Karina Di Scala

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.

Influence of drying temperature on dietary fibre, rehydration properties, texture and microstructure of Cape gooseberry (Physalis peruviana L.)

The effects of air drying temperature on dietary fibre, texture and microstructure of the Cape gooseberry fruits during convective dehydration in the range of 50–90 ºC were investigated. The ratio of insoluble dietary fibre to soluble dietary fibre was higher than 7:1 for all dehydrated samples. At 50 ºC tissue structure damage was evidenced leading to the maximum water holding capacity (47.4 ± 2.8 g retained water/100 g water) and the lowest rehydration ratio (1.15 ± 0.06 g absorbed water/g d.m.). Texture analysis showed effects of drying temperatures on TPA parameters. Changes in microstructure tissue were also observed at the studied drying temperatures. Hot air drying technology leads not only to fruit preservation but also increases and adds value to Cape gooseberry, an asset to develop new functional products.

An artificial neural network model for prediction of quality characteristics of apples during convective dehydration

In this study, the effects of hot-air drying conditions on color, water holding capacity, and total phenolic content of dried apple were investigated using artificial neural network as an intelligent modeling system. After that, a genetic algorithm was used to optimize the drying conditions. Apples were dried at different temperatures (40, 60, and 80 °C) and at three air flow-rates (0.5, 1, and 1.5 m/s). Applying the leave-one-out cross validation methodology, simulated and experimental data were in good agreement presenting an error < 2.4 %. Quality index optimal values were found at 62.9 °C and 1.0 m/s using genetic algorithm.

Dehydrated olive-waste cake as a source of high value-added bioproduct: Drying kinetics, physicochemical properties, and bioactive compounds

Olive (Olea europaea L.) oil processing produces significant amount of waste that can be utilized for the production of high value-added ingredients for various industrial applications. In this work, the effects of temperature on drying kinetics and quality indexes of the olive-waste cake during convective dehydration (40-90 °C) were investigated. Results on effective moisture diffusivity, physicochemical parameters, fatty acid profile, total phenolic, flavonoid, and flavanol contents as well as antioxidant capacity are also reported. Most of the fatty acids increased their content with respect to control sample with a temperature increase, i.e. oleic and linoleic acids increased 48% and 43% at 70 and 40 °C, respectively. Total flavanol content increased with temperature (48-62 mg catechin equivalents [CTE] 100 g-1 DM) except for 80 °C. Total phenolic and total flavonoid contents were highly correlated to antioxidant capacity (0.923 < r < 0.992), except for 70 and 80 °C, the rest of the samples maintained their initial antioxidant capacity by ORAC analysis. Thus, these parameters show that dried olive-waste cake has a high bioactive compounds with potential use as additives for the food or other industries.

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.

Assessment of lettuce quality during storage at low relative humidity using Global Stability Index methodology

Abstract During postharvest, lettuce is usually exposed to adverse conditions (e.g. low relative humidity) that reduce the vegetable quality. In order to evaluate its shelf life, a great number of quality attributes must be analyzed, which requires careful experimental design, and it is time consuming. In this study, the modified Global Stability Index method was applied to estimate the quality of butter lettuce at low relative humidity during storage discriminating three lettuce zones (internal, middle, and external). The results indicated that the most relevant attributes were: the external zone - relative water content, water content , ascorbic acid, and total mesophilic counts; middle zone - relative water content , water content, total chlorophyll , and ascorbic acid; internal zone - relative water content, bound water, water content, and total mesophilic counts. A mathematical model that takes into account the Global Stability Index and overall visual quality for each lettuce zone was proposed. Moreover, the Weibull distribution was applied to estimate the maximum vegetable storage time which was 5, 4, and 3 days for the internal, middle, and external zone, respectively. When analyzing the effect of storage time for each lettuce zone, all the indices evaluated in the external zone of lettuce presented significant differences (p < 0.05). For both, internal and middle zones, the attributes presented significant differences (p < 0.05), except for water content and total chlorophyll.

Mathematical modeling of convective air drying of quinoa-supplemented feed for laboratory rats

Drying kinetics of quinoa-supplemented feed for laboratory rats during processing at 50, 60, 70, 80 and 90oC was studied and modeled in this work. Desorption isotherm was obtained at 60oC giving a monolayer moisture content of 0.04 g water/g d.m. The experimental drying curves showed that drying process took place only in the falling rate period. Several thin-layer drying equations available in the literature were evaluated based on determination coefficient (r2), sum squared errors (SSE) and Chi-square (χ2) statisticals. In comparison to the experimental moisture values, the values estimated with the Logarithmic model gave the best fit quality (r2 >0.994, SSE < 0.00015 and χ2 < 0.00018), showing this equation could predict very accurately the drying time of rat feed under the operative conditions applied.