Design of high quality nectarine and peach nectars : from process optimization to predictive models for color and antioxidant variations durino long-term storage

Optimal color and high antioxidant content are the main quality attributes affecting consumer preference of fruit based products. Peaches and nectarines (Prunus persica) contain significant amounts of antioxidants, including hydroxycinnamic acids, monomeric and polymeric flavanols, flavonols, anthocyanins, carotenoids and ascorbic acid. These minor dietary compounds have been postulated to play a key role in vivo by preventing reactions produced by reactive oxygen and nitrogen species during the progression of different human diseases. A few peach and nectarine varieties, which have a low browning potential, are traditionally used by industry. Developing adequate technologies to process different fruit varieties into high quality nectars would be crucial both to make use of fresh market surplus and/or to bring into play selected varieties with enhanced antioxidant content. To this regard, alternative strategies were proposed to inhibit the browning of product, which include: the use of cyclodextrins (anti-browning agents), adsorption processes, photochemical treatment, high hydrostatic pressure treatments, pulping/finishing of fruits at room temperature and peeling. Any change in processing technology requires evaluation on the effects on product quality at the moment of production and also during storage. This study aimed at developing predictive models to estimate quality variations. In the first step, antioxidant stability was studied during storage. Cyanidin 3-O-glucoside was the least stable, (half-life at 37°C < 1 month), followed by procyanidins (half-life at 37 °C of about 2 months), catechin, ascorbic acid, quercetin glycosides (half-life at 37 °C of about 6 months), and hydroxycinnamic acids (half-life at 37 °C > 1 year). The colorimetric parameters of nectars were then studied as a function of storage length (in glass bottles, at room temperature in the dark) and of the storage of their corresponding purees (in a tank at room temperature, in the dark). Polynomial models described the relationships among these variables. The greatest color variations were found in the initial three months of storage and were correlated to anthocyanin degradation. The colorimetric parameters of the nectars were also normalized to account for the effects of cyanidin-3-O-glucoside degradation. Another model for their variation was developed, which can be applied to any variety or process used in the production of nectar. By means of these models, the effects of altering processing technologies on product quality could be predicted at different storage times.