Drying kinetics and physico-chemical characteristics of Osmo- dehydrated Mango, Guava and Aonla under different drying conditions

Drying kinetics and mathematical modeling of coconut meat slices: Insight into pretreatment and drying synergic effect

Coconut consumption provides nutritional and health benefits to humans. Yet, poor postharvest and preservation methods result in the loss of coconut fruit bunches yearly. Investigations into achieving drying techniques that result in optimum drying rates coupled with consumer's desired end products that are both commercially and nutritionally viable remain paramount in the food industry. Consequently, osmotic dehydration is commendable for its low-cost pretreatment merit. Therefore, the study examined the drying-kinetics, energy consumption, effective moisture diffusivity (D eff ), vitamin C retention, color, and rehydration behavior of coconut cultivars (Sri Lanka Green Dwarf × Vanuatu Tall (SGD × VTT), Catigan (CAT), and Tacunan Green Dwarf (TGD)) meat slices. Samples were osmotically pretreated with sucrose solution (30 %/30 min) and subjected to oven drying (80, 90, 100, and 110 °C (air velocity of 2 m/s) and lyophilization (-45 ± 2 °C) methods. A mathematical model was employed to predict the effect of osmotic pretreatment on drying dynamics and the assessment of utilized energy, vitamin C content, color, and rehydration of coconut meat slices at different drying conditions. The oven-dried sample's color changed (p < 0.05) compared to lyophilized samples. Drying-kinetics models were validated using determination coefficient (R2) and root mean square error (RMSE). The Asymptotic model satisfactorily suited the samples' drying data goodness fitting based on R2 ≥ 0.90 - 0.99 and low RMSE ≤ 0.01 - 0.12 compared to other models for both drying methods. D eff ranged between 1.10 × 10-07 m2s-1 and 7.90 × 10-08 m2s-1 for all the drying methods. CAT sample retained high vitamin C content compared to SGD × VTT and TGD samples. Rehydration ratio values were significant at lower temperatures among oven-dried experimental samples whereas TGD samples exhibited a significant rehydration values compared to SGD × VTT and CAT lyophilized samples. Among the drying methods, oven drying exhibited low energy consumption with shorter drying time and optimum D eff per adopted temperature ranges compared to lyophilization. The study revealed that temperature, time, the sucrose solution, and the thickness of the coconut slices strongly influenced the drying kinetics of the osmotically pre-treated coconut meat slice's drying features.

Kinetics of dehydration and appreciation of the physicochemical properties of osmo-dehydrated plum

The experiment was conducted to evaluate the dehydration kinetics and quantify its effect on the various physicochemical properties of the osmo-dehydrated plum during storage at an ambient condition. The six treatments with a combination of three different sucrose-sodium chloride concentrations and two peeling conditions were selected in the experiment. Among the treatments, peeled plum dipped into 5% NaCl solution exhibited a faster drying rate. Concerning the rehydration properties of the osmo-dehydrated plum, the whole plum immersed into 500B sucrose solution showed the highest reconstitution behavior and the lowest moisture content (wb). The highest values of water activity of 0.514 and the lowest values of texture 1.79 N-mm2 were investigated in 500B sucrose treated whole plum. The peeled plum obtained the highest lightness (L), redness (a*), and yellowness (b*) compared to the unpeeled plum. Osmo-dehydrated plum with high sugar solution contained more sugar and less total phenolic content nevertheless using only 5% NaCl resulted in less sugar and more total phenolic content after the treatment. The osmo-dehydrated whole plums prepared in 500B sucrose scored the highest overall acceptability (8.0, e.g., like very much) followed by the 500B sucrose with peeled plum envisaged the sensory evaluation analysis. In conclusion, the osmo-dehydrated plum treated in 500B sucrose and unpeeled condition performed better with a view to the overall plum quality, color, and acceptability judged by the expert panelists even after 12 months of storage at room temperature.

Influence of Pre-Drying Treatments on Physico-Chemical and Phytochemical Potential of Dried mahua Flowers

Mahua (Madhuca longifolia) flowers are boon for the local tribes of India and have been successfully utilized traditionally for the value addition, and are very prone for microbial spoilage. Local folks utilized malpractices of drying which deteriorates the quality attributes of the mahua flowers and ultimately fails to fetch a good price in the market. Present investigation was led to consider the impact of different pre-treatments i.e., blanching time; and dip of potassium meta-bisulfite (KMS) and citric acid (CA) on the physico-chemical and phytochemical potential of dried mahua flowers using response surface methodology (RSM). Maximum physico-chemical and phytochemicals attributes were observed under optimum conditions i.e., a blanching of 4.1 min followed by dipping in solution having 1285 ppm KMS and 0.77% citric acid. Qualitative analysis through Fourier transform infrared spectroscopy (FTIR) supported the findings. Sugar and phytochemical profiling by high performance liquid chromatography (HPLC) proved the significant effect of each variable. No specific cluster formation was observed during cluster analysis of whole data indicating the significant and equal effect of all variable on the quality of dried mahua flowers. The optimized conditions will definitely help the local processors as well as the industrialist to maintain the quality attributes of the dried mahua.

Optimization of osmotic dehydration of Terung Asam (Solanum lasiocarpum Dunal)

This study was designed to determine the effect of osmotic dehydration (OD) process temperature (35-55 °C), sucrose concentration (40-60% w/w) and immersion time (90-210 min) on the water loss (WL), solid gain (SG), DPPH radical scavenging activity, ferric reducing antioxidant power (FRAP) and sensory quality of the dehydrated Terung Asam slices. Response Surface Methodology with Central Composite Design was applied to investigate the influence of these variables on the aforementioned responses. The increase in the levels of these processing parameters increased the WL and SG. The antioxidant activities also increased with sugar concentration, but reduced with immersion time and temperature elevation. About 36-80% of IC₅₀ and 47-72% of FRAP were depleted after osmotic process. The loss of antioxidants was predominantly due to leaching during osmotic treatment rather than hot air drying. Despite the losses of these compounds, osmotic pretreatment was able to improve the sensory quality of the product. The optimum OD process condition was predicted as process temperature 38.1 °C, sucrose concentration 55.6% and osmotic duration 126.3 min.

Effect of osmotic dehydration pretreatment and glassy state storage on the quality attributes of frozen mangoes under long-term storage

Changes in the quality of frozen mango cuboids were investigated during long-term glassy state storage with and without osmotic dehydration pretreatment. The mango cuboids were dehydrated in mixed solutions (sucrose: glucose: fructose in a ratio of 3.6:1:3) of different concentrations (30, 40, and 50% (wt/wt)) prior to freezing and then stored at -55 °C (in the glassy state) for 6 months. The results revealed that compared with the untreated samples, osmotic pretreatment decreased total color difference (reduced by 15.6-62.3%), drip loss (reduced by 8.2-29.5%) and titration acidity (reduced by 1.3-9.4%), while increasing hardness (increased by 48.8-82.3%), vitamin C content (increased by 72.5-120.6%) and total soluble solids (increased by 21.8-53.7%) of frozen mangoes after 6 months. Dehydration with a sugar concentration of 40% was considered as the optimal pretreatment condition. In addition, a storage temperature of -55 °C provided better retention of quality than rubbery state storage at -18 °C. With prolonged storage time, the quality of frozen mangoes continued to change, even in the glassy state. However, the changes in quality of the osmotic-dehydrated samples were less than those of the untreated samples. The current work indicates that osmotic pretreatment and glassy state storage significantly improved the quality of frozen mangoes during long-term storage.

Instant vegetable from osmo-air drying of jimikand (A. campanulatus) in NaCl solution: nutritional, functional, micro-structural and other quality aspects

The aim of this work was to study the effect of osmotic dehydration on the quality of jimikand which can be used as an instant vegetable to get its nutritional and functional benefits. Osmotic dehydration was applied as pre-treatment to hot-air drying for increasing palatability, mass transfer improvement and minimizing nutritional losses. To see the effect of osmotic dehydration on various quality parameters, conditions of osmotic dehydration selected were osmotic solution concentrations (5, 10 and 15 % w/w) and temperatures (40, 50 and 60 °C) for constant process time (80 min) on the basis of mass transfer analysis. The observed values of hardness, oxalate content and water activity of osmo-dried samples varied from 66.04 ± 14.5 to 79.12 ± 14.8 N, 60.0 ± 0.40 to 69.1 ± 0.65 mg/100 g, 0.911 ± 0.001 to 0.826 ± 0.001, respectively, and found less as compared to fresh sample, i.e. 131.12 ± 9.5 N, 110.5 ± 0.78 mg/100 g and 0.990 ± 0.00 respectively. Rehydration ratio of fresh sample was 3.52 ± 0.03 and varied from 2.82 ± 0.06 to 3.57 ± 0.10 for osmo-dried samples being higher at lower concentrations and temperatures. The best conditions of osmotic dehydration found were 10 % NaCl, 50 °C temperature and 80 min duration on the basis of appreciable mass transfer, lowest oxalate content, water activity, better rehydration, textural and sensory quality. The selected osmo-dried sample was better due to low anti-nutritional content, less micro-structural damage and appreciably comparable to fresh hot-air dried in terms of total phenol, antioxidant activity, and other quality parameters.

Evolution of antioxidants in dietary fiber powder produced from white cabbage outer leaves: effects of blanching and drying methods

White cabbage outer leaves, which are usually discarded both during industrial processing and selling in a consumer market, have proven to be a good source of dietary fiber (DF) as well as antioxidants and can be effectively transformed into functional DF powder. In the past, however, only hot air drying was used to prepare DF powder from cabbage outer leaves although it is well recognized that this drying technique could lead to much quality degradation of a dried product. This work was therefore aimed at studying the evolution of selected important antioxidants, e.g., phenolic compounds and vitamin C, in white cabbage outer leaves during vacuum drying at 60, 70 and 80 °C. The effect of pretreatment viz. steam blanching was also evaluated. The results showed that there were losses of antioxidants during steam blanching; vacuum dried blanched leaves nevertheless contained higher antioxidant contents and activity than dried unblanched leaves. Losses of antioxidants during vacuum drying were also noted to be less than those during hot air drying. Overall, the results showed that there were no differences in the antioxidants retention among all the tested conditions performed in this study. Therefore, the most suitable condition for the production of antioxidant DF powder from cabbage outer leaves is vacuum drying at 80 °C as this condition requires the minimum specific energy consumption.