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This study aimed to assess the feasibility of a multi-sensor approach for predicting shrinkage of papaya during drying using computer vision methods in combination with optical scattering analysis of light at 650 nm. The top-side area and total surface area derived from computer vision were analyzed, while the illuminated area and light intensity from optical scattering images were used to interpret photon migration in the fruit tissue. The relationship between moisture content and shrinkage in terms of volume and area reduction during drying was satisfactorily explained by a linear model. The results demonstrated that the prediction of papaya shrinkage during drying from top and total surface areas of the sample was possible, but can potentially be improved. Multivariate correlations of computer vision parameters and optical scattering properties showed the enhanced performance for shrinkage prediction. This multi-sensor approach could possibly be applied as a fast, accurate and non-invasive technique for in-line quality control to monitor shrinkage in the production of dried fruits. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract: Non-invasive, sensor-based technologies are increasingly considered as preferred methods for evaluating quality attributes of agricultural products. This study investigated the feasibility of a laser light backscattering analysis at three wavelengths (532, 650, 780 nm) for predicting moisture content (MC), shrinkage (S), lightness (L*), chroma (C*) and hue (h*) changes of papaya during drying. Convective hot air drying was conducted at four temperatures (50, 60, 70, 80 °C), during which time the product was sampled and subjected to non-destructive optical analysis as well as reference measurements. From laser images, the illuminated area (A I ) and light intensity (I L ) were used to assess the backscattering profiles that represent photon migration in the fruit tissue. As expected, drying temperatures significantly affected the quality attributes of dehydrated papayas. Increasing drying temperature resulted in a decrease in MC, L*, and C* values, whereas h* and S values were increased. The results also revealed that each backscattering factor obtained can potentially be used to describe each quality change, except for C* value. In addition, multivariate correlations of measured A I and I L parameters at 650 nm wavelength were found to precisely yield the best fit for MC, L*, and h* predictions (R 2 > 0.92). Therefore, the study concludes that the use of laser backscattering methods provides a useful tool for quality control as a rapid, consistent, non-intrusive and objective method for in-line measurement of product quality in fruit drying processes. [Copyright &y& Elsevier]

The objective of this research was to study the effect 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 difference, chroma, degree of browning (DB), and 5-hydroxymethylfurfural 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 r2 value of 0.92. [ABSTRACT FROM AUTHOR]