عنوان مقاله [English]
Introduction: Grape is a non-climacteric fruit. Its ripening is associated with increased sugars, decreased acidity and development of color and flavor. Edible films and coatings could be used as a selective protection method to extend storage life of fruits. Edible coatings reduce the absorption amount of brine, osmotic solution and frying oil into foods, improve mechanical properties, facilitate displacement and storage strengthen food structure, reduce spoilage and increase its shelf-life. The coatings provide a protective layer for fresh fruits and act as like as modified atmosphere packaging, change the composition of internal gases, and increase the storage-life of fruits by reducing respiration rate. Zein, is an important protein in corn seed and consists about 45 - 50% of the corn proteins. This protein contains a group of Prolamines found in the corn endosperm. Zein has unique properties for preparing edible films and coatings in comparison to other plant proteins due to its high percentage of nonpolar amino acids. Gluten is an insoluble in water protein of wheat that its disulfide bonds play an important role in the establishment of gluten films. Prepared films from wheat gluten are pure and transparent, but commercial gluten produces an opaque film due to gelatinization of its existing starch. Wheat gluten-based films have satisfactory mechanical resistance and very low oxygen permeability. Gluten can encapsulate flavors, colors, or medicines, providing slow-release materials. Bacteria, fungi, or other pest- or weed-control agents can be encapsulated in gluten granules that are then coated with oil to slow drying and maintain vitality.
Materials and Methods: This study was carried out to investigate the effects of gluten and zein coatings on postharvest quality of grape cultivars in a factorial arrangement based on randomized completely design with application of corn’s Zein coating treatments at four levels (control, 2, 4 and 6% w/w) and also wheat gluten at four levels (control, 2, 4 and 6% w/w) were performed in the grape cultivars (Meshkin cultivar). Grape fruits were harvested from the gardens of Meshkin city and moved to the laboratory in the University of Mohaghegh Ardabili. Then, after applying the treatments, fruits were kept at 0° C and humidity of 90-95% in cold storage. In this study, pH, total soluble solids, total acidity, starch, anthocyanin, firmness, taste, fruit storage-life, TSS/TA, weight loss, appearance and vitamin C content of fruits were measured in 30 days after applying the treatments.
Results and Discussion: The results of analysis of variance showed that using of zein as grape coating had significant effect on total soluble solids, vitamin C, taste and weight loss (p < 0.01) and on the TSS /TA attribute (p < 0.05).The use ofgluten also had a significant effect on total soluble solids, anthocyanin, weight loss and vitamin C (p < 0.01) and also on the fruit starch (p < 0.05). Interaction effect of gluten and zein treatments were significant on total soluble solids, vitamin C (p < 0.01) and fruit weight loss (p < 0.05). Based on the obtained results, the highest starch content, anthocyanin, maturity index and taste were achieved by using of gluten at 4 and 6% and the lowest amount of these substances was related to control treatment. A higher amount of anthocyanin (2.45 mg / 100 g) was retained in 6% gluten treatment, Moreover, in the fruit ripening index, the best result (41) was obtained from 6% zein treatment. The taste of the fruit was also more attractive in the 6% zein treatment without gluten consumption with a score of 8.5. Also, the best results in preservation of vitamin C (17.9), soluble solids (24 brix), fruit appearance (9.5 points) and the least weight loss of fruit (6.5%) were obtained from the combination of gluten and 6% zein treatment. Comparison of the means showed that vitamin C and soluble solids were better preserved by combined using of 4 and 6% gluten with 6 and 4% zein in storage period. These results showed that vitamin C and soluble solids had the lowest stability under control conditions. Also, the control treatment had the highest weight loss and the lowest score in the fruit preservation index. In overall, the best results in most of the studied parameters were obtained from the treatment combination of 6% gluten and zein.
Conclusion: Based on the obtained results, gluten and zein coatings in comparison to control treatment at levels of 6%, had significant positive effects on post-harvest quality and storage of grapes.