WO1995027899A1

WO1995027899A1 - Process for determining the quality of malt

Info

Publication number: WO1995027899A1
Application number: PCT/ES1995/000038
Authority: WO
Inventors: Antonio LÓPEZ GÓMEZ
Original assignee: Universidad Pública de Navarra
Priority date: 1994-04-12
Filing date: 1995-04-10
Publication date: 1995-10-19
Also published as: ES2080688B1; ES2080688A1

Abstract

The invention relates to a process for determining the quality of a malt sample from any cereal, whereby it is required only to measure the water activity of said sample in the balance moisture content of the same. The process is characterised in that the determination of each of the malt quality parameters, which are representative of the status of 'modification' of the malt, is obtained by means of mathematical expressions which relate each of said malt quality parameters with the measurements of water activity and of balance moisture content of the malt sample. This process facilitates considerably the determination of the quality of malt since it does not require the use of complicate and destructive analysis methods, thereby reducing the cost of malt quality control.

Description

DESCRIPTION OF THE INVENTION

Title of the invention:

Procedure to determine the quality of the malt.

Sector of the technique to which the invention relates:

Food technology, Food quality control techniques,

State of the prior art:

The water activity parameter (represented by a) is relatively known in food technology, being its thermodynamic definition (as indicated by Hardman, TM, in an article of his appeared in 1976, in the book "Intermedíate Moisture Foods", by R.Davis , GG Birch and KJParker (Eds.), Of Applied Sci. Pub., London):

a „= P ^ / P ⁰

where P ⁵ ^ is the partial pressure of the water vapor in equilibrium with the solution and P is the vapor pressure of the pure water at the same pressure and temperature of the solution.

For practical purposes an amount called Relative Balance Humidity (HRE) would be defined as:

HRE = (small / ps t) Tp = 1 atm

where F ³ "is the partial pressure of water vapor in equilibrium with the sample in air at a total pressure of an atmosphere and temperature T, P ³ ^ is the partial pressure of saturation of water in air at a total pressure of an atmosphere and temperature T. In this way, if a hygroscopic product is put in contact with the air at atmospheric pressure, and in a closed enclosure and at a certain constant temperature, moisture will be exchanged between the product and air until a time comes when the balance between the two is achieved, and there are no significant changes in either the relative humidity of the air or the moisture content of the product. In this equilibrium situation, the Relative Humidity of the air would be the HRE and expressed as long as one coincides in value with the water activity (a. Therefore, the most used instruments to measure the water activity are those that measure the Relative Equilibrium Humidity (HRE) of a closed space in equilibrium with the food The value of HRE can be measured indirectly using a crystalline material as a resistor.The amount of current that passes through the crystal depends on its degree of hydration and is measured by a simple galvanometer that has been previously calibrated for specified levels of water activity One of these hygrometers is the NOVASINA ^® hygrometer The use and calibration of these types of instruments has been reviewed by Troller, J.

(as indicated by this author in an article of his appeared in

1977, in the journal J. Fd Sci., 42, 86-90). Other types of instruments for measuring water activity in foods have been described by the literature (as indicated by Favetto et al. In an article in the journal J. Fd. Sci., 48, 534-8, 1983; Taylor, JA in another article appeared in the journal Fd. Technology, 15, 536-7, of 1961; L buza et al. in an article appeared in the journal J. Fd. Sci., 37, 154-7, of 1982; Troller, JA in an article in J. Fd. Sci., 48, 739-41, 1983; Prior, BA, in J. Fd. Prot., 42, 668-74, 1979; Rodeel et al., in an article in Fleischwirtsch., 59, 831-6, 1979; Troller, JA, in an article in J. Fd. Prot., 46, 129-34, 1983; Rockland, LB and Stewart , GF, in the book Water Activity: Influence on Food Quality, by Academic Press, New York, published in 1981; and Jowitt et al., In the book Physical Properties of Foods, by Applied Science, London, 1983).

On the other hand, it is also known that there is a relationship between the water content in equilibrium of a food, and the different water activities of it, for a determined temperature, which is called the sorption isotherm, and that can be handled graphically or mathematically. A book of isothermal sorption was published by olf et al. (titled Sorption Isotherms and Water Activity of Food Materials, by Elsevier, published in 1985) and a similar one was published by Iglesias, H. and Chirife, J. (titled Handbook of Food Isotherms, by Academic Press, published in 1982). Labuza, TP (in an article in the book Properties of Water in Foods, Edited by D. Simatos y Muíton, JL, published by Martinus Nijhoff Pub. In 1985) makes an excellent discussion of the ways of "linking" or "union "of the water (food water) in the food and of the chemical and physical factors that affect it. Although the preponderance of the reduction of α in food is attributed to solutes, it has also been shown that relatively insoluble solids can also contribute quantitatively to the value of α in complex systems (as indicated by Chirife et al., In an article in J. Fd. Technology magazine, 20, 773-9, 1985).

In short, the water in a food exerts a vapor pressure, and this will depend on the amount of water present, the temperature and the composition of the food. Salts and sugars will be more influential on water activity than macromolecules such as starch and proteins (according to MJ Lewis, in his book Physical Properties of Foods and Food Processing Systems, published by Hellis Horwood in 1990) .

On the other hand, it is also known that during the malting of cereals an enzymatic breakage of the starchy endosperm of the cereal grain takes place. As indicated in the book by G.H. Palmer, entitled Cereal Science and Technology

(published by Aberdeen University Press, in 1989), during malting, for example, of barley grains, high molecular weight components of endosperm cell walls (β-D-glucans), proteins and granules of large and small starches are partially hydrolyzed

("modified") enzymatically making them more soluble in hot water, so that: (1) the levels and molecular weights of β-D-glucans are reduced during malting; (2) sulfydrylendoproteases and carboxypeptidases attack prolamins and glutelins (barley protein fractions), resulting in soluble nitrogen complexes of polypeptides, peptides and α-amino nitrogen; also, (3) in a "modified" malt about 40% of the protein is solubilized, so that during malting 70-75% of the soluble nitrogen found in the must is produced; and (3) although cereal starch is "modified" only about 10% during malting, it appears that small starch granules are significantly degraded during malting.

It follows that the grain of non-malted cereal (barley, for example) and the grain of the same malted cereal have a different chemical composition and also a different microstructure, which manifests itself in a behavior that is also different from steam sorption of water. That is, water vapor sorption isotherms will be different, for example, for barley - not malted - and malt - malted barley -, and will also be different depending on the quality of the malt - since the different quality of malt will imply a different degree of "modification" of the endosperm, which will correspond to a different chemical composition and a different microstructure as well, as shown in Figures 1 and 2.

Figure 1 shows the adsorption isotherms (for the temperature of 10 ° C) for malt (•) and barley samples

(D). This Figure shows that the adsorption isotherm of barley is quite different from that of barley malt. This is due to the fact that for the same year, (water activity or HRE) of the sample, the malt can absorb more moisture, so that the equilibrium moisture or equilibrium moisture content (^, in kg of water / kg dry matter) of barley malt is greater than that of barley. Figure 2 shows the adsorption isotherms (for the temperature of 30 ° C) for malt (+) and barley (x) samples. It is checked in this figure 2, if compared with Figure 1, that the differences in moisture adsorption - between barley and barley malt - for the same water activity are greater when the temperature increases from 10 ° C to 30 ° C. Therefore, the temperature of 25 ° C has been chosen for the development of this method object of the invention.

In Figures 1 and 2 the adsorption isotherms indicated have been determined by the static gravimetric method, which is described in the book by H. Iglesias and J. Chirife (titled "Handbook of Food Isotherms", and published by Academic Press, from London, in the year 1982). The equilibrium moisture content of the malt samples (h _bs ) has been determined in a vacuum oven (at a pressure below 100 mm of mercury column), and at a temperature of 65 ° C, up to constant weight.

Explanation of the invention.

Technical problem raised:

However, and despite the above, the quality of malted cereals is not determined by measuring water activity (there is no publication that relates the quality of cereal malt to water activity). In fact, many quality parameters of cereal malt are used to determine the state of disaggregation or "modification" of the malt, which involve laborious and destructive methods, with a high level of costs ^• in instruments and labor.

Thus, the purpose of this invention is to simplify, - the determination of the quality of cereal malt, in terms of its state of disaggregation or "modification", by defining a procedure that consists simply of measuring water activity of the sample of malt at a certain temperature, also measure the content of its equilibrium moisture, and determine each of the malt quality parameters - indicators of the state of disaggregation or modification of it - through mathematical expressions that relate each of these malt quality parameters to the previous measures of water activity and moisture content of malt sample balance. In this way there is a laborious procedure that would significantly reduce the quality control costs in the malt factories.

Invention:

Thus, the present invention proposes a method of determining the quality of a sample of cereal malt by measuring the water activity of that malt sample, measuring its equilibrium moisture content and using mathematical correlations between these and the different malt quality parameters, indicators of the modification status of the malt.

The mathematical correlation between the water activity of a malt sample, its equilibrium moisture content and each of the malt quality parameters indicating the status of "modification" of it has been determined as explained below.

On 56 samples of barley malt of different quality the following quality parameters were determined (according to the analytical methods of the European Brewery Convention, Analytica EBC, published in 1987): (1) Extract (of fine and coarse grinding); (2) Limit attenuation; (3) Friability; (4) Vitrosity; (5) Total protein; (6) Soluble protein; (7) Kolbach index; (8) Viscosity; (9) Hartαng index. For each of these malt quality parameters the following variation intervals have been obtained: (the minimum and maximum values found in this collection of different quality malts are given):

Friability: 40.4 (minimum) - 86 (maximum), in% Vitrosity: 2 - 42, in% Extract (fine molt.): 73.08 - 77.14, in% Extract (thick molt.): 69.13 - 75.6, in% Fine-coarse difference: 1.19 - 6.73, in% Limit attenuation: 68.63 - 81.8, in%) Kolbach index : 27.35 - 43.97, in% Hartong index: 28.74 - 45.09, in% Total protein: 10.73 - 12.86, in% Soluble protein: 3.14 - 4.92, in% Viscosity: 1.43 - 2, in mPa.s

The water activity at 25 ° C of all these malt samples has also been determined in NOVASINA ^® Hygrometer (Zürich, Switzerland), with sensor type ICI n ° 2030 and thermostated chamber type TH-2 n ° 529. Once the Measurement of Relative Humidity of Balance was constant over time, it was identified as the water activity (expressed as a percentage) of the sample at 25 ° C, and the moisture content of the sample (as moisture content) was determined equilibrium) in a vacuum oven as indicated above.

The following variation margins have been obtained:

Water activity (in percent) at 25 ° C: 38.7 - 47.1 Humidity (dry basis, in g water / g dry matter): 0.0361 - 0.07262

The results of the different quality parameters for the different malt samples and the corresponding values of water activity at 25 ° C (a ,,, in percent) and humidity (h ^, equilibrium moisture content of the sample, expressed in dry basis), have been adjusted by multiple regression to mathematical expressions of the type:

P = α.ía ² + β- .h _bs ) ² + γ.a ,, + δ.h ^ where:

P = malt quality parameter (Extract, Friability, etc.). a ,, = water activity of the malt sample, at 25 ° C, expressed as a percentage. h _t g = equilibrium moisture content, on a dry basis (g water / g dry matter), of the malt sample. a, β _# γ, δ = regression coefficients.

The statistical treatment of the results was carried out with the Statgraphics statistical package (Statistical Graphics System, version 6.0).

In short, the following expressions have been obtained, which mathematically relate each beer malt quality parameter and the water activity and equilibrium moisture content parameters of the same sample:

EXTRACT (GROSS MDLTÜRACION):

Extract (molt. Gr.) = -0.040799a _w ² +

+ 3.585298a _* - 190.745176 ^ R-SQUARE (Aj) = 0.9996

EXTRACT (FINE MOLTURATION):

Extract (molt.fina) = -0.039774a _* ² - 367.988372h _bs ² ₊ 3.459953a _* + 32.8095541 ^ R-SQUARE (Aj) = 0.9998

LIMIT ATTENTION:

Attenuation Limit = -0.056177a _* ² + 11071.569386 _bs ² + 4.871484a _* - 1151.2195951 ^ ₃ R-SQUARE (Aj) = 0.9987

FINA-GRUESA DIFFERENCE:

Thin-Thick Diff = 0.001136a _* ² - 2186.543277h _bs ² -0.137090a _{* +}

239.2860971 ^ ₃

R-SQUARE (Aj) = 0.8766 FRIABILITY:

Friability = -0.083276a _* ² + 34457.849934h _bs ² + 7.537887a _*

3714.3935811 ^ ₃

R-SQUARE (Aj) = 0.9910

VITROSITY:

Vitrosity = 0.04187a ,, ² 34292.21 ^ ₃ -3.70268a * + 3658.9666141 ^ R-SQUARE (Aj) = 0.8216

TOTAL PROTEIN:

Total protein = -0.007121a _* ² - 114.9695261V ² + 0.563418a _* +

14.17158911 ₁ , ₃

R-SQUARE (Aj) = 0.9988

SOLUBLE PROTEIN:

Soluble protein = -0.003356a _* ² + 801.6373091 ^ + 0.300466a ,, -

R-SQUARE (Aj) = 0.9948

KOLBACH INDEX: Kolbach index = -0.027115a _* ² + 7562.846283h _bs ² + 2.566832a _*

- 824.623718h _b3 R-SQUARE (Aj) = 0.9948

VISCOSITY:

Viscosity = -0.00084a _* ² - 153.124358h _bs ² + 0.068062a _{* +}

14.4540861 ^ ₃

R-SQUARE (Aj) = 0.9958

INDEX HARTQNG: Hartong index = -0.022607a _* ² + ² + 2.166104 _s 5355.342025bi- ^

- 548.5397911 ^ R-SQUARE (Aj) = 0.9932

Embodiments of the invention:

The validity of the method is shown below by exposing three significant examples made with barley malt of different quality. Example 1: What is the value of each of the quality parameters of a barley malt sample with a _* at 25 ° C of 42.10 (expressed as a percentage) and equilibrium moisture content of 0.05831 g water / g dry matter ?.

It has been obtained:

Obtained value Values% valid by means of real ΛFΓΎTÍ expressions obtained (mathematics according to effect)

Analytica-EBC d≥B)

(A) (B)

Total protein 11.53 11.64 0.90

Soluble protein 4.32 4.53 4.46 Extract (coarse molt.) 73.19 71.59 2.24 Extract (fine molt.) 75.83 74.65 1.58 Fine-coarse difference 2.76 3.21 14.0 Hartong index 37.34 37.48 0.30 Kolbach index 37.63 38.96 3.40 Limit attenuation 76.03 74.94 1.46 Viscosity 1.69 1.55 9.50 Friability 70.31 64.8 8.50 Vitrosity 15.08 19.4 22.2

Example 2: What is the value of each of the quality parameters of a malt sample with a _* at 25 ° C of 38.9 (expressed as a percentage) and equilibrium moisture content of 0.06067 g water / g matter dry ?.

It has been obtained:

Obtained value Values% varied by means of real expressions obtained (mathematics according to effect)

Analytica-EBC of B)

(A) (B)

Total protein 11.57 11.37 1.82

Soluble protein 4.25 4.49 5.23

Extract (coarse molt) 72.32 73.26 1.28

Extract (molt. Fine) 75.04 76.04 1.31

Thin-thick difference 2.85 2.94 2.87 Hartong index 36.48 37.49 2.68 Kolbach index 36.62 39.45 7.15

Attenuation limit 75.40 77.20 2.33

Viscosity 1.68 1.71 1.18

Friability 68.69 74.4 7.67

Vitrosity 15.08 14.0 7.77

Example 3: What is the value of each of the quality parameters of a malt sample with a _w at 25 ° C of 45.1 (expressed as a percentage) and equilibrium moisture content of 0.07230 g water / g matter dry ?.

It has been obtained:

Analytica-EBC of B)

(A) (B)

Total protein 11.34 11.06 2.61

Soluble protein 4.59 4.61 0.30

Extract (coarse molt) 73.67 74.43 1.01

Extract (fine molt.) 75.59 76.55 1.25

Thin-thick difference 1.99 2.21 9.56 Hartong index 40.04 43.21 7.32 Kolbach index 40.52 41.64 2.67

Attenuation limit 80.08 79.03 1.32

Viscosity 1.60 1.60 0.00

Friability 82.14 86.0 4.48

Vitrosity 3.46 2.0 73.0

Note: the high% variation obtained for the Vitrosity parameter is due to the fact that the real value (obtained in the laboratory) is relatively small, since it is a very "modified" malt with a high Friability value. But this method gives a very acceptable value of this quality parameter, if it is taken into account that vitrosity can be worth more than 40. Then this procedure of determination of Vitrosity from a _* and h ^ would be very acceptable. Industrial application:

In this way, a procedure for determining the quality of a sample of cereal malt is established, through which a fairly precise value (error of less than 10%) can be obtained from each of the quality parameters of this malt sample - indicators of the state of "disaggregation" or "modification" of malt grain - with the sole measurement of the water activity of this malt sample (at 25 ° C) - with any of the procedures and equipment of sufficient precision mentioned above - and the moisture content in equilibrium of the same malt sample - in a vacuum oven, carrying out the measurement as indicated above -, making use of the mathematical expressions indicated above.

Thus, if you want to determine what will be the value of each of the quality parameters of a malt sample

(indicators of the state of modification of the same), first the value of the water activity of this sample is determined at 25 ° C, taking 7-8 g of sample of this malt to a tightly closed bottle - located in a thermostated chamber at 25 ° C- and connected to a hygrometer to measure the HRE of this sample at this temperature of 25 ° C. Once the HRE of this malt sample is obtained, which is manifested in that the hygrometer measurements are constant, this is taken as the a _* at 25 ° C of this sample, expressed as a percentage. Then, the sample of previous malt contained in the bottle is taken, where equilibrium has been reached, and its moisture content is determined in a vacuum oven (b ^.), Expressed in g water / g of dry matter (moisture in dry base). Then . each of the previous mathematical expressions would be used to determine, from a _{* and} h _bS obtained, - each one gives the quality parameters _, of the malt sample without the need to carry out the laboratory determination of each of these Quality parameters In this way, significant laboratory material savings and significant labor savings can be achieved to determine malt quality. This procedure for determining the quality of a malt sample from the measurement of water activity (a _* ) at 25 ° C and its equilibrium moisture content (b ^) and with the use of mathematical expressions that relate in a very significant way each malt quality parameter - indicator of the state of modification of the malt - with a _* and hj- _s , could be carried out by means of a team like the one shown in Figure 3 .

This equipment would have a thermostated chamber at 25 ° C, indicated as (1) in Figure 3, where several small bottles would be placed, indicated as (2) in Figure 3. These bottles would be containers that can be opened and closed and that in Closed condition would remain completely waterproof. There would be a small bottle for each malt sample, and it would have a capacity of about 7-9 g of malt. In each bottle there would be a Relative Humidity probe (with analog electronic output, for example 10 mV /% RH) connected through an analog / digital card, indicated as (4) in the Figure

3, to a calculation unit that would be a PC computer

(Personal Computer), indicated as (3) in Figure 3. This computer would be equipped with monitoring software

(interpretation of signals received from Relative Humidity probes housed in the little boats) and calculation of each of the malt quality parameters, which would use the mathematical expressions presented above. This software would include appropriate interfaces for requesting the user of the equilibrium moisture content, and for presenting results, being able to create, edit and process data files related to the quality of the malt being determined.

Claims

1. Procedure for determining the quality of cereal malt, characterized by: -measure the water activity and the equilibrium moisture content of the corresponding malt sample, and-obtain the value of different malt quality parameters from mathematical expressions that relate each of these quality parameters to the water and moisture activity values of the sample measured previously.

2. Method according to claim 1, characterized by obtaining the value of the following malt quality parameters: Coarse grinding extract, and / or Fine grinding extract, and / or Thin-coarse difference, and / or Limiting attenuation, and / or Friability, and / or Viscosity, and / or Total Protein, and / or Soluble Protein, and / or Hartong Index, and / or Kolbach Index, and / or Vitrosity.

3. Method according to claims 1 and 2, characterized by measuring the water activity of the malt sample by hygrometric, or manometric or gravimetric methods.

4. Method according to claims 1, 2 and 3, characterized in that the equilibrium moisture content of the malt is determined in a vacuum laboratory oven or in a laboratory oven at atmospheric pressure.

5. Method according to claims 1, 2, 3, and 4, characterized by using samples of barley malt, or rice, or rye, or corn, or wheat, or oats, or sorghum.