Category Archives: Food Research

Food sauces are one of the most important condiments in the human diet and gastronomic culture around the world. The almost endless combinations of flavors, textures, and colors, as well as the sensorial characteristics that consumer feels savoring food sauces, make these products one of the most consumed and important for the economy in food industry. The food sauces market generated US$120 billion in 2016, with a trend to increase in the next years.

Products for human consumption need a careful evaluation of all physico-chemical properties and sensorial characteristics.

Rheology is the study of deformation and flow of matter under well-defined conditions and is an important tool to characterize fundamental material properties of food systems. Rheology applied to food processing and product design is an area with a huge impact due to the important information obtained. Food rheology is essential for:

  • quality and stability control
  • design flow and handling systems
  • sensory evaluation of food

Rheological and mechanical properties like consistency, degree of fluidity and flow, are the most important parameters to be determined in food sauces and will be important to determine how stable the final product will be and how long it can be stored. Rheological studies of fluid foods are so important that developments in the fields of process engineering application, equipment design and transport system are based in these results.

Rheological properties of food sauces

Food sauces are a complex mixture constituted essentially by water or oil. Hydrocolloids have an essential role in food sauces formulation once they will be responsible for viscosity control and stability of the formulation, prolonging shelf-life. Sauces are semi-solid foods, behaving as soft solids or non-Newtonian fluids and exhibiting pseudoplastic flow with a distinct yield stress and thixotropic (time-dependent) behavior.

Rheological characterization is essential to quantify the functional relationships between deformation, stresses, and the resulting rheological properties such as viscosity, elasticity or viscoelasticity. Viscoelastic properties play dominant roles in the handling and quality of the sauce. Such properties are not only dependent on time but also on processing temperature, solid contents and other ingredients used in many types of formulations.

Usually food sauces are shear-thinning (pseudoplastic) fluids and exhibit a yield stress, defined as the stress that must be exceeded for flow to occur. The consistency index, apparent viscosity, yield stress are important product properties. Thus, the rheological parameters are a useful tool in understanding changes in food structure during processing, to control the quality of the product and to consumer handling with the product. Within rheology, the oscillatory rheological method is the most popular method to characterize viscoelasticity, since relative contributions of viscous and elastic response of materials can be measured.

Main rheological parameters to determine in the quality control of food sauces

  • Viscosity

Viscosity is an important property of fluid foods. It is defined as the internal friction of a liquid or its ability to resist flow. As viscosity changes the flow properties of a liquid food changes and influences the appearance and consistency of a product. Viscosity of a food sauce is affected by factors like temperature, concentration of solute, molecules and suspended matter; it can be used as an indicator of quality by the final consumer, as in most cases a thicker food sauce is thought to have superior quality when compared to a thinner product.

Like most fluid foodstuffs, sauces show complex rheological behavior. Sauces like mayonnaise and ketchup are sold in different containers including the traditional glass bottle or plastic squeeze dispensers, so controlling the different dispensing properties is necessary. When used in a glass bottle, the sauce is not expected to flow freely until the bottle is agitated. In the plastic bottle, on the other hand, the sauce should flow when a gentle squeeze (pressure) is applied for several seconds. In general, mayonnaise and ketchup exhibit pseudoplastic behavior with a flow threshold, presenting thixotropy (shear stress dependence on the time of shear); also, the decrease in the oil content of mayonnaise normally lowers the viscosity of the final product. In Figure 1 is depicted the dependence of viscosity on shear rate, or applied motion – a higher shear rate will promote a lower viscosity and flow.

Figure 1 – Flow comparison between two commercial ketchups – both products exhibit a lower viscosity when the applied motion is higher, which is necessary for the product to flow.
  • Yield stress

Yield stress is a physical and rheological property for liquid and solid materials. Yield stress determination is an essential property of food sauces and it is a measure of the strength of the material structure, being defined as the minimum stress required to make a material flow. Pseudoplastic materials behave as solids under small applied stresses, and as liquids at high stresses. Figure 2 relates stress with strain, highlighting the yield stress as the moment when the material cannot hold more elastic deformation and flow begins.

Figure 2 – relation between stress and strain for a pseudoplastic food; the yield stress represents the moment when the elastic deformation reaches a limit and flow ensues.

In practice, the yield stress of products such as mayonnaise, ketchup, salad dressings, etc, represents the force that has to be applied by the user in order to break down its structure and initiate its dispensing. Since no more relevant stress is applied after reaching the yield point, and the material is left to rest over time, its structure rebuilds, becoming solid again.

Yield stress is also a key product characteristic which determines its texture, and thus the consumer sensory perception during use and application.

  • Polymer behavior, stability and shelf-life

Oscillatory time sweeps are important when testing materials, such as dispersions and polymers, that may undergo macro or micro structural rearrangements with time. These rearrangements directly influence rheological behavior. Oscillatory time sweeps directly provide the necessary information about how a material changes with time.

By oscillatory time sweeps of food sauces, it is possible to determine possible polymer degradation, solvent evaporation, dispersion settling, cure information and/or time dependent thixotropy of formulations. Oscillatory tests give important information about food sauces stability and shelf-life, once the evaluation of the material’s behavior with time can be monitored directly with variation of frequency and the temperature of interest.

By oscillatory time sweeps one may measure two parameters: G’, referent to the “storage” or “elastic” modulus and G’’ referent to the “loss” or “plastic” modulus.

Figure 3 – Oscillatory time-sweep showing a relationship between viscosity, G’ and G”. When the G’ is superior to G”, the food sauce will have a solid-like behavior, which will become a liquid-like behavior from the moment G” becomes superior than G’.

A stable formulation with no structural modifications is represented in a plot as shown in Figure 3, where the G’ and G’’ are independent (the formulation maintains its fluid characteristics). On the other hand, if the food sauce formulation is not stable, and its identity varies with variation of frequency or temperature, the G’ and G’’ will cross.

Instruments for rheological measurements

The increasing social and economic importance of food production, together with the complexity of production technology, processing, handling and acceptance of these highly perishable and fragile food materials require a more extensive knowledge of their physical properties.  There are numerous instruments available to the food industry to measure viscosity for quality control and thus ensure that products made are of consistent quality. These commonly-used viscometers are capable of measuring Newtonian and non-Newtonian fluids in a wide viscosity range. The consistometer determines the consistency of a food by measuring the distance it flows under its own weight. Rotational viscometers measure the torque required to turn a spindle in a sample of fluid at a known speed. Capillary viscometers, also known as U-Tube or Ostwald, measure the time for a fluid to pass between two points of a capillary tube under the force of gravity.

Once food sauces are subjected to variations in their temperature during production, transport, storage, preparation and consumption, and taking into account the influence of the overall properties of the final product, e.g., taste, appearance, texture and stability, rheological characterization is essential  to optimize processing conditions and improve product quality.


In the present demanding market, where a constant search for foods with high benefit-quality ratio is increasingly taking place, the innovation possibilities often lie in the most common and versatile everyday foods, such as the egg.

Used in almost every aspect of the gastronomy, from confectionery to soups, an egg is an important ally for all chefs and kitchen households. An egg alone is one of the most nutritious and appreciated foods on the planet. It is a high protein and low carb intake food, excellent for those who want a simple, easy and healthy snack, such as the common hard-boiled version. In fact, a whole egg contains a relevant amount of several important vitamins and minerals.

The nutritious egg – the forgotten superfood?

Along with milk, eggs contain the highest biological value for protein. One egg has only 75 calories but 7 grams of high-quality protein, 5 grams of fat, and 1.6 grams of saturated fat. According to the reference daily intake (RDI) nutrient values for a healthy adult, a large egg has vitamin A (19% RDI), responsible for immune system and good vision maintenance and a set of B vitamins, such as riboflavin (42% RDI), pantothenic acid (28% RDI), pyridoxine (9% RDI), folate (11% RDI) and cobalamin (46% RDI), essential for cell division processes and mental health.

Egg yolks are one of the few foods that naturally contain vitamin D (15% RDI), essential for strong bones and muscles, as well as overall health. In fact, the majority of the egg’s vitamins and minerals are located within the yolk. Vitamin E, iron, selenium and omega-3 fatty acids are also found in relevant concentrations in the egg.

The high quality proteins of the egg, essentially albumins, mucoproteins and globulins, contain a set of essential amino-acids like leucine, tryptophan, methionine and other non-essential aminoacids, which will act as precursor molecules in human metabolism. It is also noteworthy the high concentration of choline (60% RDI), an essential vitamin-like nutrient involved in the metabolism of molecules necessary for good neural-muscle function and its control in humans. For muscle building and fitness athletes the ingestion of these nutrients is of extreme importance for cell regeneration and muscle growth.

Cholesterol is perhaps the most controversial nutrient in the egg, one large egg containing more than two thirds of the RDI for this nutrient, currently set at 300 mg. However, several recent studies showed that there is no significant correlation between the egg’s cholesterol and an increase of blood harmful LDL cholesterol levels in healthy humans. The ingestion of one whole egg a day, preferably hard-boiled, is recurrently suggested by nutritionists and medical specialists as an important incorporation in one’s diet.

One whole egg contains an impressive set of nutrients in quite relevant concentrations.

The egg market

From over the 75 million tons of eggs produced worldwide, the Asia-Pacific region represents the biggest market for egg and egg products, being India, Indonesia, Japan and China the key players due to its population and economic growth over the last decades. China alone is responsible for almost 40% of both worldwide production and consumption. North and Latin American regions are also important markets regarding egg products, with USA leading the charts, followed by Mexico and Brazil.

In the European context, according to the last stats of the European Commission for Agriculture and Rural Development, more than 7 million tons of eggs were produced in 2018 within the economic space, where 7 of the 28 members, France, Germany, Spain, Italy and UK, were responsible for over 80% of the total production. If the Russian and Turkey markets were to be included (European countries not in EU) the Economic European Space market would represent twice its actual numbers regarding the egg production and consumption. The Portuguese case represents a modest percentage, with only 0,1 million tons of eggs produced for consumption in the last year. Although lifestyle tendencies such as veganism or higher healthcare awareness are rising in popularity, these do not seem to be threatening the growing tendency of the egg market, especially in the Asian continent.

From farm to table

An average person consumes 180 eggs per year. The majority of these eggs (about 50%) are produced by enriched feed hens in cages followed by barn-raised hens (26%), free range hens (14%) and organic feed hens (5%). The difference between all these eggs raising hens are concerned to their diet and growth space.

Eggshell size, form and specially color are commonly associated by consumers as main characteristics for egg quality, however, this is only dependent on the hens’ breed, size and feed.

Whiter breeds tend to lay white eggs while darker ones tend to lay browner eggshells. As for the yolk, the same applies, being the hens’ diet the major factor responsible for its color. While grain-fed chickens produce pale-yellow yolks, hens fed with rich pigmented and nutritious food from insects, vegetables, fruits and grasses produce deep orange yolks. The real egg quality is given by the age of the hen and its feeding over the growing process, where older hens tend to lay thinner eggshells and shorter shelf-life eggs than younger and nutrient controlled-feed hens.

The hen’s nutrition plays the major role in the colour of the final egg yolk.

Applications beyond breakfast

From cosmetic industry to medicine, the egg components are used in a wide range of areas for remarkably different goals. Nowadays it is easy to find different forms of whole egg, yolk or egg white in retail stores, ranging from solid to concentrated, crystalized, frozen or deep-frozen states. From the yolk is extracted its oil, consisting mainly of triglycerides and other elements, such as lecithin, cholesterol, biotin and xanthopylls. This non-allergic oil becomes free from egg proteins and is therefore allowed for use in cosmetics or dermatological products for hair fall, eczemas or dermatitis. The natural pigments (xanthopylls) present in the yolk, lutein (E161b) and zeaxanthin (E161h), are also of high interest for the pharmaceutical and food industry for their attractive yellow and orange colors.

Lecithin (E322) was actually first isolated from the egg yolk in 1846 by the French chemist and pharmacist Theodore Gobley. This product is currently in high demand due to its emulsifying, lubricant and stabilizing properties, which were commonly obtained with the use of soybean oil. However, EU legislation has been inciting the use of allergen-free natural lecithin food sources, minimizing the use of soybean. Lecithin is also a molecule used in a variety of pharmaceutical and cosmetic products due to its stabilizing capacities and choline enrichment.

Eggs are also used as ingredients for alcoholic drinks, as in the case of the famous eggnog, or as clarifying agents for superior category wines and rich broths. In the pharmaceutical sector, the egg has been used for over 70 years in the manufacturing of flu vaccines due to its concentration of albumins, mucoproteins and other globulins. The eggshells are also a valuable resource for organic agriculture as a source of natural calcium.

The numerous shapes that the egg can assume are a clear representation of its high acceptance and versatility, with verified health benefits at an affordable price.

CFER Labs is your partner in food R&D. Obtain your free of charge workplan by clicking here.

Miranda, J. M. et al, (2015), Egg and Egg-Derived Foods: Effects on Human Health and Use as Functional Foods, Nutrients, vol. 7, 706-729.
Garcés-Rimon M. et al., (2015) Egg protein hydrolysates: New culinary textures, International Journal of Gastronomy and Food Science, vol. 3, 17-22.
Wu Jianping et al., (2014) Eggs and Egg product processing, Food Processing: Principles and Applications, published by John Wiley & Sons,  2nd edition, chapter 19, 437-455.

The way human beings feed themselves strongly influences their physical and emotional balance. Meat products are an excellent source of nutrients and are widely consumed around the world. However, these products are also susceptible to chemical and microbiological deterioration, which creates health risks.

Consumption of contaminated food and water kills 1.8 million people annually. In addition, each person is wasting an average of 150kg of food per year, also due to lack of food conservation.

Packaged meat products arrive at the consumer’s house in good food safety conditions. However, food contamination is a serious concern at the post-opening stage of the package. It is thus urgent to create more advanced solutions of food preservation, which reduce the contamination and increase the shelf-life after the package is opened.

Sliced charcuterie may have an extended shelf-life with the developed technology.

A new technology for the preservation of charcuterie

Researchers at the University of Coimbra, Portugal, and Primor Charcutaria Prima developed a research project to address this problem. New surfactant and polymer systems were developed to promote longer shelf life through the incorporation of consumer safe edible coatings in the meat. Furthermore, this coating prevents the use of the protective N2/CO2 atmosphere in the packaging, which leads to the reduction of the amount of plastic volume used in the packaging, yielding a better environmental impact.

The various types of performed assays included: chemical, physical and microbiological tests to identify coatings with improved bacterial elimination, light scattering and rheology tests to identify the best suited coatings for spray application, and electron microscopy to compare the level of meat degradation with and without coating. Color, taste, texture and odor were continuously monitored throughout the project. After the laboratory tests, the best performance coatings were applied in semi-industrial environment.

This new results will make available to consumers a new generation of preservation for fresh meat products.

Adipose tissue is a vital connective tissue for all mammals. Its main role is to store energy in the form of lipids while insulating the body. It also contains a variety of crucial cells that act on the body’s immune and structural functions. Obesity is a medical condition defined by an excess of body fat. This disease increases the chances of developing conditions such as cardiovascular diseases, type 2 diabetes, cancer or depression,  decreasing the individual’s quality of life. Obesity is one of the leading preventable causes of death worldwide, mainly promoted by the intake of high-energy foods and low energy expenditure.

Thermogenic molecules

Some specific ingredients might contribute for one’s weight management goals with no need for extra energy expenditure or change in sedentary lifestyle. Foods such as chilli peppers, white and black pepper, ginger and cinnamon have in their composition capsaicin-like molecules, respectively piperine, gingerol and cinnamaldehyde.

Researchers found that the consumption of these food products promote the release of sympathetic-nerve mediated norepinephrine, naturally activating the brown adipose tissue thermogenesis by up-regulating the action of the uncoupling protein 1 in the mitochondria (UCP1) (Saito et. al. 2015). The UCP1 dissipates energy by oxidizing fatty acids and glucose to heat. Other ingredients, such as green tea or wasabi, also contribute to the up regulation of this protein.

Thermogenic and anti-obesity effects of capsacin-like food molecules, mediated by the release of sympathetic-nerve norepinephrine. This mechanism triggers the brown adipose tissue thermogenesis by up-regulating the action of the uncoupling protein 1 (UCP1) in the mitochondria. in Saito et. al. 2015

The consumption of these foods and spices might not always be possible in the desired concentration by consumers with weight issues. To overcome this limitation, companies may explore the potential of a new generation of anti-obesity, naturally thermogenic food products. It has been shown that the oral ingestion of capsules with capsinoids, substances naturally present in chili peppers, increases the energy expenditure mediated by the thermogenesis located in the brown adipose tissue (Yoneshiro et. al. 2012). Edible plant and spice extracts, naturally clean-label, mostly calorie free and widely available, may thus be the shining stars of a new generation of functional products for weight management issues, proven to be their safety in the public food and health system.

  • Yoneshiro, T. et al. (2012) Non pungent capsaicin analogs (capsinoids) increase energy expenditure through the activation of brown adipose tissue in humans. Am. J.Clin.Nutr. 95, 845–850