Consecutive alcoholic fermentations of white grape musts with yeasts immobilized on grape skins – Effect of biocatalyst storage and SO2 concentration on wine characteristics

Entrapped Psychrotolerant Yeast Cells within Pine Sawdust for Low Temperature Wine Making: Impact on Wine Quality

An alternative methodology is proposed for low temperature winemaking using freeze-dried raw materials. Pine sawdust was delignified and the received porous cellulosic material was applied as immobilization carrier of the psychrotolerant yeast strain Saccharomyces cerevisiae AXAZ-1. The immobilization of yeast cells was examined and verified by scanning electron microscopy (SEM). The immobilized biocatalyst and high-gravity grape must were separately freeze-dried without cryoprotectants and stored at room temperature (20–22 °C) for 3 months. The effect of storage on the fermentation efficiency of the immobilized biocatalyst at low temperatures (1–10 °C), as well as on the aromatic characteristics of the produced wines was evaluated. Storage time had no significant effect on the fermentation efficiency of the biocatalyst resulting in most cases in high ethanol production 13.8–14.8% v/v. The volatile fraction of the produced wines was examined using headspace solid-phase microextraction (HS-SPME) followed by gas chromatography mass spectrometry (GC/MS). GC-MS/SPME analysis along with the organoleptic evaluation revealed in all produced wines a plethora of fresh and fruit aromatic notes. To conclude, fermentation kinetics and aromatic profile evaluation encourages the production of high-quality sweet wines at low temperatures using pine sawdust (Pinus halepensis) entrapped yeast cells as a promoter.

Volatile Composition and Sensory Properties of Mead

Mead is a traditional beverage that results from the alcoholic fermentation of diluted honey performed by yeasts. Although the process of mead production has been optimized in recent years, studies focused on its sensory properties are still scarce. Therefore, the aim of this work was to analyse the sensory attributes of mead produced with free or immobilized cells of the Saccharomyces cerevisiae strains QA23 and ICV D47, and to establish potential correlations with its volatile composition. In the volatile composition of mead, the effect of yeast condition was more important than the strain. In respect to sensory analysis, the most pleasant aroma descriptors were correlated with mead obtained with free yeast cells, independently of the strain. Both sensory analysis and volatile composition indicates that the most pleasant mead was produced by free yeast cells. Although this study has provided a significant contribution, further research on the sensory quality of mead is still needed.

Pistacia terebinthus Resin as Yeast Immobilization Support for Alcoholic Fermentation

A natural resin retrieved from Pistacia terebinthus tree was evaluated as an immobilization carrier of Saccharomyces cerevisiae AXAZ-1 cells targeting successive fermentation batches of sugar synthetic mediums. Fermentation times below 54 h were recorded at temperatures 28–14 °C. In total, 147 compounds were detected using gas chromatography-mass spectrometry (GC-MS) analysis, including alcohols, esters, ketones, aldehydes, acids, and terpenes. Principal component analysis indicated that the state of cells (free/immobilized) and the fermentation temperature primarily affected terpenes’ composition. Importantly, no spoilage of the fermented beverages was noted during 90 days of storage at room temperature, most likely due to the high content of extracted terpenoids and phenols (up to 579.01 mg L⁻¹ and 171.8 mg gallic acid equivalent L⁻¹, respectively). Likewise, the developed novel biocatalyst (yeast cells immobilized within Pistacia terebinthus resin) was suitable for the production of low alcohol beverages with an enhanced aromatic profile. The obtained results revealed that the proposed bioprocess shows great commercialization potential in the new fast-growing low-alcohol beverages sector.