The effects of different UV-B irradiation doses on plant growth, antioxidant compounds and postharvest quality of broccolis

Increasing of air and environmental pollution due to various reasons causes a decrease in ozone layer which is negatively effects the plants and living organisms on earth. Fortunately, most of this harmful UV irradiation is filtered out by the ozone layer, which strongly absorbs UV lights. Unfortunately, especially in recent years, this protective shield is being continually damaged by different human activity and environmental pollution. Due to decreasing of the ozone layer, various gases and harmful radiations may reach to our world without any filtration. UV-B irradiation is harmful for all types of living organisms including fruit and vegetables even the most primitive single-cell plants. As with all other living organisms, horticultural crops are quite sensitive to high doses of UV-B irradiations. Several studies showed that, world food production can be decrease by 1%, with each 1% increasing of UV-B irradiation reaching to the earth. Broccoli consumption in the world and in our country has been increasing in recent years, especially due to high consumer demand since broccoli contains high amount of plant nutrients, phenolic substances and antioxidants. Therefore, the preservation of the nutrient content and antioxidant activity of broccolis after harvest is extremely important. The main nutrients in broccolis are glucosinolate, vitamin C, beta carotene and antioxidants. In this study, the effects of three different doses of UV-B irradiations during the growing period on yield, plant growth and development, plant nutrients, phenolic compounds, antioxidant activity and postharvest quality of broccoli heads were investigated. For this purpose, supplemental 2.2, 8.8 and 16.4 kJ/m2/day of three different doses of UV-B irradiations were tested on the broccoli plants grown in soilless culture in glasshouse. Use of supplemental UV-B irradiations during the growing period has resulted a lower yield, plant height, chlorophyll and head diameter while it has increased stem diameter and leaf thickness. In addition, UV-B irradiations caused a lower weight loss, titratable acidity, h° value, soluble solids and dry matter comparing to control plants. UV-B irradiations during growing period has negative effects on head appearance and visual color as well. Sulfur and sodium amount of broccoli heads were increased by increasing UV-B doses. However, phosphorus, potassium, calcium, magnesium, manganese, iron, copper and zinc contents were decreased. Antioxidant activity, carotenoids, chlorophyll a and b content were decreased with increasing UV-B irradiations levels. However, total phenolics, L ascorbic acid, sinigrin, glucotropaeolin contents were increased.