysis and determination of reducing sugar released with p-hydroxybenzoic acid hydrazide are described. Using 40 g malt, 4% w/v soluble starch reduced with sodium borohydride and a “boiled enzyme blank”, the production of reducing sugar is directly proportional to volume of added extract. Using a constant amount of extract, the reaction is directly proportional to time over a period of 30 min. The method enables the direct estimation of the diastatic power of malts with Windisch-Kohlbach values of up to 434 degrees.     

THE USE OF ELECTROPHORESIS IN TESTING FOR HIGH DIASTATIC POWER IN BARLEY

In crosses between barley cultivars differing in both electrophoretic pattern and diastatic power, these two characters were found to be closely related at any given level of grain nitrogen, when selected F₃ and F₄ lines were tested. Electrophoresis, in conjunction with the estimation of grain nitrogen content, can be used to predict diastatic power and has the advantage over other tests in being unaffected by the environment in which the plants were grown. Identification in early generations allows the character to be fixed preventing the loss of plants with high diastatic power during subsequent selection for other characters.