بررسي اثر پوشش‌هاي نانوكامپوزيت كيتوسان-رس، واكس و روغن زيتون روي برخي ويژگي‌هاي كيفي ليموشيرين در طي انبارماني عمر قفسهاي

The effect of chitosan-clay Nano composite, wax coatings and olive oil on some quality properties of sweet lemon during shelf life storage

مركبات به ‌عنوان يك محصول عمده و قابل دسترس در تمام جهان و ميوه‌اي محبوب در رژيم غذايي است. وارد آمدن آسيب به پوست ميوه ،كاهش رطوبت و چروكيدگي پس از برداشت همگي سبب كاهش بازار پسندي اين محصول مي‌ گردند. استفاده از پوشش‌هاي خوراكي يكي از مؤثرترين راه‌ها در حفظ كيفيت ميوه‌ها است. در اين پژوهش كيفيت ميوه ليموشيرين بر اساس آزمون فاكتوريل در قالب طرح كاملا تصادفي با پوشش خوراكي نانوكامپوزيت كيتوسان-رس در سه سطح، روغن زيتون و واكس كارنوبا در مقايسه با نمونه بدون پوشش طي 12 روز انبارماني مورد ارزيابي قرار گرفت. در طي دوره انبارماني ويژگي‌هاي شيميايي، pH، اسيديته ، TSS آب ميوه، درصد كاهش وزن، ويتامين سي و ويژگي‌هاي مكانيكي، ضريب كرويت، نيروي برش پوست، نيروي شكست و نيروي كشش پوست ميوه اندازه‌گيري شدند. نتايج نشان دهنده وجود تفاوت معني‌دار در سطح 1% و 5% بين پوشش‌هاي مختلف در حداكثر نيروي شكست، درصد كاهش وزن و pH بود. در ضمن تاثير زمان‌هاي مختلف انبارماني بر ميزان مواد جامد محلول در آب، pH و حداكثر نيروي شكست نيز معني‌دار بود. پوشش كيتوسان-رس 5 % كمترين ميزان درصد كاهش وزن را داشت و بيشترين ميزان درصد كاهش وزن به ترتيب براي پوشش شاهد و روغن زيتون 12/3 و 10/23 درصد بود. به طور كلي نتايج نشان داد ميوه‌هاي پوشش داده در حفظ خواص كيفي و مكانيكي نسبت به نمونه‌هاي بدون پوشش عملكرد بهتري داشتند و در بين پوشش‌هاي مصرف شده پوشش نانو كامپوزيت كيتوسان-رس 5 % موفقيت بالاتري نسبت به ساير پوشش‌ها داشت.

Introduction Citrus are one of the major agricultural production available in the world and it is one of the popular fruits in the diet. The most well-known varieties of citrus fruits include oranges, lemons, grapefruits and tangerines. Cultivation of sweet lemon requires specific climate situation that it is found in many region of Iran. However, the high quality ones are in Jahrom, Ghsre Shirin, Dezfool, Jiroft and the Sorth of Iran. Two major limitation of long-term storage for citrus fruits are decay caused by pathogens, especially fungi, skin fruit damage and water loss, which can cause wrinkles and reduce product marketability and consumer acceptability. Edible coatings are one of the most effective methods to maintaining the fruit quality. Today edible coatings can preserve citrus quality and provide attractive approach to satisfactory performance. Chitosan is used for film or edible coatings to extend the shelf life of foods such as fruits, meat and fish and foods. The results of several studies indicate the effective role of chitosan in controlling fruit during storage. Wax in the fruit is used to prevent moisture loss and wrinkle of the fruit and also to maintain the appearance of the product and its marketability. So, the final goal of this study is investigate the effect of edible coatings (chitosan-clay Nano composite, Wax coatings and olive oil) on some quality attributes of sweet lemon during shelf life storage. Materials and Methods Sweet lemon's fruits (216 N.) were harvested randomly from a citrus orchard in Dezfool, Iran. The samples immediately sent into the laboratory for storage after necessary treatments. All fruits were disinfected by immersion in 4% chlorox for 3 minutes and then dried. Chitosan with low molecular weight (43 KD) was bought from Sigma Aldrich Company. Clay was purchased from Sefid Sang Aligoodarz Company in Iran and wax coating was provided from Pooshesh Hayat sabz company in Iran. The chitosan-clay coating was prepared by dissolving a mixture of chitosan (3w/v% to solution), clay (5, 10 and 15% wt to chitosan) and glycerol (10v/w% to chitosan) and tween 80(5% v/w to chitosan) in acid lactic solution (2%). Nano structure of chitosan-clay nano-composite was approved by XRD analysis. The chemical parameters of fruit juice such as TSS (%), pH(%) and TA (%) of lemon juice were measured. TSS was determined by digital refractometer (model MA882, made in Japan). pH was measured by pHmeter ( portable p-755 model) and TA was determined by AOAC standard method. The experiment was performed at three levels of chitosan-clay nanocomposite, olive oil, Carnoba wax and uncoated samples during 12 days shelf life storage. The experimental design was factorial based on completely randomized design with three replications. Limon samples were maintained at ambient temperature of 25 ℃ and relative humidity of 80-85%. Chemical characteristics (pH, citric acid, fruit juice TSS, vitamin C) and mechanical characteristics (weight loss percentage, sphericity coefficient, maximum shear force, maximum fracture force and maximum tensile strength of the fruit skin) were measured during storage. Results and Discussion The results of experiments showed that the trend of changes in vitamin C content decreased during storage. But this decrease was slower in the different percentages of chitosan-clay, olive oil coating and carnoba wax than in the control samples. The results showed the significant differences at 1% and 5% levels between different coatings at maximum fracture force, percent weight loss and pH. In addition, the effect of storage times on TSS, pH and maximum fracture force was significant. The lowest and highest percentage of weight loss for uncoated samples and olive oil coating were 12.3% and 10.23%, respectively. Results showed that the coated fruits had the better performance in preserving the quality of properties than the uncoated samples and 5% chitosan-clay nanocomposite coatings were higher performance than the other coatings. Conclusion In this study, the effect of chitosan-clay nanocomposite, olive oil, Carnoba wax and uncoated samples during 12 days shelf life storage on Chemical characteristics (pH, citric acid, fruit juice TSS, vitamin C) and mechanical characteristics (weight loss percentage, sphericity coefficient, maximum shear force, maximum fracture force and maximum tensile strength of the fruit skin) were investigated. The results of this study showed that 5% chitosan-clay nanocomposite coatings were higher performance than the other coatings.