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1.
The application of the Rapid Visco Analyser (RVA) as a laboratory scale rheological tool for the characterisation of mash viscosity is the subject of this study. Studies were conducted to simulate an industrial mashing process, taking into account temperature/time, grist loads, adjunct amounts and enzyme levels. The RVA was used to characterise the effects of different ratios of malt: barley adjunct. The method was found to have the ability of not only detecting the major viscosity changes which occur during starch gelatinisation/liquefaction processes, but also the minor viscosity changes which were found to occur during the proteolytic and saccharification steps. Clear correlations were found between the level of barley adjunct and the output rheological data points of the peak viscosity at 50°C (PV50, R2 = 0.9931), the rate of viscosity breakdown at 50°C (BR50, R2 = 0.9522), the peak viscosity prior to gelatinisation (PVG, R2 = 0.9988), the area recorded under the gelatinisation curve (PGA, R2 = 0.9928) and the peak viscosity breakdown rate (VBR, R2 = 0.9783). The developed RVA rheological method is a useful tool for characterising grain quality (adjunct level) with regard to macromolecular viscosity compounds and the grains endogenous enzymatic capabilities.  相似文献   

2.
Proso millet is a gluten‐free cereal and is therefore considered a suitable raw material for the manufacturing of foods and beverages for people suffering from celiac disease. The objective of this study was to develop an optimal mashing procedure for 100% proso millet malt with a specific emphasis on high amylolytic activity. Therefore, the influence of temperature and pH on the amylolytic enzyme activity during mashing was investigated. Size exclusion chromatography was used to extract different amylolytic enzyme fractions from proso millet malt. These enzymes were added into a pH‐adjusted, cold water extract of proso millet malt and an isothermal mashing procedure was applied. The temperatures and pH optima for amylolytic enzyme activities were determined. The α‐amylase enzyme showed highest activity at a temperature of 60°C and at pH 5.0, whereas the β‐amylase activity was optimum at 40°C and pH 5.3. The limit dextrinase enzyme reached maximum activity at 50°C and pH 5.3. In the subsequent mashing regimen, the mash was separated and 40% was held for 10 min at 68°C to achieve gelatinisation. The next step in the mashing procedure was the mixture of the part mashes. The combined mash was then subjected to an infusion mashing regimen, taking the temperature optima of the various amylolytic enzymes into account. It was possible to obtain full saccharification of the wort with this mashing regimen. The analytical data obtained with the optimised proso millet mash were comparable to barley wort, which served as a control.  相似文献   

3.
The aim of this research was to investigate the relationship between starch composition in barley and its malted counterpart alongside malt enzyme activity and determine how these factors contribute to the fermentable sugar profile of wort. Two Australian malting barley varieties, Commander and Gairdner, were sourced from eight growing locations alongside a commercial sample of each. For barley and malt, total starch and gelatinisation temperature were taken, and for malt, α‐ and β‐amylase activities were measured. Samples were mashed using two mashing profiles (infusion and Congress) and the subsequent wort sugar composition and other quality measures (colour, original gravity, soluble nitrogen) were tested. Variety had no significant (<0.05) effect on any barley, malt, enzyme or wort characteristics. However, growing location impacted gelatinisation temperature, colour, malt protein content and original gravity. The gelatinisation temperature in malt samples was higher, by ~0.8°C, than in the equivalent barley sample. Several malt samples, even with protein contents <12.0%, had gelatinisation temperature >65°C. The fermentable sugars measured in the malt prior to mashing showed a higher proportion of maltose than glucose or maltotriose. In addition, there were significant differences in the amount of sugar produced by each mashing method with the high temperature infusion producing a higher amount of sugar and proportionally more maltose. There is scope for further research on the effect of genetics and growing environment on gelatinisation temperature, mash performance and fermentable sugar development. Routinely measuring gelatinisation temperature and providing this information on malt specification sheets could help brewers optimise performance. © 2019 The Institute of Brewing & Distilling  相似文献   

4.
Electrical conductivity measurements were applied to analyse the gelatinisation process of 12 starch or flour suspensions. The electrical conductivity of starch suspensions was found to increase upon gelatinisation because of the release of ions from starch granules. The initiation temperature of ion release, Ti, correlated well with the onset temperature in the DSC thermogram (R = 0.868), while the completion temperature of ion release, Tf, correlated with the temperature at the start of viscosity increase (R = 0.865). Thus Ti and Tf corresponded to the beginning and ending temperatures of gelatinisation respectively. The electrical conductivity measurement will be used as an on‐line technique to monitor the whole process of starch gelatinisation. © 2001 Society of Chemical Industry  相似文献   

5.
Barley malt is the preferred brewing material these days because of its high extract content and high enzyme activities. However, when substituting malted barley with oats to create a unique beer flavor and aroma, endogenous malt enzymes become the limiting factor. Therefore, the objectives of this study were to evaluate the effect of 10–40 % unmalted oats on the quality of high-gravity mashes/worts and to investigate the limitations of endogenous malt enzymes as well as the benefits of the application of industrial enzymes. The enzyme mix Ondea® Pro was found to be particularly suitable for mashing with unmalted oats and was therefore used in the present rheological tests and laboratory-scale mashing trials. In order to gain detailed information about the biochemical processes occurring during mashing, the quality of mashes was comprehensively analyzed after each mash rest using standard methods described by Mitteleuropäische Brautechnische Analysenkommission and Lab-on-a-Chip capillary electrophoresis. Mashing with up to 40 % oats resulted in increased mash consistencies, color/pH (20 °C) values, β-glucan concentrations, wort viscosities 12.0 %, and filtration times as well as decreased FAN and extract contents. The application of Ondea® Pro enormously increased the color of worts despite lower pH values but considerably improved the quality and processability of 30 or 40 % oat-containing mashes/worts. However, the substitution of up to 20 % barley malt with unmalted oats can easily be realized without the addition of exogenous enzymes.  相似文献   

6.
In this study, high‐pressure treatment (HPT) was applied to the mashing stage of beer production, which involves drying and milling of white malt and subsequent mixing with water. The following parameters were evaluated after pressurisation: β‐glucanase activity, starch gelatinisation and sugar extraction. Evaluation of starch hydrolysis from the malted barley endosperm after HPT was performed by measuring β‐glucanase activity after pressurisation; this enzyme breaks down gums and β‐glucans in wort and is desirable to obtain a good‐quality beer. Soaked malt samples pressurised at 200–600 MPa showed no increase in this activity compared with controls. Conversion of milled malt was evaluated indirectly by measuring the gelatinisation of starch, which began at 400 MPa. Soluble sugars were also measured in pressurised samples from the mashed liquid to investigate saccharification during the mashing stage. After 400 or 600 MPa treatment for 20 min, both the sucrose (g per 100 ml) and extract (l ° kg?1) values were the same as those found in mashed samples following the standard procedure used in the brewing industry (65 °C,90 min). Starch gelatinisation was analysed at different high pressures (200–600 MPa) and it was shown that gelatinisation began at 400 MPa. The HPT time would have to be shorter to make the process commercially attractive. © 2002 Society of Chemical Industry  相似文献   

7.
The objective was to develop a new simple and quick approach to predict fermentability, based on osmolyte concentration (OC). Eight malts were assayed for diastatic power, starch‐degrading enzymes [α ‐amylase, β ‐amylase and limit dextrinase (LD)] and malt OC (MOC). All malts were mashed to determine wort OC (WOC), real degree of fermentation (RDF) and sugar contents in a small‐scale mashing protocol. The results showed that MOC was correlated with malt α ‐amylase, LD, the resultant WOC, RDF and fermentable sugar (r  = 0.813, 0.762, 0.795, 0.867, 0.744, respectively), suggesting that MOC was discriminating in predicting levels of malt amylolytic enzymes, wort sugar and RDF without the mashing and fermentation process. Moreover, WOC showed stronger correlations with malt α ‐amylase, LD, RDF and fermentable sugars (r  = 0.796, 0.841, 0.884, 0.982, respectively), suggesting that WOC can be used to quickly predict wort sugar contents and RDF without a fermentation step. Furthermore, the effects of mashing temperature and duration on WOC, RDF and sugar contents are discussed. Adjusting mash temperature to 65°C or extending the mash duration dramatically increased RDF and WOC, whereas malt extract was relatively stable. Similarly, WOC showed significant correlations with RDF and fermentable sugars (r  = 0.912 and 0.942, respectively), suggesting that WOC provides a simple and reliable tool to assist brewers to optimize mash parameters towards the production of ideal wort fermentability. In conclusion, the ability of OC to predict malt fermentability and sugar content allows brewers to keep better control of fermentability in the face of variation of malt quality, and to quickly adjust mashing conditions for the consistency of wort fermentability. Copyright © 2017 The Institute of Brewing & Distilling  相似文献   

8.
Temperature and mash thickness are shown to affect both mash performance and enzyme activity. Alpha amylase was found to be considerably more resistant to heat inactivation than was beta amylase. This difference was reflected by changes in wort fermentability that were manifest at temperatures below those which affected levels of extract. Increasing the mashing temperature from 65°C to 80°C had only a slight effect on extract but reduced wort fermentability from over 70% to less than 30%. At 85°C and over, when temperature had a significant effect on alpha amylase, as well as on beta-amylase, extract was lost and starch was present in the wort. Diluting the mash with liquor had a similar effect to that of increasing temperature on both the amylolytic enzymes and on the mash performance. Thin mashes contained more starch and fewer fermentable sugars than did thick mashes at the same temperature. These changes can be related to the stability of the amylolytic enzymes.  相似文献   

9.
ABSTRACT: Honey amylase was evaluated for potential to degrade food starch and cause viscosity loss. Honey was assayed for amylase activity with diastase number (DN). A viscosity assay, developed with unmodified waxy maize starch, measured honey amylase rate of viscosity decrease (RVD). The relationship between DN and RVD was linear (R2= 0.98). Modified waxy maize starches showed resistance to honey amylase. Honey heat treatment at 85 °C reduced amylase activity 2 to 5 DN, but confirmed enzyme heat resistance. Optimum pH for honey amylase was confirmed at pH 5.3 to 5.6. RVD activity declined as pH decreased. Preventing food viscosity loss involved selecting honey with lowered DN and/or using modified starches. Complete control of activity was achieved in barbecue sauce at pH < 3.9.  相似文献   

10.
Pilot scale (1000 L) brews were carried out with a grist comprising of unmalted sorghum (50% of total wet weight of grain) (South African variety) and malted barley (50% of total wet weight of grain) grist using a mashing program with rests at 50°C, 95°C and 60°C. Mashes were supplemented with a high heat stable bacterial α‐amylase, a bacterial neutral protease and a fungal α‐amylase. A control brew containing 100% malted barley was also carried out. Saccharification difficulties were encountered during mashing, and extraction of the grist was lower for the sorghum mashes. The sorghum mashes showed comparable lautering behaviour to that of the control mash. At mashing off the sorghum worts were starch positive. Apparent degree of fermentation of the sorghum gyles were less than the control gyles. Green beer filtration proved unproblematic. The sorghum beers compared quite closely with the control beer with regard to colour, pH and colloidal stability. Foam stability deficiencies were apparent with the sorghum beer. However, the fermentability of the sorghum worts were lower. Hence the sorghum beers were lower in total alcohol. Sensory analysis indicated that no significant differences existed between the sorghum beer and both the control beer and a commercial malted barley beer with regard to aroma, mouth‐feel, after‐taste and clarity. However, the sorghum beer was found to be significantly different to both of the other beers with regard to colour, initial taste and foam stability.  相似文献   

11.
BACKGROUND: The creation of starch‐based foods incorporated with functional ingredients such as probiotics is of great current interest in the food industry. This study aimed to investigate the effects of prebiotic oligosaccharides on the phase transition temperatures and rheological characteristics of waxy rice starch dispersions. Four oligosaccharides were applied to the rice starch dispersions: chitooligosaccharides, fructooligosaccharides, isomaltooligosaccharides and xylooligosaccharides. RESULTS: The addition of 125 g kg?1 oligosaccharides elevated the onset and peak temperatures for gelatinisation of 200–400 g kg?1 waxy rice starch dispersions. The temperature of the storage modulus (G′) for gelatinisation increased markedly on adding fructooligosaccharides to 200–300 g kg?1 waxy rice starch. For gelatinisation of 300 g kg?1 rice starch dispersion the effectiveness of the oligosaccharides in changing the above parameters was as follows: chitooligosaccharides > fructooligosaccharides > isomaltooligosaccharides > xylooligosaccharides. Moreover, their effectiveness was dependent on the amylose content, as illustrated by comparing waxy and non‐waxy rice starches (amylose contents 9–256 g kg?1). Importantly, the logarithmic G95 change was linearly and negatively correlated with amylose content. CONCLUSION: The results suggest that oligosaccharide‐containing rice starch dispersions may potentially be used for the formulation of oligosaccharide‐containing starchy functional foods owing to the rheological changes of these starch dispersions. Copyright © 2011 Society of Chemical Industry  相似文献   

12.
Mucuna bean (Mucuna pruriens) starch was isolated and subjected to chemical modification by oxidation and acetylation. The proximate analysis of the non‐starch components of the native starch on a dry weight basis was 92 g kg?1 moisture, 5 g kg?1 ash, 2 g kg?1 fat, 7 g kg?1 crude fibre and 19 g kg?1 protein. Chemical modification reduced the values for all the non‐starch components except the moisture level. For all the samples, swelling power and solubility increased as the temperature increased in the range 50–90 °C. The swelling power of mucuna native starch (MNS) and mucuna acetylated starch (MAS) increased with increasing acidity and alkalinity, while that of mucuna oxidised starch (MOS) only increased with increasing pH in the acidic range. The maximal solubility of all the starches was observed at pH 12. All the starch samples absorbed more oil than water. The lowest gelation concentration followed the trend MAS < MNS < MOS. Chemical modification reduced the gelatinisation temperature (Tp), while peak viscosity (Pv), hot paste viscosity (Hv) and cold paste viscosity (Cv) decreased after oxidation but increased following acetylation. The setback tendency of the native starch was reduced significantly after chemical modification. However, the breakdown value of MNS, 65 BU (Brabender units), was lower than that of MOS (78 BU) but higher than that of MAS (40 BU). Differential scanning calorimetry studies of gelatinisation and retrogradation revealed that chemical modification reduced the onset temperature (To), peak temperature (Tp) and conclusion temperature (Tc). Oxidation and acetylation reduced the gelatinisation and retrogradation enthalpies of the native starch. The enthalpy of retrogradation of the starches increased as the length of storage increased. Copyright © 2003 Society of Chemical Industry  相似文献   

13.
To determine the relationship between sorghum grain polyphenol content, grain structure, and starch properties, starch was isolated from 10 sorghum varieties using an alkali steep and wet‐milling procedure. SV2, a tannin‐free variety with white pericarp, gave a white starch. Varieties having red or white pericarp and higher polyphenol levels gave pink starches. Hunter colour values (L, a, b) of starches were not correlated with grain polyphenol content. Grain appearance in terms of pericarp colour, or presence or absence of pigmented testa, did not relate to the intense pink colouration of sorghum starches. Starch amylose content was significantly negatively correlated (r = −0.88, p < 0.001) to grain floury endosperm texture. Sorghum starches had higher peak viscosity (PV) in pasting than commercial maize starch. The time taken to reach peak viscosity from the initial viscosity rise was less for sorghum starches than maize starch. However, sorghum starches had a higher rate of shear thinning (Rst) than maize starch. There was a significant positive correlation between grain polyphenol content and starch PV (r = 0.75, p < 0.05). Starch gel hardness was negatively correlated to pasting properties of Rst and paste breakdown (r = −0.78 and −0.77 respectively) at p < 0.01. Peak gelatinisation temperature (Tp) occurred over a narrow range from 66 to 69 °C. Tp was negatively correlated to the floury endosperm portion of the grain (r = −0.77) at p < 0.01. It is concluded that sorghum grain polyphenol content and grain characteristics influence its starch properties. © 2000 Society of Chemical Industry  相似文献   

14.
The susceptibility to amylolysis of starches derived from two improved Nigerian sorghum cultivars were evaluated at assay temperatures between 50°C and 75°C. Enhancement of gelatinisation rates at temperatures up to 65°C was not significant inspite of the apparent grain modification due to germination for four days. Greater starch gelatinisation rates (20–22%) were achieved in this study compared to previously reported values, suggesting possible roles for cultivar and malting methods. There was a statistical correlation between starch gelatinisation rates over the temperature range 65°C–75°C and the duration of grain germination (r=0.91 for KSV8 and r=0.5 for SK5912 starches). Gelatinisation rate and temperature were affected significantly by assay pH. The occurrence of two pH related maxima of starch gelatinisation for both cultivera at all temperatures examined indicates the possible presence of two sets of “binding forces” within the starch granules and features of starch retrogradation .  相似文献   

15.
Pressure-induced gelatinisation of sorghum starch was studied and compared to heat-induced gelatinisation. Starch suspensions were treated at increasing pressure (200–600 MPa) or temperature (60–95 °C) for 10 min. The degree of gelatinisation was determined using differential scanning calorimetry, changes in birefringence and damaged starch measurements. Furthermore, the pasting behaviour and structural changes during gelatinisation were investigated using rheology and microscopy. The pressure-induced as well as the temperature-induced gelatinisation curves were sigmoid-shaped. Gelatinisation occurred between 300 MPa and 600 MPa or between 62 °C and 72 °C. No significant differences were found between the rheological properties and the microstructure of the pressure-treated samples and the temperature-treated samples within the gelatinisation intervals. Granules lost their birefringence, but granular structure was maintained; however, when heated beyond the endpoint of gelatinisation, the formation of a “sponge-like” structure was observed. This change in structure at very high temperatures was reflected by a decrease in complex viscosity.

Industrial relevance

In order to apply high pressure as an alternative to temperature in the structural engineering of starch-based systems, a full understanding of the pressure-induced gelatinisation process is necessary. No rheological and ultra-structural differences were observed between pressure- and temperature-induced gelatinisation of sorghum starch. These results indicate that pressure treatment can be utilised as a replacement technology for temperature during processing of complex starch-containing products.  相似文献   

16.
BACKGROUND: Changes in the properties of starch during postharvest hardening of trifoliate yam (Dioscorea dumetorum) tubers need to be investigated. In this work the starch gelatinisation kinetics of D. dumetorum cv. Yellow stored under prevailing tropical ambient conditions (0.98–2.32 kg vapour per 100 m3 airflow) for 0, 2, 7, 14, 21 and 28 days was studied using a 3 × 5 factorial experiment with three cooking temperature (75, 85 and 95 °C) and five cooking times (0, 5, 10, 20 and 40 min). Samples were also evaluated for starch properties and gelatinisation temperature. RESULTS: Storage of D. dumetorum tubers caused starch damage. However, the starch gelatinisation temperature was between 70 and 75 °C irrespective of the tuber storage duration. The starch gelatinisation reaction followed first‐order kinetics defined by the relationship ln(1 ? α) = ? kGt. The gelatinisation rate was significantly influenced (P≤0.05) by cooking temperature and increased with tuber storage duration. The activation energy also increased with tuber storage duration. CONCLUSION: Although the gelatinisation temperature of D. dumetorum starch was not influenced by tuber storage, the starch gelatinisation process was affected by tuber storage duration, since tuber storage involved a greater need of energy for starch gelatinisation, which may be an effect of the postharvest hardening phenomenon. Copyright © 2008 Society of Chemical Industry  相似文献   

17.
The objective of this study was to investigate the rheological, thermal and microstructural properties of whey protein isolate (WPI)‐hydroxypropylated cassava starch (HPCS) gels and WPI‐cross‐linked cassava starch (CLCS) gels at different pH values (5.75, 7.00 and 9.00). The rheological results showed that the WPI‐modified starch gels had greater storage modulus (G?) values than the WPI‐native cassava starch gels at pH 5.75 and 7.00. Differential scanning calorimetry curves suggested that the phase transition order of the WPI and modified starch changed as the pH increased. Scanning electron microscopy images showed that the addition of HPCS and CLCS contributed to the formation of a compact microstructure at pH 5.75 and 7.00. A comprehensive analysis showed that the gelling properties of the WPI‐modified starch were affected by the difference between the WPI denaturation temperature and modified starch gelatinisation temperature and by the granular properties of the modified starch during gelatinisation. These results may contribute to the application of WPI‐modified starch mixtures in food preparation.  相似文献   

18.
The effect of commercial enzymes on liquefaction of starch from unmalted sorghum was studied. The effects which these enzymes had on rates of filtration were evaluated. Models were developed, validated and optimized to establish the actions of enzymes, either alone or in combination. Preliminary studies on the sorghum cultivars Safrari, Madjeru and S.35 showed that α‐amylase was the backbone enzyme for starch liquefaction among the enzymes used (α‐amylase, Filtrase, protease and β‐amylase). Models confirmed this observation as α‐amylase individually in its first order (X1) contributed 25, 11 and 17%, and in its sum of first and second orders (X1+X12) contributed a 29, 31 and 36% yield of filtrate for Safrari, Madjeru and S.35 respectively. The ease of starch liquefaction, assessed by summing the first and second orders of individual intervention of all enzymes, was found to be in the order of Madjeru, S.35 and Safrari (79, 70 and 56% of yield of filtrate respectively). The importance of the enzyme combination in starch liquefaction in Safrari, S.35 and Madjeru was shown to be 44, 30 and 21% respectively. Enzyme combinations giving maximal starch liquefaction, as identified from a Doehlert experimental matrix, displayed a similar yield of filtrate (Safrari: 85 mL, Madjeru: 84 mL and S.35: 81 mL) after filtration of a 130 mL mash during 1 h. Validation of the models revealed the model developed for Madjeru was the most reliable (R2 = 0.994), while those developed for Safrari (R2 = 0.987) and S.35 (R2 = 0.976) were slightly less reliable. Model optimization gave theoretical enzyme (Brewers Amyliq TS, Filtrase NLC, Brewers Protease and β‐amylase) combinations of 25 mg, 5.68 mg, 100 mg and 67.4 U for Safrari, 15.06 mg, 0.51 mg, 24.32 mg and 53.8U for Madjeru and 19.01 mg, 6.36 mg, 58.76 mg and 43.48 U for S.35, with a resulting yield of filtrate of 94, 87.7 and 83.8 mL respectively.  相似文献   

19.
The effect of ozone treatment on physicochemical properties of waxy rice flour and waxy rice starch was investigated. Results showed that ozone treatment increased the pasting viscosity of waxy rice flour. Compared with untreated waxy rice flour, the peak viscosities of waxy rice flour for 0.5, 1 and 2 h of ozone treatments were increased by 27.4%, 32.8% and 45.5%, respectively. The alpha‐amylase in waxy rice flour was inactivated during the treatment. The gelatinisation temperature and enthalpy of waxy rice flour were kept unchanged after the treatment. For waxy rice starch, pasting viscosity, swelling power and molecular weight were increased after 0.5 h of treatment, but decreased as treatment time extended. The ozone treatment decreased gelatinisation temperature and enthalpy of waxy rice starch.  相似文献   

20.
The changes on the molecular weight distribution (MWD) and particle size distribution (PSD) during hydrolysis of barley malt in isothermal mashing procedures were determined using asymmetrical flow field flow fractionation coupled to multiangle laser light scattering and refractive index (AF4/MALS/RI). Mash/trials were focused on amylolytic starch degradation. Therefore, temperatures (65, 70, and 75 °C) were selected according to α‐ and β‐amylases range of activity. Samples were produced by triplicate, tracking amylolytic processes over time periods from 10 to 90 min in each mash/trial. AF4/MALS/RI analysis demonstrated significant differences on the values of the MWD and PSD according to the temperature/time profile used. At mashing times over 30 min at a temperature of 65 °C, when α‐ and β‐amylase are both active, the decrease over time of the MWD and PSD was significantly higher (P < 0.005) than at 70 °C when mainly α‐amylase is active. At 75 °C, also the activity of α‐amylase decreased and the MWD and PSD were significantly lower (P < 0.005) than at 70 or 65 °C at any time of the procedure. The MWD and PSD of beer components influence beer palate fullness, thus AF4/ MALS/RI would be a powerful tool for breweries to adapt their technological processes to obtain beers with particular sensorial attributes.  相似文献   

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