Effect of Extrusion Temperature and Feed Moisture Content on the Microstructural Properties of Rice-Flour Pellets and Their Impact on the Expanded Product

Extrusion can lead to an expanded product or to a slightly expanded pellet, known as a third-generation (3G) snack. In this case, expansion occurs subsequently, in an independent thermal device (e.g., oven), out of the extruded pellet. During both processes, several structural changes occur which are linked to processing conditions, including cooking temperature, screw speed, formulation, and initial moisture content. However, a clear relationship between processing variables and the structure of pellets and expanded products has not yet been identified. Accordingly, this work aimed to study the effect of extrusion temperature (110, 135, and 150 °C) and moisture content (27, 29, and 31%) in rice-flour pellets and their microwave expansion, through a microstructural approach using micro-CT. The results showed that the lowest moisture content (27%) and the highest extrusion temperature (150 °C) led to the highest pellet volume and the highest wall thickness, which in turn led to the highest expansion after microwave heating (50 s, 800 W). Interestingly, no significant differences were observed when analyzing the ratio between the volume of the expanded products and the volume of the pellet (~2.4) when using the different processing conditions.

Studying the effect of tomato pomace incorporation on physicochemical, nutritional and storage characteristics of corn-based extrudates using response surface approach

PurposeThe present research was envisaged with an aim to optimize the system and the product responses for the development of tomato pomace-incorporated corn-based extrudates employing central composite rotatable design and determine its proximate, lycopene, consumer acceptability and storage studies.Design/methodology/approachLycopene-rich extrudates were developed from corn flour blended with different levels of tomato pomace. The independent extrusion variables, namely, feed composition (95:5 to 75:25), feed moisture (12–20%), screw speed (200–600 rpm) and barrel temperature (125–185 °C), were studied to determine their influence on dependent variables, namely, specific mechanical energy, hardness, water solubility index, lateral expansion, water absorption index, bulk density and color.FindingsAll of the quality parameters were significantly (p < 0.05) influenced by independent variables. The regression models obtained for all the responses showed high coefficients of determination (R2 = 0.85–0.95). The optimum conditions for the development of tomato pomace-incorporated corn-based extrudates were feed composition (90:10), feed moisture (14%), screw speed (300 rpm) and barrel temperature (170 °C). The moisture, fat and carbohydrate contents of the extrudates were significantly reduced, whereas protein, ash and fiber were significantly (p < 0.05) enhanced after the incorporation of tomato pomace. Aluminum laminates were found to be the suitable packaging materials for extrudates for a period of 120 days in comparison to high-density polyethylene packages.Originality/valueAs far as the authors could possibly know, scanty literature exists wherein the tomato pomace has been utilized for the development of lycopene-rich corn-based extruded snacks. Such extrudates with significantly higher fiber and lycopene contents than corn flour will serve as a suitable alternative for the development of shelf-stable ready-to-eat extruded snacks.

Physicochemical properties of extruded ready-to-eat snack from unripe plantain blends, pineapple by-products and stevia

The aim of this research was to evaluate the effect of extrusion temperature (ET 120 – 180 °C), feed moisture content (FMC 16 - 25 g/100 g), pineapple by-products proportion (PBP) (0 - 30 g/100 g) in the unripe plantain flour, and the stevia content (STC 0 - 5 g/100 g) on the physicochemical properties and sensory acceptance of ready-to-eat extruded snacks, through a central compound design, using a single-screw extruder with a compression screw ratio of 3:1. The results were analyzed by response surface. The increase in FMC, PBP and STC decreased (p < 0.05) the expansion index (EI). The increase in ET decreased (p < 0.05) the apparent density (AD), water absorption index (WAI), water solubility index (WSI) and total color difference (ΔE). The increase in FMC decreases EI, WAI, and increase AD and WSI (p < 0.05). The Increase in PBP decreased EI, WSI, and increase AD, hardness (H) and ΔE (p < 0.05). The increase in STC decreased (p < 0.05) EI, and increase AD and H. The treatments with greater general acceptability were those that contained 15 and 30 g/100 g of PBP and STC 2.5 g/100 g, and they were obtained at ET 150ºC and 20.5 g/100 g of FMC, without affecting the physicochemical properties.

Response surface analysis and process optimization of non-cereal (elephant foot yam, taro and water chestnut) snacks

The present study was conducted to develop non-cereal starch extruded products. The effects of feed moisture (15-21%), temperature (130-170 °C) and screw speed (120-160 rpm) were evaluated on the physical and functional properties of extruded snacks using response surface methodology. Feed moisture and screw speed increased the bulk density and hardness of extruded snacks. Significant decreases in water absorption index and increases in water solubility index were observed with increases in extrusion temperature. The best conditions were determined by numerical optimization. The optimized value for non-cereal snacks for feed moisture is 18.22%, temperature 155.96 °C, screw speed 142.75 rpm and, desirability is 0.75. Verification of results showed decent agreement between the responses of experimental values at certain optimum conditions and the predicted values.

Effect of selected parameters on sectional expansion index and bulk density during the extrusion of chickpea instant semolina

A four-factor Response surface methodology central composite rotatable design was used to study the effect of moisture content, barrel temperature, screw speed, and feed screw speed on sectional expansion index and bulk density during extrusion of chickpea instant semolina for the purpose of instant product. The regression models for the investigated responses were highly significant (according to P-value) with satisfactory coefficients of determination (R2) 0.894 and 0.957. These results show that the predicted models for the investigated responses are adequate, indicating that the second-order polynomial model could be effectively used to represent the relationship between the selected parameters. The study showed that the expansion was influenced by moisture and temperature and it increased with increasing temperature for moisture content from 20 to 23% and after that decreased. Bulk density decreased with increasing feed moisture and barrel temperature in the extruder. The most important consequences for the science and practice resulting from the conducted research are that the resulting extrudates after grinding can be successfully used for the preparation of instant product with good characteristics, such as bulk density and sectional expansion index.

Textural and Sensory Characteristics of Milk Protein- Maize Flour-based Extrudates

Sensory and textural characteristics of milk protein-maize-based extrudates were studied as affected by extrusion conditions and milk-proteins Rennet Casein (RC), skimmed milk powder (SMP) and whey protein concentrate (WPC) to maize ratio. Appearance attributes of products decreased significantly (P<0.05) with SMP addition and higher feed moisture content, but improved with WPC-70 and RC. Colour of extrudates was mostly affected by the milk protein- maize ratios, especially with increase in SMP concentration that led to significantly (P<0.05) darker products scoring less than five due to the presence of higher amount of lactose. Feed moisture content decreased mean sensory score for crispness and increased hardness of the extrudates. Overall acceptability of extrudates decreased with the addition of SMP and increase in feed moisture content, except in WPC-70 at 8% level of protein. Extrudate with 8% RC and 12% feed moisture treated at 40 0 C inlet and 100 0 C outlet cooking zone temperature at screw speed of 340 rpm gave minimum maillard browning, desired textural characteristics, and colour. The correlation of sensory and textural properties showed that textural characteristics can be related with appearance which affected the product most.

Gluten-Free Rice Instant Pasta: Effect of Extrusion-Cooking Parameters on Selected Quality Attributes and Microstructure

In the present study, we applied extrusion-cooking to polished rice flour so as to prepare gluten-free pasta. The aim of the work was to investigate the effect of feed moisture (28, 30 and 32%) and screw speed (60, 80 and 100 rpm) on selected rice pasta quality attributes (water absorption, cooking loss, firmness, stickiness and microstructure) and extrusion response (specific mechanical energy). Our results showed that feed moisture significantly affected all tested quality attributes of the rice pasta, while screw speed exhibited a significant effect on all quality attributes except cooking time and stickiness. Moreover, raising the feed moisture increased the cooking time, water absorption, cooking loss, hardness and stickiness, but decreased the firmness at high screw speed. In addition, increasing the screw speed enhanced the cooking loss and hardness, but diminished the water absorption and firmness of pasta with low feed moisture. Rice pasta prepared with 30% moisture content and at 80 rpm showed adequate quality, as confirmed by a firm texture and low cooking loss and stickiness. Microstructure analysis showed a compact and dense internal structure of the dry pasta, and the surface was smooth and even when at least 30% moisture was applied at 80 rpm screw speed during processing.

Effects of soy flour types and extrusion-cooking conditions on physicochemical, microstructural and sensory characteristics of puffed rice snack base

The physicochemical properties of puffed rice snack base (PRSB) prepared via extrusion cooking under various feed moisture contents and screw speeds were investigated. The moisture content, screw speed, and soy flour type significantly (p < 0.05) affected the physicochemical properties of PRSB viz; size, density, porosity, color, breaking strength, crystallinity, water absorption index (WAI) and water solubility index (WSI). While, a slight effect on pasting properties was observed between PRSB added with defatted and full-fat soy flour, respectively. Soy flour lipids significantly (p < 0.05) influenced extrusion cooking conditions especially at high screw speed and feed moisture content. The result revealed that extrusion cooking with addition of full-fatty soy flour can be exploited as a viable method to produce PRS with a high expansion ratio and low breaking strength at recommended extrusion conditions of feed moisture content of 19 % and screw speed of 300 rpm.

Food Grains and Jaggery-based Expanded Food: Optimization of Process Variables, Protein Efficiency Ratio and Consumer Acceptability

Extrusion parameters for nutritious expanded food with jaggery were optimized following box-benken design using Response Surface Methodology. Jaggery and feed moisture affected physical properties, while nutritional and sensory properties of products were influenced by jaggery only. Optimized level of extrusion parameters consisted of 100 C die head temperature, screw speed of 304 rpm, 14 % moisture and 4 g jaggery per 100 g of formulation with 80 % maize, 14 % defatted soy-meal, and 6 % sesame-based formulation having overall desirability of 0.807. This expanded food showed expansion ratio of 3.57, 173.76 kg.m-3 bulk density, 15.18 % protein with 72.55 % invitro protein digestibility and 2.63 protein efficiency ratio, 1.97 % total minerals, 2.9 mg.100 g-1 iron, 158 mg.100 g-1 calcium with acceptability score of 8.2 that also indicated the consumer acceptability ≥7 by 95.37 % using 9-point hedonic scale.

Gluten-free healthy snack with high nutritional and nutraceutical value elaborated from a mixture of extruded underutilized grains (quality protein maize/tepary bean)

An optimized gluten-free healthy snack (OGFHS) was developed from a mixture of protein quality maize/tepary bean (70:30), applying extrusion-cooking. The extrusion conditions were obtained from the axial combination of process variables (feed moisture content [FMC = 15%-25%]/extrusion temperature [ET = 120 °C-170 °C]/screw speed [SS = 50 rpm-240 rpm]). The desirability function response surface methodology was applied as an optimization technique in three response variables (expansion index [EI]/apparent density [AD]/hardness [H]) to obtain maximum EI and minimum AD and H. The best combination to produce OGFHS was FMC = 16.4%/ET = 137 °C/VT = 237 rpm. The optimized conditions to obtain OGFHS caused little change in the nutritional and nutraceutical properties of the unprocessed grains mixture. OGFHS (50 g) was compared with two commercial snacks (CheetosMR, TotisMR), showing better protein content, total dietary fiber and AoxA, as well as high acceptability and lower energy content than commercial snacks. Due to its great nutritional properties and AoxA,OGFHS could be used for health promotion and as an alternative to commercial snacks with low nutritional value and high energy content.