Clean energy can be obtained from Bio-hydrogen (Bio-H2) production from the organic fraction of solid waste, as fruit and vegetable wastes. Bio-H2 can be produced from fruit/vegetable wastes but there is a lack of information about its rheological characterization. Romero et. al. (2014) have characterized the rheological behaviour of a vegetable/fruit waste mixture and they have evaluated the effect of the solids content (%, w/w), temperature, time (tyxotropy effects) and shear rate over the apparent viscosity of the mixture. They reported that most of the mixtures showed non-Newtonian behavior. Also, the curves are typical rheofluidizing fluids.
The rheological curves were different at increasing solids contents (80%, 60%, 40% and 30%), independent from the temperature.Correlation factors R2 for the different mixtures were 0.991-0.
995 for 80%, 0.961-0.986 for 60% and 0.890-0.925 for 40%. The R2 value was beyond acceptance in the case of 30% of solids, and they found that the mixture was very near to the Newtonian behaviour. Calculated activation energies (Ea) values were 15.
98, 14.89 and 20.96 kJ/mol for the 80%, 60%, 40% mixtures, respectively. FVW purees rheological behaviour was well characterized by Carbopol solutions at given concentrations and pH values. With the aim of substantially improving the freezing tolerance of spinach leaves, Phoon et al (2008) have utilized pulsed electric fields in combination with vacuum infusion to impregnate cells with trehalose. They have done the treatment of spinach samples first with ten trains of bi-polar, rectangular electric field pulses with nominal electric field strength of 580 V/cm and immediately immersed in a 40% (w/w) solution of trehalose under vacuum for 20 min.
The samples were kept in the trehalose solution for 2.5 h at atmospheric pressure, immersed in deionised water at 4°C overnight, frozen in liquid nitrogen and thawed in water at room temperature. They have done evaluated the leaves for cell damage with microscopic observations and wilting tests anf found that that the impregnation with trehalose by the combined actions of electric fields and vacuum impregnation drastically improved the freezing tolerance of the spinach leaves.Mart??nez-Monzó et. al. (2000) studies the effect of vacuum impregnation with sucrose solutions on thermal properties of apple samples (Granny Smith). Thermal diffusivity was measured in non-impregnated (NVI) and impregnated samples in a transient heat conduction method.
They have reported that Thermal diffusivity changes due to VI were relatively low. They concluded that the proposed predictive model can be used to estimate changes in thermal properties due to VI in terms of product porosity and pore distribution and conditions of VI process. Martin-Diana et. al. (2006) analysed the Textural and micro structural changes in fresh-cut lettuce over 12 days storage. Their study revealed that samples washed with calcium lactate had significantly (p > 0.05) higher crispness values than samples washed with chlorine. However the use of 50?C treatment (heat-shock) gave better textural properties at the end of storage and significantly retarded the softening process, being in agreement with the sensorial results.
Also Cryo-SEM micrographs showed a loss of turgor (shrinkage) of the tissue cells in the samples washed with chlorine, effect not so evident in calcium lactate treated samples. The use of heat-shock in combination with calcium lactate reduced this phenomenon better than the other two treatments. Pectin methyl esterase (PME), enzyme related to textural changes, showed higher activity in samples treated with calcium lactate at 50?C. The combination of calcium lactate and 50?C washing temperature maintained objective and sensorial textural properties of fresh-cut lettuce better than the calcium lactate or chlorine washing treatments at room temperature.Moreno et.
al (2012) investigated the influence of ohmic heating (OH) and vacuum impregnation (VI) on the osmotic dehydration (OD) kinetics and microstructure of strawberries. Their results showed that applying OH during osmotic dehydration had significant effects on the mass transference kinetics and the microstructure of the treated samples. The greatest water loss was observed for the ODeOH treatment. The largest amount of solute gain was obtained for the VIeOH treatment. A loss in firmness was observed in the ODeOH samples at 50 °C. Color differences were related to an increase in clarity and a decrease in color chrome and SEM observations showed that cell rupturing were more significant in the ODeOH than in the VIeOH samples. The application of OH and VI had beneficial effects on the acceleration of mass transference.
Gonzalez et. al (1999) examined salt gain in brining of calf rennet coagulated uncooked pressed curds (20% ewe’s and 80% cow’s milk), using conventional brine immersion and brine vacuum impregnation. They found that the degree of compactness of the casein clusters in curd increased with the distance to the plunger press and the curd ageing time. They also reported that this phenomenon significantly affected the brine vacuum impregnation electiveness related with hydrodynamic mechanisms in the pronounced extra-micellar porosity. Guillemin, (2008) studied the firming of apple fruit tissues by vacuum-infusion of pectin methylesterase.
Apple pieces were vacuum-impregnated with either a pectin methylesterase (PME) or calcium solution or with water prior to pasteurization. Their study showed that pasteurized apple pieces impregnated with PME and calcium displayed a significantly higher firmness. Also, solid state 13C NMR spectroscopy of apple cell wall residues revealed an increase of their molecular rigidity. The results corroborate the hypothesis that vacuum impregnated PME action liberates free carboxyl groups along pectin chains that could interact with calcium, increasing the rigidity of pectins and finally the mechanical rigidity of apple tissue.
Moraga et. al (2009) assessed the effect of calcium lactate (2%) on osmotic dehydration kinetics and on the respiration rate, mechanical properties and shelf-life of fresh, vacuum impregnated (VI) and pulsed vacuum osmodehydrated (PVOD) grapefruit. They reported that shelf-life of grapefruit was increased from 5 to 8 days due to sample dehydration and to 11 days if calcium is added to the osmotic solution, without influencing the mechanical properties of the sample. Muujica-Paz et. al (2003) investigated the effects of vacuum pressure and its application time on the volume of isotonic solution (IS) impregnated in slices of mango, apple, papaya, banana, peach, melon, and mamey. Fruits were subjected to vacuum impregnation (VI) treatments using sucrose IS.
In the experiment, they have applied VI treatment between 3 and 45 min and vacuum pressures (VP) between 135 and 674 mbar. Their study revealed that VP had a significant effect (p60:10) on the volume of IS impregnated in fruit slices of all the studied fruits. The impregnation also depended significantly (p60:10) on the VI time, except for apple. Igual, M., (2008) studied the influence of vacuum impregnation on respiration rate, mechanical and optical properties of cut persimmon.
Cubes of persimmon of two cultivar (‘Picudo’ and ‘Rojo Brillante’) were immersed in a sucrose solution (24 Brix) for 5 min at 50 mbar plus 5 min at atmospheric pressure. The changes occurring during storage of fruits were determined (7 days, 10ºC). They reported that the porosity of persimmon increased around 3% in the samples due to VI. VI improved the initial appearance of this fruit.
Moreover VI did not prevent brownish colouring of fruits during storage and therefore some antibrowning products must be incorporated in the osmotic solution. Functional foods are very helpful for the human body in terms of health promotion and disease prevention. Vacuum and/or atmospheric impregnation techniques seem to be feasible technologies for exploitations of fruit and vegetable tissues as new matrices into which functional ingredients can be successfully incorporated, providing novel functional product categories and new commercial opportunities (Alzamora et. al, 2005). Alzamora et. al (2005) experimented on impregnation techniques and revealed that apparent absorption values with respect to calcium carbonate were 80.2%, 74.
2% and 86.8%, respectively, indicating apple matrix impregnated with Ca2+ lactate/gluconate was a vehicle to provide easily absorbable calcium. Guillemin et.
al (2006) observed the penetration of an exogenous Aspergillus niger pectinmethylesterase added by soaking or by vacuum-impregnation in apple cubes by three diverse methods. Their experiments comprises of quantitative assessment of the enzyme activity in different concentric zones of 1.5 cm apple cubes. The quantitative results were confirmed by these qualitative visual methods at a macroscopic and at a microscopic scale, respectively. They concluded that vacuum-impregnation can be used to add this exogenous enzyme to fruit pieces more quickly and more homogeneously than soaking in order to improve the firmness of thermally treated fruits.
Norul (2011) studied physical and mechanical properties of vinyl thermoplastic modified Calamus manan aged 10 and 13 years grown under rubber tree canopy. Their study comprises of selection and impregnation of Canes from diameters of 25-29 mm, 35-39mm and 40-44 mm with polystyrene (PS) and polymethyl methacrylate (PMMA) solution. Three different concentrations of 5%, 15% and 25% solutions were prepared by dilution process with methyl ethyl ketone (MEK). They concluded that modified canes with PS had greater polymer loading, thicker coat and higher water resistance but lower dimensional stability than those of PMMA. Canes modified with 25% concentration had greater coats, density, water resistance, dimensional stability but had lesser water absorption and diameter swelling than those from lower concentrations. Their study also revealed that mechanical properties of modified canes of either age or thermoplastic were improved over the untreated control, while the compression strength improved with increasing polymer concentration.
They concluded that all the mechanical properties of modified cane at 5% concentration were higher than untreated cultivated canes and commercial canes of unknown age. Dash et. al (2012) conducted modeling and design of the Sapota fruit for modified atmosphere storage with different packaging materials for the higher shelf life. They concluded that the suitable packaging films obtained for the modified atmospheric packaging of Sapota fruit were low density Polyethylene, Polyvinyl chloride, Polypropylene and Polystyrene film based on the respiration rate and permeability of the packaging material.