Ira Glazer

ABSTRACT The demand to extend the marketing period of pomegranates requires a better understanding of the processes occurring during postharvest storage. Among the important factors that limit the long-term storage of pomegranates are disorders occurring on the fruit husk: fungal decay, chilling injury, shrinkage due to weight loss, and husk scald, all leading to loss of visual quality. The aim of this study was to examine processes that taking place during storage, and to analyze the relationship between the total antioxidant capacity and total phenolics content of the husks and the development of husk disorders in seven accessions. While the level of total phenolics increased during storage, concomitantly with the color index, the level of punicalagin, the main polyphenol in the husks with the highest antioxidant activity, declined during storage. The content of titratable acidity was also reduced. Regression analysis indicates that fruit having a high antioxidant capacity, high total phenolics content, and high levels of punicalin in their husks have a better ability to resist fungal decay and weight loss, in addition to being less sensitive to husk scald. On the other hand, the results suggest that the development of most husk disorders is not correlated to the content of total soluble solids, titratable acidity, punicalagin, anthocyanin, or husk color. Nonetheless, poorly colored accessions were relatively more sensitive to chilling injury expressed as surface pitting, compared with the more colored accessions. The appearance of these chilling injury symptoms was not correlated to total phenolics or the antioxidant capacity.

Aqueous extracts of pomegranate peels were assayed in vitro for their antifungal activity against six rot fungi that cause fruit and vegetable decay during storage. The growth rates of Alternaria alternata , Stemphylium botryosum , and Fusarium spp. were significantly inhibited by the extracts. The growth rates were negatively correlated with the levels of total polyphenolic compounds in the extract and particularly with punicalagins, the major ellagitannins in pomegranate peels. Ellagitannins were also found to be the main compounds in the bioactive fractions using bioautograms, and punicalagins were identified as the main bioactive compounds using chromatographic separation. These results suggest that ellagitannins, and more specifically punicalagins, which are the dominant compounds in pomegranate peels, may be used as a control agent of storage diseases and to reduce the use of synthetic fungicides.

The current study describes differences in pomegranate fruit size and aril weight of 29 accessions grown in Israel. The contents of sugars and organic acids in their aril juices and peel homogenates, as well as color parameters, were determined. While the levels of total soluble solids (TSS) and soluble sugars in the aril juices differ only slightly, those of titratable acidity (TA) and citric acid changed significantly, suggesting that they are the main contributors to juice taste. In general, significant positive correlations were found between TA values and the red color parameters, and these two parameters, as well as TSS, appeared to be higher in the juices of accessions harvested late in the season. Peel homogenates exhibited lower levels of TSS, TA, soluble sugars and organic acids than aril juices. Some red color parameters, TA and citric acid were found to correlate significantly between the aril juices and peel homogenates.

Pomegranate juice is well known for its health beneficial compounds, which can be attributed to its high level of antioxidant activity and total polyphenol content. Our objective was to study the relationships between antioxidant activity, total polyphenol content, total anthocyanins content, and the levels of four major hydrolyzable tannins in four different juices/homogenates prepared from different sections of the fruit. To this end, 29 different accessions were tested. The results showed that the antioxidant activity in aril juice correlated significantly to the total polyphenol and anthocyanin contents. However, the homogenates prepared from the whole fruit exhibited an approximately 20-fold higher antioxidant activity than the level found in the aril juice. Unlike the arils, the antioxidant level in the homogenates correlated significantly to the content of the four hydrolyzable tannins in which punicalagin is predominant, while no correlation was found to the level of anthocyanins.