Freeze-Dried Saccharomyces cerevisiae Cells Immobilized on Potato Pieces for Low-Temperature Winemaking

Abstract

A biocatalyst was prepared by immobilization of Saccharomyces cerevisiae AXAZ-1 yeast cells on potato pieces. This biocatalyst was subjected to freeze-drying, and the effect of several protective agents and storage at 5 °C, up to 9 months, on viability and fermentative activity of yeasts cells were studied. From several protective agents tested, sodium glutamate preserved the viability of immobilized yeast cells at high levels even after 9-month storage. The freeze-drying biocatalyst was used for repeated batch fermentations of grape must at low temperatures until 5 °C. The produced wines analyzed for volatile byproducts by GC and GC/MS and the results showed that the freeze-dried biocatalysts, with sodium glutamate as protectant, produced wines with higher formation of esters than free cells and having at least similar aromatic profile to those produced by wet biocatalysts.

Freeze-Dried Immobilized Kefir Culture in Low Alcohol Winemaking

“…Immobilization on apple pieces resulted in higher (p < 0.05) survival rates of lactobacilli when 25% w/v fructose solution was used as a cryoprotectant. Similarly, cell immobilization on DCM had a significant (p < 0.05) positive effect on the survival of lactobacilli when 25% w/v fructose, 10% and 25% w/v trehalose, and 10% v/v glycerol solutions, were used as cryoprotectants, and on the survival of lactococci when 10% v/v glycerol was applied [10,46]. Likewise, immobilization on grape skins also had a significant (p < 0.05) positive effect upon the survival of lactobacilli when sugar (fructose, trehalose), glycerol solutions (regardless the concentration used) and grape must were tested [47].…”

“…In order to investigate the effect of various cryoprotectants on cell viability during freeze-drying, sugar solutions (glucose, fructose, sucrose, lactose and trehalose at concentrations of 10% and 25% w/v), glycerol solutions (10%, 25% and 50% v/v) and grape must (~10 • Be) were tested as previously described with few modifications [10,25]. All solutions were sterilized at 121 • C for 15 min prior to use.…”

“…Freeze-dried cells were rehydrated with sterilized water [25] and yeasts/molds, lactobacilli and lactococci counts were determined as described previously [7]. The % survival rate was calculated as logcfu/g after freeze-drying, divided by logcfu/g before freeze-drying, and multiplied by 100 as previously described [10].…”

“…All low alcohol wines produced were accepted during the preliminary sensory evaluation.Foods 2020, 9, 115 2 of 22 However, freeze-drying very often leads to a significant reduction of cell viability [9]. To overcome such deficiencies, cell immobilization is suggested, as it results in the maintenance of viability during the freeze-drying process [10], along with the operational stability of both wet and freeze-dried cells [10,11], and is also associated with multiple technological advantages (enhanced fermentation productivity, application of continuous configurations and cell recycling, improvement of product quality, etc.) [12].…”

“…However, these studies involved only wet immobilized kefir cultures, a technology hardly accepted by the industrial sector. Although the use of freeze-dried, immobilized cells has been investigated in winemaking [10,21] and brewing [22], leading to products with an improved taste and aroma, the optimization of the process (e.g., the use of cryoprotectants), and verification of the fermentation efficiency of newly prepared freeze-dried immobilized cultures, always constitute issues of great importance, due to viability and metabolic activity losses associated with the freeze-drying procedure [23,24].In this vein, the aim of the present study was to evaluate the suitability of freeze-dried, immobilized kefir culture in the production of low alcohol wines. Data supporting the ability of the freeze-dried kefir culture to conduct simultaneous alcoholic and ML fermentations in low alcohol winemaking, and quality improvement, are presented.…”