Kong Ah-Hen

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.

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.

Influence of air-drying temperature on drying kinetics, colour, firmness and biochemical characteristics of Atlantic salmon (Salmo salar L.) fillets

In this work the drying kinetics of Atlantic salmon (Salmo salar L.) fillets and the influence of air drying temperature on colour, firmness and biochemical characteristics were studied. Experiments were conducted at 40, 50 and 60°C. Effective moisture diffusivity increased with temperature from 1.08×10(-10) to 1.90×10(-10) m(2) s(-1). The colour difference, determined as ΔE values (from 9.3 to 19.3), as well as firmness (from 25 to 75 N mm(-1)) of dried samples increased with dehydration temperature. The lightness value L(∗) and yellowness value b(∗) indicated formation of browning products at higher drying temperatures, while redness value a(∗) showed dependence on astaxanthin value. Compared with fresh fish samples, palmitic acid and tocopherol content decreased in a 20% and 40%, respectively, with temperature. While eicosapentaenoic acid (EPA) content remained unchanged and docosahexaenoic acid (DHA) content changed slightly. Anisidine and thiobarbituric acid values indicated the formation of secondary lipid oxidation products, which is more relevant for longer drying time than for higher drying temperatures.

Chemical and physical properties of aloe vera (Aloe barbadensis Miller) gel stored after high hydrostatic pressure processing

O objetivo deste estudo foi avaliar o efeito da aplicacao de altas pressoes hidrostaticas (150, 250, 350, 450 e 550 MPa) aplicadas durante 5 minutos sobre a atividade antioxidante, concentracao de polifenois totais, cor, firmeza, taxa de reidratacao e capacidade de retencao de agua do gel de aloe vera armazenado durante 60 dias a 4 °C. As propriedades analisadas do gel pressurizado mostraram mudancas significativas depois de armazenadas. Para pressoes de 550 Mpa, registrou-se o maior aumento de polifenois totais. No entanto, observou-se uma diminuicao da capacidade antioxidante em todas as amostras, em comparacao com a amostra nao tratada (p < 0,05). As alteracoes de cor foram menores para pressoes entre 150 e 250 MPa. A aplicacao de altas pressoes hidrostaticas diminuiu a firmeza do gel, registrando-se o menor valor para 150 MPa (p < 0,05). Por outro lado, o tratamento sem pressao mostrou uma maior perda de firmeza, indicando que o tratamento por altas pressoes conserva esta propriedade. A aplicacao de altas pressoes evidenciou modificacoes da matriz do alimento, avaliadas como taxa de reidratacao e capacidade de retencao de agua.

Modelling of Rheological Behaviour of Pulps and Purées from Fresh and Frozen-Thawed Murta (Ugni molinae Turcz) Berries

Abstract The rheological behaviour of purées and pulps from fresh and frozen-thawed murta (Ugni molinae Turcz) berries was studied at 30, 45, 60 and 75 °C. The Mitschka method was shown to be applicable to the murta berries, with its products showing non-Newtonian pseudoplastic behaviour. Rheological models as Ostwald-de Waele, Herschel-Bulkley, Bingham, Casson and Mizrahi-Berk fitted the experimental data with high values for correlation coefficients. Effect of temperature was evaluated using an Arrhenius-type equation. Compared to the murta pulp, the fresh or frozen-thawed murta purées had higher apparent viscosity at any shear rate and would undergo a more rapid change in viscosity with temperature. Activation energy for fresh and frozen-thawed purées were 22.335 kJ mol-1 (R2 = 0.9225), and 16.478 kJ mol-1 (R2 = 0.9654) respectively, while for fresh and frozen-thawed pulp Ea values of 8.967 kJ mol-1 (R2 = 0.9618) and 6.943 kJ mol-1 (R2 = 0.9773) were determined respectively.

Moisture Sorption Isotherms, Isosteric Heat of Sorption and Glass Transition Temperature of Murtilla (Ugni molinae T.) Berry

Abstract Adsorption and desorption isotherms of fresh and dried murtilla (Ugni molinae Turcz) berries were determined at 20, 40 and 60°C using a gravimetric technique. The experimental data obtained were fitted to eight models, namely GAB, BET, Henderson, Caurie, Smith, Oswin, Halsey and Iglesias–Chirife. A non-linear least square regression analysis was used to evaluate the models. The GAB model best fitted the experimental data. Isosteric heat of sorption was determined from the equilibrium sorption data using the Clausius–Clapeyron equation and was found to decrease exponentially with increasing moisture content. The enthalpy–entropy compensation theory applied to the sorption isotherms indicated an enthalpy controlled sorption process. Glass transition temperature of murtilla was determined by differential scanning calorimetry and modelled as a function of moisture content by the Gordon–Taylor equation and as function of water activity by Roos and Khalloufi models, which proved to be excellent tools for predicting glass transition of murtilla.

Anthocyanin Retention of Cranberry (Vaccinium macrocarpon) Juice Subjected to Different Nanofiltration Conditions

The aim of this work was to evaluate the retention of anthocyanin during a nanofiltration process of cranberry juice. Nanofiltration membranes, HC-50P DDS with an effective area of 0.36 m2 in a plate/frame nanofilter system, DDS Lab Module, were used for the experiments. Juice feed flow rate varied from 1.0 to 12.0 L min−1 at transmembrane pressures between 20 and 40 bar (2026 and 4052 kPa). Permeate flux reached a maximum value of 41.3 L h−1 m−2 at a pressure of 40 bar and a feed rate of 12 L min−1, showing a direct dependency on these two parameters. Retention coefficients of anthocyanin of 0.94 to 0.99 corresponding to percentage recovery between 93 and 99% were obtained. Total anthocyanin content increased to values between 237 and 287 mg L−1 from original concentration of 82 to 97 mg L−1 in feed solution. Total soluble solids were also retained on the nanofilter. Both anthocyanin retentate and permeate obtained by nanofiltration could be potential functional ingredients for the food and nutraceutical industry.