Effect of cultivar, maturation and processing on the chemical, functional and sensory properties of pomegranate fruit and juice

Zusammenfassung

In recent years, the pomegranate (Punica granatum L.) has acquired wide acceptance due to the growing evidence that consumption is associated with beneficial health properties. During fruit ripening and manufacturing there are significant changes in the physicochemical, phenolic compositions and antioxidant activity. These changes are influenced by cultivar, growing region, cultivation techniques and ripening stage of the fruit at harvest. Thus, the main objective of this PhD Thesis is to evaluate the evolución in chemical, functional and sensory properties of pomegranate during cultivation, maturity stage and industrial processing. The specific objectives are: (i) evaluate the potential of pomegranate fruits removed during thinning as a source of bioactive compounds and antioxidant activity, (ii) determine the effect of the position of the fruits within the tree in the main quality and physicochemical parameters, (iii) use descriptive sensory analysis to determine the best commercial option for pomegranate fruits, either fresh consumption or juice manufacture, (iv) determine the effect of industrial processing and pomegranate juice adulteration on physico-chemical characteristics and bioactive compounds. Pomegranates fruits were used for the analysis and were collected from the thinning and during three different maturity stages. Thinning is an agricultural practice which takes place at an immature stage of the fruits at which parts of the fruits are removed to benefit the development and quality of the remaining fruits on the tree. Likewise commercial pomegranate juice was used for the analysis; to simulate adulteration, commercial pure pomegranate juice was mixed with grape juice or peach juice at different concentrations. The quality parameters under study included, organic acids, sugars, proline, minerals, total phenolic compounds, punicalagins, ellagic acid, antioxidant activity and volatile compounds, as well as titratable acidity, total soluble solids, maturity index, pH and color. In pomegranate that coming from thinning, citric and quinic acid were the main organic acids and glucose and fructose the main sugars. Potassium was the predominant mineral; the proline content in the first ripening stage ranged from 32.2 to 52.1 mg/ L. Total polyphenol content ranged from 190 to 288 g GAE/ kg dw. The antioxidant activity was assessed by four methods, DPPH, ABTS, FRAP and ORAC. The antioxidant activity values of thinning fruits were between 2 - 6 times higher than ripe pomegranate fruits. The antioxidant activity values, titratable acidity, total organic acid and total polyphenols, decrease with ripening progresses or industrial processing, as well as. The total soluble solids, maturity index, total sugars content and proline, increased significantly in pomegranate fruits. The position within the tree only had significant (p< 0.05) on external color coordinates. A total of 35 major derivatives of ellagic acid were identified by LC-PDA-QTOF/MS and quantified by UPLC-PDA methods however, only 7 of them were found in thinning and ripe fruits. The content of these compounds was higher in fruits that coming from thinning than in ripe fruits. After sensory evaluations, the results show that Wonderful cultivar was the most appreciated cultivar in by being sour and having salty and wine-like notes. On the other hand, most of Mollar and Valencia cultivars highly appreciated cultivars in Spain were characterized by being sweet and having beet, fruity-dark, fermented, and musty/earthy flavor notes. In commercial pure pomegranate juice, mixed with grape juice (10, 25 and 50 %), increased the content of Ca, Mg and Fe, volatile compounds like acetic acid, isoamyl butyrate and 1-hexanol and linalool and especially increases of tartaric acid and proline, decreased simultaneously, the content of K. Likewise, Addition of peach juice up to 10 % only resulted in a significant (p< 0.001) increase of the sucrose content and volatile compounds like butyl acetate, isobutyl butyrate, benzyl acetate and especially isoamyl butyrate. This PhD Thesis shows that pomegranate thinning fruits (especially sour-sweet cultivars), are rich in bioactive compounds, and thus, have an important potential use in food, chemical and pharmaceutical industries. Also, described the sensory profiles of pomegranate cultivars to determine the best commercial option for fruits, either fresh consumption or juice manufacture. And finally, evaluated the changes observed after adulterating pomegranate juice with different concentrations of grape or peach juices, to state simple but practical parameters to check the authenticity or adulteration of pomegranate juice.