Serial combination drying processes: A measure to improve quality of dried carrot disks and to reduce drying time

AD is a common and well established industrial drying process. As idealised in Fig. 8.1, a typical drying curve of a foodstuff can be subdivided into three periods. After an initial phase (IP), a steady state is reached in which the drying rate (evaporated water over time) is constant. Therefore, this period is called "constant rate period" (CRP). In this period the product surface is still wet and the passing airflow transfers the heat for water evaporation to the surface. Simultaneously, the air is collecting the water vapour and is transporting it away from the product surface out of the dryer. This is a simultaneous heat and mass transfer. To keep the surface wet, enough water has to flow from the inside of the food to its surface. In the constant rate period this water flow is mainly capillary-driven and the surface temperature of the product is theoretically constant. As the water evaporation consumes energy, the surface temperature is typically significantly lower than the air temperature. The temperature profile in Fig. 8.1 A is adopted from a hot air drying process of carrot slices and it shows that this constant temperature period is not necessarily exactly reflected in real data. The factors that determine and limit the drying rate in the CRP are: the state of the air (temperature and relative humidity) as well as air velocity. By changing any of these parameters the drying process may be accelerated (or delayed) considerably.

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“…Drying curves with surface temperatures in MVD of carrots at a pressure of 50 mbar and three power levels(Siebert et al, 2016).…”

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confidence: 99%

Microwave-assisted drying

Gaukel

Siebert

Erle

2017

The Microwave Processing of Foods

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“…From previous studies, combined drying methods shows advantages in improving drying times, rehydration and sensorial qualities of vegetable products [ 19 , 20 , 21 , 22 , 23 ], which could be a promising way of obtaining “ideal” rehydrated mushrooms. Generally, there are two kinds of combined drying methods: serial and parallel drying.…”

Section: Introductionmentioning

confidence: 99%

“…Several earlier studies have investigated serial combined drying [ 23 , 24 , 25 , 26 , 27 ]. Siebert [ 23 ] found that FD as pretreatment before hot air or microwave-vacuum drying creates a porous surface layer, which prevents case hardening, and retains volume similar to FD. Furthermore, FD pretreatment accelerates overall drying time.…”

Section: Introductionmentioning

confidence: 99%

“…This study therefore set out to investigate the proper combination of drying methods to obtain products with the desired rehydration quality. Based on the earlier experience of Siebert [ 22 , 23 ] and Mujumdar [ 21 , 29 ], we have devised the following serial combined drying strategy: one drying method (DIC or FD) is used to enhance the porous structure, while another conventional drying method is used to remove the water efficiently. The latter methods are applied either before or after the DIC or FD treatments, and they are chosen on the basis of their reported good rehydration performance and drying efficiency.…”

Section: Introductionmentioning

confidence: 99%

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Study on the Rehydration Quality Improvement of shiitake Mushroom by Combined Drying Methods

Xia

Yang

et al. 2021

Foods

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The aim of study is to improve the rehydration quality of dried shiitake mushrooms for their instant food manufacturers and fast restaurants. Serial combined drying methods were investigated to achieve this objective: either instant controlled pressure drop drying (DIC) or freeze drying (FD) was used as the treatments for microstructure improvement, and they were applied either before or after an additional drying step at low (35 °C) or high (65 °C) temperatures. Dried mushrooms were assessed for quality indicators like relative volume, rehydration rate, dry matter loss and sensory scores. Microstructure properties were inferred to understand the physical mechanisms of quality changes. Principal component analysis (PCA) was used to cluster treatments and to identify combinations of drying techniques, rendering improved quality. Consequently, it was shown that DIC treatment before hot air drying at 35 °C was shown to be the most promising combined drying method to enhance the rehydration quality, leading to a high volume recovery ratio, low dry matter loss after rehydration, and high rehydration rates. This good performance could be explained by the retention of pore interconnectivity resulting from the slight expansion of porous structure during DIC and the retention of cell membrane integrity.

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“…Serial combination of different single drying processes is a promising strategy to combine both short drying time and high product quality. Various studies [3][4][5][6][7][8][9] have shown the usefulness of this technique, which is why other promising processes like ultrasound-assisted drying [10][11][12] , infrared-assisted drying, intermittent drying [13][14][15][16][17][18] or osmotic pre-drying [19][20][21] are not investigated in the present study.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of the usefulness of serial combination processes for drying of apples

et al. 2019

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: Serial combination drying processes are currently studied as alternatives to conventional drying processes. Compared to freeze-drying (FD), serial combination drying appears to be faster and less expensive, while providing better product quality than hot-air drying (HAD) and microwave-vacuum drying (MVD) as previously demonstrated for carrots. Using the example of carrots, it has also been shown that the drying front moves radially outwards over the course of FD. This unexpected behaviour was suggested to originate from the carrots´ heterogeneous structure. It was hypothesized that apple pieces behave differently. Here, this hypothesis was proven by using micro-computed tomography (micro-CT) measurements of partly freeze-dried apple pieces. In order to improve the drying process of apple pieces, several single and combination drying processes were carried out. Processes were evaluated by using drying time and sample quality as relevant parameters. Sample quality was determined by analyzing the 3Dstructure, rehydration behaviour, colour and ingredient retention. Results showed that single MVD is a well suitable drying technique for apple pieces, producing dried products of equal quality to FD. Different from carrots, serial combinations are not necessary to improve the quality of dried apple pieces. Nonetheless, especially a combination of HAD and MVD was useful to obtain specific structures such as puffed pores that did not result from single MVD.

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Serial combination drying processes: A measure to improve quality of dried carrot disks and to reduce drying time

Cited by 31 publications

References 43 publications

Microwave-assisted drying

Microwave-assisted drying

Study on the Rehydration Quality Improvement of shiitake Mushroom by Combined Drying Methods

Evaluation of the usefulness of serial combination processes for drying of apples

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