EFFECT OF HIGH-PRESSURE PROCESSING ON TEXTURE AND DRYING BEHAVIOR OF PINEAPPLE

The effect of high-pressure processing on texture and drying behavior of pineapple slices was investigated. Pineapple slices were high pressure processed at 50, 100, 300, 500 and 700 MPa at 25C for 10 min. The control, hot water-blanched and high-pressure processed samples were then dehydrated at 70C. Application of high pressure reduced the sample hardness, springiness and chewiness while it had no significant effect on cohesiveness of pineapple. Elevated pressure treatment (≥500 MPa) reduced drying time more effectively than for the other pretreated samples. Experimental dehydration data were empirically fitted using six thin-layer drying models. Among the models tested, logarithmic model best described the drying behavior of pineapple slices. The effective moisture diffusivity was found to increase with an increase in the level of pressure up to 500 MPa, and the samples processed at 500 and 700 MPa had higher diffusivity values than blanched samples.

PRACTICAL APPLICATIONS

This work shows that high-pressure blanching of pineapple can be an alternative for hot water blanching, before dehydration. The results may find application in development of quality snack food from pineapple fruits.     

Effect of osmotic dehydration and ultrasound pre-treatment on cell structure: Melon dehydration

The effect of osmotic dehydration and of ultrasound pre-treatment applied at atmospheric pressure for different lengths of time on melon tissue structure was evaluated. Osmotic dehydration-induced gradual loss of shape of cell wall, disconnection between the cells and breakdown of the tissue. Ultrasound induced the formation of microscopic channels in the fruit structure but did not induce breakdown of the tissue. The changes observed on the structure of the fruit explain the effects of these two pre-treatments on the water diffusivity of the subsequent air-drying step. Osmotic dehydration when carried out for less than 30 min decreases the water diffusivity due to the incorporation of sugar, but increases water diffusivity when carried out for more than 1 h due to the breakdown of cells lowering the resistance to water diffusion. Ultrasound treatment increases water diffusivity due to the formation of microscopic channels which also offers lower resistance to water diffusion.     

Diffusivity of sulphur dioxide in green banana as a function of temperature and concentration

Effective diffusivity of sulphur dioxide uptake in green banana was measured as a function of temperature (20‐30°C) and concentration (6,000‐10,000 ppm) of dipping solutions. The effective diffusivity varied from 2.40×10^?10 to 19.05×10^?10 m²/s. Diffusivity increased with the increase of concentration and temperature of sodium metabisulfite solution. The estimated values can be used to design a sulfiting pretreatment process of green banana before drying.     

Diffusional analysis of air drying of grain sorghum

Pick's law of diffusion (moisture flux proportional to the moisture gradient) for diffusion out of spheres was successfully applied to describe the drying of grain sorghum. It was found that the diffusion coefficient of water was independent of moisture content in the approximate range of 21–6% (dry basis) moisture content. An Arrhenius type temperature dependency of moisture diffusivity was found, the energy of activation being 7.5 kcal/g mol.     

Microwave heat treatment of leek: drying kinetic and effective moisture diffusivity

The effect of microwave drying technique on moisture ratio, drying time and effective moisture diffusivity of white and green parts of leek ( Allium porrum ) were investigated. By increasing the sample amount (100–300 g) at constant microwave output power of 180 W, the drying time increased from 52 to 130 min and increased from 55 to 135 min for white and green parts of leek, respectively. Effective moisture diffusivity values for white and green parts of leek ranged from 0.618 × 10⁻¹⁰ to 2.128 × 10⁻¹⁰ m².s⁻¹ and 0.256 × 10⁻¹⁰ to 0.611 × 10⁻¹⁰ m² s⁻¹, respectively. Among the models proposed, Midilli et al. model gave a better fit for all drying conditions applied. The activation energy for microwave drying of white and green parts of leek was calculated using an exponential expression based on Arrhenius equation; found as 0.9530 and 1.2045 W g⁻¹, respectively. The dependence of drying rate constant on effective moisture diffusivity gave a linear relationship.     

Effect of ultrasound‐assisted osmotic dehydration on cell structure of sapotas

BACKGROUND: Drying is a traditional way of fruit preservation. Because of the high energy costs associated with air‐drying, osmotic dehydration is often applied as a pretreatment to reduce air‐drying time. Ultrasound is an emerging technology with several applications in food processing. The effect of ultrasound on fruit tissue depends on the tissue structure and composition, and ultrasound might be beneficial to improve air‐drying efficiency, with consequent reduction in process costs. In this study the effect of ultrasound and ultrasound‐assisted osmotic dehydration on sapota tissue structure was evaluated. RESULTS: Ultrasound induced cell disruption and breakdown of cells with high phenolic content (dense cells) and also induced elongation of parenchyma cells. Ultrasound application combined with high osmotic gradient enhanced water loss and solid gain because of the formation of microscopic channels. Ultrasound‐assisted osmotic dehydration induced gradual distortion of the shape of cells, cell breakdown and formation of microscopic channels. Micrographs of the fruit tissue showed that ultrasound preferentially affected dense cells. CONCLUSION: Ultrasonic pretreatment was able to preserve the tissue structure of the fruit when distilled water was used as liquid medium. The application of ultrasound‐assisted osmotic dehydration resulted in severe changes in the tissue structure of the fruit, with consequent increase in the effective water diffusivity, because of the formation of microscopic channels and cell rupture. Copyright © 2009 Society of Chemical Industry     

Thermophysical properties of silver hake and mackerel surimi at cooking temperatures

Thermal diffusivity values obtained using a transient method both from heating and cooling information and apparent specific heat of surimi made from silver hake and mackerel as a function of temperature (60–110 °C) and added potato starch content (3% and 7%, w/w) were determined. The water content of all samples was kept constant at about 77% (w/w) in order to determine the effect of starch. Thermal diffusivity and apparent specific heat of all samples increased with temperature. The effect of temperature on diffusivity was found significant (p=0.001) in all samples at temperatures above 85 °C. This effect may be caused by structural changes as temperature is raised. Thermal diffusivity increased with temperature more rapidly in samples with high levels of starch than in those with no starch. However, thermal diffusivity of silver hake surimi preset at 40 °C for 30 min did not show a significant increase (p<0.05) over the temperature range studied. Thermal diffusivities calculated from cooling and heating data were significantly different (p<0.05).

The differential scanning calorimetry (DSC) thermograms of silver hake and mackerel surimi showed three endothermic peaks. When starch was added to surimi samples an endothermic peak having a large area was observed, which overlapped the third highest temperature peak of surimi samples. No significant shifts in the endothermic peaks of myofibrillar proteins were detected with increasing starch content. Transition temperatures for starch–surimi system were higher than those for starch–water system. There were deviations in the apparent heat capacity function calculated from DSC measurements in surimi samples containing starch. These are attributed to gelatinization of starch and modification of water structure.     

Effect of Berry Size and Sodium Hydroxide Pretreatment on the Drying Characteristics of Blueberries under Infrared Radiation Heating

ABSTRACT:  This research studied the effect of berry size and dipping pretreatment in hot sodium hydroxide (NaOH) solution on the drying characteristics of blueberries under infrared radiation (IR) heating. Changes in the microstructure and diffusion coefficient of the berries after the NaOH pretreatment were also determined using scanning electronic microscopy and dynamic vapor sorption (DVS), respectively. To quantify the effect of berry size, non-pretreated bulk blueberries were sorted into 6 groups based on their diameters and dried at 70 °C. To determine the effectiveness of NaOH pretreatment in improving drying characteristics, bulk blueberries of different sizes, both nonpretreated and NaOH pretreated, were dried at constant temperatures of 80 and 90 °C, and variable temperatures of 70 °C for 50 min followed by 90 °C for 50 min. The NaOH pretreatment dipped blueberries in 0.1% NaOH solution with fruit to solution ratio 1:1 (w/v) at initial temperature of 93 °C for 5 s. Results showed that the drying rate increased with decreased berry size. Average moisture diffusivity was in the range of 5.89 to 8.13 m²/s at 70 °C. The NaOH pretreatment increased drying rate and moisture diffusivity and reduced the number of broken berries, especially at high drying temperatures. Results from SEM observation and DVS showed that the increase in diffusivity coefficients of berry coat and loss of intact microstructure in coat and tissue cells might contribute to the effect of NaOH pretreatment on the IR drying of blueberries.     

ANALYSIS OF VARIABLES AND MODELING OF GEVUINA AVELLANA OIL EXTRACTION WITH ETHANOL NEAR AZEOTROPE CONDITIONS

Oil extraction from Gevuina avellana Mol. (Chilean hazelnut) with ethanol, near the conditions of its azeotrope with water, was carried out in this work. The effects of solubility, liquid-to-solid ratio and moisture content of ethanol were studied using 92% ethanol, azeotropic (96%) and absolute ethanol (99.9%) as solvents. Water content had a high effect on oil solubility, which reached 140 g/L in 99.9% ethanol, whereas it was 40 g/L with azeotropic ethanol. Oil accounted for 93% of total extractable compounds with absolute ethanol.
Kinetics studies of the extraction process were performed at 50C, giving as a result apparent diffusivity values near 10 ^{− 11}  m²/s, being the highest values obtained for ethanol 92% (7.5–16  ×  10 ^{− 11} ). It was also found that the higher the liquid-to-solid ratio, the higher the diffusivity. Simulation of four-stage countercurrent extraction with azeotropic ethanol yielded 23.5% oil extraction, whereas simulation of four-stage cross-flow extraction yielded 40.7%. Ethanol can be an alternative to batch cold pressing or hexane solvent extraction, for G. savellana seeds or meal processing .

PRACTICAL APPLICATIONS

The results presented in this paper are applicable for obtaining oil from oilseeds by extraction with ethanol. It includes relevant results for the optimization of extraction conditions and particularly those regarding liquid-to-solid ratio and percentage of water. Considering the more specific focus of this research, the results are applicable to obtaining Gevuina avellana oil by using an ethanol-based process, which will allow to avoid one of the cold-pressing process drawbacks: the high oil content of the meal, which is a factor limiting its lifetime.     

Study of the Effect of High Hydrostatic Pressure (HHP) on the Osmotic Dehydration Mechanism and Kinetics of <Emphasis Type="Italic">Wumei</Emphasis> Fruit (<Emphasis Type="Italic">Prunus mume</Emphasis>)

Osmotic dehydration (OD) is the most important procedure for obtaining candied wumei (Prunus mume), which is a very popular snack in Eastern Asian countries. This study aims to evaluate the effects of high hydrostatic pressure (HHP) pre-treatment (50–400 MPa) on the mass transfer kinetics and on the water diffusivity of wumei fruit during OD and to investigate the effect on water distribution and cell viability aspects. The results showed that HHP increased initial rate and effective diffusivity of mass transfer values compared to non-treated samples. Time domain nuclear magnetic resonance revealed that, upon HHP treatment, the water redistributed in vacuole, cytoplasm/extracellular spaces, and cell wall/membrane. The application of 400 MPa probably caused some irreversible damages to the cell membranes. The cell viability study determined by fluorescein diacetate staining showed a loss of cell viability at pressures higher than 200 MPa. HHP exhibited an effective pre-treatment to increase mass transfer of wumei fruit during OD process.