Microwave vacuum drying and multi-flash drying of pumpkin slices

The effects of microwave power (MP, 100–600 W) on the drying kinetics, as well as the physical and antioxidant properties of papaya seeds dried under microwave vacuum drying (MVD) were investigated. The results found that moisture diffusivity increased in the order of 10−8 with an increase in MP. Shrinkage increased from 1.2 to 4.9% and bulk density decreased from 3,441 to 1,091 kg/m3, respectively, while the moisture content decreased. The antioxidant contents of all of the MVD samples were higher than those of the samples dried under ambient air ventilation. An increase in MP decreased the total phenolic content from 14.69 to 10.66 mg gallic acid equivalent per gram dry weight (DW), increased both the β‐carotene and the total flavonoid content in the ranges of 0.2–0.35 mg β‐carotene equivalent per gram DW and 20.71 to 23.51 mg catechin equivalent per gram DW, respectively. Higher values of antioxidant activity were obtained at higher MP. The results have shown that the use of novel MVD technique in appropriate conditions can improve the overall drying efficiency and enhance the total yield of antioxidant content. Practical Applications Papaya seeds have great potential for use as a source of antioxidants. However, the best novel techniques for retaining high values of antioxidant compounds, and therefore recouping value from the wasted seeds, has not been widely reported on. This study has found that combined microwave vacuum drying (MVD) is a very beneficial drying method for the preservation of antioxidant content. A better antioxidant yield from dried papaya seeds was obtained using MVD at a higher MP of 600 W. Trolox equivalent antioxidant capacity of seeds dried using MVD was 27.62% higher than the samples dried using ambient air ventilation.

Section: Resultssupporting

confidence: 93%

Section: Methodsmentioning

confidence: 99%

Determination of drying kinetics, some physical, and antioxidant properties of papaya seeds undergoing microwave vacuum drying

Bualuang

Onwude

Uso

et al. 2019

“…Microwave power played significant (p < 0.01) role in producing more porous product leading to higher diffusion of water through it. Similar results were obtained for tomato (Abano, Ma, & Qu, 2012), pomegranate arils (Dak & Pareek, 2014), green bell pepper (Kumar & Shrivastava, 2017a), pumpkin slices (Monteiro et al, 2018) in case of vacuum assisted microwave drying.…”

Section: Diffusion Coefficientssupporting

confidence: 83%

“…Thus, it becomes necessary to study the rehydration behavior to get the quality rehydrated product. Monteiro, Link, Tribuzi, Carciofi, and Laurindo () studied the effect of different drying methods namely air drying, freeze drying, conductive multiflash drying, microwave multiflash drying and vacuum assisted microwave drying on rehydration kinetics and rehydration indices of pumpkin slices. Rehydration was done at 25°C and it was concluded that although freeze dried product showed highest rehydration ratio but vacuum assisted microwave drying emerged as a suitable process for production of dehydrated pumpkin slices in very short drying time.…”

Section: Introductionmentioning

confidence: 99%

Shrinkage and rehydration characteristics of vacuum assisted microwave dried green bell pepper

Kumar

Devi

Panda

et al. 2019

Green bell pepper was dried under vacuum assisted microwave (VAM) drying conditions. The effect of microwave power (100, 200, 300 W) and vacuum pressure (200, 400, 600 mmHg) were observed on shrinkage and rehydration characteristics of the sample. Shrinkage was modeled as a linear function of volume change of material and its moisture content. A model was proposed where apparent density could be evaluated as a function of product's moisture content. The sample volume in case of VAM drying shrunk by 59 to 78%, while in case of hot air drying, the shrinkage occurred up to 90%. At a given power level of 100 W, equilibrium rehydration values (Req) increased from 5.04 to 5.75 for samples dried at increasing vacuum pressure from 200 to 600 mmHg. Rehydration rate constant decreased correspondingly for samples dried at higher microwave power levels. Higher level of microwave power and vacuum pressure played significant (p < 0.01) role in producing more porous (lesser shrunken) product leading to higher diffusion (and thus better rehydrated product) of water through it. Diffusion coefficient in rehydration was calculated using Fick's second law. The values of “k” and “R2” varied from 1 × 10−3 to 6.4 × 10−3 and 0.986 to 0.999, respectively. Practical applications Shrinkage and rehydration characteristics of dried vegetables are of utmost importance when it comes to culinary preparations, premixes, convenient foods and retention of sensory qualities. The model proposed in the present study will be helpful in evaluating shrinkage as a function of apparent density and moisture content of dried green bell pepper. Several changes such as shape, size, structure, color, bulk density, porosity, and rehydration capacity are induced due to structural alteration in green bell pepper followed by drying. This information could help in safe commercial packaging of dried products. Further, dried green bell pepper must be rehydrated to be used in preparation of foods such as soups, pizzas, stews, casseroles, and many other recipes. Outcome of the current study can also be referred and implemented while accessing the rehydration characteristics of dried and shrunken vegetables.

“…However, the high initial moisture content of the gel can reduce the shelf life and consequentially result in the deterioration of the product (Maan et al, ; Ravanfar, Niakousari, & Maftoonazad, ). In this regard, when drying A. vera gel, its water activity and moisture content can be reduced, retarding the microbial growth and enhancing its storability (Monteiro, Link, Tribuzi, Carciofia, & Laurindoa, ).…”

Section: Introductionmentioning

confidence: 99%

Kinetics and mathematical modeling of thin layer drying of osmo‐treated Aloe vera (Aloe barbadensis) gel slices

Moradi

Niakousari

Khaneghah

2019

In the present work, the drying kinetics of osmo‐pretreated Aloe vera gel slices (AVGS) was investigated. AVGS with an initial moisture content of 98.29% (wet basis) were subjected to 5 hr of osmosis process (10% NaCl solution, at 40°C, NaCl solution to A. vera ratio = 5:1), prior to atmospheric thin layer drying at air temperatures of 55, 70, and 85°C and air volumetric air flow rates of 0.015, 0.036, and 0.054 m3/s for the duration of 160 min. Results showed the mean values of the moisture ratio in air temperatures of 55, 70, and 85°C were categorized into three levels (p < .01) of 0.551, 0.429, and 0.336, respectively, while the corresponding values for the osmo‐convective method were 0.561, 0.418, and 0.321, respectively. Similarly, the mean values of the moisture ratio in air flow rates of 0.015, 0.036, and 0.054 m3/s for the convective and osmo‐convective method assigned to different levels (p < .01) of 0.511, 0.417, 0.385 and 0.510, 0.416, 0.372, respectively. Superposition technique was utilized to propose a new model for each drying method. The predicted moisture ratios evaluated by the superposition technique were in a good agreement with experimental values of moisture ratio. Practical Applications In the current investigation, a superposition technique was utilized to propose a new model for two drying methods (osmo‐convective and convective). Subsequently, an equation describing the drying process for each method was derived. This technique while being a simple model, delivers high accuracy data for all influencing parameters in the drying process.