Exergy analysis in industrial food processing

The sustainable provision of food on a global scale in the near future is a very serious challenge. This thesis focuses on the assessment and design of sustainable industrial food production chains and processes by using the concept of exergy which is an objective metric based on the first and second law of thermodynamics. Three case studies are presented, two on a chain level (industrial bread and mushroom production), and one on a process level (conceptual spray drying of a lactose solution). Furthermore, industrial food production chains are categorized as thermodynamic archetypes and general rules are derived for their sustainable design exergy-wise. Additional methodological aspects related to e.g. the impact of system boundaries, the allocation of exergy values to waste streams, and the influence of the selection of the environment of reference on the outcome of the analysis, are also discussed

Kinetic Characterization of Galacto-Oligosaccharide (GOS) Synthesis by Three Commercially Important b-Galactosidases

Many b-galactosidases show large differences in galacto-oligosaccharide (GOS) production and lactose hydrolysis. In this study, a kinetic model is developed in which the effect of lactose, glucose, galactose, and oligosaccharides on the oNPG converting activity of various b-galactosidases is quantified. The use of oNPG as a competing substrate to lactose yields more information than can be obtained by examining only the conversion of lactose itself. The reaction rate with lactose or oligosaccharides as substrate relative to that with water as acceptor is much higher for the b-galactosidase of Bacillus circulans than the bgalactosidases of Aspergillus oryzae and Kluyveromyces lactis. In addition, the bgalactosidase of B.circulans has a high reaction rate with galactose as acceptor, in contrast to those of A. oryzae and K. lactis. The latter two are strongly inhibited by galactose. These differences explain why b-galactosidase of B. circulans gives higher yields in GOS production than other b-galactosidases. Many of the reaction rate constants for the b-galactosidase isoforms of B. circulans increase with increasing molecular weight of the isoform. This indicates that the largest isoform b-gal-A is most active in GOS production. However, its hydrolysis rate is also much higher than that of the other isoforms, which results in a faster hydrolysis of oligosaccharides as well

Exergy analysis of membrane capacitive deionization (MCDI)

Capacitive deionization (CDI) and membrane capacitive deionization (MCDI) are widely considered as promising, highly energy efficient processes for water desalination, of which commonly used performance indicators are the average salt adsorption rate, the salt removal efficiency, and the charge efficiency. Quantification of the sustainability performance of CDI and MCDI is still scarce, and in this paper, we use exergy analysis to evaluate the resource use efficiency of membrane capacitive deionization (MCDI). The electric as well as chemical exergies of the salt solution, and the stored ions, are used to calculate the exergy efficiency (ηex) and cumulative exergy losses (CEL) ranging between 2 to 13% and 0.5 to 8 J/mol water, respectively. From an exergetic point of view, passive adsorption in combination with active desorption (−0.9 V) is favorable, yielding the highest ηex and lowest CEL values. The combination of active salt adsorption using an electric field, with either passive or active desorption gives higher productivities, but at the cost of a disproportionate amount of exergy (and energy) inpu

The Use of Exergetic Indicators in the Food Industry – A Review

Sustainability assessment will become more relevant for the food industry in the years to come. Analysis based on exergy including the use of exergetic indicators and Grassmann diagrams is a useful tool for the quantitative and qualitative assessment of the efficiency of industrial food chains. In this paper we review the methodology of exergy analysis and the exergetic indicators that are most appropriate for use in the food industry. The challenges of applying exergy analysis in industrial food chains and the specific features that food processes are also discussed

Processing concepts for the use of green leaves as raw materials for the food industry

Large-scale processing of leaves for food applications requires quick processing or stabilisation to avoid perishability, due to the high moisture content in this biomass. Leaf perishability is compounded by the seasonal availability of crops, like sugar beet plants, of which the leaves are regarded as a potential protein source. This study evaluates the resource efficiency of a hypothetical sugar beet leaf processing chain by comparing supply chain options. First, two options consider leaf processing with and without stabilising the leaves by freezing. Then, these two options are considered in a centralised and decentralised process configuration. The latter places leaf freezing and pressing at the farm and further processes occur at a central facility. Energy usage and exergy consumption were used to quantify the thermodynamic performance of the processing options. Freezing has negligible effect on the process-ability of the leaves in terms of protein content and protein yield. The overall resource efficiency of the process was dominated by the amount of leaf material effectively used, which stresses the importance of full use of all (side-)streams. This outcome also explains the limited additional energy requirements for freezing. Exergetic indicators were affected by variations on the dry matter content of the starting biomass, compared to a negligible effect of other parameters (equipment scale, efficiency or energy use). Transportation load and soil quality were also discussed for the centralised and decentralised configurations. On-farm processing of the leaves (decentralised chain) clearly reduces the transportation load due to the large difference in bulk densities of leaves (73 kg/m3) and leaf juice (1000 kg/m3). Additionally, decentralised scenarios enable direct returning of the leaf pulp to the soil and thereby improving soil quality (i.e. nutrient retention and fe rtility). Soil quality is required to fully assess the use of biomass that is currently regarded as waste, but that actually plays a role in soil fertility. Therefore, the preferred chain configuration would be a decentralised system where the leaves are directly pressed at the farm, the pulp is used to fertilise the soil, and the leaf juice is chilled transported to a centralised factory

Exergetic comparison of food waste valorization in industrial bread production

This study compares the thermodynamic performance of three industrial bread production chains: one that generates food waste, one that avoids food waste generation, and one that reworks food waste to produce new bread. The chemical exergy flows were found to be much larger than the physical exergy consumed in all the industrial bread chains studied. The par-baked brown bun production chain had the best thermodynamic performance because of the highest rational exergetic efficiency (71.2%), the lowest specific exergy losses (5.4 MJ/kg brown bun), and the almost lowest cumulative exergy losses (4768 MJ/1000 kg of dough processed). However, recycling of bread waste is also exergetically efficient when the total fermented surplus is utilizable. Clearly, preventing material losses (i.e. utilizing raw materials maximally) improves the exergetic efficiency of industrial bread chains. In addition, most of the physical (non-material related) exergy losses occurred at the baking, cooling and freezing steps. Consequently, any additional improvement in industrial bread production should focus on the design of thermodynamically efficient baking and cooling processes, and on the use of technologies throughout the chain that consume the lowest possible physical exergy

Exergetic comparison of food waste valorization in industrial bread production

This study compares the thermodynamic performance of three industrial bread production chains: one that generates food waste, one that avoids food waste generation, and one that reworks food waste to produce new bread. The chemical exergy flows were found to be much larger than the physical exergy consumed in all the industrial bread chains studied. The par-baked brown bun production chain had the best thermodynamic performance because of the highest rational exergetic efficiency (71.2%), the lowest specific exergy losses (5.4 MJ/kg brown bun), and the almost lowest cumulative exergy losses (4768 MJ/1000 kg of dough processed). However, recycling of bread waste is also exergetically efficient when the total fermented surplus is utilizable. Clearly, preventing material losses (i.e. utilizing raw materials maximally) improves the exergetic efficiency of industrial bread chains. In addition, most of the physical (non-material related) exergy losses occurred at the baking, cooling and freezing steps. Consequently, any additional improvement in industrial bread production should focus on the design of thermodynamically efficient baking and cooling processes, and on the use of technologies throughout the chain that consume the lowest possible physical exergy

Processing concepts for the use of green leaves as raw materials for the food industry

Large-scale processing of leaves for food applications requires quick processing or stabilisation to avoid perishability, due to the high moisture content in this biomass. Leaf perishability is compounded by the seasonal availability of crops, like sugar beet plants, of which the leaves are regarded as a potential protein source. This study evaluates the resource efficiency of a hypothetical sugar beet leaf processing chain by comparing supply chain options. First, two options consider leaf processing with and without stabilising the leaves by freezing. Then, these two options are considered in a centralised and decentralised process configuration. The latter places leaf freezing and pressing at the farm and further processes occur at a central facility. Energy usage and exergy consumption were used to quantify the thermodynamic performance of the processing options. Freezing has negligible effect on the process-ability of the leaves in terms of protein content and protein yield. The overall resource efficiency of the process was dominated by the amount of leaf material effectively used, which stresses the importance of full use of all (side-)streams. This outcome also explains the limited additional energy requirements for freezing. Exergetic indicators were affected by variations on the dry matter content of the starting biomass, compared to a negligible effect of other parameters (equipment scale, efficiency or energy use). Transportation load and soil quality were also discussed for the centralised and decentralised configurations. On-farm processing of the leaves (decentralised chain) clearly reduces the transportation load due to the large difference in bulk densities of leaves (73 kg/m3) and leaf juice (1000 kg/m3). Additionally, decentralised scenarios enable direct returning of the leaf pulp to the soil and thereby improving soil quality (i.e. nutrient retention and fe rtility). Soil quality is required to fully assess the use of biomass that is currently regarded as waste, but that actually plays a role in soil fertility. Therefore, the preferred chain configuration would be a decentralised system where the leaves are directly pressed at the farm, the pulp is used to fertilise the soil, and the leaf juice is chilled transported to a centralised factory