Grape Dehydration Research Articles

Control of environmental parameters in postharvest partial dehydration of wine grapes reduces water stress

The hypothesis that a controlled environmental condition of postharvest partial dehydration of wine grapes may reduce berry water stress keeping a better grape quality, was verified on white wine grapes, var. ‘Pecorino’. Grapes were harvested at 21.5% solid soluble content (SSC) and kept at 15°C, 60% relative humidity (RH), and 2.5ms−1 or 1.2ms−1 air speed (tunnel), with a vapor pressure deficit (VPD) of 7.5–8mbar; control bunches were kept in an uncontrolled condition (VPD=0.7–6.4mbar). Samplings for chemical and biochemical analyses were performed on grapes with 10, 25, 35, and 45% mass loss (m.l.). Tunnel and control samples reached 31.5% (in 24-26days) and 28.5% (in 28days) SSC, respectively. Control grapes had higher CO2 production, alcohol dehydrogenase (ADH) and lipooxygenase (LOX) activities and proline content. Ethanol and acetaldehyde contents reflected ADH activity patterns. Control grape had higher percentage of branched alcohols than control ones. An activation of aerobic fermentation in control grapes is discussed with comment on related generation of specific volatile organic compounds (VOCs).

Impact of grape dehydration process on the phenolic composition of wines during bottle ageing

The effect of grapes dehydration on, phenolic profile was evaluated in wines during bottle ageing. Wines produced with Cabernet Sauvignon and Merlot grapes, dehydrated in different percentages (30 and 40%) under controlled conditions, were analyzed by spectrophotometric and chromatographic assays during 22 months of storage. The phenolic profile of the wines and their evolution during bottle ageing was different according to the grape variety and the percentage of dehydration applied. An increase in the concentration of phenolic acids (gallic, protocateic, coumaric) and flavonols (quercetin, campferol, and myricetin) was observed in all samples during bottle ageing, along with a reduction of anthocyanin (delphinidin, malvidin, peonidine, and cyanidin 3-O-glucoside) and flavanols (+)-catechin and (−)-epicatechin). Main changes in the phenolic composition of all wines occurred during the 10th and 13th month, but the changes in wines produced from dried grapes were softer than control wines, indicating that dehydration process improve the wine phenolic stability and permit long periods of ageing for this kind of wines. Practical applications Different wine regions utilize the grape dehydration to produce differentiated and high value-added wines. This study provides an overview on the effect of grape dehydration process under controlled conditions on wine phenolic evolution during bottle ageing. The results provide relevant information about the storage time required for this kind of wine to improve its commercialization and consumption.

Comparison of fortified, sfursat, and passito wines produced from fresh and dehydrated grapes of aromatic black cv. Moscato nero (Vitis vinifera L.)

Moscato nero d'Acqui is an Italian aromatic black winegrape variety characterized by a low content of anthocyanins (mostly tri-substituted), a satisfactory content of high molecular mass tannins, and a fair amount of terpenes. The grapes were subjected to a postharvest dehydration process under controlled thermohygrometric conditions (16–18°C, 55–70 RH%, 0.6m/s air speed) with the aim to produce three different special wine types (fortified, sfursat, and passito) from fresh, partially dehydrated (27°Brix), and withered (36°Brix) grapes, respectively. Chemical traits of produced grapes and wines were then evaluated through spectrophotometric, HPLC, and GC–MS methods. Increased contents of skin phenolic compounds and reduced extractable contents of seed phenolic compounds were observed as dehydration progressed. Few significant differences were found in the anthocyanin profile of grapes, although the relative abundance of coumaroylated anthocyanins was higher in dehydrated grapes. The predominant free volatile compound found in grapes was geraniol, which decreased with increasing water loss, whereas the contents of major glycosylated volatile compounds increased even above the concentration effect. The changes in the phenolic composition among wines agreed with those among grape skins. Fortified wines were chromatically unsatisfactory probably due to the low content of total anthocyanins, whereas sfursat and passito wines meet good chromatic characteristics as a result of the concentration effect during grape dehydration. Fortified and sfursat wines had free aroma profiles richer in 2-phenylethanol and citronellol, whereas passito wines were mainly composed of 2-phenylethanol and 2-phenylethyl acetate, citronellol being the predominant terpenol in all the wine types studied.

Aromatic character of Cabernet Sauvignon and Merlot wines produced with grapes dried under controlled conditions

This study evaluated the effect of grape dehydration under controlled conditions on the aromatic character of red wines based on the volatile composition and sensory analysis. The wines were produced with Cabernet Sauvignon and Merlot grapes dehydrated (30 g/100 g and 40 g/100 g) under controlled conditions, and grapes without dehydration (control wines). In relation to the aromatic character of the wines, their volatile composition was determined by gas chromatography and quantitative descriptive sensory analysis was carried out. The chemical composition of the musts was also determined, including nitrogen compounds, by liquid chromatography. The results for total ammonium and amino nitrogen contents were higher for the musts from grapes with 30 g/100 g dehydration. The volatile composition of the wines produced with dried grapes showed higher contents of aldehyde, vanillin derivatives and fatty acids compared with the control wines. Sensory analysis showed that wines produced from dried grapes presented higher intensities of coffee, wood, vanilla and alcohol aroma descriptors. Principal component analysis confirmed that the dehydration applied to the grapes altered the aromatic character of the wines, and vanillin derivatives and aldehydes were the main compounds involved in the distinct aroma of red wines produced with dried grapes by the studied process.

Changes in grape polyphenols (V. vinifera L.) as a consequence of post-harvest withering by high-resolution mass spectrometry: Raboso Piave versus Corvina.

Grape dehydration is an oenological process used for the production of high-quality reinforced and sweet wines. Corvina and Raboso Piave are two red grape varieties used for production of high-quality Italian wines, such as Recioto, Amarone di Valpolicella and Raboso Passito. Changes of polyphenolic composition of the grapes as a consequence of the withering were studied by ultra-high performance liquid chromatography-quadrupole time of flight mass spectrometry (UHPLC/QTOF); for identification of compounds a homemade HR-MS database of grape and wine metabolites, was used. Concomitant with trans-resveratrol and viniferins, relevant increases of other stilbenes (piceatannol, resveratrol trimers and tetramers) and antioxidant compounds (quercetin, syringetin and tamarixetin) were observed. These compounds are part of the induced metabolism occurring during the withering process and in general improve the nutraceutical properties of grapes and wines. On the other hand, longer processes showed to decrease flavan-3-ols and glycoside flavonols. Constant increase of E/Z ε-viniferin ratio was observed in all samples, and this parameter can be used to monitor the process. Copyright © 2016 John Wiley & Sons, Ltd.

Assessment of Postharvest Dehydration Kinetics and Skin Mechanical Properties of “Muscat of Alexandria” Grapes by Response Surface Methodology

The dipping of berries in a dilute solution of sodium hydroxide during a short time was evaluated as pretreatment undertaken prior to convective dehydration of wine grapes. The impact of the sodium hydroxide content and dipping time on weight loss (WL) at different dehydration times was thoroughly assessed using central composite design (CCD) and response surface methodology (RSM). Furthermore, the effects of these two variables were also investigated on the skin mechanical properties of dehydrated grapes. The effect of these two pretreatment factors on the dehydration kinetics and skin hardness was satisfactorily fitted to regression models. The berry pretreatment with low sodium hydroxide contents (from 10 to 20 g/L) facilitated the dehydration process during the first 5 days when dipping times longer than 300 s were used. From the seventh day of dehydration, at which time the average WL% was close to 50, the highest values of WL% were obtained using intermediate sodium hydroxide contents and dipping times (around 45 g/L and 185 s, respectively). Because skin hardness affects the dehydration kinetics during postharvest withering, the strongest decrease in skin hardness corresponded to these last berry pretreatment conditions, whereas the greatest increase required the highest sodium hydroxide contents and longest dipping times. The quality of berries dehydrated may be influenced by the pretreatment conditions used, and the present study contributes to increase the knowledge on this effect to a better management of the alkaline pretreatment and dehydration process.

Impact of postharvest dehydration process of winegrapes on mechanical and acoustic properties of the seeds and their relationship with flavanol extraction during simulated maceration

This study represents the first time that the extraction of phenolic compounds from the seeds is assessed from instrumental texture properties for dehydrated grapes. Nebbiolo winegrapes were postharvest dehydrated at 20°C and 41% relative humidity. During the dehydration process, sampling was performed at 15%, 30%, 45% and 60% weight loss. The extractable fraction and extractability of phenolic compounds from the seeds were determined after simulated maceration. The evolution of mechanical and acoustic attributes of intact seeds was also determined during grape dehydration to evaluate how these changes affected the extraction of phenolic compounds. The extractable content and extractability of monomeric flavanols and proanthocyanidins, as well as the galloylation percentage of flavanols, might be predicted easily and quickly from the mechanical and acoustic properties of intact seeds. This would help in decision-making on the optimal dehydration level of winegrapes and the best management of winemaking of dehydrated grapes.

Ozone fumigation for safety and quality of wine grapes in postharvest dehydration

This paper proposes postharvest ozone fumigation (as a method) to control microorganisms and evaluate the effect on polyphenols, anthocyanins, carotenoids and cell wall enzymes during the grape dehydration for wine production. Pignola grapes were ozone-treated (1.5g/h) for 18h (A=shock treatment), then dehydrated or ozone-treated (1.5g/h) for 18h and at 0.5g/h for 4h each day (B=long-term treatment) during dehydration. Treatment and dehydration were performed at 10°C. No significant difference was found for total carotenoid, total phenolic and total anthocyanin contents after 18h of O3 treatment. A significant decrease in phenolic and anthocyanin contents occurred during treatment B. Also carotenoids were affected by B ozone treatment. Pectin methylesterase (PME) and polygalacturonase (PG) activities were higher in A-treated grapes during dehydration. Finally, ozone reduced fungi and yeasts by 50%. Shock ozone fumigation (A treatment) before dehydration can be used to reduce the microbial count during dehydration without affecting polyphenol and carotenoid contents.

Effect of grape dehydration under controlled conditions on chemical composition and sensory characteristics of Cabernet Sauvignon and Merlot wines

Cabernet Sauvignon and Merlot wines produced with grapes dried under controlled conditions (7 °C, 35% relative humidity and airflow of 12 m3/s) were chemical and sensory characterized. Cabernet Sauvignon and Merlot grapes were vinified at the time of harvest (control wines) and after 30 and 40 g/100 g dehydration to wines produced with dried grapes. The Merlot wine produced with 40 g/100 g dried grapes, and the Cabernet Sauvignon wine produced with 30 g/100 g dried grapes, showed the highest levels of total polyphenols and total antioxidant activity. The elemental content was highest in wines produced with dried grapes. Sensory characterization showed that wines produced with dehydrated grapes exhibited typical descriptors of liqueur wines such as red-orange colour and high viscosity and alcoholic sensation. Principal component analysis confirmed that the grape dehydration process under controlled conditions influenced the chemical composition and sensory characteristics of the wines produced, mainly from 40 g/100 g dried grape, yielding differentiated and high value-added products.

English

The partial dehydration of grapes after harvest aimed at winemaking has been shown to be a process that brings increased concentration of sugar and phenolic compounds in the must, which affects the quality of the wines produced. However, the works developed so far have studied the process for temperatures up to a maximum of 25°C and air velocity lower than 1 m.s-1. This study aimed to analyze the physical-chemical changes concentration of total soluble solids (TSS) and phenolic compounds (PC) after partial dehydration of 'Syrah' grapes subjected to two treatments combining two temperatures and one air velocity (T1= 22.9°C/1.79 m.s-1 and T2 = 37.1°C/1.79 m.s-1) and relative humidity of 40%. The water loss of the grapes was approximately 14% and the drying process lasted between 34 and 68 h for treatments T2 and T1, respectively. We experimentally and statistically verified that the treatments promoted significant increase in TSS and PC; however, for PC at the temperature of 37.1°C, the increase accounted for approximately 27%, whereas, for the temperature of 22.9°C, it was only 12%. For TSS, the increase was on average 12.47±0.9% between both treatments. The results demonstrate that it is possible to moderately dry grapes, which consequently results in improvements in their chemical composition and can improve the quality of wine. Key words: Wine, polyphenols, soluble solids, drying, instrumentation.

English

The partial dehydration of grapes after harvest and aimed wine-making, has been shown to be a process that brings increased concentration of sugar and phenolic compounds in the must, which results in the quality of the wines produced. However, the works developed so far studied the process for temperatures up to a maximum of 25°C and air velocity less than 1 m.s-1. This study aimed to analyze the physical and chemical changes (concentration of total soluble solids (TSS) and phenolic compounds (CPC)) after partial dehydration of 'Niagara Rosada' grapes at the temperature subjected to two treatments combining two temperatures and one air velocity (T1= 22.9°C/1.79 m.s-1 and T2 = 37.1°C/1.79 m.s-1), and relative humidity of approximately 40%. The loss of water in the grapes was approximately 14% and the drying process lasted between 20 to 50 h for the treatments T1 and T2, respectively. We experimentally and statistically verified that the treatments promoted significant increase in TSS and CPC; however, for CPC at the temperature of 37.1°C, the increase accounted for approximately 29%, whereas, for the temperature of 22.9°C, it was only 5%. For TSS, the increase was on average 14.4 ± 3.9% between both treatments.   Key words: Chaptalization, temperature, air velocity, winemaking.

Postharvest dehydration of Nebbiolo grapes grown at altitude is affected by time of defoliation

Background and Aims Sfursat is an Italian wine produced with partially dehydrated Nebbiolo grapes in the Valtellina region which is located at high altitude. The research aims to understand the influence of fruit exposure on the rate of water loss by harvested fruit and the influence of exposure and dehydration on the content of phenolic substances and anthocyanins in the wine. Methods and Results Clusters of Nebbiolo grapes from control vines (ND) and from vines that were defoliated at fruitset (DFS) or post-veraison (DPV) were harvested at a sugar concentration of about 230 g/L (there was no significant difference among the treatments), and dehydrated at 10, 20 or 30°C and at 60% relative humidity (RH), and air flow. Fruit were sampled at 10 and 20% weight loss (WL). Leaf removal had little effect on the physical characteristics of bunches and on the anthocyanins content and profile of harvested Nebbiolo grapes but affected dehydration. At 10 and 20°C, DFS fruit lost mass more slowly than DPV and ND fruit. In ND fruit, 20% WL reduced anthocyanins from 554 mg/kg fresh mass (FM) at harvest to 458, 432 and 396 mg/kg FM at 10, 20 and 30°C, respectively. In DFS and DPV berries, anthocyanins increased during dehydration at 10°C. At harvest, ND berries had a lower content of total stilbenes than those from defoliated vines. Dehydration (10°C, 20% WL) increased stilbene concentration in ND and DPV fruit. Dehydration at 10°C induced a rise in the flavonol concentration in fruit from defoliated vines. Catechin concentration was 106.5 mg/kg DM (dry mass), the highest value in ND berries at harvest. Wine was produced only from grapes dehydrated at 10°C. Wine from DFS fruit had a higher content of phenolic substances (2704.8 mg/L) and anthocyanins (104 mg/L) than that from DPV (2454.9 and 96.2 mg/L, respectively) and ND (2301.9 and 100.5 mg/L, respectively) fruit. Conclusions Postharvest dehydration was slower where vines had been defoliated and resulted in changes in the ratios among groups of phenolic substances as well as among single phenolic components. Significance of the Study In Nebbiolo grapes for Sfurzat wine production, defoliation at fruit set enables fruit to reach phenolic maturity at a lower sugar concentration allowing dehydration to increase sugar concentration without producing excessively alcoholic wines.

A Review of the Health Benefits of Raisins

There have been relatively few studies conducted on the health benefits of dried fruits; however, over the past few years there have been many advances regarding the health benefits of raisins. Williamson and Carughi (2012) recently reviewed the polyphenol content and health benefits of raisins. The review showed that raisins contain significant amounts of the flavonols quercetin and kaempferol and the phenolic acids caftaric and coutaric. Both quercetin and kaempferol are found in raisins as glycosides. Although the bioavailability of these compounds has not been studied in raisins, they have been shown to be well absorbed from other foods. These compounds may be responsible for some of the health benefits that have been reported with raisin consumption (Williamson and Carughi 2012). During the dehydration of grapes to raisins there is a significant loss of specific phenolic acids and polyphenols. However, total antioxidant capacity and total polyphenol contents remain relatively unchanged. Moreover, when equivalent amounts of grapes are fed either as fresh grapes, raisins, or wine (non-alcoholic) similar amounts of certain phenolic acid metabolites are detected in the urine. Thus, phenolic acids appear to be more bioavailable in raisins than in grapes and white wine (Murphy 2012). A webcast regarding the Emerging Health Benefits of Traditional Dried Fruit was presented on July 18, 2012 as a satellite session to the 2012 Institute of Food Technologists (IFT) annual meeting. This webcast was designed to review the latest research on the health benefits of raisins. The webcast included research studies regarding raisins and dental health by Allen Wong, D.D.S., Ed.D; heart disease and glycemic response by James Anderson, MD; satiety and energy intake by Barkha Patel, M.Sc.; and phytonutrient content by Rui Hai Liu, M.D., Ph.D. This supplement includes review papers from this webcast. Grape consumption, in the form of fresh grapes, raisins, and 100% grape juice, is associated with an overall increase in diet quality and nutrient intake. In “Improved Diet Quality and Increased Nutrient Intakes Associated with Grape Product Consumption by U.S. Children and Adults: National Health and Nutrition Examination Survey 2003–2008”, Debra Keast compared the diet quality of grape consumers (GC) with non-grape consumers (NGC). Compared to NGC, GC had higher intakes of total and whole fruit along with lower intakes of solid fat and added sugars. The grape consumers had higher intakes of several key nutrients including dietary fiber, vitamin A, vitamin C, calcium, and potassium. In “Raisins and Oral Health”, Allen Wong, D.D.S., Ed.D, discussed how current research shows some evidence that raisins may not contribute to dental caries, contrary to traditional thought. This paper reviews new findings with regards to raisins and the three conditions that are thought to contribute to the formation of dental caries; low oral pH, adherence of food to teeth, and biofilm (bacterial) behavior. The consumption of raisins has also been shown to improve blood glucose control and reduce risk for cardiovascular disease. In “Raisin Consumption by Humans: Effects On Glycemia and Insulinemia and Cardiovascular Risk Factors” James Anderson, M.D. reviews past research on the cardiovascular protective effects of raisins including their effects in reducing oxidized LDL (Barnes and others 2011) and reducing low-density lipoprotein (LDL) cholesterol (Puglisi and others 2008). The effect of the regular consumption of raisins on reduction of post-prandial glucose levels, HgbA1C, and blood pressure are also reviewed (Bays and others 2012 a, b) In “An After-School Snack of Raisins Lowers Cumulative Food Intake in Young Children” Barkha Patel, M.Sc. discusses how raisins as an after-school snack lower cumulative intake over the day compared to other snacks (potato chips, cookies). The researchers also discussed how the consumption of raisins before lunch can reduce calorie consumption at the subsequent meal. Researchers suggest that raisins as a snack may support appetite and weight control, thus reducing the risk for obesity (Patel and others 2011). In “Dietary Bioactive Compounds and Their Health Implications”, Rui Hai Liu, M.D., Ph.D, covered current research on phytochemicals in raisins and the prevention of chronic disease. Evidence suggests that health benefits of raisins may be attributed to the synergistic effects of phytochemicals present in whole foods.

The expression pattern of β-glucosidase genes (VvBGs) during grape berry maturation and dehydration stress

In order to understand more about the role of β-glucosidase gene expression in modulating ABA level, the expression pattern of three cDNAs (VvBG1, VvBG2 and VvBG3) which encode β-glucosidase in ripening grape berries was analyzed in the presence or absence of dehydration stress. The results show that expression of these three VvBG genes was markedly different. Expression of VvBG1 and VvBG2 increased rapidly from veraison to reach a maximum at harvest or several days immediately before harvest, and coincident with ABA accumulation during berry development and ripening. However, expression of VvBG3 differed from VvBG1 and VvBG2 in that transcript levels declined from the early young fruit stage through veraison after which there was no further change. At 10 days before harvest, dehydration treatment of detached grape berries up-regulated the expression of VvBG1 and enhanced ABA accumulation whereas the expression of VvBG2 was down-regulated, VvBG3 was unaffected by dehydration stress. However, in the leaves, dehydration treatment up-regulated the expression of VvBG1 and stimulated the accumulation of ABA but down-regulated expression of VvBG2 and VvBG3. Based on the results obtained, it is concluded that the expression pattern of the three VvBGs is both temporal and tissue specific. Furthermore, expression of the VvBGs might play a role in the regulation of ABA content during berry ripening and in the response of berries to dehydration stress.

Varietal Relationship Between Skin Break Force and Off-Vine Withering Process for Winegrapes

This article presents a detailed study on the influence of winegrape variety, skin hardness of fresh berries, and withering thermo-hygrometric conditions on the dehydration kinetics of the grape. Although some works focused on the changes in the weight loss rate during grape dehydration under different environment conditions for several varieties, the combined effect of the skin mechanical properties and the thermo-hygrometric conditions has not been previously considered. The skin break force was confirmed as the varietal marker. Furthermore, its role in the selection of the withering conditions was assessed. The fresh grape berries were classified into two groups (soft and hard) according to the skin break force, and four off-vine withering conditions were evaluated. The softer skins facilitated the dehydration process increasing the weight loss rate, but the increase was significant only at low temperatures. The increase in temperature and/or decrease in relative humidity was beneficial to the grape dehydration process. A weight loss of about 50% after 12 days of withering was achieved at an air temperature of 28°C and relative humidity of 40%. Under the same dryer environmental conditions, a certain varietal effect on the dehydration kinetics was observed because a faster weight loss occurred for those grapes characterized by lower values of skin break force. These results suggest that the grape dehydration rate, influencing the quality of dessert wines, should be planned considering the skin hardness of fresh berries and the withering conditions. The skin break force represents a new variable that should be considered in modeling the withering process and in selecting, prior to harvest, the most appropriate vineyard for the dessert wines desired.

Sensory Quality Control of Young vs. Aged Sweet Wines Obtained by the Techniques of Both Postharvest Natural Grape Dehydration and Fortification with Spirits During Vinification

Although grapes subjected to different sugar concentration methods are known to provide also different types of sweet wines, the exact influence of such methods on the sensory properties of the wines is largely unknown. The purpose of this work was to identify differences in sensory profile between young and aged wines obtained from grapes subjected to various sugar concentration techniques. Differences in sensory properties were judged by a panel of trained tasters. Young sweet wines were judged to have a sweeter balance and a dried fruit taste associated to higher global sensory attributes of odour and taste. Some differences in sensory fingerprint were due to their aging in oak barrels, which introduced flavour mainly based on attributes such as vanilla, phenolic, wood, and burnt wood tastes. There were also clear differences between sweet wines obtained by natural grape dehydration and others obtained by fortification with 96 % (v/v) ethanol fit for human consumption: naturally sweet wines were most appreciated than fortified sweet wines, since they were not only ranking higher in honey and dried fruit tastes, but also in overall colour and odour.

Application of NIR-AOTF Spectroscopy to Monitor Aleatico Grape Dehydration for Passito Wine Production

Aleatico (<i>Vitis vinifera</i> L.) grapes were harvested at 21.3 Brix and dehydrated at 20°C, 45% relative humidity, and 1.5 m/sec air flow in a small-scale thermo-conditioned tunnel. Postharvest grape dehydration was performed until the fruit lost an average of 40% initial weight. During dehydration, single destemmed grape berries were analyzed nondestructively using an acousto-optically tunable filter (AOTF) near-infrared (NIR) spectrophotometer (1100–2300 nm) in reflectance. Total soluble solids (TSS) and moisture content (%) were measured on the same berries with the objective of using spectral and nonspectral information to develop regression models for predicting these parameters. Partial least squares regression applied after different statistical pretreatments (multiplicative scatter correction, Savitzky-Golay 1^st or 2^nd derivative filter) was tested on absorbance spectra to define the most effective approach. Two prediction models were obtained (<i>n</i> = 450 for TSS, <i>n</i> = 600 for water loss) in which the coefficient of determination in cross-validation (r²) and the root mean standard error of cross-validation were 0.93 and 0.89 Brix for TSS and 0.92 and 2.16% for water loss, respectively. A model validation procedure was performed using separate sample sets (<i>n</i> = 170 for TSS, <i>n</i> = 200 for water loss) with the following results: coefficient of determination (R²) and standard error of prediction of 0.92 and 0.72 Brix for TSS and 0.9 and 1.89% for water loss, respectively.

Is intraspecific variability of growth and mycotoxin production dependent on environmental conditions? A study with Aspergillus carbonarius isolates

The aim of this study was to assess the impact of suboptimal environmental conditions on the intraspecific variability of A. carbonarius growth and OTA production using thirty isolates of A. carbonarius.Three aw/temperature conditions were tested, one optimal (0.98aw/25°C) and two suboptimal: 0.90aw/25°C and 0.98aw/37°C as suboptimal water activity and temperature, respectively, which might take place through over ripening and dehydration of grapes. For each condition, 12 Petri dishes were inoculated, and colony growth and OTA production were measured over time.ANOVA revealed significant differences among μ and λ within the 30 assayed isolates. Coefficients of variation (CV%) revealed a wider dispersion of growth rates at 0.90aw/25°C compared to 0.98aw/25°C, and a more than 4-fold higher CV at 0.98aw/37°C compared to 0.98aw/25°C. However, dispersion of lag phases was similar at 0.98aw/25°C and 0.90aw/25°C and wider at 0.98aw/37°C.There were significant differences (p<0.05) among OTA levels (ng/mm2) for the different conditions, values being lower under marginal conditions, and particularly at 0.98aw/37°C. Coefficients of variation (CV%) revealed a wider dispersion of OTA production at 0.90aw/25°C compared to 0.98aw/25°C, while CV at 0.98aw/37°C was similar to that at 0.98aw/25°C.In order to address the strain variability in growth initiation and prove the well-established notion of reducing OTA in foods by preventing fungal growth, a greater number of strains should be included when developing models for conditions that are suboptimal both for aw for OTA production and temperature levels for growth.

Electronic nose to study postharvest dehydration of wine grapes

Montepulciano grapes were dehydrated at 10 and 20 °C, 45% RH and 1–1.5 m/s of air flow. Samplings were performed at 10%, 20%, 30%, and 40% of weight loss (wl). TSS (total solids content) increased up to 43° and 36° Brix at 20 and 10 °C, respectively, in 27 and 48 days. A straight regression line between M (kg water/kg dry matter) loss and days of dehydration with R 2 values, equal to 0.97, was found but an angular coefficient of −0.048 and −0.038, respectively at 20 and 10 °C indicated a different rate of weight loss. Volatiles compounds profile changed significantly with the temperature during the dehydration process. Anaerobic metabolites such as ethanol, acetaldehyde, and ethylacetate were much higher at 20 °C than at 10 °C and rose progressively, while at 10 °C, the significant rise was observed between 30% and 40% weight loss. Alcohols and esters prevailed at 20 °C while at 10 °C larger abundances of aldehydes and terpene alcohols are observed. PCA analysis of GC/MS confirmed the volatiles compounds separation between the samples held at 20 and 10 °C. A progressive evolution of the profile is observed for the samples held at 20 °C while those held at 10 °C show a change of volatiles compounds profile only at 40% wl. Loadings analysis show that aldehydes and terpenols are oriented towards the direction of 10 °C samples while alcohols and esters in that of 20 °C samples. The behaviours of GC/MS data were partially corroborated by the data of electronic nose. Electronic nose was able to follow the progressive change of aroma profile at 20 °C while at 10 °C grouped the responses obtained at 10%, 20%, 30% wl all together but at 40% wl, it discriminated the aroma response. This result opens a window on the potential use to monitor commercially the grape dehydration.

Modifications of mechanical characteristics and phenolic composition in berry skins and seeds of Mondeuse winegrapes throughout the on‐vine drying process

AbstractBACKGROUND: Among several common drying systems used in the enological sector the dry‐on‐vine (DOV) method assumes particular importance because famous wines such as Sauternes, Tokay and Ice Wines are produced by grapes dried using this system. Knowledge about trends in mechanical properties and phenolic composition during on‐vine grape drying is scarce. The objective of this current study is therefore to increase the knowledge on these aspects.RESULTS: Berry skin break energy (+0.10 N) and berry skin thickness (+69 µm) values increase during grape dehydration, while the peduncle detach force decreases (−0.86 N). Large reductions in the anthocyanin content have also been observed (−40%), but their profile does not show significant changes. Seed hardness (−7.10 N, −1.40 mJ) decreases during the withering, and higher seed springiness has been observed. Seed proanthocyanidins (+2050 mg kg berry−1) and flavanols vanillin assay (+670 mg kg berry−1) increase progressively throughout the withering. In contrast, a distinct lowering of these substances in the skins was noted.CONCLUSION: Many modifications in the chemical–physical characteristics of berries of Mondeuse winegrapes throughout the DOV process were found. The mechanical characteristics of grapes, in particular the peduncle detachment force, are important parameters in assessing their suitability for the drying‐on‐plant process. Copyright © 2009 Society of Chemical Industry