Agricultural Water Management an International Journal, Feb 1, 2007
W. Spreer). a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e... more W. Spreer). a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / a g w a t 0378-3774/$ -see front matter #
ABSTRACT : View final version online for free until July 3, 2015, on ScienceDirect: http://www.sc... more ABSTRACT : View final version online for free until July 3, 2015, on ScienceDirect: http://www.sciencedirect.com/science/article/pii/S0168169915001209 Abstract: To meet consumer demands, the need for quick and accurate methods for quality assessment of fresh fruits is increasing constantly. This study presents a comparison of three different models for mass estimation of mango fruits (cv. ‘Nam Dokmai’) calculated by simple linear regression (SLR), multiple linear regression (MLR) and artificial neural network (ANN). Three dimensions (length, maximum width, and maximum thickness) were manually measured and included as parameters for model building. Calibration and validation were carried out on independent data sets with 820 samples (2010–2012) and 61 samples (2014), respectively. This allowed it to establish a high-performance model that can be used for further mass-size estimation in a machine-vision system. For the SLR, an existing equation for mass estimation was modified to calculate an adjusted coefficient for accurate mass estimation. A MLR model was proposed to obtain the intercept, the slopes of the three parameters length, maximum width and maximum thickness as well as the random error. In addition, an ANN model was used as it allows the network to learn linear and nonlinear relationships between inputs and outputs. Performance evaluation of three different models was based on a compilation of different statistical error parameters and goodness-of-fit measures and the outcomes of the models were compared. ANN was found to be the most accurate and robust model for mass estimation with a root mean squared error (RMSE) of 6.55 g, mean absolute percentage error (MAPE) of 1.62%, and coefficient of efficiency (E) of 0.99 after validation. Therefore, it can be applied for mass estimation of mango fruits with highest accuracy and success rate of 96.7% compared to the other models in this study.
2011 Louisville, Kentucky, August 7 - August 10, 2011, 2011
ABSTRACT Bell pepper (Capsicum Annuum L.) is a fruit rich in pigments such as chlorophylls, antho... more ABSTRACT Bell pepper (Capsicum Annuum L.) is a fruit rich in pigments such as chlorophylls, anthocyanins and carotenoids which is dried to produce spices. The aim of this research was to test the feasibility of laser light for predicting moisture content changes during drying. Green (532 nm) and red light (635 nm) were applied to the pepper tissue at different drying conditions. Detection of discoloration during the drying process using a CCD camera was also investigated by comparing of the RGB color values with CIE L*, a*, b* color coordinates measured by a Minolta Colorimeter. Cross validation analysis showed the highest correlation between laser light at wavelengths of 532 and 635 nm for yellow pepper (R=0.93). On the contrary, the behavior of green and red light in samples with corresponding colors raises questions for the ability to predict moisture content changes. Additional studies are still required to determine the suitability of digital images as an alternative method to the colorimeter for the evaluation of color change during drying of bell pepper. The described optical technology may represent a basis for future in-line quality monitoring of drying processes.
This study explored the effects of calcium chloride (CaCl2) and calcium lactate (Ca-L) pretreatme... more This study explored the effects of calcium chloride (CaCl2) and calcium lactate (Ca-L) pretreatments prior to osmotic dehydration on physicochemical characteristics and consumer acceptance of dried papaya. Three different calcium concentrations [0.5, 1.5 and 2.5% (w/v)] were applied to samples before they were soaked in a 30 °Brix sucrose solution and subsequently dried at 70 °C. The results showed that the dried samples treated with calcium exhibited significantly lower moisture content, water activity, apparent density and shrinkage, while volume was higher when compared to the control. Calcium applications did not obviously influence sugar content of samples and maintained the quality of dried papaya in terms of colour and textural characteristics. Calcium chloride at 2.5% (w/v) was found to particularly impart undesirable bitterness to the dried papaya. In contrast, using 2.5% (w/v) Ca-L provided the best acceptance scores. Thus, the use of Ca-L could be an alternative to CaCl2 in the pretreatment of fruits prior to drying as it offers improved quality.
This study aimed to investigate the effect of air drying parameters such as temperature, specific... more This study aimed to investigate the effect of air drying parameters such as temperature, specific humidity and velocity, on non-enzymatic browning behaviour and on bio-active compounds and antioxidant properties of osmotically pretreated papayas. Convection drying was conducted under through-flow mode at four temperatures (50, 60, 70, 80 C), three air velocities (0.2, 0.5, 0.7 m/s) and two specific humidity levels (10, 25 g/kg dry air). Higher drying temperatures resulted in a significant decrease in moisture content and polyphenol oxidase activity, while degree of browning and 5-hydroxymethylfurfural increased. The antioxidant activity and total phenolic compounds increased with temperature and as well with decreasing air velocity. In contrast, specific humidity did not have a major effect on quality attributes of dried samples, except for carotenoid contents. This study has shown that drying parameters can decompose and/or enhance carotenoids contents in dried papayas. To obtain the product with highest level of bio-active compounds and lowest possible melanoid formation, treatment with temperature of 70 C, specific humidity of 10 g/kg dry air and velocity of 0.2 m/s proved to be the most suitable option. Based on these results, optimization of the process, particularly drying temperature, should be considered with respect to preserving product colour and biochemical properties.
Longan is one of the most widely cropped fruits in Northern Thailand, where a significant amount ... more Longan is one of the most widely cropped fruits in Northern Thailand, where a significant amount of the annual harvest is commercially dried and exported as a commodity. Liquefied petroleum gas is generally used as the energy source for heating the drying air, but concern is growing as fuel prices are expected to increase for the foreseeable future. Meanwhile, with the ample solar radiation in Thailand, the roofs of drying facilities could be adapted to serve as solar collectors to preheat the drying air, thus reducing the energy requirement from fossil fuels. In this study, a simulation program for a flat-plate solar air heater was used to estimate the potential to preheat drying air given the conditions of several longan drying facilities. Results showed that solar collectors can replace up to 19.6% of the thermal energy demand during the drying season. Bigger collectors and smaller air channels result in more useful heat, but attention has to be paid to costs and pressure drop, respectively. Annual monetary savings can reach up to THB 56,000 (zUS$ 1800 at US$ 1 ¼ THB 31).
International Journal of Food Science & Technology, 2011
ABSTRACT Litchi is a significant cash crop in Thailand, but marketing is constrained by the peris... more ABSTRACT Litchi is a significant cash crop in Thailand, but marketing is constrained by the perishable nature of the fruit. Drying can extend the shelf life of the fruit; however, in Thailand drying technology is still in its early stages of development. With the aim of improving locally available small-scale drying equipment, the performance of a litchi batch-dryer by a farmers’ cooperative near Chiang Mai was studied. Drying conditions, energy consumption and product quality were monitored over three trials. Energy performance was analysed using instantaneous indices, leading to suggestions for possible design-modifications. About 29.8% of the heat input was used for moisture evaporation, 38.4% was lost via unsaturated exhaust air and 17.6% was lost to the ambient environment. An optimum air flow rate, one that minimises exhaust heat losses without increasing the drying time, was calculated. Temperature and air flow within the drying chamber varied, resulting in a non-uniform batch. To improve performance, a new design for the drying chamber air inlet is recommended.
The objective of this research was to study the eVect of osmotic pretreatment with combined anti-... more The objective of this research was to study the eVect of osmotic pretreatment with combined anti-browning agents (acid, glycerol and/or trehalose) on the colour characteristics of dried litchi after drying and during 5 months of storage compared to samples without pretreatment. The pretreated samples showed good inhibition of polyphenol oxidase activity when compared with the control, while the total phenolic contents in the dried products were not reduced. The results demonstrated that water activity, lightness diVerence, chroma, degree of browning (DB), and 5hydroxymethylfurfural values of all pretreated samples increased, while hue angle decreased with storage time. Samples pretreated with glycerol showed the best potential for browning retardation, followed by glycerol combined with trehalose, and trehalose, respectively. In addition, the colour parameters were used to calculate the luminescence values, representing the data in grey scale, which were correlated with a non-enzymatic browning index. The results showed grey value could be adequately used to represent the DB of dried litchi with r 2 value of 0.92.
The impact of airflow direction, namely through-flow and over-flow modes, on drying kinetics of o... more The impact of airflow direction, namely through-flow and over-flow modes, on drying kinetics of osmotically-pretreated papayas was investigated in a convective-type dryer under varied conditions (temperature, humidity and velocity). The Newton model was used to describe thin-layer drying characteristics and the dependence of drying air parameters on the drying constant (k) was expressed by an Arrhenius-type relationship. It was found that a more uniform airflow distribution in the through-flow chamber resulted in higher product temperature as well as faster drying rate, especially during the initial stage of drying. For both airflow modes, drying kinetics was most significantly influenced by temperature and velocity of the air, whereas the specific humidity had less effect on the drying rate. The value of k increased in parallel with temperature and velocity of the drying air, whereas it was reduced by increasing humidity. A model incorporating the conditions of drying air was developed for each airflow mode, which can help with optimization of practical drying operations.
International Journal of Food Science & Technology, 2014
This study explored the effects of calcium chloride (CaCl 2 ) and calcium lactate (Ca-L) pretreat... more This study explored the effects of calcium chloride (CaCl 2 ) and calcium lactate (Ca-L) pretreatments prior to osmotic dehydration on physicochemical characteristics and consumer acceptance of dried papaya. Three different calcium concentrations [0.5, 1.5 and 2.5% (w/v)] were applied to samples before they were soaked in a 30°Brix sucrose solution and subsequently dried at 70°C. The results showed that the dried samples treated with calcium exhibited significantly lower moisture content, water activity, apparent density and shrinkage, while volume was higher when compared to the control. Calcium applications did not obviously influence sugar content of samples and maintained the quality of dried papaya in terms of colour and textural characteristics. Calcium chloride at 2.5% (w/v) was found to particularly impart undesirable bitterness to the dried papaya. In contrast, using 2.5% (w/v) Ca-L provided the best acceptance scores. Thus, the use of Ca-L could be an alternative to CaCl 2 in the pretreatment of fruits prior to drying as it offers improved quality.
Moisture sorption dynamics and isotherms of fresh, osmotically-pretreated and dried papayas at te... more Moisture sorption dynamics and isotherms of fresh, osmotically-pretreated and dried papayas at temperatures of 30, 50 and 70°C and water activity in the range of 0.113-0.907 were investigated. Chemical composition as well as volume, density, porosity and microstructure of the fruits were analysed. Results showed that the time required to reach equilibrium moisture content was mainly dependent on temperature, water activity level and processing method. The difference in moisture sorption characteristics between fresh, pretreated and dried papayas was attributed to (i) changes in the contents of sugars after osmotic dehydration and (ii) structural modifications caused by drying, which were corroborated by examination of micrographs. The differences in sorption were also proven by the selected isotherm models. The modified Halsey equation described the sorption behaviour of the pretreated and dried papayas, whereas the untreated, fresh samples were better predicted by the modified Oswin equation. Further indication that osmotic pretreatment and drying influenced the interaction between the sorption sites and water molecules was imparted by the values of isosteric heat of sorption (Q st ) for fresh and dried papayas at different temperatures.
Papaya has been identified as a valuable source of nutrients and antioxidants, which are benefici... more Papaya has been identified as a valuable source of nutrients and antioxidants, which are beneficial for human health. To preserve the nutritional properties after drying, appropriate storage specifications should be considered. This study aimed to investigate the quality and stability of air-dried papaya in terms of quality dynamics and behavior of bio-active compounds during storage for up to 9months in two packaging materials: aluminum laminated polyethylene and polyamide/polyethylene. Samples with moisture content (MC) of 0.1328gg(-1) and water activity (aw) of 0.5 were stored at 30°C and relative humidity (RH) of 40-50%. The MC, aw, degree of browning (DB) and 5-hydroxymethylfurfural (HMF) content were found to notably increase as storage progressed. On the contrary, there was a significant decrease in antioxidant capacity (DPPH, FRAP and ABTS), total phenolic (TP) and ascorbic acid (AA) contents. Packaging in aluminum laminated polyethylene under ambient conditions was found to better preserve bio-active compounds and retard increases in MC, aw and DB, when compared to polyamide/polyethylene.
This article presents the thin-layer drying of peeled litchi, which was conducted under controlle... more This article presents the thin-layer drying of peeled litchi, which was conducted under controlled conditions of temperature and relative humidity. It was observed that the drying temperature has some influence on the drying rates of peeled litchi, so that the higher the temperature the less the drying time. Eight different thin-layer models were fitted to the experimental data of peeled
Modifications including air deflector installations in the plenum and insulation to improve perfo... more Modifications including air deflector installations in the plenum and insulation to improve performance of an industrial longan dryer were evaluated. Trials were carried out at a commercial drying facility according to industrial practices. Analyses of drying conditions, product quality and energy consumption were conducted. The study found that air velocity distribution was improved by plenum modifications and heat supply was more consistent after insulation. Modifications increased drying uniformity and insulation produced more homogenous product color. Evaluation of dryer performance showed that inverted mesh in the plenum and insulation reduced energy demand and increased efficiency by 1.51-4.27% respective of dryer modification. Cost savings of US$ 4-10 per batch were calculated with an estimated payback period of 5-12 batches. In conclusion, simple modifications of this dryer type show potential for improving product uniformity, reducing energy requirement and increasing profitability. Combination of the best modifications is recommended for further research.
Agricultural Water Management an International Journal, Feb 1, 2007
W. Spreer). a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e... more W. Spreer). a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / a g w a t 0378-3774/$ -see front matter #
ABSTRACT : View final version online for free until July 3, 2015, on ScienceDirect: http://www.sc... more ABSTRACT : View final version online for free until July 3, 2015, on ScienceDirect: http://www.sciencedirect.com/science/article/pii/S0168169915001209 Abstract: To meet consumer demands, the need for quick and accurate methods for quality assessment of fresh fruits is increasing constantly. This study presents a comparison of three different models for mass estimation of mango fruits (cv. ‘Nam Dokmai’) calculated by simple linear regression (SLR), multiple linear regression (MLR) and artificial neural network (ANN). Three dimensions (length, maximum width, and maximum thickness) were manually measured and included as parameters for model building. Calibration and validation were carried out on independent data sets with 820 samples (2010–2012) and 61 samples (2014), respectively. This allowed it to establish a high-performance model that can be used for further mass-size estimation in a machine-vision system. For the SLR, an existing equation for mass estimation was modified to calculate an adjusted coefficient for accurate mass estimation. A MLR model was proposed to obtain the intercept, the slopes of the three parameters length, maximum width and maximum thickness as well as the random error. In addition, an ANN model was used as it allows the network to learn linear and nonlinear relationships between inputs and outputs. Performance evaluation of three different models was based on a compilation of different statistical error parameters and goodness-of-fit measures and the outcomes of the models were compared. ANN was found to be the most accurate and robust model for mass estimation with a root mean squared error (RMSE) of 6.55 g, mean absolute percentage error (MAPE) of 1.62%, and coefficient of efficiency (E) of 0.99 after validation. Therefore, it can be applied for mass estimation of mango fruits with highest accuracy and success rate of 96.7% compared to the other models in this study.
2011 Louisville, Kentucky, August 7 - August 10, 2011, 2011
ABSTRACT Bell pepper (Capsicum Annuum L.) is a fruit rich in pigments such as chlorophylls, antho... more ABSTRACT Bell pepper (Capsicum Annuum L.) is a fruit rich in pigments such as chlorophylls, anthocyanins and carotenoids which is dried to produce spices. The aim of this research was to test the feasibility of laser light for predicting moisture content changes during drying. Green (532 nm) and red light (635 nm) were applied to the pepper tissue at different drying conditions. Detection of discoloration during the drying process using a CCD camera was also investigated by comparing of the RGB color values with CIE L*, a*, b* color coordinates measured by a Minolta Colorimeter. Cross validation analysis showed the highest correlation between laser light at wavelengths of 532 and 635 nm for yellow pepper (R=0.93). On the contrary, the behavior of green and red light in samples with corresponding colors raises questions for the ability to predict moisture content changes. Additional studies are still required to determine the suitability of digital images as an alternative method to the colorimeter for the evaluation of color change during drying of bell pepper. The described optical technology may represent a basis for future in-line quality monitoring of drying processes.
This study explored the effects of calcium chloride (CaCl2) and calcium lactate (Ca-L) pretreatme... more This study explored the effects of calcium chloride (CaCl2) and calcium lactate (Ca-L) pretreatments prior to osmotic dehydration on physicochemical characteristics and consumer acceptance of dried papaya. Three different calcium concentrations [0.5, 1.5 and 2.5% (w/v)] were applied to samples before they were soaked in a 30 °Brix sucrose solution and subsequently dried at 70 °C. The results showed that the dried samples treated with calcium exhibited significantly lower moisture content, water activity, apparent density and shrinkage, while volume was higher when compared to the control. Calcium applications did not obviously influence sugar content of samples and maintained the quality of dried papaya in terms of colour and textural characteristics. Calcium chloride at 2.5% (w/v) was found to particularly impart undesirable bitterness to the dried papaya. In contrast, using 2.5% (w/v) Ca-L provided the best acceptance scores. Thus, the use of Ca-L could be an alternative to CaCl2 in the pretreatment of fruits prior to drying as it offers improved quality.
This study aimed to investigate the effect of air drying parameters such as temperature, specific... more This study aimed to investigate the effect of air drying parameters such as temperature, specific humidity and velocity, on non-enzymatic browning behaviour and on bio-active compounds and antioxidant properties of osmotically pretreated papayas. Convection drying was conducted under through-flow mode at four temperatures (50, 60, 70, 80 C), three air velocities (0.2, 0.5, 0.7 m/s) and two specific humidity levels (10, 25 g/kg dry air). Higher drying temperatures resulted in a significant decrease in moisture content and polyphenol oxidase activity, while degree of browning and 5-hydroxymethylfurfural increased. The antioxidant activity and total phenolic compounds increased with temperature and as well with decreasing air velocity. In contrast, specific humidity did not have a major effect on quality attributes of dried samples, except for carotenoid contents. This study has shown that drying parameters can decompose and/or enhance carotenoids contents in dried papayas. To obtain the product with highest level of bio-active compounds and lowest possible melanoid formation, treatment with temperature of 70 C, specific humidity of 10 g/kg dry air and velocity of 0.2 m/s proved to be the most suitable option. Based on these results, optimization of the process, particularly drying temperature, should be considered with respect to preserving product colour and biochemical properties.
Longan is one of the most widely cropped fruits in Northern Thailand, where a significant amount ... more Longan is one of the most widely cropped fruits in Northern Thailand, where a significant amount of the annual harvest is commercially dried and exported as a commodity. Liquefied petroleum gas is generally used as the energy source for heating the drying air, but concern is growing as fuel prices are expected to increase for the foreseeable future. Meanwhile, with the ample solar radiation in Thailand, the roofs of drying facilities could be adapted to serve as solar collectors to preheat the drying air, thus reducing the energy requirement from fossil fuels. In this study, a simulation program for a flat-plate solar air heater was used to estimate the potential to preheat drying air given the conditions of several longan drying facilities. Results showed that solar collectors can replace up to 19.6% of the thermal energy demand during the drying season. Bigger collectors and smaller air channels result in more useful heat, but attention has to be paid to costs and pressure drop, respectively. Annual monetary savings can reach up to THB 56,000 (zUS$ 1800 at US$ 1 ¼ THB 31).
International Journal of Food Science & Technology, 2011
ABSTRACT Litchi is a significant cash crop in Thailand, but marketing is constrained by the peris... more ABSTRACT Litchi is a significant cash crop in Thailand, but marketing is constrained by the perishable nature of the fruit. Drying can extend the shelf life of the fruit; however, in Thailand drying technology is still in its early stages of development. With the aim of improving locally available small-scale drying equipment, the performance of a litchi batch-dryer by a farmers’ cooperative near Chiang Mai was studied. Drying conditions, energy consumption and product quality were monitored over three trials. Energy performance was analysed using instantaneous indices, leading to suggestions for possible design-modifications. About 29.8% of the heat input was used for moisture evaporation, 38.4% was lost via unsaturated exhaust air and 17.6% was lost to the ambient environment. An optimum air flow rate, one that minimises exhaust heat losses without increasing the drying time, was calculated. Temperature and air flow within the drying chamber varied, resulting in a non-uniform batch. To improve performance, a new design for the drying chamber air inlet is recommended.
The objective of this research was to study the eVect of osmotic pretreatment with combined anti-... more The objective of this research was to study the eVect of osmotic pretreatment with combined anti-browning agents (acid, glycerol and/or trehalose) on the colour characteristics of dried litchi after drying and during 5 months of storage compared to samples without pretreatment. The pretreated samples showed good inhibition of polyphenol oxidase activity when compared with the control, while the total phenolic contents in the dried products were not reduced. The results demonstrated that water activity, lightness diVerence, chroma, degree of browning (DB), and 5hydroxymethylfurfural values of all pretreated samples increased, while hue angle decreased with storage time. Samples pretreated with glycerol showed the best potential for browning retardation, followed by glycerol combined with trehalose, and trehalose, respectively. In addition, the colour parameters were used to calculate the luminescence values, representing the data in grey scale, which were correlated with a non-enzymatic browning index. The results showed grey value could be adequately used to represent the DB of dried litchi with r 2 value of 0.92.
The impact of airflow direction, namely through-flow and over-flow modes, on drying kinetics of o... more The impact of airflow direction, namely through-flow and over-flow modes, on drying kinetics of osmotically-pretreated papayas was investigated in a convective-type dryer under varied conditions (temperature, humidity and velocity). The Newton model was used to describe thin-layer drying characteristics and the dependence of drying air parameters on the drying constant (k) was expressed by an Arrhenius-type relationship. It was found that a more uniform airflow distribution in the through-flow chamber resulted in higher product temperature as well as faster drying rate, especially during the initial stage of drying. For both airflow modes, drying kinetics was most significantly influenced by temperature and velocity of the air, whereas the specific humidity had less effect on the drying rate. The value of k increased in parallel with temperature and velocity of the drying air, whereas it was reduced by increasing humidity. A model incorporating the conditions of drying air was developed for each airflow mode, which can help with optimization of practical drying operations.
International Journal of Food Science & Technology, 2014
This study explored the effects of calcium chloride (CaCl 2 ) and calcium lactate (Ca-L) pretreat... more This study explored the effects of calcium chloride (CaCl 2 ) and calcium lactate (Ca-L) pretreatments prior to osmotic dehydration on physicochemical characteristics and consumer acceptance of dried papaya. Three different calcium concentrations [0.5, 1.5 and 2.5% (w/v)] were applied to samples before they were soaked in a 30°Brix sucrose solution and subsequently dried at 70°C. The results showed that the dried samples treated with calcium exhibited significantly lower moisture content, water activity, apparent density and shrinkage, while volume was higher when compared to the control. Calcium applications did not obviously influence sugar content of samples and maintained the quality of dried papaya in terms of colour and textural characteristics. Calcium chloride at 2.5% (w/v) was found to particularly impart undesirable bitterness to the dried papaya. In contrast, using 2.5% (w/v) Ca-L provided the best acceptance scores. Thus, the use of Ca-L could be an alternative to CaCl 2 in the pretreatment of fruits prior to drying as it offers improved quality.
Moisture sorption dynamics and isotherms of fresh, osmotically-pretreated and dried papayas at te... more Moisture sorption dynamics and isotherms of fresh, osmotically-pretreated and dried papayas at temperatures of 30, 50 and 70°C and water activity in the range of 0.113-0.907 were investigated. Chemical composition as well as volume, density, porosity and microstructure of the fruits were analysed. Results showed that the time required to reach equilibrium moisture content was mainly dependent on temperature, water activity level and processing method. The difference in moisture sorption characteristics between fresh, pretreated and dried papayas was attributed to (i) changes in the contents of sugars after osmotic dehydration and (ii) structural modifications caused by drying, which were corroborated by examination of micrographs. The differences in sorption were also proven by the selected isotherm models. The modified Halsey equation described the sorption behaviour of the pretreated and dried papayas, whereas the untreated, fresh samples were better predicted by the modified Oswin equation. Further indication that osmotic pretreatment and drying influenced the interaction between the sorption sites and water molecules was imparted by the values of isosteric heat of sorption (Q st ) for fresh and dried papayas at different temperatures.
Papaya has been identified as a valuable source of nutrients and antioxidants, which are benefici... more Papaya has been identified as a valuable source of nutrients and antioxidants, which are beneficial for human health. To preserve the nutritional properties after drying, appropriate storage specifications should be considered. This study aimed to investigate the quality and stability of air-dried papaya in terms of quality dynamics and behavior of bio-active compounds during storage for up to 9months in two packaging materials: aluminum laminated polyethylene and polyamide/polyethylene. Samples with moisture content (MC) of 0.1328gg(-1) and water activity (aw) of 0.5 were stored at 30°C and relative humidity (RH) of 40-50%. The MC, aw, degree of browning (DB) and 5-hydroxymethylfurfural (HMF) content were found to notably increase as storage progressed. On the contrary, there was a significant decrease in antioxidant capacity (DPPH, FRAP and ABTS), total phenolic (TP) and ascorbic acid (AA) contents. Packaging in aluminum laminated polyethylene under ambient conditions was found to better preserve bio-active compounds and retard increases in MC, aw and DB, when compared to polyamide/polyethylene.
This article presents the thin-layer drying of peeled litchi, which was conducted under controlle... more This article presents the thin-layer drying of peeled litchi, which was conducted under controlled conditions of temperature and relative humidity. It was observed that the drying temperature has some influence on the drying rates of peeled litchi, so that the higher the temperature the less the drying time. Eight different thin-layer models were fitted to the experimental data of peeled
Modifications including air deflector installations in the plenum and insulation to improve perfo... more Modifications including air deflector installations in the plenum and insulation to improve performance of an industrial longan dryer were evaluated. Trials were carried out at a commercial drying facility according to industrial practices. Analyses of drying conditions, product quality and energy consumption were conducted. The study found that air velocity distribution was improved by plenum modifications and heat supply was more consistent after insulation. Modifications increased drying uniformity and insulation produced more homogenous product color. Evaluation of dryer performance showed that inverted mesh in the plenum and insulation reduced energy demand and increased efficiency by 1.51-4.27% respective of dryer modification. Cost savings of US$ 4-10 per batch were calculated with an estimated payback period of 5-12 batches. In conclusion, simple modifications of this dryer type show potential for improving product uniformity, reducing energy requirement and increasing profitability. Combination of the best modifications is recommended for further research.
Image processing techniques are increasingly applied in sorting applications of agricultural prod... more Image processing techniques are increasingly applied in sorting applications of agricultural products. This work has assessed the use of image processing for inspecting surface color of two Thai mango cultivars. A computer vision system (CVS) was developed and experiments were conducted to monitor peel color change during the ripening process. Conversion of RGB to CIE-LAB values was done via image processing and prediction models were developed to estimate color parameters from CVS data. Performance evaluations showed insufficient prediction for L values (R2 = 0.42-0.58), but better results for A and B values (R2 = 0.90-0.95 and 0.80-0.82, respectively). Compared to the calculated color values hue angle and chroma, a yellowness index computed from intermediate XYZ values was found to be much more adept at accurately predicting peel color from CVS data. Correlations were strong for both cultivars (R2 = 0.93 for ‘Nam Dokmai' and R2 = 0.95 for ‘Maha Chanok'). Results from classification analysis indicated satisfactory results for classifying fruits according to ripeness based on yellowness. Success rates of true positives in the categories unripe, ripe and overripe ranged 72{\%}-92{\%} for ‘Nam Dokmai' and 98{\%}-100{\%} for ‘Maha Chanok'. Therefore, it was shown that the CVS was capable of producing accurate color values for the two mango cultivars investigated. The findings of this study can be incorporated for development of a robust system for quality prediction and establishment of a CVS for automatic grading and sorting of mangos.
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