Alice Vilela

Phenotypic and metabolic traits of commercial Saccharomyces cerevisiae yeasts

Currently, pursuing yeast strains that display both a high potential fitness for alcoholic fermentation and a favorable impact on quality is a major goal in the alcoholic beverage industry. This considerable industrial interest has led to many studies characterizing the phenotypic and metabolic traits of commercial yeast populations. In this study, 20 Saccharomyces cerevisiae strains from different geographical origins exhibited high phenotypic diversity when their response to nine biotechnologically relevant conditions was examined. Next, the fermentation fitness and metabolic traits of eight selected strains with a unique phenotypic profile were evaluated in a high-sugar synthetic medium under two nitrogen regimes. Although the strains exhibited significant differences in nitrogen requirements and utilization rates, a direct relationship between nitrogen consumption, specific growth rate, cell biomass, cell viability, acetic acid and glycerol formation was only observed under high-nitrogen conditions. In contrast, the strains produced more succinic acid under the low-nitrogen regime, and a direct relationship with the final cell biomass was established. Glucose and fructose utilization patterns depended on both yeast strain and nitrogen availability. For low-nitrogen fermentation, three strains did not fully degrade the fructose.This study validates phenotypic and metabolic diversity among commercial wine yeasts and contributes new findings on the relationship between nitrogen availability, yeast cell growth and sugar utilization. We suggest that measuring nitrogen during the stationary growth phase is important because yeast cells fermentative activity is not exclusively related to population size, as previously assumed, but it is also related to the quantity of nitrogen consumed during this growth phase.

Sucrose Replacement by Sweeteners in Strawberry, Raspberry, and Cherry Jams: Effect on the Textural Characteristics and Sensorial Profile—A Chemometric Approach

Sucrose is the main sugar used in jams preparation; however his excessive consumption has been related to several diseases; therefore its replacement by alternative sweeteners is an attractive solution. Nonetheless, substitution of sucrose in jam’s preparation can cause changes in texture, structure, and flavor, making them less attractive to the consumers. Thus, the aim of this work was to develop strawberry, raspberry, and cherry jams with more adequate nutritional profile, maintaining their textural and flavor characteristics in comparison with the traditional formulation. Sucrose was replaced by fructose, sorbitol, or fructooligosaccharides (FOS), given the product different nutritional profiles: potential low glycemic index, reduced calories in the case of sorbitol and FOS, and enrichment with dietary fiber, in the case of FOS. After sensorial and rheological evaluation we found that the sweeteners used interfered, significantly, in the parameters measured. Fructose was the alternative sweetener yielding jams more similar to those of sucrose; however, the use of formulations containing fructose and FOS or sorbitol and FOS resulted in a 51% to 68% decrease of the energy value. Nevertheless, consumer sensorial tests are needed to evaluate, in a more consistent way, the use of these alternative sweeteners for jams production at industrial level.

Wine Microbial Spoilage: Advances in Defects Remediation

Abstract Despite good modern winemaking practices, microbial contaminations can occur. Therefore, quality wine production requires attention to possible sources of contamination during winemaking and aging. Spoilage microorganisms besides affecting wine healthiness can be unsafe for human consumption, by producing biogenic amines (BA) and precursors of ethyl carbamate. The main spoilage microorganisms include species and strains of yeasts, lactic acid bacteria, and acetic acid bacteria. Defects include bitterness, off-flavors, and sensory visual faults, such as film formation, turbidity, viscosity, and sediments. Filamentous fungi may be responsible for depreciating wine quality by the production of mycotoxins. Strains selection for performing alcoholic and malolactic fermentations, gathering the best oenological characteristics, may be the first step for achieving wines with good quality. In addition, the ability of detoxifying mycotoxins and BA must be an additional strain selection criterion for winemaking. Optimization of fining treatments will also be necessary, to remove off-odor, mycotoxins, or BA from wine.

Genotype, Environment and Management Practices on Red/ Dark-Colored Fruits Phenolic Composition and Its Impact on Sensory Attributes and Potential Health Benefits

Phenolic compounds are secondary metabolites abundant in our diet. These compounds may affect positively or negatively the sensory characteristics of food with important impacts on color, flavor, and astringency. An adequate consumption of phenolic com‐ pounds may also offer health benefits. After the consumption of fruits, the colon is the main site of microbial fermentation, where high molecular weight phenolic compounds are transformed into low molecular weight phenolic compounds such as phenolic acids or lactone structures by intestinal microbiota, which produce metabolites with biological and antioxidant activity, with evidence on health benefits for humans. A large amount of different phenolic compounds are responsible for physicochemical and sensory char‐ acteristics of table grapes and wines. Also, sweet cherry (Prunus avium L.) is one of the most popular temperate table fruits; they contain flavonoids, flavan‐3‐ols, and flavonols in addition to non‐flavonoid compounds. Anthocyanins are the major polyphenols in blueberries, and this group of phytochemicals is thought to be responsible for many of the health benefits of berry consumption. Therefore, considering the importance of red/dark‐colored fruits phenolic composition, the purpose of this chapter is to make a review of the most recent publications about these fruits’ phenolic composition and their impact on sensorial properties as well as the effect of microorganisms on fruit phenolic composition.

4-Ethylphenol, 4-ethylguaiacol and 4-ethylcatechol in red wines: Microbial formation, prevention, remediation and overview of analytical approaches

ABSTRACT The presence of 4-ethylphenol, 4-ethylguaiacol and 4-ethylcatechol in red wines affect negatively their aroma conferring horsy, barnyard, smoky and medicinal aromatic notes. These volatile phenols formed from free hydroxycinnamic acids and their ethyl esters by Dekkera/Brettanomyces yeasts, can contaminate wines. Their formation can cause serious negative economic impact to the wine industry worldwide as consumers tend to reject these wines. For these reasons various preventive and remedial treatments have been studied. This review summarises the wine microbial volatile phenols formation, preventive measures during winemaking and remedial treatments in finished wines along with their advantages and limitations for dealing with this sensory defect and impact on wine quality. Also it is important to control the levels of volatile phenols in wines using fast and convenient analytical methods namely with a detection limit below their olfactory perception threshold. The analytical methods available for quality control and performance characteristics as well their advantages and disadvantages when dealing with a complex matrix like wine are discussed in detail.

Targeting Demalication and Deacetification Methods: The Role of Carboxylic Acids Transporters

As weak organic acids, carboxylic acids partially dissociate in aqueous systems, like wine, establishing equilibrium between uncharged molecules (undissociated form) and their anionic form, according to the medium pH and their pKa. This property influences yeasts cell-behaviour, particularly the mechanisms by which the molecules can cross biological membranes. Occasionally wines may present an excessive amount of organic acids. In the mouth they will seem unbalanced and sometimes excessive sourness diminishes their quality. Moreover, these acids originated from grapes or from the fermentation process itself, negatively affect wine yeasts, yeast fermentation process and the final wine quality. Two of those acids are L-malic acid and acetic acid. The first one affects the wine mainly in his tastiness, making it much to sour; the second one, being a volatile compound, besides the excessive sourness, also imprints the wine with an unpleasant vinegar flavour. One approach to solving this problem is biological deacidification by Saccharomyces and non-Saccharomyces wine yeasts. To these biological processes of wine acidity bio-reduction we can call wine bio-demalication (malic acid bio-degradation) and wine biodeacetification (acetic acid consumption by yeasts).

Grape and Wine Metabolites: Biotechnological Approaches to Improve Wine Quality

Grape metabolites can be affected by many extrinsic and intrinsic factors, such as grape variety, ripening stage, growing regions, vineyard management practices, and edaphoclimatic conditions. However, there is still much about the in vivo formation of grape metabolites that need to be investigated. The winemaking process also can create distinct wines. Nowadays, wine fermentations are driven mostly by single-strain inoculations, allowing greater control of fermentation. Pure cultures of selected yeast strains, mostly Saccharomyces cerevisiae, are added to grape must, leading to more predictable outcomes and decreasing the risk of spoilage. Besides yeasts, lactic acid bacteria also play an important role, in the final wine quality. Thus, this chapter attempts to present an overview of grape berry physiology and metabolome to provide a deep understanding of the primary and secondary metabolites accumulated in the grape berries and their potential impact in wine quality. In addition, biotechnological approaches for wine quality practiced during wine alcoholic and malolactic fermentation will also be discussed.