Digestibility Properties Research Articles

Incorporation of germinated lupin into corn-based extrudates: Focus on starch digestibility, matrix structure and physicochemical properties

The research aimed to assess the effects of incorporating germinated Lupinus angustifolius flour into corn extrudates for different periods (3, 5, and 7 days), focusing on starch digestibility, morphological structure, thermal, and pasting properties. Extrudate with germinated lupinus flour for 7 days (EG7) significantly increased the content of slowly digestible starch up to 10.56% (p < 0.05). Crystallinity increased up to 20% in extrudates with germinated flour compared to extrudates with ungerminated flour (EUG), observing changes at the molecular level by FTIR that impact the thermal and pasting properties. X-ray diffraction revealed angles of 2θ = 11.31, 16.60, 19.91, and 33.04 as a result of the germination and extrusion processes. Microstructural analysis indicated starch-protein interactions influencing changes in calorimetry, viscosity, X-ray diffraction, and digestibility. PCA allowed establishing that the addition of germinated flours significantly affected the properties and microstructural characteristics of extruded products, potentially affecting digestibility and nutritional quality.

Rheological properties of the swim bladder colloid from Atlantic cod (Gadus Morhua) and its digestive characteristics

The swim bladder colloid (SWG) was prepared by the swim bladder (SW) from Atlantic cod (Gadus Morhua), and its physicochemical, rheological and digestive properties were evaluated. It showed SW mainly consisted of collagens and chondroitin sulfate. The optimal condition of SWG was treated with acetic acid for 4.0 h, operated with high temperature and pressure time for 30 min and homogenized twice at 100 MPa pressure. The viscosity of SWG, containing the mixed system of proteins and polysaccharides, decreased with the increasing of shear rate, exhibiting shear thinning behavior, which conformed to pseudoplastic fluid. It demonstrated larger values for G″ than that for G′ at the frequency of 20 Hz at 25 °C, which reached 30.8 Pa and 5.15 Pa at 60% concentration, respectively. Moreover, when the concentrations increased from 20% to 80%, the gelation temperatures and the melting temperatures increased from 6.79 ± 0.01 °C and 12.61 ± 0.06 °C to 13.73 ± 0.06 °C and 18.31 ± 0.05 °C, respectively. All of G''/G′ were much less than 0.1, confirming the presence of solid-like elastic behavior at 4.0 °C. When the temperature increased from 40 °C to 85 °C, the viscosity at 20% concentration of SWG decreased from 34.50 mPa s to 8.07 mPa s at the shear rate of 100 s−1. Furthermore, it exhibited that SWG was digested and degraded after simulated digestion in vitro, and bioactive peptides were produced.

Amylopectin content rather than amylose or protein content is critical to determining the starch digestion rate in high-amylose rice

The starch digestion properties of cooked rice are associated with the chemical compositions of the rice grain. However, limited information is available on the chemical composition governing starch digestion properties in high-amylose rice. To overcome this knowledge gap, correlation plot analysis and partial correlation analysis were utilized to assess the correlations between active digestion duration, total glucose production, and glucose production rate of cooked rice to amylose, amylopectin, and protein content of rice grains throughout 17 high-amylose varieties. The correlation plot analysis identified significant positive or negative linkages between total glucose production and the glucose production rate of cooked rice with grain amylose, amylopectin, and protein content. Nevertheless, partial correlation analysis only characterized a significant positive correlation between glucose production rate and grain amylopectin content. The findings of this study indicate that grain amylopectin content rather than grain amylose or protein content is critical for the determination of the rate of starch digestion in high-amylose rice.

Improving resistant starch content of cassava starch by pulsed electric field-assisted esterification

This study aims to investigate the effect of pulsed electric field (PEF) assisted OSA esterification treatment on the multi-scale structure and digestive properties of cassava starch and structure-digestion relationships. The degree of substitution (DS) of starch dually modified at 1.5–4.5 kV/cm was 37.6–55.3 % higher than that of starch modified by the conventional method. Compared with native starch, the resistant starch (RS) content of esterified starch treated with 3 kV/cm significantly increased by 17.13 %, whereas that of starch produced by the conventional method increased by only 5.91 %. Furthermore, assisted esterification at low electric fields (1.5–3 kV/cm) promotes ester carbonyl grafting on the surface of starch granules, increases steric hindrance and promotes the rearrangement of the amorphous regions of starch, which increases the density of the double-helical structure. These structural changes slow down starch digestion and increase the RS content. Therefore, this study presents a potential method for increasing the RS content of starch products using PEF to achieve the desired digestibility.

Structural, physicochemical, and digestive properties of enzymatic debranched rice starch modified by phenolic compounds with varying structures

The physicochemical properties of starch and phenolic acid (PA) complexes largely depend on the effect of non-covalent interactions on the microstructure of starch. However, whether there are differences and commonalities in the interactions between various types of PAs and starch remains unclear. The physicochemical properties and digestive characteristics of the complexes were investigated by pre-gelatinization of 16 structurally different PAs and pullulanase-modified rice starches screened. FT-IR and XRD results revealed that PA complexed with debranched rice starch (DRS) through hydrogen bonding and hydrophobic interaction. Benzoic/phenylacetic acid with polyhydroxy groups could enter the helical cavities of the starch chains to promote the formation of V-shaped crystals, and cinnamic acid with p-hydroxyl structure acted between starch chains in a bridging manner, both of which increased the relative crystallinity of DRS, with DRS-ellagic acid increasing to 20.03 %. The digestion and hydrolysis results indicated that the acidification and methoxylation of PA synergistically decreased the enzyme activity leading to a decrease in the digestibility of the complexes, and the resistant starch content of the DRS-vanillic acid complexes increased from 28.27 % to 71.67 %. Therefore, the selection of structurally appropriate PAs can be used for the targeted preparation of starch-based foods and materials.

Glycogen and zinc-enriched ferritin as bioavailable nanoparticulate nutrients released from gastrointestinal digestion of pacific oyster (Crassostrea gigas)

Oyster is a low-carbon animal food enriched with protein, glycogen, and trace minerals. Nano-nutrients are increasingly perceived as an unignorable part of foods. Here, simulated gastrointestinal digestion released a considerable amount of nanoparticulate nutrients from raw and cooked oysters. They were identified as glycogen monomers with size of 20–40 nm and their aggregates, as well as 6 nm-sized bare cores of ferritin containing iron and zinc (4:1, w/w). FITC-labeling and flow cytometry unveiled the efficient uptake of oyster glycogen by polarized Caco-2 cells via macropinocytosis and receptor-mediated endocytosis. Calcein-fluorescence-quenching assay revealed divalent-metal-transporter-1- and macropinocytosis-mediated enterocyte iron absorption from oyster ferritin. Zinquin-fluorescence flow cytometry and ex-vivo mouse ileal loop experiments demonstrated the ready intestinal zinc absorption from oyster ferritin via macropinocytosis, as well as the good resistance of oyster ferritin to phytate's inhibition on zinc absorption. Overall, our results offer a new insight into the digestive and chemical properties of oysters.

Influence of gelatinized octenyl succinic anhydride-modified waxy adlay seed starch on the properties of astaxanthin-loaded emulsions: Emulsion properties, stability and in vitro digestion properties

Octenyl succinic anhydride (OSA)-modified starch is a commonly used food emulsifier and its emulsifying properties are positively correlated with the degree of substitution (DS). However, the maximum concentration of OSA in starch approved by the FDA and the China National Food Safety Standards is 3%. This study aims to enhance the emulsifying properties of OSA-modified waxy adlay seed starch by gelatinization under a limited DS and investigate its use in preparing delivery systems. The gelatinized OSA starch exhibited a more flexible macromolecular structure and better emulsifying activity (20.19 m2/g). The gelatinized OSA starch-stabilized astaxanthin-loaded emulsions showed high retention of astaxanthin (>50%) and long-term stability (56 days). In vitro digestion, the emulsion system showed a protective effect on astaxanthin, and the bioaccessibility of astaxanthin was increased to 16.32%. This study indicated that gelatinization could enhance the emulsifying properties of OSA starch, and this starch-stabilized emulsion was an effective system for astaxanthin.

Effects of black bean cell wall pectin by exogenous calcium ions: Insight into the metabolomics, physicochemical properties and anti-digestive capacity

In this work, the metabolomics, physicochemical and in vitro digestion properties of black beans influenced by different calcium ion solutions (0, 0.5 %, 1 %, and 2 %) were explored. The addition of calcium ions had a significant effect on the metabolic processing of black beans, including 16 differential metabolites and 4 metabolic pathways related to the cell wall. From the results of FT-IR and ICP-OES, it was confirmed that calcium ions can interact with COO− in non-methylated galacturonic acid in pectin to form calcium carboxylate strengthening the middle lamellae of the cell wall. Based on this mechanism, the soaked beans with an intact and dense cell structure were verified by the analyses of SEM and CLSM. Compared with other soaked beans, BB-2 exhibited lower cell permeability with electrical conductivity value decreased to 0.60 μs·cm−1. Additionally, BB-2 demonstrated slower digestion properties with digestion rate coefficient at 0.0020 min−1 and digestion extent only at 30.83 %, which is attributed to its increasingly compact cell wall and densely cellular matrix. This study illustrates the effect of calcium ions on the cellular structure of black beans, providing an effective process method for low glycemic index diets.

Effect of Fe(III) on soybean protein-gallic acid hydrogel: Structure, functional properties, and digestive properties

A soy protein isolate-gallic acid (SPI-GA) complex was synthesized, mediated using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide. Different amounts of Fe3+ were then added to the SPI-GA complex to produce hydrogels (SPA@Fe) containing metal-phenolic network without heating the protein. Spectral analysis revealed that these hydrogels contained multiple modes of cross-linking, such as Schiff bases, hydrogen bonds, and coordination bonds. Coordination bonds formed between GA and Fe3+ mainly had a coordination number of three, and they changed the structure of the protein. Furthermore, these coordination bonds also endowed SPA@Fe with a more compact crosslinked network, thus improving the hydrogel's textural characteristics, thermal stability, storage modulus, and glucose adsorption capacity. The SPA@Fe hydrogel exhibited the best performance when the molar ratio of GA to Fe3+ was 1, with the thermal stability, hardness, springiness, and glucose adsorption capacity being 3.9, 1.84, 1.22, and 1.93 times higher than those of the SPI-GA hydrogel, respectively. Moreover, in-vitro digestion tests showed that SPA@Fe could control the release of loaded curcumin, had good capacity for adsorbing bile salt, and showed delayed degradation. This hydrogel system may offer a safe and feasible way to deliver bioactive substances such as curcumin.

Amylose molecular weight affects the complexing state and digestibility of the resulting starch–lipid complexes

Previous RS5 (type 5 resistant starch) research has significantly broadened starch use and benefited society, yet the effects of the molecular weight of amylose on RS5 remain underexplored. In this study, amyloses with different molecular weights were complexed with caproic acid (C6), lauric acid (C12), and stearic acid (C18) to observe the effects of the molecular weight of amylose on the structure and in vitro digestive properties of RS5. Gel permeation chromatography revealed that the peak average molecular weight (Mp) values of high-amylose cornstarch NF-CGK (CGK), high-amylose cornstarch obtained via cornstarch via autoclave (high temperature and high pressure)-cooling combined pullulanase enzymatic hydrolysis (CTE), and high-amylose cornstarch NF-G370 (HCK) were 21,282, 171,537, and 188,084 before fatty acid complexation, respectively. Additionally, their weight average molecular weight (Mw) values of 32,429, 327,344, and 410,610 and hydrolysis rates of 58.12 %, 86.77 %, and 64.58 %, respectively. The hydrolysis rate of low-Mw amylose (GCK) complexes with fatty acids was lower than that of HCK and CTE starch–lipid complexes. However, HCK and CTE having similar molecular weights, there was no significant difference in the hydrolysis rate of starch–lipid complexes. X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and complexing index analyses confirmed the formation of these complexes. This study proposed the mechanism of RS5 formation and provided guidance for its future development.

Comparative Genomics and the Salivary Transcriptome of the Redbanded Stink Bug Shed Light on Its High Damage Potential to Soybean.

The redbanded stink bug, Piezodorus guildinii (Westwood) (Hemiptera: Pentatomidae), is a significant soybean pest in the Americas, which inflicts more physical damage on soybean than other native stink bugs. Studies suggest that its heightened impact is attributed to the aggressive digestive properties of its saliva. Despite its agricultural importance, the factors driving its greater ability to degrade plant tissues have remained unexplored in a genomic evolutionary context. In this study, we hypothesized that lineage-specific gene family expansions have increased the copy number of digestive genes expressed in the salivary glands. To investigate this, we annotated a previously published genome assembly of the redbanded stink bug, performed a comparative genomic analysis on 11 hemipteran species, and reconstructed patterns of gene duplication, gain, and loss in the redbanded stink bug. We also performed RNA-seq on the redbanded stink bug's salivary tissues, along with the rest of the body without salivary glands. We identified hundreds of differentially expressed salivary genes, including a subset lost in other stink bug lineages, but retained and expressed in the redbanded stink bug's salivary glands. These genes were significantly enriched with protein families involved in proteolysis, potentially explaining the redbanded stink bug's heightened damage to soybeans. Contrary to our hypothesis, we found no support for an enrichment of duplicated digestive genes that are also differentially expressed in the salivary glands of the redbanded stink bug. Nonetheless, these results provide insight into the evolution of this important crop pest, establishing a link between its genomic history and its agriculturally important physiology.

A new dietary low-fat custard formulation made by waxy corn starch and xylitol: Rheological, sensory and in vitro digestibility investigation

Custard is a dairy starch-based dessert, in which presence of milk increases its nutritional value and sensitivity to freezing, pH, and storage. Producing a custard with less phase separation during storage and improving its functionality is challenging. The present study has investigated the effect of starch type (native corn starch and waxy corn starch), fat content (2.67% & 0.1%) and sucrose-xylitol ratio (1:0, 1:1, 0:1) on rheological, textural, enzyme digestibility and sensory properties of custard desserts. The back extrusion test showed a significant increase in consistency (40.60 mJ) by using xylitol and decreasing fat content compared to the control sample (2.16 mJ). Also, applying waxy corn starch diminished hardness (1.66 N) compared to the control (13.55 N), which was accompanied by a decrease of syneresis after five days of storage from 10.29% to 0.02% and improvement of sensory properties of creaminess, smoothness and taste intensity. Accordingly, low-fat custard formulation containing waxy corn starch and xylitol indicated high creaming stability (98.08%), adhesiveness (9.45 mJ), viscosity at a constant shear rate of 50 s−1 (3.58 Pa s), and water holding capacity after five days of storage at 4 °C (99.99%) and thickness (9.53). Also, xylitol reduced custards’ glucose release after amylase objection.

Evaluación de las propiedades proximales, estructurales, morfológicas fisicoquímicas y de digestibilidad in vitro en mezclas de harinas de ñame y batata

Yam (Dioscorea spp.) and sweet potato (Ipomeas batata) flours must be treated through modification processes because they have limitations in their physicochemical and structural properties for use in agri-food matrices. This study aimed to evaluate the effect of different proportions of flours on the proximate, structural, morphological, physicochemical, pasting, and in vitro digestibility properties of yam and sweet potato flour blends. Flours were obtained by drying the tubers with hot air at 55 °C, and mixtures were prepared at 25:75, 50:50, and 75:25 w/w sweet potato and yam flour proportions, respectively. The yam starch granules were spherical, oval, irregular, and larger than those of sweet potatoes, which are ovoid and flared. Furthermore, yam and sweet potato granules presented with type-B and type-A diffraction patterns, respectively, which, together with the starch content, amylose, non-starch components, and their molecular interactions, influenced the decrease in the molecular order and degree of crystallinity of the flour blends, without altering the morphological characteristics of the simple flours. Additive and non-additive effects were observed on flour blends’ swelling power and water absorption capacity. Likewise, breakdown and setback viscosity increased, which decreased thermal stability, increased the tendency to retrogradation, and elevated the fractions of rapidly digestible starch and resistant starch. These results suggest the high potential of flour blends in preparing baked products from the Caribbean Region, such as white bread, cookies, and cakes.

Enhancing rheology and reducing lipid digestion of oil-in-water emulsions using controlled aggregation and heteroaggregation of soybean protein isolate-peach gum microspheres

There is a growing interest in developing highly viscous lipid foods using plant protein and polysaccharide gum-based emulsion technology. However, gaps remain in understanding the rheological, microstructural, and digestive properties of plant proteins like soybean protein isolate (SPI) in combination with various gums. This study investigates how combining SPI and peach gum (PG) affects rheology and lipolysis of oil-in-water (O/W) emulsions containing 20 wt% soybean oil. Emulsions with varying SPI and PG compositions including SPI-PG single and SPI/PG mixed droplet systems were prepared. Heating induced alterations in viscosity (e.g., SPI-PG from 14.88 to 90.27 Pa·s and SPI/PG from 9.66 to 85.32 Pa·s) and microstructure revealing aggregate formation at oil-water interface. The viscosity decreased significantly from the oral to intestinal phase (SPI-PG: 28.10 to 0.19 Pa·s, SPI/PG: 21.27 to 0.10 Pa·s). These changes affected lipid digestion, notably in SPI-PG and SPI/PG emulsions where a compact interface hindered lipolysis during digestion. Interestingly, free fatty acid (FFA) release during small intestinal phase followed a different order: SPI (82.51 %) > SPI-PG (70.77 %) > SPI/PG (63.60 %) > PG (56.09 %). This study provides insights into creating highly viscous O/W spreads with improved rheology, stability, and delayed lipid digestion, offering potential benefits in food product formulation.

Ultrasonic-Assisted Extraction and Gastrointestinal Digestion Characteristics of Polysaccharides Extracted from Mallotus oblongfolius

The polysaccharides were extracted from the leaves of Mallotus oblongifolius (MO) using an ultrasonic-assisted extraction method in this study. The main variables affecting the yield of polysaccharides extracted from Mallotus appallatus (MOPS) were identified and optimized while concurrently investigating its antioxidant capacity, hypoglycemic activity, and digestive properties. The results indicated that the optimal ultrasound-assisted extraction of MOPS involved an ultrasound power of 200 W, a liquid-to-solid ratio of 25:1 (mL:g), an extraction temperature of 75 °C, and an ultrasound time of 45 min, leading to an extraction yield of (7.36 ± 0.45)% (m/m). The MOPS extract exhibited significant scavenging activity against DPPH and ABTS radicals with IC50 values of (25.65 ± 0.53) μg/mL and (100.38 ± 0.38) μg/mL, respectively. Furthermore, it effectively inhibited the enzymatic activities of α-glucosidase and α-amylase with IC50 values of (2.27 ± 0.07) mg/mL and (0.57 ± 0.04) mg/mL, respectively. The content of MOPS remained relatively stable in the stomach and small intestine; however, their ability to scavenge DPPH radicals and ABTS radicals and exhibit reducing power was attenuated, and the inhibition of α-amylase and α-glucosidase activity was diminished. In conclusion, the ultrasonic extraction of MOPS showed feasibility and revealed antioxidant and hypoglycemic effects. However, the activities were significantly reduced after gastric and small intestinal digestion despite no significant change in the MOPS content.

Effect of pH on the soybean whey protein–gum arabic emulsion delivery systems for curcumin: Emulsifying, stability, and digestive properties

A novel curcumin (CUR) delivery system was developed using soybean whey protein (SWP)-based emulsions, enhanced by pH-adjustment and gum arabic (GA) modification. Modulating electrostatic interactions between SWP and GA at oil/water interface, pH provides favorable charging conditions for stable distribution between droplets. GA facilitated the SWP form a stable interfacial layer that significantly enhanced the emulsifying properties and CUR encapsulation efficiency of the system at pH 6.0, which were 90.15 ± 0.67%, 870.53 ± 3.22 m2/g and 2157.62 ± 115.31%, respectively. Duncan's test revealed significant improvements in thermal, UV, oxidative, and storage stabilities of CUR (P < 0.05). At pH 6.0, GA effectively protected CUR by inhibiting SWP degradation during gastric digestion and promoting the release of CUR by decreasing steric hindrance with oil droplets during intestinal digestion, achieving the highest CUR bioaccessibility (69.12% ± 0.28%) based on Duncan's test. The SWP-GA-CUR emulsion delivery system would be a novel carrier for nutrients.

Rod-Shaped Starch from Galanga: Physicochemical Properties, Fine Structure and In Vitro Digestibility.

This work investigated the physicochemical properties, structural characteristics, and digestive properties of two non-conventional starches extracted from Galanga: Alpinia officinarum Hance starch (AOS) and Alpinia galanga Willd starch (AGS). The extraction rates of the two starches were 22.10 wt% and 15.73 wt%, which is lower than widely studied ginger (Zingiber officinale, ZOS). But they contained similar amounts of basic constituents. AOS and AGS showed a smooth, elongated shape, while ZOS was an oval sheet shape. AOS and ZOS were C-type starches, and AGS was an A-type starch. AOS showed the highest crystallinity (35.26 ± 1.02%) among the three starches, possessed a higher content of amylose (24.14 ± 0.73%) and a longer amylose average chain length (1419.38 ± 31.28) than AGS. AGS starch exhibits the highest viscosity at all stages, while AOS starch shows the lowest pasting temperature, and ZOS starch, due to its high amylose content, displays lower peak and trough viscosities. Significant differences were also found in the physicochemical properties of the three starches, including the swelling power, solubility, thermal properties, and rheological properties of the three starches. The total content of resistant starch (RS) and slowly digestible starch (SDS) in AOS (81.05%), AGS (81.46%), and ZOS (82.58%) are considered desirable. These findings proved to be valuable references for further research and utilization of ginger family starch.

Physicochemical and digestible properties of corn starch/gelatin complexes: Effect of pH, type of gelatin, and gelatin/starch ratio

Reducing the starch digestibility is particularly important for the prevention of obesity, diabetes and other related diseases. This work evaluated the effects of type-A gelatin (GA) or type-B gelatin (GB) of different ratios (12.5%, 25.0% and 50.0%, gelatin/starch, w/w) on the in vitro digestibility of corn starch (CS) at pH 4.0, 5.0 and 6.0. The complexation of CS and gelatin was electrostatic interactions and hydrogen bonds. The gelatin addition increased the turbidity of the system, the gelatinization temperature of CS, decreased the rapidly digestible starch (RDS) content, crystallinity, gelatinization enthalpy and viscosity of CS, and embedded within the internal CS matrix. At the same pH, the RDS content decreased with the increase of GA/CS or GB/CS ratio except for the TS -25.0%GA sample at pH 4.0. Ranked in order of RDS content, the pH values of the complexes were generally as follows: pH 5.0 > pH 6.0 > pH 4.0. Compared to GB, GA significantly reduced RDS content of CS under the same gelatin/starch ratio and pH conditions. The TS-25.0%GA complex exhibited the lowest RDS content of 56.36% at pH 4.0. These results will help to learn more about the mechanism of interaction between CS and gelatin, as well as the development of low content RDS corn starch-based food.

Pomegranate seed as a novel source of plant protein: Optimization of protein extraction and evaluation of invitro digestibility, functional, and thermal properties.

This research was carried out to optimize the extraction process of proteins from pomegranate seeds and characterize their invitro digestibility as well as their thermal and functional properties. For this purpose, the study screened five parameters (liquid/solid ratio, pH, temperature, NaCl concentration, and time) that could potentially influence the extraction process. This screening was conducted using a two-level Placket-Burman design (PBD). The significant parameters (pH and NaCl concentration) were subsequently optimized using a three-level face-centered central composite design (FCCD) to determine the optimum extraction conditions. A maximum protein recovery of 83.8% was obtained at pH 11.0 and NaCl concentration of 0.0 M. Pomegranate seed protein isolate (PSPI) with a protein content of 92.4% (w/w) was obtained through the isoelectric precipitation of pomegranate seed protein extracted under the optimized conditions. An emulsifying activity index of 14.1 m2 g-1 was observed at the isoelectric pH, where the emulsion stability index was at 8.2%. PSPI also showed high water- and oil-holding capacities (3.7 and 4.3 g g-1, respectively). The essential amino acid levels in PSPI (except for valine and isoleucine) exceeded the recommended amounts set by WHO/FAO/UNU for adults, highlighting its high nutritional value. Based on thermal analysis data, denaturation of PSPI could occur at 89.5°C. The invitro digestibility of PSPI was found to be 74.3%. PSPI shows a potential as a novel ingredient for substituting animal-based proteins in various food applications.

Screening transparent model fluids to emulate the rheological properties of high solid anaerobic digestate of food waste

Due to the opacity of high solid anaerobic digestate, optical visualization techniques (e.g., particle image velocimetry) cannot be used directly for measuring the flow field inside high solid anaerobic digestion (HSAD) systems. This study mainly focused on selecting suitable surrogate fluids for optical visualization techniques by comparing the flow curves, thixotropic properties, viscoelastic behavior and creep recovery properties of HSAD digestate with a total solid from 10 % to 15 % (w/w) and transparent model fluids. Results indicated that the Bingham model outperformed the power-law model and Herschel-Bulkley model in describing the flow curves of HSAD digestate, xanthan gum and laponite. The digestate and xanthan gum had a similar thixotropic kinetic coefficient of 0.003 and 0.004, respectively. Besides, the digestate and xanthan gum had a similar modulus transformation trend with a power function whose power exponents were 0.17 and 0.19, respectively. In general, xanthan gum can be a suitable substitute for HSAD digestate with a total solid from 10 % to 15 %. The results can guide the implementation of optical visualization techniques to understand the flow pattern within HSAD systems, and improve the mass and heat transfer efficiency during food waste disposal processes.