اثر نیتریک اکسید و دما بر حفظ کیفیت آریل انار رقم ملس

شکل ظاهری میوه مهمترین شاخص ارزیابی بازارپسندی آن است. وجود هرگونه علایم آلودگی، پوسیدگی و نرم‌شدگی طی انبارمانی باعث کاهش بازارپسندی آن می‌شود. به‌منظور ارزیابی اثرات تیمار طبیعی و دما بر ویژگی‌های کمی و کیفی در مرحله پس از برداشت آریل انار، آزمایشی در قالب آزمایش فاکتوریل بر پایه طرح کاملاً تصادفی در مرکز تحقیقات کشاورزی و منابع طبیعی اصفهان انجام گرفت. در این پژوهش عوامل مورد بررسی شامل نیتریک اکسید به‌عنوان ترکیب طبیعی (با غلظت‌های صفر، 5 و10 میکرومولار) و دما (2، 4 و 8 درجه سانتی‌گراد) بود. خواص مختلف کیفی میوه درفاصله زمانی هفت روز مورد ارزیابی قرار گرفتند. بر اساس نتایج به‌دست آمده، غلظت 10 میکرومولار نیتریک اکسید و نگهداری در دمای 8 درجه سانتی‌گراد نقش موثرتری را نسبت به سایر تیمارها بر ویژگی‌های افت وزن، حفظ مواد جامد محلول، اسید آسکوربیک، فنل کل، آنتوسیانین، آنزیم پراکسیداز، شاخص طعم و ظرفیت آنتی‌اکسیدان داشت و به‌طور چشمگیری باعث کاهش محتوای مالون دی‌آلدهید و نشت الکترولیت در طول انبارمانی شد. با گذشت زمان میزان فعالیت آنزیم پلی‌فنل اکسیداز در تمام تیمارها افزایش یافت. اما آریل‌های تیمار شده کمترین میزان فعالیت آنزیم را داشتند. آریل‌های تیمارشده با 10 میکرومولار نیتریک اکسید در دمای 8 درجه سانتی‌گراد بالاترین کیفیت ظاهری را داشتند.

Effect of Nitric oxide and storage temperature on maintenance quality of malas pomegranate arils

Introduction: Pomegranate (Punica granatum L.) is an important horticultural fruit that is generally very well adapted to the Mediterranean climate. Arils are the edible part of this fruit, being rich in anthocyanins and bioactive compounds such as phenolic compounds and flavonoids which act as antioxidants and free radical scavengers. Susceptibility to chilling injury in pomegranate fruits is a major limiting factor in storing fruits at low temperatures. Below 5 °C, pomegranate fruits show symptoms such as surface pitting, browning, discoloration, and decay. The control of temperature is an effective tool for extending the shelf life of fresh horticultural products. Oxidative stress, as caused by an excess of reactive oxygen species (ROS), is usually associated with chilling injury in fruits. Nitric oxide (NO) is an important gas molecule, the involvement of which in many physiological processes can protect plant cells against oxidative stress by reducing the accumulation of ROS. Postharvest studies have shown that the application of NO gas can extend the storage life of a range of horticultural produce by delaying ripening or senescence. Due to the high number of pomegranate cultivars in Iran, limited amounts of information exist on how the qualitative characteristics of arils in the Malas pomegranate can be affected by nitric oxide and different temperatures during storage. The Malas cultivar comprises a large share of pomegranate exports from Iran. In this research, the positive effects of nitric oxide were examined on reducing the chilling injury and maintaining the fruit quality of pomegranate. The application of this treatment at different concentrations and different storage temperatures led to variable effects on the qualitative characteristics of arils in the Malas pomegranate.; ;Materials and methods: Malas pomegranate fruits were harvested commercially from Isfahan Province and were transferred to the Food Industry Laboratory of Isfahan Natural Resources Research. The fresh arils were separated from fruit tissues and were immersed in solutions of nitric oxide (0, 5 and 10 μM/L) for 5 min. After draining, the arils were placed in packaging films of polyethylene and were immediately stored at 2, 4 and 8 °C for 21 days. Several parameters were measured every 7 days during the storage time. These were the weight loss, total soluble solids, titratable acidity, TSS/TA, acid ascorbic, total phenol, total anthocyanin content, antioxidant activity, MA, ion leakage, POD, PPO activity and sensory evaluation. The current study was carried out as a factorial assay and was based on a completely randomized design with three replications. Data were processed by ANOVA using the SAS software version 9.4. Significant differences were identified using Duncan’s test at 1% probability level.; ;Results and discussion: Results showed that the total anthocyanin content, total phenol, antioxidant activity, and titratable acidity decreased during storage time. The control group and the treatment with low temperatures significantly reduced the qualitative characteristics of arils during storage. The water content of arils treated with 5 and 10 μM nitric oxide was maintained considerably for 21 days during storage. According to these results, unlike titratable acidity and ascorbic acid which decreased in both treated and untreated fruits, there was an increase in the total soluble solids and POD activity of arils during storage. However, nitric oxide reduced the rate of these changes, whether it be the decrease or increase in the measured parameters. During the experiment, the control samples showed lower values of quality regarding all parameters. The use of nitric oxide in fruits reduced lipid peroxidation and ion leakage significantly, whereas the antioxidant activity increased. The decrease in ion leakage was observed most notably in fruits that were treated with 10 μM nitric oxide. Furthermore, low temperatures managed to disrupt the metabolic balance of reactive oxygen species, leading to the accumulation and destruction of antioxidant enzymes. In the present study, exogenous treatments with nitric oxide at 5 and 10 μM significantly reduced the lipid peroxidation content and electrolyte leakage of arils being stored at cold temperatures, compared to untreated arils. Nitric oxide suppressed the activity of polyphenol oxidase (PPO) and preserved the physical appearance and the internal quality of pomegranate arils. The decrease in phenolic compounds (29.32%) and antioxidant activity (39.91%), besides the increase in lipid peroxidation (38.37%) and ion leakage (36.98%), caused deteriorations in the appearance and organoleptic properties of the control samples. To alleviate these problems, nitric oxide has beneficial effects on maintaining the anthocyanin content of pomegranate arils by partially inhibiting PPO enzyme activity during storage. It prolongs the postharvest life, helps to preserve the quality of pomegranate arils, suppresses the formation of ethylene, reduces the respiratory rate and controls weight loss, in addition to maintaining the firmness of fruits. Delaying the changes in peel color and TSS are also considered as useful effects of nitric oxide on pomegranate arils. Nitric oxide impeded the process of senescence by slowing down PPOrelated activities, thereby maintaining the total phenolic content of pomegranate arils.;In conclusion, the application of nitric oxide was observed to reduce ion leakage and PPO activity in pomegranate arils, while also maintaining the quality of arils. Ultimately, the use of 10 µM nitric oxide at 8 °C can be suggested as the most optimum treatment herein.