Effect of Needle Micro-Perforation Pretreatment as an Alternative to Alkaline Dipping Solution in Grape Drying on Bioactive Compounds

Özet

Grape (Vitis sp.) is widely consumed and cultivated globally. In addition to being consumed fresh, as wine, juice, or dried fruit, it is known for its bioactive compounds, such as flavonoids, polyphenols, anthocyanins, and tannins, which provide health benefits, including antioxidant, anti-inflammatory, and cardioprotective effects. However, grapes are highly susceptible to microbial spoilage due to their high water content, limiting their shelf life. Drying is one of the most common methods used to extend grape shelf life. Pre-treatments before drying facilitate moisture removal, accelerating the drying process and preserving nutrients.

This study investigates the potential of needle micro-perforation (0.5 mm, 1 mm, and 1.5 mm needle lengths) as an alternative to the widely used dipping method. The total phenolic content, antioxidant capacity (DPPH and CUPRAC), and anthocyanin content of Kavacık grapes (Vitis vinifera L. "Alphonse Lavallée" variety) were analyzed. Pre-treated grapes were dried using static and convective methods at 60°C, 70°C, and 80°C, and their bioactive compounds were evaluated.

Results showed that different pre-treatments had varying effects on bioactive compounds. Needle micro-perforation was as effective as the dipping method in preserving total phenolics, antioxidants, and anthocyanins. In static drying, the total phenolic content of samples with needle micro-perforation was approximately 250 mg per 100 g of dry matter higher than that of samples with the dipping treatment. In convective drying, this difference increased to about 400 mg per 100 g of dry matter. Similarly, antioxidant capacity was about 10 µmol Trolox equivalent per gram of dry matter higher in needle micro-perforation samples under static drying and 20 µmol higher under convective drying.

In conclusion, needle micro-perforation effectively preserves bioactive compounds and can be considered an alternative to the dipping method.