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There is insufficient information on the effect of temperature, moisture content (MC), and oil concentration on the mechanical properties of fried potatoes. The static mechanical testing capabilities of a dynamic mechanical analyzer (DMA) were utilized to measure the stress relaxation function of fried potatoes as a function of frying time, temperature, and testing temperature. The French fries were prepared in oil heated at 177°C, 184°C, and 191°C, and their MC and oil content (OC) values were measured as a function of frying time. The samples loaded in DMA were subjected to 2% strain, and the stress relaxation was performed for 600 s. The DMA furnace temperature was set at 37°C, 60°C, and 90°C. A two‐element generalized Maxwell model was fitted into the DMA data. French Fries lost more than 70% of their moisture and absorbed more than 80% of their final OC during the first 180 s of frying. During the same interval (up to 180 s), the relaxation modulus parameters (G0, G1, and G2) did not change significantly and then increased linearly. These parameters also did not change considerably for MC above 2 g/g solids. At lower MC values, G1 and G2 increased as the MC was reduced, but the elastic modulus G0 stayed almost constant, independent of the MC. [ABSTRACT FROM AUTHOR]

Hybrid mixture theory-based multiscale fluid transport equations were solved for drying of strawberries and carrots to predict the moisture transport during the process. The fluid transport equation was coupled with the selected product quality and nutritional attributes to predict changes in stress distribution, shrinkage, color parameters, and ascorbic acid/β-carotene content. The fluid transport equation includes a non-Fickian term that incorporates the effect of glass transition on moisture transport. A transformation between Eulerian and Lagrangian coordinates was used to include the moving volume effects due to shrinkage. Good agreements between the experimental and the predicted values of moisture content (RMSE ≤ 0.095, RMSE ≤ 0.579), color parameters (R2 ≥ 0.958, R2 ≥ 0.934), and volume changes (R2 ≥ 0.871, R2 ≥ 0.865) were obtained for strawberries and carrots, respectively. Drying in the vicinity of glass transition regime led to sharper moisture profiles, indicating non-Fickian transport. However, drying at temperatures higher than glass transition temperature of strawberries and carrots resulted in Fickian characteristics-round and smooth drying profiles for drying at 70 °C. Drying at higher temperature caused higher loss of quality attributes; it resulted in samples with lower color parameters and ascorbic acid or β-carotene content. Higher drying temperature resulted in greater shrinkage and deformation throughout the structure, leading to cracks and openings and faster degradation in quality attributes. The developed model would allow improving quality attributes and finding optimum processing conditions of strawberries and carrots. [ABSTRACT FROM AUTHOR]

Quality properties of concentrate pineapple juice obtained by block freeze crystallization (BFC) and evaporation technology are investigated. After three concentration cycles, the solutes were approximately 3.2 times compared to the initial condition and the final color was darker than that of the fresh juice. BFC allowed for higher bioactive compounds retention than evaporation in terms of total phenolic, flavonoid, and anthocyanin content. The cryoconcentrate juice showed a similar aromatic profile to the fresh juice, with 26 and 23 compounds, respectively. Conversely, only seven volatile compounds were identified in the evaporate sample. Finally, BFC is an effective technology to preserve important quality properties from fresh fruit juices such as color, polyphenols, and aromatic profile. [ABSTRACT FROM AUTHOR]

Background The availability and movement of water inside the food materials play essential roles for food stability by affecting their physical and chemical properties, and microbiological activity. Understanding the moisture sorption behavior is a necessary step to control food properties. Food processing unit operations like drying and cooking influence the behavior of starch since such systems trigger swelling or shrinkage as a result of moisture sorption or desorption mechanisms. Also, these processes alter many aspects of starch-containing foods such as acceptability, nutritional value, quality, and shelf-life. Scope and approach Therefore, understanding the water transport in starchy foods and the changes occurring in functional properties of starch has a great importance to describe and model their sorption and drying behavior. First, the primary mechanisms occurring during water transport such as moisture sorption, swelling, gelatinization, and glass transition are discussed using experimental results presented in the literature. Additionally, the hybrid mixture theory (HMT) and its potential for predicting transport mechanisms in starchy foods is discussed. Key findings and conclusions In addition to experimental considerations, the mathematical modeling provides complementary information to predict the heat and fluid transfer. The hybrid mixture theory based multiscale models are able to describe the physico-chemical changes and general transport mechanisms occurring within a porous food matrix. This theory can also be used to predict the quality changes in food products during processing. [ABSTRACT FROM AUTHOR]

It is important to understand the viscoelastic properties of cereals as they affect product texture. Therefore, the stress relaxation behavior of oat flakes was studied using static testing. The oat flakes exhibited linear viscoelastic behavior at strain levels under 2%. The relaxation modulus was directly influenced by the moisture content of the samples; it was low at higher moisture levels. A two-element generalized Maxwell model fitted well to describe the viscoelastic behavior of oat flakes with its high R 2 and low RMSE. The first and second stress coefficients ( G 1 a n d G 2 ) and the second relaxation time component ( τ 2 ) of the model generally decreased as the moisture content of the samples increased, which implied that samples showed lower resistance against applied force and relaxed faster with the increase in moisture content. The viscoelastic behavior of oat flakes was a function of both moisture content and temperature. The viscoelastic properties obtained in this study can be used to improve the textural attributes of oat-based products and further utilized in mathematical models describing drying or sorption processes. [ABSTRACT FROM AUTHOR]

Pressure evolution and material deformation during frying and post-frying of foods affect transport processes and food's textural attributes. Pressure and volume measurements have received limited attention in the frying literature. In this study, the changes in moisture content, oil uptake, temperature, pressure, and volume were measured as a function of frying time for potato cylinders. The volume change immediately after frying and after the cylinders had cooled was measured using a modified liquid displacement method. Fried cylinders continued to shrink post-frying. During frying, pressure and temperature showed similar increasing trends followed by plateauing of the temperature and a drop in pressure in the core. The measured gauge pressure remained positive throughout frying (t = 300 s) and up to 100 s after frying. The measured gauge pressure dropped to negative values for the remaining cooling period. The temperature decreased during cooling, which is expected to have led to water vapor collapse and a drop in gas pressure. A high capillary pressure is expected to have developed in the food matrix due to water loss, causing the effective gauge pressure to become negative. The negative gauge pressure is expected to drive oil uptake and shrinkage of the food matrix post-frying. • Modifications were made to improve a rapid volume measurement technique. • Temperature and pressure show a similar increasing trend initially during frying. • Gauge pressure is positive during frying but drops to negative values during cooling. • Negative gauge pressure is expected to drive oil uptake and shrinkage during cooling. [ABSTRACT FROM AUTHOR]

Information on viscoelastic properties is useful in industrial processing of foods as it provides insight into the structure of the material as a function of processing conditions. Corn kernels were hand sanded to obtain smooth and closely uniform samples with minimum damage to the kernel structure. The sample was tested using a dynamic mechanical analyzer. A miniature three point bending clamp was used to test the samples over a temperature range of 5-110°C at frequencies of 1 and 10 Hz in the moisture content ranging from 11.9-%24.7% (db). The average value of storage modulus (G') showed a decreasing trend with increase in the moisture content. The corresponding tan δ curve showed a peak representing the glass transition temperature. The kernels exhibited a transition in the range of 20-60°C, which is expected to be the glass transition range. The transition range is consistent with the results of similar studies on cornstarch. It embodies an average of several transition temperatures that arise due to the compositional diversity in the kernel. The individual corn kernels exhibit a wide sample-to-sample variation and structural heterogeneity. A very large number of test replications are required for consistent results. The accuracy and applicability of the dynamic testing in corn is limited due to the rigid sample specifications and testing conditions. Sample preparation and selection of appropriate loading conditions are also addressed. [ABSTRACT FROM AUTHOR]

Pasta samples were tested in the linear viscoelasticity range using a dynamic mechanical thermal analyzer over the temperature range of 25 to 95C and the water content range of 12 to 20% (weight of water/weight of solids). To obtain wholesome pasta samples at different moisture levels, the intermittent sorption technique was used. The behavior of G′ and tanδ versus temperature curves exhibited a transition, which was determined to be the glass transition by making comparisons to the literature values of glass transition for starch and semolina extrudates. At 12.5% water content, glass transition initiated at 48.7C. With increase in water content values, the initiating glass transition temperature decreased. At 19.7% water content, glass transition was observed in the temperature range of 36.9 to 57.3C. Although pasta contains about 13% protein fraction, it did not seem to affect the major part of glass transition range because the pasta proteins become mobile at temperatures greater than 80C and water content greater than 17%. [ABSTRACT FROM AUTHOR]

Abstract: Physico-chemical properties of fried rice crackers were studied as a function of fish powder content, processing conditions, frying temperature and frying time. The results showed that addition of fish powder content at 5, 10 and 15g/100g reduced the oil uptake by approximately 10, 14 and 22g/100g (db), respectively in comparison to the control without fish powder. The deep fried rice crackers mixed with fish powder tended to be lower in hardness, lower in expansion ratio and higher in bulk density in comparison to the control sample. The color parameter, L ∗ of fried rice crackers decreased with increase in fish powder content. In contrast, a ∗ and b ∗ values increased with increase in fish powder content. The moisture content of deep fried rice crackers decreased with increase in frying temperature and frying time. The oil uptake in fried rice crackers increased with increase in frying time but decreased with increase in frying temperature. With increase in frying temperature and time, the texture of rice crackers became harder, the bulk density increased, and the expansion ratio decreased. The optimum conditions resulting in desirable physico-chemical properties and minimum oil uptake were rice crackers with fish powder content of 9g/100g, fried at a temperature of 220°C for 60s. [Copyright &y& Elsevier]