SciELO - Scientific Electronic Library Online

 
 issue13Analysis of interphase velocities during directional horizontal solidification of Zn-10%Al alloysViscosity and density of grape juice (Isabella) for process applications author indexsubject indexarticles search
Home Pagealphabetic serial listing  

Services on Demand

Journal

Article

Indicators

  • Have no cited articlesCited by SciELO

Related links

  • Have no similar articlesSimilars in SciELO

Share


Revista de Ciencia y Tecnología

On-line version ISSN 1851-7587

Rev. cienc. tecnol.  no.13 Posadas June 2010

 

INGENIERÍA-TECNOLOGÍA-INFORMÁTICA

Study of ashes and their use to determine twig content in yerba mate

Estudio de las cenizas y su utilización en la determinación del contenido de palo en la yerba mate

 

Liliana R. Ybarra*1, Jorge A. Duce**1, Sylvia A. Bordenave***1, Miguel E. Schmalko****1

*Liliana Rosalba Ybarra. Licenciada en Genética, (FCEQyN, Universidad Nacional de Misiones -UNaM-). Maestrando de la Maestría en Tecnología de los Alimentos (FCEQyN, UNaM). Jefe de Trabajos Prácticos Exclusiva en las Cátedras de Microbiología de Farmacia; Biología General de la carrera de Licenciatura en Genética y Biología de la carrera de Ingeniería en Alimentos. Integrante Investigador categoría IV Programa Nacional de Incentivos. Decreto 2427/93. lybarra@fceqyn.unam.edu.ar.
**Jorge Alberto Duce. Ingeniero Químico, (FCEQyN, Universidad Nacional de Misiones -UNaM-). Magíster en Tecnología de los Alimentos (FCEQyN, UNaM). Profesor Titular Dedicación Semi-exclusiva en la Cátedra de Microbiología de la Carrera de Farmacia y de Microbiología General y de los Alimentos de la carrera de Ingeniería en Alimentos (FCEQyN, UNaM). Director Categoría III del Programa de Incentivos de la Nación a los docentes investigadores. Decreto 2427/93. joduce@fceqyn. unam.edu.ar.
***Sylvia Alicia Bordenave. Profesora de Biología. Facultad de Humanidades (UNaM-Universidad Nacional de Misiones-). Licenciada en Genética (Facultad de Ciencias Exactas, Químicas y Naturales -UNaM-). Especialista en Educación Superior. Facultad de Ingeniería. Oberá (UNaM). Jefe de Trabajos Prácticos Exclusiva de las Cátedras Microbiología General de la carrera de Ingeniería Química y Microbiología de los Alimentos de la carrera de Ingeniería en Alimentos, Ingeniería Química, Farmacia y Bioquímica. Investigador Categoría IV del Programa de Incentivos de la Nación a los docentes investigadores. sab@fceqyn.unam. edu.ar.
****Miguel Eduardo Schmalko. Ingeniero Químico (Universidad Nacional de Misiones). Master en Tecnología Química (Instituto Químico de Sarriá, España). Doctor de la Universidad de Buenos Aires, área Ciencias Químicas.Profesor Titular de Operaciones de Transferencia de Masa y Operaciones y Procesos en la Industria de los Alimentos de la Facultad de Ciencias Exactas, Químicas y Naturales, Universidad Nacional de Misiones. Investigador Categoría I del Programa de Incentivos de la Nación a los docentes investigadores. mesh@fceqyn.unam.edu.ar.
1. Laboratorio de Microbiología de Alimentos y Biotecnología "Dr. Fernando O. Benassi", Facultad de Ciencias Exactas, Químicas y Naturales. Universidad Nacional de Misiones. lybarra@fceqyn.unam. edu.ar, joduce@fceqyn.unam.edu.ar, sab@fceqyn.unam.edu.ar, mesh@ fceqyn.unam.edu.ar.

 


Abstract

In the technique used to determine percentage of twigs in yerba mate (according to Argentinean Food Code), the sample is sieved and separated into three fractions. In the two upper fractions twigs and leaves are separated manually. The lower fraction (<40 mesh per inch), called powder, is considered as leaves because it is very difficult to separate it manually. Previous researchers predicted the twig content in this fraction, using properties that are very different in leaves and twigs (crude fiber, water extract and color parameters). In this research, another property was used in order to predict twig content in the powder: ash content. In order to obtain the calibration line, percentage of ashes were determined in samples prepared with different percentage of twigs. The fitted line had a very high estimate error (± 8.3 % of twig). Using this line, percentage of twigs was estimated in commercial samples. Powder fraction should contribute, additional quantities varying between 0.1 and 11.4 % to twig percentage.

Key words: Yerba mate; Total ashes; Twig percentage; Quality.

Resumen

En la técnica utilizada para determinar el porcentaje de palos en la yerba mate (de acuerdo al Código Alimentario Argentino), la muestra es tamizada y separada en tres fracciones. En las dos fracciones superiores las hojas y los palos son separados manualmente. La fracción inferior (<a 40 mallas por pulgada), denominada polvo, se considera como hoja debido a que es imposible de separar manualmente. Los investigadores trataron de predecir el porcentaje de palos en esta fracción, utilizando propiedades que eran diferentes en las hojas y los palos (fibra cruda, extracto acuoso y parámetros de color). En este trabajo, se trata de predecir el porcentaje de palos en el polvo utilizando otra propiedad, el contenido de cenizas.
Para obtener la línea de calibrado, se determinó el porcentaje de cenizas en muestras preparadas con diferentes porcentaje de palos. La misma tuvo un error de estimación elevado (±8,3 % de palos). Utilizando esta línea, se estimó el porcentaje de palos en muestras comerciales. La fracción de polvo, podría contribuir al porcentaje de palos en cantidades adicionales que varían entre el 0,1 y 11,4 %.

Palabras claves: Yerba mate; Cenizas totales; Porcentaje de palos; Calidad.


 

Introduction

Quality parameters in yerba mate suggested by the Argentine Food Code are: moisture content, caffeine, water extract, total and insoluble ashes, twig percentage and impurities [1, 2, 3].
Some of the analytical techniques in the determination of these parameters are the ones used in numerous highly- technological developed countries, like the determination of water extract, moisture content and, total and insoluble ashes [4].
Other techniques can be considered less accurate (like those for caffeine and twig content). Thus, in the determination of caffeine, the use of Cortés method is suggested instead of chromatographic or spectrophotometric techniques [5, 6].

The use of the screening technique is proposed to determine twig content. The Argentine Food Code [1] suggests the use of the technique that transcribed says: the of 1 x 20 mm and N° 40 openings sieves are used (40 meshes per inch). The fraction retained by the 1 x 20 mm sieve will be considered twig and it should be less than 12.5 % in the analyzed sample weight.
The fraction passing N° 40 sieve will be considered leaf. With an aliquot of the fraction retained in N° 40 sieve coming from successive divisions, twig chips and barks will be separated with pincers and twig content will be quantified in this fraction.
This percentage plus the one retained in the 1 x 20 sieve will constitute the percentage of twig of the analyzed sample.
The disadvantage of this technique is that the ground twig passing N° 40 mesh cannot be detected.
In some cases the ground twigs are used to adulterate yerba mate. The increase of the twig content contributes to yerba mate becoming mild washing out more quickly reducing the quality of the product.
Numerous alternative techniques were studied to determine twig content. One of them was the search for the correlation of water extract and twig content [7]. This technique had good results working with a specific trademark but highly relevant errors were found when samples of trademarks from different origins were used.
A second method studied correlated the content of crude fiber with twig percentage. Good results were found, but this technique had the disadvantage of its long duration and the difficulty for its application in a routine control [8].
A third reported method consisted in measuring color parameters and correlating the twig percentage [9]. The authors found that the color parameter "L" had very good correlation with the twig percentage, but they had a disadvantage similar to that of the technique of water extract, with a not very accurate application as a general measuring method.
Total ashes constitute a parameter of quality in many food products. In some of them like in honey it is used to determine its quality and origin [10, 11].
In vegetables in general the content of ashes varies with the crop season -as in tea- [12] and in the different components of a compound product like bread in which it is used to determine the fractions of bran in the flour [13].
In yerba mate, Bertoni et al. [14, 15] found that the total ashes were different in the leaves and in the twigs and their content depended on the crop season. Great differences in ash content were found between young and old leaves.
Young leaves had lower values than old ones. When the ash content was determined in leaves and twigs, leaves had higher values than twigs.
The objectives of the present work were: to study the relationship between twig
• content and total ashes of yerba mate.
• to apply this technique to determine the twig percentage in different trademarks and the different fractions of the sieved samples.

Materials and methods

Sixty samples of manufactured yerba mate which were purchased in the Argentine Republic in 2004. In each of them the following determinations were carried out: percentage of twig, moisture content and total ashes. Samples were prepared by manually separating leaves from twigs and they were ground in a laboratory hammer crusher, with an output mesh of 1 mm sieve. Then the samples were prepared by mixing different percentages of twigs (between 0 and 100 % each 10 %).
To determine calibration line samples of the fraction retained in the sieve 40 mesh were used and twig and leaves were handled separated.

Twig percentage

To determine twig percentage, the opening 1 x 20 mm and N° 40 sieves were used (40 mesh per inch) [1].
The fraction retained by the 1 x 20 mm sieve was wholly considered twigs. The fraction which passed the N° 40 sieve was considered leaf.
With an aliquot of the fraction retained in the N° 40 sieve coming from successive division's chips and barks of twigs present were extracted with pincers. This way, the quantity of twig was quantified in the fraction.
This percentage together with that retained in the 1 x 20 sieve constituted the twig percentage of the sample analyzed.
When an inter laboratory assay (8 laboratories) was done in order to measure the error of this technique a variation coefficient of 15.8 % was found (Mean value = 18.24 %, Standard deviation = 2.88) [8].

Total ashes

Five g of the ground sample were weighed and heated in a capsule at a temperature of 100 °C until elimination of water [16].
The capsule was placed in the regulated muffle at 525± 25 °C until the ashes were visibly free exempt of carbonaceous film, which took approximately 2 hours.
Then it was cooled down, moistened with water for analysis, evaporated until dryness in a double boiler and then in a heating plate.
The capsule was placed again in the muffle where it was maintained for 60 minutes, cooled down in the desiccators and weighed.
Then the sample was warmed in the muffle during 30 minutes, cooled down and weighed until constant weight. The ashes were determined by difference of weight [17].

Statistical analysis

For the statistical analysis, the program Statgraphics [18] was used. Regression analysis was used to explain the dependence of total ashes content with twig percentage. A variance analysis (one factor) was used to compare total ash content in the different sieved fractions of yerba mate. A frequency distribution analysis was use to analyze the dispersion of total ash content in the commercial samples and in the powder of yerba mate.

Results

Total ashes and twig percentage

First, total ashes content in prepared mixtures (twig and leaves) were determined. With this purpose, mixtures with different percentages of twigs varying between 0 % and 100 % with ranges of 10 % were prepared. The values of the content of ashes varied between 4.14 and 6.63 %.
When a regression analysis was carried out, it was found that the data were fitted to a straight line given by Equation 1:

In this equation "Y" is the content of total ashes in dry basis and "X" is the percentage of twigs. The fit was very significant with p<10-4.
Figure 1 shows the experimental values, the fitted line and its 95 % confidential limits. But when an estimation of the twig percentage from total ashes content is to be made, the estimate error is relatively high, ±8.3 %.


Figure 1. Linear regression of total ashes and twig percentage (g/100 g dry basis)

This relatively high error is mainly due to low value of the slope of the line.
This value is higher than that found by Schmalko et al, [8] where color parameters were used to determine the twig percentage (±4 %) and the one found by Escalada et al, [7] when determining twig percentage using water extract (±4.6 %).

Measures of the commercial samples

First, total ashes of the sixty trademarks of yerba mate were determined (Figure 2).


Figure 2. Frequency distribution of total ashes in commercial trademarks.

The values found varied between 5.70 % and 6.84 %. According to these results and to Equation 1, twig percentages which varied between 44 % and 3 % were determined.
The total ashes of the different sieved fractions of commercial samples were also determined: the one retained in 1 x 20 mesh, the one retained one in 40 mesh, and the fraction that passed mesh 40 or powder (Figure 3).


Figure 3. Total ashes content in different sieved fractions (g/100 g dry solid). Mean values and their confidence interval.

As can be observed, very high differences between fractions retained in 1 x 20 meshes (considered as a twig) and the other two fractions were found.
It is noticeable that total ashes in the fraction retained in 40 mesh is higher than total ashes in the powder (P<0.0004). This unexpected result would indicate contrary the one predicted that the fraction of leaves in that fraction is higher than in the powder.
Ashes in powder fraction In the powder values of total ashes varied between 5.80 % and 6.82 % were found (Figure 4). They were similar to those found in the sample without sieving.


Figure 4. Frequency distribution of total ashes in powder fraction.

Percentage of powder found in the samples varied between 2.8 % and 29.0 %. Using the Equation 1, twig percentage in the powder could be estimated. Contribution of this fraction to the total twig percentage would be between 0.1 % and 11.4 %. This additional contribution to the twig percentage would make many commercial trademarks accepted today, to be rejected because they have higher values than the maximum admitted in the Food Code.
Using this new method, the twig percentage in the commercial samples would vary between 17.4 % and 38.5 %.
Twig percentage could be also estimated using the determination of total ashes in the whole sample. But, in this case the estimation error would be greater, because it is applied to a higher weight (100 % of the sample, instead to the powder, a fraction lower than 20 %).
This suggestion was already made in the IRAM 20514 Standards [8] where crude fiber content is used to estimate the twig percentage.

Conclusions

When this study of total ashes content in mixtures of twig and leaves of yerba mate was carried out, it was found that the variations could be explained with a straight line. This fit was statistically significant.
If the line fitted was used to estimate twig content with the total ashes value, the estimations error is relatively high: (±8.3 %).
When total ashes in the commercial samples were determined and these values were used to estimate twig content atypical values were obtained.
If this method is used to determine twig percentage in powder, values between 0.1 % and 11.4 % are found, which should be added to twig percentage determined with the method reported in the Argentine Food Code. The use of this methodology is recommended to determine the total twig percentage in the sample.

References

1. Código Alimentario Argentino. Artículo 1194-1198. Ediciones La Rocca. Buenos Aires: p. 348-349. 2000.         [ Links ]

2. Código Alimentario Brasileño. Portaría, M S Nº 519. Cha Maté e outros Chás- Anexos: Reglamento Técnico para fixacao de identidades e qualidade de chás-plantas desinadas a preparacao de infusioes ou decocoes: p. 74-81. 1998.         [ Links ]

3. INTN . Instituto Nacional de Tecnología y Normalización. Norma Paraguaya. 3.500.193 yerba mate. Especificaciones. Segunda Edición. Asunción. Paraguay. 1995.

4. AOAC (Association of Analytical Chemists) "Official Methods of Analysis". Gaiterburg Maryland 16 th Edition. 1995.

5. IRA M 20512. Instituto Argentino de Racionalización de Materiales. yerba mate: determinación del contenido de cafeína. Método por cromatografía líquida de alta resolución. 2003.

6. IRA M 20513. Instituto Argentino de Racionalización de Materiales. yerba mate: Determinación del contenido de cafeína. Método por espectrofotometría en el ultravioleta. Método de referencia. 1998.

7. Escalada, M. A.; Schmalko, M. E. y Kanzig, R. G. El extracto acuoso como una medida del contenido de palos en la yerba mate. Rev. Ciencia y Tecnología 1: p. 40-44. 1998.

8. IRA M 20514. Instituto Argentino de Racionalización de Materiales. Yerba mate: Determinación del contenido de palo. 2005.

9. Schmalko M.E. et al El color como una medida del porcentaje de palos en la yerba mate. Actas Congreso CYTAL. Ciencia y Tecnología de los Alimentos. 2005.

10. Popek, S. A procedure to identify a honey type. Food Chemistry 79: p. 401-406. 2002.

11. Amin Wafaa A., Safwat M., El-Iraki Samir M. Quality criteria of treacle (black honey). Food Chemistry 67: p. 17-20. 1999.

12. Ravichandran R. The impact of pruning and time from pruning on quality and aroma constitutents of black tea. Food Chemistry 84: p. 7-11. 2004.

13. Sidhu Jiwan S., Al-Hooti Suad N., Al-Saqer Jameela M. Effect of adding wheat bran and germ fractions on the chemical composition of high-fiber toast bread. Food Chemistry 67: p. 365-371. 1999.

14. Bertoni M.H. et al Hojas frescas de Ilex paraguariensis Saint Hill II. Composición química general en función del grado de desarrollo (joven, intemedio y maduro) y de la época de cosecha para tres clones. An. Asoc. Quim. Arg. 80: p. 75-80. 1992.

15. Bertoni M.H. et al Hojas frescas de Ilex paraguariensis Saint Hill III. Influencia de las distintas etapas del proceso tradicional de elaboración de yerba mate (sapecado, secado + canchado y estacionamiento) sobre la composición de hoja fresca del clon 44/75 cosecha 1988. An. Asoc. Quim. Arg. 80: p. 493-501. 1992.

16. IRA M 20503. Instituto Argentino de Racionalización de Materiales. yerba mate: Determinación de la pérdida de masa a 103ºC. 1995.

17. IRA M 20505. Instituto Argentino de Racionalización de Materiales. Determinación de las cenizas totales. 1995.

18. STATGRAP HIC S PL US (VER SIÓN 7 FOR DO S) STATGRAPHICS. User Manual. Manugistics,Inc. Rockville, Maryland. USA. 1993.

Recibido: 06/07/07.
Aprobado: 04/06/10.

Creative Commons License All the contents of this journal, except where otherwise noted, is licensed under a Creative Commons Attribution License