www.fmfi‐journal.org Focusing on Modern Food Industry (FMFI), Volume 5 2016 doi: 10.14355/fmfi.2016.05.003
Optimization of Microwave Drying of Celery Using Response Surface Method Zehra Yildiz*, Ayse Sarımeseli *Department of Energy Systems Engineering, Faculty of Technology, MEU, Mersin, Turkey *zyildiz@mersin.edu.tr Abstract In this article, a microwave system was used to dry the celery. Response surface methodology (RSM) was used to determine the influence of process variables and arrive at optimal processing conditions to reduce the moisture ratio of the celeries to a safe level based on a three‐level central composite design (CCRD) involving the variables A vegetable load (53.18‐86.82 g) (97.73‐ 602.27 W) X1, B microwave power X2 and C drying time (5.27‐18.73 min) X3, RSM for the moisture ratio and drying rate. In this study, a CCRD was created with 20 runs, 8 cube points, 4 center points per cube, 6 axial points, 2 center points per axial, and =1.68179. Data obtained from RSM on the moisture ratio and drying time of the celery were subjected to ANOVA and analyzed using a second‐order polynomial equations which resulted in the optimized process conditions. Keywords Microwave Drying, Celery, CCRD, RSM
Introduction It is a significant problem for the food sector that the rest of products after the consumption of fresh fruit and vegetables to be preserved for a long time. For the storage of fresh food not to be decomposed for a long time are various drying techniques. These include things such as hot air drying, vacuum drying, solar drying, microwave drying and freeze‐drying. They have some disadvantages like inability to handle large quantities to achieve consistent quality standards, contamination problems, and low energy efficiency, which is not a desirable situation for the food industry. Microwave drying is an alternative method because of its uniform energy and high thermal conductivity to the insides of the material, space utilization, energy savings, precise process control, and fast startup and shutdown conditions. It also reduces the drying time and prevents food from decomposing (Demirhan E. and Ozbek B., 2011, Decareau, 1985, 1992; Zhang et al., 2006, Askari G. R. et al., 2008, Cui Z. et al., 2008, Wu,G. et al., 2010) Response surface methodology combines mathematics with statistics for designing experiments, building models, evaluating the controlling factors and determining optimum processing conditions. In RSM, several factors are simultaneously varied. The multivariate approach reduces the number of experiments, improves statistical interpretation possibilities, and evaluates the relative significance of several affecting factors even in the presence of complex interactions. It is employed for multiple regression analysis using quantitative data obtained from properly designed experiments to solve multivariable equations simultaneously. There are several work which has been carried out on te optimization of vegetables by RSM method (Uddin et al., 2004; Corzo and Gomez, 2004; Eren and Ertekin 2007; Singh et al., 2007; Singh et al., 2008, Han,Q. et al., 2010, Alibas I. 2014 ). However, no information is found on the statistical modeling of celery drying by microwave system. Hence the present work aims to model the moisture ratio and drying rate as a function of the process variables and to find the optimum operating conditions that minimize the moisture ratio and drying rate using response surface methodology. Experimental Method Material and Drying Process Fresh organic celery samples were purchased from a local superstore, then thoroughly washed with water to remove adhering soil and other debris. They were stored at 4±0.5°C until the drying process. Microwave drying trials were performed in domestic digital microwave oven. The adjustment of microwave output power and
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