Drying kinetics and optimization for thin-layer drying processes of raspberries (Rubus coreanus Miq.) using statistical models and response surface methodology

Raspberries are a good resource of polyphenols and have a powerful antioxidant activity, but shelf life for raspberries is short which brings a lot of economic losses. In this study, we try to use cool-air ($20{\sim}40^{\circ}C$) or hot-air ($60{\sim}100^{\circ}C$) to produce semi-dried raspberries with extended shelf life, and to determine the best method for improving fruit quality by minimizing nutrient losses during drying processes. The effects of process variables (drying temperature and processing time) on the quality of final dried raspberries were investigated. Response surface methodology was employed to establish statistical models for simulating the drying processes, and the moisture residue content and the loss ratios of total phenolic content (TPC), vitamin C (VC), and ellagic acid (EA) that result from the drying processes of raspberries using either hot or cool-air were predicted. Superimposed contour plots have been successfully used in the determination of the optimum zone within the experimental region. Optimal conditions determined for achieving minimal losses of TPC, VC, and EA, and a final moisture residue of 45% using the hot-air drying process were a drying temperature of $65.75^{\circ}C$ and a processing time of 4.3 hr. While for the cool-air process, the optimal conditions predicted were $21.3^{\circ}C$ and 28.2 hr. Successful application of response surface methodology provided scientific reference for optimal conditions of semi-drying raspberries, minimizing nutrient losses and improving product quality.

통계적 모델과 반응표면분석을 이용한 복분자의 건조조건 최적화 및 건조거동

ANOVA 분석을 통해 건조온도와 건조시간이 열풍건조와 냉풍건조의 중요변수임을 알 수 있었으며 복분자의 반건조를 위해서는 열풍건조의 경우 $65.8^{\circ}C$, 4.3시간이 적당하였고 냉풍건조의 경우 비슷한 정도의 건조수분함량까지 28.2시간이 걸렸다. 그러나 건조온도가 높아지면 vitamin C와 ellagic acid의 함량이 줄어드는 등 품질적 열화가 심하게 나타났다. 또한 생리활성물질들은 냉풍건조에서 전반적으로 더 잘 보존 되었으며 총폴리페놀의 함량에서는 더욱 그러하였다. 따라서 냉풍건조방법은 고품질의 반건조 복분자 제조에 적합한 건조방법이며 최적 건조조건은 $21.3^{\circ}C$, 28.2시간으로 나타났다.