Polyphenols in kombucha: impact of infusion time on extraction and investigation of their behavior during “fermentation”

The parameters that determine the grape quality, and therefore the optimal harvest time, suffer variations during berry ripening, related to climate change, with the widely known problem of the gap between technological and phenolic maturities. However, there are few studies about its incidence on grape nitrogen composition. For this reason, the use of an elicitor, methyl jasmonate (MeJ), alone or with urea, is proposed as a tool to reduce climatic decoupling, allowing to establish the harvest time in order to achieve the optimum grape quality. The aim was to study the effect of MeJ and MeJ+Urea foliar applications on the evolution of Tempranillo amino acids content throughout the grape maturation. Three treatments were foliarly applied, at veraison and 7 days later: control (water), MeJ (10 mM) and MeJ+Urea (10 mM+6 kg N/ha). Grape samples were taken at five stages of maturation: day before the first and second applications, 15 days after the second application (pre-harvest), harvest day, and 15 days after harvest (post-harvest). The amino acids analysis of the samples was carried out by HPLC. Results showed that the evolution of amino acids was similar regardless of the treatment; however, foliar applications influenced the nitrogen compounds content, i.e., there was no qualitative effect but quantitative one. Most of the amino acids reached their maximum concentration in pre-harvest, being higher in grapes from the treatments than in the control. In general, no differences in grape amino acids content were observed between MeJ and MeJ+Urea treatments. Foliar applications with MeJ and MeJ+Urea enhanced the grape amino acids content, without affecting their profile, helping to optimize their quality and allowing to establish a more complete grape ripening standard. Therefore, MeJ and MeJ+Urea foliar applications can be a simple agronomic practice, which has shown promising results in order to enhance the grape quality.

Aging process is an essential stage in the improvement of wine quality. This process is usually performed by contact with oak wood whose compounds are released and transferred to wine, acquiring typical aging bouquet. Although the use of oak chips is a practice generally accepted as alternative to barrels to shorten aging process, the application of emerging technologies is being unfolded to accelerate this stage.

Despite their trace concentrations, volatile sulfur compounds (VSCs) are an important category of flavour-active compounds that significantly contribute to desirable or undesirable aromas of many foods and beverages. In wines, VSCs in the form of polyfunctional thiols, notably 3-sulfanylhexan-1-ol (3-SH), 3-sulfanylhexyl acetate (3-SHA), and 4-sulfanyl-4-methyl-pentan-2-one (4-MSP), possess extremely low olfactory thresholds (≈ ng/L) and pleasant “tropical aroma” notes. They have received much attention with respect to their sensory contributions, quantitative occurrences, biogenesis, and thiol management through viticulture and winemaking. However, the fate of these potent volatiles are still not fully understood.

Context and purpose of the study. Epidermal Patterning Factors are a family of small peptides that are highly conserved in the plant kingdom and are involved in several physiological and developmental processes.

In winemaking grapes, it is known that most aroma compounds are present as non-volatile precursors, such as glycosidic precursors. In fact, there is strong evidence supporting the connection between the content of aroma precursors and the aromatic quality of wine [1]. Acid hydrolysis is preferred to reveal the aroma potential of winemaking grapes, as it predicts more accurately the chemical rearrangements occurring during fermentation in acidic environments [2]. In this study, a method involving a fast fermentation followed by acid hydrolysis at 75ºC was used to evaluate the accumulation of aroma compounds over time in fractions obtained from six different varieties of winemaking grapes.