Determination of rheological property and its effect on key aroma release of Shanxi aged vinegar

Characterization of key aroma compounds and relationship between aroma compounds and sensory attributes in different aroma types of Fu brick tea

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Aroma characteristics of Fu brick tea were classified into three types.

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Key aroma compounds in three aroma types of Fu brick tea were identified.

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Relationship between aroma compounds and aroma attributes was illuminated.

Aroma is one of the most important sensory properties of tea. Floral-fungal aroma type, ripe-fungal aroma type and fresh-fungal aroma type were the main aroma types of Fu brick tea by QDA. A total of 112 volatile compounds were identified and quantified in tea samples by HS-SPME/GC–MS analysis. Ten voaltiles in floral-fungal aroma type, eleven voaltiles in ripe-fungal aroma type, and eighteen voaltiles in fresh-fungal aroma type were identified as key aroma compounds for the aroma characteristics formation in three aroma types of Fu brick tea. In addition, PLS analysis revealed that 3,4-dehydro-β-ionone, dihydro-β-ionone, (+)-carotol and linalool oxide Ⅱ were the key contributors to the ‘floral and fruity’ attribute, α-terpineol contributed to ‘woody’ and ‘stale’ attributes, and thirteen aroma compounds related to ‘green’ attribute. Taken together, these findings will provide new insights into the formation mechanism of different aroma characteristics in Fu brick tea.

Investigation of the traditional organic vinegars by UV-VIS spectroscopy and rheology techniques

Optical, rheological and metabolic properties of the apple, hawthorn, artichoke, grape, rosehip and blackberry organic vinegar produced by deep culture method (handmade traditional method) were analysed using UV-Vis spectroscopy and rheology techniques. Flow behaviours for all samples were analysed in the shear rate range of 10^-3 to 10³ 1/s and in frequency range of 10^-3 to 10³rad/s, respectively. Absorption spectra for six organic vinegars was observed two peaks around 215 and 285nm due to the presence of phenolic compounds and organic acids such as acetic. The effects of optical transitions of organic molecules on the absorption coefficient values for vinegars were determined. Optical energy band gaps of all samples were found to be consistent with Planck's radiation approach known as Rayleigh-Jeans law and Tauc law. The rheological/flow properties of the all vinegars were found to be relevant with non-Newtonian flow behaviour and Ostwald-de Waele model. From the results of optical and rheological analysis, which determines the quantity and quality characteristics of all organic vinegars, it was concluded that these vinegars are in a level that people can drink easily.

Effect of Respiratory Growth on the Metabolite Production and Stress Robustness of Lactobacillus casei N87 Cultivated in Cheese Whey Permeate Medium

Cheese whey permeate (WP) is a low-cost feedstock used for the production of biomass and metabolites from several lactic acid bacteria (LAB) strains. In this study, Lactobacillus casei N87 was cultivated in an optimized WP medium (WPM) to evaluate the effect of anaerobic and respiratory conditions on the growth performances (kinetics, biomass yield), consumption of sugars (lactose, galactose, glucose) and citrate, metabolite production [organic acids, volatile organic compounds (VOCs)] and stress survival (oxidative, heat, freezing, freeze-drying). The transcription of genes involved in the main pathways for pyruvate conversion was quantified through Real Time-PCR to elucidate the metabolic shifts due to respiratory state. Cultivation in WPM induced a diauxic growth in both anaerobic and respiratory conditions, and L. casei N87 effectively consumed the lactose and galactose present in WPM. Genomic information suggested that membrane PTS system and tagatose-6-P pathway mediated the metabolism of lactose and galactose in L. casei N87. Respiration did not affect specific growth rate and biomass production, but significantly altered the pyruvate conversion pathways, reducing lactate accumulation and promoting the formation of acetate, acetoin and diacetyl to ensure the redox balance. Ethanol was not produced under either cultivation. Pyruvate oxidase (pox), acetate kinase (ack), α-acetolactate decarboxylase (ald), acetolactate synthase (als) and oxaloacetate decarboxylase (oad) genes were up-regulated under respiration, while L-lactate dehydrogenase (ldh), pyruvate formate lyase (pfl), pyruvate carboxylase (pyc), and phosphate acetyltransferase (pta) were down regulated by oxygen. Transcription analysis was consistent with metabolite production, confirming that POX-ACK and ALS-ALD were the alternative pathways activated under aerobic cultivation. Respiratory growth affected the production of volatile compounds useful for the development of aroma profile in several fermented foods, and promoted the survival of L. casei N87 to oxidative stresses and long-term storage. This study confirmed that the respiration-based technology coupled with cultivation on low-cost medium may be effectively exploited to produce competitive and functional starter and/or adjunct cultures. Our results, additionally, provided further information on the activation and regulation of metabolic pathways in homofermentative LAB grown under respiratory promoting conditions.

Effect of sodium sulfite, tartaric acid, tannin, and glucose on rheological properties, release of aroma compounds, and color characteristics of red wine

In this study, we evaluated the effect of addition of non-volatile compounds (sodium sulfite, tartaric acid, tannin, and glucose) on the rheological properties, release of aroma compounds, and color of the red wine. While determining the rheological properties of the supplemented samples, non-Newtonian fluidic and shear-thinning behavior of samples was noticed. The viscosity of these samples was found in negative correlation with the dose of addition of various non-volatile substances. The aroma profile of red wine after additions showed the change in the release of the nine key aroma compounds. Among them ethyl hexanoate, phenylethyl alcohol, octanoic acid, diethyl succinate, and ethyl octanoate were profoundly increased. Further, the color of red wines was improved in the presence of tartaric acid and tannin. Overall, supplementation of various substances during storage period of three different wines could enormously affect the sensory characteristics in a dose dependent manner.