Effects of Low Moisture Extrusion on the Structural and Physicochemical Properties of Adlay (Coix lacryma-jobi L.) Starch-Based Polymers

Research Progress on the Physicochemical Properties of Starch-Based Foods by Extrusion Processing

Extrusion is a crucial food processing technique that involves mixing, heating, shearing, molding, and other operations to modify the structures and properties of food components. As the primary energy source material, the extrusion process induces significant physical and chemical changes in starch that impact the quality of final products. This review paper discusses novel technologies for starch extrusion and their influence on the physical and chemical properties of starch-based foods, such as gelatinization and retrogradation properties, structural characteristics, and digestion properties. Additionally, it examines the application of extrusion in starch processing and the interactions between starch and other food components during extrusion. This information sheds light on the structural and property alterations that occur during the extrusion process to create high-quality starch-based foods.

Dietary fiber-rich Lentinula edodes stems influence the structure and in vitro digestibility of low-moisture extruded maize starches

Low-moisture extrusion (LME) can be used to improve the utilization of dietary fiber-rich Lentinula edodes stems (LES). The incorporation of dietary fiber can affect heat-induced interactions of starch molecules, which are critical for modifying starch characteristics via LME. In this work, a blend of LES and maize starch was extruded into a product at low moisture (30 %, w/v). The structure, physicochemical properties, and in vitro digestibility of extruded maize starches were investigated at different LES levels. The results showed that low levels (<7 %) of LES increased the crystallinity of LME-produced starch, while high levels (>7 %) did not. Because of the LES's soluble to insoluble dietary fiber ratios, the increased crystallinity of LES-added starch led to greater molecular ordering and the formation of an elastic gel after LME. At a suitable LES level (~3 %), highly crystallized starches were resistant to enzymolysis and had a high proportion of resistant starch. The obtained findings would contribute to a better understanding of how dietary fiber-rich LES affects starch extrusion and provide an alternative use for boosting the value of LES by-products.

Understanding the mechanism for sodium tripolyphosphate in improving the physicochemical properties of low-moisture extrusion textured protein from rapeseed protein and soybean protein blends

Our previous experiments found that rapeseed protein (RP) has applicability in low-moisture textured proteins. The amount of RP added is limited to <20 %, but the addition of 20 % RP still brings some negative effects. Therefore, in order to improve the quality of 20%RP textured protein, this experiment added different proportions of sodium tripolyphosphate (STPP) to improve the quality of the product, and studied the physical-chemical properties and molecular structure changes of the product to explore the possible modification mechanism. The STPP not only improved the expansion characteristics of extrudates, but also increased the brightness of the extrudates, the rehydration rate. In addition, STPP increased the specific mechanical energy during extrusion, decreased the material mass flow rate. Furthermore, STPP decreased the starch digestibility, increased the content of slow-digesting starch and resistant starch. STPP increased the degree of denaturation of extrudate proteins, the proportion of β-sheets in the secondary structure of proteins, as well as the intermolecular hydrogen bonding interactions. The gelatinization degradation degree of starch molecules also decreased with the addition of STPP. STPP also increased the protein-starch interactions and enhanced the thermal stability of the extrudate. All these indicate that STPP can improve the physical-chemical properties of extrudate.

Exploring the relationship between starch structure and physicochemical properties: The impact of extrusion on highland barley flour

Highland barley (HB) is an intriguing plateau cereal crop with high nutrition and health benefits. However, abundant dietary fiber and deficient gluten pose challenges to the processing and taste of whole HB products. Extrusion technology has been proved to be effective in overcoming these hurdles, but the association between the structure and physicochemical properties during extrusion remains inadequately unexplored. Therefore, this study aims to comprehensively understand the impact of extrusion conditions on the physicochemical properties of HB flour (HBF) and the multi-scale structure of starch. Results indicated that the nutritional value of HBF were significantly increased (soluble dietary fiber and β-glucan increased by 24.05%, 19.85% respectively) after extrusion. Typical underlying mechanisms based on starch structure were established. High temperature facilitated starch gelatinization, resulting in double helices unwinding, amylose leaching, and starch-lipid complexes forming. These alterations enhanced the water absorption capacity, cold thickening ability, and peak viscosity of HBF. More V-type complexes impeded amylose rearrangement, thus enhancing resistance to retrogradation and thermal stability. Extrusion at high temperature and moisture exhibited similarities to hydrothermal treatment, partly promoting amylose rearrangement and enhancing HBF peak viscosity. Conversely, under low temperature and high moisture, well-swelled starch granules were easily broken into shorter branch-chains by higher shear force, which enhanced the instant solubility and retrogradation resistance of HBF as well as reduced its pasting viscosity and the capacity to form gel networks. Importantly, starch degradation products during this condition were experimentally confirmed from various aspects. This study provided some reference for profiting from extrusion for further development of HB functional food and "clean label" food additives.

The properties of the rice resistant starch processing and its application in skimmed yogurt

Extrusion is typically employed to prepare resistant starch (RS). However, the process is complicated. In this study, the effects of twin-screw extrusion on the crystallinity, thermal properties, and functional properties of starch formed in different extrusion zones were investigated. The effects of this process on the rheological properties and microstructure of RS-added skimmed yogurt were also studied. According to the results, the RS content increased from 7.40 % in the raw material to 33.79 % in the extrudate. The A-type crystal structure of the starch was not observed. The dissociation temperature of the extruded starch ranged from 87.76 °C to 100.94 °C. The glycemic index (GI) of skimmed yogurt fortified with 0.4 % RS was 48.7, and the viscosity was also improved. The microstructure exhibited a uniform network of the starch-protein structure. The findings may serve as a theoretical basis for the application of RS in the food industry.

Extrusion as pretreatment for complexation of high-amylose starch with glycerin monostearin: Dependence on the guest molecule

Low-moisture extrusion (LME) can modify starch structures and enrich their functionality. These LME-made starches may efficiently form inclusion complexes (ICs) with hydrophobic guest molecules, which is profoundly impacted by the guest molecule concentration. In this work, the influence of glycerin monostearin (GMS) concentration on the structure and in vitro digestibility of pre-extruded starch-GMS complexes was investigated. The results showed that LME pretreatment increased the complex index of high-amylose starch with GMS by 13 %. The appropriate GMS concentrations produced ICs with high crystallinity and excellent thermostability. The presence of IC retarded amylose retrogradation and dominated bound water in starches. In addition, highly crystallized ICs were resistant to enzymolysis and had a higher proportion of resistant starch. The acquired knowledge would provide a better understanding of the LME-modified starch and GMS concentration-regulated IC formation.

Impact of moisture content on microstructural, thermal, and techno-functional characteristics of extruded whole-grain-based breakfast cereal enriched with Indian horse chestnut flour

The use of non-conventional seed flour is of interest in obtaining healthy breakfast cereals. The research aimed to study the physico-functional, bioactive, microstructure, and thermal characteristics of breakfast cereals using scanning electron microscopy, X-ray diffractometry, and differential scanning calorimeter. The increase in feed moisture content (16 %) enhanced the bulk density (5.24 g/mL), water absorption index (7.76 g/g), total phenolic content (9.03 mg GAE/g), and antioxidant activity (30.36 %) having desirable expansion rate (2.84 mm), water solubility index (48 %), and color attributes. The microstructure showed dense inner structures with closed air cells in extruded flours. Extrusion treatment rearranged the crystalline structure from A-type to V-type by disrupting the granular structure of starch, reducing its crystallinity, and promoting the formation of an amylose-lipid complex network. Increasing conditioning moisture enhanced the degree of gelatinization (%), peak gelatinization temperature (Tp), and starch crystallinity (%) and reduced the gelatinization enthalpy (ΔHG) and gelatinization temperature ranges. The results reported in this study will help industries to develop innovative and novel food products containing functional ingredients.

Mechanochemical Degradation of Biopolymers

Mechanochemical treatment of various organic molecules is an emerging technology of green processes in biofuel, fine chemicals, or food production. Many biopolymers are involved in isolating, derivating, or modifying molecules of natural origin. Mechanochemistry provides a powerful tool to achieve these goals, but the unintentional modification of biopolymers by mechanochemical manipulation is not always obvious or even detectable. Although modeling molecular changes caused by mechanical stresses in cavitation and grinding processes is feasible in small model compounds, simulation of extrusion processes primarily relies on phenomenological approaches that allow only tool- and material-specific conclusions. The development of analytical and computational techniques allows for the inline and real-time control of parameters in various mechanochemical processes. Using artificial intelligence to analyze process parameters and product characteristics can significantly improve production optimization. We aim to review the processes and consequences of possible chemical, physicochemical, and structural changes.

Extrusion assisted interaction of rice starch with rice protein and fibre: Effect on physicochemical, thermal and in-vitro digestibility characteristics

Rice starch has high digestibility due to its large carbohydrate content. Macromolecular enrichment of starch has the tendency to retard rate of starch hydrolysis. Hence, the current investigation was aimed to check the combined effect of extrusion assisted addition of rice protein (0, 10, 15 and 20 %) and fibre (0, 4, 8 and 12 %) to rice starch on physico-chemical and in-vitro digestibility characteristics of starch extrudates. It was observed from the study that 'a' and 'b' values, pasting temperature and resistant starch of starch blends and extrudates increased with the addition of protein and fibre. However, lightness value, swelling index, pasting properties and relative crystallinity of blends and extrudates decreased with the addition of protein and fibre. Maximum increase in thermal transition temperatures was observed for ESP₃F₃ extrudates due to absorption capacity of protein molecules which led to late onset of gelatinization. Therefore, enrichment of protein and fibre to rice starch during extrusion can be considered as a novel approach to reduce rate of rice starch digestion for catering nutritional requirements of diabetic population.

A review of extrusion-modified underutilized cereal flour: chemical composition, functionality, and its modulation on starchy food quality

Compared with three major cereals, underutilized cereals (UCs) are those with less use but having abundant bioactive components and better functionalities after proper processing. As a productive and energy-efficient technology, extrusion has been used for UC modification to improve its technological and nutritional quality. Extrusion could induce structural and quantitative changes in chemical components of UC flour, the degree of which is affected by extrusion intensity. Based on the predominant component (starch), functionalities of extruded underutilized cereal flour (EUCF) and potential mechanisms are reviewed. Considering bioactive compounds, it also summarizes the physiological functions of EUCF. EUCF incorporation could modulate the dough rheological behavior and starchy foods quality. Controlling extrusion intensity or incorporation level of EUCF is vital to achieve sensory-appealing and nutritious products. This paper gives comprehensive information of EUCF to promote its utilization in novel staple foods.

The effects of extruded endogenous starch on the processing properties of gluten-free Tartary buckwheat noodles

The lack of gluten in Tartary buckwheat has always been the main limiting factor of their development. This paper explored how to improve the processing quality of gluten-free Tartary buckwheat noodles (GF-TBNs) by introducing extruded starch into Tartary buckwheat flour (TBF) and the underlying mechanism was also elucidated. Extruded Tartary buckwheat starch (ETBS) was obtained under different extrusion conditions. The thermal properties, molecular weight, and viscosity of ETBS were examined to determine the key parameters closely related to the water distribution and rheological properties of the dough sheet, and tensile properties of GF-TBNs. The results showed that ETBS with a low molecular weight and high viscosity contributed greatly to the GF-TBNs with good tensile properties. It is proposed that ETBS with a low molecular weight and high viscosity might form a gel-entrapped network inside GF-TBNs, which was confirmed by the morphology of GF-TBNs.

Effects of different moisture contents on the structure and properties of corn starch during extrusion

Herein, corn starch samples with different moisture contents (native corn starch, 30, 35, 40, 45, and 50%) were prepared by twin-screw extrusion, and the structural and physical properties were analyzed and correlated. Scanning electron microscopy observed the morphology, attenuated total reflection-Fourier transform infrared spectroscopy investigated the double helix structure, X-ray diffraction analyzed the crystal region, ion chromatography observed the chain length distribution, and rapid viscosity analyzer measured the viscosity of corn starch samples. We found that the corn starch crystallinity, degree of order, and double helix degree decreased with increasing moisture content. The moisture content has a crucial role in the peak viscosity, breakdown, final viscosity, and setback in pasting property experiments. With the increase in moisture content, the longer chain was transformed into a shorter chain, and the dispersion of molecular weight distribution continuously increased. This study provides a theoretical basis for the production of extruded corn starch.