Nutritional quality of heat-sensitive food materials in intermittent microwave convective drying

Microwave assisted fluidized bed drying of bitter gourd: Modelling and optimization of process conditions based on bioactive components

Bitter gourds were dried under varied drying conditions in a microwave assisted fluidized bed dryer, and the process was optimized using response surface methodology. Microwave power, temperature and air velocity were used as process variables for drying and the process parameters were varied between 360 and 720 W, 40-60 °C and 10-14 m/s, respectively. The responses determined for deciding the optimal criteria were vitamin C, total phenolics, IC₅₀, total chlorophyll content, vitamin A content, rehydration ratio, hardness and total color change of the dried bitter gourd. Statistical analyses were done by using response surface methodology, which showed that independent variables affected the responses to a varied extent. The optimum drying conditions of 550.89 W microwave power, 55.87 °C temperature, and 13.52 m/s air velocity were established for microwave assisted fluidized bed drying to obtain highest desirability for the dried bitter gourd. At optimum conditions, validation experiment was done to ensure the suitability of models. Temperature and drying time plays an important role in the deterioration of bioactive components. Faster and shorter heating led to the greater retention of bioactive components. Taking the aforesaid results into consideration, our study recommended MAFBD as a promising technique with minimum changes in quality attributes of bitter gourd.

Effect of intermittent microwave convective drying on physicochemical properties of dragon fruit

The study was carried out to investigate the effect of Intermittent microwave convective drying (IMCD) on the overall quality of dried dragon fruit in terms of total phenolic content, color change, and rehydration ratio. Three levels of microwave power (200-600 W) and a temperature of 60 °C for hot air were applied alternately throughout the process with three levels of pulse ratio such as 1:10, 1:20, and 1:40, respectively. The total phenolic content of the dragon fruit slice obtained by IMCD was ranged between 5.750 and 6.575 mg GAE/g dry weight. Within the experimental range of process variables under IMCD conditions, the drying efficiency, color change, and rehydration ratio of the dried dragon fruit slices were 15.287-51.930%, 18.643-24.847, and 1.908-3.239, respectively. The Weibull model scale (α) parameter was found to vary between 27.512 - 498.174 , while the shape (β) parameter was found to vary between 0.769 - 0.851 . The Weibull model parameters were shown to decrease with increasing microwave power at constant pulse ratio. The IMCD method produced a dried dragon fruit slices with reduced color changes and higher total phenolic content and rehydration ratio values. This investigation would contribute to the development of effective drying techniques for increased food quality and product consistency in the drying of diverse fruits and vegetables.

Possibility of Pulsed Electric Field and Essential Oil Pre-treatment, Microwave-air Dehydration to the Quality of the Dehydrated Sesban (Sesbania sesban) Flower

Non-heat ahead-treatment in advance of the main dehydration is essential to preserve the quality and ensure food safety. Pulsed electric field (PEF) utilizes a high-voltage electric field in a very short duration to inhibit microbes and enzymes while maintaining the most sensory and nutritional characteristics. For thermal sensitive components, the dehydration process should be performed at low temperatures. Freeze dehydration, vacuum dehydration required high cost for equipment, energy consumption, low quantity in long dehydration time. Microwave-air dehydration is considered as a promising alternative technical approach. Sesban (Sesbania sesban) flower contains numerous phytochemical components promoting health-benefit. However, it’s highly perishable after harvesting. Consumers enjoy the dried sesban flower as a healthy drink. This study examined the possibility of PEF ahead-treatment in microbial inhibition and enzymatic inactivation; essential oil and Microwave-air dehydration on retention of total phenolic content (TPC), vitamin C, 2,2 diphenyl-1-picrylhydrazyl of free radical scavenging (DPPH), ferric reducing antioxidant power (FRAP) of the dehydrated sesban flower. Research also monitored the microbial stability of the dehydrated sesban flower during 12 months of preservation. Results showed that PEF at pulse strength 1000 kV/cm, pulse duration 90 µs, pulse number 45 was remarkably inactivated polyphenol oxidase and peroxidase in raw material. Rosemary essential oil soaked for sesban flower before dehydration positively preserved the ascorbic acid, phenolic content and antioxidant capacity. These PEF and essential oil ahead-treatments strongly facilitated for the main Microwave-air dehydration. Among different air temperatures from 20°C to 40°C in microwave-air dehydration, the highest Vitamin C, TPC, DPPH and FRAP of the dried flower were recorded at air temperature from 20°C to 30°C with no significant difference. Meanwhile, airspeed 1.2 m/s showed the highest Vitamin C, TPC, DPPH and FRAP of the dried flower with no significant difference with airspeed 1.4 m/s and 1.6 m/s. There was no significant difference in Vitamin C, TPC, DPPH and FRAP of the dried flower by microwave power from 1.15 to 1.45W/g. Therefore, a combination of microwave and air dehydration at air temperature 25°C, airspeed 1.2 m/s, the microwave energy density of 1.45 W/g was recommended to better preserve vitamin C, TPC, DPPH, FRAP. Microbial stability of the dehydrated flower was also observed during 12 months of storage by 3 month-interval sampling. Coliform, yeast and mold criteria in dried product were stable within acceptable limits.

Evaluating the Performances of Interval Starting Accessibility Drying (ISAD) through Protein and Total Polyphenol Contents of Blue Crabmeat (Portunus segnis)

Blue crab (Portunus segnis) proliferation on Tunisian coasts started in 2014/2015. It has heavily impacted the balance of other species, local biodiversity, and fishing activity. Limiting these drawbacks may be achieved through ways promoting crabmeat. For this purpose, two different drying modes were tested: Conventional convective drying (CCD) and interval starting accessibility drying (ISAD) under 45 °C and relative humidity of 40%. Several air velocities were assayed under CCD: 1.5, 2.5, 3.5, and 5 m.s−1. Two different ISAD tests were run with different time-related conditions: drying period of 15 s and tempering period of 15 or 60 s. Drying modes and operating conditions performances were compared through proteins and total polyphenol contents (TPCs) evolution during the treatment. Important polyphenol and protein losses were observed between raw and processed crabmeat. Airflow velocities have a significant effect on crabmeat quality preservation. ISAD method under 15 s/60 s allowed the best preservation of these quality parameters. TPC and proteins losses and kinetics during drying under CCD or ISAD were modelled and correlations were established between the quality parameters, the residual water content at all drying times, and the evaporation rate.

The impact of raw and differently dried pineapple (Ananas comosus) fortification on the vitamins, organic acid and carotene profile of dairy rasgulla (sweetened cheese ball)

Pineapple, a tropical fruit that is well known for its excellent nutritional characteristics. Rasgulla (sweetened cheese ball) is a dairy based popular sweet found all over India. To enrich the nutritional profile, vitamin content, organic acid and carotene content profile of normal dairy rasgulla (sweetened casein ball) and to make it functionally more active for human health, fortification of rasgulla has been done by using normal pineapple pulp along with hot air, freeze, microwave and microwave convective dried pineapple pulp for overall comparative analysis and they are coded as PP, PH, PF, PMW and PMWC respectively. By using RP-HPLC method quantification of vitamin A, vitamin B group (B₁, B₂, B₃, B₅, B₆, B₇ and B₁₂), tocopherols (α, β, γ and δ form), vitamin C, carotene (α, β, γ and δ form) profile and organic acid profile (oxalic acid, tartaric acid, malic acid, lactic acid, acetic acid, citric acid, propionic acid, succinic acid [SA], and fumaric acid) of all the rasgulla samples are estimated. A significant increase is found for differently fortified rasgulla samples in terms of vitamins content, organic acid and carotene content. B₁, B₃, B₇ and B₁₂ are found maximum in PF whereas B₅, B₆ and B₂ are found maximum for PMWC, PP and NR. The maximum amount of vitamin C and tocopherol are found in PP and PF. PMWC is reported to have maximum carotene content compared to all other samples.

Comparison of Traditional and Novel Drying Techniques and Its Effect on Quality of Fruits, Vegetables and Aromatic Herbs

Drying is known as the best method to preserve fruits, vegetables, and herbs, decreasing not only the raw material volume but also its weight. This results in cheaper transportation and increments the product shelf life, limiting the food waste. Drying involves the application of energy in order to vaporize and mobilize the moisture content within the porous products. During this process, the heat and mass transfer occurs simultaneously. The quality of dehydrated fruits, vegetables, and aromatic herbs is a key problem closely related to the development and optimization of novel drying techniques. This review reports the weaknesses of common drying methods applied for fruits, vegetables, and aromatic herbs and the possible options to improve the quality of dried products using different drying techniques or their combination. The quality parameters under study include color, bulk density, porosity, shrinkage, phytochemicals, antioxidant capacity, sugars, proteins, volatile compounds, and sensory attributes. In general, drying leads to reduction in all studied parameters. However, the behavior of each plant material is different. On the whole, the optimal drying technique is different for each of the materials studied and specific conditions must be recommended after a proper evaluation of the drying protocols. However, a novel or combined technique must assure a high quality of dried products. Furthermore, the term quality must englobe the energy efficiency and the environmental impact leading to production of sustainable dried products.

A mathematical model for predicting the transport process and quality changes during intermittent microwave convective drying

Intermittent microwave convective drying (IMCD) is an advanced drying method where volumetric heating of samples drives the drying process. Understanding of the physical effects of IMCD on simultaneous heating and mass transfer as well as quality changes during IMCD is essential to predict accurately drying processes and quality attributes of end products. However, there is a lack of studies in this particular interest area. The aim of this research was to develop an IMCD model coupled with quality degradation kinetics by integrating a simultaneous heat and mass transfer model with Maxwell's equations for microwave heating and the chemical reaction kinetics model. The simulated results were compared with experimental results and a good agreement was observed. As it was found that power ratio (PR) had a vital role in altering quality attributes, different PR and drying conditions were considered to investigate the effects of IMCD on the drying kinetics. The simulated results showed that the model was capable of predicting accurately moisture and temperature distributions along with heath beneficial compounds, such as total phenolic content (TPC) and ascorbic acid (AA) as well as colour changes during IMCD processing. About 70% of AA was degraded during IMCD drying using PR of 1/3. However, losses were reduced when PR was reduced to 1/4 or 1/5. Likewise, TPC degraded significantly during the early stages (first 60 min) of IMCD processing but stabilised at later stages.

Physical and viscoelastic properties of carrots during drying

It is essential to understand the physical and mechanical properties of a product since these properties affect the structure, texture, and ultimately consumer acceptance. The effect of drying conditions on dynamic viscoelastic properties, stress relaxation function and creep compliance, and physical properties, such as moisture distribution, color parameters, and shrinkage, was studied. An increase in drying temperature and duration resulted in a decrease in moisture content and volume, which were highly correlated (R = .988). Water evaporation followed the falling rate period, demonstrating that the water transport was limited by internal resistances. The decomposition of carotenoids led to a decrease in magnitude of color parameters (L, a, and b), between 30.1% and 51.6% with 4 hr drying. It was observed that the material shrinkage and moisture content highly affected the mechanical properties; increased stress relaxation modulus and decreased creep compliance values of the sample. The creep behavior, expressed with Burger's model (R²  ≥ .986), was highly dependent on moisture content. The linear viscoelastic region of carrots was found to be at strains lower than 3%. The three-element Maxwell model well fitted to describe the viscoelastic behavior of carrots (R²  ≥ .999, RMSE ≤ 2.08 × 10^-4 ). The storage moduli (G') were higher than loss moduli (G″), indicating that samples presented solid-like behavior. The findings can be used to improve the textural attributes of carrots and carrot-based products.