The DPPH assay is one of the most commonly employed methods for measuring antioxidant activity. Even though this method is considered very simple and efficient, it does present various limitations which make it complicated to perform. The range of linearity between the DPPH inhibition percentage and sample concentration has been studied with a view to simplifying the method for characterising samples of wine origin. It has been concluded that all the samples are linear in a range of inhibition below 40%, which allows the analysis to be simplified. A new parameter more appropriate for the simplification, the EC20, has been proposed to express the assay results. Additionally, the reaction time was analysed with the object of avoiding the need for kinetic studies in the method. The simplifications considered offer a more functional method, without significant errors, which could be used for routine analysis.

Colorimetry allows every color to be defined as a combination of three values, known as color coordinates. Color coordinates allow researchers to universalize and standardize their color measurements, and nowadays, determining the color coordinates of samples is a routine method applied by organic and analytical chemists, students, and specialists like enologists. Although the colorimetry method requires a simple experimental procedure, many students, researchers and teachers might find the mathematical treatment of the data too difficult. In this paper, we introduce two workbooks using Microsoft Excel with Microsoft Visual Basic that simplify the use of colorimetry: one of these workbooks is specifically oriented to students and teachers, and it includes explanations and information about each color model. The second workbook is aimed at researchers, and it allows them to introduce and analyze numerous samples at the same time. Finally, another workbook has been included that contains various sample spectra that teachers can use to improve student comprehension of color coordinates.

Winemaking by-products are considered to be a rich source of bioactive compounds. Grape pomace is susceptible to microbial degradation due to the degree of residual moisture, so the drying of this pomace for conservation is considered to be an essential first step. Previous studies concerning the way in which drying affects winery by-products have produced contradictory results. In this study, a new methodology for drying grape pomace in a climatic chamber has been evaluated. Five red grape pomace varieties were dried in a climatic chamber at 40 °C and 10% relative humidity and the phenolic content and antioxidant activity of the dried and wet pomace samples were compared. The results indicate that this drying process is both feasible and beneficial because significant increases in the extractability of phenolic compounds and antioxidant activity were achieved.

This work intends to determine the effect on the aroma profile, phenolic content and antioxidant activity of prickly pear vinegars produced by the surface culture at two different fermentation temperatures and using different acetic acid bacteria (AAB) inocula. Prickly pear wine was fermented at two temperature levels (30 and 37 °C) by using bacteria inocula containing Acetobacter, Gluconobacter or a mixture of bacteria isolated from Sherry vinegars. Eighty-five individual volatile compounds from different families and sixteen polyphenolic compounds have been identified. It was confirmed that the highest temperature tested (37 °C) resulted in a lower concentration of volatile compounds, while no significant effect on the vinegars’ volatile composition could be associated with the AAB inoculum used. Contrariwise, the highest content of polyphenolic compounds was detected in those vinegars produced at 37 °C and their concentration was also affected by the type of AAB inoculum used. Prickly pear wine displayed greater antioxidant activity than juices or vinegars, while the vinegars obtained through the mixture of AAB from Sherry vinegar showed higher antiradical activity than those obtained through either of the two AAB genera used in this study. It can be therefore concluded that, although the volatile content of vinegars decreased when fermented at a higher temperature, vinegars with a higher content in polyphenols could be obtained by means of partial fermentations at 37 °C, as long as thermotolerant bacteria were employed.

Thinning is a common viticulture practice in warm climates, and it is applied to increase the quality of the harvest. Thinning clusters are usually discarded, and they are considered another oenological industry waste. To valorize this by-product, the phenolic content and antioxidant activity of three red varieties (Tempranillo, Cabernet Sauvignon, and Syrah), thinned at three different times between veraison and harvest, were studied: the first at the beginning of the veraison stage, in a low ripening stage; the second in an intermediate ripening stage; and, finally, the third sampling in the highest ripening stage. These by-products showed high values of total phenolic contents (10.66–11.75 mg gallic acid equivalent/g), which is of the same order as or even higher than that found in grape pomace. In thinned grape were identified 24 phenolic compounds, being the flavan-3-ols (catechin and epicatechin) of particular interest, with mean contents ranging from 105.1 to 516.4 mg/kg of thinned grape. Antioxidant activity similar to that of the vintage grape was found. It is concluded that thinned grape is a good source of phenolic compounds. Its content does not depend mainly on the grape variety; however, it has been possible to establish differences based on the maturity stage of the thinning grapes: the intermediate ripeness stage, with a Brix degree in the range of 15–16 for this area, would be the optimum collection time for cluster thinning. In this intermediate ripeness stage, thinning grapes present a higher antioxidant activity and there is also appreciable anthocyanin content, which is not found for the lowest ripeness stage, since these samples present an intermediate composition in all the families of determined phenolic compounds: anthocyanins, flavonols, flavan-3-ols, cinnamic acids, and benzoic acids. It is important to note that the experiments in this study have been carried out with whole tinned grapes, without separating the skin or the seeds.