Changes in Antioxidant and Color Properties of Raisins According to Variety and Drying Method

Abstract

Raisins are a significant grape product with an annual trade volume of approximately USD 2 billion. There are various methods employed for drying grapes into raisins. This study aimed to investigate the effects of different drying methods on raisins, specifically, without pretreatment (SD), treatment with potassium carbonate (5%) containing 2% olive oil (POT), and treatment with ashy water with 2.5% olive oil (AOW). The study examined the changes in raisin weight, physicochemical characteristics, total phenolics, antioxidant and anthocyanin contents, color properties, and protein content in three grape varieties: Deyvani, Haseni, and Reşek. The results indicated that POT treatment resulted in the lightest raisins in Deyvani (0.48 g) and Reşek (0.58 g), while Haseni exhibited the heaviest raisins (0.64 g) under the same treatment. The variations in physicochemical characteristics were relatively limited compared to the changes observed in phenolic and antioxidant properties. Nontreated raisins had the lowest anthocyanin content across all varieties. Protein content was significantly affected by the POT treatment, while the effects of the AOW and SD treatments were comparatively minor. SD drying resulted in slightly brighter raisins, but lower phenolic content and significantly lower color properties. The findings of this study highlight the differential effects of drying methods on different grape varieties, emphasizing the importance of considering a variety-specific approach when selecting the drying method.

Fine-Tuning Grape Phytochemistry: Examining the Distinct Influence of Oak Ash and Potassium Carbonate Pre-Treatments on Essential Components

“…The substantially higher malvidin-3-O-glycoside acetyl and delphinidin-3-O-glycoside content in the oak ash treatment emphasizes its importance as a pre-treatment choice for influencing this specific anthocyanin, consistent with previous studies underscoring the role of pre-treatment in shaping the anthocyanin profile in grapes [25]. The analysis of the anthocyanin content revealed intriguing disparities between the K 2 CO 3 and oak ash treatments, aligning with prior studies highlighting the impact of pre-treatments on anthocyanin content modulation [33].…”

“…Furthermore, the notably higher flavones content in the oak ash solution suggests its efficacy in conserving these compounds, which is significant considering the potential health benefits associated with flavones [28,29]. The significant variance in the flavanols' content, with K 2 CO 3 surpassing oak ash, is in line with a previous study indicating the sensitivity of flavanols to different pre-treatment techniques [25]. Similarly, the notably higher pterostilbene content in the oak ash treatment emphasizes its potential positive impact on this phytoalexin.…”

“…A comparison of phytoalexins and flavonoids between the K 2 CO 3 and oak ash solutions also yielded notable insights. The significantly higher anthocyanidins content in the oak ash solution underscores the promise of this pre-treatment method in enhancing these compounds, aligning with the findings of Ünal et al [25]. The elevated catechins content in the oak ash solution highlights its potential as a preferred choice for enriching these compounds, known for their antioxidant properties [26,27].…”