In order to improve the edible quality of hybrid indica rice (Type 9718) in China, extrusion technology might be considered to create the so‐called “reformed rice.” Effects of extrusion parameters such as feed water content, barrel temperature and extruder screw speed on physicochemical properties of rice extrudates were investigated. Water‐soluble carbohydrates and enzyme sensitivity (α‐amylase) of extrudates were basically higher than those of parboiled rice. Water absorption index of all extrudates was lower than that of parboiled rice (4.95 g/g), which indicated that extrusion cooking was not only a heating procedure but also a process with shear force, degradation of rice starch. Through statistical analysis, it was found that both barrel temperature and feed water content could positively be correlated with physicochemical properties of extrudates excluding bulk density. Texture studies indicated that hardness of all hybrid indica rice (Type 9718) extrudates was lower than that of cooked raw rice and parboiled rice. The scanning electron microscope images demonstrated that there was indeed a granular gel network formed within the rice extrudates. PRACTICAL APPLICATIONS Extrusion cooking technology is used for cereal and protein processing in the food. In the present study, this technology was employed to investigate the effects of feed water content, barrel temperature and extruder screw speed on the physicochemical properties of hybrid indica rice (Type 9718) extrudates. It was found that extrusion cooking was not only a heating procedure but also a process with shear force and pressure, destruction and degradation of rice starch, the most important constituent which could affect physicochemical properties in rice extrudates. Textural studies had shown that under proper extrusion parameters, the texture of hybrid indica rice (Type 9718) extrudates was in fact much better than that of cooked raw rice and parboiled rice.

Soy protein, one of the most commonly used raw materials for texturised vegetable protein, has an important influence on texturised soy protein (TSP) with its 7S and 11S fractions. In this study, soy 7S and 11S proteins were extracted from soybean isolate and added back to the raw material to prepare TSP and analyse the effect of both on the physical properties of TSP. The results showed that the addition of 5% soy 7s or 11s protein increased the water-holding capacity (up to 9.04%) and rehydration rate (up to 25.71%) of TSP. Compared with adding soy 11s protein, adding soy 7s protein has a faster rehydration rate at a lower temperature (30 and 45 °C). After extrusion, the content of free sulphhydryl groups, total sulphhydryl groups, and disulphide bonds was significantly reduced (P < 0.05). The extrusion treatment caused degradation of the protein chains, and the proteins mainly formed insoluble polymers. Electrophoretic analysis revealed that the sodium dodecyl-sulphate (SDS) reducing the extractable rate of the precipitate after SDS non-reduction extraction of the TSP added with 5% soy 7S and 11S proteins were lower than that of the control. The proportion of different soybean protein components in TSP could change its texture, water-holding, and rehydration characteristics of it, which provides a new method for the characteristics design of TSP.

To investigate which protein properties affect the quality of high moisture textured vegetable protein (HTVP), we compared 12 commercial Soy Protein Concentrate (SPC). The comparison revealed that characteristics of different SPCs vary greatly, significant impact on the quality of extrusion products. There were significant differences in the degree of texturization, textural properties, and the sensory score of products. Statistical correlation analysis between SPC raw materials and products showed that the quality of products was significantly affected by the nitrogen solubility index (NSI), water holding capacity (WHC), emulsifying properties (EAI), foaming capacity (FC), gel strength, and sulfhydryl content of SPC raw materials. Our research provides a way to stabilize extrusion product quality.

No abstract

The effects of cysteine addition (0%, 0.05%, 0.10%, 0.15%, 0.20%, 0.25%) on the physicochemical properties of plant-based extrudates by high-moisture extrusion were investigated. The texturization degree, rheological properties, hardness, springiness and chewiness of the extrudates significantly improved with the addition of cysteine (<0.15%). Analysis of the microstructure showed that the addition of cysteine (<0.15%) improved the formation of the fiber structure in the extrudates. Cysteine (<0.15%) promoted the formation of new disulfide bonds and non-covalent bonds by changing the disulfide bonds of protein molecules and enhanced the cross-linking degree between proteins. However, the excessive addition of cysteine (>0.15%) had a negative impact on the formation of fiber structure. Analysis of secondary structure suggested that the ordered β-sheet structures gradually converted to the disordered β-turn and random coil structures with the addition of cysteine (>0.15%). In addition, analysis of odor properties with the addition of cysteine using an electronic nose showed the difference in volatile components of the extrudates mainly existed in halides, hydrocarbons, sulfides and amines. On the whole, the addition of cysteine could improve the quality of plant-based extrudates.