تاثیر پوشش خوراکی کیتوزان بر ویژگی‌های فیزیکوشیمیایی و فعالیت آنزیمی میوه انگور رقم فخری در شرایط سردخانه

استفاده از پوشش های خوراکی طبیعی برای افزایش عمر پس از برداشت محصولاتی همانند میوه ها، امروزه بسیار متداول شده است. کیتوزان با قابلیت کنترل میکروارگانیسم‏های بیماری‏زا و کاهش سرعت تبخیر و تعرق آب از بافت گیاه، به عنوان یک ماده غیرسمی طبیعی و یک پوشش خوراکی طبیعی شناخته شده است. این پژوهش، با هدف بررسی اثر تیمار کیتوزان (صفر، 0/25، 0/5 و 1 درصد) و زمان انبارمانی (صفر، 20، 40 و 60 روز) بر حفظ کیفیت و عمر انبارمانی میوه انگور رقم فخری، به‏صورت فاکتوریل در قالب طرح کاملاً تصادفی در سه تکرار انجام شد. شاخص‏های مورد ارزیابی شامل درصد کاهش وزن، درصد آلودگی، درصد ریزش حبه، میزان قهوه‏ای شدن حبه، اسیدآسکوربیک، اسیدیته قابل تیتراسیون، فنل کل، میزان فعالیت آنزیم‏های فنیل‏آلانین‏آمونیالیاز، پلی‏فنل‏اکسیداز و پراکسیداز بود. نتایج نشان داد که غلظت 1 درصد کیتوزان به‏خوبی توانست آلودگی، ریزش حبه، کاهش اسیدیته قابل تیتراسیون و کاهش اسیدآسکوربیک را کنترل نماید و بیش‏ترین میزان فعالیت آنزیم پلی‏فنل‏اکسیداز در غلظت 1 درصد کیتوزان مشاهده گردید و غلظت 0/5 درصد کیتوزان نیز سبب جلوگیری از کاهش وزن و قهوه‏ای شدن حبه‏ها نسبت به سایر غلظت‏ها و نمونه شاهد گردید و بیش‏ترین میزان فنل کل و  بالاترین میزان فعالیت آنزیم فنیل‏آلانین‏آمونیالیاز و پراکسیداز نیز مربوط به غلظت 0/5 درصد کیتوزان بود، این در حالی است که بین دو غلظت 0/5 و 1 درصد کیتوزان در بیش‏تر صفات تفاوت معنی‏داری در سطح 5 درصد مشاهده نشد.

the effect of chitosan edible coating on physicochemical properties and enzymatic activity of grape fruit cultivar fakhri in cold storage conditions

introduction chitosan, as a bio-polymer, has many applications in agriculture. coating fruits and vegetables with chitosan plays a positive role in increasing their shelf-life, since the chitosan coating reduce growth of fungi and preserves the quality of the fruits longer.materials and methods this study was conducted to evaluate the effect of chitosan treatments (0, 0.25, 0.5 and 1%) and storage time (0, 20, 40 and 60 days) on maintaining quantitative and qualitative parameters and shelf life of grape fruit of fakhri cultivar. the experiments were factorial based on a completely randomized design with three replications. the fruits were stored for 2 months. some characteristics of fruits including percentage of weight loss, percentage of berries abscission, percentage of decay of berries, browning of berries and biochemical characteristics including titratable acidity, ascorbic acid content, total phenol, enzymes activity including peroxidase (pod), phenylalanine ammonia-lyase (pal) and polyphenol oxidase (ppo) were measured in order to investigate the best treatment. results and discussion  the results showed that the traits under study were affected by different concentrations of chitosan, with the lowest percentage of weight loss associated with the concentration of 0.5% chitosan. chitosan, by forming a semi-permeable membrane, regulates gases,and reduces the transfer of water from fruit tissues. the lowest amount of browning of berries was observed in the concentration of 0.5% chitosan. chitosan is partly prevented from increasing the activity of brown-peroxidase in chitosan-treated fruits. there was no significant difference in concentration of 0.5% chitosan with 1% concentration. the lowest percentage of contamination and percentage of berries abscission was observed in 1% chitosan concentration. it seems that these treatments prevent the effects of ethylene levels and the formation of a swab layer at the site of fruit attachment to the cluster. the slightest increase in the titratable acidity and the lowest decrease of ascorbic acid was observed in the concentration of 1% chitosan. higher levels of ascorbic acid in fruits that are coated with chitosan may be due to decreased oxygen levels and respiration inhibition. the highest total phenol was related to the control treatment, which may be due to the loss of chlorophyll and the onset of synthesis of phenolic compounds. the highest level of activity of pal enzyme was observed in the concentration of 0.5% chitosan and the control. this enzyme is stimulated by various live and non-living stresses. in general, the highest activity of peroxidase enzyme was observed in the concentration of 0.5% chitosan and the highest activity of polyphenol oxidase in 1% concentration of chitosan.conclusion  it seems that the concentration of 1% chitosan can improve the quality of fruits for a longer time while increasing the shelf life of fruit.