KINETICS ON COLOR CHANGES DURING DRYING OF SOME FRUITS AND VEGETABLES

Abstract

The effect of drying conditions on color changes of apple, banana, carrot and potato during conventional and vacuum drying was investigated. The Hunder color scale parameters redness, yellowness and lightness were used to estimate color changes during vacuum and conventional drying at 50, 70 and 90°C. Air humidity during conventional drying was regulated at 15, 30 and 40%. Air temperature and humidity affected redness and yellowness, but not lightness. A first order kinetic model was fitted to experimental data adequately for both redness and yellowness. The rate of color deterioration was found to increase as temperature increased and air humidity decreased, for both drying methods and all the examined materials.     

EFFECT OF OSMOTIC PRE-TREATMENT AND INFRARED RADIATION ON DRYING RATE AND COLOR CHANGES DURING DRYING OF POTATO AND PINEAPPLE

A combination of intermittent infrared and continuous convection heating was used to dry various osmotically pretreated sample of potato (in solutions of 10%, 20% and 30% NaCl) and pineapple (in solutions of 30%, 50%, 70% Brix). The effect of drying conditions on color changes of potato and pineapple was investigated. The Hunter color scale parameters (redness, yellowness and lightness) were measured to quantify the color changes. With appropriate choice of infrared intermittency as well as osmotic pretreatment, it is possible to reduce the overall color change while maintaining high drying rates. As expected, osmotic pretreatment resulted in a shift in the sorption isotherms for both products.     

Effect of Air-Drying Temperature on Kinetics of Quality Attributes of Lemon (Citrus limon cv. lunari) Peels

The aim of this work was to determine the effect of air drying temperature (40 °C, 50 °C, and 60 °C) on the degradation kinetics of quality parameters of lemon peels. Drying at 40 °C was in favor of maximal water and oil retention capacities and lowest color loss (35%), but it also induced lower phenolic and flavonoids residual contents. First-order reaction model showed a good fit for lightness and yellowness color parameter. Zero-order reaction model fitted well redness color parameter and total color difference. A higher value of activation energy indicated greater heat sensitivity of lightness and redness during air drying.     

EFFECT OF OSMOTIC PRE-TREATMENT AND INFRARED RADIATION ON DRYING RATE AND COLOR CHANGES DURING DRYING OF POTATO AND PINEAPPLE

A combination of intermittent infrared and continuous convection heating was used to dry various osmotically pretreated sample of potato (in solutions of 10%, 20% and 30% NaCl) and pineapple (in solutions of 30%, 50%, 70% Brix). The effect of drying conditions on color changes of potato and pineapple was investigated. The Hunter color scale parameters (redness, yellowness and lightness) were measured to quantify the color changes. With appropriate choice of infrared intermittency as well as osmotic pretreatment, it is possible to reduce the overall color change while maintaining high drying rates. As expected, osmotic pretreatment resulted in a shift in the sorption isotherms for both products.     

EFFECT OF OSMOTIC DEHYDRATION ON COLOR AND SORPTION CHARACTERISTICS OF APPLE AND BANANA

Color and sorption characteristics of osmotically treated and air dried apple and banana were studied during air drying at 70^°C. The color parameters: Lightness (L), Redness (a) and Yellowness (b) were studied, using a Hunter Lab chromatometer. A first order kinetic model was fitted to the experimental data adequately for color parameters, while sorption data for treated and air dried products were fitted to the GAB model. Untreated fruits showed an extensive browning which was monitored by a significant drop of the lightness (L) and an increase of redness (a) and yellowness (b). Osmotically pretreated samples did not brown as much as the untreated samples and the lightness L decreased only slightly while a, b increased slightly. Osmotic pretreatment resulted in a shift in sorption isotherm for both fruits. Osmotic dehydration prevented color damages and decreased the sorption capacity of dehydrated products.     

EFFECT OF OSMOTIC DEHYDRATION ON COLOR AND SORPTION CHARACTERISTICS OF APPLE AND BANANA

ABSTRACT

Color and sorption characteristics of osmotically treated and air dried apple and banana were studied during air drying at 70^°C. The color parameters: Lightness (L), Redness (a) and Yellowness (b) were studied, using a Hunter Lab chromatometer. A first order kinetic model was fitted to the experimental data adequately for color parameters, while sorption data for treated and air dried products were fitted to the GAB model. Untreated fruits showed an extensive browning which was monitored by a significant drop of the lightness (L) and an increase of redness (a) and yellowness (b). Osmotically pretreated samples did not brown as much as the untreated samples and the lightness L decreased only slightly while a, b increased slightly. Osmotic pretreatment resulted in a shift in sorption isotherm for both fruits. Osmotic dehydration prevented color damages and decreased the sorption capacity of dehydrated products.     

Drying Kinetics and Quality of Soy Residue (Okara) Dried in a Jet Spouted-Bed Dryer

The objective of this study was to investigate experimentally the effects of various drying parameters, i.e., inlet air velocity, inlet air temperature, initial bed height and heating duration, on both the drying kinetics and various quality attributes of dried okara viz. percentage changes of the total protein content, color, urease index, as well as the specific energy consumption during drying in a jet spouted-bed dryer. It was observed that all drying conditions tested could reduce the amount of urease to an acceptable level and increasing the heating duration, air velocity, and hot air temperature led to a significantly higher rate of reduction of urease activity. The percentage change of the total protein content of okara undergoing different drying conditions was not significantly different, however. After drying, the redness of okara was the highest changing color index, but its absolute value was still much lower than those observed for the lightness and yellowness. Hence, dried okara appeared light-brown. The specific energy consumption of the process was found to be in the range of 3.69 to 5.89 MJ/kg evaporated water.     

Drying Kinetics and Quality of Soy Residue (Okara) Dried in a Jet Spouted-Bed Dryer

ABSTRACT

The objective of this study was to investigate experimentally the effects of various drying parameters, i.e., inlet air velocity, inlet air temperature, initial bed height and heating duration, on both the drying kinetics and various quality attributes of dried okara viz. percentage changes of the total protein content, color, urease index, as well as the specific energy consumption during drying in a jet spouted-bed dryer. It was observed that all drying conditions tested could reduce the amount of urease to an acceptable level and increasing the heating duration, air velocity, and hot air temperature led to a significantly higher rate of reduction of urease activity. The percentage change of the total protein content of okara undergoing different drying conditions was not significantly different, however. After drying, the redness of okara was the highest changing color index, but its absolute value was still much lower than those observed for the lightness and yellowness. Hence, dried okara appeared light-brown. The specific energy consumption of the process was found to be in the range of 3.69 to 5.89 MJ/kg evaporated water.     

Color Changes of Birch Wood During High-Temperature Drying

In low-temperature drying, a high drying rate has been found to be adequate for silver birch (Betula pendula) and European white birch (B. pubescens) timber as far as wood colour is concerned. During high-temperature drying, however, birch timber darkens significantly if steam is used as the drying medium. The objective of this research was to study the effects of drying force (wet-bulb depression), timber thickness, and initial moisture content on the color of high-temperature-dried birch wood. The reflectance spectrum of wood was measured and transformed to the CIEL?a?b? color scale.

The increase in drying force increased the lightness and decreased the redness and the yellowness of wood. At the same time, the difference in color between the surface layer and the interior of boards increased. Increase in thickness and in initial moisture content increased the difference in color between the surface and the interior of boards. Pretreatment of timber with water soaking decreased the difference in color between the surface layer and the interior of boards when low drying force was used, but this difference was increased when high drying force was used.     

Drying Kinetics and Physicochemical Characteristics of Laboratory-Prepared Corn/Wheat Distillers Grains and Solubles Dried with Superheated Steam and Hot Air

The effect of superheated steam (SS) drying and hot air (HA) drying on drying kinetics and changes in the color, crude protein, and amino acid concentrations (in particular, lysine content) of corn/wheat wet distillers grains (WDG) and centrifuged solubles (CS) was evaluated. An inversion temperature was reached at 139°C for WDG and 132°C for CS, above which moisture evaporation rate and qualitative changes under SS drying conditions exceeded the values noted in HA, and below which the reverse was observed. A significant decrease (from 8 to 50%) in the lysine content of WDG and CS was reported during SS and HA. The overall changes in the color (ΔE*) of corn/wheat WDG and CS ranged from 7.9 ± 2.6 to 27.2 ± 1.9 during SS drying and from 11.9 ± 3.7 to 32.0 ± 0.5 during HA drying. The observed deterioration in color was attributed mainly to changes in lightness (L*) and yellowness (b*) of dried samples. The values of L* and b* were reliable predictors of the lysine content of corn/wheat distillers co-products.     

Vacuum Frying of Carrot Chips

Abstract

Vacuum frying is an alternative method to produce high quality vegetable or fruit chips. The effect of frying temperature and vacuum degree on moisture content, oil content, color, and texture of fried carrot chips were investigated. During the early stage of vacuum frying, the rate of moisture removal and oil absorption increased with increasing frying oil temperature and degree of vacuum. Statistical analysis of the color data showed that there were no significant differences P > 0.05) in lightness (L), redness (a), and yellowness (b) of carrot chips as a function of vacuum degree and temperature. The breaking force of carrot chips decreased with increasing frying temperature and vacuum degree. The statistical analysis also showed that there were no significant differences P < 0.05) in the breaking force as a function of temperature, but the breaking force was significantly (P < 0.05) affected by the vacuum degree.     

Effect of Variety on Drying Characteristics and Selected Quality Attributes of Dried Carrots

The effects of variety on drying characteristics, color, and water absorption of carrots were investigated. Six different varieties of carrots, viz. Kazan, Maxima, Nandor, Nektarina, Simba, and Tito were evaluated. The hot air drying characteristics of carrot cubes dried under forced convection conditions were determined and drying data were analyzed to obtain parameters of Page and first-order kinetic models as well as moisture diffusivity. Color characteristics were determined for fresh, dried, and dehydrated samples by measuring lightness (L*), redness (a*), and yellowness (b*). Water absorption data were analyzed for ground samples. It was observed that drying characteristics, such as color and water absorption were significantly influenced by variety. The varieties of Kazan and Nektarina were found to be characterized by highest and lowest moisture diffusivity of 7.52 × 10^-9 and 3.31 × 10^-9m²/s respectively. Kazan variety was also characterized by shortest drying time. The lowest changes in color caused by drying were observed for Tito variety. The variety of Kazan was characterized by the highest resistances to color changes affected by drying followed by rehydration. Nandor and Tito varieties displayed the highest water absorption near to 560 g/100 g. The best drying characteristics and good water absorption accompanied by the high color attributes of dried and rehydrated samples implies that Kazan variety is expected to be the most useful to drying industry.     

Variation in Drying Behavior and Final Moisture Content of Wood during Conventional Low Temperature Drying and Vacuum Drying of Betula pendula Timber

Conventional and vacuum drying experiments were conducted on Betula pendula timber, which was sawn from trees felled during three different seasons. The influence of the wood procurement season on drying behavior differed, on the one hand, between the drying phases above and below 30% moisture content in the conventional drying, and, on the other hand, between the conventional and vacuum drying methods. During the first steps of the conventional drying process, relative humidity in the kiln, as well as drying time and drying rate, varied according to the felling season. Variations in environmental conditions outside the kiln and the seasonal variation in the physical properties of the wood were presumed to be the reasons for differences in drying behavior. The difference in moisture content gradient, i.e., the difference in final moisture content between the inner wood and the surface layer of boards, was greater in conventionally dried timber than in vacuum-dried timber. In conventionally dried timber there was a clear seasonal variation in the gradient of final moisture content, which was greatest for winter-felled wood. The premature drying of the surface layer during the first steps of the conventional drying process of winter-felled wood was the reason for the higher gradient of moisture content. Storage of wood as logs decreased the standard deviation of the final moisture content.     

Effect of Variety on Drying Characteristics and Selected Quality Attributes of Dried Carrots

The effects of variety on drying characteristics, color, and water absorption of carrots were investigated. Six different varieties of carrots, viz. Kazan, Maxima, Nandor, Nektarina, Simba, and Tito were evaluated. The hot air drying characteristics of carrot cubes dried under forced convection conditions were determined and drying data were analyzed to obtain parameters of Page and first-order kinetic models as well as moisture diffusivity. Color characteristics were determined for fresh, dried, and dehydrated samples by measuring lightness (L*), redness (a*), and yellowness (b*). Water absorption data were analyzed for ground samples. It was observed that drying characteristics, such as color and water absorption were significantly influenced by variety. The varieties of Kazan and Nektarina were found to be characterized by highest and lowest moisture diffusivity of 7.52 × 10^?9 and 3.31 × 10^?9m²/s respectively. Kazan variety was also characterized by shortest drying time. The lowest changes in color caused by drying were observed for Tito variety. The variety of Kazan was characterized by the highest resistances to color changes affected by drying followed by rehydration. Nandor and Tito varieties displayed the highest water absorption near to 560 g/100 g. The best drying characteristics and good water absorption accompanied by the high color attributes of dried and rehydrated samples implies that Kazan variety is expected to be the most useful to drying industry.     

A Study of Vacuum-Drying Characteristics of Sugi Boxed-Heart Timber

In this study, we evaluated the effects of drying under atmospheric and vacuum pressure on the drying time, checking, and color change of sugi boxed-heart timber dried at the same dry-bulb temperature and the same wet-bulb depression. The results obtained were as follows: Sugi boxed-heart timber specimens dried at any temperature under vacuum pressure had a shorter drying time than the specimens dried under atmospheric pressure. At moisture content above fiber saturation point and at the same dry-bulb temperature, the specimens dried under vacuum pressure had a drying rate that was almost twice as fast as that of the specimens dried under atmospheric pressure. Sugi boxed-heart timber specimens dried under both atmospheric and vacuum pressure at a higher drying temperature had a shorter drying time than the specimens dried at a lower drying temperature. Apart from the sugi boxed-heart timber specimen dried at a temperature of 100°C under atmospheric pressure, no surface checks were observed for the specimens dried under vacuum pressure or at the other temperatures dried under atmospheric pressure. Slight internal checks were observed in sugi boxed-heart timber specimens dried at a temperature of 100°C under both atmospheric and vacuum pressure. After planer shaving, there was no significant difference between kiln drying under atmospheric pressure and that done under vacuum pressure in terms of the color change (ΔE*) for both sapwood and heartwood of sugi boxed-heart timber specimens.     

Effect of Drying Conditions and Level of Condensed Distillers Solubles on Protein Quality of Wheat Distillers Dried Grain with Solubles

Reduced protein quality is one of the concerns currently confronting the supply and utilization of wheat distillers dried grain with solubles (DDGS) as an animal feed ingredient. This study assessed the protein quality of wheat DDGS, expressed as acid detergent insoluble crude protein (ADICP) and lysine content, by blending wet distillers grain (WDG) with varying condensed distillers solubles (CDS) levels and drying using forced air convection, microwave, and microwave–convection methods. As the CDS level was increased, the protein content of wheat DDGS generated from the three drying methods increased. Interactions of CDS level with drying air temperature, microwave power, and microwave–convection settings had a significant effect (p < 0.05) on average ADICP and lysine contents. Higher ADICP and lower lysine contents were observed in samples dried at higher temperature, microwave power, and microwave convection settings. Further, the CDS level significantly affected the color parameters of microwave- and microwave–convection-dried samples and the drying air temperature–CDS level interaction significantly affected the color of forced air convection–dried samples. Significant lysine content–redness, ADICP–lightness color parameter, and ADICP–total color difference correlations were found in forced air convection–, microwave-, and microwave–convection-dried samples, respectively. Microwave and microwave–convection drying achieved desirable protein quality associated with low-temperature drying at much shorter times.     

Variation in Drying Behavior and Final Moisture Content of Wood during Conventional Low Temperature Drying and Vacuum Drying of Betula pendula Timber

Conventional and vacuum drying experiments were conducted on Betula pendula timber, which was sawn from trees felled during three different seasons. The influence of the wood procurement season on drying behavior differed, on the one hand, between the drying phases above and below 30% moisture content in the conventional drying, and, on the other hand, between the conventional and vacuum drying methods. During the first steps of the conventional drying process, relative humidity in the kiln, as well as drying time and drying rate, varied according to the felling season. Variations in environmental conditions outside the kiln and the seasonal variation in the physical properties of the wood were presumed to be the reasons for differences in drying behavior. The difference in moisture content gradient, i.e., the difference in final moisture content between the inner wood and the surface layer of boards, was greater in conventionally dried timber than in vacuum-dried timber. In conventionally dried timber there was a clear seasonal variation in the gradient of final moisture content, which was greatest for winter-felled wood. The premature drying of the surface layer during the first steps of the conventional drying process of winter-felled wood was the reason for the higher gradient of moisture content. Storage of wood as logs decreased the standard deviation of the final moisture content.     

Effect of Microwave-Assisted Vacuum Frying on the Quality of Potato Chips

We investigated the applicability of microwave-assisted vacuum frying in producing potato chips. Three microwave power levels (600, 800, 1000 W) were used for frying times of up to 360 s. The moisture loss and oil uptake histories were measured as a function of the microwave power levels. The textural crispness (breaking force) and color parameters (lightness, redness, and yellowness) were also measured as a function of microwave power levels and frying time. The application of microwave-assisted vacuum frying significantly increased the moisture evaporation and oil uptake rates in potato chips. At the same time, the amount of oil uptake was similar to that in vacuum-fried chips not assisted by microwave. The chips produced using microwave-assisted vacuum frying were crispier (lower breaking force), visually appealing, and could be produced in a shorter time.     

Process-Based Drying Temperature and Humidity Integration Control Enhances Drying Kinetics of Apricot Halves

The effects of drying temperature (50, 60, and 70°C) and absolute humidity (65, 90, 115, 140 g/kg at the initial stage) on drying kinetics and color attributes of apricot halves under process-based drying temperature and humidity integration control (PDTHIC) were investigated. Results indicated that appropriate PDTHIC could reduce the drying time by 18.75% compared to the control group. The absolute humidity parameter should be controlled well rather than continuously dehumidify for traditional practices. The moisture effective diffusivity (D_eff) at 70°C presented drastic fluctuations with increasing absolute humidity parameters, calculated using the Weibull distribution model. The activation energy (E_a) of samples treated by continuous dehumidification and PDTHIC were 31.40 and 74.18 kJ/mol, respectively. The variation trend of color parameters was different from the conventional hot air drying probably due to the dehydration mechanism. Observation of the microstructure of the dried samples indicated that the PDTHIC process can enhance the drying rate of apricot through generating a larger pore network compared to continuous dehumidification at the same temperature. The findings of the current work clearly indicated that process-based drying temperature and humidity integration control enhances the drying kinetics of apricot halves, leading to a promising technology for energy savings.     

Effect of low temperature on the microwave-assisted vacuum frying of potato chips

The objective of this study was to investigate the effect of low temperature on the microwave-assisted vacuum frying of potato chips. A newly built, in-house, microwave-assisted frying machine was developed and used in this study. The effect of low temperature on the microwave-assisted vacuum frying of potato chips was investigated via comparing sample properties prepared with frying temperatures of 90°C, 95°C, and 100°C. The experience was taken at the same vacuum degree in every frying process. Parameters of included moisture content, oil content, color parameters (lightness, redness, and yellowness), and textures (hardness, crispness) were used to evaluate the effect of different frying temperatures on the microwave-assisted vacuum frying of potato chips. Results showed that with lower temperature in microwave-assisted frying, the rate of moisture evaporation of potato chips was slowed down and the time of the ending of frying was prolonged from 10 min with a frying temperature of 100°C to 14 min with 90°C and 12 min with 95°C. Meanwhile, the oil content in fried potato chips was increased with lower temperature in microwave-assisted vacuum frying. The breaking force of final products are not significantly (p > 0.05) affected in different frying temperatures of microwave-assisted vacuum frying. Also, the frying temperature of 100°C in microwave-assisted vacuum frying had better preservation of natural color than the lower frying temperature with prolonged frying time. Results showed that the temperature is one of the main factors that affect the quality of microwave-assisted vacuum frying of potato chips and the producer could find suitable temperature conditions according to experience.