Effect of Sun, Oven and Freeze-Drying on Anthocyanins, Phenolic Compounds and Antioxidant Activity of Black Grape (Ekşikara) (Vitis vinifera L.)

Abstract

The aim of this study was to determine whether a change occurs in the phenolic compounds and antioxidant activity of grapes after drying. Grapes pre-treated with potassium hydroxide solution were dried using three different drying methods, namely freeze drying, oven drying and sun drying. The effectiveness of the drying methods was evaluated in terms of total phenolic content, antioxidant activity (ABTS, FRAP and DPPH), individual phenolics and anthocyanins. Losses in total phenolic content of the grapes were found to be 1.89, 20.26 and 46.79% for freeze-, oven-and sun-dried grapes respectively. The DPPH and ABTS antioxidant activities of the grapes decreased after drying by all three methods, while an increase was observed in the FRAP value of freeze-dried grapes compared to the fresh sample. No significant effect of drying methods was observed on the gallic acid, 2,5-dihydroxybenzoic acid and (-)-epigallocatechin gallate contents of the grapes. The highest levels of procyanidin B1, (+)-catechin, (-)-epicatechin, (-)-epicatechin gallate, chlorogenic acid, trans-resveratrol and rutin were determined in freeze-dried grapes. Sun and oven drying caused drastic decreases in all anthocyanins, while no loss of anthocyanin was observed in freeze-dried grapes. Sun drying was found as the most detrimental drying method for grapes in terms of phenolic compounds and antioxidant activity when compared to the other drying methods.

Assessment of Elemental Content, Antioxidant Activity and Total Phenolic Content of Vitis sylvestris Gmelin

“…The highest value for total phenolic content found to be 20.21 mg/g DW in fresh grapes, but this value in the freeze-, oven-and sun-dried samples continued to decrease. The values of DPPH and ABTS antioxidant activities in fresh grapes determined as 66.07 mmol TE/kg DW and 137.65 mmol TE/kg DW (29). Total phenolic compounds of red grape varieties examined by Correia and Jordão found to be average 1341.0 mg/L, and antioxidant capacities determined varying from 3.96 to 32.96 mm/L Fe(II) (30).…”

Proximate and phenolic composition of selected native Australian food plants

“…Typha orientalis which recorded the highest amount of moisture loss (93.6%) showed more moisture loss in 2017 compared to 2019 ( P < 0.05). Freeze‐drying has been reported as a less aggressive drying method (de Torres et al , ; Çoklar & Akbulut, ) due to its ability to prevent loss of volatile polyphenols and potential antioxidants, thus maintaining the TPC of the samples during processing (Mediani et al , ). Our results indicate that freeze‐drying in addition to its less aggressiveness in dehydrating the samples is also an efficient moisture remover, consistent with the findings of Puranik et al () who after a comparative study of different drying techniques on the quality of garlic, concluded that freeze‐dried samples had maximum water loss, than fluidised bed drying, oven‐drying and microwave heating methods.…”

Enrichment of Mango Fruit Leathers with Natal Plum (Carissa macrocarpa) Improves Their Phytochemical Content and Antioxidant Properties

“…The drying temperature of the oven also affects the concentration of cyanidin derivatives; drying sour cherries at 50 • C reduced cyanidin-3-glucoside, compared to fresh ones [31]. In addition, extraction of the phenolic compounds affected the reduction in particle size, solvent types used for extraction, and the porosity of the dried samples [32].…”

“…Thus, on this note, the sugar content in Natal-plum fruit leather snack may not offset any potential benefits of bioactive components. In the presence of hydrophilic groups (such as those from pectin, fibre, and other soluble solids), drying can take longer, but longer drying times are associated with degradation of phytochemicals [32].…”