Effect of Must Hyperoxygenation on Sensory Expression and Chemical Composition of the Resulting Wines

This paper evaluates the effect of must hyperoxygenation on final wine. Lower concentrations of caftaric acid (0.29 mg·L−1), coutaric acid (1.37 mg·L−1) and Catechin (0.86 mg·L−1) were observed in hyperoxygenated must in contrast to control must (caftaric acid 32.78 mg·L−1, coutaric acid 5.01 mg·L−1 and Catechin 4.45 mg·L−1). In the final wine, hydroxybenzoic acids were found in higher concentrations in the control variant (gallic acid 2.58 mg·L−1, protocatechuic acid 1.02 mg·L−1, vanillic acid 2.05 mg·L−1, syringic acid 2.10 mg·L−1) than in the hyperoxygenated variant (2.01 mg·L−1, 0.86 mg·L−1, 0.98 mg·L−1 and 1.50 mg·L−1 respectively). Higher concentrations of total flavanols (2 mg·L−1 in hyperoxygenated must and 21 mg·L−1 in control must; 7.5 mg·L−1 in hyperoxygenated wine and 19.8 mg·L−1 in control wine) and polyphenols (97 mg·L−1 in hyperoxygenated must and 249 mg·L−1 in control must; 171 mg·L−1 in hyperoxygenated wine and 240 mg·L−1 in control wine) were found in both the must and the control wine. A total of 24 volatiles were determined using gas chromatography mass spectrometry. Statistical differences were achieved for isobutyl alcohol (26.33 mg·L−1 in control wine and 32.84 mg·L−1 in hyperoxygenated wine), or 1-propanol (7.28 mg·L−1 in control wine and 8.51 mg·L−1 in hyperoxygenated wine), while esters such as isoamyl acetate (1534.41 µg·L−1 in control wine and 698.67 µg·L−1 in hyperoxygenated wine), 1-hexyl acetate (136.32 µg·L−1 in control wine and 71.67 µg·L−1 in hyperoxygenated wine) and isobutyl acetate (73.88 µg·L−1 in control wine and 37.27 µg·L−1 in hyperoxygenated wine) had a statistically lower concentration.

When metabolic prowess is too much of a good thing: how carbon catabolite repression and metabolic versatility impede production of esterified α,ω-diols in Pseudomonas putida KT2440

Background Medium-chain-length α,ω-diols (mcl-diols) are important building blocks in polymer production. Recently, microbial mcl-diol production from alkanes was achieved in E. coli (albeit at low rates) using the alkane monooxygenase system AlkBGTL and esterification module Atf1. Owing to its remarkable versatility and conversion capabilities and hence potential for enabling an economically viable process, we assessed whether the industrially robust P. putida can be a suitable production organism of mcl-diols. Results AlkBGTL and Atf1 were successfully expressed as was shown by oxidation of alkanes to alkanols, and esterification to alkyl acetates. However, the conversion rate was lower than that by E. coli, and not fully to diols. The conversion was improved by using citrate instead of glucose as energy source, indicating that carbon catabolite repression plays a role. By overexpressing the activator of AlkBGTL-Atf1, AlkS and deleting Crc or CyoB, key genes in carbon catabolite repression of P. putida increased diacetoxyhexane production by 76% and 65%, respectively. Removing Crc/Hfq attachment sites of mRNAs resulted in the highest diacetoxyhexane production. When the intermediate hexyl acetate was used as substrate, hexanol was detected. This indicated that P. putida expressed esterases, hampering accumulation of the corresponding esters and diesters. Sixteen putative esterase genes present in P. putida were screened and tested. Among them, Est12/K was proven to be the dominant one. Deletion of Est12/K halted hydrolysis of hexyl acetate and diacetoxyhexane. As a result of relieving catabolite repression and preventing the hydrolysis of ester, the optimal strain produced 3.7 mM hexyl acetate from hexane and 6.9 mM 6-hydroxy hexyl acetate and diacetoxyhexane from hexyl acetate, increased by 12.7- and 4.2-fold, respectively, as compared to the starting strain. Conclusions This study shows that the metabolic versatility of P. putida, and the associated carbon catabolite repression, can hinder production of diols and related esters. Growth on mcl-alcohol and diol esters could be prevented by deleting the dominant esterase. Carbon catabolite repression could be relieved by removing the Crc/Hfq attachment sites. This strategy can be used for efficient expression of other genes regulated by Crc/Hfq in Pseudomonas and related species to steer bioconversion processes.

Study of Wine Volatile Composition of Tempranillo versus Tempranillo Blanco, a New White Grape Variety

The aim of this work was to analyze and compare the concentration of higher alcohols, esters, and acids in wines from Tempranillo and Tempranillo Blanco. Tempranillo Blanco is a new and little-studied white variety that originated from Tempranillo by a natural mutation. During three seasons, grapevines of both varieties were harvested, and nine wines were made from each. The volatile composition of the wines was determined by GC-MS. In the wines of both varieties, the content of higher alcohols was higher than those of esters and acids. Wines from Tempranillo Blanco had lower content of 2-phenylethanol, methionol, 1-hexanol, benzyl alcohol, and total higher alcohols, but higher hexyl acetate and ethyl decanoate than Tempranillo wines. Total ethyl esters and total esters were higher in Tempranillo wines due to the higher ethyl lactate and ethyl succinate content derivate from the malolactic fermentation that was not made in Tempranillo Blanco. The content of hexanoic and octanoic acids and total acids was also higher in Tempranillo Blanco wines than in Tempranillo. This is one of the first studies carried out on the wine volatile composition of Tempranillo Blanco and therefore contributes to a better understanding of the oenological characteristics of this white variety.

Trans-2-Hexenal-Based Antifungal Packaging to Extend the Shelf Life of Strawberries

Strawberries are valuable because of their nutritional value, but they are also highly perishable fruits. Fungal decay is the overriding factor that alters the overall quality of fresh strawberries. Because no hygienic treatments to reduce the initial microbial load are feasible, molds develop during postharvest when using conventional packaging. In this study, an antifungal packaging system for strawberries was developed to improve safety and quality. Trans-2-hexenal (HXAL), a natural compound in strawberries, was incorporated into the modified atmosphere packaging (MAP) systems. Zero, 100, and 250 µL of HXAL were included in cellulosic pads and were covered with a polyamide coating to control its release. The pads were placed on the bottom of plastic trays; an amount of250 g of strawberries was added, flow packed in micro-perforated PP bags, and stored at 4 °C for 14 days. Fungal infection was monitored during the storage period, and the optical and textural properties of the strawberries were measured at days 0 and 14. Analysis of the package headspace was conducted to check for the HXAL concentration. HXAL was partially retained in the fruits and was converted into hexyl acetate and 2-hexen-1-ol acetate, but this was only measurably present in the headspace of the active systems. Mold growth was fully inhibited in active packaging although the strawberries were softer and darker than those in the control packages. The active package was not as efficient if the fruits were stored under thermal-abuse conditions (15 and 22 °C).

Aroma and Sensory Profiles of Sauvignon Blanc Wines from Commercially Produced Free Run and Pressed Juices

Sauvignon blanc is the most important grape cultivar within the New Zealand wine industry, and wines from the Marlborough region are renowned for their intense aromas including tropical, passionfruit, and green capsicum. Quality Sauvignon blanc wines are usually made from free run juice, although press fractions can be included. The chemical aroma composition and sensory profiles of two wine sets made from three press fractions (free run, light press and heavy press) were compared. The compounds 3-mercaptohexan-1-ol and 3-mercaptohexyl acetate were found to decrease between free run and heavily pressed wines while hexyl acetate, hexanol, and benzyl alcohol increased. The accompanying sensory analysis showed that free run wines were marked by aromas of Passionfruit/sweaty, Boxwood and Fresh green capsicum, while the heavy pressed wines were described by French vanilla/bourbon, Floral and Banana lolly attributes, consistent with the aroma chemical composition.

Semiochemical-Based Attractant for the Ambrosia Pinhole Borer Euplatypus parallelus

A semiochemical-based attractant for Euplatypus parallelus was identified and field-tested. Analyses of headspace volatile extracts of conspecific males revealed the presence of 1-hexanol along with lesser amounts of 3-methyl-1-butanol, hexyl acetate, 1-octanol and trans-geraniol, which were not found in equivalent extracts from females. Emission of 1-hexanol coincided with the emergence of adults of both sexes during afternoon hours. A synthetic blend of these compounds, with and without ethanol, was tested in the field. The blend alone attracted a small number of females and no males. Ethanol alone attracted a small number of females (not significantly different from the blend alone) but significantly more males than the blend alone. More females were caught with the blend combined with ethanol than the combined catch of either attractant alone, suggesting a synergistic interaction. Attraction of males appeared to be a response to ethanol alone. During the trials, two potential natural enemies of E. parallelus were caught, indicating that they might be eavesdropping on the semiochemical channels of their prey. Traps containing the male-specific volatile compounds combined with ethanol could be applied as an effective attractant for detection and monitoring of E. parallelus as well as for recruitment of its natural enemies.

Functional Analysis of Odorant-Binding Proteins 12 and 17 from Wheat Blossom Midge Sitodiplosis mosellana Géhin (Diptera: Cecidomyiidae)

The wheat blossom midge Sitodiplosis mosellana, one of the most disastrous wheat pests, depends highly on olfactory cues to track suitable plants. To better understand the olfactory recognition mechanisms involved in host selection, in the present study we cloned two S. mosellana adult antenna-specific odorant binding protein (OBP) genes, SmosOBP12 and SmosOBP17, and evaluated bacterially expressed recombinant proteins for their selectivity and sensitivity for host wheat volatiles using the fluorescence-based ligand binding assay. The results showed that both SmosOBPs effectively bound alcohol, ester, ketone, and terpenoid compounds. Particularly, SmosOBP12 had significantly higher affinities (Ki < 10.5 μM) than SmosOBP17 (Ki2 > 0.1 μM) to 3-hexanol, 1-octen-3-ol, D-panthenol, 3-carene, (Z)-3-hexenylacetate, hexyl acetate, methyl salicylate, heptyl acetate, and ethyl heptanoate. Consistently, S. mosellana females were attracted to all these chemicals in a behavioral assay using Y-tube olfactometer. SmosOBP12 also bound aldehyde, but neither bound alkanes. Notably, SmosOBP12 exhibited strong affinity to ocimene (Ki = 8.2 μM) that repelled S. mosellana. SmosOBP17, however, was insensitive to this compound. Taken together, our results indicate that SmosOBP12 may play a greater role than SmosOBP17 in perceiving these biologically active plant volatiles.

Free and Bound Volatile Aroma Compounds of ´Maraština´ Grapes as Influenced by Dehydration Techniques

Dehydration or drying of grapes is one of the most important steps in the production of Croatian traditional dessert wine Prošek. The natural sun drying of grapes is the traditionally used method in Prošek production. Alternative methods, such as dehydration under controlled conditions, have been studied as safer and faster methods than the traditional sun drying but without precise knowledge of the effect on volatile compounds. The objective of this work was to study how dehydration of grapes carried out in a greenhouse and an environmentally controlled chamber impacts on the free and glycosidically bound volatile compounds of native grape cv. ‘Maraština’. The 36 volatile compounds were identified and quantified using headspace solid-phase micro extraction coupled with gas chromatography-mass spectrophotometry (HS-SPME-GC/MS). The results showed that the aroma profile of dehydrated grapes was significantly different from that of fresh grapes. Regarding free forms, significant increases in the concentration of 2-methyl-1-propanol, 1-butanol, 2-hexen-1-ol, 1-hexanol, ethyl hexanoate, hexyl acetate, o-cymene, linalool oxide, and terpinen-4-ol and geraniol were found in greenhouse-dried grapes, whereas increases in cis-limonene-epoxide, trans-limonene epoxide, and γ-hexalactone were higher in chamber-dried grapes compared to greenhouse-dried grapes. Glycosidically bound forms of o-cymene, linalool oxide, linalool, and terpinen-4-ol were increased in both types of drying, whereas β-damascenone was increased only in greenhouse-dried grapes.