Drying and Dehydration of Food

The present study is carried out to standardize the pretreatment of onion slices and study drying characteristics during
convective drying. The effect of process parameters during osmotic dehydration such as osmosis, concentration and
temperature of syrup on mass reduction, water loss and salt gain increased with increase of syrup concentration and
temperature. The water loss and solid gain during osmosis at 5, 12.5 and 20 ˚Brix was varied in the range of 15.88 to 25.65 and
6.63 to 10.15 per cent at 35, 45 and 55˚ C temperatures respectively. The drying temperature and pretreatment as osmotic
dehydration had a significant effect on the rehydration ratio and colour. The drying times of un-osmoses and osmoses onion
slices by convective drying at 40 and 60 per cent drying temperature were 12, 10 and 8 and 6 hrs respectively. Quality of dried
product in respect to colour and rehydration was superior. The osmo-convective dehydrated samples were found more
acceptable than convective dried ones. The onion dried at 20˚C brix solution concentration, 55˚C osmosis temperature and
70°C drying temperature was more acceptable on the basis of colour and rehydration.

Abstract: This work investigated the technique of vacuum freeze drying of avocado pulp (Persea americana var. Pollock) to produce a dried cake which could be blended into a powder to be used in various food applications.  Frozen, mashed avocado pulp samples were dried in a Benhay SB-4 vacuum freeze dryer. For comparison, fresh pulp samples were also oven-dried in a Unitemp drying cabinet at 60°C.  Samples were dried until constant weight was achieved after which they were blended into powders and analysed.  Analyses included determination of moisture content, water activity, pH and total soluble solids content, colour assessment, proximate analyses, physical properties, rehydration behaviour and a preliminary storage assessment.  Drying data was used to generate rate and Moisture Ratio (MR) curves and thin layer models applied to the MR data.  The moisture content and water activity values of the fresh pulp averaged 3.16 g H2O/g dry matter (76.0% wet basis) and 0.889, respectively.  Samples were successfully dried in the freeze dryer to an average moisture content of 0.02 g H2O/g dry matter (2.1% wet basis) after 72h, and a final average water activity of 0.356.  Drying occurred in the falling rate period and the drying rate constant (k1) averaged 0.2496 1/h. The Verma model was found to best fit the Moisture Ratio (MR) data.  Compared with oven-dried samples, the freeze-dried samples dried to lower equilibrium moisture values, did not show any signs of browning and was higher in protein and fat content.  The freeze-dried ‘cake’ was easier to blend to a light, free-flowing powder which easily rehydrated to a form which closely resembled fresh avocado puree.  Freeze drying is therefore an attractive option to produce a high-quality Pollock avocado powder, without the use of heat or the application of chemical preservatives to preserve colour.
Keywords: Avocado, Freeze-drying, Oven-drying, Drying kinetics, Curve fitting

Vacuum drying can dehydrate materials further than dry heat methods, while protecting sensitive materials from thermal degradation. Many industries have shifted to vacuum drying as cost- or time-saving measures. Small-scale vacuum drying, however, has been limited by the high costs of specialty scientific tools. To make vacuum drying more accessible, this study provides design and performance information for a small-scale open source vacuum oven, which can be fabricated from off-the-shelf and 3-D printed components. The oven is tested for drying speed and effectiveness on both waste plastic polyethylene terephthalate (PET) and a consortium of bacteria developed for bioprocessing of terephthalate wastes to assist in distributed recycling of PET for both additive manufacturing as well as potential food. Both materials can be damaged when exposed to high temperatures, making vacuum drying a desirable solution. The results showed that the open source vacuum oven was effective at drying both plastic and biomaterials, drying at a higher rate than a hot-air dryer for small samples or for low volumes of water. The system can be constructed for less than 20% of commercial vacuum dryer costs for several laboratory-scale applications, including dehydration of bio-organisms, drying plastic for distributed recycling and additive manufacturing, and chemical processing.

The study investigated the air drying characteristics of aerial yam in a fabricated air dryer within a temperature range of 50 to 70°C. Prior to drying, the sample was divided into two portions; one part was boiled at 100°C for 20min and the other part left fresh. The drying data was fitted to twelve well-known thin layer drying models. Among the models used, the Midilli et al., Verma et al., Diffusion Approach, Wang and Singh, Parabolic and Simplified Fick’s Diffusion models were found to be the best models to predict the moisture ratio values during the drying process with high capability. The effective moisture diffusivity was found to vary between the range of 1.401 ×10-10 m2/s to 6.720 x 10-10 m2/s for the fresh yam slabs and 7.223 x 10-11 m2/s and 2.306 x 10-10 m2/s for the boiled yam slabs over the temperature range of 50 to 70°C. The values for activation energy were 28.42kJ/mol, 30.33kJ/mol for fresh yam samples of thicknesses of 0.5cm and 1cm respectively, whereas the values for boiled yam were 6.77kJ/mol and 15.37kJ/mol for slabs of 1cm and 0.5cm thicknesses respectively. Pre-treating the aerial yam by boiling will be beneficial in the optimisation of processing method for the D.bulbifera.

Pumpkin seeds are a major agricultural waste from the fresh-cut produce industry. The objective of this study was to investigate the drying behavior of untreated, whole pumpkin seeds in a fluidized bed dryer at 50-80 • C (2.87 m/s), with a view to producing a high-quality pumpkin powder from dried seeds. Seeds were dried at 50-80 • C to an average equilibrium moisture value of 0.035 to 0.006 g H 2 O/g DM (3.4 to 0.6% wb). Drying occurred in the falling rate period only and drying rate constants ranged from 0.0226 to 0.0900 1/min with corresponding diffusivity values for the first falling-rate period ranging from 4.68 to 18.63 × 10 −10 m 2 /s. The activation energy (E a)-for the first falling rate period was determined to be 43.9 kJ/mol. Of the nineteen thin layer models tested, the Alibas model could be successfully used as a general model to predict the Moisture Ratio (MR) data for all temperatures investigated. After drying, seeds were blended to produce powders, which were found to be high in fat, crude protein and fiber.

Keskin M, Y Soysal, A Arslan, YE Sekerli, N Celiktas. 2018. Predicting Drying Temperature of Infrared-Dried Pepper Powders Using FT-NIRS and Chromameter. International Conference on Energy Research (ENRES2018), 1-2 November 2018, Alanya, Turkey, Proceedings Book, pp.305-319. ............ ............. .............. .............. ............. .......... .......... ............ .............. ............ ............. ............. ............... ............ ..........
Abstract: Higher drying temperatures result in quality degradations in dried agricultural products. Moreover, it is difficult to separate the food products dried by different methods and drying temperatures with naked eyes. Pepper is gaining importance as a food, medicinal and industrial crop. No study was found on the determination of drying temperature of dried pepper powders. Thus, this study aimed to predict the drying temperature of powdered green-stage and red-stage peppers dried by infrared (IR) radiation at different drying temperatures (50, 60 and 70°C) using a hand-held chromameter and FT-NIRS system. Both color and NIR data were analyzed using PLS (Partial Least Square) regression method. It was found that the drying temperature was a crucial factor on the color (L*a*b, L*C*h) and NIR reflectance of the dried pepper powders. The total color difference (ΔE*) values were lower at higher drying temperatures for both green-stage and red-stage pepper samples. Very high correlation (up to r = 0.98) was obtained between drying temperatures and the color parameters. Results revealed that the drying temperature can be predicted both from color (R2=0.99; SEP: 1.06°C) and NIR data (R2=0.99; SEP: 1.37°C). Both the chromameter and FT-NIRS performed quite well for the estimation of the drying temperature. Also, a mathematical model was developed to predict the drying temperature from color data. The hand-held chromameter has an advantage of being inexpensive, portable and practical. ........... ............. .............. .............. ............. .......... .......... ............ .............. ............
Özet: Yüksek kuruma sıcaklıkları kurutulmuş tarım ürünlerinde kalite bozulmalarına neden olmaktadır. Ayrıca, farklı yöntemlerle ve kurutma sıcaklıklarıyla kurutulmuş gıda ürünlerini çıplak gözle ayırmak zordur. Biber gıda, tıbbi ve endüstriyel ürün olarak önemi artan bir üründür. Kurutulmuş toz biberin kuruma sıcaklığının tahmini üzerine bir çalışmaya rastlanmamıştır. Bu nedenle, bu çalışma, el tipi bir renk ölçer ve FT-NIRS kullanılarak, farklı kurutma sıcaklıklarında (50, 60 ve 70°C) kızılötesi (IR) ışınımla kurutulan yeşil ve kırmızı toz biberlerin kurutma sıcaklığını tahmin etmeyi amaçlamıştır. Hem renk hem de NIR verileri PLS regresyon yöntemi ile analiz edilmiştir. Kurutma sıcaklığının, kurutulmuş biber tozlarının rengi (L*a*b, L*C*h) ve yakın kızıl ötesi (NIR) yansıma değerleri üzerinde önemli bir faktör olduğu belirlenmiştir. Toplam renk değişimi değerinin (ΔE *) hem yeşil hem kırmızı biber örnekleri için yüksek kurutma sıcaklıklarında daha düşük olduğu belirlenmiştir. Kurutma sıcaklıkları ve renk parametreleri arasında yüksek korelasyon değerleri (r=0.98'e kadar) elde edilmiştir. Sonuçlar, kurutma sıcaklığının hem renk (R2=0.99; SEP: 1.06°C) hem de NIR yansıma verilerinden (R2=0.99; SEP: 1.37°C) tahmin edilebileceğini göstermiştir. Hem renk ölçer hem de FT-NIRS, kurutma sıcaklığının tahmini için oldukça iyi performans göstermiştir Ayrıca, kurutma sıcaklığının renk verilerinden tahmini için matematiksel bir model geliştirilmiştir. El tipi renk ölçer, ucuz, taşınabilir ve pratik olma avantajına da sahiptir.

Effect of boiling, thickness (0.5 and 1cm) and temperature on drying time of Dioscorea bulbifera was investigated in a fabricated hot air drier at a temperature range of 50 -70°C. . The drying process was conducted in triplicates and average values recorded. The average moisture ratio was used to plot the drying characteristics curves for the temperature range studied with dimensionless moisture ratio against drying time. Drying took place mainly in the falling rate period whiles increased slab thickness influenced drying time for both the boiled and fresh yam slabs at all temperatures. Boiling was shown to have led to a decrease in the rate of moisture movement which led to increase in drying time of the yam slice at both thickness (0.5, 1cm).  Drying time subsequently reduced with increase in hot air temperature.  70°C is therefore recommended for drying aerial yam. These results will provide food processors with information to determine the best processing conditions for the dioscorea bulbifera which will finally lead to elimination of waste.

Arslan A, Y Soysal, M Keskin. 2020. Mathematical Modeling, Moisture Diffusion and Color Quality in Intermittent Microwave Drying of Organic and Conventional Sweet Red Peppers. AgriEngineering, 2, 393–407; doi:10.3390/agriengineering2030027
......... ......... ......... ......... ......... ......... ......... ......... ......... ......... ......... ......... ........ ........ ........ ......... ......... Abstract: The aims of this research were to evaluate the influence of intermittent microwave drying on the moisture diffusion and color qualities of organically and conventionally grown sweet red peppers and mathematically express drying kinetic data. Pepper samples of 150 g were dried at 150, 300 and 450 W using a microwave oven. Results showed that intermittent microwave drying at 450 W occurred mainly in the falling rate period, whereas drying at lower powers resulted in relatively longer constant rate periods for both peppers types. The Midilli model provided the best fit for all data. The moisture diffusivity (De) values of organic and conventional samples ranged from 59.69 x 10-10 to 182.01 x 10-10 m2s-1 and from 59.11 x 10-10 to 181.01 x 10-10 m2s-1, respectively, and the difference was insignificant. The pre-exponential factor for the Arrhenius equation (D0) and activation energy (Ea) values were almost identical for both product types. Overall, organic or conventional growing did not alter the structural features related to the heat transfer properties. Intermittent microwave drying at 150 and 300 W for organic peppers and 150 W for conventional peppers gave the highest ΔL*, Δa* and a*/b* values, producing the most bright and red pepper powders. Thus, these treatments can be used to produce higher color quality powders. ......... ......... ......... ......... ......... ......... ......... ......... ......... ......... ......... ......... ........ ........ ........ .........
......... Özet: Bu araştırmanın amacı, kesikli mikrodalga kurutma yönteminin organik ve geleneksel yöntemle üretilmiş olan tatlı kırmızı biberlerin nem difüzyonu, renk özellikleri ve kurutma kinetiği verilerinin matematiksel modellemesi üzerindeki etkisini değerlendirmekti. 150 g'lık biber örnekleri, mikrodalga fırın kullanılarak 150, 300 ve 450 W'da kurutulmuştur. Bulgular, her iki biber türü için, 450 W kesikli mikrodalga ile yapılan kurutmanın azalan değerli kuruma şeklinde meydana geldiğini, daha düşük güçlerde yapılan kurutmanın ise nispeten daha uzun süreli sabit oranlı kuruma şeklinde sonuçlandığını göstermiştir. Midilli kuruma modelinin tüm veriler için en uygun model olduğu saptanmıştır. Organik ve geleneksel biber örneklerinin nem difüzyonu (De) değerleri sırasıyla 59.69 x 10-10 ila 182.01 x 10-10 m2s-1 ve 59.11 x 10-10 ila 181.01 x 10-10 m2s-1 arasında değiştiği ve aradaki farkın önemli olmadığı tespit edilmiştir. Arrhenius denklemi üstel faktörü (D0) ve aktivasyon enerjisi (Ea) değerlerinin her iki ürün tipi için de hemen hemen aynı olduğu belirlenmiştir. Genel olarak, organik veya geleneksel yetiştirme yöntemi, ürünlerin ısı transfer özellikleri ile ilgili yapısal özelliklerini değiştirmemiştir. Organik biberler için 150 ve 300 W, geleneksel biberler için 150 W kesikli mikrodalga kurutma, en parlak ve kırmızı biber tozlarını üreten en yüksek ΔL*, Δa* ve a*/b* değerlerini vermiştir. Bu nedenle, bu işlemler daha yüksek renk kalitesinde biber tozu üretmek için kullanılabilir.