fermentation Review Schizosaccharomyces pombe: A Promising Biotechnology for Modulating Wine Composition Iris Loira * ID , Antonio Morata ID , Felipe Palomero, Carmen González and José Antonio Suárez-Lepe Departamento de Química y Tecnología de Alimentos, Universidad Politécnica de Madrid, Av. Puerta de Hierro, nº 2, 28040 Madrid, Spain; [email protected] (A.M.), [email protected] (F.P.); [email protected] (C.G.); [email protected] (J.A.S.-L.) * Correspondence: [email protected] Received: 26 July 2018; Accepted: 21 August 2018; Published: 23 August 2018 Abstract: There are numerous yeast species related to wine making, particularly non-Saccharomyces, that deserve special attention due to the great potential they have when it comes to making certain changes in the composition of the wine. Among them, Schizosaccharomyces pombe stands out for its particular metabolism that gives it certain abilities such as regulating the acidity of wine through maloalcoholic fermentation. In addition, this species is characterized by favouring the formation of stable pigments in wine and releasing large quantities of polysaccharides during ageing on lees. Moreover, its urease activity and its competition for malic acid with lactic acid bacteria make it a safety tool by limiting the formation of ethyl carbamate and biogenic amines in wine. However, it also has certain disadvantages such as its low fermentation speed or the development of undesirable flavours and aromas. In this chapter, the main oenological uses of Schizosaccharomyces pombe that have been proposed in recent years will be reviewed and discussed. Keywords: Schizosaccharomyces pombe; oenological uses; maloalcoholic fermentation; stable pigments; wine safety 1. Origin and Features of Schizosaccharomyces pombe Schizosaccharomyces pombe, also known as fission yeast, was discovered by Lindner in 1983 [1]. The cells of this species have a characteristic rod shape with sizes varying between 3–5 × 5–24 µm (Figure1). However, immediately after cell division, new cells formed have a more rounded shape due to the turgor pressure [2]. It has a peculiar mode of vegetative reproduction by fission (cross-wall formation) instead of budding, which is more common among yeasts [3]. Cells are separated by the formation of a transverse septum. The spores are formed as a result of sexual reproduction by conjugation of the cells when adverse conditions occur, such as nutrient starvation, and, in the case of S. pombe, between two and four (most often) haploid spores originate in the ascus [4]. Its growth rate is very slow, with a long lag phase and high vitamin requirement. However, it has a low nitrogen requirement [5]. In normal minimal or complex media, the generation time is between 2 and 4 h [6]. Usually, S. pombe does not develop properly in most culture media due to its aforementioned low growing rate, thus making its isolation from the environment more difficult. A selective-differential medium based on the resistance of S. pombe to actidione (antibiotic) and to benzoic acid (inhibitory agent) has been recently proposed to isolate strains of this genus from media with high sugar content [7]. S. pombe strains have been isolated from grape juice, molasses, and kombucha tea [1,8]. In addition to glucose, S. pombe can also use glycerol, sucrose, raffinose, and maltose as carbon sources [9]. Fermentation 2018, 4, 70; doi:10.3390/fermentation4030070 www.mdpi.com/journal/fermentation Fermentation 2018, 4, 70 2 of 12 Fermentation 2018, 4, x 2 of 12 Figure 1. Optical microscope image of SchizosaccharomycesSchizosaccharomyces pombe ((S. pombepombe).). The transversetransverse septum formed during the asexual reproductionreproduction isis indicatedindicated byby anan arrow.arrow. Another peculiarity of S. pombe is that it can can grow grow in in environments environments with with low low water water activity, activity, that is, it is anan osmophilicosmophilic yeast, and therefore can be foundfound inin mediamedia withwith highhigh sugarsugar contentcontent [[1].1]. It can also develop in in very very low low pH pH environments environments and and in ina wide a wide range range of temperatures of temperatures [10]. [ 10Moreover,]. Moreover, it is itsomewhat is somewhat resistant resistant to food to foodpreservatives, preservatives, such suchas sulphur as sulphur dioxide, dioxide, actidione, actidione, benzoic benzoic acid, acid,and anddimethyl dimethyl dicarbonate dicarbonate [10,11]. [10 ,11]. Regarding its fermentative performance, it is able to ferment glucose to an alcoholic degree of around 10–15% v//vv ethanol,ethanol, depending depending on on the the yeast yeast strain strain and and the the aeration aeration conditions [10]. [10]. As As already already mentioned, the genus Schizosaccharomyces isis known for its slow growth rate and excessive excessive production of hydrogenhydrogen sulphidesulphide during during fermentation fermentation [12 ].[12]. These These two two features, features, together together with highwith volatile high volatile acidity, areacidity, the mainare the limitations main limitations for its use for in its winemaking. use in winemaking. The production The production of acetic acid of acetic is strain-dependent, acid is strain- usuallydependent, ranging usually between ranging 0.8 andbetween 1.4 g/L 0.8 [13 and]. Nevertheless, 1.4 g/L [13]. throughNevertheless, the selection through of strainsthe selection and their of usestrains in combinationand their usewith in combination yeasts of the with genus yeastsSaccharomyces of the genus, wines Saccharomyces of quality, wines can be of obtainedquality can from be unbalancedobtained from musts unbalanced with high musts total with acidity. high total acidity. Currently, thanksthanks to recentto recent research research that presentsthat presents new possibilities new possibilities for their use, for non- theirSaccharomyces use, non- yeastsSaccharomyces are shedding yeasts theirare shedding bad reputation, their bad and reputation, it is possible and toit is find possibleS. pombe to findyeasts S. encapsulatedpombe yeasts inencapsulated alginate beads in alginate being beads marketed being as marketed an alternative as an alternative to malolactic to malolactic fermentation fermentation or chemical or deacidificationchemical deacidification [14]. An advantage[14]. An advantage of using theseof usin encapsulatedg these encapsulated yeasts is thatyeasts they is that can bethey removed can be fromremoved the mediumfrom the at medium a desired at time a desired and, in time addition, and, in the addition, same capsules the same can capsules be reused can in severalbe reused cycles in (upseveral to 5 cycles times), (up although to 5 times), with a although slight loss with of degrading a slight loss activity of degrading [15,16]. Regarding activity sensory[15,16]. Regarding properties, thesensory wines properties, obtained by the sequential wines obtained fermentation by sequential of S. pombe fermentationand S. cerevisiae of S. werepombe full-bodied, and S. cerevisiae with betterwere structure,full-bodied, balance, with better and length structure, than thebalance, controls and made length without than usingthe controls this deacidification made without technique using [this16]. deacidification technique [16]. 2. Wine Acidity Modulation 2. Wine Acidity Modulation Wine acidity is mainly responsible for freshness. After L-tartaric acid, L-malic acid is the second organicWine acid acidity in wine is mainly that contributes responsible significantly for freshness. to its After total acidity.L-tartaric Its acid, average L-malic content acid in is wine the second highly dependsorganic acid on thein grapewine that variety contributes and the climate,significantly varying to its widely total betweenacidity. Its 1 and average 10 g/L content [17]. Reaching in wine anhighly appropriate depends balance on the betweengrape variety the sugar and contentthe clim andate, the varying total acidity widely of between the wine 1 is and fundamental 10 g/L [17]. to Reaching an appropriate balance between the sugar content and the total acidity of the wine is Fermentation 2018, 4, x 3 of 12 Fermentation 2018, 4, 70 3 of 12 fundamental to ensure its optimum quality. In addition, excessive amounts of malic acid may cause microbiologicalensure its optimum instability quality. in In wine. addition, These excessive are the two amounts main reasons of malic to acid modulate may cause wine microbiological pH. instabilityThe biological in wine. Thesedeacidification are the two of main wine reasons through to the modulate use of wineSchizosaccharomyces pH. pombe has been studiedThe thoroughly biological deacidification[18,19], since itsof ability wine to through transform the malic use of acidSchizosaccharomyces into ethanol and pombecarbonhas dioxide been wasstudied discovered thoroughly in [the18, 19early], since 20th its abilitycentury to [20]. transform Thanks malic to acidthis intoability ethanol of S. andpombe carbon to develop dioxide wasmaloalcoholic discovered fermentation in the early 20th (MAF) century (Figure [20]. 2), Thanks it is possible to this ability to modulate of S. pombe theto pH develop of the maloalcoholic wine by the consumptionfermentation (MAF)of practically (Figure2 ),all it isthe possible malic toacid modulate present the in pH the of themust wine with by thethe consumption corresponding of practicallystoichiometric all theproduction malic acid of ethanol. present inUnlike the must S. cerevisiae, with the in corresponding