Extrusion cooking of barley flour and process parameter optimization by using response surface methodology

BACKGROUND: The nutritional profile of barley places it in a prime position for development of a new extruded–expanded snack food with health benefits. It was therefore the aim to investigate the effect of extrusion processing variables on system parameters (specific mechanical energy, die pressure and die melt temperature) and physical properties (expansion, bulk density, texture and color) of barley flour extrudates and to optimize processing conditions for production of extruded snack food from barley flour by response surface methodology. RESULTS: Barley flour with 219.7 g kg^?1 moisture content was extruded at different die temperatures (140–160 °C) and screw speeds (150–200 rpm) through a co‐rotating twin‐screw extruder. The system parameters as well as product responses were mainly dependent on temperature, whereas the screw speed imparted a lesser effect. Extrudates produced under extrusion conditions of 160 °C, 150 and 200 rpm and at 164 °C and 150 rpm had higher preference levels of appearance, taste, texture and overall acceptability than that of other selected extrudates for sensory analysis. The optimal conditions for minimum bulk density and desired textural characteristics and color of extrudates correspond to a temperature of 156 °C and screw speed of 166 rpm. CONCLUSION: The results suggested that use of barley flour in extruded snack products offers a desirable variation in diet and can take advantage of the nutritional quality of barley. Copyright © 2008 Society of Chemical Industry     

Residence Time Distribution (RTD) in a Single Screw Extrusion of African Breadfruit Mixtures

Mixtures of African breadfruit (Treculia africana Decne), corn, and defatted soybean were extruded in a single-screw Brabender laboratory extruder at process variables derived from a second-order central composite design. The variables consisted of feed composition (0–100% breadfruit, 0–55% soybean, and 0 or 5% corn); fed moisture (15–27%), and screw speed (100–180 rpm). Effects of these variables on residence time distribution were investigated using Congo red as tracer. The extrudate spent longer time in the extruder as feed moisture or screw speed was decreased from 27% to 15% or 180 to 100 rpm, respectively, thereby increasing the residence time distribution characteristics. At 70% feed composition and screw speed of 140 rpm, mean residence time ([`(t)]\overline t ) increased from 40 to 50 s, whereas extrudate total collection time (t <sub>c</sub>) increased from 65 to 70 s. At screw speed of 100–180 rpm, mean residence time ([`(t)]\overline t ) decreased from 55 to 35 s, whereas extrudate total collection time (t _c) decreased from 75 to 65 s. At 100% African breadfruit composition, these time values decreased to 35 and 70 s, respectively, at the same screw speed, indicating the significant influence of feed composition and soybean addition to the mixture on residence time distribution. Residence time distribution curves indicated an early breakthrough time of 20 s at maximum screw speed (180 rpm), minimum tail of 65 s, and a plug flow pattern of the extrudates.     

Effect of extrusion conditions on the physicochemical properties of a snack made from purple rice (Hom Nil) and soybean flour blend

Soy flour was added at levels of 5%, 10%, and 15% of Hom Nil rice flour for extrusion at 190 °C barrel temperature and 350 rpm screw speed. The extruded snack qualities decreased inversely with soy flour. However, product qualities were considered to be optimised when soy flour at 5% was added. The effect of feed moisture content (15, 17, 19 g (100 g)^?1 wb), barrel temperature (150, 170, 190 °C) and screw speed (350, 400, 450 rpm) on physicochemical properties of the snack were then investigated. The physicochemical properties of the product including expansion ratio, density, water absorption index (WAI), water solubility index (WSI) and hardness were evaluated. All properties were related, as linear equations, in terms of feed moisture content, barrel temperature, screw speed with relative correlation (R²) at 0.83–0.94. The snack properties along with consumer acceptance were all highest when the extruded condition were 15 g (100 g)^?1 wb feed moisture content, 170 °C of barrel temperature and 450 rpm of screw speed.     

Enhancing an Extruded Puffed Snack by Optimising Die Head Temperature,Screw Speed and Apple Pomace Inclusion

Extrusion cooking is recognised as a smart technology for food processors. It requires low cost, high temperature, short-time process and few ingredients to create a puffed snack. The only drawback is that it contains multiple parameters that need to be rigorously trialled to develop an optimal process. This study investigated the effects of two extruding parameters (die head temperature and screw speed) and examined the addition of apple pomace into a corn flour-based extruded snack formulation. A response surface design was utilised. A D-optimal design was chosen, which generated 21 combinations; within these combinations, the control formulation existed. Extrudate characteristics, i.e. bulk density and porosity, textural properties, cooked starch properties and moisture, were analysed. Screw speed was found to have the greatest effect on extrudate quality, e.g. bulk density increased as the screw speed increased (p?<?0.001). Both apple pomace addition and screw speed impacted expansion ratio; as they increased, expansion decreased (p?<?0.0001). The optimised and validated formulation contained the following parameter levels: 7.7 % apple pomace, 150 °C die head temperature and a screw speed of 69 rpm. As apple pomace and corn flour are naturally gluten free, the extruded product would appeal to people who suffer from intolerances, allergies and coeliac disease.     

Physico‐chemical and antioxidant properties of extrudates developed from honey and barley

Barley flour and honey, being concentrated source of nutrients, were used to develop extruded product using twin‐screw extruder. Response surface methodology was applied to study the effects of honey (5–25%), moisture content (17–21%) temperature (120–160 °C) and screw speed (180–220 rpm) on product responses. The variation in moisture content and die temperature affected the physicochemical properties of extrudate but screw speed had significant effect only on hardness. It was established that with increase in honey levels from 5% to 20%, there was increase in antioxidant activity (up to 106.9%), total phenolic content (up to 90.2%) and total flavonoid content (up to 89.2%) in interaction with other extrusion cooking variables. The optimal condition corresponds to honey content of 18.86%, feed moisture of 18%, die temperature of 148.62 °C and screw speed of 209.99 rpm. The results suggest that honey can be extruded with barley flour into a healthful snack food.     

Twin-screw Extrusion of Corn Flour and Soy Protein Isolate (SPI) Blends: A Response Surface Analysis

The effects of feed moisture, screw speed, and barrel temperature on physical properties of extruded corn flour and soy protein isolate (SPI) blends were investigated in a co-rotating twin-screw extruder using a response surface methodology. Corn flour and SPI were mixed with a ratio of 4:1. The screw speed was set at five levels between 60 and 140 rpm, barrel temperature between 140 °C and 180 °C, and feed moisture between 18% and 38%. All physical properties of the extruded material evaluated—included expansion ratio, bulk density, breaking strength, water solubility index, rehydration ratio, and color—were significantly (p < 0.05) affected by the three process variables. Feed moisture was the most significant variable with quadratic effects on most of the physical properties. Response surface regression models were established to correlate the physical properties of the extruded product to the process variables. Understanding the effect of these variables on the product physical properties was deemed useful for the development of protein-rich extruded products.     

Effect of formulation and processing parameters on acrylamide formation: A case study on extrusion of blends of potato flour and semolina

Acrylamide formation in extruded snacks prepared using blends of potato flour:semolina in ratios ranging from 30:70 to 70:30 showed maximum acrylamide formation in the 70:30 blend. The extrusion was carried out at a screw speed of 120 rpm, temperature of 170 °C and moisture content of 18%. Further, the influence of extrusion processing parameters on the acrylamide formation in extruded snacks prepared from a 70:30 blend of potato flour:semolina was investigated using response surface methodology (RSM). The feed moisture was varied from 12.6% to 19.4%, die temperature from 163 to 197 °C and screw speed from 106 to 173 rpm. The extrudates so obtained showed acrylamide content ranging from 704 to 1560 μg/kg. The effect of different additives such as citric acid, calcium salts, amino acids, vitamins and their combinations on the mitigation of acrylamide formation showed calcium chloride at 50 μmol/g flour blend to reduce acrylamide formation by 65% without altering the sensory properties of the extrudates.     

The Effect of Extruded Orange Pulp on Enzymatic Hydrolysis of Starch and Glucose Retardation Index

Orange pulp was extruded using a Brabender laboratory single screw extruder (20:1 L/D). The independent variables evaluated were barrel temperature (83, 100, 125, 150, and 167 °C), feed moisture content (22, 25, 30, 35, and 38/100 g), and screw speed (126, 140, 160, 180, and 194 rpm). The apparent density and apparent viscosity values of the extruded orange pulp increased during extrusion, while the oil absorption index decreased, in comparison with the values for raw orange pulp. In vitro studies showed that at the end of the incubation time, 90.68% of the starch was hydrolyzed in the control sample, while only 77.82% and 69.40% pulp of the starch experienced hydrolysis in the presence of raw fiber and extruded orange pulp, respectively. Extruded orange pulp showed a higher glucose retradation index (16.04–25.92%) after 30 min of dialysis and after 60 min (11.66% and 18.33%) than raw orange pulp (8.33%). These results indicated that glucose could be bound with compacted fiber matrices and inhibit alpha-amylase activity. These mechanisms may create a definite benefit by decreasing the rate of glucose absorption and eventually lowering the concentration of postprandial serum glucose. The potential hypoglycemic effects of extruded orange pulp suggest that orange pulp is a good and abundant dietary fiber resource that could be of great benefit in controlling glucose levels in the blood. It could also be added to high-fiber foods as a low-calorie bulk ingredient to reduce the calorie level.     

Effect of Thermo-extrusion Process Parameters on Selected Quality Attributes of Meat Analogue from Mucuna Bean Seed Flour

Flour from mucuna beans (Mucuna pruriens) were used in producing texturized meat analogue using a single screw extruder with the intention to monitor modifications on some functional properties of the extrudate. Response surface methodology based on Box Behnken design at three levels of barrel temperature (110, 120, 130°C), screw speed (100, 120, 140 rpm) and feed moisture content (44, 47, 50%) were used in 17 runs. Regression models describing the effect of process variables on the product quality attributes were obtained. Result obtained showed that the moisture contents of the meat analogue samples decreased from 13.23 to 6.53%. Increasing feed moisture content resulted in extruded meat analogue with a higher density (0.988), water absorption index (WAI) (2.30), oil absorption index (OAI) (2.350), swelling power (3.47) and lower lateral expansion (0.84). Lateral expansion, OAI and swelling power increased as barrel temperature increased with peak values of 1.39, 2.39 and 3.47 respectively, while bulk density and WAI decreased. The product functional responses with coefficients of determination (R²) ranging between 0.658 and 0.894 were most affected by changes in barrel temperature and feed moisture and to lesser extent by screw speed. Optimization results based on desirability concept indicated that a barrel temperature of 120.15°C, feed moisture of 47% and screw speed of 119.19 rpm would produce meat analogue of preferable functional properties.     

Effect of Extrusion Variables on Cassava Extrudates

Cassava flour was extruded by varying parameters of feed moisture; temperature; screw speed and feed rate. We investigated significance of each variable and interactions between variables on each extrudate characteristic. Optimum expansion (2.82) was at 11% feed moisture 120–125 °C; screw speed, 520rpm; feed rate, 250g/min. Effect of feed moisture was most significant on expansion, bulk density and extrudate moisture. Increasing temperature, increased expansion and water solubility, but decreased bulk density, extrudate moisture and water absorption. Screw speed most influenced water absorption and solubility. Extrudate moisture correlated negatively (P<0.01) with extrudate expansion. Water solubility index of extrudate negatively correlated (P<0.05) with extrudate moisture and water absorption index but correlated positively (p<0.05) with expansion.     

ENERGY CONSUMPTION IN SINGLE-SCREW EXTRUSION PROCESSING OF FULL FAT AFRICAN BREADFRUIT (TRECULIA AFRICANA) BLENDS

Full fat African breadfruit, corn and defatted soy blends with moisture content range of 6.20–7.50% (wet basis) were extruded in a single‐screw Brabender laboratory extruder (DCE 330, Brabender Instruments Inc., South Hackensack, NJ) at varying independent process variables of feed composition (fc), feed moisture (fm) and screw speed. A central composite design was employed to study the effects of these variables and extrusion cooking on several quality characteristics of the center point blend, and energy input as torque and specific mechanical energy (SME). SME is relevant in that the more the energy applied, the greater the degradation of starch while torque is directly correlated with power usage. Extrusion cooking significantly (P ≤ 0.05) affected bulk density, water absorption, water solubility and nitrogen solubility indices. Torque and SME ranged from 4.00 to 8.50 N·m and 216 to 376 kJ/kg, respectively. Regression analysis of data generated of experimental data showed that fc had significant (P ≤ 0.05) quadratic effect on both energy measurements. Screw speed and fm showed significant (P ≤ 0.05) linear effects on SME while screw speed alone showed significant (P ≤ 0.05) linear effect on torque. At 160‐rpm screw speed and 85% fc, the torque value was maximum (8.50 N·m). Maximum SME value of 376.72 kJ/kg was obtained at 85% fc, 24% fm and 120‐rpm screw speed. Economically, therefore, extruded products made from blends of breadfruit, corn and soy flours will require lower extruder power usage given the fat and fm levels. Findings of this research might be useful to processors for better process control and optimal energy utilization when extruding these or related blends in a single‐screw extruder.     

Physico-chemical and sensory quality of extruded light red kidney bean (Phaseolus vulgaris L.) porridge

A laboratory co-rotating twin-screw extruder was used to study the effect of extrusion conditions on physical, chemical, and sensory characteristics of extruded light red kidney beans (Phaseolus vulgaris L). Raw bean flour was extruded at 25 g/100g and 36 g/100g moisture content. Other extrusion parameters were: barrel temperatures, 120 °C/105 °C (BT-1) and 130/115 °C (BT-2); screw speeds, 118 rpm (SS-1), 194 rpm (SS-2), and 253 rpm (SS-3); and feed rates of 80 and 120 g/min (FR-1 and FR-2, respectively). Extrudates were analyzed for expansion ratio (ER), bulk density (BD), water absorption index (WAI), water solubility index (WSI), and lectins, as phytohemagglutinin (PHA) activity. Sensory evaluation of bean porridge, obtained after coarsely grinding extrudates, was done to compare it to Sosuma, a traditional Rwandan porridge. Feed rate significantly influenced average ER, which was determined to be 1.22 and 1.30 for FR-1 and FR-2, respectively. Increasing moisture content from 25 g/100g to 36 g/100g significantly increased average BD. The WAI and WSI values did not show a clear trend under extrusion conditions used in this study. For all extruded samples, lectin was reduced to less than one-tenth of that in the raw beans. Sensory evaluation of bean porridge, on a 1-9 hedonic scale (1 = dislike extremely and 9 = like extremely), exhibited scores of 7.65, 7.69, 6.25, and 6.94 for color, texture, flavor, and overall acceptability, respectively.     

Effect of Pre-Treatments on Mechanical Oil Expression of Soybean Using a Commercial Oil Expeller

The effect of expeller screw press and pre-treatments on the quality and quantity of soybean oil and cake was studied using a commercial oil expeller. The pretreatments included whole soybean crushing, soy grits crushing, and crushing of soy grits extruded at 135°C. The screw speeds were 28, 35, and 45 rpm. The moisture content of soybean used in the experiment was 10% wet basis. The average capacity of the oil expeller was found to be 145 kg/h, 110 kg/h, and 120 kg/h for whole, grits, and extrudate, respectively at 45 rpm. The average capacity of oil expression from whole soybean did not vary significantly from 28 to 45 rpm. In the case of soy grits, however, the capacity was higher when the expeller speed was lowest, i.e., 28 rpm. In the case of extrudate, even in a single pass, the recovery was higher, i.e., to 71% at both 45 and 35 rpm. The color of oil from soy grits was lighter followed by extrudate, and the color of oil obtained from whole soybean was dark. The FFA in oil from all the samples was below 1%, however the lowest percentage was for oil obtained from extrudate at 0.5%. The urease activity of the extruded cake was 0.15 pH units, and the protein and oil content were about 48% and 5%, respectively. The optimum process variables for mechanical expelling of soybean were found to be extrusion as a pretreatment and speed of expeller screw at 45 rpm, which yielded throughput capacity 103 kg/h, oil recovery of 70.5%, and urease activity of the cake at 0.15.     

Effects of extrusion conditions on secondary extrusion variables and physical properties of fish, rice-based snacks

A formulation containing rice flour, fish powder, menhaden oil and vitamin E was extruded at a feed rate of 10 kg/h using a co-rotating twin-screw extruder. Primary extrusion (independent) variables were temperature (125-145 °C), screw speed (150-300 rpm) and feed moisture (19-23 g/100 g db). Response surface methodology (RSM) was used to study the effects of extrusion conditions on secondary extrusion variables (product temperature, pressure at the die, motor torque, specific mechanical energy input and mean residence time) and physical properties of the extrudates. Second-order polynomial models were computed and used to generate contour plots. Increasing feed moisture and screw speed decreased pressure at the die. Increased screw speed increased product temperature at the die but increased feed moisture lowered it. Increased barrel temperature, feed moisture and screw speed decreased motor torque. Increased screw speed increased specific mechanical energy, while increased feed moisture reduced it. Longer mean residence times were observed at lower screw speeds. Product density increased as feed moisture increased, but decreased with screw speed. Increased feed moisture decreased radial expansion.     

Consumer-based optimization of a third-generation product made from peanut and rice flour

ABSTRACT:  Indirectly puffed snacks were produced by an extrusion process with partially defatted (12% fat) peanut flour (30%, 40%, 50%) at different levels of screw speed (200, 300, 400 rpm) and feed rate (4, 5, 6 kg/h). Extrudates were dried to obtain half-products (11% to 12% MC) followed by puffing with deep-fat frying. The puffed snack prototypes were subjected to consumer acceptance test. Consumers rated higher than 6.0 (= like slightly) for all products produced within the experimental factor ranges on the attributes of crispness and texture, whereas consumer scores for appearance, color, flavor, and overall liking were lower than 6.0 for the product containing 50% peanut flour regardless of screw speed and feed rate. The product extruded with 50% peanut flour at screw speed of 400 rpm and feed rate of 6 kg/h received the lowest score of 5.5 on overall liking in a 9-point hedonic score. Predicted regression models indicated that feed rate had the largest effect on consumer attributes followed by peanut flour and screw speed. From the superimposed contour plot of individual contour plot of consumer attributes, the optimum region was identified as the area beginning at the 42.0% to 43.0% peanut flour and 4.0 kg/h feed rates, rising to a maximum at 45% peanut flour and 4.6 kg/h feed rates and decreasing to the 33.0% to 34.0% peanut flour and 6.0 kg/h feed rates. Verification confirmed the ability of predictive regression models to identify peanut-based snacks, which would be scored higher than 6.0 by consumer evaluation.     

The effect of rice bran on physicochemical,textural and glycaemic properties of ready-to-eat extruded corn snacks

In this work, corn extruded snack products were enriched with rice bran (RB) at 10% and 15%. A co-rotating twin-screw extruder was used with a feed moisture content of 16 g 100 g⁻¹, a screw speed of 240 r.p.m. and four heating sections of the barrel (100, 140, 150 and 150 °C). The impact of RB inclusion on nutritional profile, starch digestion, physicochemical and textural properties of snack products was evaluated. RB-enriched extrudates showed a lower specific volume and hardness and higher crispness than control. RB at 15% gave a water-holding capacity lower than control. Rheology of extrudate dispersions indicated an increase in elastic interactions and solid-like behaviour with RB supplementation. Differences in rheological properties resulted in attenuation of predictive glycaemic response for RB-enriched snacks.     

Tapioca-Fish and Tapioca-Peanut Snacks by Twin-Screw Extrusion and Deep-Fat Frying

Two half-products were prepared from tapioca starch/catfish fillet-belly flap mince (60:40) and tapioca starch/partially defatted peanut flour (PDPF) (60:40) by twin-screw extrusion. The process variables were temperature in the last two zones of the extruder (90,95,100°C) and screw speeds (100, 250, 400 rpm). Moisture content (40%, wet basis) and feed rate (27 g/min) were held constant. Simultaneously increasing temperature and screw speed resulted in increased expansion, and decreased bulk density and shear strength. Degree of starch gelatinization in half-products ranged from 87 to 95%. Optimum conditions predicted by response surface methodology were: for fish half-products 94–100°C and 220–400 rpm and for peanut half-products, 95–100°C and 230–400 rpm.     

Response surface analysis and extrusion process optimisation of maize–mungbean‐based instant weaning food

This study was conducted to produce high‐quality weaning food from easily available and low‐cost raw materials by extrusion technology. Weaning mix was developed using extrudates of maize (Zea mays) and mungbean (Vigna radiata) flour with a twin‐screw extruder. Experiments were designed using three independent variables [feed moisture (12.6 – 19.4%), screw speed (349 – 601 rpm) and barrel temperature (108 – 192 °C)] and five dependent variables (specific mechanical energy, bulk density, water absorption index, water solubility index and degree of gelatinisation) at five levels of central composite rotatable design (CCRD). Optimisation results indicated that feed moisture of 14.33%, screw speed of 524 rpm and barrel temperature of 174 °C would produce maize–mungbean extrudates of preferable functional properties. The optimised weaning mix contained maize–mungbean extrudates 40%, skim milk powder 35% and sugar 25% (w/w). The nutrient content of the weaning mix was in accordance with the standards specified by PFA, (2004) with high protein and starch digestibility.     

Expansion characteristics of a nutritious extruded snack food using response surface methodology

Response surface methodology was used to analyze the effect of screw speed (220–340 rpm), feed moisture (11.0–15.0%, wet basis) and feed rate (22.0–26.0 kg/h, wet basis) on the physical properties (i.e., bulk density, expansion, porosity) of a nutritionally balanced extruded snack food. Regression equations describing the effect of each variable on the responses were obtained. Responses were most affected by changes in screw speed followed by feed moisture and feed rate (P<0.05). Expansion and porosity increased with screw speed and feed moisture whereas the opposite was observed for bulk density. Radial expansion was found to be a better index to measure the extent of expansion than the axial and overall expansions, indicated by a higher correlation coefficient.     

Instant flour from quality protein maize (Zea mays L). Optimization of extrusion process

Traditional nixtamalization process for producing instant flours is highly time and energy consuming; in addition, it presents problems of high liquid waste discharges (3–10 L H₂O/kg maize). Extrusion represents an alternative technological for producing instant flours and does not generate effluents. The objective of this work was to determine the best combination of extrusion process variables for the production of instant flour from quality protein maize (QPM) (Zea mays L) V537 variety. Prior to extrusion, the maize kernels were broken to obtain grits (1−2 mm) which were mixed with lime and water to reach a moisture content of 28 g/100 g. The single screw extruder operation conditions were selected from a factorial combination of process variables: extrusion temperature (ET, 70–100°C), lime concentration (LC, 0.1–0.3 g/100 g maize) and screw velocity (SV, 30–80 rpm). A central composite experimental design with five variation levels was chosen. Response surface methodology was applied as optimization technique, over four response variables: in vitro protein digestibility (PD), total color difference (ΔE), water absorption index (WAI) and pH. Predictive models for response variables were developed as a function of process variables. The conventional graphical method was applied to obtain maximum PD, WAI, pH and minimum ΔE. Contour plots of each of the response variables were utilized applying superposition surface methodology, to obtain three contour plots for observation and selection of a superior (optimum) combination of ET (79.4°C), LC (0.24 g/100 g maize) and SV (73.5 rpm) to obtain optimized extruded maize flour (EMF) from QPM with a single screw extruder. Optimized EMF had similar physico-chemical and functional characteristics than commercial nixtamalized maize flours (NMF).