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. 2021 Jun 18;10(6):1416.
doi: 10.3390/foods10061416.

Improvement of Must Fermentation from Late Harvest cv. Tempranillo Grapes Treated with Pulsed Light

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Improvement of Must Fermentation from Late Harvest cv. Tempranillo Grapes Treated with Pulsed Light

Carlos Escott et al. Foods. .

Abstract

Pulsed light irradiation is a nonthermal technology currently used for the elimination of pathogens from a diverse range of food products. In the last two decades, the results obtained using PL at laboratory scale are encouraging wine experts to use it in the winemaking industry. PL can reduce native yeast counts significantly, which facilitates the use of starter cultures, reducing SO2 requirements at the same time. In this experimental set up, Tempranillo grapes were subjected to pulsed light treatment, and the fermentative performance of non-Saccharomyces yeasts belonging to the species Schizosaccharomyces pombe, Lachancea thermotolerans, Torulaspora delbrueckii, Metschnikowia pulcherrima and Hanseniaspora vineae was monitored in sequential fermentations against spontaneous fermentation and pure culture fermentation with the species Saccharomyces cerevisiae. The experimental analyses comprised the determination of anthocyanin (High performance liquid chromatography with photodiode array detector-HPLC-DAD), polyphenol index and colour (Ultraviolet-visible spectroscopy-UV-Vis spectrophotometer), fermentation-derived volatiles (Gas chromatography with flame ionization detector-GC-FID), oenological parameters (Fourier transform Infrared spectroscopy-FT-IR) and structural damage of the skin (atomic force microscopy-AFM). The results showed a decrease of 1.2 log CFU/mL yeast counts after pulsed light treatment and more rapid and controlled fermentation kinetics in musts from treated grapes than in untreated samples. The fermentations done with treated grapes allowed starter cultures to better implant in the must, although a larger anthocyanin loss (up to 93%) and an increase in hue values (1 unit) towards more yellow hues were observed for treated grapes. The development of biomass was larger in musts from treated grapes. The profile of volatile compounds and oenological parameters reveals that fermentations carried out with untreated grapes are prone to deviations from native microbiota (e.g., production of lactic acid). Finally, no severe damage on the skin was observed with the AFM on treated grapes.

Keywords: AFM; Tempranillo; anthocyanins; lactic acid; non-Saccharomyces; pulsed light; volatiles.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Sequence showing (A) interior of the PL treatment chamber; (B) grapes cut in half and placed under the lamps; (C) thermal camera used (above) and thermal effect (below).
Figure 2
Figure 2
Details of the indentation done with the atomic force microscopy (AFM) on treated skin (A) and untreated skin (B) are seen in the top images, and the details on the roughness of the skin are seen on the bottom images.
Figure 3
Figure 3
Kinetics of the alcoholic fermentation as a percentage of the estimated ethanol produced (% v/v) after the 2nd inoculation (sequential inoculation). (A) Vinifications from untreated grapes; (B) vinifications from PL-treated grapes.
Figure 4
Figure 4
Percentage loss of anthocyanins in (left) wines produced with untreated grapes and (right) wines produced with treated grapes.

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