Yacon Slices Research Articles

Secagem por microondas a vácuo de Yacon pré-tratado por desidratação osmótica pulsada como alternativa de preservação de fruto-oligosacarídeos

ABSTRACT Yacon, a perennial plant from the Andean region, is particularly rich in fructo-oligosaccharides (FOS) and inulin. However, these saccharides are rapidly hydrolyzed after harvest, affecting the functional characteristics of yacon. Therefore, a preservation technology such as drying is warranted to preserve the FOS content of yacon products during the off-season. To this end, we dried yacon slices, either untreated or pretreated with pulsed vacuum osmotic dehydration (PVOD), in a microwave vacuum (MWV). PVOD was performed using a sorbitol solution (38 °Brix, 35 °C, and 681 mmHg during the first 10 min). A three-level experimental design with three initial power densities (PDs) of 3.6, 6.3, and 9.9 W.g−1 and three vacuum pressures (VPs) of 0, 300, and 600 mmHg was employed to perform the MWV drying experiments. FOS content, drying kinetics, diffusivity, shrinkage, yacon temperature, and rehydration were investigated. We observed that during PVOD, as microwave PD increased, the drying time, moisture, and water activity decreased. Moreover, an increase in PD positively affected FOS retention, diffusivity, temperature, and shrinkage. Furthermore, VP significantly affected FOS retention in pretreated samples and facilitated drying. In addition, microwaves with a higher PD increased the effective diffusivity and facilitated FOS retention. VP also affected the drying and FOS retention of pretreated samples. In general, yacon browning was observed under all treatment conditions, independent of pretreatment. For osmotically dehydrated samples, processing conditions with a PD of 9.9 W.g−1 and vacuum pressure of 600 mmHg are ideal for drying yacon slices via microwave vacuum, thereby increasing the FOS content by approximately 40%.

Process and quality parameters of convective dried yacon: Influence of ethanol treatment

Yacon is a highly perishable tuberous root, rich in fructooligosaccharides (FOS). Convective drying preceded by ethanol treatment (ET) is an alternative for increasing shelf life in a shorter process. The aim of this study was to investigate the impact of ET and temperature (50 °C and 70 °C) on quality parameters (fructan retention, total phenolic content, antioxidant capacity, shrinkage, color and microstructural parameters) and process parameters (drying time, drying kinetics, and energy consumption) in the convective drying of yacon slices. The ET induced structural alterations in the tissues and cells that aids in the reduction of drying time up to 28.00 %. ET resulted in an increase in effective diffusivity and leaded to noteworthy reduction in energy consumption (up to 22.72 %). The quality parameters such as color, shrinkage, and total phenolic content showed no significant differences among the treatments. The use of ethanol promoted highest preservation of antioxidant activity; however, it caused degradation of FOS. The ethanol pretreated drying at 50 °C was the better condition for lower consumption and preservation of quality parameters as total phenolic content, antioxidant capacity and fructan retention, but the samples dried at 50 °C were the ones with the highest fructan retention (55.11 ± 2.19 %).

Dried yacon with high fructooligosaccharide content

AbstractThe convective drying of yacon was investigated (40–70°C). Pulsed vacuum osmotic dehydration (PVOD) (sorbitol 38 °Brix, 35°C, 681 mmHg in the first 10 min) as pretreatment was tested. Drying behavior, energy consumption, diffusivity, fructooligosaccharide (FOS) retention, shrinkage, water activity, shrinkage, and color were measured. Fick's model was adequate for drying kinetics adjustment, mainly for untreated samples with shrinkage consideration. PVOD pretreated dried yacon was a less shrunken product in a shorter drying time with up to 60% FOS retention. Nevertheless, the best tested condition for FOS retention (88%) was the convective drying at 60°C without PVOD application.Practical ApplicationsThe yacon is a seasonal plant that presents high concentrations of functional compounds. Like most vegetables, its shelf life is short and storage difficult. Therefore, improved techniques for conservation are required. The present paper evaluates the effects of drying temperature on the production of fresh and osmodehydrated yacon slices during convective drying. This study could offer an interesting response to the changes promoted by these processes, relating to the modifications to the physicochemical properties of osmodehydrated yacon.

Yacon-based Beverage as Non-dairy Vehicle for Bifidobacterium animalis ssp. lactis: Stability and In vitro Probiotic Viability

Probiotics are health-promoting microorganisms commonly applied to functional foods. Dairy products are the most common source of probiotics, which difficult probiotics’ consumption by lactose intolerants. In this work, a yacon-based (Smallanthus sonchifolius) beverage was evaluated as a non-dairy vehicle for probiotics (Bifidobacterium animalis ssp. lactis, BB-12®), concerning stability and probiotics viability, during 28 days. x The yacon-based beverage was properly obtained. To determine the better treatment to stabilize it during storage, combined treatments were optimized via experimental design, and the color stability evaluated the initial changes. The beverage was incubated with the probiotic strain Bifidobacterium animalis ssp. lactis and the fermentation were carried out at 45 °C and 35 °C for 10 h in anaerobic jars. The storage viability was evaluated for 28 days, and the viable cell counting was carried out every seven days. A combination of the immersion of yacon slices into ascorbic acid 0.5% (w/v), blanching (3 min), and the addition of 0.4% (w/v) of ascorbic acid as an antioxidant was the most promising treatment to maintain color stability. Moreover, the fermentation applying 35 °C maintained the beverage with probiotic status for 14 days. In this work, a probiotic beverage was proposed, with potential health benefits, based on an underused root with great productivity, which will result in a potential low-cost probiotic product compared to dairy-based probiotic beverages.

Reuse of sorbitol solution in pulsed vacuum osmotic dehydration of yacon (Smallanthus sonchifolius)

The osmotic solution (OS) used in pulsed vacuum osmotic dehydration (PVOD) could represent an environmental problem. The reuse of the solution minimizes the cost, but has to consider the properties of the dehydrated product and the solution itself. The reuse of sorbitol solution, 38 kg/100 kg solution, in 15 successive PVOD of yacon slices (35°C, 300 min) was studied. The evaluation was based on alterations of soluble solids, water activity, pH, turbidity, electrical conductivity, viscosity, density, color, and microbiological stability. The weight loss, moisture content, and soluble solids of the food were also evaluated. Among the OS characteristics, only the color, electrical conductivity, and turbidity of the solution changed significantly, alterations that could be reduced with filtration. The food properties were not significantly affected. The microbiological content was retained in acceptable levels. The reuse of the sorbitol solution could be performed without relevant alterations in the food or the solution. Practical applications The osmotic solution is used in osmotic dehydration to promote a partial removal of the moisture content of the food. However, after the osmotic process, the solution is diluted and contains native solutes from the food. For obtaining a dehydrated product within a standard production, the solution should also present standard characteristics. This works presents the evolution of some analysis as soluble solids, water activity, pH, turbidity, electrical conductivity, viscosity, density, color, and microbiological stability in a solution of sorbitol. Sorbitol solution is an alternative to sucrose for obtaining semidehydrated products with glycemic index. It was shown that the solution could be used for at least 15 times in yacon dehydration.

A Novel Color Parametric Technique for Kinetic Evaluation of Thermal Degradation and Stability of Fresh-Cut Yacon Slices

Abstract Fresh-cut yacon slices were first heat treated (60–80 °C, 5–25 min) and then exposed to air at room temperature for up to 10 min. Color parameters of internal surface were measured and two kinetic models were evaluated: 1) Color degradation during thermal treatment, and 2) Color stability during subsequent air exposure. More severe treatments led to lower color quality but higher stability. The relative white index was the best color parameter and the color changes followed a zero-order kinetics. The temperature dependence of rate constants were evaluated using the Arrhenius model. The activation energy for color degradation was 14.7 kJ/mol, and for color stability it was 47.9 kJ/mol indicating color stability parameters to be more sensitive to temperatures than color degradation. The color parameter models developed were comparable to polyphenoloxidase inactivation model and provided a rapid physical method for evaluating color degradation and subsequent color stability of yacon slices.

Mass Transfer Kinetics of the Osmotic Dehydration of Yacon Slices with Polyols

Osmotic dehydration using different polyols was studied. Yacon slices were immersed in solutions of xylitol, maltitol, erythritol, isomalt and sorbitol. The kinetics of solid gain (SG), water loss (WL) and water activity (aw) were evaluated (0, 10, 30, 45, 60, 90 and 120 min). The effective diffusion coefficients of water (Dₑffw) and solids (Dₑffₛ) were calculated with the models of Fick and Barbosa Junior et al. At the end of the process, the highest SG was obtained with erythritol solutions; the lowest with sorbitol and maltitol and intermediate values of SG were acquired in osmotic processes with solutions of isomalt and xylitol. The samples treated in sorbitol, xylitol and erythritol solutions presented the highest Dₑffw and were more effective at increasing WL and reducing aw. The model of Barbosa Junior et al. presented the best fitness. The Dₑffw/Dₑffₛ ratio showed better results for osmotic processes involving sorbitol and xylitol. PRACTICAL APPLICATIONS: Yacon tuber is typical from Latin America. It is considered an important source of fructooligosaccharides (FOS). This class of carbohydrate is employed on the control of diseases such as obesity and diabetes, due its low glycemic index. However, yacon roots are highly perishable and techniques for conservation are required. Osmotic dehydration is a pretreatment process that provides partial water removal from a food product, with low energy consumption. Polyols are widely employed as osmotic agents due their low caloric value. The kinetics of mass transfer on osmotic process are function of process variables, sample matrix characteristics, molecular weight of osmotic agents and others. This study investigate the water loss, solid gain, effective diffusivity and water activity of the OD of yacon with five different polyols and provide information about mass transfer kinetics of osmotic processes using two different empirical models.

Osmotic dehydration of yacon (Smallanthus sonchifolius): Optimization for fructan retention

Yacon presents prebiotic and hypoglycemic properties with a high fructan content. Pulsed vacuum osmotic dehydration (PVOD) is a process that can reduce water activity with small variations in nutritional properties. Yacon slices were dehydrated with two different solutions: fructose and sorbitol. The experiments were based on a central composite rotational design and the optimum condition set for the highest retention of fructans. The PVOD experiments were performed in 300 min, with vacuum pulse in the first 10 min. The independent variables were temperature (24–44 °C), vacuum pressure (49.4–200.6 mmHg) and osmotic solution concentration (22.0–60.8 °Brix). The dependent variables were fructan retention, weight reduction, water loss, solid gain, water activity and total color difference. The highest fructan retention was obtained with sorbitol, ranging from 28.13 to 82.03%, in contrast to the range of 2.79–39.48% obtained for the sample dehydrated with fructose. The optimum PVOD condition with sorbitol was concentration of 38 °Brix, temperature of 35 °C and vacuum pressure of 74 mmHg. For PVOD with fructose, the best results were obtained with a solution concentration of 35 °Brix, temperature between 24 and 30 °C and vacuum pulse above 100 mmHg.

Evaluating Strategies to Control Enzymatic Browning of Minimally Processed Yacon (Smallanthus sonchifolius)

To control enzymatic browning in minimally processed yacon (Smallanthus sonchifolius), strategies combining anti-browning agents and modified atmosphere were investigated. Yacon slices were immersed in anti-browning agent solutions—sodium metabisulfite (0.5 %), L-cysteine (0.5 %), or the acids lactic (1 %), malic (1 %), succinic (1 %), ethylenediaminetetraacetic (EDTA; 1 %), ascorbic (3 %), citric (3 %) or tartaric (3 %), or a control (0.5 % de sugar)—for 5 min, then packaged with air or modified atmosphere (N2) and stored at 5 °C. Sensory and physical-chemical (soluble solids, phenolic content, peroxidase activity, pH, color, instrumental texture, and mass variation) analyses were performed. For a given anti-browning agent, any significant difference was not found between yacon slices stored under air or N2. However, when comparing the different anti-browning agents, only ascorbic, citric, and tartaric acids were effective enzymatic browning inhibitors without significantly changing typical sensory attributes of yacon. Among them, tartaric acid is not often reported in literature for controlling enzymatic browning in vegetal products, contrarily to the two others.

Optimization of osmotic dehydration of yacon slices

ABSTRACTOsmotic dehydration assisted by ultrasound (ODAU) at low temperatures reduces water activity (aw) and maintains nutrients. The influence of solution concentration (SC; 20 to 60° Brix, xylitol and sorbitol) and ultrasound application time (tus, 0 to 40 min) in ODAU of yacon was studied with the aid of a response surface method. The optimum condition with respect to mass transfer parameters, aw, and fructan retention was SC of 60° Brix for both solutions and tus of 2.67 min for xylitol samples and 0 min for sorbitol samples. The application of ultrasound improved dehydration but resulted in depolymerization of fructans.

<b>Thermophysical properties of yacon (<i>Smallanthus sonchifolius</i>): experimental determination and effect of moisture content

The knowledge about thermophysical properties of foods is especially important in thermal processing, influencing the design, optimization and cost reduction of the process, as well as the quality and safety of the final product. This article deals with the determination of some thermophysical properties of yacon, namely, specific mass, specific heat, thermal conductivity and thermal diffusivity during the osmo-convective drying. Yacon is a root with approximately 90% w.b. of moisture content, whose high concentration of fructooligosacharydes and antioxidants has gained attention in the food research field. Yacon slices were osmotically dehydrated for 2 hours in a sucralose solution and then dried in a convective tray dryer for 2 hours, varying the osmotic solution’s temperature and stirring rate and temperature of the drying air. All thermophysical properties were determined during the drying process at 30-minute intervals. The thermophysical properties were determined not only experimentally but also calculated by models available in literature based on the product’s centesimal composition. A satisfactory agreement between experimental and predicted results was obtained. Further, empirical models obtained by nonlinear regression were successfully fitted to the experimental data, as a function of moisture content, within a 94% - 3% w.b. range.

Measurement parameter of color on yacon (Smallanthus sonchifolius) slices using a computer vision system

The aim of this research was to design, implement and calibrate a Computer Vision System (CVS), for use in real-time, in order to measure the color on minimally processed yacon slices. For this purpose, a device (software and hardware) was designed and implemented which consisted of two steps: a) image acquisition and b) image processing and analysis. For both, an algorithm and a graphical user interface (GUI) were developed in MatLab. CVS calibration was performed with a conventional colorimeter (Model CIE L*a*b*). Minimally processed yacon slices were obtained and stored at 5 °C. Color changes were estimated every 2 h, for 26 h, obtaining its color parameters. L* decreased from 65.9 to 60.8, with a tendency to a black color; a* increased from 7.3 to 17.7, approaching a red color; b* increased from 35.1 to 41.5, presenting a tendency to a yellow color. Moreover, C* increased from 35.9 to 40.1, H* decreased from 78.2 to 66.9 and ΔE* increased from 2.6 to 13.2. Low errors calculated (eL* = 5.001%, and ea* = 2.287%, and eb* = 4.314%) ensure suitable and efficient application in industrial process automation and quality control in the food industry.

Heat and mass transfer modeling of the osmo-convective drying of yacon roots (Smallanthus sonchifolius)

Osmotic treatments are often applied prior to convective drying of foods to impart sensory appeal aspects. During this process a multicomponent mass flow, composed mainly of water and osmotic agent, takes place. In this work, a heat and mass transfer model for the osmo-convective drying of yacon was developed and solved by the Finite Element Method using COMSOL Multiphysics®, considering a 2-D axisymmetric geometry and moisture dependent thermophysical properties. Yacon slices were osmotically dehydrated for 2 h in a solution of sucralose and then dried in a tray dryer for 3 h. The model was validated by experimental data of temperature, moisture content and sucralose uptake (R2 > 0.90).

Mathematical modeling on thin-layer heat pump drying of yacon (Smallanthus sonchifolius) slices

Heat pump drying kinetics and quality characteristics of yacon at different drying temperatures (5, 15, 25, 35 and 45°C) and air velocities (0.5, 1.0, 1.5 and 2.0m/s) were investigated. Results indicated that drying took place in the falling rate period. The drying temperature and air velocity had a significant effect on drying behavior of yacon slices. Drying time decreased with increasing drying temperature and air velocity. Eight mathematical models were selected to describe and compare the drying kinetics of yacon. Comparisons were based on the coefficient of determination (R2), reduced chi-square (χ2) and root mean square error (RMSE). Among the models tested, the Midilli et al. model achieved the best fit. Moisture transfer from yacon slice was described by applying the Fick’s diffusion model. Effective diffusivity coefficients (Deff) increased with increasing drying temperature and were found to range from 1.092 to 7.388×10−7m2/s. The temperature dependence of the effective diffusivity was described by the Arrhenius-type relationship and the activation energy for the diffusion of the moisture associated with the yacon was found to be 30.00kJ/mol. Drying temperature and air velocity had little effects (p>0.05) on the total color difference, shrinkage rate and rehydration rate of dried yacon slcies.

Antioxidants in yacon products and effect of long term storage

Yacon (Smallanthus sonchifolius (Poepp. and Endl.) H. Robinson) is a storage root originally grown in the Andean highlands. The fresh roots are perishable and quickly turn brown during handling and processing. Aiming to prolong shelf-life and to preserve the antioxidant compounds in yacon roots, 3 mm thick yacon slices were dried in a drying cabinet at 40, 50, and 60 ºC to a moisture content of 10-14%, and yacon strips were sun dried to a moisture content of 15-20%. The total phenolic content was measured by the Folin-Ciocalteu method, and the quenching capacity was evaluated by measuring the amount of DPPH (1,1-diphenyl-2-pidrylhydrazyl) inhibited in samples after drying and after 7 months of storage. The results showed that it is possible to preserve the antioxidant capacity in yacon after cabinet or sun drying. Both yacon chips and strips presented total phenolic content values similar to those of fresh yacon roots. Both products also showed a high inhibition capacity of DPPH (1,1-diphenyl-2-pidrylhydrazyl). A significant decrease in the phenolic content was observed in the yacon chips after storage, which indicates that the sun dried strips are more suitable for storage.

Vacuum Drying Kinetics of Yacon (Smallanthus sonchifolius) and the Effect of Process Conditions on Fractal Dimension and Rehydration Capacity

This work aimed at studying the drying kinetics of yacon slices during vacuum drying and evaluating the effect of drying temperature, slice thickness, and citric acid concentration in the enzymatic inhibition solution on the fractal dimension and rehydration ratio of yacon slices. The drying kinetics was tentatively fitted to various thin-layer drying models, and the best fit was obtained using the modified Page model. The fit was validated after evaluating the values of coefficient of determination and parameters percentage error. The final product's fractal dimension, as calculated by the box counting method, was be between 1.5904 and 1.8358, which confirms that vacuum-dried yacon slices are fractals. Among the studied factors, drying temperature was found to negatively affect the fractal dimension and slice thickness was found to negatively affect the rehydration ratio. A good correlation was established between fractal dimension and moisture content, rehydration ratio, and hue angle, suggesting that the moisture, rehydration, and color measurements during yacon vacuum drying could be substituted or complemented by an image analysis.

EFFECT OF VACUUM DRYING CONDITIONS ON THE QUALITY OF YACON (SMALLANTHUS SONCHIFOLIUS) SLICES: PROCESS OPTIMIZATION TOWARD COLOR QUALITY

This study was aimed at studying the effect of the drying temperature, slice thickness and citric acid concentration in the enzymatic browning inhibition solution on yacon slices' color and texture during vacuum drying and at optimizing the operation conditions toward final product quality. Color was expressed as CIE L*a*b* and CIE L*C*h* parameters, and texture was expressed as hardness. Vacuum drying caused decrease in L* and reflectance and increase in a* and b* values. Product hardness varied little on initial stages of drying, followed by softening and hardening. The effects of the factors on final product L* value and average value of b* and C* were very well fitted by polynomial models. The desirable product quality is represented by high L* values (low browning), high b* values (golden yellow color) and high C* values (high colorfulness), which can be achieved by combining high-drying temperature, low slice thickness and high acid concentration. PRACTICAL APPLICATIONS This work provides optimized drying conditions in order to obtain shelf-stable dried yacon with ideal appearance. Yacon is a functional tuber that is rich in phenolic compounds and dietary fiber. Appearance is the first quality attribute evaluated by consumers when choosing a food product. Vacuum drying showed to be appropriate for drying yacon, as lower temperatures can be used in this process. In this way, the functional and sensory features of yacon are preserved. This work can be used as a reference for drying yacon, increasing the shelf life of this food system while preserving its desirable original features.