The kneading process: A systematic review of the effects on dough rheology and resulting bread characteristics, including improvement strategies

High freeze-thaw stability of Pickering emulsion stabilized by SPI-maltose particles and its effect on frozen dough

Pickering emulsions with good freeze-thaw stability are essential in frozen food applications. This study developed a high freeze-thaw stabilized soy protein isolate (SPI)-maltose (M) Pickering emulsion and applied it to frozen doughs to investigate and reveal its impacts on the processing properties of the frozen dough. The results showed that after the freeze-thaw cycle, with a volume ratio of 1:2 of SPI to M, the appropriate amount of M changed the structure of SPI. This resulted in the Pickering emulsion prepared by the SPI exhibiting the least droplet coalescence and the best freeze-thaw stability. The results of dough rheological properties, textural properties, and binding capacity with water demonstrated that Pickering emulsions effectively inhibited the loss of gluten protein network structure in the dough after freeze treatment and increased the binding capacity of gluten proteins with starch and water in the dough. The best results were obtained with the incorporation of 3 % SPI-M high freeze-thaw stability, where the amount of bound water following three freeze-thaw cycles was 4.27 times higher than in doughs without Pickering emulsion. Overall, this study is significant for enhancing the freeze-thaw stability of Pickering emulsions stabilized by proteins and providing a new application route for Pickering emulsions.

Innovations in nondestructive assessment of baked products: Current trends and future prospects

Rising consumer awareness, coupled with advances in sensor technology, is propelling the food manufacturing industry to innovate and employ tools that ensure the production of safe, nutritious, and environmentally sustainable products. Amidst a plethora of nondestructive techniques available for evaluating the quality attributes of both raw and processed foods, the challenge lies in determining the most fitting solution for diverse products, given that each method possesses its unique strengths and limitations. This comprehensive review focuses on baked goods, wherein we delve into recently published literature on cutting-edge nondestructive methods to assess their feasibility for Industry 4.0 implementation. Emphasizing the need for quality control modalities that align with consumer expectations regarding sensory traits such as texture, flavor, appearance, and nutritional content, the review explores an array of advanced methodologies, including hyperspectral imaging, magnetic resonance imaging, terahertz, acoustics, ultrasound, X-ray systems, and infrared spectroscopy. By elucidating the principles, applications, and impacts of these techniques on the quality of baked goods, the review provides a thorough synthesis of the most current published studies and industry practices. It highlights how these methodologies enable defect detection, nutritional content prediction, texture evaluation, shelf-life forecasting, and real-time monitoring of baking processes. Additionally, the review addresses the inherent challenges these nondestructive techniques face, ranging from cost considerations to calibration, standardization, and the industry's overreliance on big data.

Technological and Nutritional Aspects of Bread Production: An Overview of Current Status and Future Challenges

Bakery products, especially bread, exist in many homes worldwide. One of the main reasons for its high consumption is that the main raw material is wheat, a cereal that can adapt to a wide variety of soils and climates. However, the nutritional quality of this raw material decreases during its industrial processing, decreasing the value of fibers, proteins, and minerals. Therefore, bread has become a product of high interest to increase its nutritional value. Due to the high consumption of bread, this paper provides a general description of the physicochemical and rheological changes of the dough, as well as the sensory properties of bread by incorporating alternative flours such as beans, lentils, and soy (among others). The reviewed data show that alternative flours can improve fiber, macro, and micronutrient content. The high fiber content reduces the quality of the texture of the products. However, new processing steps or cooking protocols, namely flour proportions, temperature, cooking, and fermentation time, can allow adjusting production variables and optimization to potentially overcome the decrease in sensory quality and preserve consumer acceptance.

Wheat Flour Quality Assessment by Fundamental Non-Linear Rheological Methods: A Critical Review

Wheat quality assessment involves physical, physicochemical, chemical, and sensory characterization of wheat kernels and the resulting wheat flour, dough, and bread. The physical tests conducted on wheat flour dough are mostly based on empirical methods. Empirical methods have been useful in industry and research to relate wheat flour quality to baking performance. However, these methods have the disadvantage of providing data in arbitrary units, which makes the fundamental interpretation of results difficult. Therefore, this review focuses on the use of fundamental rheological methods to determine wheat flour quality in terms of processing performance. During the transition from wheat flour to bread, wheat flour dough is mostly exposed to large deformations, and the quality of wheat flour determines its response to these large deformations and its baking quality. For this reason, this review only focuses on the application of fundamental rheological tests that are conducted in the non-linear viscoelastic region where wheat flour dough experiences large deformations.

Effects of quinoa flour (Chenopodium Quinoa Willd) substitution on wheat flour characteristics

Quinoa is a pseudo-cereal with great nutritional and functional qualities, serving as an excellent substitution to develop quinoa-containing foods. This study aimed to explore the influence of quinoa flour substitution on quality characteristics of wheat flour (WF). WF was substituted with different level of quinoa core flour, ground quinoa whole flour and recombined quinoa whole flour. Increasing levels of quinoa flour in WF declined dough swelling index, while increased falling number of composite flours. Besides, quinoa flour substitution considerably decreased the chemical forces of gluten in composite flours. The proportions α-helix and β-sheets reduced, while the random coil proportion increased in gluten secondary structure. SEM images revealed that the gluten network structure was severely damaged. Our findings indicated that substitution of WF with quinoa flours was promising to be developed as an ingredient for food products.

Application of CO2 Gas Hydrates as Leavening Agents in Black-and-White Cookies

In this unprecedented study, the application of CO₂ gas hydrates (GH) as a leavening agent to produce black-and-white cookies by replacing ammonium bicarbonate is investigated. Ammonium bicarbonate, the principal leavening ingredient in black-and-white cookies, has been linked to the creation of a carcinogenic substance known as acrylamide. Three distinct GH concentrations, 20%, 40%, and 50%, were utilized to determine the necessary amount to obtain a good leavening effect. However, the abrupt reduction in temperature brought on by the addition of GH had an inadmissible effect on the cookie dough. Consequently, an innovative kneading method carried out in a closed mixing unit at a high temperature was developed. The specific volume of the cookies when employing 50% GH as a baking agent was more than half that produced when using ammonium bicarbonate. In the cookies with GH, the springiness and hardness, which are the quality-determining textural characteristics of the pastry, remained within an acceptable range. The amount of acrylamide was reduced from 24.8 µg/Kg to around 18 µg/Kg by this research. Therefore, the presented study demonstrates the possibility of using CO₂ GH as a leavening agent in black-and-white cookies and in other products for a healthier future.

Effect of Mixing Time on Properties of Whole Wheat Flour-Based Cookie Doughs and Cookies

This study investigated if whole wheat flour-based cookie dough's physical properties were affected by mixing time (1 to 10 min). The cookie dough quality was assessed using texture (spreadability and stress relaxation), moisture content, and impedance analysis. The distributed components were better organized in dough mixed for 3 min when compared with the other times. The segmentation analysis of the dough micrographs suggested that higher mixing time resulted in the formation of water agglomeration. The infrared spectrum of the samples was analyzed based on the water populations, amide I region, and starch crystallinity. The analysis of the amide I region (1700-1600 cm^-1) suggested that β-turns and β-sheets were the dominating protein secondary structures in the dough matrix. Conversely, most samples' secondary structures (α-helices and random coil) were negligible or absent. MT3 dough exhibited the lowest impedance in the impedance tests. Test baking of the cookies from doughs mixed at different times was performed. There was no discernible change in appearance due to the change in the mixing time. Surface cracking was noticeable on all cookies, a trait often associated with cookies made with wheat flour that contributed to the impression of an uneven surface. There was not much variation in cookie size attributes. Cookies ranged in moisture content from 11 to 13.5%. MT5 (mixing time of 5 min) cookies demonstrated the strongest hydrogen bonding. Overall, it was observed that the cookies hardened as mixing time rose. The texture attributes of the MT5 cookies were more reproducible than the other cookie samples. In summary, it can be concluded that the whole wheat flour cookies prepared with a creaming time and mixing time of 5 min each resulted in good quality cookies. Therefore, this study evaluated the effect of mixing time on the physical and structural properties of the dough and, eventually, its impact on the baked product.

Identifying key factors and strategies for reducing oil content in fried instant noodles

Fried instant noodles have become a popular instant food in recent years, favored by consumers for their unique flavor and taste. Unfortunately, the oil content of instant noodles is generally high, so the rise of fat-related diseases poses a major health issue. From the perspective of the cost of instant noodle manufacturers and the health of consumers, it is of great significance to reduce the oil content of instant noodles. The aim of this review article is to provide an overview of the main factors, such as raw materials and production processes, affecting oil content in instant noodles in order to suggest specific strategies to reduce the oil content in the end product. From the literature reviewed, adding acetylated potato starch/carboxymethyl cellulose, hydroxypropyl methylcellulose, or preharvest-dropped apple powder in the noodle formulation could be a better choice to reduce oil uptake by 5%-20%. Instant noodles with lower oil content can be produced using novel alternative frying technologies, including microwave and vacuum frying. The proper management of the production processes and the implementation of enhancement strategies may result in a reduction of oil content in the end product.

Delineating the dynamic transformation of gluten morphological distribution, structure, and aggregation behavior in noodle dough induced by mixing and resting

To understand the formation of gluten network and its regulation on noodle qualities upon mixing and resting, the dynamic distribution and molecular transformation of gluten were tracked and quantified. Confocal laser scanning microscopy and scanning electron microscopy images showed that appropriate mixing (8 min) and resting (60 min) induced a compact gluten network with higher gluten junctions. Both height and width of protein molecular chains were increased by hydration during mixing and reduced after excessive resting (90 min). According to the size exclusion/reversed phase-HPLC profiles, mixing induced slight depolymerization of large glutenin polymer, and α-gliadin subunits were more susceptible to polymerization after appropriate mixing and resting. Increased mixing time was accompanied by the strengthening of ionic and hydrogen bonds, and the weakening of hydrophobic interaction. PCA and correlation analysis revealed the accurate regulation of mixing and resting induced dynamic distribution and evolution of gluten on the macroscopic noodle qualities.

Comparative study of physicochemical, nutritional, phytochemical, and sensory properties of bread with plantain and soy flours partly replacing wheat flour

Plantain flour (PLF) and soy flour (SF) were used to substitute wheat flour (10% and 20% w/w) in composite bread. Physicochemical, phytochemical, and sensory properties were investigated. Partial substitution by PLF significantly increased (p < .05) starch, amylose, ascorbic acid, and potassium content in bread samples. In contrast, a significant improvement (p < .05) in protein, fat, amylopectin, and calcium content was observed with SF substitution. Composite bread with PLF and SF together lowered the hydrolysis index (HI) and glycemic index (GI) as compared with whole wheat flour. The molar phytate to minerals (iron, zinc, and calcium) ratio in all composite loaves was lower than reported critical values, except for phytate to iron. Significant differences (p < .05) were found in color, specific volume, and texture characteristics of loaves made from partial substitution with PLF and SF. Sensory evaluation revealed that bread with 10% PLF exhibited better scores for appearance and willingness to pay than the control. In contrast, SF negatively affected (p < .05) the appearance, texture, color, overall acceptance, and willingness to pay. The trade‐off analysis indicated that PLF can be utilized to produce bread that meets consumers' demands, while incorporating SF as an alternative high‐nutrient density bread will be beneficial to health.

Normal rice flours perform better in gluten-free bread than glutinous rice flours

This study aims to determine gluten-free bread-making potential of different types of rice, particularly comparing normal rice versus glutinous rice flours. Proximate and chemical compositions, hydration, and dough mixing and pasting properties of ten rice cultivars (i.e., seven types of normal rice and three types of glutinous rice), and quality parameters (specific volume, texture profile, and crumb structure) of gluten-free bread from these flours were assessed. Significant differences were observed in flour properties among different types of rice. Significant correlations were observed between bread specific volume and rice amylose content (r = 0.91, p < 0.01), as well as pasting peak time (r = 0.86, p < 0.01) and final viscosity (r = 0.77, p < 0.01). Further, strong correlations were observed between bread resilience and properties of rice flour, such as amylose content (r = 0.91, p < 0.01), pasting peak viscosity (r = 0.83, p < 0.01), and final viscosity (r = 0.93, p < 0.01). In conclusion, the normal rice types exhibited much better gluten-free bread-making performances than glutinous flour. Important parameters of rice flour determining its gluten-free bread-making properties include amylose content, water retention capacity, and pasting properties. PRACTICAL APPLICATION: Compared with glutenous rice flour, normal rice flour leads to more viscous paste and gluten-free breads with larger volume, evener texture, and better resilience. This study provides guidance for practical uses of rice flours in improving gluten-free dough and bread quality.

Characteristics of Dough Rheology and the Structural, Mechanical, and Sensory Properties of Sponge Cakes with Sweeteners

Changes in the rheological properties of dough, as well as the microstructural, mechanical, and sensory properties of sponge cakes, as a function of the substitution of sucrose in a formulation with maltitol, erythritol, and trehalose are described. Moreover, the relationship between the examined properties was investigated. The replacement of sucrose with maltitol or trehalose did not affect the consistency index, whereas erythritol caused a decrease in its value. X-ray tomography was used to obtain the 2D and 3D microstructures of sponge cakes. All studied sweeteners caused the sponge cakes to have a typical porous structure. Erythritol and maltitol resulted in about 50% of the pores being smaller than 0.019 mm² and 50% of the pores being larger than 0.032 mm². Trehalose resulted in a homogeneous microstructure, 98% of whose pores were similar in size (0.019 to 0.032 mm²). The sponge cakes with polyols had a higher structure index than did the trehalose and sucrose samples. There were also significant differences in color parameters (lightness and chromaticity). The crust of the sponge cake with sweeteners was lighter and had a less saturated color than the crust of the sponge cake with sucrose. The sponge cake with maltitol was the most similar to the sponge cake with sucrose, mainly due to the mechanical and sensory properties. Trehalose led to the samples having high adhesiveness, which may limit its application as a sucrose substitute in sponge cake. Sensory properties were strongly correlated to cohesiveness, adhesiveness, and springiness and did not correlate to the 2D and 3D microstructures. It was found that 100% replacement of sucrose allows for a porous structure to be obtained. These results confirm that it is not the structure, but most of all the flavor, that determines the sensory perception of the sponge cakes.

Effect of yerba mate (Ilex paraguariensis) leaves on dough properties, antioxidant activity, and bread quality using whole wheat flour

This study investigated the effects of different yerba mate (YM) proportions (1.5, 2.5, and 4.5 g YM/100 g whole wheat flour (WWF) and particle sizes (245, 415.5, and 623.9 µm) on dough rheological properties, antioxidant activity, and bread characteristics. The addition of YM leaves led to a possible interaction between its phenolic compounds and the gluten network within the dough, without negative effects on dough formation. However, the larger YM particle size (623.9 µm) caused a weakening of the protein network, resulting in lower quality product compared to the other samples. Improved bread quality was found when the YM leaves were added at 2.5 g YM/100 g WWF. The total amount of phenolic compounds and the antioxidant activity increased as the proportion of YM increased in both flour and bread. Moreover, the phenolic compounds in 2.5 g YM/100 g WWF breads were stable during baking, showing no significant losses in the amount of phenolic compounds and antioxidant activity. These results suggest the YM can be successfully incorporated into baked product, improving its functional characteristics. PRACTICAL APPLICATION: This study evaluates the technological quality of bakery product made by incorporating yerba mate leaves in whole wheat flour. The results will contribute to the production of a bread with greater functional properties due to the presence of polyphenols and phytochemicals.

An extensive review: How starch and gluten impact dough machinability and resultant bread qualities

Wheat flour can form dough with a three-dimensional viscoelastic structure that is responsible for gas holding during fermentation and oven-rise, creating a typical fixed, open-cell foam structure of bread after baking. As the major components of dough, the continuous reticular skeleton formed by gluten proteins and the concentrated starch granules entrapped in gluten matrix predominantly determine dough rheological behaviors and bread qualities. This review surveys the latest literatures and draws out a conclusion from a plethora of information related to the filling effects of starch granules on gluten matrix and the cross-linking mechanisms between gluten proteins and starch granules, which is of great significance to provide sufficient scientific knowledge for development of bread with satisfactory attributes and quality control of end products.

History, mechanism of action, and toxicity: a review of commonly used dough rheology improvers

Dough rheology improvers, which often are oxidative reagents in nature, have long been used in bread-making industry to enhance protein crosslinking and subsequently improve the dough rheological properties and bread qualities. Numerous studies were conducted to explore the effects of these oxidative agents on dough quality improving, however, the underlying mechanism of their action during dough development has not been fully understood. Due to the public health concerns, multiple oxidative reagents were banned in some countries across the world, while others are still permitted in accordance with regulations. Therefore, a comprehensive understanding of their application, significance, and safety in bread manufacturing is necessary. This review aims to provide a detailed information about the evolutionary history of several commonly used oxidants acting as dough rheology improvers, their mechanisms of action, as well as their potential toxicity.

Evaluation of Fourteen Bread Wheat (Triticum aestivum L.) Genotypes by Observing Gas Exchange Parameters, Relative Water and Chlorophyll Content, and Yield Attributes under Drought Stress

Water scarceness is a major threat to wheat productivity under changing climate scenarios, especially in arid and semi-arid regions. However, growing drought-tolerant wheat genotypes could be a sustainable option to enhance wheat productivity under drought stress conditions. The aim of this study was to evaluate the effect of mild to severe drought stress on gas exchange parameters, relative water content, SPAD-chlorophyll value, and yield-related parameters of 14 wheat genotypes being cultivated in arid to semi-arid areas on large scale. The genotypes were grown in earthen pots under three drought levels, namely (1) control-well watered, (2) mild water stress, i.e., 60% water holding capacity, and (3) severe water stress, i.e., 40% water holding capacity. The drought was imposed from the jointing stage to physiological maturity. Drought significantly decreased net photosynthesis, stomatal conductance, relative water contents, 100-grain weight, and grain yield in all genotypes. However, the reduction percentage was different in different genotypes under drought stress compared with well-watered conditions. The highest relative water content (65.2%) was maintained by the genotype Galaxy-2013, followed by AAS-2011 (64.6%) and Johar-2016 (62.3%) under severe drought conditions. Likewise, Galaxy-2013 showed the highest net photosynthesis and stomatal conductance under severe drought conditions. The highest grain yield per plant (6.2 g) and 100-grain weight (3.3 g) was also recorded in Galaxy-2013 under severe drought conditions, while the highest grain yield under well-watered conditions was recorded in Johar-2016, followed by Galaxy-2013. These results suggest that wheat variety Galaxy-2013 could be cultivated extensively to obtain good wheat yield under limited water conditions.

Nutritional and Rheological Characteristics of Composite Flour Substituted with Baobab (Adansonia digitata L.) Pulp Flour for Cake Manufacturing and Organoleptic Properties of Their Prepared Cakes

Revalorization of Adansonia digitata L. "Baobab" pulp flour (BPF) to produce a notorious and functional cake in the current study was assessed. Wheat flour (WF 72%) was partially substituted by BPF at 5, 10, and 15% to prepare composite flour (WF + BPF) for potential cake manufacturing. Approximate chemical composition, macro- and microelements content, amino acids (AAs), total phenolic content (TPC), and antioxidant activity (AOA) of partially substituted composite flour (WF + BPF) were determined. The rheological properties of the composite flours were assessed using MIXOLAB. Moreover, an organoleptic evaluation of the baked cakes was performed with 20 trained panelists. The substitution with BPF significantly increased the total ash and crude fiber content in composite flour in a level-dependent manner, while moisture, crude fat, crude protein, available carbohydrates contents, and energy values were not significantly changed. Interestingly, macroelements such as Ca, K, and P were significantly increased, while Na was significantly decreased, whereas Mg content was not significantly changed. Similarly, microelements such as Zn, Fe, and Cu increased with the increase of BPF substitution. Significant increases in TPC and AOA were found by increasing the substitution with BPF. The biological value (BV), essential amino acid index (EAAI), protein efficiency ratio (PER), as well as essential amino acids (EAAs) requirement index (RI) were positively improved in WF + BPF. Adding BPF up to 10% not only improved the water absorption, α-amylase activity, and viscosity, but also caused a slight weakness in the gluten network, to produce a composite flour suitable for cake making. Conclusively, this study revealed that fortification with BPF up to 5-10% improved the nutritional quality without adverse effects on technological, and organoleptic characteristics and providing economic, commercial, and health benefits.

Challenges and Opportunities in Wheat Flour, Pasta, Bread, and Bakery Product Production Chains: A Systematic Review of Innovations and Improvement Strategies to Increase Sustainability, Productivity, and Product Quality

Pasta, bread, and bakery products are considered worldwide as essential foods for human nutrition. In particular, ancient wheats and whole wheat flours, despite being able to provide health benefits via bioactive compounds, present significant technological problems related to poorer dough rheological properties and final product characteristics. Moreover, both the food industry and consumers are increasingly sensitive to environmental impacts, highlighting the urgent need for sustainable innovations and improvement strategies, from cradle to grave, for the entire production chains, thus motivating this review. The aim of this review is to provide technological innovations and improvement strategies to increase the sustainability, productivity, and quality of flours, pasta, bread, and bakery products. This review is focused on the main operations of the production chains (i.e., wheat cultivation, wheat milling, dough processing, and, finally, the manufacturing of pasta, bread, and bakery products). To achieve this goal, the use of life-cycle assessment (LCA) analysis proved to be an effective tool that can be used, from early stages, for the development of eco-friendly improvement strategies. The correct management of the wheat cultivation stage was found to be essential since it represents the most impacting phase for the environment. Successively, particular attention needs to be paid to the milling process, the kneading phase, to breadmaking, and, finally, to the manufacturing of pasta. In this review, several specifically developed solutions for these essential phases were suggested. In conclusion, despite further investigations being necessary, this review provided several innovations and improvement strategies, using an approach “from cradle to grave”, able to increase the sustainability, productivity, and final quality of flour, semolina, pasta, bread, and bakery products.

Compliance with COVID-19 Preventive and Control Measures among Food and Drink Establishments in Bench-Sheko and West-Omo Zones, Ethiopia, 2020

Introduction

Despite the implementation of many preventive and control systems developed by governments, the spread of COVID-19 and its resulting infection rate are alarmingly increasing from time to time all over the world. In Ethiopia, public places visited by large numbers of people where preventive and control measures are poorly practiced are considered to be potentially contributing to the spread of the disease. Food and drink establishments are among the highly susceptible public establishments visited by large numbers of people who interact among themselves and with employees. Hence, this study aimed to measure the compliance with COVID-19 preventive and control measures among food and drink establishments in the selected towns of Bench-Sheko and West-Omo Zones in Ethiopia.

Methods

A cross-sectional study was conducted among food and drink establishments in selected towns of Bench-Sheko and West-Omo zones from May 15, 2020 to June 15, 2020. A census of all 324 food and drink establishments found in the study area was conducted, and data were obtained from managers of the establishments through face-to-face interviews. Data were entered in to Epidata manager and exported to SPSS version 24.0 for analysis. Percentage compliance score was computed to describe the level of compliance. Ethical approval was obtained from Mizan-Tepi University Institutional Review Board, and written informed consent was obtained from every participant.

Results

The overall compliance level with COVID-19 preventive and control measures was 55.5%. The majority (89%) of the food and drink establishments had functional hand washing facilities at the main entrance gate. Less than half of the food and drink establishments had posted written materials promoting hand washing, arranged tables and chairs in a manner that they accommodate not more than four people at once and at least 2 meters apart, carry out daily cleaning and disinfection of frequented touched surfaces, and provided education or training for their workers about COVID-19.

Conclusion

The overall compliance level with COVID-19 preventive and control measures among food and drink establishments was very poor. Thus, it is highly recommended that the federal government of Ethiopia, the federal ministry of health, and local health authorities consider a move towards more solid, strict, and comprehensive compulsory measures, including fines that can lead up to the closure of non-compliant establishments.

A Systematic Review of Gluten-Free Dough and Bread: Dough Rheology, Bread Characteristics, and Improvement Strategies

High-quality, gluten-free doughs and bakery products are clearly more difficult to produce than wheat flour-based products. The poor quality of the breads that are currently available demonstrates that manufacturing remains a significant technological problem. This is mainly due to the absence of gluten, which has a huge negative impact on dough rheology and bread characteristics. Gluten replacement is still the major challenge in the development of doughs and baked goods. The literature documents various improvement strategies. The most active approach seeks to identify alternative ingredients that can mimic the viscoelastic properties of the gluten network, notably hydrocolloids, enzymes, emulsifiers, and alternative sources of protein. However, other innovative strategies, such as high pressure, using heat to dry flour, and sourdough fermentation, have been investigated. In this context, the first aim of this review is to summarize current knowledge regarding gluten-free doughs, breads, and bakery products. Secondly, as it is clear that the manufacture of gluten-free products remains a key challenge, it suggests some improvement strategies that can boost their nutritional, technological, and sensorial characteristics.