Use of Saccharomyces cerevisiae var. boulardii in co-fermentations with S. cerevisiae for the production of craft beers with potential healthy value-added

Highlights

• S. cerevisiae var. boulardii was tolerant to stresses from wort fermentation.

• In mixed fermentation yeast strains interact metabolically each other.

• S. cerevisiae var. boulardii in mixed starter did not affect negatively beer aroma.

• Probiotic strain in mixed starter caused an increase of beer antioxidant properties.

Abstract

In recent years, the awareness of consumers about the impact of food on health is constantly increasing. A high amount of dietary antioxidant intake can be supplied by beverages widely consumed, such as wine, coffee, beer. Recently, an increase in the consumer interest was observed for beer, in consequence of the high phenolic antioxidants and low ethanol content present in this beverage. Among all beer types, in recent years, consumption of craft beers has gained popularity. Being an unpasteurized and unfiltered, craft beer is potentially a new vehicle for delivering health effects. While health benefits of lactic acid bacteria as probiotics are well known, few data are available on probiotic yeasts in fermented food. Therefore, this study was aimed to analyse the effect of integrating the well-known probiotic yeast strain of S. cerevisiae var. boulardii (S.b) in mixed cultures with S. cerevisiae strains for production of beers with increased healthy benefits. The probiotic strain of S.b was tested in mixed cultures with selected S. cerevisiae strains, during wort fermentation. As the viability during processing operations is one of the criteria for selecting suitable strains of probiotic microorganisms, the survival of probiotic yeast during the fermentation and the presence of highly viable cells at the end of fermentations were evaluated. In almost all the mixed fermentations, at the end of the process the probiotic yeast was predominant on S. cerevisiae strain, and the experimental beers contained a high number of viable cells of S.b strain (ranging between 8 × 10⁶ and 7.0 × 10⁷/mL). The analysis of experimental beers for the content of main volatile compounds showed that the inclusion of S.b strain in mixed starter did not affect negatively beer aroma. Moreover, the inclusion of S.b strain in mixed starters determined an increase in the antioxidant activity and polyphenols content, in comparison to beers from single starter fermentations, indicating the influence of S.b strain on these parameters. Some mixed starter cultures tested in this study resulted a very promising tool to increase the healthy quality of the product, such as the improve the antioxidant activity and polyphenols content of beer.

Introduction

Beer is the third most popular drink worldwide after tea and coffee, and is the most preferred alcoholic beverage (Rodhouse and Carbonero, 2017). As a fermented beverage, beer inherently relies on microbial metabolism for production. Traditionally, Saccharomyces cerevisiae and S. pastorianus (synonym S. carlsbergensis, a partial amphitetraploid, which was generated upon an interspecific fusion-cross between S. cerevisiae and S. bayanus), are the two species widely used as starter cultures for the production of the two most diffused categories of industrial beer, which are ‘ale’ and ‘lager’ beers. In brewing, the use of starter cultures is aimed to increase the fermentation efficiency, to develop new beers, and to enhance the sensory complexity of the beer that is produced. In response to increased consumer demand toward new products, nowadays, there is a worldwide increase in popularity of craft beers, a new generation of products obtained in small breweries that are focused on the production of traditional ales, lagers, and even beer styles that do not fit in any of the two main styles. Craft beer is generally unfiltered, unpasteurized and without additional nitrogen or carbon dioxide pressure. The producers emphasize the typical and distinctive flavour of their beers, due to the addition of fruits, herbs, and spices that can transform ordinary beer into specialty beer, along with other flavorings and fermentable substrates (Aquilani et al., 2015; Canonico et al., 2014).

New technologies and innovations were developed by brewing industry for increase typologies of specialty beers; among them, the most diffused are: low calories, low/no alcohol, novel-flavored, gluten free and functional beers. Functional beers are obtained by enrichment with health-promoting substances, therefore they are considered as beers giving health benefits, if consumed in moderate amounts. These specialty beers are produced by using non-conventional yeasts, able to produce or transform some beneficial compounds (Basso et al., 2016), such as melatonin, a hormone able to regulate sleep in mammals and possessing antioxidant properties; some yeasts can produce this substance during beer fermentation (Maldonado et al., 2009).

Among the functional beers, an absolute novelty is represented by probiotic beer, obtained by incorporating probiotic microorganisms. Studies have shown that consuming food and beverages with live counts of probiotics are more effective in delivering health effects than products containing inactive probiotics. Craft beer, which is unpasteurized and unfiltered, can be considered as a new tool to provide health effects. Otherwise, the technologies applied to pasteurized or filtered beers are not suitable at this purpose, as heat or filtration can kill or remove, respectively, the probiotics, unless it is used the probiotics addition after pasteurization or filtration. Therefore, because viability is crucial for the efficacy of probiotics, a craft beer could be more suitable to be produced as probiotic beer than an industrial beer. Most probiotic microorganisms are bacteria, whereas Saccharomyces cerevisiae var. boulardii (synonym S. boulardii) is the only yeast used extensively as a probiotic and often marketed as a dietary supplement (McFarland, 2010). S. cerevisiae var. boulardii possesses many properties that make it a potential probiotic agent, i.e. the survival at body temperature (37 °C), the resistance to stomach acids and bile acids and the survival to competitive environment of the intestinal tract (Czerucka et al., 2007; McFarland, 2010; Kelesidis and Pothoulakis, 2012).

In the present study, we tested a probiotic strain of S. cerevisiae var. boulardii (S.b), in mixed cultures with selected S. cerevisiae strains, during wort fermentation. It was evaluated the influence on the analytical and antioxidant profile of beers, as well as the potential of surviving until the end of fermentative process, of S.b strain with the aim to select a suitable starter culture for production of a novel unfiltered and unpasteurised beer with potential probiotic activity.