Aroma profile of pilot plant-scale produced fruit vinegar using a thermotolerant Acetobacter pasteurianus strain isolated from Moroccan cactus

In this study, new thermotolerant Acetobacter pasteurianus CV01 strain recently isolated from local product of Morocco has been investigated for its ability to perform efficient acetous fermentation at a large-scale. Firstly, the thermotolerance basis bioconversion of CV01 strain was compared to other mesophilic and thermotolerant acetic acid bacteria. Subsequently, CV01 strain was assessed for its ability to produce and tolerate high amount of acetic acid at optimal and thermal stress conditions in lab-scale bioreactor. It was found that the studied strain exhibited thermotolerant properties compared to reference strains and could withstand the increase in temperature during acetous fermentation in fermenter. Furthermore, gas chromatography-mass spectrometry (GC-MS) was used on the samples prepared with solid phase microextraction (SPME) to determine the volatile compounds of the pilot plant produced apple vinegar based on developed start-up and semi-continuous fermentation protocol. The operation strategy in the 500-L pilot plant scale acetator allowed achieving 7.3% (w/v) of final acetic acid concentration recording high yield and acetification rate. The aroma profile of experimentally produced vinegar was found different from that of the commercial reference one. According to the literature, the results obtained show that major volatile compounds found in pilot-plant produced apple vinegar are related to good aromatic note descriptors which could have a positive impact on the organoleptic quality of industrial vinegar. Consequently, it can be concluded that CV01 Acetobacter strain is well suited for large-scale production of high quality fruit vinegar.

The flavor and taste of cereal Chinese vinegars

A lexicon for describing Chinese cereal vinegars (CCVs) was developed using trained panels of tasters that defined and referenced 23 significant olfactory descriptors, in concert with taste and trigeminal sensation. The sensory analysis was performed on 27 samples, representative of the five well-known Chinese provinces producing vinegar: Shanxi, Jiangsu, Sichuan, Fujian and Tianjin. Several aromatic descriptors define the sensory lexicon, e.g.: licorice, chocolate, meat broth, toasted, walnut, yogurt, coffee; together with five basic tastes, such as acid, sweet, salty, umami and bitter; and four for trigeminal sensations, astringent, pungent, metallic, and piquant (spicy). This preliminary study will be useful to CCVs producers because this lexicon reliably differentiates and characterizes this kind of vinegar.

Biotechnologically relevant features of gluconic acid production by acetic acid bacteria

The many uses of gluconic acid and some of its salts are arousing increasing interest in these compounds and in their production levels. Although gluconic acid and gluconates can be obtained chemically, they are currently almost exclusively biotechnologically produced, mostly by fungus based methods. There is, however, an ongoing search for alternative microorganisms to avoid the problems of using fungi for this purpose and to improve the productivity of the process. Especially promising in this respect are acetic acid bacteria, particularly Gluconobacter strains. This paper discusses the main variables and operating conditions to be considered in optimizing gluconic acid production by Gluconobacter.

Fermentation strategy to produce high gluconate vinegar

Gluconic acid is a non-volatile acid that has many applications in food, pharmaceutical and cleaning fields. Gluconic acid has been detected as main oxidation product of <em>Acetobacter</em> and <em>Gluconobacter</em> strains growing on grape must, and it plays an important role in Traditional Balsamic Vinegar. Commonly, high gluconate vinegars have a greater physical stability and a greater preference by consumers because are perceived less pungent. In fact, gluconic acid reduces the pH and increases fixed acidity of the vinegar without increasing the sensation of pungency typical of acetic acid. Its taste is acid but mild sweet and, therefore, gluconic acid has influence on the sensory complexity of the vinegar. The aim of this work is to set up a fermentation procedure that improves the quality of balsamic vinegar by using selected yeasts and acetic acid bacteria strains able to oxidize glucose in grape must-based media having a different sugars concentration. In particular, <em>Saccharomycodes</em> <em>ludwigii</em> UMCC 297 and <em>Acetobacter</em> <em>pasteurianus</em> UMCC 1754 strains were chosen as selected starter cultures for small-scale fermentation of cooked grape must, to evaluate the physical-chemical parameters affecting gluconic acid production in the obtained vinegar. The strains used and the control of all production process have been fundamental for obtaining the vinegar with the desired characteristics.

4th International Conference on Acetic Acid Bacteria - Vinegar and other products (AAB 2015)

This Abstract Book contains oral and poster presentations from the <em>4^th International Conference on Acetic Acid Bacteria - Vinegar and other products (AAB 2015)</em>, held in Taiyuan, P. R. China, 15-19 September 2015.

Contribution to the discussion of current state and future perspectives of sensory analysis of balsamic vinegars

Not required

Sensory analysis of traditional balsamic vinegars: current state and future perspectives

Quality evaluation of traditional balsamic vinegar (TBV) is primarily based on sensory analysis. For every TBV batch, official sensory panels give a final score, which determines its assessment into quality and price categories. Therefore, an effective and objective sensory analysis is a core aspect in TBV production and marketing and it should fulfill at least two conditions: i) the panelists have been properly trained on the TBV features; ii) the panelists have to be free from any psychological and physical conditions which might affect human judgments. Traditionally, a panel of trained members assesses the TBV sensory attributes evaluating visual, olfactory, gustatory and trigeminal features at the same time. The result is that visual appearance significantly affects the subsequent stages of the sensory analysis, and even the olfactory and gustatory sensations will greatly affect each other. The aim of this work was to review the procedures for the sensory analysis of TBV and to define a set of TBV attributes. A new assessment questionnaire has been proposed to establish the appropriate sensory vocabulary for a complete description of TBV sensory properties.

Cheese whey recycling in traditional dairy food chain: effects of vinegar from whey in dairy cow nutrition

Selected yeast (<em>Kluyveromyces marxianus</em> Y102 strain) and an acetic acid bacterium (<em>Acetobacter aceti</em>, DSM-G3508 strain) were used as inocula respectively in cheese whey for alcoholic and acetic fermentations. The experimental tests were carried out at both laboratory and pilot plant (20 L and 2000 L) levels. The data from the trials (working period 28 days) show increased ethanol production, increased acetic acid yield, and greater fermentation stability with biomass recycling (18.6 g L^&ndash;1). Batch and fed-batch fermentation tests resulted in increased and standardized alcoholic fermentation, and allowed acetic acid recovery (average lactose consumption 56%, ethanol 6.7 g L^&ndash;1 d^&ndash;1 and acetic acid production 4.35 g L^&ndash;1 d^&ndash;1). The effects administration were then investigated on milk yield and composition, nutritional status of dairy cows and physical characteristics of total mixed ration (TMR). Twenty Holstein cows were divided into two groups; group C, receiving the traditional TMR, and group W, receiving the TMR plus 10 L wheynegar. The dietary treatment, lasted 35 days, did not affect milk yield and composition except for the urea content, significantly lowered in group W. The selection of coarse (&lt;19 mm), medium (8-19 mm) and fine (&lt;8 mm) dietary particles was not influenced by the wheynegar administration however a tendential lower selection against coarse particles was noted in W. The results highlight that microbial biotechnologies may significantly contribute to both the valorization of whey and the development of a stable nutrient recycling system as a ingredient in dairy cattle diet.

Significance and management of acetic acid bacteria culture collections

Acetic acid bacteria (AAB) are obligate aerobic microorganisms which have large significance in human life. Traditionally, AAB species have been used to produce fermented food and beverages thanks to their ability to oxidize ethanol to acetic acid. Moreover, in the last decades, they have been extensively investigated for other industrial biotechnology applications as the development of processes for highvalue products or biosensors. The potential exploitation of AAB diversity requires the existence of microbial culture collections, which are able to supply not only strains but essential data for fundamental microbial research. Therefore, microbial collections can be helpful to provide critical insights into AAB physiology and metabolism as well as integrate sequence data with transcriptional and functional studies to better define complex traits and develop new potential microbial processes. This article reviews the significance of microbial collections, with an overview of the well-known European Biological Resources Centers (BRCs) collecting AAB, and provides an insight into their cultivability and metabolic activity. It also discusses appropriate techniques in preserving <em>authentic</em> strains, quality control implications, databases and BRC networking as well as connections among collections and stakeholders.

The inactive and active forms of the pyrroloquinoline quinone-alcohol dehydrogenase of Gluconacetobacter diazotrophicus: a comparative study

<em>Gluconacetobacter diazotrophicus</em> as a member of the acetic acid bacteria group, oxidize alcohol to acetic acid through two sequential reactions catalyzed by the alcohol dehydrogenase (ADH) and the aldehyde dehydrogenase, both enzymes are membrane-bound and oriented to the periplasmic space. ADH is a quinohemoprotein carrying one pyrroloquinoline quinone moiety, one [2Fe:2S] cluster and four c-type cytochromes, as prosthetic groups. In recent years has been described the presence of the inactive ADH (ADHi) in the acetic acid bacteria. In the present review we make a comparative study of the molecular and catalytic properties of the active and inactive forms of ADH purified from <em>G. diazotrophicus</em>, variation in the redox state of enzymes <em>as purified </em>could explain the notorious differences seen in the activity power of the compared enzymes.