Particle Size Reduction and its Impact in the Food Industry


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Particle Size Reduction and its Impact in the Food Industry:

Particle Size Reduction and its Impact in the Food Industry


Background Food particle size has become increasingly more important to the food industry. Many food ingredients exist in some particulate form whether it be powders, emulsions, suspensions, and/or pellets. Moreover, the shape and size of these particles as well as their distribution affect flavor, texture, and appearance of foods that we eat. Size and shape of ingredients also affect the stability of a given product as well as processability and functionality of the desired end product. Advancements in research in terms of general food technologies, biotechnologies, and nanotechnologies are bringing about an awareness of the importance of food particle size/shape and its significance on palatibility , digestion, bioavailability, and metabolism along with handling, packaging, storage and transport of food stocks. The physical and chemical properties of food ingredients such as particle size are of increasing importance to insure consistent quality and safety of products. These properties are also important to keep processing equipment working properly and keep maintenance to a minimum.

Background (con’t):

For those of you who are chocolate lovers, chocolate particle size is critical for sensory perception. The particle size will determine how the product feels in your mouth, taste, and how it melts. Continued production and development of new products is dependent on sensory and textural properties for continued success to prevent product failures that have been seen in the past. Proper texture and sensory experiences tends to ensure repeat consumer purchases. As the public is demanding the production of healthy foods that contain less fat and sugar, there is a need to find bioactive or nutraceutical ingredients. These types of ingredients provide health and medical benefits that have have been tested through research and clinical trials and are known to prevent and treat diseases. As the food ingredients are changing, this requires different forms of processing not only for taste and texture but proper machine handling as well as new types of processing equipment. Background ( con’t )

Background (Con’t):

The medical community has made it clear that diets that are low in fat and cholesterol and high in fiber reduce the risk of cardiovascular disease, diabetes, and certain cancers. If you recall, the first foods that came out that were high in fiber tasted like the cardboard box they came in. That certainly didn't settle well with the consumer so these products did not sell well. However, we have come a long way since then but this has taken millions of dollars of research to get here. A fair amount of research has been done on particle size distribution where pasting and rheological properties are concerned in terms of starch and flour powders. This impacts how creamy a product is as well as how crispy and crunchy it is. Pasting refers to foods that have been pounded until they are reduced to a smooth creamy mass. Whereas, rheology refers to the flow of liquids and/or soft solids. Creamy texture and liquid flow are commonly found with substances that have complicated micro-structures as is often found in foods and food additives. Background ( Con’t )

Background (Con’t):

Background ( Con’t ) All in all, many industries depend on some form of particle size reduction. This allows for separation of components to create a desired product while controlling taste, texture, quality, and safety. This is particularly important for the food and pharmaceutical industry. Particle size determines bioavailability for both nutrients in food as well as medications.

Particle Size Contribution :

Particle Size Contribution Particle size controls a number of chemical and physical properties which include; reaction and dissolution rate, packing density, sedimentation, appearance, and texture. This list is by no means exhaustive but covers the major contributions of particle size effects.

Rate of Reaction:

Rate of Reaction Chemical reactions are dependent on the surface area of a particle. Smaller particles are more likely to participate in the making and breaking of bonds than larger ones. Biological systems have developed enzymes to increase the rate at which chemical reactions take place. Non-biologically, particle size is another way to increase reaction rates.

    Dissolution Rate:

Dissolution Rate Particle size also effects how well it will go into solution. This is particularly important for the food and pharmaceutical industries. This is directly related to bioavailability. The smaller the particle whether drug or food, the greater the chance of it being absorbed by the gut. Whether the particle of interest is water or fat soluble determines dissolution rate as well. Molecules that are both water and lipid soluble often have the best of both worlds.

Packing Density:

Packing Density Packing density refers to how well particles fit together. Usually, larger particles don't pack as well in that they have more space between them because they have a larger surface area. Smaller particles tend to pack more densely because they have a smaller surface area. This is probably more important when you are concerned about unoccupied volumes if you are trying to maximize content and minimize cost of packaging and shipping. Flour sacks often pack down during shipping and handling. Manufacturers often suggest that you sift the flour before you use it. Food products such as chewy health bars require larger particles to maintain their integrity. Smaller food particles tend to be to hard to chew and crumble. Packing density is particularly important to the metal industry where unoccupied space creates a flawed product.


Sedimentation Sedimentation has to do with a particle's ability to precipitate out of solution or soft solid. This is of particular interest to the food and drug industries. Many products require that they remain evenly distributed in solution (suspended). This may be important to maintain drug dosages when the drugs come in the form of a liquid. On the other hand, it could be salad dressings (oil and vinegar suspension) which has more to do with product perception.

Product Appearance:

Product Appearance Particle size and distribution is an important characteristic contributing to product appearance. Particle size affects the overall bulk properties of the food item such as visual texture and density as well as color. Larger particle size may indicate a chewy food, whereas smaller particle size may indicate crunchy and less moist.

Product Texture:

Product Texture Product texture can be easily affected by particle size. Particle size also affects how you perceive a given product. Large particle size and hence a more coarse texture alters flavor. Large particle size tends to have less distinct flavor, whereas fine particles have more flavor. One way to think of this on a larger scale is with lunch meats. Consider the slice thickness of prosciutto. A thick slice of this is difficult to chew and has an unpleasant flavor. Thinly sliced, it melts in your mouth and has a very delicate flavor.

Research on Chocolate and Grains:

Research on Chocolate and Grains

Chocolate Study:

Chocolate Study Researchers at the University of Nottingham, School of Biosciences, in the UK have demonstrated the impact on particle size on rheological and textural properties of chocolate with reduced fat content. As the public is concerned with consuming chocolate with a lower fat content due to health concerns, this group of researchers were interested in how this would change the molten chocolate viscosity. It was known that reducing fat content would increase viscosity. This leads to a loss in mouth melting properties which makes the chocolate hard and difficult to swallow. Current literature demonstrated that optimizing particle size distribution (increased packing fraction) actually decreases the viscosity of suspensions that are highly concentrated.

Chocolate study (con’t):

Chocolate study ( con’t ) Their focus was on the impact of particle size distribution and fat content on flow properties (rheology) and melting characteristics in this dispersion of sugar in fat. They were able to demonstrate that optimizing the particle size distribution while reducing the fat content to a critical amount (22 percent by weight) can decrease the viscosity of the heated material and at the same time reduce the hardness of crystallized chocolate. This decreases the inter-particle contact which in turn reduces particle aggregate strength and structure buildup during melting. In its crystallized state, the molecular network is less connected providing for lower resistance to breakage and meltdown. This allows the chocolate to have a lower fat content and still be creamy. In this case, particle size and distribution allows for a healthier chocolate product (lower in fat) that retains a positive sensory input important for palatability.

Grain Study:

Grain Study Researchers at the University Department of Medicine in Bristol UK looked at the effects of plasma glucose and insulin responses to changes in particle size of wheat, maize, and oat meal as well as the rate of starch digestion in vitro. Data was collected from normal volunteers who ate isocaloric wheat-based meals and their plasma glucose and insulin levels were monitored. Isocaloric refers to a diet that has moderate carbohydrate and fat intake where the dieter can take in the same amount of carbs, proteins, and fats each day. This diet is often used by bodybuilders for quick weight loss with minimal muscle (protein) loss.

Grain study (con’t):

Grain study ( con’t ) In this study, wheat-based plasma insulin levels increased in a step wise fashion with whole grains less than cracked grains less than coarse flour less than fine flour. They also found that insulin levels were also greater with fine maize meal than with whole or cracked maize grains but were similar with whole groats , rolled oats, and fine oatmeal. The high-to-low ratio of blood glucose was greater with wheat flour than cracked or whole grains. They also demonstrated that in vitro starch hydrolysis by the pancreatic enzyme amylase was faster with decreasing particle size with all 3 cereals. They were able to determine that particle size influences the digestion rate and changes in metabolism of wheat and maize but not oats. They suggest that the increased insulin response to finely ground flour may be relevant to the cause of diseases linked to hyperinsulinemia (excess blood insulin levels) and to the management of diabetes.


Summary Food technology has come a long way. Research is paving the way to finding approaches that create a balance between particle size reduction and improving the functional aspects of foods. Particle size reduction increases sensory perception such as taste and texture while increasing bioavailability of bioactive molecules while improving on the nutritional properties. This is great news for the consumer as well as the medical community.

Resource List::

Resource List : General information on food processing and new equipment Particle size of wheat, maize, and oat test meals: effects on plasma glucose and insulin responses and on the rate of starch digestion in vitro. Pasting Characteristics of Wheat and Sweet Potato Flour Blends Impact of particle size distribution on rheological and textural properties of chocolate models with reduced fat content. Fat reduced chocolate: can it ever taste good?

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