engleski

Recovery of pumpkin by-products by hybrid vacuum drying and ultrasound pre-treatment

According to the new guidelines for waste management, procedures to prevent the generation of waste and techniques to recover it take precedence over recycling and disposal. Plant food waste (organic residues) and by-products from fruits and vegetables represent a nutritionally valuable source rich in numerous specialized metabolites important for human health. Therefore, the recovery of such by-products into valuable resources is crucial for the production of new food products, especially in order to reduce food waste. The pumpkin by-product is also a valuable source of numerous metabolites, especially vitamins, dietary fibers, polyphenolic compounds and carotenoids, and therefore represents a valuable material for further utilization. One of the ways to produce new products is the drying process, which very often has a negative impact on the nutrient composition of the plant material due to the high temperature and is also energy consuming. For this very reason, innovative pre-treatment methods such as ultrasound and hybrid drying techniques (vacuum-conduction) are being developed. Vacuum drying uses low pressure to evaporate water at lower temperatures, preserving heat-sensitive bioactive compounds such as vitamins, carotenoids, and other phytochemicals, while ultrasound pre-treatment also offers a number of benefits, most notably significantly shortening the drying process and preserving nutrients. The aim of this study was to determine the influence of temperature (60 and 70 °C) and ultrasound pre-treatment (37 kHz, 380W, Elmasonic P 300H, ultrasonic bath 100%) during hybrid vacuum-conduction drying (100 mbar) of pumpkin organic residue on the content of specialized metabolites. Drying processes were performed in a vacuum drying oven VO 200 (Memmert, Germany) at a pressure of 100 mbar. The pumpkin slices were dried to a final water content of 14%. The highest vitamin C content (439.14 mg/100 g DW) was determined in pumpkin samples pre-treated with ultrasound for 5 min and dried at 70 °C ; total phenolic content (1655 mg GAE/100 g DW) was also determined by vacuum drying at a temperature of 70 °C without ultrasound pre-treatment. The β-carotene content was best preserved by vacuum drying at 60 °C with ultrasound pre-treatment for 10 min. In general, all dried pumpkin samples are characterized by high antioxidant capacity, proving that hybrid vacuum drying combined with ultrasound pre-treatment has a positive effect on nutritional potential. In conclusion, ultrasonic pre-treatment had a significant effect on the preservation of bioactive compounds in the dried pumpkin samples, while drying by vacuum (100 mbar) at both combined temperatures (60 and 70°C) showed no negative effects on the nutritional composition of the pumpkin samples. Therefore, it can be concluded that this method of drying and ultrasonic pre-treatment is an efficient way to preserve the nutritional composition of the raw material, thus giving the organic residues the possibility of additional recovery and further use and utilization.

Bioactive compounds ; Vacuum ; Ultrasonic bath ; Antioxidant capacity ; Organic residue

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