Modeling of rice hydration using finite elements

Great effort has been devoted towards developing models that describe cooking processes. A difficulty towards developing such models arises from the fact that during cooking, the physical properties and quite often sample geometry are time dependent. In this work a finite element model describing cooking of rice and water uptake using a Fickian diffusion model was developed, assuming axisymmetric conditions. Effective diffusivity was considered a function of moisture content. The numerical model compared favorably with experimental results. The value of the effective water diffusivity was estimated to be in the order of 7 × 10⁻¹⁰ m²/s, by minimizing the error between experimental and numerically predicted results.The effect of grain size on the cooking was also investigated using the model. Cooking time, i.e. the time to reach about 70% moisture content (wet basis), appeared to be a strong function of the initial size distribution.     

Physicochemical properties of different thickeners used in infant foods and their relationship with mineral availability during in vitro digestion process

Locust bean gum (LBG) and modified starches are commonly used as thickeners in food products for infants. However, there is no consensus on their possible effects on infant nutrition, especially on mineral availability. The aim of the present work was to characterize the effect of LBG, cross-linked, hydroxypropylated maize starch (Mhdp) and pre-gelatinized rice starch (gRS) on Ca, Fe and Zn availability during a gastric and intestinal in vitro digestion assay in relation to their physicochemical properties in solution (apparent viscosity, solubility, molar mass (M) and conformational properties) through the simulated digestion process. LBG gave the highest decrease in Ca and Fe gastric (17.96% and 17.6% respectively) and intestinal (19.5% and 13.5%) solubility with respect to the reference without thickeners. Ca (11.1% ± 1.1), Fe (2.77% ± 0.3) and Zn (7.78% ± 0.6) dialyzability was also lower than for the reference (23.4% ± 2.9; 19.65% ± 3.53 and 27.74% ± 3.3 respectively). LBG solubility remained stable during gastric digestion, decreasing significantly from a range of 65–69% to 61.1% after intestinal digestion. LBG viscosity remained stable during the digestion process, being these findings attributable to its resistance to enzymes. On the other hand, the addition to Mhdp or gRS slightly affected Ca and Fe solubility or Ca dialyzability, decreasing after gastric digestion and then increasing after intestinal digestion with respect to the reference. These results correlated to the changes in their viscosity enhancing properties, which increased during gastric digestion and decreased after intestinal digestion, being attributable to their digestion by pancreatic enzymes. Gastric digestion resulted in an increase in M for the modified starches (more pronounced for gRS). The increase in mineral solubility and dialyzability after intestinal digestion with respect to the gastric stage was explained by the degradation of starches by intestinal enzymes, which resulted in a decrease in apparent shear viscosity (from 1.2 to 1 Pa s, measured in a shear rate range 0.00–50 s⁻¹) and an increase in solubility (from 3 to 6% to approximately 70%) after intestinal digestion. In conclusion, LBG could be more effective than Mhdp and gRS as thickener, providing higher viscosity and resistance to digestive process. However, its negative effect on mineral solubility and dialyzability should be taken into account. On the contrary, Mhdp and gRS showed to be degraded after intestinal digestion.     

The influence of preparation method on children’s liking for vegetables

This study aimed to investigate how different preparation methods influence children’s liking for vegetables. Participants were children from three age groups (4–6 years N = 46; 7–8 years N = 25; 11–12 years N = 23) and young adults (18–25 years N = 22). The participants tasted and ranked six preparation methods for carrots and French beans: mashed, steamed, boiled, stir-fried, grilled and deep-fried. In addition, the different vegetable preparations were rated on 15 attributes. All participants preferred boiled and steamed vegetables over the other preparations (p < 0.05). Boiled and stir-fried were the most familiar preparation methods for both vegetables. Vegetable liking was positively related to a uniform surface and the typical vegetable taste, and moderately related to crunchiness, whereas brown colouring and a granular texture were negatively related to vegetable liking. On the basis of these results, we conclude that children’s vegetable liking is influenced by a complex mixture of a uniform appearance, easily controllable textures and a typical, familiar vegetable taste.     

Water absorption as an evaluation method of cooking quality for yam (Dioscorea alata) and cassava (Manihot esculenta crantz)

Water absorption as a new method of cooking quality (hard cooking or mealy cooking) of yam and cassava cultivars determination was studied by cooking eight (08) cultivars. 30 g of each were boiled in 500 ml of water during 20 minutes and dried at 70 °C for 15 hours and 103 °C for 3 hours in a vacuum oven. Results showed that cassava and yam have different cooking quality. Dry matter content does not influence the cooking quality of yam and cassava. Mealy cooking quality of yam absorbs less water (6.6%) during cooking but looses more soluble dry matter (9.5%) during the same process. Hard cooking quality of yam absorbs much water (23.5%), but looses less soluble dry matter (3.9%). The soluble dry matter is the main parameter to determine the quality of D. alata. It stands at 9.5% ± 2.9 for mealy cooking quality and 3.9 ± 0.73 for hard cooking quality cultivars of D. alata. Water absorbed by mealy cooking cassava (27.6%) is significantly (p < 0.05) higher compared to water absorbed of hard cooking cassava (12.4%). Water absorbed during cooking is the main parameter in determining the quality of cassava cultivars. Water absorbed stands at 27.6% ± 8.8 for mealy cooked quality and 12.4% ± 1.9, for hard cooked quality of cassava cultivars. A close relation between water absorption and cooking quality was revealed to contribute to a better selection procedure for cultivars in the frame of food security.     

Initial work on developing a cooking protocol for producing re-structured meat under controlled conditions

Restructured meat is made by binding individual pieces of meat together. To study the effect of mechanical work on the meat binding process, a standard cooking protocol must be established. This paper details the establishment of a standard cooking protocol for the cooking process using untreated beef semitendinosus muscle. The effect of different cooking temperatures and applied loads during cooking were investigated. Meat samples were cut in 20 mm cubes size from beef semitendinosus muscle and two pieces were held together with the muscle fibre parallel to each other by wrapping them with a plastic food wrap. Then the samples were placed inside square steel tubes, that act as a mold for cooking, and different weights (0, 250, 500, 750 and 1000 g) were placed on top of the meat cubes during cooking. The temperatures used for cooking were 60, 70 and 80 °C. There was a significant temperature effect, with increases noted between 60 °C and 70 °C and between 70 °C and 80 °C. At 60 °C neither myosin nor collagen has gelatinized, leading to low binding strengths. At 70 °C the myosin component will have gelatinized. At 80 °C the collagen component will be contributing to the bond. To keep the collagen effect to a minimum the meat should be cooked at 70 °C. The effect of applied cooking load was significant at all cooking temperatures once sufficient load had been applied against no load to ensure good contact at the joint. There was a significant effect of applied load noted at 80 °C with increases up to 750 g and a drop occurring between the 750 and 1000 g loadings. The drop has been attributed to collagen being squeezed out of the joint as a bead of white material was noted around the joint.     

Effect of high voltage electrostatic field thawing on the lipid oxidation of frozen tuna fish (Thunnus albacares)

Changes in the quality, such as color, and TBA values are compared between tuna fish (Thunnus albacares) cuts thawed by high voltage electrostatic field (HVEF) and those thawed conventionally as control. The tuna cubes (2 × 4 × 4 cm³) are thawed under HVEF at three different voltages from the corona starting to the breakdown voltage one with electrode gaps of 3, 4.5, and 6 cm. The control specimens are subjected to no HVEF but thawed conventionally at 20 °C. The results show that thawing under HVEF increases significantly the TBA and ΔE values of the frozen tuna fish cubes (p < 0.05). Tuna fish cubes were observed to oxidize faster at high electrostatic field intensities than at lower ones. Among the two models considered in this study (zero-order and first-order), the first yielded excellent fits for the TBA value experiment.Industrial relevanceThe degree of fish oxidation due to application of a high-voltage electrostatic field method for fish thawing is an important issue that needs serious attention. Application of HVEF thawing is found to lack the potential to extend the freshness of thawed tuna fish due to lipid oxidation and color changes.     

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.     

Effect of Boiling and Frying on the Total Carbohydrate,Vitamin C and Mineral Contents of Irish (Solanun tuberosum) and Sweet (Ipomea batatas) Potato Tubers

In a study aimed at ascertaining whether boiling or frying best conserves nutrients; since the two methods are commonly adapted in Nigeria, the effect of boiling and frying on total carbohydrate, vitamin C and mineral contents of Irish (Solanum tuberosum) and sweet (Ipomea batatas) potato tubers were investigated. The determination of total carbohydrate was carried out using the phenol-sulphuric acid method and the spectrophotometric method was used to determine vitamin C content at 520 nm. The minerals evaluated are iron, zinc, magnesium, sodium, calcium and copper. These were determined by the atomic absorption spectrophotometric method. There was no significant difference (p > 0.05) in the total carbohydrate content of the boiled and fried sweet and Irish potatoes compared with their raw tubers. There was significant difference (p < 0.05) in the vitamin C content of the boiled and fried potato tubers. Boiling and frying of Irish potato resulted in a loss of 37.34 mg/100 ml (63.90%) and 30.44 mg/100 ml (53.90%) vitamin C respectively. Boiled sweet potato lost 51.16 mg/100 ml (72.37%) and fried lost 43.05 mg/100 ml (60.90%) of vitamin C. The mineral compositions of the boiled and fried Irish and sweet potatoes were significantly different (p < 0.05) from their raw tubers. Boiling retained more iron and copper while frying retained more zinc, magnesium, sodium and calcium in both Irish and sweet potato tubers. Boiling retained more carbohydrate while frying retained more vitamin C and minerals.     

Aluminium contents in baked meats wrapped in aluminium foil

In this investigation, the effect of cooking treatments (60 min at 150 °C, 40 min at 200 °C, and 20 min at 250 °C) on aluminium contents of meats (beef, water buffalo, mutton, chicken and turkey) baked in aluminium foil were evaluated. Cooking increased the aluminium concentration of both the white and red meats. The increase was 89–378% in red meats and 76–215% in poultry. The least increase (76–115%) was observed in the samples baked for 60 min at 150 °C, while the highest increase (153–378%) was in samples baked for 20 min at 250 °C. It was determined that the fat content of meat in addition to the cooking process affected the migration of aluminium (r² = 0.83; P < 0.01). It was also found that raw chicken and turkey breast meat contained higher amounts of aluminium than the raw chicken and turkey leg meat, respectively. Regarding the suggested provisional tolerable daily intake of 1 mg Al/kg body weight per day of the FAO/WHO Expert Committee on Food Additives, there are no evident risks to the health of the consumer from using aluminium foil to cook meats. However, eating meals prepared in aluminium foil may carry a risk to the health by adding to other aluminium sources.     

Influence of cooking conditions on cooking loss and tenderness of raw and marinated chicken breast meat

The influence of different cooking treatments on tenderness and cooking loss, as main quality characteristics of chicken breast meat, was investigated. Industrial skinless chicken breast meat samples were designated as raw and marinated and cooked in the oven by hot air and hot air-steam mixture at 130, 150 and 170 °C, for 4, 8 and 12 min. Cooking losses were evaluated by weight changes before and after cooking, and tenderness changes were determined on cooked samples by measuring shear force using instrumental texture analysis. Results showed that marination, followed by air-steam cooking is the best combination to obtain the most tender chicken breast slices. The time and temperature of cooking showed similar effects on cooking loss and tenderness: short cooking time (4 min) and temperatures of 130–150 °C resulted in lower cooking losses and best meat tenderness, in both not marinated and marinated meat. Statistically significant correlations between tenderness and cooking loss indicated that the cooking loss correlated better with cooking time than with cooking temperature. An opposite phenomenon was observed for meat tenderness.     

Preliminary investigations on the effects of ageing and cooking on the Raman spectra of porcine longissimus dorsi

The influence of ageing and cooking on the Raman spectrum of porcine longissimus dorsi was investigated. The rich information contained in the Raman spectrum was highlighted, with numerous changes attributed to changes in the environment and conformations of the myofibrillar proteins.Predictions equations for shear force and cooking loss were developed from the Raman spectra of both raw and cooked pork. Good correlations and standard errors of prediction were obtained for both WB shear force and cooking loss, with the raw and the cooked samples showing almost identical results R² = 0.77, root mean standard error of prediction (RMSEP)% of mean = 12% for shear force; R² = 0.71, RMSEP% of mean = 10% for cooking loss. The Raman spectra were also able to predict the extent of cooking that occurred within the pork (R²_val = 0.94, RMSEP% of range = 5.5%).Raman spectroscopy has considerable potential as a method for non-destructive and rapid determination of pork quality parameters such as tenderness. Raman spectroscopy may provide a means of determining changes during cooking and the extent to which foods have been cooked.     

Effect of boiling and peeling on manganese content of some vegetables determined by derivative anodic stripping chronopotentiometry (dASCP)

The purpose of this paper was two-fold: to optimise an analytical method based on derivative anodic stripping chronopotentiometry (dASCP) for reliable trace manganese determination in different fresh vegetables and aromatic plants, and to use this technique to asses the effect of boiling and peeling processing on their manganese content. The deposition potential was −1700 mV and the deposition time 120 s; in this conditions the limits of detection 8.0 ng kg⁻¹ (ppt) and the accuracy of the method, assessed using certified reference materials, was within 95.0%. Among the studied fresh vegetables, the highest content of manganese was found in vegetables with dark green leaves as chicory and spinach (respectively, 3.5 and 3.3 mg/100 g), while vegetables with light green leaves as lettuce, together with carrots, garlic and pore mushrooms had manganese levels lower than 1.0 mg/100 g. Boiling processing cause a significant decrease of manganese levels in artichokes, tomatoes, chicory, garlic, mushrooms, peeled carrots and potatoes, spinach, and string beans (p ⩽ 0.005, ANOVA). Fennels, lettuce, marrow, unpeeled carrots and unpeeled potatoes did not show any statistical significant changes after boiling. Also peeling significantly influenced the content of manganese of carrots and potatoes (p ⩽ 0.01, ANOVA) and favoured manganese loss during boiling.     

Application of simultaneous combination of microwave and steam cooking to improve nutritional quality of cooked purple sweet potatoes and saving time

The influence of simultaneous combination of microwave and steam cooking on contents of specific phytochemicals, carbohydrate and antioxidant activity of purple sweet potatoes (PSPs) was investigated, and compared to those of individual steaming and microwaving. Results showed that the contents of phytochemicals including total phenolics, flavonoids and anthocyanins and phenolic acids except caffeic acid increased after cooking to different extent depending on cooking methods. The PSPs cooked by simultaneous combination of microwave (500 W) and steam (1700 W) for 12 min (M₅₀₀-S₁₇₀₀-12) contained the highest of total phenolics, flavonoids, phenolic acids and anthocyanins. Simultaneous combination of microwave and steaming resulted in higher content of soluble sugar in PSPs. PSPs cooked by M₅₀₀-S₁₇₀₀-12 showed the highest antioxidant activity, which was well accordance with higher contents of phytochemicals. The findings suggest that appropriate simultaneous combination of microwave and steaming could better preserve active phytochemicals in PSPs, but significantly shorten cooking time compared with individual steaming.Industrial relevanceSimultaneous combination of microwave and steam cooking is a new technology for cooking food. However, the information about the effects of simultaneous combination of microwave and steam cooking on quality of food is limited. The present findings showed that the appropriate combination of microwave and steam cooking could significantly decrease the cooking time and improve nutrition value of cooked PSPs. This research is not only of importance for understanding the changes of food composition during different heating process, but also has important practical significance for choosing a scientific cooking methods and developing new type of cooking utensils which can better satisfy current consumers' needs.     

Release of multifunctional peptides by gastrointestinal digestion of sea cucumber (Isostichopus badionotus)

Sea cucumber is a benthic marine organism distributed worldwide and used as food in several Asian countries. The species Isostichopus badionotus is captured intensively off the Yucatan Peninsula, Mexico. Boiled I. badionotus was subjected to in vitro simulated gastrointestinal digestion using pepsin and a pepsin–Corolase PP^® mixture. ACE-inhibitory and radical scavenging activities, iron reducing capacity and cytotoxic effects against colorectal cancer cells were evaluated in the hydrolysates and their ultrafiltered fractions. ACE-inhibitory activity was potent in fractions containing peptides <3000 Da, an effect augmented with combined action of gastric (pepsin) and intestinal (Corolase PP^®) enzymes (IC₅₀ = 0.038 ± 0.004 mg/mL). Antioxidant activity was exerted by peptides with low and high molecular weights, depending on hydrolysis method. This is the first report of cytotoxic capacity against colorectal HT-29 cells in peptides from sea cucumber. Sea cucumber hydrolysates and ultrafiltered fractions are potential ingredients for development of functional foods.     

Milk enhances intestinal absorption of green tea catechins in in vitro digestion/Caco-2 cells model

The effect of milk on the absorption of polyphenols is still controversial so far. In order to determine the impact of milk addition on green tea catechins bioaccessibility and intestinal absorption an in vitro digestion/Caco-2 cell model was applied. Green tea extract (GTE) was solubilized in distilled water at 23 °C and 100 °C, combined with skimmed milk (GTE + 10% milk and GTE + 25% milk) and subjected to simulated gastric and intestinal digestion, followed by transepithelial absorption in Caco-2 cells monolayers. In the mixture with milk, gallated catechins: ECG and EGCG showed binding to milk proteins while EC and EGC seemed to have weaker affinity. Catechins were stable during gastric incubation and very sensitive to intestinal digestion. Bioaccessibility of green tea catechins brewed at 100 °C was higher than brewed at 23 °C. Catechins from digested GTE with 10% and 25% milk exhibited enhanced intestinal permeability in Caco-2 model in comparison to non-digested GTE and digested GTE without milk. Apparent permeability coefficients (P_app) of EGCG and ECG in digested GTE with 25% milk were significantly higher compared to those in GTE with 10% milk, and amounted to 2.41 × 10^− 6 cm/s and 1.39 × 10^− 6 cm/s. The recoveries of all catechins in GTE with milk in Caco-2 cells after 2 h incubation were significantly higher than that without milk. To summarize, these data suggest that milk addition may increase catechin bioavailability by enhancing their transepithelial absorption and uptake from green tea extract.     

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.     

Antioxidant and Anti-diabetic Properties of Caryota Urens (Kithul) Flour

Starch extracted from pith of Caryota urens L. (Family: Arecaceae) palm is known as “Kithul flour” and is claimed to have health benefits according to folklore and Ayurveda. Antioxidants are believed to possess numerous health benefits. However, as yet, health benefits of C. urens flour have not been scientifically investigated. Antioxidant properties of C. urens flour were tested using different in vitro assays namely, 2,2-azino-bis 3-ethylbenzothiazoline-6-sulfonic acid (ABTS⁺), ferric reducing antioxidant power, oxygen radical absorbance capacity and ferrous ion chelating assays. Total Phenolic Content (TPC) and Total Flavonoid Content (TFC) were also evaluated. Anti-diabetic properties were estimated using alpha amylase and alpha glucosidase enzyme inhibition assays. Dried methanolic extracts of both boiled and raw samples were used in all assays. Results of the study showed that C. urens flour possess free radical scavenging activity(raw 0.02± 0.01 and boiled 0.04±0.01 mg trolox equivalent (TE)/ g flour), electron donating reducing power (raw 0.10±0.03 and boiled 0.36±0.11 mg TE/g flour), oxygen radical absorbance capacity (raw 2.29± 0.71 and boiled 192.3 ± 57.71 mg TE/1 g flour) and metal ion chelating capacity (raw 0.03±0.01 and boiled 0.14±0.04 mg EDTA equivalents /g flour) exhibiting its antioxidant potential. TPC (raw 1.1±0.3 and boiled 5.12 ± 1.89 mg GAE/g flour) and TFC (raw 1.65 ± 0.47 and boiled 6.69 ± 1.27 μg QE/g flour) which are said to be contributed to antioxidant activities were also found. In addition, boiled flour which is generally consumed as a food has shown higher antioxidant activity. Caryota urens flour did not contain marked anti-diabetic properties. It is evident from results that Caryota urens flour has moderate antioxidant property which may associate with its traditional health claims.     

Radio frequency heating of corn flour: Heating rate and uniformity

Non-uniform heating is a major challenge for using radio frequency (RF) heat treatment in pasteurization of low moisture food products. The objective of this study was to evaluate the effect of different electrode gaps, moisture content (MC), bulk density and surrounding materials on RF heating uniformity and rate in corn flour. Additionally, the dielectric and thermal properties of corn flour were determined as affected by MC, temperature (°C), and frequency (MHz). Changes in MC, water activity (a_w) and color in the sample after RF heating were measured to evaluate treatment effect on food quality. A precision LCR meter and a liquid test fixture were used to study DP of the sample at RF frequency ranging from 1 to 30 MHz. The RF heating uniformity and temperature profiles of corn flour as exposed to RF heating were obtained with an infrared camera and a data logger connected to a fiber optic sensor. The DP values increased with increasing MC and temperature, but decreased with frequency. The heating rate increased from 3.5 to 6.8 °C min^− 1 with increasing MC (from 10.4 to 16.7%), but decreased from 12.7 to 5.2 °C min^− 1 with increasing electron gap (from 11 to 15 cm). The corner and edge heating were observed at all layers of the samples for all the distances, and the hottest and the most uniform layer were determined as the middle layer at an electrode gap of 15 cm. Glass petri dish provided better uniformity than those of polyester plastic petri dish. Covering by foam led to more uniform RF heating uniformity in corn flour, and better moisture and a_w distribution. This study provided useful information to develop an effective RF process as an alternative of conventional thermal treatments for pasteurization of low-moisture products.Industrial relevanceThis paper describes a novel methodology based on Radio Frequency heating to pasteurize food powder while maintaining the quality. The study addresses the ever-increasing global demand from consumers for safe food products.     

Effect of cooking and irradiation on the labile vitamins and antinutrient content of a traditional African sorghum porridge and spinach relish

Irradiation is a potentially useful technology for ensuring the safety and extending the shelf-life of food products in Africa. However, nutritional changes may result. The effects of cooking followed by irradiation (10 kGy) on vitamins B₁ and C, and the antinutritional factors, phytic acid and nitrates, in a ready-to-eat meal of sorghum porridge and spinach-based relish were investigated. Cooking reduced vitamin B₁ and C contents of the spinach relish, and irradiation caused further losses. Cooking did not alter vitamin B₁ content of the sorghum porridge but irradiation decreased it drastically. Cooking did not decrease phytic acid in the sorghum porridge, but irradiation caused a significant decrease. The reduction of antinutritional factors by cooking, followed by irradiation, is promising for the application of this technology to traditional African cereal and leafy vegetable foods. However, ways need to be found to minimise vitamin loss, such as blanching and cooking in minimum water and irradiation at cryogenic temperatures in an oxygen-free atmosphere.