María Dolores Ortolá

Control of citrus surface drying by image analysis of infrared thermography

Citrus surface drying is one of the most important unit operations in a fresh fruit processing plant. A common risk in citrus surface driers (CSD) is using an excessive air temperature or keeping the fruit in the drier too long, since an important loss in sensorial quality may occur as well as a decrease in the fresh fruit shelf life. Nowadays, most of the new CSD use systems to control air temperature, but do not include elements to monitor the process by defining the required drying time. A new system to control the surface drying time by image analysis of the fruit surface temperature distribution, using infrared techniques was tested. The control of fruit surface temperature during drying allowed us to determine the moment when the surface drying finishes and the peel drying begins. Oranges (var. Valencia Late) washed with water or covered with a commercial wax were dried at 20, 25 and 35 °C with 1, 1.5 and 2 m/s air velocities. During the first drying step the lowest surface temperature of the fruit was measured from infrared images captured with an AGEMA 470 camera and was assumed to be the wet bulb temperature. Drying time could be well established when temperature at any point on the fruit surface exceeded this value. An empirical model was developed to correlate drying times with air conditions. Parameters of the model may be used in control systems for industrial CSD equipment.

Influence of roasting temperature on physicochemical properties of different coffees

Arabica and robusta coffees from different origins were characterized before and after roasting at different temperatures (between 220 and 295°C). Samples were roasted (dark roast) until they attained the same colour. Colour development of the ground samples was measured throughout using CIE L*a*b* co-ordinates. The roasting temperature did not affect final weight loss and moisture content of the different coffees significantly, but slight differences were detected in the mean weight losses for the different coffees. Roasting temperature affected bulk and bean densities, grain volume increase, and soluble solids and acidity of coffee extracts. Robusta coffees were less sensitive to the bean volume increase, but showed a stronger temperature effect on the content of soluble solids and in the acidity of the aqueous extract, which can benefit its quality parameters.

Long Term Osmotic Dehydration Processes of Orange Peel at Atmospheric Pressure and by Applying a Vacuum Pulse

Osmotic dehydration is a useful tool to obtain orange peel products with good sensory acceptance and stability. Osmodehydration of orange peel has been carried out in different osmotic solutions (65 Brix sucrose, 55 Brix glucose and concentrated rectified grape must) at 40 and 50 C for different durations (0–10 days), at atmospheric pressure and by applying a vacuum pulse at the beginning of the process. Changes in sample composition (water and soluble solid contents), weight, volume, density and porosity were analyzed. In all conditions, samples reached the same sample solute content as the osmotic solution at about 24 h of treatment, and the concentration rate was faster when vacuum pulse was applied. Mass transfer behavior showed that impregnation of the peel pores occurred to a great extent, not only when applying vacuum pulse, but also in treatments at normal pressure, due to the capillary effects and pressure gradients generated in the tissue associated with structural changes. Impregnation contributed to compositional changes and weight development of the sample. The greater the osmotic solution viscosity, the lower the impregnation level at equilibrium, which was always promoted by vacuum pulse.

Influence of thermal treatment and storage on astringency and quality of a spreadable product from persimmon fruit

The aim of this work was to develop osmodehydrated products from cubes of persimmon (var. Rojo Brillante), which could be spread as a jam but keeping the typical aroma, flavour and colour of fresh fruit. The application of a thermal treatment in the filling stage has been studied, with or without a later pasteurisation step at 90°C for 20min. These spreadable products were stored at room temperature or in refrigeration. The chemical composition, pH, aw, colour, astringency, antioxidant capacity and the growth of yeast, moulds and aerobic mesophiles were analysed after the manufacture process and throughout the storage (approximately 3.5months). Sensorial analyses were also performed after 24h of being prepared and after 49days of refrigeration. The product obtained without thermal treatment was the best since it maintained the characteristic persimmon colour better and showed higher antioxidant capacity. Furthermore, it was the best, according to the panel, not only for appearance but also for flavour.

Physicochemical characteristics of citrus jelly with non cariogenic and functional sweeteners

AbstractIn this study the effect of sweeteners with low glycemic index and non-cariogenic characteristics (isomaltulose, oligofructose and tagatose) in jelly prepared with citrus juice has been evaluated considering a citrus jelly formulated with sucrose as reference. The soluble solids, moisture content, pH, water activity, antioxidant capacity, optical and mechanical properties of jelly made using different sweeteners was determined during storage. Besides, mesophilic aerobics and moulds and yeasts was also counted to determine their stability over time. Sensory evaluation of the citrus jelly has also been done. The results showed the antioxidant activity decreased during storage in all formulations. Tagatose increased lightness whereas coordinates a*, b* and chrome of all the jellies prepared using new sweeteners were lower than jellies with sucrose. However, citrus jelly with only oligofructose or tagatose or with the mixture of isomaltulose and tagatose were most closely resembled to the control jelly with respect to mechanical properties. Jelly prepared with the combination of isomaltulose and tagatose in equal proportions obtained the best score in the sensorial analysis.

Washing of cut persimmon with thyme or lemon essential oils

The aim of this study was to develop a minimally processed persimmon product by applying different concentrations of thyme essential oil or lemon essential oil on the product in order to increase its shelf life. Essential oils were applied on cut persimmon in a preliminary stage of immersion, and the samples were then stored at 4 ℃ for seven days. Moisture content, soluble solids content, antioxidant capacity, total phenols, pH, optical and mechanical properties and microbiology counts were periodically analysed. Noteworthy was that the application of thyme essential oil in the washing stage improved the preservation of the fruits’ colour. All samples would be considered safe according to microbiology requirements and based on the period of study, regardless of the type of essential oil applied.

Influence of Low Glycaemic Index Sweeteners on Antioxidant, Sensory, Mechanical, and Physicochemical Properties of a Watermelon Jelly

The replacement of sucrose by new noncariogenic and low glycaemic index sweeteners (isomaltulose and tagatose) and the addition of natural watermelon juice in jelly have been assessed in terms of composition, texture, colour, antioxidant activity, microbiology, and sensory properties. These analyses were performed initially and after 15 days of storage. Furthermore, the values were compared with those obtained in the analyses of a commercial watermelon jelly. The results showed that the antioxidant activity increased with the storage time in the control sample and in samples combining isomaltulose and tagatose. In addition, noncariogenic and low glycaemic index sweeteners did not affect the instrumental texture. However, the colour changed, especially in the sample containing tagatose only. Finally, the dessert containing tagatose and isomaltulose in equal proportion achieved a similar score in the sensory evaluation as the commercial one, showing the feasibility of using these sweeteners to reformulate watermelon jelly.

Effect of replacing sucrose with tagatose and isomaltulose in Mandarin orange marmalade on rheology, colour, antioxidant activity, and sensory properties

The aim of this study was to make mandarin orange marmalades, in which sucrose is replaced by sweeteners, such as tagatose and isomaltulose, which are non-cariogenic and have a low glycemic index. Analyses of rheology, colour, antioxidant activity, microbiology, and sensory properties were carried out on marmalades on their first day, and after 90, 180, and 360 days of storage. The results showed that marmalades made with healthy sweeteners had a less elastic character and were thinner in consistency than those made with sucrose. Lightness was shown to be highest in mandarin orange marmalades made with tagatose, although colour was stable for 180 days to one year of storage. Tagatose also enhanced the antioxidant activity of these marmalades. All marmalades were microbiologically stable. Finally, marmalades made with tagatose alone scored the highest for global acceptance and intention of buying by consumers.