Effect of freeze drying, oven drying and their combination for energy conservation and quality of carrot slices
Zobabalo Mina is a Masters candidate at the Postharvest and Agroprocessing Research Centre at the University of Johannesburg, South Africa. Her research is focused on the development of a shelf-stable carrot product for multiple applications in the South African food and beverage industries. An efficient and effective drying method is crucial for preserving fresh carrots. Simultaneously, the dried product needs to maintain its color, shape and nutritional quality for better consumer acceptability. The objective of this study was to investigate the effect of oven drying (OD) at 50°C, freeze drying (FD) at -60°C and 0.03 mbar, and a combination of oven and freeze drying (OD+FD) on the drying behavior, color, phytochemical content, antioxidant activity, energy requirements, and cost implications for dried carrots. The drying conditions included 36 h of FD, 1 h of OD + 21 h of FD, 2 h of OD + 18 h of FD, 3 h of OD + 15 h of FD, and 9 h of OD. Although the OD treatment had the shortest (9 h) drying time, the finished product was of poor quality. Results showed that a combination of OD and FD reduced the time by 39-50%. The β-carotene content, lycopene content and antioxidant capacity were highest for freeze drying > combined drying > oven drying. However, OD+FD provided a significant advantage in total phenolic content retention, decreasing the total color difference (8.05-20.76) and the energy cost by 40-56% compared to only FD. In summary, combined drying of 2 h OD + 18 h FD was the least time consuming and most energy-efficient drying method to produce nutrient-rich dried carrot slices.
Zobabalo Mina won the ISHS Young Minds Award for the best oral presentation at the III International Symposium on Beverage Crops in Spain in April 2023.
Zobabalo Mina, University of Johannesburg, Auckland Park, 2092 Gauteng Johannesburg, South Africa, e-mail: email@example.com
The article is available in Chronica Horticulturae