ANALYSIS OF OPEN SUN DRYING EXPERIMENTS

Open sun drying has lost its previous importance due to the fact that different factors affect its reliability and the quality of the products obtained.

One of the set-backs for the analysis of solar drying exoeriments is their deoendence on a non-controlled source of energy, i.e. solar radiation depends on climatic conditions and experiments are difficult to compare. It is thus necessary to investigate the advantages of a particular set up as well as the climatic influences. Open sun drying could constitute the natural reference, allowing the comparison of different drying strategies.

A new way of standardizing drying times, based on solar radiation inout, is proposed, to allow better evaluation of the experiments. An equivalent time is defined, allowing comparison of experiments carried out under different circumstances. Carrots and potatoes were used in these experiments.

The use of the average daily solar radiation 15.28 MJ m^-2.d^-1 in Palma de Mallorca (39.33°N, 2.37°E), is proposed for comparison purposes. An improvement of more than 12 % in the explained variance was observed, the unexplained variance being lower than 1 %.     

SIMULATION OF COUNTER-DIFFUSIONAL MASS TRANSFER

The mathematical formulation of mass transfer in food processes is often based on the diffusion equation with the diffusion coeffcients considered as effective parameters. In some cases, more than one specie can be simultaneously diffusing in opposite directions. Therefore, the movement of one component could affect the movement of the remaining components. The aim of this work is to describe a mathematical procedure to obtain the diffusion coeffcients of different species that simultaneously diffuse in such a situation that each mass flux is affected by the existence of the others. The correspondent microscopic mass balances combined with Fick's law were simultaneously solved using a numerical finite difference method.     

Dehydration kinetics of red pepper (Capsicum annuum L var Jaranda)

Shredded and whole red pepper samples were dehydrated in a laboratory drier with a through‐flow air velocity of 0.5 m s^?1 at 50, 55, 60 and 70 °C. Shredded peppers dried faster than whole peppers. The drying behaviour of whole samples was characterised by a constant‐ and a falling‐rate drying period, whilst that of shredded samples was characterised by a falling‐rate drying period only. The mass transfer coefficient for whole samples during the constant‐rate period was computed experimentally. The effect of temperature on the mass transfer coefficient was described by the Arrhenius model. The activation energy was 58 kJ mol^?1. In the falling‐rate period the mass transfer was described by a diffusional model, and the effective diffusion coefficient at each temperature was determined. Diffusion coefficients were estimated to lie between 4.38 × 10^?11 and 10.99 × 10^?11 m² s^?1 for whole peppers and between 37.23 × 10^?11 and 99.61 × 10^?11 m² s^?1 for shredded peppers. The effect of temperature on the effective diffusion coefficient was described by the Arrhenius equation, with an activation energy of 44 kJ mol^?1 for whole peppers and 56 kJ mol^?1 for shredded peppers. © 2003 Society of Chemical Industry     

The role of K+ and H+ transport systems during glucose‐ and H2O2‐induced cell death in Saccharomyces cerevisiae

Glucose, in the absence of additional nutrients, induces programmed cell death in yeast. This phenomenon is independent of yeast metacaspase (Mca1/Yca1) and of calcineurin, requires ROS production and it is concomitant with loss of cellular K⁺ and vacuolar collapse. K⁺ is a key nutrient protecting the cells and this effect depends on the Trk1 uptake system and is associated with reduced ROS production. Mutants with decreased activity of plasma membrane H⁺‐ATPase are more tolerant to glucose‐induced cell death and exhibit less ROS production. A triple mutant ena1‐4 tok1 nha1, devoid of K⁺ efflux systems, is more tolerant to both glucose‐ and H₂O₂‐induced cell death. We hypothesize that ROS production, activated by glucose and H⁺‐ATPase and inhibited by K⁺ uptake, triggers leakage of K⁺, a process favoured by K⁺ efflux systems. Loss of cytosolic K⁺ probably causes osmotic lysis of vacuoles. The nature of the ROS‐producing system sensitive to K⁺ and H⁺ transport is unknown. Copyright © 2010 John Wiley & Sons, Ltd.     

Influence of pre-treatment and storage temperature on the evolution of the colour of dried persimmon

Drying could be a way of increasing in the value of the large quantity of persimmon that is rejected for fresh consumption, being the colour one of the main attributes of the product. Although the use of sulphites is one of the most widely extended methods of preservation their undesirable effects on asthma sufferers currently limit their application. An interesting alternative could be to use citric acid combined with an adequate storage temperature. To that end, dried persimmon slices were stored at 4 temperatures (2, 10, 18 and 28 °C) for 409 days. Before drying, one group of samples was pre-treated (15 min) in a solution of potassium meta-bisulphite (3% w/w), other two groups (15 and 35 min respectively) in a solution of citric acid (3% w/w) and the last group (control) was untreated. The L, a and b CIE-Lab coordinates were measured during storage and the colour change, ΔE, was estimated. The experimental results were modelled using first-order kinetics and Peleg’s model. The citric acid pre-treatment turned out to be an interesting alternative to SO₂ taking into account that its effect was more effective at temperatures lower than 18 °C. No significant differences were found between the two citric acid pre-treatments, being, therefore, the shortest pre-treatment the most interesting one. More experiments are necessary to establish an optimum content of citric acid in samples.     

SOLAR DRYING OF FRUITS IN A MEDITERRANEAN CLIMATE

Two twin forced convection dryers of 1.5 m³ were built in Majorca (Spain). They are of a mixed kind, with solar air collectors and a green house type chamber. A wooden frame supports polycarbonate walls. After two years operation they have been proven weather resistant. Six solar air collectors 2.12 × 1.05 m were used in each dryer.

Apricots were processed in both dryers and at open sun. Three different tray heights were tested 5, 9 and 12 cm. The best results were obtained with 12 cm trays. Recycling part of the exhaust air improves the efficiency of the dryer. Blanching the fruits makes no difference to the dehydration rate. The rate of SO₂ loss during the drying process is higher within the chamber.     

ANALYSIS OF OPEN SUN DRYING EXPERIMENTS

ABSTRACT

Open sun drying has lost its previous importance due to the fact that different factors affect its reliability and the quality of the products obtained.

One of the set–backs for the analysis of solar drying exoeriments is their deoendence on a non–controlled source of energy, i.e. solar radiation depends on climatic conditions and experiments are difficult to compare. It is thus necessary to investigate the advantages of a particular set up as well as the climatic influences. Open sun drying could constitute the natural reference, allowing the comparison of different drying strategies.

A new way of standardizing drying times, based on solar radiation inout, is proposed, to allow better evaluation of the experiments. An equivalent time is defined, allowing comparison of experiments carried out under different circumstances. Carrots and potatoes were used in these experiments.

The use of the average daily solar radiation 15.28 MJ m^-2.d^-1 in Palma de Mallorca (39.33°N, 2.37°E), is proposed for comparison purposes. An improvement of more than 12 % in the explained variance was observed, the unexplained variance being lower than 1 %.     

Monitoring of blood glucose. Biosensors, a new monitoring system

The education on the diabetic field, carried by nurses most of the time, is the most important therapeutic measure for the reduction of acute and chronic complications of the diabetic patient. One of the most important parts of the educational contribution consist on self-control; in order to reach said self-control, it is necessary to practise the self analysis, being the best one the control of the capillary blood glucose. In this article, we are presenting a meter for glucose control of the latest generation; the meter has a biosensor technology and it extend its benefits when connected to a personal computer.     

Water sorption isotherms for lemon peel at different temperatures and isosteric heats

Lemon peel constitutes a potential source of dietary fiber to formulate new and healthier products, as well as a source of essential oils. The relationship between moisture content and water activity provides useful information for lemon peel processing, especially for drying and storage. Water sorption isotherms of lemon peel were obtained using a standardized conductivity hygrometer at four different temperatures (20, 30, 40 and 50 °C) and wide ranges of moisture content (5.381-0.002 kg water/kg dry solid) and water activity (0.984-0.106). One theoretical (GAB) and four empirical equations (Oswin, Henderson, Halsey and Ratti) were used for modelling sorption isotherms. After evaluating the models according to several criteria, the GAB model appeared as the best option. Isosteric heats of sorption were assessed from experimental sorption isotherm data using different methods.