Browsing by Author "Karakus, Sinem"

Now showing 1 - 3 of 3

Comparison of Contents of Sugars, Organic Acids and Free Amino Acids in Raisins Obtained From Gok Uzum (Vitis Vinifera L.)
(Hohere Bundeslehranstalt & Bundesamt Wein-& Obstbau Klosterneuburg, 2023) Karakus, Sinem; Ates, Fadime; Keskin, Nurhan; Turan, Metin; Kaya, Ozkan
Raisins are known as an important source of many bioactive compounds such as organic acids, free amino acids, and sugars. In this study, oak ash and potassium carbonate solutions applied before drying were compared for their effects on the Gok Uzum raisin, more specifically, its contents of organic acids, free amino acids, and sugar profile. The total acidity quantified in the samples of raisin, ranged from 20.30 to 117.08 ng/mu L DW for the potassium dipping solution, while values ranged from 17.98 to 164.72 ng/mu L DW for the oak ash dipping solution. In samples from either dip solution, serine was predominant, followed by alanine, asparagine, glutamine, aspartate, sarcosine, glutamate, and leucine, whereas glycine, arginine, proline, histidine, and valine were found to be the lowest amino acids. In the samples examined, fructose was the most abundant sugar, whereas the lowest sugars in raisins were xylose for oak ash application and galactose for potassium carbonate application. There was wide variation in the sugar profiles for both variants, with values ranging from 3043.48 to 0.71 g/100 g DW. Drying Gok Uzum grapes after the treatment of oak ash dipping solution promotes a higher content of organic acids, amino acids and sugars as compared to drying after potassium carbonate solution treatments. These results could be used for the development of an attractive pre-drying solution in further studies for the production of both, raisins and perhaps other dried fruits.
Modulation of Biochemical Traits in Cold-Stored 'Karaerik’ Grapes by Different Edible Coatings
(Mdpi, 2025) Keskin, Nurhan; Karakus, Sinem; Hatterman-Valenti, Harlene; Kaya, Ozkan; Cavusoglu, Seyda; Tekin, Onur; Karadogan, Birol
Understanding the effects of edible coatings on postharvest quality and shelf life of 'Karaerik' grapes is crucial for improving storage outcomes and reducing losses. However, limited information exists regarding the effectiveness of different coating materials on this regionally significant variety. In this study, 'Karaerik' grapes were treated with carboxymethyl cellulose (CMC) and locust bean gum (KB) coatings and stored under cold conditions (0 +/- 0.5 degrees C, 90-95% relative humidity) for 0, 25, 45, and 60 days. Storage duration and coating treatments significantly affected most physical, physiological, and biochemical parameters. During storage, grape weight loss progressively increased, reaching 9.60% in the control by day 60. Coatings slightly reduced this loss, with KB showing the lowest (5.11%) compared to the control (5.69%). Respiration initially declined but surged again at day 60, especially in the control (96.4 mu mol CO2/kg center dot hour), while coatings helped mitigate this rise. Ethylene release remained unchanged. A slight pH decline (similar to 4.6%) was observed in the control, while KB-treated grapes maintained higher pH and lower acidity. Soluble solids remained stable across treatments. Color changed notably during storage: a* nearly doubled (more redness), b* increased (less blue), and chroma (C*) declined by similar to 25%, especially in uncoated grapes. Total sugar dropped by similar to 43% in KB-treated grapes, with the control retaining the most. Tartaric acid decreased by similar to 55%, notably in KB samples. Antioxidant activity and total phenolics declined significantly (similar to 66%) in the control. CMC coating better-preserved antioxidant capacity, while the control showed the highest phenolic levels overall. Ferulic, gallic, and chlorogenic acids increased toward the end of storage, particularly in coated grapes. In contrast, rutin and vanillic acid peaked mid-storage and were better preserved in the control. The heatmap showed significant metabolite changes in fruit samples across 0D, 25D, 45D, and 60D storage periods under CMC, CNT, and KB treatments, with distinct clustering patterns revealing treatment-specific biochemical responses. The correlation matrix revealed strong positive relationships (r > 0.70) between total sugar, glucose, and fructose levels, while ethylene showed significant negative correlations (-0.65 to -0.85) with maturity index, pH, and total soluble solids, indicating interconnected metabolic pathways during fruit ripening and storage. We conclude that edible coating selection significantly influences grape biochemical stability during cold storage, with CMC emerging as a superior choice for maintaining certain quality parameters.
Timing Matters, Not Just the Treatment: Phenological-Stage Effects of Seaweed and Ethanol Applications on Postharvest Quality of 'Tarsus Beyazı' Grapes
(Mdpi, 2025) Tarim, Guzin; Karakus, Sinem; Keskin, Nurhan; Hatterman-Valenti, Harlene; Kaya, Ozkan
In the context of increasing consumer demand for high-quality, residue-free fruits and the growing emphasis on sustainable postharvest technologies, identifying effective, eco-friendly treatments to maintain grape quality during storage has become a critical focus in modern viticulture. Over the course of this study, we examined the influence of seaweed extract (derived from Ascophyllum nodosum) and ethanol-based postharvest treatments on the postharvest quality of the 'Tarsus Beyaz & imath;' grape. The seaweed extract was applied at six specific phenological stages according to the BBCH scale: BBCH 13 (3rd-4th leaf stage, 0.40%), BBCH 60 (first flower sheath opening, 0.50%), BBCH 71 (fruit set, 0.50%), BBCH 75 (chickpea-sized berries, 0.50%), BBCH 81 (start of ripening, 0.60%), and BBCH 89 (harvest maturity, 0.60%). After harvest, grape clusters were subjected to four different postharvest treatments: untreated control, control + ethanol (20% ethanol immersion for 10 s), seaweed extract alone (preharvest applications only), and seaweed extract + ethanol (combining both preharvest and postharvest treatments). Grapes were stored at 0-1 degrees C and 90-95% RH for three weeks, followed by a shelf-life evaluation period of three days at 20 degrees C and 60-65% RH. The findings revealed that seaweed treatments, especially when applied during cluster formation and berry development, effectively mitigated physiological deterioration, preserving stem turgidity and enhancing berry firmness. In contrast, ethanol showed variable responses, occasionally exerting negative effects, with only marginal benefits observed when applied at optimal developmental stages. Both the type and timing of application emerged as critical determinants of key quality attributes such as weight loss, decay incidence, and must properties (TSS, pH, TA). Correlation and heat map analyses indicated the interrelationships among these parameters and the differential impacts of treatments. These results suggest that phenological-stage-specific seaweed applications hold significant potential as a sustainable strategy to extend the storage life and maintain the market quality of 'Tarsus Beyaz & imath;' grapes.