the oxalic acid content in selected barley varieties growing in poland, as well as in their malts...

8/12/2019 The Oxalic Acid Content in Selected Barley Varieties Growing in Poland, as well as in their Malts and Worts

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VOL. 117, NO. 1, 2011 67

The Oxalic Acid Content in Selected Barley

Varieties Grown in Poland, as well as in their

Malts and Worts

Andrzej Brudzyski and Agnieszka Salamon*

ABSTRACT

J. Inst. Brew. 117(1), 6773, 2011

The purpose of this work was to try to answer the questionWhat factors influence the oxalic acid content in barley, maltand wort? Samples of three malting barley varieties (Prestige,Sebastian and Jersey, registered and grown in Poland) were in-vestigated for their oxalic acid content. Laboratory scale maltingand kilning of these samples and investigation of their oxalic

acid content were conducted. Furthermore, the oxalic acid con-tent was analysed in worts obtained from these malts. Testedbarley samples, originating from various regions of Poland,showed different oxalic acid contents, ranging from 17.2 to 66.8mg/kg d.m. basis. A higher temperature of germination (an in-crease from 14C to 18C with the same length of time) resultedin a decrease in oxalic acid content in the resultant worts. Inmost cases a positive linear correlation was found between theoxalic acid content in the malts and worts, and the initial barleysamples. Oxalic acid content in barley appears to depend on thegrowth region rather than on the variety, but the data was notsufficient to draw any firm conclusions on this subject.

Key words:malt, malting barley, oxalic acid, wort.

INTRODUCTION

Calcium oxalate precipitations in beer are cited bysome authors25,26 as the most important factor evokinggushing problems. There are others who maintain thatoxalates are only one, among a wide variety of suspectedfactors, such as barley and malt contamination by fila-mentous fungi, mainly of the genus Fusarium, producingthe gushing evoking hydrophobins19, some other surface-active substances, including a peptide from the fungusNigrospora, a tetrapeptide from Penicillium, a glucopep-tide from Stemphyllium, some barley proteins, metal ions,iron (Fe+2) and copper (Cu+2), isomerised hop extractsetc.12,20

Oxalic acid in beer comes mainly from malt7,25. Its

content in barley malt usually ranges from 10 to 20mg/100 g d.m. basis (but sometimes to twice this value).In lager worts, around 25 to 32 mg/L can be found.

Barley (Hordeum vulgare) is classified as a low-ox-alate plant and, like many other crops, produces and accu-mulates oxalic acid, but its biosynthesis, accumulation,and catabolism are not yet sufficiently known23. alikan4reported that oxalic acid and its salts are produced andstored in different amounts in all parts of plants, but thattheir levels may vary depending on the age of the plant,the growing season and cultivation conditions. Formationof oxalic acid may occur by several metabolic pathways.Libert and Franceschi9indicate that the main pathways ofmetabolism of oxalic acid are the tricarboxylic acid cycle(Krebs) and glyoxylate cycle. The precursor of oxalic acidmay be oxalacetate, which cleaves into oxalate and ace-tate8.

The literature reports show that microbiological infec-tion caused by fungi may be a potential source of oxalicacid in some plants6,7,12,24. In malting, the humidity duringgermination of barley contributes to the development ofmicroorganisms colonizing the grain and some fungi maybe able to synthesize oxalic acid22.

In recent years, new varieties of malting barley havebeen introduced, but there is little information on theirlevels of oxalic acid. A few authors5,7have reported thatthe content of this acid in malt depends on the variety,growing conditions and the malting process.

MATERIALS AND METHODS

Materials

Samples of spring malting barley varieties harvested in2005, currently registered and cultivated in Poland, werethe materials for the study.Three varieties (Jersey, Pres-tige and Sebastian) were investigated. These were grownin various parts of Poland, namely in the region of Pozna(Wielkopolska), in West Pomerania, in Lower Silesia andin the region of Zamo(Zamojszczyzna).

Micromalting procedure

The samples were malted in laboratory scale maltingsat our institute using as a basis standard method 2.5.3.1 asdescribed in the MEBAK methodology10. The procedurewas slightly modified as to steeping and germination tem-peratures and time, to come nearer to industrial scale con-ditions. Steeping with aeration was performed until thewater content in the various samples reached 41%, 43%and 45% according to the following: 1 day 5 h flood and19 h air rest, 2 day 4 h flood and 20 h air rest, 3 day

Department of Beer, Malt and Pro-health Food Technology, Institute

of Agricultural and Food Biotechnology, 36 Rakowiecka St., 02-532

Warsaw, Poland*Corresponding author. e-mail: [email protected]

Publication no. G-2011-0218-1075

2011 The Institute of Brewing & Distilling


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68 JOURNAL OF THE INSTITUTE OF BREWING

water spray to obtain grain moisture in the air phase. Thesteeping and germination temperatures of parallel maltedsamples were 1415C and 1819C. Samples for kilningwere taken after 4, 6 and 8 days of germination. Themalting was then terminated using an increasing kilningregime of 50C 16 h, 60C 1 h, 70C 1 h and 80C 5 h for a total 23 h. Dried samples were stored for furtheranalysis.

Mashing procedureMalt (50 g) was milled on a DLFU grinder (Bhler-

Miag, Germany) using a fine grind (0.2 mm) and a coarsegrind (1.0 mm). Laboratory-scale mashings were carriedout in a mashing bath LB 12 Electronic (Lochner La-bor+Technik, Germany), programmed according to theEBC method 4.5.12and heated to 45C prior to insertionof the beakers. Each beaker contained 50 g of ground maltand was mashed-in with 200 mL of deionised water, lead-ing to a net mashing-in temperature of 45C. The mashingapparatus set the stirrers in motion and maintained a con-stant mashing temperature for 30 min. Thereafter, themash temperature was increased at a rate of 1C/min until70C. Deionised water (100 mL) previously heated to

70C was dispensed into each beaker, and the mash waskept for a further 60 min at that temperature. After mash-ing, the contents were cooled for a period between 10 and15 min. The contents were adjusted to 450 g by the addi-tion of cold deionised water. Filtration was performedusing Whatman No. 1 fluted filter paper.

Oxalic acid standards

The oxalic acid standard was obtained from Fluka(Switzerland) in a crystalline powder form. A stock solution(250 mg/L) was prepared by dissolving 0.3 g of oxalic aciddihydrate in 1,000 mL of deionised water. The solution wasleft overnight at room temperature to ensure complete dis-solution of the crystalline oxalic acid. A standard stock

solution of oxalic acid, in volumes of 0.5, 5, 10 and 15 mLrespectively, was transferred to four 100 mL volumetricflasks. The flasks were filled with water to the mark, andthe working solutions were used to calibrate the standardcurve in the chromatographic analysis. Standard stock andworking solutions were prepared for each analysis.

Chemicals for HPLC analysis

All reagents were of analytical grade and were obtainedfrom POCh (Poland), except for gluconic acid (50% aque-ous solution) for synthesis which came from Merck (Ger-many) and acetonitrile HPLC from Lab-Scan (Ireland).Lithium borate/gluconate eluent was prepared according tothe procedure of Waters (USA). Boric acid, lithium hy-

droxide monohydrate, gluconic acid and glycerine, fromwhich the lithium borate/gluconate concentrate was pre-pared, were first dissolved in deionised water. The concen-trate can be stored for up for 6 months at room temperature.The mobile phase was a lithium borate/gluconate con-centrate and acetonitrile solution in deionised water (pH8.5). The mobile phase was filtered through a 0.45 mmembrane filter (Millipore, USA). Eluent was prepared foreach analysis. In all analytical steps, highly purified (de-ionised) water generated by an automatic system of demin-eralization from EuroWaters (Denmark) was used.

Sample preparation

The barley sample (ca. 20 g) was milled (coarse grist)on a Miag grinder (Miag, Germany) and malt samples ona disc mill (Bhler-Miag, Germany) using a fine grind (2mm). Deionised water at room temperature (50 mL) wasadded to 10 g of flour in an Erlenmeyer flask (100 mL)and acidified to pH 2 using 1.0 M HCl. The mixture washomogenized for 2 min (17,500 rpm) on an Ultra-TurraxT25 Basic (IKA-WERKE, Germany). Then the flask con-taining a magnetic stirring bar was tightly capped andcontents were stirred for 15 min (50C, 1,000 rpm). Theextract was cooled to room temperature and centrifugedfor 15 min at 20C (14,000 rpm) in MPW 375 (MPWMed. Instruments, Poland). The supernatant (ca. 23 mL)was filtered through a 0.45 m syringe filter (Waters,USA) prior to injection onto the HPLC column. The wortsample (20 mL) was pipetted into a 100 mL Erlenmeyerflask and 1.0 M HCl was added to promote dissolution ofthe calcium oxalate for the determination of total oxalicacid. The flask was tightly capped and placed for 15 minin an ultrasonic bath (Polsonic, Poland). Hydrochloricacid extract of wort was filtered through a 0.45 m sy-ringe filter (Waters, USA). The prepared samples of bar-ley, malt and wort were placed into autosample vials andcapped for analysis.

Determination of oxalic acid in barley, maltand wort

Barleys, malts and worts were analysed for their oxalicacid content using the HPLC method with conductometricdetection, according to the modified MEBAK method3.10.211, using a Waters HPLC system (Alliance 2695Separations Module, 432 Conductivity Detector, oven ofcolumn controlled by a 2414 Refractive Index Detector).Purified extracts (10 L) were separated using an IC-PakA HR column (75 mm 4.6 mm 6 m) preceded by a

guard column of the same packing material (Waters,USA). The column was maintained at 35C and elutedwith a mobile phase (lithium borate/gluconate) at a flowrate of 1.0 mL/min. Peak detection was determined usinga conductivity detector operated at a sensitivity setting of10 S full-scale deflection. The results were integratedand analyzed by Empower2 software (Waters, USA).

Other analytical methods

Barley samples were also analysed for their maltingquality. The moisture, sizing of grains, germination powerand germination capacity were determined according tothe Polish standard PN-R-74110:199817. General proteinin malting barley by the Kjeldahl method was analysed

according Polish standard PN-A-04018:197513. The labo-ratory scale malts and worts were analysed according tothe Polish standards on fine grind and coarse grind ex-tracts15, total and soluble proteins (Kolbach index)16 andfriability of malt14. The malting yield, i.e. the percentageratio of the amount of malt produced to the amount ofbarley used, was calculated on a dry matter basis.

Statistical analysis

All analyses were performed at minimum in duplicate.The mean and standard deviations for each analysis were


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VOL. 117, NO. 1, 2011 69

calculated and reported. Statistical analysis of results wasperformed using the Version No. 6.0 of software STATIS-TICA. A Students t-test was used to interpret the differ-ences between the results of the oxalic acid content forsamples of barley, malt and laboratory wort. Probability() values of 0.05 were considered significant. Correla-tion analysis was performed aiming at the qualification oflinear dependence among two sets of data. The Pearsonscorrelation coefficient accepts the values in the range

from 1.0 to 1.0 exclusively.

RESULTS AND DISCUSSION

Method performance

The ion chromatographic assay was linear in the rangeof 1.2537.5 mg/L oxalic acid in a standard solution forwort, and was in the range of 5.0165.0 mg/kg for barleyand malt. The coefficient of variation obtained by inject-ing samples of barley, malt and wort at three levels ofoxalic acid content for the seven injections was 6.3%,7.1% and 1.8%, respectively. Recovery with the HPLCmethod of determination of oxalic acid in samples of bar-ley, malt and wort was under 100%. The lowest recovery

was obtained for the malt (approx. 82%), and the highestfor wort (approx. 92%). Figure 1 shows a typical chroma-

togram of an autosampler injection of a diluted malt sam-ple.

Quality parameters and oxalic acid content ofbarley, malt and wort

All barley samples, prior to their use for malting, wereanalysed to ascertain their malting quality, which in allcases proved satisfactory (Table I). Humidity, according tothe Polish standards, was normal for good malting barley,

germinative energy was up to around 98%, protein contentwas at the proper level, i.e. between 9.3 and 11.4% d.m.basis, grading (fraction 2.5 mm) was above 88.2%, up to96.2%.

The oxalic acid content in the barleys is shown in TableII. The lowest oxalic acid level among barley samples,17.2 mg/kg d.m. basis, was found in the variety Prestigegrown in the region of Pozna. The highest level, 66.8mg/kg d.m., was in the Sebastian variety barley grown inthe region of Zamo (S.-E. part of Poland). Most of in-vestigated barley samples showed an oxalic acid contentbetween 39.5 and 65.3 mg/kg d.m. Compared to datacited by Wagner23, the oxalic acid content found in ourbarley samples seems to be quite low. Among most, with a

confidence level ranging 95%, there were substantial sta-tistical differences within the same variety.

Fig. 1. Typical chromatogram of separation of diluted malt extract.

Table I.Selected quality parameters of malting barley harvest in 2005.

Barley variety PRESTIGE JERSEY SEBASTIAN

Growth region

Region of

Zamo

West

Pomerania

Region of

Pozna Lower Silesia Region of Zamo Lower Silesia

Germinative energy (3 days), % 97 90 90 89 90 95Germinative energy (5 days), % 98 93 93 91 91 97Moisture content, % 12.4 13.4 14.0 13.0 13.1 12.9Total proteins, % d.m. 9.3 10.2 11.4 10.2 9.4 10.3Sizing of grains (2.5 mm), % 96.2 94.6 88.2 92.4 93.5 90.9


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Analysis of the mean air temperatures and total pre-cipitation in 200521 indicates that the region of Pozna(mean: 9.2C; 496 mm) and Lower Silesia (mean: 9.2C;529 mm) were in comparison to West Pomerania (mean:8.2C; 668 mm) and region of Zamo(mean: 8.3C; 771mm) characterized by higher average temperatures andless rainfall. Therefore, it appears likely that warmer andless humid areas are favourable for the cultivation of bar-ley with a lower oxalic acid content in the grain; examples

are the barley varieties Prestige from the regions ofPoznaand Sebastian from the Lower Silesia. This sug-gests that the level of oxalic acid in barley may depend onclimatic conditions, as well as soil factors, as reported in afew publications57.

Laboratory scale malting of the barley samples men-tioned above was conducted under the following condi-tions: steeping up to 43% of water content and germina-tion 6 days at 14C. In addition to the malting, yield wascalculated. All results indicated good brewing quality pa-rameters i.e., the extract yield ranged between 82.5 and84.4% d.m. basis and the friability value was 8398%.The results are shown in Table III.

The results of the oxalic acid analysis in the malts and

worts were of the most interest for this study and these arepresented in Table II. The lowest level of oxalic acid wasfound in a sample of malt obtained with the variety Pres-tige grown in the region of Zamo (20.4 mg/kg d.m.),and the highest was in a malt of the same variety from theregion of Pozna (40.4 mg/kg d.m.). Consequently onecould assume that the level of oxalic acid in the malt isassociated with malting yield (Table III); the smaller theprocess loss (less rootlets), the less oxalic acid content inmalt. Kanauchi et al.8present a similar point of view.

As for the oxalic acid content in worts, the two ex-tremes were yielded by malt samples from barley grownin the Zamoregion, namely the lowest from the Prestigevariety (8.8 mg/L), and the highest from the Sebastian

variety (16.0 mg/L).The results for the same varieties as

Prestige and Sebastian differed with statistical signifi-cance in both samples of barley and malt, as well as labo-ratory wort.

In the two malt samples, Prestige from the Poznare-gion and Sebastian from Lower Silesia (Table II), the ox-alic acid content was surprisingly higher than in the corre-sponding barley samples. It must be remembered thatoxalic acid is a step link or element in the Krebs cycle andis released during germination9and this may explain the

increase in content. In contrast, in the remaining four maltsamples the oxalic acid content was twofold lower than inthe corresponding barley samples. One can only assumethe same explanation as above, that during the germina-tion processes the oxalic acid content may be variable.

Some authors3,9 have reported the presence of oxalicacid in all plant tissues. However, it is also known thatduring growth, plants can both synthesize and decomposeoxalic acid. It is noted that the enzymes capable of theoxidation and decarboxylation of oxalic acid, such as ox-alate oxidase and oxalate decarboxylase, occur in plants.Consequently one could assume that during the germina-tion of barley, that oxalic acid is accumulated in rootlets.To some extent this is shown as well by the increase of

oxalate oxidase activity in germinating seeds3,8,9,18. Thiscould also explain the decrease in oxalic acid content insome samples of kilned malt whose rootlets were alreadyremoved, as well as by the partial oxidation by the en-zyme8.

During barley germination there is also a growth of mi-croorganisms including moulds. alikan and Cuming3reported that some moulds produce oxalic acid and re-lease it to the environment. This may contribute as well tothe increase of oxalic acid content in the malt.

The oxalic acid content in malt and wort andtime of germination of barley

The effect of time of germination of barley on the con-

tent of oxalic acid in malt and laboratory wort was investi-

Table III.Physicochemical parameters of malt samples from various crop regions in Poland obtained during the malting process.*


Growth regionRegion ofZamo

WestPomerania

Region ofPozna Lower Silesia Region of Zamo Lower Silesia

Extract fine grind, % d.m. 83.8 82.5 83.4 82.9 84.4 83.4Extract difference, % 0.2 0.9 3.2 1.1 0.9 1.1Total protein, % d.m. 8.8 10.1 10.6 9.3 8.6 9.5Wort soluble protein, % d.m. 4.70 4.56 4.69 4.75 4.72 4.77Kolbach Index, % 53 47 44 51 55 50Friability, % 96 92 83 94 98 90Malting yield, % 89.4 91.5 93.2 90.8 86.6 89.9

* Malting parameters: humidity 43%, germination 6 days, temperature 14C.

Table II.Oxalic acid content in samples of barley from various growing regions in Poland, as well as in the malts and worts.*


Growth region

Region of

Zamo

West

Pomerania

Region of

Pozna Lower Silesia Region of Zamo Lower Silesia

Oxalic acid in barley, mg/kg d.m. 39.5 1.0a 65.3 1.1b 17.2 0.5c 60.6 1.5b,d 66.8 2.5d,e 17.3 0.4b,c,f

Oxalic acid in malt, mg/kg d.m. 20.4 1.4a 34.0 1.3b 40.4 0.2c 27.4 0.4d 28.4 0.2d,e 35.9 0.6b,f

Oxalic acid in wort (per wort8.6Plato), mg/L 8.8 0.4a 12.5 0.2b 14.2 0.4c 11.1 0.2d 16.0 0.2e 13.2 0.5b,c,f

* Values in rows followed by the same letter are not significantly different at a confidence level of 95%.


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gated on the samples of the barley variety Prestige fromthe region of Zamoand the variety Sebastian of LowerSilesia. Data is shown in Fig. 2.

Table IV presents the results of the physicochemicalquality of the malts produced from selected samples ofmalting barley varieties and malting yield.

Malts obtained under equal conditions of laboratorymalting were similar and conformed to standard quality.Their friability was quite high (above 80%), and the Kol-

bach index sometimes a bit too high or even flatly overrun(4453%). Better qualities were shown in malts obtainedfrom the barley variety Prestige grown in the Zamo re-gion. Remarkably the malts obtained from barley varietySebastian, grown in Lower Silesia region, were twice asrich in oxalic acid, compared to malts from the varietyPrestige grown in the Zamoregion.

Generally, it was observed that germination for 6 days,compared to samples that were germinated for 4 days,contributed to a decrease in oxalic acid in the malt. How-ever, contrary to expectation, the longer germination time,up to 8 days, did not contribute to a further decline. Thedrop in oxalate content observed in day 6 of the germina-tion could be the result of simultaneous growth of oxalate

oxidase activity as well as of the transfer of oxalic acid tothe rootlets. The accumulation in day 8 may be the result

of slowing of both these processes. Such fluctuations ofenzyme activity during germination are normal1.

The extension of germination time from 6 to 8 dayswas followed in the Sebastian variety from Silesia with anincrease in oxalic acid content from 35.9 to 49.1 mg/kgd.m. Similar results were obtained for the Prestige variety.It is assumed that this phenomenon may be linked withthe decrease of activity of oxalic acid oxidase at the endof the germination period. This finding does not conform

to other data from the literature8, but the germinating bar-ley kernel is a living organism and its physiology can varywith even slightly changing conditions.

Data from Table IV and Fig. 2 show that with the in-crease of enzyme activities linked to malt modification,i.e. endo--glucanases, proteases and amylases, some de-crease of oxalic acid content in related worts was ob-served. This is difficult to explain as there are many fac-tors involved.

The temperature of germination of maltingbarley grains and oxalic acid content in maltand laboratory wort

The effect of temperature of germination on the oxalic

acid content in the malt and wort was also studied. Qual-ity parameters of malts from the Prestige and Sebastianvarieties, harvested in the Zamo region and malted attwo different temperatures, are presented in Table V. Thecorresponding content of oxalic acid in the barley andmalt (mg/kg d.m.) and in the wort of 8.6Plato (mg/L), areshown at the Fig. 3.

These data show substantial differences in the oxalicacid content between the samples of both barley varietiesgerminated at the two different temperatures. The Sebas-tian variety malted at 14C, contained 28.4 mg/kg d.m.,which was 9.3 mg/kg d.m. less than in the sample germi-nated at 18C. For the Prestige variety, non-substantial butcontrary differences were found. As expected, malts ger-minated at a lower temperature were characterized byslightly better quality and by a lower malting loss than thesamples malted at 18C.

The level of steeping of barley and oxalic acidcontent in malt and wort

Malts produced from the barley variety Prestige, har-vested in the Poznaregion, were studied to determine ifthere was a correlation between the degree of steeping,

Table IV.Quality parameters of malt samples depending on germination time of varieties Prestige from the region of Zamoand Sebastian of LowerSilesia.*

Barley variety PRESTIGE SEBASTIAN

Growth region Region of Zamo Lower Silesia

Malt germination, days 4 days 6 days 8 days 4 days 6 days 8 days

Extract fine grind, % d.m. 83.9 83.8 84.1 83.6 83.4 83.5Extract difference, % 0.5 0.2 0.5 1.7 1.1 0.8Total protein, % d.m. 9.0 8.8 9.0 9.8 9.5 10.0Wort soluble protein, % d.m. 4.41 4.70 4.46 4.50 4.77 4.42Kolbach Index, % 49 53 50 46 50 44Friability, % 87 96 95 82 90 90Malting yield, % 91.3 89.4 91.3 91.5 89.9 90.4

* Malting parameters: humidity 43%, temperature of germination 14C.

Fig. 2. Oxalic acid content in barley, malt and wort, with threegermination times using the barley varieties Prestige from regionof Zamoand Sebastian of Lower Silesia (steeping of barley upto 43% humidity, temperature of germination 14C). Values fol-lowed by the same letter are not significantly different at a con-fidence level of 95%.


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measured by water content in barley after this operation(an important malt quality parameter) as well as the oxalicacid content in the malt and wort. The results are shown inFig. 4 and Table VI.

The highest level of oxalic acid was found with asteeping degree of 45%. In general, the steeping degreewas of little impact on the oxalic acid level in malts andworts. A statistically significant difference (0.05) wasfound between samples of steeping degree 41% and 45%.The content of the oxalic acid in the wort also differedsignificantly.

The test correlation between the oxalic acid

content in barley, malt and wortTest results of one variant of this study (humidity

43%, temperature 14C, germination 6 days) andother samples (unpublished data) indicated a relationshipbetween the content of oxalic acid in the barley, malt andlaboratory wort.

The data show a strong degree of dependence betweenthe amount of oxalic acid in the malt and its content inwort. For these data sets of variables, a high positive cor-relation was obtained, indicated by Pearsons factor (rxy=0.793). The dependence was statistically significant at aconfidence level of 95%. As would be expected, there wasa positive linear dependence between the increase of ox-alic acid content in barley, malt and resultant wort (Table

VII).

CONCLUSIONS

The quantitative determination of oxalic acid contentin barleys, malts and worts was possible due to use of anHPLC method with conductometric detection. Good pre-cision and good repeatability characterized the resultsobtained using this analytical method. The oxalic acidcontent in samples of the same barley variety, comingfrom various regions of Poland, differed significantly. No

Table V.Quality parameters of malt samples depending on temperature of germination ofvarieties Prestige and Sebastian from the region of Zamo.*

Barley variety PRESTIGE SEBASTIAN

Growth region Region of Zamo Region of Zamo

Temperature of germination, C 14C 18C 14C 18C

Extract fine grind, % d.m. 83.8 83.2 84.4 83.0Extract difference, % 0.2 0.5 0.9 0.2Total protein, % d.m. 8.8 8.9 8.6 9.0Wort soluble protein, % d.m. 4.70 4.15 4.72 4.49

Kolbach Index, % 53 47 55 50Friability, % 96 97 98 97Malting yield, % 89.4 88.0 86.6 86.4

* Malting parameters: humidity 43%, germination 6 days.

Fig. 3.Oxalic acid content in samples of barley, malt and wortwith two temperatures of germination using the barley varietiesPrestige and Sebastian from cultivation of the region of Zamo(humidity 43%, germination 6 days). Values followed by thesame letter are not significantly different at a confidence level of95%.

Table VI.Quality parameters of malt samples depending on steepinglevel of variety Prestige from the region of Pozna.*

Barley variety (Growth region) PRESTIGE (Region of Pozna)

Malt steeping level, % 41% 43% 45%

Extract fine grind, % d.m. 81.3 83.4 81.2Extract difference, % 1.3 0.9 0.5Total protein, % d.m. 10.6 10.6 10.8Wort soluble protein, % d.m. 4.57 4.69 4.17Kolbach Index, % 43 44 39

Friability, % 83 85 86Malting yield, % 92.5 93.2 90.8

* Malting parameters: temperature of germination 14C, germination 6days.

Fig. 4.Oxalic acid content in samples of malt and wort obtainedfrom malting barley variety Prestige grown in the region ofPozna, depending on steeping level (temperature 14C, germi-nation 6 days). Oxalic acid content in sample barley - 17.2mg/kg d.m. Values followed by the same letter are not signifi-cantly different at a confidence level of 95%.


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influence of barley variety on the oxalic acid content in

malt was confirmed. The most important quantities ofoxalic acid were found in the laboratory worts obtainedfrom malts of the Sebastian variety. Steeping (attainedhumidity) and the temperature of malt germination ap-peared to have little influence on the oxalic acid level inmalts and worts. Laboratory worts obtained from maltsgerminated at 18C were poorer in oxalic acid contentthan malts germinated at 14C. A high linear positive cor-relation between the oxalic acid content in malts andworts was observed and these dependencies were statisti-cally significant.

REFERENCES

1. Agu, R. C. and Palmer, G. H., The effect of temperature on theendosperm modification of sorghum and barley during malting.Process Biochem.,1997, 32,501-507.

2. Analytica EBC 4.5.1 Extract of Malt: Congress Mash, Fachver-lag Hans Carl: Nrnberg. 2004.

3. alikan, M. and Cuming, A.C., Spatial specificity of H2O2-generating oxalate oxidase gene expression during wheat em-bryo germination. Plant J., 1998, 15,165-171.

4. alikan, M., The metabolism of oxalic acid. Turk. J. Zool.,2000, 24,103-106.

5. Havlov, P., ernoch, I., Prma, J. and Mikulkov, R., Oxalatecontent in a barley caryopsis, in malt and beer (Abstract 4thInternational Symposium on Brewing and Malting). Kvas.Prm., 2004, 50(7-8),198-212.

6. Havlov, P., Lancov, K., Vov, M., Havel, J. and Hajlov, J.,The effect of fungicidal treatment on selected quality parame-

ters of barley and malt. J. Agric. Food Chem., 2006, 54, 1353-1360.

7. Jacob, F., Calcium-oxalic acid technological importance.Brauwelt Int., 2000, 18, 58-59.

8. Kanauchi, M., Milet, J. and Bamforth, C. W., Oxalate and ox-alate oxidase in malt.J. Inst. Brew.,2009, 115,232-237.

9. Libert, B. and Franceschi, V.R., Oxalate in crop plants. J. Agric.Food Chem., 1987, 35, 926-938.

10. MEBAK 2.5.3.1 Kleinmlzung, In: Brautechnische Analysen-methoden. Vol. I, Selbstverlag der Mitteleuropische Brautech-nische: Freising, 1997.

11. MEBAK 3.10.2 Anionen. Bromide, Chlorid, Fluorid, Nitrat,Oxalat, Phosphat und Sulfat in Wasser, Malz, Hopfen, Wrze

und Bier, In: Brautechnische Analysenmethoden. Vol. III,Selbstverlag der Mitteleuropische Brautechnische: Freising,1996.

12. Pellaud, J., Gushing-State of the Art. In: J. De Clerck Chair X.Bacteria, Yeasts and Moulds in Malting and Brewing. 15-18thSeptember 2002, Leuven.

13. Polish standard: PN-A-04018:1975 Agricultural food products.Determination of nitrogen by the Kjeldahl method and express-ing as protein.

14. Polish standard: PN-A-79083-4:1998 Brewery malt. Test meth-ods. Determination of malt friability.

15. Polish standard: PN-A-79083-6:1998 Brewery malt. Test meth-ods. Determination of extract contents, extract difference, maltsaccharificating, wort run-off time and brightness.

16. Polish standard: PN-A-79083-9:1998 Brewery malt. Test meth-ods. Determination of general protein and soluble protein con-tent and Kolbachs number calculating.

17.Polish standard: PN-R-74110:1998 Barley. Test methods.18. Requena, L. and Bornemann, S., Barley (Hordeum vulgare)oxalate oxidase is a manganese-containing enzyme. Biochem.

J., 1999, 343,185-190.19. Sarlin, T., Nakari-Setl, T., Linder, M., Penttil, M. and

Haikara, A., Fungal hydrophobins as predictors of the gushingactivity of malt.J. Inst. Brew., 2005, 111,105-111.

20. Schur, F., Gushing tendency and foam stability. Brauwelt Int.,2001, 19, 302-304.

21. Stan fitosanitarny rolin uprawnych w Polsce w roku 2007 ispodziewane wystpienie agrofagw w 2008. In: Opracowaniezbiorowe. F. Walczak, Ed., Instytut Ochrony Rolin: Pozna2008.

22. Stempniewicz, R. and Witkowska, D., Aktywnoci enzy-matyczne kultur starterowych jako kryterium selekcji szczepwo potencjalnym zastosowaniu w sodownictwie. VIII Szkoa

Technologii Fermentacji pt. Enzymy w piwowarstwie dzi ijutro. 26-29th March 2003, Jamrozowa Polana.23. Wagner, G. J., Vacuolar deposition of ascorbate-derived oxalic

acid in barley. Plant Physiol., 1981, 67,591-593.24. Winkelmann, L., The gushing puzzle a success story.Brauwelt

Int., 2004, 22,343-345.25. Zepf, M. and Geiger, E., Gushing problems caused by calcium

oxalate (1).Brauwelt Int., 2000, 18,473-475.26. Zepf, M. and Geiger, E., Gushing problems caused by calcium

oxalate (2).Brauwelt Int., 2001, 19,420-421.

(Manuscript accepted for publication September 2010)

Table VII.Pearsons linear correlation factors (rxy) between the oxalic acid content in barley, malt and laboratory wort (n= 26).*

Oxalic acid in malting barley Oxalic acid in malt Oxalic acid in wort (8.6Plato)

Oxalic acid in malting barley 1Oxalic acid in malt 0.515* 1Oxalic acid in wort (8.6Plato) 0.729* 0.793* 1

* Statistically significant dependence at 0.05.

the oxalic acid content in selected barley varieties growing in poland, as well as in their malts...

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