EFFECT OF SOLAR DRYING ON THE COMPOSITION OF ESSENTIAL OIL OF SACHA CULANTRO (ERYNGIUM FOETIDUM L.) GROWN IN THE PERUVIAN AMAZON

Two solar drying methods (direct cabinet solar dryer and indirect cabinet solar dryer) were tested under tropical conditions for drying aerial parts of sacha culantro ( Eryngium foetidum L.) in Pucallpa City (Peruvian Amazon). The drying behavior was monitored during all experimental runs. Dried samples and fresh leaves were hydrodistilled and isolated oils were analyzed using gas chromatography with flame ionization detector and gas chromatography-mass spectrometry. ( E )-2-dodecenal was determined as the main constituent of the sacha culantro essential oil, averaging 61.8–62.2%, followed by n -dodecanal (10.9–15.5%), ( E )-2-tetradecenal (6.7–7.6%) and 1-tetradecene (3.6–5.7%). When comparing both solar drying methods, the indirect method was found as more suitable for drying E. foetidum since the dried product resembled the fresh herb more closely in its chemicalcomposition and had better appearance. However, a better drying efficiency of 10.3% was achieved when drying in the direct solar dryer compared with 5.8% for the indirect solar dryer.

PRACTICAL APPLICATIONS

Harvested leaves of sacha culantro are widely used as a condiment in a range of Peruvian, Latin American and Caribbean foods, including vegetable and meat dishes, canned food and sauces. There is lack of any postharvest processing of this herb although it may extend possibilities for use of the herb and facilitate the product export from local production areas and might be a good economic source for poor local farmers. This study shows solar drying as a reasonable preservation technique of sacha culantro leaves which may have a practical application in case of postharvest processing of the herb in the target region of Pucallpa City in Peruvian Amazon.     

Production of a red–purple food colorant from Opuntia stricta fruits by spray drying and its application in food model systems

Opuntia stricta fruit juice is a potential source of betacyanin pigments which can be used as a natural red-purple food colorant. In this work a powder food colorant was obtained by co-current spray drying of O. stricta fruit juices with a bench-scale two fluid nozzle spray dryer. Glucose syrup (DE 29) was used as drying aid. Optimum conditions for spray drying were as follow: juice content (20% v/v; 1.2 °Brix), glucose syrup content (10% w/v), liquid feed rate (0.72 l/h), spray air flow-rate (0.47 m³/h), drying air flow-rate (36 m³/h), and inlet drying air temperature 160 °C. Color was retained during the drying process (>98%) and drying yield was high (58%). The powder colorant showed high color strength (4.0), being this color strength stable when stored at room temperature for one month. This colorant was successfully applied in two food model systems: a yogurt and a soft-drink. Food presented a vivid red-purple tonality very attractive for consumers that was maintained after one month under refrigeration (4 °C) (ΔE < 5).     

SOLAR OSMOVAC-DEHYDRATION of PAPAYA

A solar osmotic dryer was designed and constructed to test the utilization of solar energy in the two-step osmovac-dehydration of papaya. Drying rates measured in solar versus nonsolar osmotic dehydration experiments showed that solar osmotic drying had higher drying rates and sucrose uptake in the papaya samples (0.6 cm thick × 4 cm long × 2 cm wide) than in the nonsolar runs. In separate experiments, drying rates from solar vacuumdrying (as a second step of the osmovac-drying process) were about twice those of nonsolar vacuum-drying. Drying rates of both solar and nonsolar vacuum-drying reached the end of the constant-rate period in about 3 h. Sensory qualities of solar osmovac-dried papaya were comparable to those of vacuum-dried or solar osmotic-nonsolar vacuum-dried. These results suggest the possibility of drying rate increase and quality retention in utilizing solar energy in the osmovac-dehydration process.     

Determination of convective heat transfer coefficient and specific energy consumption of potato using an ingenious self tracking solar dryer

In the present work, an attempt has been made to experimentally determine the heat transfer properties of potato in terms of convective heat transfer coefficient, specific energy consumption and specific heating rate. Drying experiments with potato cylinders have been performed in an in-house fabricated laboratory scale natural convection indirect solar dryer with self tracking mechanism. The convective heat transfer coefficient of cylindrical potato samples was evaluated by considering the combined effects of heat capacities of food product as well as radiative heat transfer from drying chamber to the food product. This study revealed that the convective heat transfer coefficient for potato cylinders was varying from 11.73 to 16.23 W/m² °C with an experimental error of 7.86 %. The specific energy consumption was decreasing exponentially with drying time, and the average value was estimated to be 3,491 kJ/kg. It was also observed that the specific heating rate for potato cylinders decrease with dimensionless moisture content.     

Thermal energy storage based solar drying systems: A review

Solar dryer based on thermal energy storage materials is quite effective for continuously drying agriculture and food products at steady state in the temperature range (40 °C–60 °C). Such dryers have globally become a potential viable substitute to the solar dryers based on fossil fuel, due to the utilization of clean energy resources and cost-effectiveness. Storage materials utilized in these dryers can store energy during the sunshine hour and deliver the stored energy during off-sunshine. It reduces the existing load on the gap between energy demand and supply, hence plays a vital role in energy sustainability. A number of studies have been done in last few decades for drying agriculture and food products with a solar dryer based on thermal energy storage concept. This paper mainly presents a review on the important contributions made so far in the field of solar drying systems based on the thermal energy storage medium, with a focus on recent updates in thermal energy storage technology available in terms of materials capable of storing heat as sensible and latent heat.Industrial relevance

• 1.Solar energy defuses in the nature and provides low grade heat. This characteristic of solar energy is good for drying at low temperature, high flow rate with low temperature rise.
• 2.Worldwide, there is huge demand of efficient solar dryers utilized by various food and agricultural products.
• 3.Solar energy based solar dryers are not only cost efficient but also can be used across the globe, specially contributing to cleaner energy resources.
• 4.Novel system designs and techniques related to solar dryers are being explored to increase the efficiency and performance of solar dryers, which could in turn be much more commercially utilized by the end user.
• 5.Phase change materials can store energy during sunshine hours and retrieve during off-sunshine hours for drying purpose, hence solar dryers embedded with such materials could be quite useful.

     

Drying of red pepper slices in a solar greenhouse dryer and under open sun: Experimental and mathematical investigations

The present work is mainly focused on the study of the solar drying of red pepper grown in the North of Tunisia. A new mixed mode solar greenhouse dryer (SGD) with forced convection was used in the drying experiments. To further understand the characteristics of the SGD, an open sun drying experiment was conducted under the same climatic condition. The results show that the constant rate period is absent from the experimental drying curves. The experimental drying curves show only the falling rate period. Thus, the drying time which was three days in the open sun decreased to two days in the SGD. The drying data were fitted to eight different mathematical models. The fit quality of the proposed models was evaluated by using the coefficient determination (R²), reduced chi-square (χ²) and root means square error (RMSE). Among the models, Modified Henderson and Pabis model for the forced solar drying and the open sun drying was found to best explain the thin-layer drying behaviour of pepper slices. The instantaneous thermal efficiency of the solar collector varied between 30% and 80%, at a mass flow rate of 0.047 kg/s. The overall energy efficiency of the solar dryer was 34%. Finally an economic evaluation was calculated using the criterion of payback period which was found very small 1.02 years compared to the life of the dryer (SGD) 20 years.     

Performance of a solar-heated,forced-air,fully automated lumber dryer

A 3.5 m³, external collector type kiln has been designed and constructed to dry green lumber to M.C. low enough for use in furniture. The kiln uses a hot air transfer-circulation system and its ratio of collector area to lumber capacity is 2.9 m²/m³. The kiln is equipped with a fully automated supervisor system. The energy efficiency and performance of the solar kiln have been evaluated through a series of operational tests. The solar collectors operate at 71 to 75% efficiency, while the drying chamber at an efficiency of 46%. The kiln has been found able to use 33% of the available solar energy for lumber drying, Control system has been proved able to run the process to the drying gradient required by any given species of wood. The performance of the dryer, evaluated by direct comparison with air drying, is satisfactory in respect of the final moisture content and drying time. A final M.C. of 10% was attainable at all times of the year.     

Dehydration of potato

Drying behaviour of potato in a natural convection, solar dryer was investigated. In drying experiments conducted at low air velocity, as found in the solar dryer, it was shown that air flow conditions are of critical importance for drying behaviour. As a result of the presence of extensive, external mass transport resistances in deep bed drying, the air flow behaviour of the bed was more important than the drying behaviour of the single pieces. Thus, for deep bed solar drying, 10x10 mm french cut potatoes dried faster than 5 mm slices. (This result was opposite to that found for drying in thin layers). Drying time was noted to increase less rapidly than bed depth increased, so overall dryer productivity increased with increasing bed depth, within the constraint that drying be completable in 1 day.     

Drying performance and economic analysis of novel hybrid passive-mode and active-mode solar dryers for drying fruits in East Africa

In East Africa, post-harvest loss of fresh perishable fruits is enormous, causing recurrent seasonal deficits. In response, a modified passive-mode hybrid solar dryer hereafter called; ‘an Improved Solar Dryer (ISD)’, was developed as a potential low-cost technology alternative for drying fruits in Uganda. An improved PV-assisted hot air dryer using active-mode hybrid solar dryer hereafter called; ‘Solar Photovoltaic and Electric (SPE)’ was also fabricated. The ISD dryer utilises freely-available solar energy to dry the produce. In contrast, the SPE dryer uses both solar photovoltaic and electricity sources. In this study, the drying performance of the ISD and SPE dryers were performed and compared to that of the traditional open sun drying (OSD) method. Relative to the OSD method, the economic performance of the ISD and SPE dryers was analysed. The drying performance results show that the mean drying air temperatures achieved by the ISD and SPE dryers were 31.9 and 41.1 °C respectively; relative to the 27.6 °C for the OSD method. On average, the thermal energy attained by the ISD and SPE dryers were 3551 and 5757 Watts (W) respectively, as compared to 2952 (W) obtained for the OSD method. It took the ISD and SPE dryers 10 and 18 h to effectively dry the fruit (pineapple) products, respectively as opposed to the 30 h taken by the OSD method. The results confirm the superior performance of the ISD and SPE dryers than the OSD method. Results for the economic performance analysis show more reduced costs of drying the products using the ISD than the SPE dryer. Similarly, the pay-back period for the ISD was 2.4 times shorter than that of the SPE dryer. Joint results for economic analysis and drying performance confirm the ISD as a better drying technology than the SPE dryer in the context of the resource-constrained farmers/agro-processors without electricity in Uganda and East Africa.     

Measurement of evaporated acrylamide during heat treatment of food and other biological materials

It is established that acrylamide could be formed during heating of food products. In the present work we have studied whether the formed acrylamide could evaporate from food at elevated temperatures used in cooking (>160 °C) or used in determination of dry matter in laboratory analysis (ca. 105 °C). It was demonstrated that acrylamide evaporates from food samples during both cooking and temperatures used for drying. Up to ca. 4 μg/m³ could be measured above the fry pan during frying of potato. In parallel we have also studied whether acrylamide could be formed and evaporate during the elevated temperatures of 65-130 °C used for dry matter determinations in other types of samples containing biological material, like agricultural and environmental samples. It was found that acrylamide is formed during conditions for drying of soil, sediment and silage samples, as well as cereals, animal feed, etc. After drying, levels of acrylamide up to about 100 μg/kg were found, e.g. in samples of sediment and sludge. The measurements showed in the food, agricultural and environmental samples tested a minor fraction, roughly estimated to be 0.15-7.2% of the formed acrylamide evaporates at the used elevated temperatures.     

Simulation of food drying processes by Computational Fluid Dynamics (CFD); recent advances and approaches

BackgroundUnderstanding the mechanisms underlying the drying processes has a critical role in dehydration of food and agricultural products. Advanced computer modeling and simulation techniques can help in developing new dryers, modification of current systems, energy saving and process optimization. Also the most important parameter during the drying food products is food quality (moisture content, crack formation, case hardening, etc.) which can be enhanced through using appropriate modeling. Computational Fluid Dynamics (CFD) is a well-known modeling technique which has received more attention in the food industry in the recent years. Hydrodynamics of fluid flow, heat and mass transfer during drying can be predicted using CFD.Scope and ApproachThis article reviews fundamentals, merits and shortcomings of CFD in the drying process modeling with a special focus on dehydration of food products. Since the drying is a growing unit operation, there is an emphasis on investigation of CFD utilization in modeling emerging drying processes of food products such as microwave assisted drying, infrared and superheated steam drying besides conventional convective drying systems notably in recent 5 years.Key Findings and ConclusionsCFD has been considered as a promising method which could help developing the design of new dryers, enhancing current dryers and the most important aspect of utilization of this method in the food industry research and development is “food quality” improvement.     

Drying rate and air circulation in a fully automated solar kiln

A fully automated solar kiln, operating on logical venting principles and controlled according to a drying schedule, was used to dry wood. The drying rates in the solar kiln and an air dryer were compared in the moisture content ranges above and below fibre saturation point (fsp). The effect ofair circulation on drying rates in the solar kiln was also investigated both above and below fsp.     

超声技术在食品工业中的应用研究进展

超声波是频率超过20 k Hz的声波,其声场具有独特的空化现象,可同时产生热效应和机械效应,在食品加工领域应用具有处理效率高、可控性好、成本低等优点,近年来在食品加工领域被广泛关注。本文从超声技术作用机制出发,综述了国内外有关超声技术在食品加工业中的应用和研究新进展,主要包括利用高频和低频超声对不同食品原料进行超声提取、超声降解、超声辅助酶解、超声干燥、超声灭菌、超声乳化和超声嫩化等方面,并对其可能的作用机制进行了分析归纳。超声技术除具有传统破碎、断裂原料细胞作用之外,超声辅助酶解等生物物理结合加工方式也符合"十三五"食品科技创新专项规划中发展现代食品绿色加工与低碳制造技术的要求。本文为食品绿色制造和产业转型升级提供了理论依据。     

低温热泵穿流干燥新鲜稻谷实验研究

利用自主研发的搅拌式-热泵穿流干燥仓,研究了新鲜稻谷的脱水过程。考察了热泵干燥条件对稻谷干燥品质和过程性能的影响。结果表明,稻谷热泵干燥一直处于降速干燥阶段;当热泵干燥温度为35℃时,干燥仓可用7.5h将300kg稻谷从25%的初始含水率降至14%,过程单位能耗为2022kJ/kgwater,爆腰增率为1.3%。通过与热风干燥、自然晒干过程比较发现,较之自然晒干,热泵干燥可以大幅度缩短干燥时间,阻止稻谷发霉;较之热风干燥,温和的热泵干燥可以获得较低的爆腰增率,单位能耗低。该结论可以为基于热泵干燥技术的循环式干燥机以及间歇式大型干燥机械的开发提供依据。      

Industrial paddy drying and energy saving options

Paddy drying is an energy-intensive process and influences rice quality. In this study, the energy consumption of paddy drying in a large-scale milling plant was investigated. Furthermore, some drying experiments were conducted in a laboratory. The aims were to gain practical information and to propose more economical drying options to the industry. The results indicated that the current drying in the plant consumed specific primary energy of between 3.874 and 4.421 MJ/kg of water evaporated. The experimental results showed that two-stage drying with tempering by using a fluidised bed dryer at 100–110 °C in the first stage and drying with ambient air using a solar dryer for the second stage provided rice quality that was comparable to that of the plant. Also, from the calculation, the energy cost of the plant could be reduced if an in-store dryer was used after the first-stage drying by LSU dryer.     

Mathematical modeling and computational fluid dynamics simulation of cabinet type solar dryer: Optimal temperature control

The mathematical model for determination of auxiliary energy required to maintain set air temperature in the drying chamber is proposed for cabinet type solar dryer. The model is developed considering the heat exchanges across the dryer control volume with solar radiation intensity and set temperature as input. The sole purpose is to minimize the auxiliaries. The computational fluid dynamics (CFD) technique is used to simulate the air flow inside the drying chamber for different operating conditions. The simulations results for the temperature are very close to the results from mathematical model. The dryer configuration discussed in illustrative example found to have minimum auxiliary consumption at 45°C with total auxiliary expense of 97.3 kWh per day. When applied to full calendar year, the optimum temperature is found to be function of ambient temperature and solar radiation intensity. The results obtained from mathematical model are found to be in well agreement with simulation results. The simulation results provide a region with 1.2 m to 1.6 m on X-ordinate, 0.8 m to 1.0 m on Y-ordinate and 0.7 m to 1.2 m and 3.7 m to 4.3 m on Z-ordinate where average temperature can be sensed. It helps in modulating the auxiliary input/s in integration with solar heat.     

微波干燥技术在食品中的应用

微波干燥是一种新兴加热技术。本文分析了微波加热机理及加热特点。讨论了微波在食品干燥中的应用,着重论述了在果疏干燥中的应用。     

OPTIMIZATION OF MARINE FISH DRYING USING SOLAR TUNNEL DRYER

Studies were conducted to optimize fish-drying process in a Hohenheim-type solar tunnel dryer to produce safe and high quality dried fish products. Five commercially important tropical marine fish species in the Bay of Bengal such as silver jew fish, Bombay duck, big-eye tuna, Chinese pomfret and ribbon fish were used and drying was performed at 45 to 50 and 50 to 55C temperature ranges. Moisture content of the fish samples reached 16% after 36 and 32 h of drying at temperature ranges of 45 to 50 and 50 to 55C, respectively. Products produced at 45 to 50C were found to be excellent on the basis of flavor, color and texture. Their rehydration ability ranged from 65 to 80% with minimum in big-eye tuna and maximum in silver jew fish. Values of total volatile base, peroxide and aerobic plate count of all the final dried products were within the acceptable limit.

PRACTICAL APPLICATIONS

In this experiment, we optimized the drying process in a Hohenheim-type solar tunnel dryer, constructed using locally available materials, for several commercially important marine fish species in the Bay of Bengal over a wide range of temperature, humidity and moisture content. The data obtained in this study are now successfully used for large-scale production of dried fish of high quality, providing better market price for its producers as well as greater acceptability to the consumers. We also developed another low cost solar tunnel dryer using bamboo, hemp, canvas, rope and polythene sheets, which became very popular among small-scale dry fish producers in the coastal areas of Bangladesh.     

变性淀粉应用于喷雾干燥微胶囊配料工艺探讨

随着食品工业的发展,越来越多的食品配料采用喷雾干燥进行加工。各种亲水性胶体和变性淀粉正在被广泛的应用于这一领域,用于改善食品配料的分散性、抗吸潮性和速溶性。文中探讨了以食用变性淀粉对酱油粉进行微胶囊处理的实例,详细介绍了变性淀粉微胶囊壁材系统应用于粉末配料生产的工艺,同时介绍了粉末配料生产时喷雾干燥参数选择的依据。