Pre-harvest application of chitosan and nano-chitosan on enzymatic activities, quality and sensory indicators of fresh pistachios (Pistacia vera L. cv 'Ahmad Aghaei')

Pistachio (Pistacia vera L.) is one of the most important and popular tree nuts in the world. The kernels of this product are rich in oil (more than 50%) and contain linolenic, linoleic and oleic acid, which are essential for the human diet. Pistachio is also one of the important export products that is of strategic importance in the field of non-petroleum exports and currency and its role in the agricultural and national economy is significant and valuable. In addition to its economic value, pistachios are rich in essential nutrients such as phenolic compounds, anthocyanins, unsaturated and tonic fatty acids, the consumption of which has a great impact on health, well-being and community empowerment. The use of biodegradable, edible, and antimicrobial films and coatings as a suitable alternative to synthetic preservatives is important in order to maintain food security and prevent wastage of capital.

This study was performed in 2021 in the Faculty of Agriculture, Lorestan University and Green Tat Research Garden in Qazvin province. In this experiment, the effect of pre-harvest foliar application of chitosan (0, 500 and 1000 mg/l) and nano- chitosan (0, 250 and 500 mg/l) on the qualitative and sensory characteristics, activity of antioxidant enzymes and shelf life of fresh pistachios 'Ahmad Aghaei' cultivar in four different times (0, 25, 50 and 75 days after harvest) were stored in the cold storage at 4 ±0.5° C and 80% RH. The studied traits included, fruit kernel firmness, weight loss percentage, antioxidant enzyme activity, acid value, peroxide values (PV) and sensory properties were measured at different times.

The results showed that the fruits treated with nano-chitosan 500 mg/l had the highest tissue firmness (8.13 N). The lowest percentage of weight loss was observed in nano-chitosan 250 mg/l treatment on the 25th day (0.14%). The activity of superoxide dismutase enzyme in fruits treated with nano-chitosan 500 mg/l also increased. The lowest polyphenol oxidase activity belonged to nano-chitosan 250 mg/l treatment and the highest guaiacol peroxidase activity was observed in chitosan 1000 mg/l treatment. The lowest and highest amount of peroxide values was obtained in the treatment of nano-chitosan 250 mg/l and control, respectively, on days 0 and 75 days after storage. The amount of free fatty acids increased during storage and the increase was slower in chitosan and nano-chitosan treatments, so that the lowest amount of free fatty acids in nano-chitosan treatment was 250 mg/l in day 0 and the highest amount of free fatty acid in control treatment was observed on the 75th day. Fresh pistachios coated with nano-chitosan 500 and 250 mg/liter significantly showed the highest average sensory scores in marketability index, skin appearance, smile and texture crispness compared to the control.

According to the results, it can be stated that the application of nano-chitosan 250 mg/l in the pre-harvest stage, due to maintaining qualitative and sensory characteristics, and increasing the shelf life of fresh pistachios up to 75 days compared to the control, and as a natural and biodegradable compound is recommended.