Pulque: Natural Mexican Drink with Probiotic Properties

Pulque is probably the oldest and most traditional Mexican alcoholic beverage. It is produced by fermenting aguamiel (mead), the sweet sap extracted from several species of agave that grow in the central highland states. The fresh mead is filtered and poured into vessels containing the "seed", pulque from the previous production that serves as inoculum to accelerate the fermentation process, inside a closed room (tinacal). The finished product is a white, viscous, strong-smelling alcoholic beverage that may have probiotic properties.

In traditional indigenous medicine, pulque has been used in the treatment of various diseases since pre-Hispanic times. Archaeological evidence and colonial compilations suggest that it has been used as an enema to treat gastrointestinal disorders and infections.

Recently it has been proven that this practice can have beneficial effects on human health, due to the enrichment of the digestive tract by microorganisms with probiotic potential, especially those with antagonistic activity against some pathogenic bacteria and fungi.

Pulque can be considered a probiotic product due to the presence of lactic acid bacteria (Lactobacillus acidophilus and Leuconostoc mesenteroides) and yeast (Saccharomyces cerevisiae) during its fermentation process.

How is pulque made?

The traditional production of pulque has remained practically unchanged since pre-Hispanic times. For the extraction of aguamiel, the most important part of the process consists of cutting the inflorescence of the plant (quiote) before it develops, an operation known as "capar al maguey". Once capped, some leaves (pencas) are cut to clear the work area (maguey door) and the central part of the plant (mezontete) is chopped to form a concave cavity (cajete) where the sap collects. The wall of the cajete is scraped daily to keep the mead flowing and deposited at the bottom of the cavity.

To ferment into pulque, the daily collection of mead is poured into one or more vats where the seed has been previously transferred. Fermentation takes several hours depending on the quality of the mead, the microorganisms present in the seed, and the environmental conditions in a special room (tinacal) whose purpose is to maintain the proper temperature and ventilation for the mead to ferment. The degree of fermentation of pulque varies according to the producer and is considered adequate when it reaches a level of viscosity, alcohol content, and characteristic odor. Pulque is consumed naturally or added with fruits, vegetables, or seeds, this type of pulque is known as "cured".

Microbes and pulque

Several microorganisms participate in the fermentation of pulque: those present in the cajete during the accumulation of mead, those incorporated during its collection and transport, and those found in the seed. Several studies have proposed that the essential microorganisms in pulque fermentation are acid lactic acid bacteria (Lactobacillus spp. and Leuconostoc mesenteroides), yeast (Saccharomyces cerevisiae), and the bacterium Zymomonas mobilis.

These develop three distinctive products during different stages of the process: lactic acid in acid fermentation, produced by Lactobacillus spp. and Leuconostoc sp., ethanol in alcoholic fermentation, synthesized mainly by S. cerevisiae and Z. mobilis, and polysaccharides from the sugar (sucrose) metabolized by Leuconostoc sp. and Z. mobilis in viscous fermentation. The products derived from this complex fermentation process characterize pulque as an acidic, alcoholic, and viscous beverage.

The analysis of bacterial diversity in pulque samples shows that acid lactic acid bacteria, particularly those related to Lactobacillus aciduphilus, are the most abundant group of microorganisms present in pulque. Their presence allows considering pulque as a probiotic product.

Pulque as a probiotic

Recent research suggests that probiotics improve immune response modulation properties and lactose tolerance, lower cholesterol levels and increase nutrient utilization. In practice, probiotics are essentially considered to be lactobacilli and bifidobacteria, since they do not include pathogenic strains within the species to which they belong.

Another of the requirements that microorganisms have to meet to be qualified as probiotics is to show tolerance to the conditions of the environment where they exert their action to remain alive and functionally active in the gastrointestinal tract. To do so, they must resist damage by gastric secretions and bile, in addition to possessing the ability to adhere to the intestinal epithelium, as well as the ability to colonize the gastrointestinal tract, even for short periods.

According to several studies, microorganisms of the Leuconostoc and Lactobacillus species, present in mead and pulque, show resistance to the antimicrobial barriers of the gastrointestinal tract, as well as adherence to the intestinal mucosa. In this sense, the traditional treatment of infections and gastrointestinal disorders through the moderate consumption of pulque has been related to the antimicrobial activity of the acid lactic acid bacteria present in its fermentation, such as Lactobacillus aciduphilus and L. plantarum.

Although pulque has some advantages over probiotics of dairy origin, such as the absence of cholesterol and milk allergens, and despite its great historical, religious, social, medical, and economic importance, it is difficult to promote its consumption as a probiotic due to its alcoholic content.

Nevertheless, pulque is now the focus of research in many laboratories, not only because of its nutritional properties but also because of the complex microbial diversity responsible for its fermentation. The possibility that acid lactic acid bacteria isolated from mead and pulque can be used as probiotics is of great relevance since it could open the door to the production and consumption of probiotics developed in Mexico.

Pulque is more than tradition

This drink is slowly gaining ground. In 2017, 217.7 million liters were produced, of which Hidalgo contributed 69.6 percent, according to figures from the Agrifood and Fisheries Information Service. Currently, several researchers agree that the new generations do not have a negative perception of pulque, its stigma disappears and, with it, an ancestral tradition is vindicated.

Information from the Digital Library of Mexican Traditional Medicine of the UNAM indicates that taken in moderation it works as a nutritional supplement due to its content of proteins and vitamins C and B complex. Drinking it regularly (three times a day) implies a contribution of 2.2 to 12.4% of calories and 0.6 to 3.2% of protein required in the daily diet. In addition, it has medicinal properties, among which are the protection of the intestinal flora, acts as a diuretic, reduces insomnia, being a good nutritional supplement, and combats anemia.

Pulque is a very special drink that we should appreciate, both for its history and its essence, and if not, read the following:

"Marquise Calderón de la Barca (Englishwoman married to a Spaniard), one day in 1839 expressed: -For the first time I conceived the possibility of liking pulque. We found it rather refreshing, with a sweet taste and a creamy foam. Then he fell in love with the pineapple curado: "Very good," he confessed. And two years later, already packing his bags to return, he lamented about our pulque: -I find it excellent now, and I think it will be very difficult for me to live without it!"

Notes

Probiotics: live microorganisms that when administered in adequate amounts confer a health benefit to the host.

Enema: a liquid that is introduced into the body through the anus with a suitable instrument to propel it, and usually serves to clean and discharge the intestine.

Biological antagonism: interaction between organisms or substances that causes the loss of activity of one of them, such as the action of antibiotics against bacteria.

Sources:Authors: Elia Ballesteros-Rodriguez and Lorenzo Felipe Sanchez-Teyer, Elementos No.121/Vol.28 Gob.mx