Extrusion effects on the starch and fibre composition of Canadian pulses

Abstract Pulses are important as alternative sources of protein and carbohydrates for the animal industry and, thus, require accurate evaluation of their nutrient profile during processing. Extrusion is a thermal processing of ingredients to induce physiochemical changes that convert them into more valuable products. The current study evaluated the effects of extrusion on the starch and fibre components of Amarillo peas, Dun peas, chickpeas, faba beans, lentils, and soybean meal (SBM). Pulses were extruded at 18% or 22% moisture and 110, 130, or 150 °C. Extrusion decreased (P < 0.05) the starch content in Amarillo and Dun peas but increased (P < 0.05) the same in faba beans, lentils, and SBM when compared with their whole counterparts. There was no difference in the total dietary fibre content of whole and extruded Amarillo peas, Dun peas, chickpeas, and SBM. Extrusion increased (P < 0.05) the soluble dietary fibre (SDF) content of all pulses and SBM except chickpeas. Extrusion increased (P < 0.05) for all fibre types in faba beans. Results indicate that extrusion increased the starch and SDF content of most pulses but had negative or no effects on other fibre components in all pulses except faba beans.


Introduction
To ensure food security, research that promotes the continuous production of livestock in an efficient and sustainable manner using nonconventional feedstuffs must be carried out.Pulses are a group of leguminous seeds that serve as a food staple for humans as well as an alternative protein and carbohydrate source for livestock.Common pulses such as field peas (Pisum sativum), faba beans (Vicia faba), lentils (Lens culinaris), and chickpeas (Cicer arietinum) are being investigated as low-cost alternatives to soybean meal (SBM) in the diets of monogastric animals due to their low-fat content and density of nutrients such as protein, starch, vitamins, and minerals (Babatunde et al. 2021).Pulses are also an excellent source of bioactive peptides that are associated with health benefits for humans and livestock (Morales et al. 2015b;Arribas et al. 2019a).In addition, pulses are high in dietary fibre that contributes towards the energy requirement of livestock as well as supporting gut motility and health (Yagci et al. 2020).However, pulses must undergo processing from the raw form to increase the nutritional value, palatability, and to ensure the removal of antinutritional factors such as trypsin inhibitors, tannins, and phytic acid (Rathod and Annapure 2016;Yagci et al. 2020).
Common feed processing techniques for pulses include dehulling, grinding, and sometimes pelleting.The effects of grinding and pelleting on the nutrient composition of Canadian grown pulses have been previously described by Babatunde et al. (2023) and Cargo-Froom et al. (2022).Other forms of processing such as boiling, extrusion, microwave irradiation, and radiofrequency introduce external factors such as moisture, pressure, shear, or heat to modify the physiochemical properties of pulses and improve their economic and nutritional quality (Dust et al. 2004).Extrusion involves the use of high temperatures, moisture, and shear force to process food materials and has been commonly used in the food manufacturing industry to produce a variety of specialty items such as breakfast cereals, snack foods, and pet foods (Guy 2001).The process has been utilized to improve the quality of feed ingredients such as cereals and legumes.In addition, extrusion has been reported to improve the digestibility and bioavailability of nutrients in feed ingredients such as corn and soybeans (Alonso et al. 2000;Rathod and Annapure 2016).Due to the high temperatures involved in extrusion cooking, some studies have reported changes in the starch, protein, and dietary fibre components of feed ingredients such as oats, SBM, and corn (Dust et al. 2004;Onyango et al. 2004).
The extrusion process involves forcing a dough of single or mixed ingredients through a heated barrel and dying at high pressures and temperatures.To ensure uniformity and the quality of the extrudate, certain variables in the extrusion process, such as temperature, feed moisture content, time, and screw speed, are of utmost importance and must be adjusted accordingly (Pasqualone et al. 2020).Changes in the extrusion temperature or moisture content may alter the nutrient composition of the final product.Limited studies have investigated the effects of extrusion on the nutrient composition of Canadian sourced pulses except for a recent report by Cargo-Froom et al. (2023), which focused on effects on protein composition.Thus, the objectives of this trial were to investigate the effects of extrusion processing on the starch and dietary fibre composition of some Canadian pulses as well as characterize any alterations of these components in the extrudates due to differences in moisture content and temperatures used in the extrusion process.

Ingredients and processing
Pulses selected were grown in Canada, while SBM was included as a control since its nutrient profile and the effects of processing have been well characterized (Karr-Lilienthal et al. 2005).Selected pulses included Amarillo peas (IDFN 5-08-481; CDC Amarillo Variety; Oren and Marlene Robinson, Landis, SK, Canada), Dun peas (CDC Dakota; Faba Canada, Tisdale SK, Canada), chickpeas (Kabuli variety; AGT Foods, Regina, SK, Canada), faba beans (IDFN 5-09-262; Snowbird variety; Faba Canada, Tisdale SK, Canada), lentils (Laird variety; AGT Foods, Regina, SK, Canada), and SBM (IDFN 5-04-604; Cargill Animal Nutrition; North Battleford, SK, Canada).Before extrusion, ingredients were ground at the Canadian Feed Research Centre (North Battleford, SK, Canada) using a hammermill (G.J. Vis.Model: VISHM2014, Oakbluff, MN, Canada) and passed through a 2/64 screen.Average particle size for ground ingredients was as follows: Amarillo peas (255 μm), Dun peas (278 μm), chickpeas (216 μm), faba beans (272), lentils (296 μm), and SBM (370 μm).Ground ingredients were then extruded at the Agri-Food Innovation Centre (Saskatoon, SK, Canada) using a twin-screw extruder (Clextral EV 32 twinscrew extruder, Firminy, France) through a 2.7 mm die.The extruder was operated at 397 ± 2 rpm with a flow rate of 30.5 ± 0.2 kg/h.Ingredients were extruded in a 2 × 3 factorial design with two moisture levels (18% and 22%) and three temperatures (110, 130, 150 • C).Temperatures and moisture levels were selected based on common extrusion parameters used for pulses in the industry and for research.Sample collection started only after the ingredients had been extruded at a steady temperature for 1 min and was collected for all runs at the beginning (sample 1), middle (sample 2), and end (sample 3) of the extrusion run for each ingredient processing parameter.Extrudates were dried using an electric dryer after passing through the die and allowed to cool to room temperature prior to storage.Further information on the extrusion process in this study has been previously described by Cargo-Froom et al. (2023).

Statistical analysis
Data were analyzed using fixed models via PROC GLIM-MIX in SAS (SAS v 9.4; SAS Institute Inc., Cary, NC, USA).A fixed model was used to compare whole vs. extruded samples, where processing was the fixed effect.A second fixed model was used to compare extruded samples, where moisture, temperature, and their interactions were fixed effects.A Tukey's HSD test was used for means comparisons between samples.Differences were deemed significant when P ≤ 0.05.

Amarillo peas
The extrusion of Amarillo peas resulted in increased (P ≤ 0.05) DM and soluble dietary fibre (SDF) but reduced (P < 0.01) TS when compared with whole Amarillo peas (Table 1).There was no difference in the CF, TDF, and insoluble dietary fibre (IDF) between whole and extruded Amarillo peas.Within extruded Amarillo peas, there were no interaction effects of moisture and temperature on the nutrient composition.Amarillo peas extruded at 22% moisture had an increased (P < 0.05) IDF content but reduced (P < 0.05) SDF content when compared with extrusion at 18% moisture.Differences in moisture did not affect the DM, TS, CF, and TDF contents of Amarillo peas.In addition, there was no effect of temperature on the fibre composition of extruded Amarillo peas.

Dun peas
There was an increase (P < 0.05) in DM and SDF but a reduction (P < 0.01) in TS when whole and extruded Dun peas were compared (Table 2).However, there was no effect of extrusion over whole Dun peas when CF, TDF, and SDF contents were considered.There was no interaction effect of moisture and temperature on the nutrient composition of extruded peas.Except for DM, there was no impact of moisture on the nutrient composition of extruded Dun peas.With increasing temperatures from 110 to 150 • C, the DM content of extruded Dun peas increased (P < 0.01) while the IDF content decreased (P < 0.05).

Chickpeas
There were no differences in the fibre composition of whole and extruded chickpeas except for DM, which was higher (P < 0.01) in extruded chickpeas (Table 3).There were interactions (P ≤ 0.05) between moisture and temperature in extruded chickpeas, with the highest DM content found in chickpeas extruded at 18% moisture level and 130 • C. In addition, the highest CF content was found in chickpeas extruded at 22% moisture level and 130 • C, and the highest SDF content was observed in chickpeas extruded at 22% moisture level and 150 • C. Chickpeas extruded at 22% moisture level had lower (P < 0.05) TS content and higher (P < 0.05) TDF and IDF contents as compared with chickpeas extruded at 18% moisture.Changes in extrusion temperature significantly impacted (P < 0.05) the TS and TDF contents of extruded chickpeas.

Faba beans
Extrusion increased (P < 0.05) the DM, starch, and fibre contents observed in extruded faba beans as compared with whole faba beans (Table 4).Within extruded faba beans, there was no interaction effect of moisture and temperature on nutrient composition.Similarly, there was no effect of moisture level on the nutrient composition of extruded faba beans.Faba beans extruded at 130 • C had lower (P = 0.05) TS content than those extruded at other temperatures.Changes in temperature had no impact on other nutrients analyzed in extruded faba beans.

Lentils
Extruded lentils had higher (P ≤ 0.01) DM, TS, and SDF contents but lower (P < 0.01) TDF and IDF contents as compared with whole lentils (Table 5).There was no impact of extrusion on the CF content of lentils.Lentils extruded at 18% moisture level and 110 • C had the highest DM content as compared with lentils extruded at other conditions, resulting in a moisture by temperature interaction (P = 0.01).A similar interaction (P = 0.01) was observed with the TS content in extruded lentils, with the highest value observed in lentils extruded at 18% moisture level and 150 • C.There were no other effects of moisture or temperature on the fibre contents of extruded lentils.

Soybean meal
Whole SBM had lower (P < 0.05) DM, TS, and SDF contents but higher (P < 0.05) IDF contents when compared with extruded SBM (Table 6).There was no difference between the CF and TDF contents of whole and extruded SBM.An interaction (P < 0.05) between moisture level and temperature was observed on the CF, TDF, and IDF contents of extruded SBM, with values dependent on the temperature within each moisture level.SBM extruded at 18% moisture had higher (P < 0.05) DM and SDF contents as compared with SBM extruded at a 22% moisture level.There was no effect of temperature on the DM and TS contents of extruded SBM; however, increasing temperatures caused an increase (P = 0.05) in the SDF content of extruded SBM.
Effect of extrusion temperature and moisture on nutrient composition of whole and extruded Amarillo peas, % dry matter basis.

Note:
Means with differing superscript letters (a, b, c) in the same row are significantly different (P ≤ 0.05).Means with a significant interaction effect (moisture × temperature) only report differences between means for interaction effect.

Discussion
Extrusion cooking has been largely utilized by the food manufacturing industry to produce several ready-to-eat products such as snacks, breakfast cereals, and sports foods (Moscicki 2011;Offiah et al. 2019).Previously, extrusion was thought to be more effective with materials such as cereals and soybeans due to their ability to rapidly expand (Pasqualone et al. 2020).However, the use of pulses such as lentils, chickpeas, and faba beans as raw materials for extruded products have gained traction due to their high levels of protein and starch (Morales et al. 2015a).In the livestock industry, extrusion is utilized in the processing of raw ingredients, such as soybean and corn, into more valuable products with improved nutrient bioavailability and digestion (Osman 2007;Ghumman et al. 2016).In addition, given its high temperatures, extrusion has also been utilized to remove antinutrients found in pulses (Hegazy et al. 2017).In agreement with reports from Arribas et al. (2019b), extruded Canadian pulses in the current trial had a higher DM content as compared with whole pulses.This was due to the high temperatures used during the extrusion process and the postextrusion drying procedures.There was no ideal extrusion temperature and moisture content combination for all pulses with regard to DM.However, pulses extruded at an 18% moisture level at high temperatures (>110 • C) generally had a higher DM content than those extruded at 22% moisture.
Starch comprises about 40%-50% of the nutrient content of pulses and is an important source of dietary energy.The main components of starch are amylose and amylopectin, and the ratio of both fractions determines the typical properties of starch, including solubility, gelatinization, and cooking time.Contrary to results from Wang et al. (2008), extrusion in this study reduced the TS content of Amarillo and Dun peas.However, Brummer et al. (2015) reported decreases in the TS content of extruded field peas as compared with raw peas.Some pulses, such as pinto and navy beans (Phaseolus vulgaris), have been reported to have a very rigid cell wall structure that restricts the passage of water into their starch granules under high temperatures (Brummer et al. 2015).The disruption of the cell wall is important for the hydrolysis of starch during in vitro digestion.Thus, the cotyledon cell structure of field peas in the current study may have been responsible for the reduced TS content observed in the extruded peas.Another possible reason for the reduction in TS could be the dextrinization of the starch granules in field peas.Dextrinization occurs due to the exposure of starch to very high temperatures and results in the alteration of the molecular arrangement of amylose and amylopectin and the reduction of the molecular size of starch (Huang and Perdon 2020).Therefore, extrusion temperatures may have reduced the size of starch granules present in field peas.
In this study, extrusion increased the TS content in Canadian faba beans and lentils by 29% and 6%, respectively.Morales et al. (2015a) and Arribas et al. (2019b) also reported increases in the TS content of feed mixtures containing lentils and carob beans.The increase in starch content has been attributed to modifications of the starch components due to cell disruption that occurs during extrusion, resulting in the production of reducing sugars from complex carbohydrates (Arribas et al. 2019b).Additionally, the total or partial gelatinization of starch that occurs during cooking at high temperatures often increases the susceptibility of starch granules to α-amylase degradation during TS determination.This may explain the increased TS content observed in those pulses (Bjorck and Asp 1983;Alam et al. 2016) and the increased digestibility of starch in extruded pulses (Rathod andAnnapure 2016, 2017).Last, extrusion cooking has also been reported to eradicate the activity of α-amylase inhibitors present in some pulses (El-Sayed et al. 1997;El-Hady and Habiba 2003).The absence of these inhibitors may contribute to enhancing the digestive capacity of amylase during in vitro digestion used in starch determination.
There was no effect of extrusion on the TS content in Canadian chickpeas, which is in agreement with results from Berrios et al. (2010), who observed no changes in the total carbohydrate content in extruded chickpea blends.However, Cardoso-Santiago and Areas (2001) reported increases in the starch content of extruded chickpeas.These variations in results among studies may be due to differences in extrusion parameters or the combination of chickpeas with other ingredients as opposed to the current trial, where chickpeas were extruded as a single ingredient.Within extruded pulse samples in the current trial, higher moisture content and temperatures tended to induce higher TS content as compared with other conditions.Increases in temperature and moisture content during extrusion often result in increased gelatinization of starch and a significant rise in in vitro starch digestibility (Bjorck and Asp 1983;Ljokjel et al. 2004;Rathod and Annapure 2017).The TS content of extruded SBM was increased by 422% when compared with whole SBM.Since the cell wall structure of soybean had been broken down during the processing of SBM, the starch granules in SBM would readily have been hydrolyzed and expanded during extrusion, allowing for easy access to enzymes during TS determination.
Pulses are well known as fibre-rich food sources that are high in both SDF and IDF (Tosh and Yada 2010).Diets high in dietary fibre are promoted for lowering the risks of heart diseases, diabetes, and gastrointestinal diseases in humans (Brummer et al. 2015).In livestock, TDF contributes toward supporting digestion, gut viscosity, gut motility, hindgut fermentation, and gut microflora (Chen et al. 2020).Given that extrusion is a common processing parameter for livestock feed, understanding the effects of extrusion on TDF, IDF, and SDF can be important for livestock health.The effects of extrusion on fibre have been studied in several feed ingredients, including wheat bran (Rashid et al. 2015), rice (Andersson et al. 2017), sugarbeet pulp, and soybean (Jing and Chi 2013).In the food industry, extrusion cooking has been widely used to increase the SDF content of high IDF sources such as pea seed coats, orange pomace, and rye bran (Wolf 2010;Jing and Chi 2013;Huang and Ma 2016;Andersson et al. 2017).Canada is a major producer of pulses.However, limited work has been done on examining the effects of extrusion on the fibre content of Canadian-grown pulses.
In the current study, there was no effect of extrusion on the CF and TDF of most pulses except faba beans.However, the IDF content in Dun peas, lentils, and SBM was reduced while the SDF content of all pulses except chickpeas increased.This agreed with results from Zhong et al. (2019), where extrusion increased the SDF content, reduced the IDF content, and had no effect on the TDF content in lupin seed coats.A similar trend was observed when blast extrusion was carried out on soybean residues, with increases in the SDF content and no effects on TDF (Chen et al. 2014).It has been reported that the combination of intense instantaneous heat and other factors such as friction, cavitation, and impact compression are responsible for the conversion of IDF into SDF in feed materials (Li et al. 2012).Thus, in IDF-rich ingredients such as oat bran, extrusion cooking has been used to extract the SDF fractions with reported increases in solubility, swelling capacity, and viscosity, which are properties usually associated with SDF (Zhang et al. 2009).
Since most of the whole pulses and SBM in the current trial were low in SDF, extrusion was able to extract additional SDF from the IDF by increasing the solubility of some of the IDF fractions.However, extrusion had no effect on the fibre content of chickpeas.When the characterization of fibres from pulses was carried out by Brummer et al. (2015), it was reported that the physiochemical structure of fibres in chickpeas was unusual and characterized by high molecular weight but low intrinsic viscosity, suggesting a highly branched polymer structure.This unusual fibre structure in chickpeas may have limited any physiochemical changes from occurring during extrusion.Increases in temperature, moisture content, and screw speed have been reported to increase the SDF extraction efficiency of the extrusion process (Brummer et al. 2015).However, in the current study, changes in the fibre content of pulses varied across the different extrusion conditions, suggesting that pulse type may play a factor in the effect of extrusion parameters on the dietary fibre profile.
In conclusion, extrusion processing induced positive changes in the starch and fibre content, particularly in the SDF content, of some Canadian-grown pulses.This indicates that extruded pulses may play a role in supporting the gut health of livestock by supplying substrates that could be fermented by beneficial bacteria in the hindgut.However, effectiveness may be dependent on pulse type and/or extrusion conditions.In addition, the current study only extruded a single ingredient at a time as opposed to a livestock diet comprising several ingredients.Thus, more work is required to ascertain if changes in starch and fibre profiles, as well as other macro-and micronutrients, are observed when pulses are extruded in combination with other foods and nutrients.
Means with differing superscript letters (a, b, c, x, y) in the same row are significantly different (P ≤ 0.05).Means with two sets of superscripts indicate effects of moisture (first value: a, b, and c) and temperature(second value: x and y).Means with a significant interaction effect (moisture × temperature) only report differences between means for interaction effect.

Table 2 .
Effect of extrusion temperature and moisture on nutrient composition of whole and extruded Dun peas, % dry matter basis.
Note:Means with differing superscript letters (a, b, x, y) in the same row are significantly different (P ≤ 0.05).Means with two sets of superscripts indicate effects of moisture (first value: a and b) and temperature (second value: x and y).Means with a significant interaction effect (moisture × temperature) only report differences between means for interaction effect.

Table 3 .
Effect of extrusion temperature and moisture on nutrient composition of whole and extruded chickpeas, % dry matter basis.

Table 4 .
Effect of extrusion temperature and moisture on nutrient composition of whole and extruded faba beans, % dry matter basis.
Note:Means with differing superscript letters (a, b) in the same row are significantly different (P ≤ 0.05).Means with a significant interaction effect (moisture × temperature) only report differences between means for interaction effect.

Table 5 .
Effect of extrusion temperature and moisture on nutrient composition of whole and extruded lentils, % dry matter basis Note:Means with differing superscript letters (a, b, c) in the same row are significantly different (P ≤ 0.05).Means with a significant interaction effect (moisture × temperature) only report differences between means for interaction effect.

Table 6 .
Effect of extrusion temperature and moisture on nutrient composition of whole and extruded soybean meal, % dry matter basis