Cooking Stage Research Articles

Impact of dissolved matter in the oxygen delignification stage

The presence of dissolved matter in the pulp suspension in an oxygen (O2) delignification stage, consisting mainly of dissolved lignin, is normally considered to negatively affect the delignification rate due to the competing reactions between the fiber bound lignin and the lignin dissolved in the filtrate. Recirculated oxidized filtrate from the post-O2 washing is usually considered to be less harmful to the delignification efficiency than unoxidized dissolved matter originating from the cooking stage. To develop a better understanding of the mechanisms of the dissolved matter’s reactions and impact on the O2 stage performance, laboratory oxygen delignification experiments with varying levels of unoxidized and oxidized dissolved matter were conducted. The results showed that unoxidized dissolved matter had a negative impact on the delignification in the O2 stage, whereas oxidized dissolved matter actually had a positive effect. The delignification efficiency of the laboratory experiments thus depends on both the amount of dissolved matter and its origin. The pulp viscosity decreased with increasing dissolved matter content irrespective of its origin but at higher COD levels; however, the viscosity drop was larger for the unoxidized dissolved matter. In terms of selectivity, the oxidized filtrate had a similar impact as additional NaOH charge. Both types of filtrates consumed hydroxide and the final pH decreased with increasing dissolved matter content. The final pH was significantly lower in the unoxidized filtrate experiments at higher COD levels, indicating a high reactivity between the unoxidized dissolved matter and the oxygen in the reactor. Based on the results, further understanding is achieved about the relation between pre-O2 washing performance and process configuration in an actual mill case, as well as the impact of dissolved matter on delignification. The importance of efficient removal of harmful unoxidized dissolved matter is verified, but the results also suggest that the oxidized dissolved matter that is recirculated from post-O2 washing actually has a significant positive impact on the delignification and is not just a potential problem in case of carryover to the bleach plant. Subsequently, pulp washing efficiency is critical both pre- and post-O2.

Food Chain Evaluator, a tool for analyzing the impacts and designing scenarios for the institutional catering in Lombardy (Italy)

A method was developed and applied to evaluate the impacts of food production for improving institutional catering in Lombardy (northern Italy) and to outline possible improved scenarios. The research takes into account different crop managements (i.e. organic agriculture and adoption of local products) and different dietary choices able to guaranty the same nutritional contents. The non-renewable energy consumed for the production of foods managed by the institutional catering system is proposed as indicator to compare different policies together with other indicators as productive land and productive cost. A case of study is presented to test the overall method. The outcomes of the work could support a reorientation of both the production and consumption systems. In general, the shift towards local and organic products implies a reduction of the impacts evaluated. Further, the important impacts of beef consumption, in particular in terms of energy and land consumption are demonstrated.The work permits an interesting insight about institutional catering, taking into account not only the single food chains but also the composition of the meals by different food products. An improvement of the tool is in progress in order to properly evaluate the stages of cooking, refrigeration, packaging, energy consumption in catering areas and food waste management. A sensitivity analysis will be carried out for assessing the reliability of the results. Finally, other complex environmental indicators such as carbon footprint or ecological footprint could represent other future interesting developments of the tool.

Improved impregnation efficiency and pulp yield of softwood kraft pulp by high effective alkali charge in the impregnation stage

Abstract A pulp yield increase up to 2% can be achieved by impregnation with a liquor containing 2 M effective alkali (EA) concentration instead of 1 M. The yield increase is due to higher cellulose and glucomannan contents in the pulp, which can be rationalized by less yield loss by peeling, as impregnation is more effective at an elevated EA level. A rapid loading of chips with alkali can be realized due to a high diffusion rate. When the temperature becomes higher in the cooking stage, enough alkali is available for delignification reactions without the risk of alkali depletion in the chip core, so that the delignification is more homogeneous.

Physicochemical properties and starch digestibility of Chinese noodles in relation to optimal cooking time

Changes in the physicochemical properties and starch digestibility of white salted noodles (WSN) at different cooking stage were investigated. The noodles were dried in fresh air and then cooked for 2–12min by boiling in distilled water to determine the properties of cooking quality, textural properties and optical characteristic. For starch digestibility, dry noodles were milled and sieved into various particle size classes ranging from 0.5mm to 5.0mm, and hydrolyzed by porcine pancreatic α-amylase. The optimal cooking time of WSN determined by squeezing between glasses was 6min. The results showed that the kinetics of solvation of starch and protein molecules were responsible for changes of the physicochemical properties of WSN during cooking. The susceptibility of starch to α-amylase was influenced by the cooking time, particle size and enzyme treatment. The greater value of rapidly digestible starch (RDS) and lower value of slowly digestible starch (SDS) and resistant starch (RS) were reached at the optimal cooking stage ranging between 63.14–71.97%, 2.47–10.74% and 23.94–26.88%, respectively, indicating the susceptibility on hydrolysis by enzyme was important in defining the cooked stage. The study suggested that cooking quality and digestibility were not correlated but the texture greatly controls the digestibility of the noodles.

Correlation of Thermal Conductivity of Instant Noodles with their Textural Property for Rehydration Study

AbstractA transient plane source method was introduced to an instant noodle system to characterize the rehydration property of noodles. The thermal conductivity of the white and whole wheat noodles was measured and correlated to their texture properties. The thermal conductivity of the noodles had a tendency to increase with increasing moisture content. Furthermore, a linear relationship (R2 > 0.95) was observed between the thermal conductivity of the noodles and their maximum extensional force depending on the moisture content. The thermal conductivity and maximum extensional force of noodles distinctly varied at the initial stage of cooking and then reached a plateau. However, their sensory firmness had a tendency to linearly decrease with cooking time. The change in the thermal conductivity of the noodles during cooking favorably correlated to the pattern of their maximum extensional force and rehydration rate.Practical ApplicationsThe improvement of rehydration rate of instant noodles has been a challenge faced by the food industry. However, the study on noodle rehydration is generally dependent on empirical and subjective measurements. In this study, a novel thermal technology based on the modified transient plane source method was utilized to characterize the rehydration property of instant noodles. One‐dimensional upward heat flow was applied to measure the thermal conductivity of disc‐shaped flat noodles. The thermal conductivity of the noodles was correlated with their instrumental and sensory texture properties depending on moisture content and cooking time. The method applied in this study can be utilized as a feasible tool to study the rehydration property of noodles during cooking by providing more scientific and fundamental thermal information.

Process design and economics of an aluminium chloride catalysed organosolv process

In this work, an organosolv process using beech wood as the feedstock, a mixture of water and methanol (50 vol%) as the solvent and aluminium chloride as the catalyst is designed. Different to other organosolv processes, the formation of the high value-added product furfural occurs already in the cooking stage with a quite high yield (40 mol% based on a lab scale literature process). Different to furfural producing processes, the cellulose remains in the solid phase in high quantity (93 wt% of the initial based on a lab scale literature process). The plant is designed in the way that 99.7 wt% of methanol is recovered. Another specification is the isolation of 95 wt% furfural with a purity of more than 99.5 wt%. After consecutive conversion of cellulose, the minimum sugar selling price of glucose as a dilute solution is calculated as 329 $/t depending strongly on the furfural yield as well as the application of lignin and the corresponding selling price.

INVESTIGATION OF THE APPROPRIATE COOKING TEMPERATURE FOR FRESHLY HARVESTED MATURE CORN COBS

The investigation of the appropriate cooking temperature for freshly harvested mature corn cobs is presented. The process of Combination cooking method was utilized in the experimentation to ensure the achievement of the appropriate temperature and duration for the cooking stage. The appropriate cooking temperature and duration was found to be 195 o C and 30 minutes respectively. Variations in initial moisture content of the freshly harvested cobs (69.7 85.3% wb) did not affect the cooking temperature and duration. Cooking at the determined appropriate temperature and duration resulted in a properly cooked corn cob.

Indoor emission, dispersion and exposure of total particle-bound polycyclic aromatic hydrocarbons during cooking

Cooking processes highly contribute to indoor polycyclic aromatic hydrocarbon (PAH) pollution. High molecular weight and potentially carcinogenic PAHs are generally found attached to small particles, i.e., particulate phase PAHs (PPAHs). Due to the fact that indoor particle dynamics have been clear, describing the indoor dynamics of cooking-generated PPAHs within a specific time span is possible. This paper attempted to quantify the dynamic emission rate, simultaneous spatial dispersion and individual exposure of PPAHs using a cooking source. Experiments were conducted in a real-scale kitchen chamber to elucidate the time-resolved emission and effect of edible oil temperature and mass. Numerical simulations based on indoor particle dynamics were performed to obtain the spatial dispersion and individual inhalation intake of PPAHs under different emission and ventilation conditions. The present work examined the preheating cooking stage, at which edible oil is heated up to beyond its smoke point. The dynamic emission rate peak point occurred much earlier than the oil heating temperature. The total PPAH emission ranged from 2258 to 6578 ng upon heating 40–85 g of edible oil. The overall intake fraction by an individual within a period of 10 min, including 3 min for heating and 7 min for natural cooling, was generally ∼1/10,000. An important outcome of this work was that the overall intake fraction could be represented by multiplying the range hood escape efficiency by the inhalation-to-ventilation rate ratio, which would be no greater than the same ratio. The methodology and results of this work were extendible for the number-based assessment of PPAHs. This work is expected to help us understand the health risks due to inhalation exposure to cooking-generated PPAHs in the kitchen.

Physico-chemical properties of fractionated softwood kraft lignin and its potential use as a bio-based component in blends with polyethylene

This study describes a systematic characterization of lignin samples fractionated from industrial black liquor and an evaluation of their suitability as a component (50 wt.%) in thermoplastic blends with polyethylene with a special emphasis on tensile and impact properties. Industrial softwood kraft lignin was isolated from three different cooking stages and subsequently fractionated by sequential acid precipitation. Altogether, nine lignin fractions were subjected to several chemical/thermal analyses to compare their structural features and thermal decomposition properties. Lignin samples precipitated at pH 10.5 exhibited the highest molecular weight (Mw) and purity, demonstrated by the lowest content of sulfur and polysaccharides. In contrast, samples precipitated at a low pH in general exhibited higher amount of impurities and low methoxyl group content. It was found that lignin precipitated at low pH contained the biggest share of sulfur present in kraft lignin. However, about 70 % of sulfur in these samples is present in non-bounded form and could be extracted with CS2. Additionally, low Mw lignin exhibited a significantly lower Tg value, which could favor material processing. A notable decrease in the thermal stability of the tested lignin samples was observed with a decrease in the molecular weight. In addition, lignin with a low Mw, high phenolic hydroxyl groups, and lower number of double bonds seems to be favorable for increased tensile strength and elastic modulus of the polyethylene–lignin blend materials.

Oxygen Delignification of Acid Sulfite and Bisulfite Softwood Pulps

This study discusses alternatives for the production of sulfite pulps cooked to high kappa numbers, and a subsequent oxygen treatment by using the same cation in the cooking and in the oxygen stages. Magnesium was used as a cation during both the cooking and oxygen delignification stages. By using the same cation in the cook and in oxygen delignification, it is theoretically possible to recover filtrates and send them to the chemical recovery system, meaning that the discharge of pollutants will be very low. Acid sulfite and bisulfite pulps at yields between 56 and 57% (kappa number between 50 and 55) were produced and then delignified with oxygen and magnesium hydroxide to a kappa number between 25 to 30. It was found that the delignification process time was shorter and the yield and viscosity increased, compared with delignification to the same kappa number (25 to 30) for a single cooking stage. The tear and tensile strengths were however unchanged, regardless of delignification process used.

Odor and VOC emissions from pan frying of mackerel at three stages: raw, well-done, and charred.

Many classes of odorants and volatile organic compounds that are deleterious to our wellbeing can be emitted from diverse cooking activities. Once emitted, they can persist in our living space for varying durations. In this study, various volatile organic compounds released prior to and during the pan frying of fish (mackerel) were analyzed at three different cooking stages (stage 1 = raw (R), stage 2 = well-done (W), and stage 3 = overcooked/charred (O)). Generally, most volatile organic compounds recorded their highest concentration levels at stage 3 (O), e.g., 465 (trimethylamine) and 106 ppb (acetic acid). In contrast, at stage 2 (W), the lowest volatile organic compounds emissions were observed. The overall results of this study confirm that trimethylamine is identified as the strongest odorous compound, especially prior to cooking (stage 1 (R)) and during overcooking leading to charring (stage 3 (O)). As there is a paucity of research effort to measure odor intensities from pan frying of mackerel, this study will provide valuable information regarding the management of indoor air quality.

Characterization of dissolved lignins from acetic acid Lignofibre (LGF) organosolv pulping and discussion of its delignification mechanisms

Abstract Birch chips were cooked by means of the Lignofibre (LGF) organosolv process in acetic acid (AA) and phosphinic acid (H3PO2) at 150°C. The delignification rate and structure of the dissolved lignin was followed as a function of time. The degree of delignification increased steadily up to 88% during the 120 min treatment time. The dissolved lignins were precipitated from the spent liquor (SL) by water addition, washed, and purified for the analyses. Elemental analysis, 31P nuclear magnetic resonance (NMR), heteronuclear single-quantum coherence (HSQC) NMR, pyrolysis-gas chromatography/mass spectrometry (GC/MS), and gel permeation chromatography (GPC) were applied for the structural elucidation. It was found that the cleavage of the β-aryl ether linkages is the main reaction leading to delignification, accompanied by the formation of free phenolic hydroxyl groups and reduction in the content of aliphatic hydroxyl groups. The structure of the dissolved lignin remained the same after the drastic changes at the early stages of cooking (up to 30 min cooking time), indicating that secondary reactions (e.g., condensation) do not take place to a significant extent. H3PO2 probably enhances the acidolysis reaction via an ester derivative that both boosts the cleavage reaction and prevents the formation of the carbocation intermediate that induces condensation. Homolytic cleavage reactions may take place parallel to the acidolytic reactions.

Design and construction of low shear laminar transport system for the production of nixtamal corn dough

The tortilla is obtained by the traditional process of nixtamalization. This process has two disadvantages: production of liquid waste and it is in batches. Extrusion has resolved the problem of liquid waste, however, extrusion as of yet, has not been able to replace the traditional process of nixtamalization. This is because corn dough is a pseudoplastic fluid, which changes its viscosity in the presence of high shear velocities that occur inside the extruder. With this in mind, the following investigation proposes the mechanical design and construction of a low shear laminar transport system (LSLTS) for the production of corn dough for tortillas. This system consists of two thermally isolated stages: transport and cooking stages. The results showed that the prototype obtained meets the characteristics of homogenous cooking, low shear, absence of liquid waste and the product meets the specifications for nixtamal dough.

Effect of Processing Conditions on Calcium Content, Firmness, and Color of Papaya in Syrup

Calcium impregnation is used as a pretreatment in the processing of papaya in syrup. The effect of process temperature (30 and 45°C), calcium source (calcium gluconate and calcium lactate), calcium concentration (0.5 and 1.5% w/w), and pH (4.2 and 6) were studied. The mineral source affected significantly the calcium uptake and the fruit firmness, and therefore, the product quality maximum content of calcium in the fruit was 240 and 72 mg/100 g fresh fruit in 8 h of treatment with calcium lactate and calcium gluconate, respectively. Greater firmness was observed in samples impregnated with calcium lactate. Impregnation treatments did not affect the surface color of fruit. Finally, the effect of cooking in sucrose syrup on product quality attributes (calcium retention, firmness, and color) was analyzed. Cooking in syrup had a positive effect on tissue firmness, despite the decrease of calcium content. During cooking in syrup, calcium content of treated fruit decreased between 9% and 37%. However, the calcium content of fruit in syrup was up to 6 times higher than in fresh fruit. Moreover, the cooking stage had a strong influence on color parameters, leading to a processed product darker than fresh fruit.

Additional cooking fuel supply and reduced global warming potential from recycling charcoal dust into charcoal briquette in Kenya

Rising demand for energy is one of the major challenges facing the world today and charcoal is a principal fuel in Kenya. Faced with energy poverty many poor households turn to briquette making. This study assessed the additional cooking fuel obtained from recycling charcoal dust into charcoal briquettes. It applied Life Cycle Assessment (LCA) to assess the global warming potential (GWP) from use of charcoal and production of briquettes from charcoal dust and cooking a traditional meal for a standard household of five people. Native vegetation of Acacia drepanolobium and a low efficiency kiln were considered the common practice, while an Acacia mearnsii plantation and a high efficiency kiln was used as an alternative scenario. Charcoal and kerosene were considered as reference fuels. Recovering charcoal dust for charcoal briquettes supplied an additional 16% cooking fuel. Wood carbonization and cooking caused the highest GWP, so there is a need for technologies to improve the efficiency at these two stages of charcoal briquettes and charcoal supply chain. Supplying energy and cooking a traditional meal in a combined system using charcoal and recovering charcoal dust for charcoal briquettes and charcoal alone accounted for 5.3–4.12 and 6.4–4.94 kg CO2 eq. per meal, respectively, assuming trees were not replanted. These amounts declined three times when the carbon dioxide from the carbonization and cooking stages was assumed to be taken up by growing biomass. This requires replanting of trees cut down for charcoal if the neutral impact of biomass energy on GWP is to be maintained.

Effects of process stages on Turkish delight/lokum microbiological quality

SummaryThe sources of microbiological contamination at the lokum production lines of two local confectionaries were determined. Surface samples from the production lines were evaluated by standard and ATP bioluminescence methods. Microbial loads of raw materials were also determined. The trays and cutting knives were found to be the primary contamination sources, and personnel hands were found to be the secondary contamination sources, while all of them were found to be the secondary sources when the standard swab method was applied. Raw materials were not sources of contamination, because of their microbiological loads and the following high‐temperature cooking stages. The microbial loads of lokum also were not high, due to product contents and the processes applied to lokum. There is a need for further studies related to the effects of process steps on the physical and the chemical quality of lokum. Training for workers in food safety at the confectionaries is also needed.

The structural features of hemicelluloses dissolved out at different cooking stages of active oxygen cooking process

This work described the morphologic changes of corn stalk and the structural characterization of its hemicelluloses dissolved in yellow liquor at different cooking stages. The results showed that active oxygen cooking process was an efficient method to depolymerize the corn stalk into cellulose, hemicelluloses, and lignin as a pretreatment of biomass conversion. This cooking process can also be divided into three phases: bulk delignification, extended delignification, and residual delignification. During the heating-up period 57.67% of hemicelluloses and 62.31% of lignin were removed from the raw material. However, only 15% of hemicelluloses and 23.21% of lignin were removed during at temperature’ period. The hemicelluloses from the corn stalk and yellow liquor were composed of (1→4)-β-D-xylopyranose backbones substituted with α-l-arabinofuranosyl, 4-O-methyl-α-D-glucuronic acid, and some methoxyl residues. The backbones of hemicelluloses were gradually cleaved during the cooking process. The acetyl groups substituted with xylopyranosyl residues were completely cleaved during the cooking process.

Effect of curd washing on cheese proteolysis, texture, volatile compounds, and sensory grading in full fat Cheddar cheese

Curd was washed to varying degrees during Cheddar cheese manufacture, by partial replacement of whey with water at the early stages of cooking, to give target levels of lactose plus lactic acid in cheese moisture of 5.3 (control), 4.5, 4.3 and 3.9% (w/w). The cheeses were matured at 8 °C for 270 days. While curd washing had little effect on composition or the mean levels of proteolysis (as measured by pH 4.6 soluble nitrogen and levels of free amino acids), it led to cheeses that were, overall, firmer and less brittle. Curd washing resulted in cheeses having lower levels of some volatile compounds, and being less acid, more buttery, sweeter, saltier and creamier than non-washed cheeses that had more 'sweaty', pungent and farmyard-like sensory notes. The results suggest that curd washing during Cheddar manufacture may be used as a means of creating variants with distinctive flavour profiles.

Reed Three-Stage Counter-Current Batch Cooking with Ethanol-Water

This article studied the pulp contrast of reed three-stage counter-current cooking and single-stage cooking, meanwhile analyzed the regulation of the yield , the hardness of pulps and the properties of the waste liquor from each cooking stage of reed three-stage counter-current batch cooking with ethanol-water process. The SEM and IR-FT were employed to gain more understanding on the change of lignin on fiber surface and the structural change of lignin separated from waste liquor of each stage. The results show that single-stage cooking need to keep 190°C for 4.0 hours to get the best results, while the three-stage counter-current cooking need 1.5 hours more, but the highest temperature fallen by 20°C and the screened pulp yield increased by 3.9%, also the Kappa number decreased by 11. In the process of reed three-stage counter-current batch cooking with ethanol-water, the degradation and removal of lignin and glycan occurs mainly in the first stage. After the first stage cooking, most fibroblasts did not reach the fiber separation point and the screened pulp yield is only 38.7%. After the second and third stage cooking, the fiber separation became better ,the screened pulp yield increased to 49.72% and the Kappa number decreased to 25.6 . As the analysis of the results from the each-stages lignin by IR-FT, the structure of lignin had no significant difference .

Design of a sustainable packaging in the food sector by applying LCA

The choice of a sustainable packaging alternative is a key issue for the improvement of the environmental performances of a product, both from a production perspective and end-of-life management. The present study is focused on the life cycle assessment (LCA) of two packaging alternatives of a poultry product, in particular a polystyrene-based tray and an aluminum bowl (70 wt% primary and 30 wt% secondary aluminum) were considered. The LCA was performed according to ISO 14040-44 and following a “from-cradle-to-grave” perspective. The following stages were considered: production, use phase (i.e., cooking), and end-of-life. Different end-of-life scenarios were hypothesized. Greenhouse Gas Protocol, Cumulative Energy Demand, and ILCD midpoint method were used in the impact assessment (LCIA). The aluminum bowl was carefully designed in order to allow its use during the cooking stage of the poultry product in the oven and to reduce the cooking time (40 min instead of 50 min needed when using a conventional bowl) at 200 °C: cooking time reduction allows electric energy savings equal to 0.21 kWh (1.38 kWh instead of 1.59 kWh). Electric energy savings become of primary importance to reduce overall emissions, in particular CO2 eq emissions, especially in those countries such as Italy and Germany where there is a predominance of fossil fuels in the electric energy country mix. Over the entire life cycle of the two alternatives considered (taking into account production, transport, cooking, and end-of-life), cooking stage has the most impact; so, the specific design of the packaging bowl/tray can allow significant lowering of the overall CO2 eq emissions. In addition, when designing an aluminum-based packaging, the content of the secondary material can be significantly increased in order to reach higher sustainability during the production stage.