Introduction

The non-timber forest products are a resource that has been ignored by decision makers, as there are great difficulties in developing systems plantation, production, harvesting and harvesting as well as mechanisms to encourage commercialization and sustainable use. Shrub communities in arid and semiarid regions have been called together as desert scrub and occupy about 40% of the land area ( ^{HYPERLINK \l "mkp_ref_011"} ). The amount of non-timber species used is very small however have such potential and diversity that stands as a sustainable economic development alternative for the people.

This vegetation type is used in construction and for making textiles, fuel, food, medicinal and ornamental plant. Some species have been subject to intensive exploitation by trade and industry, which has affected the natural density of this ecosystem and endangered species some species. Paradoxically, many resort owners consider worthless, so they do indiscriminate removal. Proper use of renewable natural resources is one of the problems that most concern today, hence the need to recognize widely uses that may have the species and address problems related to management and conservation ( ^{HYPERLINK \l "mkp_ref_005"} ). The multipurpose trees are one of the essential components of any agroforestry system, so it is important to know the native species of each region, such as arid and semiarid areas of the country.

The mesquite (Prosopis laevigata) and huizache (Acacia farnesiana) are two of the most frequent and overexploited species, which can get a lot of products such as f lour, honey, rubber, coal, medicine, crafts and food. Seize rationally through research, to define appropriate uses, development programs, maintenance and operation, would improve the standard of living of the inhabitants of the arid and semiarid regions ( ^{HYPERLINK \l "mkp_ref_003"} ). Gums mesquite and huizache can be an input of the cosmetic, medical and food industries, and could reduce the high demand has gum arabic, presenting an alternative for industrial use ( ^{HYPERLINK \l "mkp_ref_009"} ).

An advantage of the first is that its production involves not cut the whole tree. Currently, the rubber of the species mentioned occurs in the north, where it is collected empirically: only exuded naturally, no silvicultural production method is applied. This research includes a proposal to implement a system of collection of the gum with the support of a hormonal treatment based on ethylene stimulates tree physiology, which results in the acceleration of the secretion of rubber. The experiment was conducted in an agroforestry plantation INIFAP-Campo Experimental Bajío de Celaya, Guanajuato.

The aim is to maximize use of resins Prosopis laevigata and Acacia farnesiana replacing gum arabic is currently used in the market as a natural food preservative. Kader et al. (2006) have conducted studies of biochemical composition of gum arabic and Acacia spp. and Prosopis spp. finding important similarities. This study aims to generate low-cost technology for extracting and mesquite gum huizache and thereby provide an alternative productive development in agroforestry systems and seasonal zones.

Materials and methods

This research was conducted in two phases: cabinet and field. The first involved the review of literature throughout the process of research and/or experimentation. The field was divided into stages as: location and general characteristics of the experimental area; plantation management and experimental units, experimental design and analysis; application of treatments in the field; and finally gum collections and analysis.

The work was developed in the Experimental Bajío (CEBAJ) belonging to the National Institute of Forestry, Agriculture and Livestock (INIFAP), located at km 6.5 of the highway Celaya-San Miguel de Allende s/n, col. Roque Celaya, C. P. 38110, Celaya, Guanajuato.

The CEBAJ coordinates are 20° 32' north latitude and 100° 48' west longitude, altitude of 1 752 meters above sea level; precipitation and average annual temperature is 19.8 °C and 578 mm, respectively (Guanajuato Produce, 2012). The drought period comprising from november to may; june first rain falls and the highest temperature recorded year. The highest rainfall recorded in july, although it is considered low compared with southern regions of Mexico. The soil is classified as vertisol, loamy texture, pH 7.8, containing organic matter 2.31%, nitrogen N 5.6 mg kg^-1, phosphorus P 12.3 mg kg^-1 and potassium K, 1 016 mg kg^-1.

Figure 1 Location of area CEBAJ-INIFAP. 

The experimental agroforestry INIFAP Bajío area of Celaya, has several plots with different native tree species of semiarid Mexican. Agroforestry plantations have 10 years of establishment in the experimental field, no management, exposed to the natural conditions of the semiarid own environment. The area where the three blocks are located mesquite is called batch 26 of the experimental field of Bajío. In another area of the lot 34 experimental field, called Arboretum, where huizache is located.

Each block has dimensions mesquite 12 m x 15 m, with a spacing of 6 m between groove and 3 m between individual; each block has 15 individuals for a total of 45 that were sampled. Meanwhile, the blocks have a dimension huizache 6 m x 15 m, with a spacing of 3 m between rows and 3 m between individuals; each plot has 15 individuals, of which 12 sampled only because in each plot were three other individuals involved in experimentation; therefore, the experiment was conducted with a total of 36 individuals. During the field phase characteristics as similar as possible to the sampling units (Vernon et al., 2000) were considered. From approximately 0.6 m from the base of the main stem the incision where the treatment was performed,

The trees ranged from 0.08 to 0.13 m diameter and height 2.5 to 5 m, so an optimal category diametric and favorable for the use of both species (mesquite and huizache) height was considered. A caliper or diameter tape and a ruler or estadal of 2 m was used for this activity. As for the secondary branches, wounds were made at chest height. The phenological state of both agroforestry plantations was observed, considering that they were awakening from their winter dormancy. In general stressed trees were found, no large amount of foliage without efflorescence.

The experimental design was randomized blocks (DBA), with five treatments, three repetitions and three sample treatment units (tree). Later in that same way (random) was performed for each of the blocks and/or repetitions of each of the species studied different treatments. For statistical analysis program SAS, version 9.3 with DBA was used. After recording the observations, diameter, height and phenological state, he continued to the implementation of treatments:

T1= exudate naturally (witness)

T2= incision with application in ethylene concentration to 10% (Wilde, 1971), in main trunk to 0.6 m from the base

T3= incision with application of ethylene concentration to 10% (Wilde, 1971), secondary branch

T4= incision main trunk to 0.6 m from the base, without hormone application.

T5= secondary branch incision without hormone application.

The application of the treatments was performed once. To mesquite on March 20, 2012 and huizache the next day, when the trees begin to awaken from their winter dormancy. It was labeled to each individual or experimental unit (tree) with their respective randomized treatment.

A chisel and a hammer drilled to a depth of approximately 1 cm to not interfere negatively on the flow of water and nutrients from the tree was used for the incision or wound on the main trunk or secondary branch. The incision is made at an angle of 45 °C. the 3ml syringe needle was also used, a container, ethylene (ethrel) in proportion to 10%; i.e., homogenized with 0.5 ml of distilled water and 0.5 ml of ethylene to the treatments required so (T2 and T3) and only incision T4 and T5. The collection was made monthly in the three months after the application, in the summer season. In order to provide sufficient recovery time to the species for the following exudation of rubber trees in experimental huizache and mesquite three dates collection they were performed: 18 and 19 April (f1), respectively; May 17 (f2) and June 20 (f3) the same year.

A small spatula to take off the rubber had already solidified out large agglomerates or lumps forming used in the collection, but inside it was cool. Then allowed to dry on brown paper bags while others took off and collect rubber lumps. The collection of small lumps was simple, as they are easily peeled off and extraction was performed manually. A marker to identify them properly was also necessary. Moving field to the laboratory was conducted in brown paper bags. Weighing both gums one granataria balance was used, recording the results in a database. Later they took laboratory for analysis and determination of quality according to species, age and treatment.

Until that time was found in the literature the application of ethylene in some agroforestry system or handling treated in trees, however other use for ripening fruit was detected. In this research the application of ethylene in two treatments in order to observe the behavior of trees and accelerate the emanation of exudate stimulation due to stress conditions was considered. Vigor and tree physiology was also recorded before and after application of ethylene and the part that exuded as much gum.

The classification of the gums was visually according to their integrity (whole, fractional or powdered), size (greater than 1 cm), hue tear (light, dark, black) and impurities, using the method proposed by Yolanda l. López Franco model, Research Center for Food and Development (ACCIADAC) and CONAFOR, in July 2009. This procedure was done for both species. Once classified, 20 g of each of the category A were weighed and placed in small bags of waxed paper to be taken to the laboratory of food biotechnology INIFAP- CEBAJ ( HYPERLINK \l "t1" and HYPERLINK \l "f2" ).

Table 1 Manual classification of mesquite gum (GM) 

Then the images of the classification shown gums:

Figure 2 Manual classification of the gums. 

To determine the proximate analysis, the following methods were followed:

Crude protein. The total protein content was determined according to ^{HYPERLINK \l "mkp_ref_015" )}, by the method of Micro-Kjeldahl.

Humidity. The moisture content was determined according to AOAC (¹⁹⁹⁰).

Ashes. The ash content was determined according to AOAC (¹⁹⁹⁰). Ash of a food product is the inorganic residue remaining after burning organic matter. The ash represents the total content of minerals in foods.

Ether extract. The content ether extract according to AOAC (¹⁹⁹⁰); the ethereal extract name corresponds to the use of hexane as a solvent.

Dietary total fiber. Enzymatic gravimetric method was used described by ^{HYPERLINK \l "mkp_ref_010" )} with slight modifications.

Carbohydrates. This component is determined by the weight difference with 100 g sample, subtracting the sum of the content of protein, ether extract, ash and total dietary fiber.

Tannins. Condensed tannins were quantified according to the test of vanillin Desphande and Cheryn (1985).

Results and discussion

The months of data collection was completed in April, May and June, to avoid the rain drip off the rubber. The amount of GM for each of the experimental units shown in ( HYPERLINK \l "t2" ).

Table 2 Production of mesquite gum (GM). 

f1= 18 de abril; f2= 17 de mayo y f3= 20 de junio, goma (g)= rendimiento, cantidad de goma obtenida. Fuente: elaboración con datos tomados en el Campo Experimental Bajío INIFAP 2012.

For GH were recorded ( HYPERLINK \l "t3" ) the following amounts of the experimental units.

Table 3 Production of gum huizache (GH). 

f1= 19 de abril; f2= 17 de mayo y f3= 20 de junio, Goma (g)= rendimiento,cantidad de goma obtenida. Fuente: Elaboración con datos tomados en el CampoExperimental Bajío. INIFAP 2012.

Immediately a comparative graph ( HYPERLINK \l "f3" ) is shown to highlight the performance difference between exudate GM and GH.

Figura 3 Rendimiento de la producción de GM y GH. 

The results of HYPERLINK \l "t2" and 3 show that the emanation of gum amount was more promising with Acacia farnesiana species as an amount of 1077 and 1050 gap proximately registered. An analysis of variance with Statyscal Analysis System program (SAS, 2010), version 9.0, with the following statistical model randomized block design was performed: Yij = μ +Ti + βj + Eij ( HYPERLINK \l "t4" ).

Table 4 ANOVA mesquite gum (GM). 

Huizache results are presented in HYPERLINK \l "t5" .

Table 5 ANOVA gum huizache (GH). 

Finding that for both gums no significant differences for blocks showing high significance values for treatments.

The proximal chemical analysis were conducted in late june and july 2012, at the INIFAP-CEBAJ in food biotechnology laboratory with the methods described in the following HYPERLINK \l "t6" .

Table 6 Variables and methods performed for proximal analysis. 

In the results for each variable can be observed and analyzed in HYPERLINK \l "t7" .

Table 7 Proximal chemical composition mesquite and huizache gum. 

The similarity between the huizache and mesquite is known, but not with gum huizache, according to the results obtained in its proximal chemical composition, exceeds in quality.

The GM is not approved for FDA and FAO-WHO, CODEX. Although Mexico has already been approved by the Ministry of Health (SS) in 1996 for use in processed foods; especially in the soft drink industry. Both mesquite gum and huizache gum contain polyphenolic compounds or tannins; however it has not been observed that present risk to the health of the population ( ^{HYPERLINK \l "mkp_ref_008"} ). Minimum standards for gum arabic good quality have been defined in the Pharmacopoeia of the United States, Edition XVII (1965) of as follows: 4% of total ash (maximum), 0.5% acid insoluble (maximum) ash, 1% of water-insoluble residue (maximum). HYPERLINK \l "t8" shows the respective comparison as to the parameters established for each of the gums is done.

Table 8 Comparative parameters mesquite gum, huizache gum and arabic gum. 

*NR= no reportado. Fuente: elaboración con datos de laboratorio CEBAJ del INIFAP, Celaya, Guananjuato.

It is important to mention that both tires are potentially substitute for gum arabic meet all specifications and are even surpassed in some parameters.

Conclusions

Mesquite and huizache responded satisfactorily to the application of established treatments to accelerate the extraction of rubber. With the application of ethylene in treatments 2 and 3 higher yields of mesquite gum and huizache gum they were obtained. However, the amount of gum huizache is greater than mesquite gum presenting a growth ratio of 5 to 1. It was also found by proximal chemical analysis of both gums mesquite and huizache have similarity and even improves the parameters required by the Food and Drug Administration for the use of gum arabic in the food industry, impurities and tannins are lower gums Acacia farnesiana and Prosopis laevigata finding in this research values of 0.15 and 0.27% respectively; while in gum arabic contains up 0.49% tannins.

So both gums (mesquite and huizache) can be a substitute product. However, it is important to mention that although mesquite gum was already approved in Mexico for use in the food industry by the Ministry of Health since 1996; there are still major challenges for approval by the Food and Drug Administration and other European agencies to compete globally. It is possible to adopt this management with ethylene in producing communities of both legumes; i.e. that mesquite trees and huizache located in the wild can be managed with this system and be revalued as trees and bushes important multipurpose as is the removal of your gums, restorers erosion processes in soil (fixers nitrogen), fodder (livestock feed) honey, coal. Besides being a significant income for communities in arid and semiarid areas of the country.