Oil partitioning between surface and structure of deep-fat fried potato slices: A kinetic study

The present work deals with the kinetics of partitioning of oil on the surface as well as in the structure during holding of fried potato slices at elevated temperatures (100, 120, 140, 160 and 180 °C) compared with controls. After frying, the oil present on the surface migrates into structure due to condensation of vapor inside the product resulting in the creation of a vacuum. However, the oil present on the surface need not migrate into the structure, if the fried product is held at elevated temperatures. Further, the excess oil, which did not migrate into structure, can be removed by absorbent paper. The oil partition coefficient, defined as the ratio of oil present on the surface to the structure, during holding of samples at 180 °C was found to be 3.06, whereas the oil partition coefficient of the sample held at ambient temperature was 0.53, which indicates the availability of oil on the surface of fried product held at elevated temperature. The mass transfer coefficient of oil corroborated with the above finding. The holding of deep-fat fried product at 180 °C followed by the removal of oil from the surface using high absorbent paper reduced the oil content of the final product from 0.440 to 0.332 kg of oil/kg dry solids.     

Kinetics of oil uptake during frying of potato slices:: Effect of pre-treatments

Oil uptake in fresh, blanched and, blanched and dried potato slices was studied during frying. Potato slices blanched in hot water (85 °C, 3.5 min) and potato slices blanched (85 °C, 3.5 min) and then dried until to a moisture content of ∼60 g/100 g (wet basis) were deep fried in sunflower oil at 120, 150 and 180 °C. A control treatment consisted of unblanched potato slices without the pre-drying treatment (fresh samples). It was studied applying two empirical kinetic models in order to fit the oil uptake during frying: (i) a first order model; (ii) a proposed model, with a linear time behavior for short times, while time independent for long times. Oil uptake was high even for short frying times at the different temperatures tested suggesting that oil wetting is an important mechanism of oil uptake during frying. For control slices, oil uptake increased approximately by 32% as the frying temperature decreased from 180 to 120 °C at moisture contents ?1 g water/g dry solid. No apparent effect of frying temperature in oil uptake was observed at moisture contents ?0.5 g water/g dry solid in fried slices previously blanched and dried. The two kinetic models studied fitted properly the values of oil uptake during frying, with similar correlation coefficient r².     

Reduction of acrylamide formation in potato slices during frying

Reduction of acrylamide formation in potato chips was investigated in relation to frying temperature and three treatments before frying. Potato slices (Tivoli variety, diameter: 37 mm, width: 2.2 mm) were fried at 150°C, 170°C and 190°C until reaching moisture contents of ∼1.7 g water/100 g (total basis). Prior to frying, potato slices were treated in one of the following ways: (i) soaked in distilled water for 0 min (control), 40 min and 90 min; (ii) blanched in hot water at six different time-temperature combinations (50°C for 30 and 70 min; 70°C for 8 and 40 min; 90°C for 2 and 9 min); (iii) immersed in citric acid solutions of different concentrations (10 and 20 g/l) for half an hour. Glucose and asparagine concentration was determined in potato slices before frying, whereas acrylamide content was determined in the resultant fried potato chips. Glucose content decreased in ∼32% in potato slices soaked 90 min in distilled water. Soaked slices showed on average a reduction of acrylamide formation of 27%, 38% and 20% at 150°C, 170°C and 190°C, respectively, when they were compared against the control. Blanching reduced on average 76% and 68% of the glucose and asparagine content compared to the control. Potato slices blanched at 50°C for 70 min surprisingly had a very low acrylamide content (28 μm/kg) even when they were fried at 190°C. Potato immersion in citric acid solutions of 10 and 20 g/l reduced acrylamide formation by almost 70% for slices fried at 150°C. For the three pre-treatments studied, acrylamide formation increased dramatically as the frying temperature increased from 150°C to 190°C.     

The effects of oils and frying temperatures on the texture and fat content of potato crisps

The purpose of the study was to determine the effects of oils and frying temperatures on fat content and texture of potato crisps.     

Characterization of the frying process of fresh and blanched potato strips using response surface methodology

r ² was better and the lack of fit was not significant, although high-temperature short-time blanching before frying resulted in loss of firmness and discolouring, and increased the percentage of oil retained by the strips, causing sensorial quality loss. Received: 4 October 1999 / Revised version: 15 December 1999     

Modeling water loss and oil uptake during vacuum frying of pre-treated potato slices

The objective of this research was to determine the kinetics of water loss and oil uptake during frying of pre-treated potato slices under vacuum and atmospheric pressure. Potato slices (diameter: 30 mm; width: 3 mm) were pre-treated in the following ways: (i) raw potato slices “control”; (ii) control slices were blanched in hot water at 85 °C for 3.5 min; (iii) blanched slices were dried in hot air until reaching a moisture content of ∼0.6 g water/g dry basis. The slices were fried under vacuum (5.37 kPa, absolute pressure, at 120, 130 and 140 °C) and atmospheric conditions (at 180 °C). Two models based on the Fick's law were used to describe water loss: (i) with a constant effective diffusive coefficient; and (ii) with a variable effective diffusive coefficient. Oil uptake data were fitted to an empirical model, with a linear behavior for short times whereas the model was time independent for long times. The variable diffusivity model better fitted experimental water loss, giving values of effective diffusivity between 4.73 × 10⁻⁹ and 1.80 × 10⁻⁸ m²/s. The proposed model for the study of the kinetics of oil uptake fitted the experimental data properly. Control and blanched vacuum fried potato chips increased their final oil contents to 57.1% and 75.4% respectively, when compared with those fried at atmospheric pressure. However, the oil absorption of dried vacuum fried potato chips diminished by ∼30%.     

Optimization of processing conditions to reduce oil uptake and enhance physico-chemical properties of deep fried rice crackers

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 15 g/100 g reduced the oil uptake by approximately 10, 14 and 22 g/100 g (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 9 g/100 g, fried at a temperature of 220 °C for 60 s.     

Effect of hydrocolloid coatings on the heat transfer and oil uptake during frying of potato strips

The effect of the hydrocolloid coatings (gellan gum and guar gum) of a food matrix on the heat transfer during a frying process was investigated and correlated with the oil uptake. While the potato strips coated with the hydrocolloid solutions were fried at 170 °C, the hydrocolloid coatings significantly reduced the heat transfer coefficients as well as oil uptake which became more apparent at higher concentrations. Thus, the oil uptake was found to have a good polynomial correlation (R² > 0.99) with heat transfer coefficients, suggesting that a rapid heat transfer led to an increase in the oil content of the fried samples.     

Influence of the vacuum break conditions on oil uptake during potato post-frying cooling

Reduced pressure frying is an alternative to conventional frying that enables products to be obtained at lower processing temperatures with lower fat content. The oil uptake in frying mainly occurs during the subsequent cooling stage. With vacuum frying, this stage necessarily includes a period of vacuum break when the system recovers the initial pressure. The different conditions under which this pressurisation occurs can influence the final oil content of the product. To study this effect, potatoes of the “Monalisa” variety, with different geometries, were fried at 140 °C and moderate vacuum (24.9 kPa). Various combinations of draining times (30, 60, and 90 s) and vacuum break velocity, VBV (0.75, 2.21, 4.43 and 12.43 kPa s⁻¹), were tested for this stage, and the final oil content of the product determined by comparison with the dry weight. The results showed that both parameters have a significant influence (α < 0.05) on oil uptake. A short draining time and a low vacuum break velocity result in greater final fat content. There is a linear relationship between the oil uptake and the inverse of VBV, following the Washburn equation. The influence of VBV is such that differences of up to 70% in the final fat content can be obtained in the range tested.     

Understanding potato chips crispy texture by simultaneous fracture and acoustic measurements, and sensory analysis

The fracture and acoustic properties of six commercial potato chips that differ in sensory hardness and sensory crispness were analysed and related in this work. Principal component analysis showed a correlation among the sensory attributes and the instrumental parameters (both mechanical and acoustic). Two components mainly explained the behaviour of the different potato chips. The first component was positively related to the number of force and sound events, to sound pressure level maximum, to the area under the force curve, and to sensory crispness, and negatively related to fat content; and the second component was positively related to the gradient (slope of the first part of the curve), the potato chip thickness, and to sensory hardness and sensory crispness. The behaviour of the different potato chips was explained by either one of the two components or by both components. Results indicate that certain degree of sensory hardness is necessary for higher crispness perception.     

DEFINITION OF OUTLIERS USING UNSUPERVISED PRINCIPAL COMPONENT SIMILARITY ANALYSIS FOR SENSORY EVALUATION OF FOODS

ABSTRACT

As unsupervised classifications, principal component similarity (PCS) and cluster analysis (CA) were compared for outlier detectability in panel evaluation. By rotating the reference, PCS can define outlying panelists based on the similarity of their evaluation patterns with that of the reference panelist. As a result, the outliers detected on PCS scattergrams are dependent on the reference selected, whereas, outliers detected by CA are based on dissimilarity, thus being rather unilateral. The definition of outliers in PCS is new as it is different from the currently most popular definitions based on dissimilarity. For verifying the outliers thus obtained, random-centroid optimization (RCO) was applied for selecting the best samples by each cluster of panelists. This combination of PCS/RCO may be useful in finding the likeness distribution among consumers and then in creating food products to correctly respond to the demands of different consumer groups.     

Starch transformation and structure development in production and reconstitution of potato flakes

Changes of parenchymous tissue structure and transformations of starch in the production and reconstitution of drum-dried potato flakes as instant mashed potatoes were investigated by light microscopy, iodine binding capacity, thermal analysis, wide-angle X-ray powder diffraction and rheology. Instant mashed potatoes are suspensions which are formed by separating whole potato tissue into individual cells. Mechanical stress during mashing and the subsequent steps also lead to undesirable cell disruption and extracellular starch. The stabilizing effect on starch by gelatinization and retrogradation in the preheating and cooling step was found to be far less important than mentioned in literature. While amylopectin does not retrograde, amylose crystallizes de novo during preheating, probably further aggregates during the cooling step and the ageing of mashed potatoes and melts fully during drum drying. The total amount of cells and the proportion of single cells to cell clusters as dispersed phase determine product flow properties as much as the amount of extracellular starch in the continuous fluid phase. Therefore, the iodine binding value of extracellular starch cannot serve as only measure to judge texture of mashed potato products.     

Color changes and acrylamide formation in fried potato slices

The objective of this work was to study the kinetics of browning during deep-fat frying of blanched and unblanched potato chips by using the dynamic method and to find a relationship between browning development and acrylamide formation. Prior to frying, potato slices were blanched in hot water at 85 °C for 3.5 min. Unblanched slices were used as the control. Control and blanched potato slices (Panda variety, diameter: 37 mm, width: 2.2 mm) were fried at 120, 150 and 180 °C until reaching moisture contents of ∼1.8% (total basis) and their acrylamide content and final color were measured. Color changes were recorded at different sampling times during frying at the three mentioned temperatures using the chromatic redness parameter a¹. Experimental data of surface temperature, moisture content and color change in potato chips during frying were fit to empirical relationships, with correlation coefficients greater than 90%. A first-order rate equation was used to model the kinetics of color change. In all cases, the Arrhenius activation energy decreases alongside with decreasing chip moisture content. Blanching reduced acrylamide formation in potato chips in ∼64% (average value) in comparison with control chips at the three oil temperatures tested. For the two pre-treatments studied, average acrylamide content increased ∼58 times as the frying temperature increased from 120 to 180 °C. There was a linear correlation between acrylamide content of potato chips and their color represented by the redness component a¹ in the range of the temperatures studied.     

Changes of polysaccharide content and texture of potato during French fries production

The purpose of the present study was to determine the changes in non-starch polysaccharide and lignin contents of potato during French fries production and also the relationship between the texture of the finished product and half-products, as a result of processing at each stage under investigation. The samples for laboratory studies were taken from potato tubers, strips and French fries collected from nine locations of a technological line. The greatest changes in non-starch polysaccharide content and texture of potatoes resulted from blanching and frying. The texture of French fries was mainly affected by pectin and cellulose. The texture of French fries can be predicted from the measurements of the texture of potato strips after blanching.     

Vacuum frying reduces oil uptake and improves the quality parameters of carrot crisps

Recent consumer trends towards healthier and low fat products have had a significant impact on the snack industry. The objective of this study was to examine the most important quality parameters of vacuum and atmospheric fried carrot slices in order to identify the specific advantages of vacuum technology. Said parameters include oil uptake, colour changes, and trans α and β-carotene degradation. Equivalent thermal driving forces were used (ΔT = 60 °C and 80 °C) to compare the processes, maintaining a constant difference in temperature between the oil and the boiling point of water at the working pressure. The results showed that vacuum frying can reduce oil content by nearly 50% (d.b.) and preserve approximately 90% of trans α-carotene and 86% of trans β-carotene. This process also allowed for the raw carrot colour to be preserved, which was reflected by good correlations between a∗ and trans β-carotene content, b∗ and trans α-carotene content, and hue and total carotenoid content.     

Effects of frying parameters on the colour development of fried potatoes

The effects of frying time and temperature on the colour development of potatoes during frying was studied. Potato disks 0.025 m in diameter and 0.005 m thick were used. Sunflower oil was used as a frying medium at temperatures 150 °C, 160°C, 170°C and 180°C. Colour parameters of Hunter L and b values followed first-order reaction kinetics during frying. The temperature dependence of the rate constants for Hunter L and b values showed good agreement with Arrhenius relation, the activation energies, Ea, being equal to 22.67 kcal/mol and 17.13 kcal/mol, respectively. Hunter a value increased as frying time and/or temperature increased. A multiple regression equation was developed for total colour change as a function of time and temperature. The increase in time and temperature increased total colour change. Received: 22 October 1999     

Effect of enzymatic treatments on the rheological and oil-resisting properties of wheat flour-based frying batters

A new enzymatic approach was introduced to reduce the oil uptake of batter-coated fried foods. Cross-linking (transglutaminase) and cell wall-degrading (viscozyme) enzymes were incorporated into the formulation of wheat flour-based frying batters, and their rheological/oil-resisting effects were evaluated. The transglutaminase treatment increased the pasting viscosities of wheat flour whereas viscozyme distinctly reduced these properties. The batters treated with transglutaminase exhibited the highest steady-shear viscosity, followed by the control and viscozyme-treated samples. Dynamic viscoelastic results showed that transglutaminase improved the elastic properties of frying batters, while their viscous characteristics became more dominant when viscozyme was used. These rheological features were favorably correlated with the adhesive properties of batters. During frying, the moisture loss of frying batters was retarded by transglutaminase. The incorporation of transglutaminase reduced the oil uptake of frying batters by 19.6%, thus contributing to the enhancement of the oil-barrier property.     

切片马铃薯护色及涂膜保鲜

研究了不同护色处理对去皮切片马铃薯护色效果的影响，并采用可食性膜对马铃薯切片进行涂膜保鲜。研究结果表明：护色效果最理想的护色液为1．5％柠檬酸 1．0％抗坏血酸 0．15％氯化钙。采用低功率微波辐射对抑制马铃薯多酚氧化酶活性也有明显的效果。护色的马铃薯后再经1．5％的壳聚糖或1．5％的海藻酸钠涂膜处理，在冷藏条件下贮藏1周，其外观色泽基本保持良好。     

Development of low-fat gluten and starch fried matrices with high fiber content

Low-fat and high dietary-fiber diets are important elements in the prevention of chronic diseases. The objective of this work was to understand the effect of wheat bran inclusion in large amounts to a gluten–starch matrix, in structure formation and associated quality attributes, during deep-fat frying. Matrices were prepared mixing 12 g of gluten and 88 g of wheat starch per 100 g of dry solids, ensuring a moisture content of 40 g water/100 g dough. Starch was gradually replaced by wheat bran (up to 40 g/100 g dry solids), and lack of structure formation was overcome by partially replacing starch with pregelatinized corn starch. Samples were fried at 170 °C and oil absorption in high fiber products was reduced through post-frying centrifugation. Pregelatinized corn starch addition allowed obtaining an adequate structure in formulations with high wheat bran content, reducing oil absorption by 35% in formulations with up to 20 g wheat bran/100 g dry solids. It was possible to obtain a low-fat product (70% reduction) with high fiber content (40 g/100 g dry solids) after centrifugation, confirming the importance of oil absorption during post-frying cooling.     

Effect of salt and sucrose content on dielectric properties and microwave freeze drying behavior of re-structured potato slices

Potato puree was used to prepare re-structured potato slices. The effect of salt and sucrose content on microwave freeze drying (MFD) and the variation of the dielectric properties of the potato slices were studied. Results showed that the dielectric constant (ε′) and loss factor (ε″) of the potato purees decreased significantly after freezing. Both salt and sucrose addition increased ε′ and ε″ of the samples at low temperatures (−25 to −5 °C). The salt content had greater influence relative to sucrose content on dielectric properties of the samples. Sucrose addition shows insignificant influence on dielectric properties of the thawing samples; while for the salted samples, ε′ decreased gradually with increasing salt content and ε″ increased significantly with increasing salt content and temperature. MFD drying rate was significant higher after adding salt and sugar.