Effect of postharvest irradiation on health and sensory related properties of apples and broccoli

Sammendrag

Flavonoids and chlorogenic acid can be induced postharvest in apple skin. However, the effect of postharvest irradiation on product quality in general has been investigated in fresh fruit and vegetables to a very limited extent. As examples we have studied the effects of post-harvest radiation treatments on several parameters of apples and broccoli related to taste and human health. Norwegian grown broccoli and apples were treated 10-12 days with various combinations of visible light and UV radiation in controlled climate at 5ºC and 10ºC, respectively. L-ascorbic acid, chlorogenic acid and flavonoids were quantitated by HPLC, and total phenols, soluble solids and titratable acidity by other methods. Antioxidant capacity was measured in methanol extracts by the ORAC (Oxygen Radical Absorbance Capacity) method. In broccoli, the levels of flavonols and the antioxidant capacity were much higher in flower buds than in stalks. The natural variation between broccoli plants was very large in flower buds: tenfold for flavonol content and twofold for antioxidant capacity. This variation was not reduced by the radiation treatment. Flavonol levels in flower buds tended to increase after treatment with visible light + UV-A + UV-B, but the increase was just outside the border of statistical significance. Radiation treatment did not change the antioxidant capacity in broccoli. Treatment of apples with UV-B and visual light increased red colour, antioxidant capacity and the contents of flavonols, anthocyanins, chlorogenic acid and ascorbic acid in the peel, but not in the flesh. The effect was strongest in suboptimal (green) apples harvested from the inner tree canopy. The only changes after treatment with visible light were increases in quercetin glycosides and ascorbic acid in the skin of green apples. There was no influence on the contents of catechins, procyanidins, phloridzin, total phenols, soluble solids or titratable acidity in apples after any of the treatments. The study shows that it is possible to increase not only the contents of specific phenolic constituents but also other health-related properties in apples by postharvest irradiation, while at the same time sensory related properties did not change. The broccoli experiment was probably carried out at sub-optimal conditions and the number of properties studied was small. The fact that controlled radiation treatment postharvest can change the health-related quality is an indication that also the incident light during distribution of fruit and vegetables could have an effect, which might be positive or negative depending upon the conditions.