Effect of extrusion temperature and screw speed on properties of oat and rice flour extrudates

Effect of extrusion cooking on the chemical and nutritional properties of instant flours: a review

Satisfying the nutritional requirements of consumers has made food industries focus on the development of safe, innocuous, easy-to-prepare products with high nutritional quality through efficient processing technologies. Extrusion cooking has emerged as a prominent technology associated with the nutritional and functional attributes of food products. This review aims to establish a theoretical framework concerning the influence of extrusion parameters on the functional and nutritional properties of precooked or instant flours, both as end-products and ingredients. It highlights the pivotal role of process parameters within the extruder, including temperature, screw speed, and raw materials moisture content, among others, and elucidates their correlation with the modifications observed in the structural composition of these materials. Such modifications subsequently induce notable changes in the ultimate characteristics of the food product. Detailed insights into these transformations are provided within the subsequent sections, emphasizing their associations with critical phenomena such as nutrient availability, starch gelatinization, protein denaturation, enhanced in vitro digestibility, reduction in the content of antinutritional factors (ANFs), and the occurrence of Maillard reactions during specific processing stages. Drawing upon insights from available literature, it is concluded that these effects represent key attributes intertwined with the nutritional properties of the end-product during the production of instant flours.

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.

The effect of Vaccinium bracteatum Thunb. leaves addition on antioxidant capacity, physicochemical properties, and in vitro digestibility of rice extrudates

Vaccinium bracteatum Thunb.leaves (VBTL) are a traditional Chinese herbal medicine with potential natural pigments and antioxidants. Its application information on extrusion is limited. In this study, to increase the usage of foods containing VBTL, rice-based extrudates with VBTL were investigated. The extrusion was performed at a wide temperature range (60-140°C) and with different VBTL supplementations (3%-10%). The extrudates with 10% VBTL showed a significant decrease in total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activity upon extrusion. TPC and TFC increased with the rise of barrel temperature. The VBTL color was stable during the wide-temperature extrusion process. The bioactivities of the extrudates were positively correlated with the VBTLsupplement (R = 0.943-0.989). In addition, different addition levels of VBTL significantly changed the water absorption index (WAI), water solubility index (WSI), pasting properties, and in vitro starch digestibility of the extrudates. Moreover, extrudates with 3% VBTL showed the highest WAI and peak viscosity but the lowest in vitro starch digestibility. These results may suggest that rice extrudates with a low supplement of VBTL have an acceptable color and may be used as functional additives for high antioxidant and low glycemic response diets. PRACTICAL APPLICATION: The results showed that the Vaccinium bracteatum Thunb. leaves (VBTL) color and antioxidation were stable during the wide-temperature extrusion process. Extrusion processing can be used to enlarge the usage of VBTL and simplify its traditional processing method. Applying VBTL to the process of extrusion appears to be a suitable method of producing value-added and low glycemic response extrudates.

Considerations for improvising fortified extruded rice products

Micronutrient fortification of rice by extrusion is an effective strategy to enhance micronutrient levels within rice-consuming individuals. The success of extrusion-based fortification is associated with micronutrient retention, enhanced bioavailability, low postprocessing losses, prolonged storage stability, and minimal sensory changes. The success of an optimally fortified product is primarily reliant upon the compositional considerations, but many attributes of extrudates can be indebted to the processing parameters too. Hence, an exhaustive investigation of this technology has been taken-up here, emphasizing on the compositional parameters in association with process parameters, which influence the final quality attributes like nutrient stability, bioavailability, and sensory properties. Based on these attributes of the end product, a collected data have been presented here to bring out the optimal compositional requirements. These together with cooking processes, extrusion process parameters, and storage conditions will enable formulate a product with enhanced sensory acceptance, better retention during cooking and storage, improved texture, and acceptable color. This review will thus help to optimize a need-based product, its quality, and enhance benefits of fortified extruded rice products.

Development of novel functional snacks containing nano-encapsulated resveratrol with anti-diabetic, anti-obesity and antioxidant properties

In this study, functional snacks with addition of nanoenapsuated resveratrol were prepared to evaluate the nutraceutical and physical properties. The nanoencapsulated resveratrol was prepared from horse-chestnut (HRP), water-chestnut (WRP) and lotus-stem starch particles (LRP) and added to the wheat flour at the level of 0.4% for preparation of snacks by extrusing process. After extrusion, 43-53% and 5.42% of resveratrol was retained in snacks containing encapsulated and free resveratrol (FRP), respectively. The HRP, WRP and LRP showed significantly less peak viscosities and less elastic behaviour than native product (NP) which can influence the human sensory perception. The shift of few peaks towards higher wavelength and presence of additional peaks at 1384, 1229, 1513 and 1613 cm^-1 depicts change in molecular pattern and presence of resveratrol in functional snacks. The functional snacks containing encapsulated resveratrol showed significantly higher antioxidant, anti-diabetic and anti-obesity properties than snacks containing no or free resveratrol.

Use of Legumes in Extrusion Cooking: A Review

The traditional perception that legumes would not be suitable for extrusion cooking is now completely outdated. In recent years, an increasing number of studies have been conducted to assess the behavior of various types of legume flours in extrusion cooking, proving that legumes have excellent potential for the production of extruded ready-to-eat foods by partially or totally replacing cereals. This review identifies the optimal processing conditions for legume-based and legume-added extruded foods, which allow the improvement of the expansion ratio and give the extrudates the spongy and crisp structure expected by consumers. In particular, the effect of the individual processing parameters on the physical-chemical and nutritional properties of the final product is highlighted. The extrusion cooking process, indeed, has a positive effect on nutritional characteristics, because it induces important modifications on starch and proteins, enhancing their digestibility, and reduces the content of trypsin inhibitors, lectins, phytic acid, and tannins, typically present in legumes. Therefore, the extrusion of legume flours is a viable strategy to improve their nutritional features while reducing home preparation time, so as to increase the consumption of these sustainable crops.

Investigation on mild extrusion cooking for development of snacks using rice and chickpea flour blends

A study was conducted to optimize the mild extrusion cooking conditions for development of rice and chickpea based extrudates. The independent variables i.e. extrusion parameters (Screw speed, barrel temperature), feed moisture and proportions of rice flour and chickpea flour were varied using central composite rotatable design (CCRD), and their effects on system parameter- Specific mechanical energy (SME) and product characteristics i.e., water absorption index (WAI), water solubility index (WSI), bulk density (BD), expansion ratio (ER), breaking strength (BS), colour values (L*, a* and b*) and overall acceptability (OA) were studied. All the system and product responses were significantly affected by independent variables. Response surface and regression models were established to determine the responses as function of process variables. Models obtained were highly significant with high coefficient of determination (R² ≥ 0.889). The optimum mild extrusion conditions obtained by numerical optimization for development of snacks were 102 °C barrel temperature, 281 rpm screw speed, 18.3% feed moisture and rice to chickpea flour ratio as 90:10. Storage studies confirmed that the developed snacks can be stored better in laminated pouches than in high density polyethylene (HDPE) bags for a period of 6 months under ambient conditions.

Application of extrusion technology in plant food processing byproducts: An overview

The food processing industry generates an immense amount of waste, which leads to major concerns for its environmental impact. However, most of these wastes, such as plant-derived byproducts, are still nutritionally adequate for use in food manufacturing. Extrusion is one of the most versatile and commercially successful processing technologies, with its widespread applications in the production of pasta, snacks, crackers, and meat analogues. It allows a high degree of user control over the processing parameters that significantly alters the quality of final products. This review features the past research on manufacture of extruded foods with integration of various plant food processing byproducts. The impact of extrusion parameters and adding various byproducts on the nutritional, physicochemical, sensory, and microbiological properties of food products are comprehensively discussed. This paper also provides fundamental knowledge and practical techniques for food manufacturers and researchers on the extrusion processing of plant food byproducts, which may increase economical return to the industry and reduce the environmental impact.