Effect of hot-water and citric acid blanching on nutritional, phenolic composition and microbiological quality of hot-air and freeze-dried “Chuyskaya krasavitsa” plums

Dried plums are valued as functional foods because of their nutritional composition and health-promoting properties. However, plum drying is challenging due to the waxy fruit cuticle, which limits moisture diffusion and prolongs drying time. Although blanching is commonly used to improve drying efficiency, its effects on phenolic compounds, minerals, and microbiological quality remain insufficiently studied, particularly in regional plum cultivars. Therefore, this study evaluated the effects of hot-water and 1% citric acid blanching combined with different drying methods on the nutritional, antioxidant, and microbiological quality of dried plums of the regional cultivar “Chuyskaya krasavitsa”. Dried plums contained 16–21 g of sorbitol, 26–42 g of mono- and disaccharides, 2–2.8 g of protein, 2.2–3.9 g of ash, and 2.9–4.5 mg of vitamin C per 100 g (wet basis). The predominant amino acids were aspartic acid, glutamine, and proline, while neochlorogenic acid, hyperoside, and chlorogenic acid were the major phenolic compounds. Dried plums were also rich in potassium (1294 mg/100 g on average), whereas freeze-dried samples retained higher mineral concentrations. Pretreatment significantly affected microbiological parameters, including aerobic colony count ( p < 0.001) and yeast and mould count ( p < 0.01), as well as protein, sugar, and total phenolic contents ( p < 0.05). Citric acid blanching reduced the levels of several phenolic compounds compared with hot-water blanching and freeze-drying. These findings provide practical guidance for optimising dried plum processing while balancing nutrient retention, phenolic preservation, and microbial safety.