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Third-generation (3G) rice pellets were obtained using rice flour (RF) and rice grits (RG), raw materials of similar compositions but different particle sizes. The samples were mixed with water to 25% moisture and extruded using a laboratory single-screw extruder (Kompakt KE 19/25 extruder) and three compression ratios (1:1, 2:1, and 3:1). The pellets were expanded using a microwave oven subjected to 1000 W/g power. After evaluating the expansion kinetics and the sectional expansion index (SEI), it was observed that the 3:1 compression ratio allowed for greater expansion, while the particle difference showed no significant difference (p > 0.05) in the SEI. [ABSTRACT FROM AUTHOR]

A Brabender Kompakt extruder KE 19/25 was used to create third-generation corn pellets using a high moisture content (25, 30, and 35%) and moderate temperature. The pellets were subjected to microwave expansion, and the drying curves were fitted to Page, Logarithmic, and Midilli–Kucuk mathematical models. The Page model best fits the experimental data, closely followed by the Midilli–Kucuk model. The variables evaluated were appearance, sectional expansion index (SEI), and volumetric expansion index (VEI), and they showed a strong dependency on moisture content. According to the results, the recommended expansion times for mixtures with a 25, 30, and 35% moisture content are 50, 60, and 60–75 s, respectively.

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.

Extruded snacks are products which are easy to consume, tasty, crispy, with thousands of shapes, flavours, textures and are consumed worldwide. They can be expanded directly or indirectly. Directly expanded products are cooked, expanded, shaped and cut off the extruder, dried and packaged. It is a less complicated process than the indirect expansion, products have low bulk density, and are seasoned with different types of flavours and oils. Indirectly expanded products are stable during storage and have high bulk density, provide opportunity to produce a wide range of products. Different types of raw materials (corn, potato, wheat, oat, by-products of food industry, etc.) and combination of ingredients can be incorporated into the products. Non-starch ingredients such as protein, fibre, vitamins and minerals are more likely to be incorporated into indirectly expanded products than into directly expanded products. This makes them delicious, healthier and more interesting to customers. The most commonly used ways of expansion are deep fat frying, hot-air puffing and microwave heating. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]