INTRODUCTION

The production of craft beer generates solid waste in significant quantities, which are not given adequate use, due to the difficulty of managing a product with high moisture content (80 %). In addition to this, the polysaccharide content of these residues makes them very susceptible to microbial growth, which causes their deterioration in a short term; therefore, it is necessary to apply a drying process for its conservation and storage.

The craft brewing industry has been increasing, due to the taste for this type of beer, in 2016; this type of industry grew 56 %, adding more than 400 small businesses (^{Villamil, 2016}). The Mexican craft brewery produces at least 15,000 liters per year and it is usually made with four ingredients: barley malt, water, hops and yeast. However, despite the fact that the demand for artisanal beer has grown, there are disadvantages, such as a higher amount of taxes than major brewers, higher production costs due to the volume of raw material purchases and import of inputs from Germany, France or USA; since the national producers work for the big brewers (^{Bernáldez, 2013}).

It is known that the production of beer in our country begins after the first years of Spanish colonization. However, malting barley began its development in Mexico in 1906, looking for to encourage the cultivation of this cereal to meet domestic needs (Galarza et al., 2006). According to data from the Ministry of Agriculture, Livestock, Rural Development, Fisheries and Food (SAGARPA, according its acronyms in Spanish) during 2016, malting barley production increased by 33.4%, compared to the previous year with an annual production of 965 thousand 332 tons; Guanajuato is the entity that produced the most with 372,167 tons (SAGARPA, 2017). Malt barley differed from forage barley because of its lower protein content, with an average of 11.5 and 14 % respectively (Schwentesius, Aguilar and Gómez, 2004).

Grains such as barley, as well as most of the ingredients used during the brewing process are regularly sold wet and these are used in the feeding of cattle, horses, pigs and sheep. As for the cost of production of pigs, food represents between 70 and 80% of total expenses (^{Gabosi, 2012}: ^{Rodríguez, Rodríguez and Villamil 2012}), which is why alternatives are sought for the formulation of new foods, being organic solid waste from the brewing industry is a viable option.

The voluntary consumption of the food requires the gustatory stimulation, through direct effects of neurophysiological processes that achieve a sensory perception (taste, smell, texture, and gastrointestinal signals), helping the animals to relate the food with their nutritional quality; which also influences the appetite stimulus, as a result of the education of preferred tastes within a learned behavior that leads to an improvement in the productivity of the animals (^{López, 2014}). The "umami" taste is highlighted in pigs as a pleasant and characteristic taste of protein sources, of animal or vegetable origin, which causes a sensory stimulation generated by some amino acids, peptides and nucleotides, among other compounds (^{Roura et al., 2008}).

The present investigation seeks to perform a proximal chemical analysis in solid waste of craft beer with the purpose of detecting its acceptance in the diet of reproductive sows.

MATERIAL AND METHODS

During the development of this research, organic solid waste from three types of beer: clear, amber and dark were ground and sieved with a 4.2 mm mesh, stored in plastic containers at room temperature (between 24-26 °C) for further analysis. Each test was performed in triplicate.

Determination of dry matter (MS). Approximately 2g of sample was weighed on porcelain capsules and placed in an oven at 105 °C for 24 hours, until constant weight was achieved according to the provisions of ^{NMX-F-257-S-1978}.

Determination of ashes (C). 3g of sample was weighed in porcelain capsules at constant weight, to subsequently pre-calcine the sample on a grid and bring it to a total calcination in the muffle at 700 °C for 2 h. Once the samples were cold, they were weighed to determine the ash percentage according to ^{NMX-F-066-S-1978}.

Determination of ether extract (EE). The test was performed in accordance with ^{NMX-F-089-S-1978}. Approximately 2g of the previously dried sample was weighed at 60 °C and determined with the Soxhlet equipment with ethyl ether as solvent for a period of 6h; the fat was then recovered in flasks previously dry to constant weight and the rest of the ether was removed at 100 °C; the flask was then weighed with fat and the percentage of ether extract was obtained by weight difference.

Determination of crude fiber (FC). The degreased malt samples obtained in the ether extract determination were used. The standard ^{NMX-F-613-NORMEX-2003} was used, which indicates the acid digestion with 0.2N sulfuric acid, washed with hot water and basic digestion with 0.2N sodium hydroxide. The determination of the crude fiber was made based on the weight of the ashes of the digested sample.

Determination of crude protein (PC). It was carried out in Kjedahl equipment for the analysis of total nitrogen according to the ^{NMX-F-608-NORMEX-2011}. 1 g of sample was used for the digestion with sulfuric acid; after digestion it was taken to an automatic distiller. Distilled the sample was valued with 0.1 N hydrochloric acid. The factor 6.25 was used, which was multiplied by the percentage of nitrogen obtained for the calculation of total protein.

Determination of nitrogen-free extract (ELN). The content of ELN was calculated with the following formula:

Determination of Total Digestible Nutrients (TND). It was calculated by adding all the organic compounds from the proximal analysis in the feed (crude proteins, ether extract, crude fiber and nitrogen-free extract), multiplied by its digestibility coefficient using the following formula:

The acceptance test of the food. The three solid residues of beer previously dried and ground were mixed and offered as the first choice of food in the morning to 30 sows in reproductive stage, chosen at random and divided into two groups of 15 each; from two different farms in the municipality of Salvatierra, Gto., identified as farm 1 (G1) and farm 2 (G2). The first test was to provide one kilogram of ground solid waste (RSM1) to the animals as the only option in the morning. During the second test the animals were given the ground solid waste mixed with a commercial concentrate with 40% crude protein (RSM2) in a formulation already established in each farm; sorghum was replaced by solid waste and the result was also offered a Kg as the only option in the morning. The results were recorded as acceptance when the food was consumed in the first 15 minutes, or rejection when after 15 minutes had not been consumed the food offered.

A multivariate analysis of variance (ANOVA) was performed to compare the results of the bromatological analysis of the solid waste of barley malt of the three types of beer (light, amber and dark), as well as to compare the data of their acceptance or rejection of the food offered alone and as a member of a balanced feed, offered to sows in two different farms.

RESULTS AND DISCUSSION

The bromatological analysis of the solid residues of barley malt is presented in table 1.

Although the malting process of the barley for the elaboration of the three types of beers (light, amber and dark) is different, the percentage of the components (MC, C, EE, FC, PC and TND) in the residues do not present a significant difference between them (P> 0.05); indicating that the different procurement processes do not alter the chemical composition of the final product.

The results found in this study for protein of 10.91 % are similar to those reported by ^{Callejo (2002}), for the barley grain with a range of crude protein of 10 to 11 %; however, this value is lower than that reported by Enrique et al., (2014) of 12.08 %, of the ^{NRC (2001)} of 12.4 % and of ^{Castillo et al., (2012}) of 13.16 %; suggesting that residues in the beer production process are affected in the chemical composition of the barley grain protein.

In this study, an average of nitrogen-free extract of 64.2 % was found, while ^{Castillo et al., (2012}) reported 69.1 % for the barley grain, and as for the TND, differences were also found; in the analysis performed an average of 73.47 % was observed, while the ^{NRC (2001)} reports 82.7 % in the barley grain. This may be due to the fact that carbohydrate is the material that is required in brewing beer.

In relation to the acceptance test of these residues, applying two treatments in two farms (G1 and G2) of the municipality of Salvatierra Gto, after having carried out the acceptance test it was observed that RSM1 in the G1 was accepted by 12 animals and rejected by three, and in G2 it was accepted by 13 and rejected by two; being a total rejection of 16.6 %. The test with RSM2 in the two farms (G1 and G2) was accepted by 100 % of the animals (Table 2).

According to the statistical analysis, it was found that there is a significant difference (P <0.05) between the acceptance and rejection variables of the RSM1 and RSM2, for a 95 % reliability in the two farms (G1 and G2).

Wet beer residues have regularly been used in cattle feed (^{Mussatto, Dragone and Roberto 2006}). Recent research has shown that brewery derivatives can be an option for animal supplementation, achieving adequate daily weight gains (GDP), similar to other energy supplements commonly used by producers, such as corn and sorghum; in addition to reducing the costs of feeding livestock and increasing profits (^{Rivas et al., 2017}).

The acceptance of solid waste ground by the sows is explained by the characteristics of the cereal and by the content of dextrins, maltose, glucose and maltotriose, produced during the fermentation process by hydrolytic enzymes, such as alpha-amylase, beta-amylase and beta-glucanase (^{Badui, 2006}). The umami taste is a flavor similar to that of meat and it is found in foods rich in proteins and fermented products. In addition, hydrolysis generates sweet, salty, bitter, acid and umami flavors in foods, acting synergistically to increase the perception of flavor (Badui, 2006, ^{López, 2014}). According to ^{Roura (2011}) pigs have a high sensitivity for umami taste, which increases voluntary consumption. They also have a positive preference for some amino acids that are not perceived as umami by humans, such as: glutamine, alanine, asparagine, proline, aspartic acid, glutamic acid, tryptophan and threonine.

It is considered necessary more tests to evaluate the economic and nutritional impact of wet beer residues in all stages of the pig that increase weight and feed conversion, aspects that can be reviewed as continuity of this work.

CONCLUSION

The different production processes of craft beer (light, amber and dark) do not cause significant differences in the chemical composition between the three types of waste; maintaining an important amount of nutrients that can be used for animal feed, which is related to a very good acceptance by reproductive sows.