Paola Piombino

Bacterial populations and the volatilome associated to meat spoilage

Microbial spoilage of meat is a complex event to which many different bacterial populations can contribute depending on the temperature of storage and packaging conditions. The spoilage can derive from microbial development and consumption of meat nutrients by bacteria with a consequent release of undesired metabolites. The volatile organic compounds (VOCs) that are generated during meat storage can have an olfactory impact and can lead to rejection of the product when their concentration increase significantly as a result of microbial development. The VOCs most commonly identified in meat during storage include alcohols, aldehydes, ketones, fatty acids, esters and sulfur compounds. In this review, the VOCs found in fresh meat during storage in specific conditions are described together with the possible bacterial populations responsible of their production. In addition, on the basis of the data available in the literature, the sensory impact of the VOCs and their dynamics during storage is discussed to highlight their possible contribution to the spoilage of meat.

Saliva from Obese Individuals Suppresses the Release of Aroma Compounds from Wine

Background Recent evidence suggests that a lower extent of the retronasal aroma release correspond to a higher amount of ad libitum food intake. This has been regarded as one of the bases of behavioral choices towards food consumption in obese people. In this pilot study we investigated the hypothesis that saliva from obese individuals could be responsible for an alteration of the retro-nasal aroma release. We tested this hypothesis in vitro, by comparing the release of volatiles from a liquid food matrix (wine) after its interaction with saliva from 28 obese (O) and 28 normal-weight (N) individuals. Methods and Findings Amplicon sequencing of the 16S rRNA V4 region indicated that Firmicutes and Actinobacteria were more abundant in O, while Proteobacteria and Fusobacteria dominated in N. Streptococcaceae were significantly more abundant in the O subjects and constituted 34% and 19% on average of the saliva microbiota of O and N subjects, respectively. The Total Antioxidant Capacity was higher in O vs N saliva samples. A model mouth system was used to test whether the in-mouth wine aroma release differs after the interaction with O or N saliva. In O samples, a 18% to 60% significant decrease in the mean concentration of wine volatiles was detected as a result of interaction with saliva, compared with N. This suppression was linked to biochemical differences in O and N saliva composition, which include protein content. Conclusion Microbiological and biochemical differences were found in O vs N saliva samples. An impaired retronasal aroma release from white wine was detected in vitro and linked to compositional differences between saliva from obese and normal-weight subjects. Additional in vivo investigations on diverse food matrices could contribute to understanding whether a lower olfactory stimulation due to saliva composition can be a co-factor in the development/maintenance of obesity.

The same microbiota and a potentially discriminant metabolome in the saliva of omnivore, ovo-lacto-vegetarian and Vegan individuals.

The salivary microbiota has been linked to both oral and non-oral diseases. Scant knowledge is available on the effect of environmental factors such as long-term dietary choices on the salivary microbiota and metabolome. This study analyzed the microbial diversity and metabolomic profiles of the saliva of 161 healthy individuals who followed an omnivore or ovo-lacto-vegetarian or vegan diet. A large core microbiota was identified, including 12 bacterial genera, found in >98% of the individuals. The subjects could be stratified into three “salivary types” that differed on the basis of the relative abundance of the core genera Prevotella, Streptococcus/Gemella and Fusobacterium/Neisseria. Statistical analysis indicated no effect of dietary habit on the salivary microbiota. Phylogenetic beta-diversity analysis consistently showed no differences between omnivore, ovo-lacto-vegetarian and vegan individuals. Metabolomic profiling of saliva using 1H-NMR and GC-MS/SPME identified diet-related biomarkers that enabled a significant discrimination between the 3 groups of individuals on the basis of their diet. Formate, urea, uridine and 5-methyl-3-hexanone could discriminate samples from omnivores, whereas 1-propanol, hexanoic acid and proline were characteristic of non-omnivore diets. Although the salivary metabolome can be discriminating for diet, the microbiota has a remarkable inter-individual stability and did not vary with dietary habits. Microbial homeostasis might be perturbed with sub-standard oral hygiene or other environmental factors, but there is no current indication that a choice of an omnivore, ovo-lacto-vegetarian or vegan diet can lead to a specific composition of the oral microbiota with consequences on the oral homeostasis.

Earthy off-flavour in wine: evaluation of remedial treatments for geosmin contamination.

Seven treatments (activated charcoal, bentonite, PVPP, yeast cell walls, potassium caseinate, zeolite and grape seed oil) were evaluated for their efficacy in decreasing the concentration of geosmin, responsible for earthy off-flavour in wine. In the red wine the potassium caseinate and grape seed oil treatments decreased the concentration of geosmin by 14% and 83%, respectively, while in the white wine, the activated charcoal and the grape seed oil were able to decrease the concentration of geosmin by 23% and 81%, respectively. The effective treatments in decreasing geosmin also decreased aroma volatile compounds, most of all esters, responsible for fruity notes. Considering the OAVs (concentration/odour threshold) only the treatment with grape seed oil was able to decrease the relative contribution of geosmin to the profile of the odour active compounds, both in red and in white wine. Sensory analysis confirmed the efficacy of the grape seed oil as a remedial treatment.

Free and Enzymatically Hydrolysed Volatile Compounds of Sweet Wines from Malvasia and Muscat Grapes (Vitis vinifera L.) Grown in Sardinia

The aroma of Muscat of Sorso-Sennori and Malvasia di Bosa wines obtained from grapes grown in Sardinia was evaluated by instrumental analysis. Gas chromatography/mass spectrometry was used to identify and quantify the content of free and bound volatile compounds. The odour activity value (OAV) was also calculated. Higher alcohols and esters were quantitatively the largest group of free volatile compounds in both wines, while terpenes were the main class of bound volatiles. A total of 52 free and 26 bound volatiles were detected. Malvasia di Bosa sweet wine had a higher content of alcohols, esters and acids in comparison to Muscat of Sorso-Sennori, which was richer in some terpenes, like nerol, geraniol and geranic acid, and also in bound volatile compounds. A total of 12 compounds were above the OAV. The main aroma-active compounds of Muscat were 3-methylbutyl acetate (banana), ethyl octanoate and hexanoate (fruity), and linalool (flowery), Malvasia wine was characterised particularly by ethyl octanoate and by 3-methylbutyl acetate.

Treatment by fining agents of red wine affected by phenolic off-odour

Although phenolic off-odour is very detrimental for red wine quality, there is a lack of easy-to-use methods able to decrease the levels of the responsible compounds 4-ethylphenol (4-EP) and 4-ethylguaiacol (4-EG) and to improve the sensory quality of the contaminated wines. To this aim, an alternative use of fining agents (activated charcoal, PVPP and zeolite) was evaluated. Two levels of ethylphenol contamination were considered: a naturally low contaminated red wine and the same wine spiked with 4-EP and 4-EG. The impact of the treatments on desirable aroma volatiles, polyphenols and colour was also evaluated. The effectiveness in diminishing the intensity of the phenolic off-odour was assessed by descriptive sensory analysis. The activated charcoal and PVPP significantly decreased the concentrations of 4-ethylguaiacol and 4-ethylphenol in the naturally contaminated wine, while none of the tested fining agent was effective in the spiked one. Polyphenols and colour were slightly affected, to the same extent for the two treatments. Charcoal and PVPP additions negatively impacted the concentration of the aroma volatiles, especially esters, with the activated charcoal achieving a higher decrease. The sensory outcome of both treatments was the decrease in the intensity of phenolic off-odour, with charcoal achieving a higher decrease. Interestingly, in spite of the decrease in esters, also a significant increase in the intensity of “red fruit” odour occurred.

Effect of Bottle Storage on Colour, Phenolics and Volatile Composition of Malvasia and Moscato White Wines

The effect of bottle storage on the colour, phenolics and volatile composition of Malvasia and Muscat wines obtained from grapes grown in Sardinia was evaluated. Colour was evaluated by UV-VIS spectrophotometry and by tristimulus colorimetry. Polyphenols were analysed by UV-VIS spectrophotometry and HPLCDAD. GC/MS was used to identify and quantify the content of free and bound volatile compounds. As expected, the absorbance values at 420 nm increased significantly for both wines during storage, due to oxidative browning, while difference in colour (DE*) from the beginning of storage and after 18 months was more intense in the Muscat wine than in the Malvasia wine. A significant decrease was observed in different phenolic compounds over time, especially in the Malvasia wine. In-bottle storage for 18 months at 20°C in the dark resulted in a significant decrease in all the classes of free and bound volatiles. These finding enhance knowledge regarding the effects of bottle storage on Muscat and Malvasia wines. This is of interest because, rather surprisingly, this topic has been poorly investigated in relation to these two varieties.

Orthonasal vs. retronasal: Studying how volatiles' hydrophobicity and matrix composition modulate the release of wine odorants in simulated conditions

In this study a Retronasal Aroma Simulator was employed to compare the release of volatiles from two different white wine matrices (TW: table, SW: sweet) with and without the addition of human or artificial saliva to simulate retronasal and orthonasal conditions, respectively. The headspace volatiles were isolated by Solid Phase Microextraction under dynamic conditions and identified and quantified by Gas-Chromatographic analyses. Compared to the orthonasal, the retronasal conditions modified the release of odorants from both wines and the observed trends cannot be ascribed only to dilution consequent to saliva addition. The relative amounts of volatiles belonging to different chemical classes were modified in the presence of saliva with possible sensory implications concerning some fruity (esters), oxidative (furans) and varietal (linalool, vitispirane) odorants. Regression analyses show that the impact of saliva depends on the volatile (concentration and hydrophobicity) and the non-volatile (residual sugars) composition of the wine. The highly significant linear models (TW: R2 = 0.988; SW: R2 = 0.993) indicate that the release of volatiles is logP octanol/water dependent in both the wines but the slopes change with matrix composition. This suggest that in the presence of human saliva the release of odorants with similar hydrophobicity vary as a linear function of their initial headspace concentration above the wine and is modulated by the composition of the wine matrix. Differences between artificial and human saliva confirmed that the retronasal release of wine odorants is affected by the whole salivary composition and suggest that salivary components different from mucin and α-amylase are involved in the retention of the most hydrophobic volatiles as well as in the metabolization of some aromas.