Metabolic and structural effects of dehydration and ozone postharvest treatments on wine grape
Author(s)
De Sanctis, Federica
Date Issued
May 30, 2014
Type
Doctoral Thesis
Abstract
This PhD thesis is aimed to study metabolic, biochemical and structural changes on white wine grape, red wine grape and raisins using ozone post-harvest treatments without addiction of sulfites.
In wine production, sulfur dioxide is currently used for its positive effects on wine stabilization but it’s even known its negative effects on grape and human health(Bush, 1986).
Ozone was approved in 2001 by FDA ( Food and Drug Administration) as GRAS (generally recognized as safe) for food sanitation and it started to be used in many food industry as natural alternative to chemicals disinfection process. The use of ozone in the food industry represent an important step forward towards technological innovations.
To evaluate the effect of ozone on wine grape was studied first to what happen when O3 is applied on white and red wine grape and then on the modification caused by its application during postharvest dehydration.
Grape clusters variety Sauvignon Blanc (Castello de "La Sala" winery,Orvieto, Italy), Cabernet Sauvingon (Fresno State University, California) and Pignola (Cantine Di Villa, Valtellina, Italy ) were carefully hand harvested, selected and placed in a single layer into perforated crates (60 x 40 x 15 cm) until 6 kilograms Kg (±500 g) each, and divided into thermohygrometric controlled rooms (12 m3) at 10 (±1)°C and UR 70%.
The O3 exposure effects on Cabernet S. was studied on three different stages of grape ripening, 21,3°BRIX (unripe stage), 23,6°BRIX (ripe stage), 26°BRIX (overripe stage) and each one was treated with 300, 800 and 1300 ppb of ozone.
Sauvignon blanc sampling was performed at the beginning and then after 4, 8 and 16 hours of ozone treatment (European pending patent 12704901.3-1357 PC Engineering srl, Uggiate Trevano, Italy).
Pignola grapes, after a primary sampling, was subsequently exposed to three different treatments:
O3 for 18 hours followed by dehydration; O3 for 18 hours followed by dehydration with 0.5g/h of O3 for 4 hours every day; and not treated grapes (CK), dehydrated until 20% and 35% of weight loss. Sampling was performed at the beginning and then at 20 and 35% weight loss(wl).
Color parameters, weight loss, total SSC, CO2 production and TA remained quite constant right after ozone treatment. On the contrary, important differences have been found on phenolic content.
Some fraction as cinnamates and flavonols resulted to be positively affected by the treatment whereas catechins and epicatechin are resulted to be more susceptible.
Anthocyanins content are resulted to be less sensitive to the treatments, indeed, an increase was shown on unripe grape exposed to medium ozone concentration, while others samples remain quite stable after the exposure.
Glycosilated volatiles organic compounds (VOCs) increased significantly in Sauvignon blanc treated samples expecially benzyl alcol, methoxyeugenol, Coniferol 2, 7-OH a-terpineol and Isogeraniol, while free VOCs, whom are perceptible directly from the berry, as expected after ozone treatment fallen.
High O3 concentration for long term intensified the oxidant strength of ozone on carotenoids content especially when it’s used during postharvest dehydration.
Cell wall enzymes activity increased on ozonated grapes especially during drying and cell wall composition is modified by the exposure that caused a release of neutral sugars and a decrease of cellulose and uronic acid.
Additional information
Dottorato di ricerca in Biotecnologie degli alimenti
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