Product Quality When Processing Pulse-Based Products

In this interview, Emily Moore, Ph.D., the Field Application Scientist at PerkinElmer Inc., talks to AZoM about quality control solutions for pulse processing. 

How has the market for pulses expanded in recent years, and what has affected their popularity and availability?

Pulses - sometimes referred to as grain legumes - are dried edible seeds of lentils, chickpeas, peas and beans, as well as their relatives. Pulses have become increasingly popular in recent years because they are nutritious, healthy and sustainable.

Pulses contain about twice the amount of protein found in conventional cereal grains, and they are high in dietary fiber, vitamins and minerals, but low in fat. Their complex carbohydrates lower the glycemic impact on blood glucose levels. They are also gluten-free.

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Pulses can also impart many unique functional properties when used as ingredients in foods, such as binding, emulsifiers, or gelling agents. Plants which produce pulses are more eco-friendly and drought-resistant than most crops.

From a market perspective, many consumers are now adopting flexitarian diets, incorporating more plant-based foods into their diets to align with personal values like animal ethics and environmental awareness.

In 2016, over 1,000 new pulse-based products entered the market in the US and Canada alone. The governments of Canada and India have recognized the importance of pulses and are funding farming and process innovations.

What is the typical composition of a pulse, and does is this affected by processing?

Looking inside a typical bean can provide a good insight into the overall properties of pulses.

The whole contains most of the insoluble fiber. This layer also contains lipids that influence flavor and antinutritional factors that can interfere with nutrient absorption. The toughness of the whole fiber can complicate milling, so, where possible, this is removed before processing.

The cotyledon - which comprises around 90% of the total dry weight in a mature bean - contains most of the starch and protein that the embryo needs to grow. There are small numbers of cell fibers distributed throughout the cotyledon tube, and some pulses, like chickpeas, peas and beans, have been reported to possess a protein gradient.

For example, the outer two-thirds of a kidney bean's cotyledon has a higher concentration of protein. De-hauling must therefore be done carefully to avoid reducing the protein yields.

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The granular structure of starch consists of two types of neatly organized glucose polymers. Milling the grain disrupts these polymers' orderly arrangement and can cause structural modification or starch damage, transforming functional properties like water absorption.

An improved understanding of the nutrient distribution and structure in pulse greens can help millers and processors efficiently develop new ingredients with desired benefits.

Could you give our readers an overview of how pulses are generally processed?

Pulse-processing, like any other food processing, is the transformation of raw ingredients by physical or chemical treatment into value-added products. This includes improving nutrient profiles and functional properties, such as providing forms that are easier to blend to ensure a more uniform formulation.

A significant number of conventional, time-served processing methods are still practiced today. Innovative processing technologies such as anti-medic treatment and extrusion are emerging all the time, with research and the opening of new processing facilities continuing to drive this field.

Many of these processes can be performed sequentially or as pre-treatments to ease milling, which increases efficiency, yield, protein content­ and quality.

Milling is a process that essentially reduces particle size. The milling of pulses typically consists of de-hauling, splitting and flour milling, followed by either dry or wet fractionation into the pulse's major constituent concentrates or higher purity isolates.

The processes can vary where necessary; for example, in some grain types, the haul is left on to produce wholemeal flour.

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In fractionation, the purity of each resulting fraction is dictated by the technology used. Fibers can help provide structure to food systems such as baked goods and texture to extruded snacks.

There is currently a lot of interest in pulse proteins, which contain high amounts of essential amino acids that complement those found in cereal grains. Research is ongoing into the medic modification and de-flavoring of pulse proteins to provide plant-based replacements for animal dairy or egg proteins like casein and ovalbumin.

There are also many studies looking into new uses of pulse starch. As it is a co-product of protein isolation, pulses are a relatively inexpensive source of starch compared to other green sources.

What factors influence product quality when processing pulse-based products?

Product quality is a function of ingredient, quality and process interactions, and a better understanding of and control over these factors can help mitigate some of the challenges that processors face.

First, it is important to be aware of how the source material will influence results.

Composition affects milling performance in several ways: higher amounts of fiber result in coarser particles that require a second round of milling. Higher protein and lipid contents have been associated with higher ductility, meaning that more energy is needed to create new fraction surfaces in the grains.

Moisture content can also influence the energy consumption of the milling process, also affecting yield, flour, fineness and milling capacity at higher milling speeds. A 'sweet spot' for moisture content is considered to be around 10% to 11%.

Storage and bidding practices are also important. For example, storage at high temperatures and humidity can cause starch, protein and fiber to undergo molecular rearrangement, developing a hardness in the grain that cannot be softened by cooking. This is known as the 'hard to cook' phenomenon.

There is a lot for a miller to consider in terms of receiving raw materials and designing an optimum process.

Milling itself can result in up to 15% of avoidable losses at different stages, depending on the method in use.

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Dry milling typically involves using physical or mechanical forces to break the greens into fine particles which are then separated by air classification. Large amounts of cotyledon can be lost in dry milling, causing high starch damage – this is especially prevalent when milling at high speeds.

In contrast, wet milling generally offers better separation and high-purity fractions, but if pH and temperature are not carefully controlled, then protein functionality can be lost.

This method is not environmentally friendly due to its high water and energy requirements, and the process is more labor intensive and costly as a result. Due to this, dry separation tends to be the method of choice for most processors.

How important is it to monitor processes such as milling, and what tools does PerkinElmer offer to help producers do this?

Ultimately, the processing method used will be selected based on target product quality, which is dependent on particle size, purity and level of starch damage. With all of these variables to consider, it is essential to have the right tools to guide the selection of grains and process conditions for optimal results.

Quality and safety solutions from PerkinElmer offer an ideal means of keeping processes running seamlessly. At busy times of the year, like the harvest, these solutions help producers rapidly sift through incoming raw materials to sort and bin them effectively.

By testing at this early stage, producers can also ensure that they are only receiving the quality goods that they paid for, with the proper moisture and protein levels. Proper testing can filter out any subpar materials that may compromise the quality of downstream products.

PerkinElmer's in-process solutions provide real-time monitoring, allowing producers and processers to optimize yield and control the uniformity of products, flours and pulse fractions even further down the line.

In terms of the instrumentation available from PerkinElmer, there are four main classes of compositional analysis instruments: benchtop NIR systems, in-process options, whole grain and flour specialized NIR systems and various miscellaneous options.

Most of these instruments are based on near infrared (NIR) detection technology. This technique involves light from a lamp being shined onto the sample, with some of that light then passed onto the detector - either by transmission through the sample or by  reflection off the sample.

The detector measures this light in the near infrared portion of the spectrum, using this information and previous experience to determine the amounts of moisture, protein and other substances present in the sample.

Using this learned relationship or calibration, the instrument quickly reports multiple parameters like moisture and protein simultaneously and in a matter of seconds.

Could you give our readers a brief summary of some of the specific instruments available and their operation?

The DA 7250 is an at-line NIR instrument available in two designs: a general-purpose version with a plastic exterior and a sanitary design model with a stainless steel casing. Both models are dustproof and water resistant.

The DA 7250 can be operated anywhere, including grain receival points and even processing areas where fine particles may be in abundance.

The instruments offer robust dietary detectors which ensure excellent stability, accuracy and reproducibility. This feature allows producers to confidently compare the effects of different crop years and the regional variability of the grains.

Samples can be measured as whole grains; these can be ground or prepared as slurries or pastes. A range of accessories provides additional flexibility, allowing producers to measure even the smallest samples, including a single grain or volumes of several hundred milliliters.

The analysis is simple and takes just six seconds. A sample is poured into the dish, the user selects the corresponding product on screen, then places the sample on the platform. The instrument does the rest - the tray is positioned by magnets and spun while taking a large volume of snapshots, so a representative composition of the sample is reported.

When the analysis is complete, everything is recoverable, and there is minimal cleaning required. The instrument also performs routine automated checks to ensure it is delivering optimal performance at all times.

A number of calibrations are available for pulse applications in the DA 7250. These include moisture and protein for whole and ground peas, lentils, chickpeas and a range of other pulse types.

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For peas and lentils, we also offer amino acid calibrations. Other parameters include fat, fiber, ash or starch for certain products. Custom calibrations are also available.

To capture any compositional variability due to growing region, crop year and processing conditions, it is recommended that producers run samples on the instrument and compare these against local lab results to validate a calibration for the specific sample before routine measurements.

Inline solutions are ideal for producers looking to continuously monitor their processes. These allow for the precise control of moisture levels and drying efficiencies, segregating fractions according to protein content, creating specific blends and ensuring the uniformity and purity of a product.

The DA 7350 In-line NIR sensor or its next-generation model can be welded onto pipes. It has a built-in camera that lets the operator detect any foreign debris, fractured grains or discoloration. The DA 7440 operates in an overbuilt configuration, however.

Both models can also be used in further downstream processes like monitoring extruded snack foods or pasta.

Calibrations from the DA 7250 can be transferred to the process instruments, and incorporating one of these systems in a process gives producers immediate feedback on potential issues, allowing them to make timely corrections to avoid waste and improve product yield.

Monitoring of processes can also be done remotely. These instruments offer cloud-based networking capabilities that let producers review results or configure the units from anywhere, even across multiple sites.

It is possible to verify trends over time and generate reports, and there are also settings that identify outliers or classify samples by comparing these to a product library to determine which product is being measured.

The Inframatic 9500 NIR Grain Analyzers are specialized whole grain and flour analyzers. These are ideal for positioning at grain receival points to screen incoming whole grains and ensure proper specifications of finished flours after milling.

These instruments are also available in two versions. The standard model runs on a sample volume of around 300 milliliters and reports approximate values in about 25 seconds.

The taller unit can also measure test weight or check the leader weight (the bulk density of the grain) with a higher value corresponding to better quality and higher pricing.

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To run a sample of whole grains, simply select the product type on the touch screen and pour the sample into the top of the analyzer. Once analysis is completed, operators can recover the sample from the bottom drawer.

A cuvette module accessory can be used to enable the measurement of pulse flours. To do this, the sample cuvette is placed into a holder, and the cover closed. Operators then sprinkle the flour over the top of the two holes and even out the top surface to ensure there are no major air pockets.

Excess flour is cleared off, and the lids are then closed before the cuvette is inserted into the grooves at the top opening.

The IM 9500 is a diffuse transmittance type NIR system, meaning that there needs to be an appropriate amount of light passing through the sample in order to reach the detector.

The instrument automatically adjusts the sample chamber using a motorized gate, depending on the physical properties of the sample; for example, lentils of a darker color will have a shorter path length than the lighter varieties.

Available calibrations for pulses on the IM 9500 include moisture and protein for a variety of whole pulses, pulse flours and fractions.

The flours and fraction calibrations available currently include pea and fava bean samples processed with or without the wholes. Calibrations are also available for different particle sizes and enrichment levels from air classification.

The IM 8800 is a portable NIR system that gives producers the freedom to measure in the field, at storage sites and at processing locations wherever this is required.

The instrument can be recharged via a car battery, and its GPS functionality means producers can link coordinates to generate a protein map, enabling better-informed harvesting decisions.

The FT 9700 is a new instrument based on Fourier transform technology. This instrument provides the producers with the flexibility to transfer data from other brands of instruments and is currently used in research to better understand natural variability in pulse crops and to help breeders identify varieties with higher protein quality.

Finally, the AN 5200 is a rapid moisture analyzer that uses a slightly different technology from NIR spectroscopy - UMG technology. This technology simplifies the process of calibration development for new specialty crops.

The instrument offers ready-to-use moisture calibrations for a wide variety of pulses, delivering results on test weight, hectoliter weight or sample temperature in as little as 10 seconds.

What is functional analysis, and what role does this play in monitoring the properties of pulses?

The role of functional analysis can be understood by looking at an example scenario occurring further downstream to the ones discussed so far.

For example, a company may be looking to manufacture a new breakfast cereal via pea flour extrusion. Two products may look identical and compositional analysis may reveal that they have a similar makeup; but, pouring milk over product B causes this to become soggy right away while product A remains crisp.

The properties responsible for this difference in functional analysis results should be investigated; for example, it could be the ingredients or the process that prompted this change in behavior.

The Rapid Visco Analyser (RVA) is able to determine those hidden properties responsible for ingredient performance. The RVA is the industry standard tool for starch quality characterization, but it can do so much more.

It heats, cools and mixes the ingredients in line with user-defined programs, measuring changes in sample viscosity or resistance to float over time. The RVA then provides information on how the investigated batch behaves and how this compares to previous batches.

The RVA can quantify the effects of heat, mechanical shear, particle size, cyber chemical treatment, storage or processing conditions. The instrument will measure and explore these parameters for a variety of materials and can accommodate individual ingredients, process intermediates and finished products.

Unlike conventional radiometers, the RVA uses a rotating pedal that prevents any sedimentation of particles. It keeps the sample uniformly mixed and evenly dispersed, and it measures viscosity in terms of the torque experienced by this paddle.

PerkinElmer offers two RVA models. The RVA 4800 can reach temperatures as high as 140 °C by using a sealed canister, meaning that tests can be performed in this vessel beyond 100 °C without boiling or evaporation.

Highly customizable temperature and shear programs can be defined from a computer, and a huge library of presets is available. Users can simply insert a sample, set the program and the RVA will perform the analysis automatically.

Several features help ensure operator safety when using the RVA at high temperatures and pressure. Cans and paddles are disposable after use, eliminating the risk of sample carryover and the need to clean between runs.

The RVA can be used to analyze a wide range of sample types, including liquids, slurries, powders and pastes. It is a robust and user-friendly tool, and because it uses no glass, the instrument can be safely operated in the mill or processing area.

Could you provide an example of a typical process using the RVA?

An RVA test can be run on a starch sample. First, it is necessary to define the temperature and shear program, for example, a common heating and cooling cycle.

The process starts by equilibrating to an initial hold temperature, then raising the temperature at a constant rate. The process holds the sample at a high temperature for a few minutes, then returns this to the original temperature for few minutes and holds this again. The shear is typically rapid at the start and set to a constant rate throughout.

Starch granules contain two main types of polysaccharides: linear amylose and branched amylopectin, both of which are made up of glucose units. These are arranged in a very specific way within the starch granule - multi-cross-shaped pattern.

Unmodified search granules are generally insoluble in water below 50 °C, and because these do not absorb water, the initial viscosity in an RVA test is usually negligible.

As the starch solution is heated beyond a critical temperature, the molecules inside begin to rearrange. This irreversible structural change - called gelatinization - leads to the solubilization of starch, but there is still no viscosity change.

The internal reorganization causes the starch granules to swell to many times their original size, causing a rapid rise in viscosity. This marks the start of a process called pasting.

The temperature at the onset of this steeping client is known as the 'pasting temperature,' a parameter that can be used to indicate the minimum temperature needed to cook a sample.

The shearing action of the RVA breaks apart these swollen granules, and the molecules inside escape into solution. This causes the viscosity to drop.

This process reaches a peak viscosity when the rate of granule swelling is equal to the rate of its breakdown. This parameter provides a great deal of useful information.

As the granules continue to disintegrate, the viscosity falls to a minimum, and then with cooling, the free molecules associate and the viscosity increases again. The final viscosity at the end of this test is a good indicator of gel firmness and product characteristics, such as shelf life.

Many other useful parameters can be extracted from RVA measurements, and these can help define optimal processing conditions.

Are there any examples where the RVA has been central to research into pulse properties?

Compared to other plant sources, pulse ingredients tend to show limited viscosity development. This is because their heat-stable starches and proteins restrict the swelling of the starch granules. There have been a number of examples of RVA-supported research which has aimed to investigate this further.

Research using the RVA 4800 showed that for many pulses, temperatures above 110 °C are needed to promote granule swelling, amylose leaching and dilation. The RVA 4800 is ideally placed to support improved understanding of high temperature processes on pulsing gradients like extrusion, jet cooking or retarding.

When working with kidney bean flours, raising the program temperature from 95 to 130 °C will result in increased viscosity development. The addition of salt further improves this.

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This effect is attributed to changes in protein starch interactions from high temperatures and the presence of salt, which lets the free starch granules swell more. These better-defined RVA parameters were found to be useful in predicting the texture of canned kidney beans.

In this experiment, using the RVA 4800 allowed a process that would normally have taken an entire day's soaking, canning and measuring to be done in under 30 minutes and at gram scale.

Can the RVA be used to predict and avert issues surrounding poor product performance?

The RVA is advantageous when looking to minimize poor product performance, particularly when working with pulse proteins.

Heat treatment during fractionation and drying of protein ingredients greatly influences their functionality, and proteins heated beyond a certain temperature can unfold and stick together to form a gel. Monitoring these structural changes in food ingredients is important in predicting poor performance.

Insects and weather damage can severely affect the grains before they reach the mill, but these features are reflected in the RVA's test results, allowing them to be detected and monitored.

A particularly pronounced change takes place during sprouting. Sprouted grains have a higher level of alpha amylase enzyme that breaks the sugar polymers down and reduces starch viscosity at high temperatures.

The falling number test is the industry standard for testing sprout damage in cereal grains, and this has also been used to characterize some germinated pulse flour blends. Since the falling number tests rely on viscosity to determine the degree of damage, the RVA can also be used to measure this.

In a recent experiment, flours milled from germinated yellow peas were tested via the RVA's standard heating-cooling cycle. There is a general observable trend of decreasing pasting viscosity with increased germination time, but this trend can be captured much earlier in the pasting curve.

The standard string number test typically consists of a three-minute hold at 95 °C to observe the viscosity change over that time. The RVA can perform faster tests with reduced operator time and more flexibility in the test temperature range.

The RVA tests also showed a loss in viscosity with prolonged storage, highlighting that the final viscosity of split yellow pea flour decreases with storage time. A similar trend was also reported for the storage of bean flours.

Thermal or mechanical processing has a significant influence on several RVA parameters. In cereal grains, starch damage from milling typically shows as an early shelter in the RVA curve. This is because damaged starch is broken up into smaller pieces that absorb water more readily and swell earlier on.

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Grains that spend a long time in the mill tend to have an earlier or more prominent shelter peak. These features have also been related to particle size.

There is currently limited published information in this area that is specifically related to pulses, but there have been a number of examples of RVA successfully distinguishing many thermal and mechanical processing effects on pulses.

Returning to the scenario of the two breakfast cereals from earlier, analysis with the RVA would highlight clear differences in their early viscosity.

Product A would resemble its raw material characteristics, which would suggest the application of a mild cooking process. Product B would likely show signs of a harsh thermal chemical process like extrusion, causing this to soak up water, even at room temperature.

With this knowledge available, it would be possible to modify the formulation or process to get the right conditions, potentially saving days or weeks of process optimization and waste.

It is possible to fingerprint internal processes or reverse engineer competitive products by recreating the conditions determined by the RVA.

By rapidly reproducing even high temperature processes in a controlled way, the RVA can act as a miniature pilot plant and accelerate pulse product innovation.

About Emily Moore, Ph.D.

Emily Moore, Ph.D. is a Field Application Scientist in PerkinElmer's food analytics department. Based on Ontario, Canada, she collaborates with industry leaders, helping to connect the best available analytical solutions with each customer's unique situation. This includes partnering with researchers, food scientists, producers, processors, and colleagues across multiple disciplines. Day-to-day, Emily supports new application development, instrument training, and public information sessions.

About PerkinElmer Food Safety and Quality 

PerkinElmer Food Safety and Quality is committed to providing the innovative analytical tools needed to ensure the global supply of high-quality, safe and unadulterated foods.