Harris N. Lazarides

Osmotic concentration of liquid foods

Vast amounts of liquid food are industrially concentrated in order to reduce storage, packaging, handling and transportation costs. Vacuum evaporation is the predominant method used by the food industry to produce liquid food concentrates, despite serious drawbacks (poor product quality, high energy demand). This paper describes the research efforts to develop alternative techniques that could be applied on an industrial scale to overcome the disadvantages of currently used concentration methods. A major part of these attempts is focused on the application of osmotic membrane techniques, namely direct osmosis, membrane distillation and osmotic distillation.

Mass transfer kinetics during osmotic preconcentration aiming at minimal solid uptake

A model fruit (apple) was used to study mass transfer kinetics during osmotic preconcentration aiming at minimal solid uptake. The effects of process temperature, osmotic solution concentration and ‘molecular size’ of osmotic solute on water loss (WL) and solid gain (SG) were evaluated. Temperature and concentration effects were evaluated with 45–65% (by weight) sucrose solutions at 20–50 °C. The effect of solute size was monitored using corn syrup solids with different degrees of polymerisation (dextrose equivalent (DE) levels between 18 and 42). Increased temperatures gave increased WL and SG rates, favouring faster water loss (higher WL/SG ratios). Increased concentrations also resulted in higher WL and SG rates; yet, they favoured faster solid uptakes (lower WL/SG ratios). Among all sucrose treatments, preconcentration in 55% sucrose solution at 50 °C gave the highest WL/SG ratio. Overall mass (solids) transfer coefficient decreased with the size of osmotic solute. Corn syrup solids of larger ‘molecular size’ (<38 DE) gave negative net solid gain values, indicating a sugar uptake marginally inferior to leaching of fruit solids; the 42 DE corn solids gave by far the highest WL/SG ratio among all experimental treatments.

Apparent mass diffusivities in fruit and vegetable tissues undergoing osmotic processing

Abstract Apparent mass (water and solute) diffusivities were measured during osmotic processing of model fruit (apple) and vegetable (potato) tissues. Among process parameters, temperature had the largest positive effect on moisture ( D w ) and soluble solids ( D ss ) diffusivity. Increased concentration gave increased moisture and decreased solute diffusivities. The dehydration efficiency index ( D w D ss ratio) increased with concentration but decreased or remained constant with temperature. Using the right size of osmotic solute it was possible to maintain satisfactory moisture diffusivities with nearly zero net solute uptake. Freeze/ thaw-induced tissue damage caused a dramatic decrease in dehydration efficiency. Both moisture and solute diffusivities followed Arrhenius kinetics with activation energies ( E a ) ranging between 21.2 and 29.7 kJ mol −1 K −1 . Cell level explanations on response differences are attempted.

Kinetics of osmotic dehydration of a highly shrinking vegetable tissue in a salt-free medium

Abstract The kinetics of water removal and solute uptake during osmotic dehydration of a highly shrinking vegetable tissue (potato) in a salt-free osmotic medium (corn syrup solids) were studied. Increased temperatures (up to 45 °C) gave highly increased rates of dehydration and net loss of soluble solids ranging between 4.4 and 13.4% of total initial solids. Half dehydration time at 50 °C, was half of that measured at room temperature. Processing at 50 °C, however, was followed by extensive, nearly linear (with time) sugar uptake, reaching 50% of initial solids within 5 h. Half dehydration time and mass (water) diffusivity followed Arrhenius type kinetics with activation energies of 21.2 and 28.7 kJ mole −1 , respectively. Shrinkage experiments revealed a very strong correlation between the rate of volume decrease and the rate of moisture removal. Within the industrially applicable processing time, volume of removed water was identical to shrinkage induced loss of product volume. Concentrated solutions of corn syrup solids seem to be suitable for efficient osmotic dehydration of potato-like vegetable tissues, without suffering the negative impact of extensive solute uptake.

Olive Mill Wastewater Treatment

The cultivation of olive trees and the production and use of olive oil has been a well-known and established practice in the Mediterranean region for more than 7000 years. The consumption of olive oil is rapidly increasing worldwide, due to its high dietetic and nutritional value. According to the IOOC (2004), the production of olive oil increased from 1.85 million tons in 1984 to 3.17 million tons in 2003 (70% increase) (Table 8.1). There are approximately 750 million productive olive trees worldwide, 98% of them located in the Mediterranean region, where more than 97% of olive oil is produced. The three major olive oil producers worldwide are Spain, Italy, and Greece, followed by Turkey, Tunisia, and to a lesser extent Portugal, Morocco, and Algeria. The data presented in Figure 8.1 reflect the importance of the olive oil sector in the Mediterranean area and consequently the magnitude of the problems related with the disposal of large amounts of wastes produced during olive oil production. The traditional press extraction method as well as the continuous three-phase decanter process, which is most widely used for the production of olive oil, generate three products: olive oil (20%) and two streams of waste: a wet solid waste (30%) called ‘‘crude olive cake’’ or ‘‘olive husk’’ and an aqueous waste called ‘‘olive mill wastewater’’ or ‘‘olive mill effluent’’ or ‘‘alpechin’’ (50%). The solid waste (crude olive cake) is the residue that remains after the first pressing of the olives and is a mixture of olive pulp and olive stones. At present, olive husk is processed in seed oil factories in order to extract the small amount of oil remaining in the waste. Both crude and exhausted olive cake can be used as solid fuels (due to their high heating

Drying and Shrinkage Kinetics of Solid Waste of Olive Oil Processing

The problems created in managing olive mill wastewater (OMW) have been extensively investigated during the last few years. In most cases, dehydration of olive mill wastes is a first step before developing further applications. The subject of this study was to determine the drying behavior of OMW solid fraction (OMWS). Drying (moisture vs time) and shrinkage (image vs time) data were obtained on slabs of OMWS in an air dryer operated at 60–80°C. The effective diffusivity was determined using (a) the simplified solution of Ficks second law and (b) the method of slopes of the drying curve, taking into account the effect of moisture content on diffusivity and sample shrinkage. The combined effect of moisture content and temperature on effective diffusivity was expressed by an empirical model. In addition, each moisture loss and shrinkage curve was fit to 10 simplified drying models. The dependence of the best descriptive model constants on drying temperature was expressed by an appropriate type of model.

Sustainability and Ethics Along the Food Supply Chain

Sustainable food supply chains are mostly based on sustainable agricultural production and food processing schemes. They employ efficient production; processing; distribution systems that protect quality, assure safety, and promote fair and transparent distribution of created value; consumer access to wholesome-healthy food at acceptable prices; and sustainable development of rural communities. Ensuring a safe and abundant food supply, and contributing to healthier people everywhere, poses a double challenge with a significant impact on future developments in food process technology and food sciences in general. There is a need to formulate, design, process, and label food to help the average consumer live on a healthier diet, moving away from obesity and diet-related diseases. There is also a need to reconsider and upgrade the role and impact of food sciences in the sustainable food supply chain, so as to increase visibility, responsibility, and effectiveness on feeding the starving population groups all over the world, including the “developed” countries. Securing adequate and safe food, at the primary production level, requires reorientation of production schemes toward sustainable methods, moving away from intensification-induced food crises (i.e., BSE, dioxins, antibiotics, growth hormones). Sustainable processing calls for minimal (often nonthermal) processes with low energy inputs and minimal mass/quality losses, with due respect to environmental issues. At the consumer level, there is a need to improve consumer awareness of real values in food (nutrition, quality, safety). Finally, there is a great deal of corporate responsibility for proper design and fair marketing of foods that promote consumer health and well-being.