عنوان مقاله [English]
Introduction: Because of harvesting of widespread volume of pomegranate production in a short time from late summer to early autumn and due to the lack of appropriate conditions of storage, a large part of which is lost prior to the market presentation or its cost is reduced due to the widespread presentation. Some studies investigated different methods for long-term storage of pomegranate, including use of alternative heating, low temperature, controlled atmosphere and growth plant regulators. Pomegranates are usually kept at temperatures below 5 °C only for 2 months, and then, frostbite to form of surface stains, skin browning; discolouration and browning of Arils and separator membrane are appeared. However, sensitivity to frostbite is a major problem for pomegranate storage, but generally the most important limiting factor for pomegranate storage is the growth and development of fungal contaminations, especially on the part of the throat. This problem is usually intensified at temperatures above 5 °C to prevent frostbite pomegranate. Therefore, for long-term storage of pomegranate, dual problem exists. It means that to reduce frost, we have to use higher temperatures or plastic covers, and on the other hand all these conditions can intensify the fungal decay in pomegranate. Recently, the interest of consumers has increased to food products with better quality, fresher and easier access. In this regard, packaging materials and packaging methods with the use of modern and appropriate techniques play vital role in reducing food wastes and production which is caused to healthier products. Considering the importance of extended life storage along with the preservation of favorite pomegranate quality, so the objective of this study was to investigate the effects of four types of coverage on the quality of pomegranate.
Materials and Methods: Maikhosh pomegranate cultivar was used for this study. Samples were taken directly from the Najaf Abad city orchards at the same conditions. Fruit weight was measured at the beginning of the experiments using a digital balance and then pomegranate samples were coated and stored at 4 °C for 105 days and every 35 days, the physical and chemical properties of pomegranates were measured. Initial weight of the samples stored were measured every 35 days and the percent of weight loss was calculated using Equation (initial weight-secondary weight / initial weight) × 100. In addition, the outer skin browning of fruits as one of the frostbite indices was examined. The sphericity coefficient i.e., the degree of similarity of each sample to sphere was expressed as Q = (abc) ^(1/3) / a ×100 The total surface area of the samples was determined using relationship S= π〖((abc)〗^(1/3))^2. Area brown skin of the samples was calculated by application of Imag j software. The percent of browning index was calculated by relationship (brown area of sample)/( total surface sample area), and each percentage of browning fruit were given from zero to five and frostbite percent was measured using relationship, percent of frostbite = (marks total ×100)/(number of biopsied sample×5). Firmness was measured using a manually penetrometer (ABI-ASA, Netherlands) equipped with a probe with 8 mm diameter. The pH values were measured using a pH-meter (MTT65, Iran) for the measurement of pH, 1 ml of pomegranate juice was mixed with 9 ml of distilled water using two device buffer solution with pH = 4 and pH =7. The TA was determined by mixing 1 ml of pomegranate juice with 9 ml of distilled water in the presence of phenolphthalein and titrating with 0.1 mol L-1 NaOH (PH 8.1) and using a calculated relationship TA=(M×0/0064×100)/W. TSS contents were recorded in a soluble refractometer (ATAGO, Japan) with values being expressed as 0Brix. The color content and intensity were measured using strewing pomegranate juice into centrifuge tubes with length of 20 ml and was centrifuged at 4000 rpm for 15 minutes. Then, the absorbance within 420-520 nm was measured in a spectrophotometer, and finally the color content and intensity was calculated by A520 + A420 and A420 /A520, respectively. Statistical analysis was performed using SAS software. Differences among means were tested for significance by ANOVA procedures and LSD test.
Results and Discussion: The analysis results showed that the coating treatments had a significant effect on all properties while storage period had a significant effect only on pH, percent of weight loss, frosting percent, acidity and soluble solids content. The samples coated by chitosan solvent 1% showed greatly weight loss in comparison with other coating treatments. Because the high concentration of chitosan causes preservation moisture between chitosan and skin of fruit that this could increase the activity of the aerobic pathogens, decay and higher weight loss. Firmness of fruits coated by liquid paraffin greatly reduced during storage period in comparison with other coating treatments. The soluble solids content of fruits covered by chitosan solvent 1% showed greatly an increase during storage period in comparison with other coating treatments. Coating treatments had a significant effect on the color content and intensity at level of 0.05 and 0.01, respectively. The coating aloevera gel treatment showed the lowest color intensity and content which suggests maintaining anthocyanin pigments and reducing brown pigments in samples. Among all coating treatments, the pomegranate peel extract indeed of conservation of apparent quality of fruits and seeds, showed the lower frosting percent approving the favorable effect of this treatment on the preservation of fruit in cold storage.
Conclusions: The results showed that among applied coatings, pomegranate peel extract is the best option due to the conservation of apparent quality of fruits and seeds as well as the lower frosting percent. The coating treatments aloevera gel and pomegranate peel extract showed the lowest color content and intensity and they are more appropriate options due to conservation of transparency and color red, respectively. Therefore, the treatment coating pomegranate peel extract and aloevera gel were chosen as the best options in pomegranate storage.