Antonio Vega-Gálvez

Stevia rebaudiana Bertoni, source of a high-potency natural sweetener: A comprehensive review on the biochemical, nutritional and functional aspects

Stevia rebaudiana Bertoni, an ancient perennial shrub of South America, produces diterpene glycosides that are low calorie sweeteners, about 300 times sweeter than saccharose. Stevia extracts, besides having therapeutic properties, contain a high level of sweetening compounds, known as steviol glycosides, which are thought to possess antioxidant, antimicrobial and antifungal activity. Stevioside and rebaudioside A are the main sweetening compounds of interest. They are thermostable even at temperatures of up to 200°C, making them suitable for use in cooked foods. S. rebaudiana has a great potential as a new agricultural crop since consumer demand for herbal foods is increasing and proximate analysis has shown that Stevia also contains folic acid, vitamin C and all of the indispensable amino acids with the exception of tryptophan. Stevia cultivation and production would further help those who have to restrict carbohydrate intake in their diet; to enjoy the sweet taste with minimal calories.

Effect of temperature and air velocity on drying kinetics, antioxidant capacity, total phenolic content, colour, texture and microstructure of apple (var. Granny Smith) slices

The aim of this work was to study the effect of temperature and air velocity on the drying kinetics and quality attributes of apple (var. Granny Smith) slices during drying. Experiments were conducted at 40, 60 and 80°C, as well as at air velocities of 0.5, 1.0 and 1.5ms(-1). Effective moisture diffusivity increased with temperature and air velocity, reaching a value of 15.30×10(-9)m(2)s(-1) at maximum temperature and air velocity under study. The rehydration ratio changed with varying both air velocity and temperature indicating tissue damage due to processing. The colour difference, ΔE, showed the best results at 80°C. The DPPH-radical scavenging activity at 40°C and 0.5ms(-1) showed the highest antioxidant activity, closest to that of the fresh sample. Although ΔE decreased with temperature, antioxidant activity barely varied and even increased at high air velocities, revealing an antioxidant capacity of the browning products. The total phenolics decreased with temperature, but at high air velocity retardation of thermal degradation was observed. Firmness was also determined and explained using glass transition concept and microstructure analysis.

Effective moisture diffusivity determination and mathematical modelling of the drying curves of the olive-waste cake.

Olive cake is an important agro industrial by-product with the dried cake being the input material of many applications areas. In this research, the drying kinetics of olive cake during convective dehydration at five temperatures (50, 60, 70, 80 and 90 degrees C) was investigated. Several empirical mathematical models were selected to describe experimental drying kinetics data, namely, Page, Modified Page, Henderson and Pabis, Modified Henderson and Pabis, Two-Terms, Logarithmic and Weibull. Air temperature showed a significant effect on drying rates. Based on the statistical tests results (sum squared errors, chi-square and correlation coefficients), the Modified Henderson and Pabis equation is the most suitable model to describe the experimental drying curves. Effective moisture diffusivity of olive cake was in the range of 2.03x10(-9)-1.71x10(-9) m(2) s(-1). An activation energy value of 12.43 kJ mol(-1) was determined. The findings allow the successful simulation of olive cake drying between 50 and 90 degrees C.

Combined Infrared-Convective Drying of Murta (Ugni molinae Turcz) Berries: Kinetic Modeling and Quality Assessment

Murta (Ugni molinae Turcz) berries were dried under convective and combined convective-infrared conditions at 40, 50 and 60°C and 400–800 W in order to determine the drying characteristics and to compare the dried products quality. To model the drying kinetics, seven mathematical equations were fitted to experimental data. According to statistical tests performed, the Midilli-Kuçuk model best fitted experimental data and was closely followed by the logarithmic model. Effective moisture diffusivity also showed dependency on drying conditions and varied between 7.59 × 10−10 to 44.18 × 10−10 m2/s and 11.34 × 10−10 to 85.41 × 10−10 m2/s for air-convective drying and combined infrared-convective drying. As to quality attributes of the berries, total surface color difference (ΔE) and total phenolic content (TPC) were determined. It was found that chromaticity coefficients a* and b* changed significantly, showing ΔE to be dependent on the mode of heat supply. TPC under all drying conditions decreased and was significantly different from the initial value in fresh samples. However, at a constant drying temperature, an increase in infrared power enhanced retention of TPC in samples. In particular, working at 40°C/800 W resulted in dried samples with the highest TPC.

Effect of Osmotic Pretreatment on Hot Air Drying Kinetics and Quality of Chilean Papaya (Carica pubescens)

The effect of osmotic pretreatment on the mass transfer kinetics and quality of dried rehydrated Chilean papaya was researched. Osmotic treatments were sucrose solutions of 40, 50, and 60% w/w and dried at 60°C; non-pretreated samples were dried at different temperatures (40, 60, and 80°C). Quality parameters were analyzed: proximal composition, rehydration ratio, water-holding capacity, color, vitamin C content, firmness, and microstructure. Non-pretreated samples showed a clear turgor loss, color loss. and low ascorbic acid retention when rehydrated. Osmotic pretreatment improved the quality of rehydrated papayas, showing higher ascorbic acid retention and best firmness and color. Microstructure is better preserved in the pretreated papayas than in the non-pretreated samples, although this difference is minimal.

Effect of high hydrostatic pressure on functional properties and quality characteristics of Aloe vera gel (Aloe barbadensis Miller).

The aim of this study was to evaluate the effects of high hydrostatic pressure treatment at three pressure levels (300, 400 and 500Mpa) on the functional and quality characteristics of Aloe vera gel including vitamin C and E, aloin, minerals, phenolic content and antioxidant activity. The results show that HHP exerted a clear influence on minerals content, vitamin C and E content, antioxidant activity, total phenolic and aloin content. After 35days of storage all treated samples presented a decrease in mineral content, except for phosphorus. Total phenolic content and vitamin C and E content decreased at high pressures (500MPa), while all pressurised samples showed a higher antioxidant activity and aloin content than untreated sample after 35days of storage. The maximum values of antioxidant activity and aloin were 6.55±1.26μg/ml at 300MPa and 24.23±2.27mg/100g d.m. at 400MPa.

KINETIC STUDY OF CONVECTIVE DRYING OF BLUEBERRY VARIETY O'NEIL (Vaccinium corymbosum L.)

The aim of this research was to study and to model the drying kinetics of the blueberry (Vaccinium corymbosum L.) at three temperatures (60, 70 and 80 oC) with an airflow of 2.0 ± 0.2 m s -1. Modeling of the desorption isotherm was carried out with the GAB (Guggenheim, Anderson and de Boer) equation, showing a good fit to experimental moisture data, giving as a result a monolayer moisture level of 0.084 g water g-1 dm. Newton, Henderson-Pabis, Page, Modified Page and Logarithmic mathematical models were applied in the study and in the modeling of the drying kinetics of this fruit. Kinetic parameters k of each model showed dependence on temperature, and were evaluated by an Arrhenius-type equation, with an activation energy of between 36.2 and 54.5 kJ mol-1. Logarithmic and Modified Page models gave the best fits for each drying curve, based on the statistical test determination coefficient, sum square error, root mean sum errors and Chi-square. In consequence, both models are excellent tools for estimating the drying time of this product.

Influence of contrasting environments on seed composition of two quinoa genotypes: nutritional and functional properties

Quinoa ( Chenopodium quinoa Willd.) in Chile represents a source of germplasm with high nutritional value. However, there is little information available related to quinoa seed quality grown under contrasting environments. In this study we evaluated the changes on seed composition of seeds of two lowland/coastal quinoa genotypes grown under arid (Vicuna) and cold-temperate (Temuco) conditions in Chile. Results showed that in the case of ‘Regalona Baer’ and ‘Villarrica’ genotypes the arid location (with irrigation) led to a significant increase (P < 0.05) in grain yield (4.2 and 5.1 t ha-1, respectively), soluble dietary fiber (16.8± 0.4 and 28.9 ± 2.1 g kg-1 DM, respectively), vitamin B3 (2.44 ± 0.005 and 2.26 ± 0.04 mg 100 g-1 DM, respectively), saponins (3.22 ± 0.38 mg 100 g-1 DM, ‘Regalona Baer’), phenolic compounds (19.2 ± 5.48 and 31.92 ± 1.14 mg gallic acid 100 g-1 DM, respectively) and components of proximate analysis, except protein content. The cold-temperate climate (rainfed) affected positively seed size (2.22 ± 0.17 mm ‘Villarrica’) and 1000 seed weight (3.08 ±0.08 and 3.29 ± 0.08 g, respectively), as well as insoluble dietary fiber content (112.3 ± 23.8 g kg-1 DM, ‘Regalona Baer’). Furthermore, vitamin C was higher in ‘Regalona Baer’ genotype at arid locality (31.22 ±4.2 mg 100 g-1 DM), but much higher content was registered in ‘Villarrica’ genotype at cold-temperate climate (49.3 ± 5.36 mg 100 g-1 DM). The environment-induced relationship among variables and genotypes was consistent with principal component analysis (PCA). The arid region of Vicuna in Chile represents a potential area for quinoa cultivation for lowland/coastal quinoa genotypes, whose nutritional and functional features were affected positively, due to the much more stressing climatic conditions.

Mathematical Modeling of Mass Transfer during Convective Dehydration of Brown Algae Macrocystis Pyrifera

The aim of this research was to study and to model the drying kinetics of the brown algae Macrocystis pyrifera at 50, 60, 70, and 80°C. GAB equation showed a good fit on the sorption experimental data. Ficks diffusional model, together with Newton, Henderson-Pabis, Page, modified Page, logarithmic, and Midilli-Kukuc models were applied on the drying kinetics of the alga. The Dwe increased from 5.56 to 10.22 × 10−9 m2/s as temperature increased from 50 to 80°C. Midilli-Kukuc and logarithmic models obtained the best-fit quality for drying curves based on the statistical tests. In consequence, both models are excellent tools for estimating the drying time of this product.

Moisture sorption isotherms and isosteric heat determination in Chilean papaya (Vasconcellea pubescens)

The moisture sorption isotherms of Chilean papaya were determined at 5, 20, and 45 oC, over a relative humidity range of 10-95%. The GAB, BET, Oswin, Halsey, Henderson, Smith, Caurie and Iglesias-Chirife models were applied to the sorption experimental data. The goodness of fit of the mathematical models was statistically evaluated by means of the determination coefficient, mean relative percentage deviation, sum square error, root-mean-square error, and chi-square values. The GAB, Oswin and Halsey models were found to be the most suitable for the description of the sorption data. The sorption heats calculated using the Clausius-Clapeyron equation were 57.35 and 59.98 kJ·mol-1, for adsorption and desorption isotherms, respectively.