Optimization of coconut osmotic drying preceded by microwave treatment by Response Surface Methodology

Osmotic dehydration is an intermediate stage in drying processes in which water is extracted using a hypertonic solution, but it is a slow process, especially in hard foods such as coconut. Microwaves use an electromagnetic field which can raise the temperature in the depth of samples as a result of friction, which facilitates mass transfer due to molecular expansion and increased porosity. The aim of this study was to investigate the effect of a microwave pre-treatment on the quality of the osmotic drying of coconut and optimize the whole process by response surface methodology (RSM). The independent variables were the microwave power (X1), the sugar solution concentration (X2) and the duration of the process (X3.). The responses (dependent variables) were the moisture content difference (MD), weight reduction (WR), water loss (WL) and solids gain (SG). The results showed that the linear terms of X2and X3 had significant effects on all the dependent variables but the linear term of X1 only significantly affected WL, SG and WR (p< 0.05). The interaction of X1X2 significantly affected WL and WR and the interaction of X2X3 significantly affected all the dependent variables, but the interaction of X1X3 only significantly affected MD (p < 0.05). On the other hand, X22 significantly affected SG and WR (p < 0.05). The two-factor model (2FI) was able to express the changes in MD and WL, but only the quadratic model adequately fitted SG and WR, the determination coefficients being 0.98, 0.99, 0.99 and 0.99 respectively. Finally, the optimized condition was obtained with a power of 900 watts, concentration of 47.80% and duration of 5 hours.

The effects of solution type temperature and time on antioxidant capacity of osmotically dried celery leaves

Osmotic drying (OD) of celery leaves was studied in two osmotic solutions (ternary aqueous solution and sugar beet molasses), at three temperatures (20, 35 and 50?C), and diverse immersion periods (1, 3 and 5 h). The aim was to examine the influence of the used hypertonic agent, temperature and immersion time on antioxidant capacity (AOC) and colour characteristics of the samples. AOC of celery leaves was assessed by the spectrophotometric assays (ABTS, FRAP and DPPH), as well as two direct current polarographic assays, HPMC assay based on the decrease of anodic current of Hydroxo Perhydroxo Mercury (II) complex and MRAP assay based on the decrease of a cathodic current of Hg (II) reduction. Total phenolic content was determined by Folin-Ciocalteu assay. The Relative Antioxidant Capacity Index (RACI), calculated by assigning equal weight to all applied assays was used to achieve a more comprehensive comparison between analyzed samples, as well as applied assays. The obtained results indicated decreases in the AOC of celery leaves during the OT in ternary solution, while the AOC was increased in sugar beet molasses solution. According to RACI evaluation the most convenient process parameters were temperature of 35oC and immersion time of 5h.

Effect of osmotic drying on physicochemical properties of pansies (viola × wittrockiana)

The objective of this work was to study the effect of osmotic drying, using different hypertonic solutions (sucrose and sodium chloride), on physicochemical characteristics of pansies (Viola × wittrockiana). The same treatments were applied to lettuce to compare the behavior of flowers with other vegetables. Pansies' superhydrophobic surface structure, called papillae, increased the resistance to exchanges with hypertonic solutions. No weight loss was observed after most treatments (sucrose: between 2.2 and 6.8 %; NaCl: between -23.0 % and 1.5 %), aw maintained high values (>0.94) and monomeric anthocyanins were preserved (fresh 0.10 and 0.19 mg Cy-3glu/g fresh matter for 20%/1 h in NaCl and 60%/1 h in sucrose). When applying more drastic conditions, as sodium chloride for more than 1 hour, undesirable textural and color changes were observed. For lettuce, all treatments caused osmotic dehydration, weight loss (ranged between -9.3 to -30.3 % for 80%/1 h in sucrose and 15%/1 h in NaCl) and a reduction on aw (<0.97) and carotenoids, with sodium chloride causing more damage in visual appearance than sucrose. Therefore, immersion in osmotic solutions can be applied to lettuce but the desired effect was not achieved for pansies due to the morphological structure of the flowers' epidermis.