Physicochemical stability of cashew apple pomace phenolic extracts obtained with green solvents

Cashew (Anacardium occidentale) is a native Brazilian crop that holds major socioeconomic importance for the Northeast region economy. The cashew apple is an important part of the cashew producer’s income, and it is utilized mostly in juice production, which generates Cashew Apple Pomace (CAP), a by-product rich in macro- and micronutrients, polyphenolic compounds, carotenoids, and pectin. Since phenolic compounds can bring health benefits and functional properties such as antioxidant, anti-inflammatory, and cardioprotective, one possibility for valorization of this by-product is through extract development. Green solvents, in particular Natural Deep Eutectic Solvents (NADES) are important to create ready-to-use alternatives since they are composed of natural compounds that already exist in a broad range of aliments. However, applying NADES-based extracts as food ingredients requires understanding their stability during storage. Therefore, this study aimed to evaluate the stability of phenolic-rich CAP extracts obtained using NADES and hydroethanolic (control) extraction, under different storage conditions. To assess stability, three extractions were performed in an ultrasonic bath using optimized parameters with two betaine-based NADES combinations: Betaine:Glycerol (BG) - 1:2 molar ratio and Betaine: Malic Acid (BM) - 1:1. This study also evaluated a 50% (m/m) hydroethanolic mixture. The extracts were then conditioned under two storage conditions (ambient temperature and refrigerated). For the evaluation of stability, the extracts were evaluated for 20 weeks through the determination of pH, water activity, colorimetry, viscosity, humidity, total phenolic content (TPC), and antioxidant activity using the DPPH assay. The results were evaluated using descriptive and statistical analysis (one-way ANOVA and Tukey post-hoc test). During storage, the extracts behaved differently depending on the extraction system and temperature. Viscosity decreased in BG-25 °C and BM-25 °C, whereas BG-4 °C and BM-4 °C showed an initial increase followed by a decrease. Viscosity also decreased in ethanolic extracts, with a more pronounced reduction at 4 °C. Regarding color, BG-25 °C showed the greatest change, with the hue angle decreasing from 85.19 to 29.69, whereas the other treatments displayed smaller variations. The TPC showed greater stability under refrigeration, while a reduction was observed in BG-25 °C. Overall, NADES exhibited greater antioxidant capacity in the DPPH assay, although BG activity decreased at 4 °C. Refrigerated extracts also showed greater relative pH stability. Water activity ranged from 0.782 to 0.992 and was only slightly affected by storage temperature. In general, the samples were stable, stability was improved under refrigeration, and NADES can undergo more pronounced transformations in color parameters. This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001. The authors acknowledge CAPES for funding this research through scholarships and extend the appreciation to the Central Support Laboratory (LAC/FEA).