Improvement of radio frequency (RF) heating uniformity on low moisture foods with Polyetherimide (PEI) blocks

Radio frequency (RF) heating is rapid, volumetric, and can penetrate most food packaging material. Thus, it is suited for in-packaged food pasteurization applications. However, the non-uniform heating problem needs to be resolved. In this study, a method of adding Polyetherimide (PEI) cylindrical blocks on top of and at the bottom of peanut butter samples in a cylindrical jar (d = 10 cm, h = 5 cm) was evaluated to improve RF heating uniformity. A computer simulation model built with COMSOL Multiphysics® was used for heating pattern prediction, and a new temperature uniformity index was proposed to suitably evaluate pasteurization process heating uniformity. Results showed that a pair of PEI blocks with a diameter of 8 cm among all five diameters (2, 4, 6, 8, and 10 cm) added to the cold spots of a given peanut butter sample could make the sample reach the best heating uniformity. Furthermore, the best height of PEI blocks with a diameter of 8 cm that allows the sample to be heated most uniformly was found to be 1.3 cm after sweeping from 0.1 to 2.3 cm with a step of 0.1 cm. Simulation results also showed that the combination of PEI surrounding and the addition of 8 cm diameter PEI blocks could further control the temperature distribution range in peanut butter within 7.1 °C when the peanut butter was heated from 23 to 70 °C. The newly developed temperature uniformity index provided a more reasonable evaluation on heating uniformity of pasteurization process than the traditional uniformity index.     

Computational modelling of the impact of polystyrene containers on radio frequency heating uniformity improvement for dried soybeans

Radio frequency (RF) heating has been explored as a new method for postharvest pasteurization and disinfestations, but the non-uniform heating problem needs to be solved. In this study, an experimentally validated simulation model was developed to investigate effects of applying a surrounding polystyrene container on RF heating uniformity improvement in dried soybeans. The computer model was built for soybeans with both low and high moisture contents placed in the rectangular shaped polypropylene and polystyrene containers and heated in a parallel plate RF system. Results showed that the temperature uniformity was greatly improved by placing soybean samples in the polystyrene container other than the polypropylene one. The maximum temperature difference and uniformity index (UI) were reduced. The inner corner radius of 8 cm combined with container thickness of 8 cm could provide the best heating uniformity for soybeans. This newly developed technique can be easily implemented to improve the RF heating uniformity of other low-moisture legumes for industrial applications.Industrial relevanceRadio frequency (RF) heating has been explored as a new method for postharvest pasteurization and disinfestations of low-moisture granular legumes, but the non-uniform heating problem needs to be solved before being applied in industry. A validated simulation model was used to demonstrate the better container material and design for ensuring good temperature distributions in practical RF treatments. The optimal parameters from computer simulation may save time and reduce the cost to facilitate the design and scaling-up of the RF treatment protocols.     

Dielectric properties,heating rate,and heating uniformity of wheat flour with added bran associated with radio frequency treatments

The purpose of the study was to determine influences of dielectric properties (DPs) on radio frequency (RF) heating rate and uniformity and provide essential information for developing effective pasteurization processes of wheat flour. DPs of the wheat flour as a function of frequency, moisture content (MC), wheat bran content (WBC) and temperature were determined using an impedance analyzer. A 27.12 MHz, 6 kW pilot-scale RF system at an electrode gap of 100 mm was used to evaluate the heating rate and temperature distribution in each wheat flour-bran mixture. The results showed that DPs of wheat flour increased with increasing temperature and MC but with decreasing WBC due to high fat content in wheat bran, and their relationship can be represented by cubic or quadratic models. The heating rate of wheat flour decreased first and then increased with increase in MC while decreased with decreasing WBC due to the increasing difference between dielectric constant (ε′) and loss factor (ε″). Decreased WBC also resulted in decreasing uniformity index (λ) value. Reducing MC and WBC in wheat flour-bran mixtures could help to improve RF heating uniformity.     

A novel strategy for improving radio frequency heating uniformity of dry food products using computational modeling

This study attempted to quantify effects of dielectric properties (DPs) and densities of a surrounding container and treated food products on heating uniformity in a 6 kW, 27.12 MHz parallel plate radio frequency (RF) system. A computer simulation model was established with finite element-based commercial software, COMSOL Multiphysics®, and experiments with 1.5 kg soybean flour packed in a rectangular polystyrene container were performed to validate the developed model. Surface temperature distributions of soybean flour in three different horizontal layers were obtained with an infrared camera, and temperature–time histories at two representative locations inside the container were monitored with two optical fiber sensors. The uniformity index (UI) was used as a criterion to evaluate the RF heating uniformity within food products. Results showed that the RF heating uniformity in food samples was clearly influenced by DPs and density of the surrounding container. UI was the lowest when the surrounding container dielectric constant was in a comparable range of the sample's, with the loss factor values of surrounding container lying between 0.01–0.1% of the sample's. The optimum RF heating uniformity in food products could be achieved with a smaller density value of the surrounding container. The correlations of DPs and density between surrounding container and food products derived from the validated simulation model could provide valuable information and strategy to improve the RF heating uniformity in low moisture foods for insect or microbial control. Thus, the established strategy can further be used for developing effective industrial-scale RF treatment protocols after optimization of this process by the food industry.Industrial relevanceAlthough the most important characteristic of radio frequency (RF) treatments is fast and volumetric heating generated by dipole rotation and ionic conduction, edge over-heating is still a major problem for foods heated in rectangular containers. The validated model was used to study the effects of dielectric properties and density of sample and surrounding container on sample uniformity index. Simulated results illustrated that the RF heating uniformity could be improved when the dielectric constant and density of surrounding container and sample were in accordance with the established relationships. The established strategy may provide valuable optimized methods to ensure RF heating uniformity in industrial applications.     

Storage stability of pistachios as influenced by radio frequency treatments for postharvest disinfestations

There has been an increased interest in developing alternative physical methods for disinfesting postharvest nuts under growing international pressures to replace chemical fumigation due to its adverse effects on human health and environment. The present research explored the possibility of using radio frequency (RF) heating as a non-chemical treatment for disinfestations of pistachios. A pilot-scale, 27 MHz, 6 kW RF unit was used to study RF heating uniformity, develop a treatment protocol, and evaluate quality attributes and storage stability in treated samples. Only 5.6 and 5.5 min were needed to raise the centre temperature of 1.8 kg in-shell and 2.0 kg shelled pistachios to reach 55 °C using RF energy, respectively, compared to about 82 and 117 min when using hot air heating at 55 °C. RF heating uniformity in both types of pistachios was improved by adding forced hot air, sample movements on the conveyor and a single mixing in the middle of the treatment time. The final average temperatures on the surface and in the interior of both types of pistachio kernels exceeded 52 °C, following a holding step at 55 °C for 2 min using hot air. This provided a conservative and 100% mortality of fifth-instar Indianmeal moth (Plodia interpunctella [Hübner]). RF treated samples were not significantly different from control samples in weight loss, peroxide values, fatty acid values, fatty acid composition and kernel colour. RF treatments can, therefore, potentially provide an effective and rapid protocol against stored product pests in pistachios as an alternative to chemical fumigation.Industrial relevanceA pilot-scale 6 kW RF system with conveyor belt was used to determine the heating uniformity and quality changes of pistachios. For a combination with hot air surface heating and mixing, an effective and continuous RF disinfestation method could be developed for pistachios. The RF heating technology has been successfully demonstrated for disinfesting walnuts in California, USA. We tried to expand the industrial applications of RF heating for disinfesting pistachios, to replace the chemical fumigation. This research may provide potential industrial applications of RF treatments for disinfestations based on fast and uniform heating.     

The effect of moisture content and compaction on the strength and arch formation of wheat flour in a model bin

An experimental study was carried out to determine the effect of compaction on arching of wheat flour in storage. A model bin 475 mm in height and 600 × 375 mm in cross-section was used to conduct tests and wheat flour at moisture contents (MC) of 8.6% and 14.2% was tested. Direct shear tests were performed to determine the angle of internal friction and cohesion of wheat flour subjected to various compaction pressures. It was observed that the internal friction angles were about the same for the wheat flour at two moisture contents (37.6° vs. 37.5°), but cohesion for 14.2% MC was 72% higher than that for 8.6% MC. The flowability of wheat flour decreased with increasing compaction pressure sharply at the initial stage of compaction. Compaction led to a 64% increase in required hopper opening for arching-free flow for flour at 8.6% MC, and 49% at 14.2% MC. However, compaction pressure had little effect on arch formation after it reached above 5 kPa.     

ZnO nanoparticles combined radio frequency heating: A novel method to control microorganism and improve product quality of prepared carrots

Effects of ZnO nanoparticles combined radio frequency (RF) heating on the sterilization and product quality attributes (hardness, color, carotenoids and microstructure) of prepared carrots were investigated comparing to ZnO nanoparticles or RF heating treatment alone. The results showed that the combined sterilization effect of ZnO nanoparticles with radio frequency treatments was superior to ZnO nanoparticles or RF heating treatment alone and extended the shelf life of prepared carrots up to 60 days. ZnO nanoparticles combining RF heating 20 mm/20 min (plate spacing/RF heating time) reduced the loss of hardness, color difference value (ΔE), and carotenoids of prepared carrots. The Scanning electron micrographs (SEM) showed that the cell microstructure of prepared carrots that treated by RF treatments within 20 min was most closely integrated with each other. Therefore, the experimental results of ZnO nanoparticles combined with radio frequency heating could be helpful for food processing industries to produce high quality sterilized prepared carrots.Industrial relevanceZnO nanoparticles combined with radio frequency heating achieved logarithmic reduction of bacterial population and met China's national standard while preserving the color, texture and nutrition better. This information can be helpful for food processing industries to produce high quality sterilized prepared carrots and this same approach can be applied to many other prepared food formulations.     

Application of radio frequency pasteurization to corn (Zea mays L.): Heating uniformity improvement and quality stability evaluation

Mildews caused grain losses and serious outbreaks have been becoming increasing concerns in domestic and international corn processing industry. This study intended to explore the possibility of using radio frequency (RF) heating as an effective treatment to eliminate the mold contamination and reduce the damage to corn quality. A pilot-scale, 27 MHz, 6 kW RF unit was used to study the heating uniformity in corn samples with five moisture contents (MC) and using three plastic material containers, and develop a treatment protocol for a corn sample with the MC of 15.0% w.b. and evaluate quality attributes and storage stability of treated samples. The results showed that only 7.5 min was needed to raise the central temperature of 3.0 kg corn samples from 25 °C to 70 °C using the RF energy, but 749 min for samples to reach 68.6 °C using hot air at 70 °C. The RF heating uniformity was improved by adding forced hot air, moving samples on the conveyor, and mixing during the treatment. An effective RF treatment protocol was finally developed to combine 0.8 kW RF power with a forced hot air at 70 °C, conveyor movement at 6.6 m/h, two mixings, and holding at 70 °C hot air for 14 min, followed by forced room air cooling through thin-layer (2 cm) samples. Corn quality was not affected by RF treatments since quality parameters of RF treated samples were better than or similar to those of untreated controls after the accelerated shelf life test. RF treatments may hold great potential as a pasteurization method to control molds in corns without causing a substantial loss of product quality.     

Pasteurization of fermented red pepper paste by ohmic heating

Ohmic heating was applied to a Korean traditional fermented food containing red pepper paste, called Gochujang with low thermal conductivity (0.458 W/m ∙ K), by varying frequencies (40–20,000 Hz) and applied voltages (20–60 V). Contrary to conduction heating, the entire sample was heated uniformly, and the specific heating rate was found to be highly dependent on the frequency, peaking at 5 kHz and 60 V. The results showed that complex differential equation and the Runge–Kutta fourth-order method are suitable for simulating the temperature profile during ohmic heating. The deactivation of vegetable cells of Bacillus strains on fermented red pepper paste by ohmic heating was indicated by a 99.7% reduction, compared with conduction heating for 8 min at 100 °C producing a 81.9% reduction. The organoleptic and physicochemical qualities of the samples pasteurized by ohmic heating were nearly the same as those of raw samples, and higher than those of conventionally heated samples.Industrial relevanceThe present study designed and implemented a novel sterilization process based on a static ohmic heating system with low-frequency AC at the laboratory scale for fermented red pepper paste with a low thermal conductivity (0.458 W/m ∙ K).The developed system was used to investigate the mechanisms and characteristics underlying the induction of ohmic heating and then, tested the pasteurization effect against microorganisms in fermented red pepper paste.Comparing with conventional heating processes, ohmic heating could provide rapid and uniform heating, thereby is more suitable for pasteurization and sterilization of viscous foods as fermented red pepper paste on industrial thermal processing.     

Effect of Pre-Treatments on Mechanical Oil Expression from Dika Kernels

The effect of pre-treatments on mechanical oil expression from dika kernels was investigated in this study. The parameters considered were particle sizes (fine and coarse), moisture content (4, 6, and 8%), heating temperature (30, 40, and 50°C), heating time (15, 35 and 45 min) and applied pressure (5, 10 and 15 MPa). The results showed that the oil point pressure of dika kernels reduced with increase in heating temperature and time and moisture content. The highest oil point pressure for coarse particles was recorded at 2.11 MPa; whereas oil point pressure for fine particles was below 1 MPa. The lowest pressure at which oil began to flow was 0.41 MPa (at 50°C and 8.3% MC) while the highest was 0.65 MPa (at 30°C and 4.2% MC). The optimal oil point pressure ranged from 0.55 to 0.65 MPa for fine particles and 1.51 to 2.11 MPa for coarse particles. The least oil yield was at 4% moisture content at 5 Mpa for coarse particles; whereas the highest yield was obtained at 4% moisture content at 15 MPa for fine particles. For coarse particles, resistance to oil flow decreased significantly with increase in moisture content, heating temperature and heating time. The optimal oil expression occurred at pressure range of 0.55 to 0.65 MPa for fine particles and 1.51 to 2.11 MPa for coarse particles. Dika kernel has a high oil content, which makes it valuable for oil production. An understanding of the response of oil yield to various pre-treatments will provide valuable information for the optimization of dika oil expression.     

Functional properties of corn and corn–lentil extrudates

Functional properties of corn and corn–lentil extrudates were investigated as a result of extrusion conditions, including feed rate (2.5–6.8 kg/h), feed moisture (13–19% wet basis) and extrusion temperature (170–230 °C). Lentil was used in mixtures with corn flour at a ratio of 10–50% (legume/corn). The water absorption index of extrudates increased with extrusion temperature and feed moisture content and decreased with feed rate and lentil/corn ratio. The water solubility index of extrudates increased with temperature, but decreased with feed moisture content and feed rate. The oil absorption index of extrudates increased with extrusion temperature and decreased with feed rate, feed moisture content and lentil/corn ratio. Generally, the use of lentil flour led to products with lower values for functional properties. Principal component analysis of functional properties discriminated samples with appropriate functionality based on industrial use.     

Studies on the granular structure of resistant starches (type 4) from normal,high amylose and waxy corn starch citrates

Granular and crystalline structure of starch citrates from normal, high amylose and waxy corn starch were characterized using scanning electron microscopy (SEM), optical microscopy, X-ray diffraction and Fourier transform infrared spectroscopy (FT-IR) in this study. SEM showed that citric acid treatment induced changes in the morphology of starch granules. The granule structure of starch citrates was not collapsed or destroyed even after heating. Normal and high amylose corn starch citrates maintained birefringence but lost it upon heating at 100 °C for 30 min. However, waxy corn starch citrate showed no birefringence, even before heating. Starch citrates showed different X-ray diffraction patterns before and after heating. A new peak at 1724 cm⁻¹ (ester bond) was observed in FT-IR for all starch citrates before and after heating, indicating starch citrates were heat-stable. After the deconvolution of spectra, the intensity ratio of 1016 cm⁻¹/1045 cm⁻¹ was used to calculate the ratio of amorphous to crystalline phase in the starch citrates. The ratio of 1016 cm⁻¹/1045 cm⁻¹ increased with an increase in the degree of substitution.     

Sedimentation field-flow fractionation: Size characterization of food materials

Sedimentation field-flow fractionation (SdFFF) was applied to characterize particle size distributions of food materials. Two types of food particles were examined, including milk suspensions and flour samples. Milk eluted in the normal mode SdFFF, whereas the steric mode of retention was used for flour samples. Various types of milk being investigated were from cereal and cow’s origins. The cereal milk samples included corn, job’s tear, rice, and soy milk, whereas the bovine milk included chocolate and fresh full-fat milk. Most samples exhibited monomodal size distributions, whereas corn milk displayed a slight deviation from monomodal characteristic. The mean particle sizes were detected to be approximately 0.4 μm for all cereal milk, except that they were approximately 0.5 μm for corn and all bovine milk. The application of SdFFF for micrometer size food particles was demonstrated for four types of flour samples, including corn, mung bean, rice, and tapioca flours. Significantly differences in the particle size characteristics of all flour samples were observed, by which corn, mung bean, rice, and tapioca yielded mean particle sizes of 16.7, 31.5, 13.5, and 19.9 μm, respectively. The ability of SdFFF for size separation of flours was confirmed by comparing the results obtained with those from scanning electron microscopy (SEM). Further, a new way to examine flour swelling was proposed. This study has demonstrated the potential value of SdFFF technique for food scientists.     

Physical and structural changes induced by high pressure on corn starch,rice flour and waxy rice flour

The impact of high pressure (HP) processing on corn starch, rice flour and waxy rice flour was investigated as a function of pressure level (400 MPa; 600 MPa), pressure holding time (5 min; 10 min), and temperature (20 °C; 40 °C). Samples were pre-conditioned (final moisture level: 40 g/100 g) before HP treatments. Both the HP treated and the untreated raw materials were evaluated for pasting properties and solvent retention capacity, and investigated by differential scanning calorimetry, X-ray diffractometry and environmental scanning electron microscopy. Different pasting behaviors and solvent retention capacities were evidenced according to the applied pressure. Corn starch presented a slower gelatinization trend when treated at 600 MPa. Corn starch and rice flour treated at 600 MPa showed a higher retention capacity of carbonate and lactic acid solvents, respectively. Differential scanning calorimetry and environmental scanning electron microscopy investigations highlighted that HP affected the starch structure of rice flour and corn starch. Few variations were evidenced in waxy rice flour. These results can assist in advancing the HP processing knowledge, as the possibility to successfully process raw samples in a very high sample-to-water concentration level was evidenced.Industrial relevanceThis work investigates the effect of high pressure as a potential technique to modify the processing characteristics of starchy materials without using high temperature. In this case the starches were processed in the powder form - and not as a slurry as in previously reported studies - showing the flexibility of the HP treatment. The relevance for industrial application is the possibility to change the structure of flour starches, and thus modifying the processability of the mentioned products.     

Moisture diffusivity and shrinkage of broad beans during bulk drying in an inert medium fluidized bed dryer assisted by dielectric heating

Drying behavior of broad beans (Vicia faba) was studied in a pilot scaled fluidized bed dryer with inert particles assisted by dielectric heating. The effective diffusion coefficient of moisture transfer was determined by Fickian method at four different air drying temperatures of 35, 45, 55 and 65 °C. Correlations for moisture diffusivity as a function of moisture content and temperature of the drying medium were developed. The values of moisture diffusivity were obtained within the range of 1.27 × 10^?9–6.48 × 10^?9 m²/s and the activation energies for FBD and FBD + DE were found to be 27.71 and 17.10 kJ/mol, respectively. The shrinkage behavior of the broad beans was also investigated by considering the volume ratio of (V/V_O) to be function of moisture content alone and fitting a polynomial of the third order. The dielectric heating power was also found to be effective on the rate of drying.     

Bread from composite cassava-wheat flour: I. Effect of baking time and temperature on some physical properties of bread loaf

The use of composite cassava-wheat (CCW) flour for commercial breadmaking purposes and consumption of CCW bread are relatively new in Nigeria. This study investigated the effect of baking temperature and time on some physical properties of bread from composite flour made by mixing cassava and wheat flour at ratio of 10:90 (w/w). A central composite rotatable experimental design was used while the baking temperature and time investigated ranged from 190 to 240 °C and 20 to 40 min, respectively. Loaf volume, weight and specific volume varied significantly (p < 0.001) from 440 to 920 cm³, 162 to 183 g and 3.31 to 5.32 cm³/g, respectively. The tristimulus color parameters such as L¹ (lightness) and brownness index (BI) of the crust varied significantly (p < 0.01) from 31 to 72 and 68 to 123, respectively. Moreover, Fresh crumb moisture, density, porosity and softness as well as the dried crumb hardness were also significantly (p < 0.01) affected by both the baking temperature and time with values ranging from 34% to 39%, 0.16 to 0.20 g/cm³, 0.69 to 0.80, 13.00 to 18.05 mm and 0.90 to 2.05 kgf, respectively. Due to the complex effect of temperature and time combination, most of the measured properties could not be reliably predicted from the second order response surface regression equations except the loaf weight and crumb moisture. Further studies are required to optimize the CCW bread baking process based on some storage and consumption qualities.     

Effect of radio frequency (RF) heating on the texture,colour and sensory properties of a comminuted pork meat product

Radio frequency (RF) cooking is a form of dielectric heating in which products are heated by subjecting them to an alternating electromagnetic field between two parallel electrodes. Although similar in some respects to Microwave heating, RF has been proposed to be more suitable for industrial heating of meats because of the greater penetration depths possible with this technology. In this study an RF cooking protocol was developed and its effect on selected quality attributes of pork based white pudding was examined. Whilst cooking of the product in air proved unfeasible due to arcing, use of a polyethylene cell with circulating hot water (80 °C) facilitated successful heating of the product. Application of RF using an optimised cooking protocol (RF power = 450 W, cell volume = 500 ml and continuous circulation) resulted in a mean end-point temperature of 73 °C after 7 min 40 s. Similar mean end-point temperatures in water bath and steam oven heated products were achieved after 29 and 33 min, respectively. A factorial experiment was conducted to assess selected quality attributes of the cooked puddings. Results show that RF heated puddings were not significantly different (P > 0.05) from water bath and steam oven heated products with regard to instrumental colour, instrumental texture (Kramer shear and texture profile analysis) and expressible fluid. Furthermore, results of a sensory similarity test involving 60 panellists indicated that panellists were not able to detect differences between puddings cooked by RF and conventional methods. Overall this suggests that RF heating technology could have potential in pasteurisation of meat products though further work is needed to verify this.     

Moisture diffusivity coefficient estimation in solid food by inversion of a numerical model

Knowledge of moisture diffusivity coefficients of water in food is a very important physical parameter for design, modelling and simulation of different food plants and related processes such as baking, drying and ripening. Unfortunately specific moisture diffusivity values are not easily found in literature, particularly for processed foods. The aim of this study was to develop a method, based on the inversion of finite element models, to estimate the moisture diffusivity in different solid food products. An example on salami, biscuit and flat bread is shown. The research work was divided in three phases: experimental determination of the moisture concentration versus time in various food products stored in water saturated atmosphere; development of a numerical model of water transfer inside the food product for the numerical determination of moisture content versus time and parameter estimation of moisture diffusivity, by minimizing the distance between numerical model and experimental results using the Levenberg–Marquardt algorithm.The estimated moisture diffusivity coefficients resemble those reported in literature for almost similar products (3.857E − 12, 6.804E − 11 and 1.792E − 12 m²/s for salami, biscuits and flat bread respectively). The obtained values were then used for solving direct models, in unsteady conditions, showing a good agreement with experimental data.The method may be used on different food materials and it is possible to hypothesize an integrated automatic instrument, useful both for laboratory and industrial purposes.     

Pithecellobium jiringa legume flour for potential food applications: Studies on their physico-chemical and functional properties

Jering seeds are traditionally consumed as a legume in South-East Asia. In the present study, we evaluated the physico-chemical, functional and cooking properties of jering seed flour with a major aim to popularise this seed for development of new food products. The seed flour had high moisture (58.55%) and crude protein contents (14.19%). Results on the functional properties revealed significant differences in the protein solubility, which showed a decrease from pH 2 to pH 4, with high water absorption (2.83 ml/g) and oil absorption (1.83 ml/g) capacities. The emulsifying activity and stability of the seed flour was highest at 0.4 M (26.27% and 75.75%, respectively). Addition of carbohydrates (lactose, maltose and sucrose) decreased the least gelation capacity. Results of this study showed functional properties of jering seed flour to be dependent on the concentration, pH and ionic strengths, which can be suitably modified for development of new food products.     

Acid and moisture uptake in steamed and boiled sweet potatoes and associated structural changes during in vitro gastric digestion

Orange-fleshed sweet potatoes are a good source of phytochemicals. For these nutrients to be absorbed, they must be released from the food matrix as a result of physical and chemical breakdown. A key factor in food breakdown is gastric acid diffusion into the matrix, and its influence on structural changes. Cooking treatment may influence mass transport properties and structural changes of foods during digestion. The objective of this study was to determine the acid and moisture uptake into sweet potatoes and its influence on macro- and micro-structures during in vitro gastric digestion as a result of varying cooking treatments. Sweet potatoes were cut into cubes and cooked (boiled or steamed) for different times. In vitro oral and gastric digestions were simulated in a shaking water bath at 37 °C. Acidity, moisture content, and solid loss were measured after 9 digestion times (15 to 240 min). Hardness of individual cubes and microstructure (light microscopy) were completed before and after digestion. Effective diffusivity of acid and moisture into the cubes was estimated using MATLAB. Cooking method, cooking severity, and digestion time significantly influenced moisture uptake (p < 0.0001). Acid uptake was significantly influenced by digestion time (p < 0.0001). The change of softening after digestion was influenced by cooking method and severity (p < 0.05). Effective diffusivity of acid ranged from 0.03 × 10^− 10 (mild steamed) to 11.40 × 10^− 10 m²/s (severely boiled). Percent texture decrease after digestion from the initial hardness ranged from 16% (severely steamed) to 34% (mild boiled). Textural changes were related to cell wall breakdown and starch degradation. In general, mass transport properties and macro- and microstructural changes were influenced by cooking treatment and gastric digestion. The link between food cooking and behavior during digestion is crucial in determining optimal food processing and cooking methods for specific food functional properties.