Development of Healthy Low-Fat Snacks: Understanding the Mechanisms of Quality Changes During Atmospheric and Vacuum Frying

Excess consumption of fat, a main component in fried food, is a key dietary contributor to coronary heart disease and perhaps some types of cancer. Although consumers are interested in healthier snacks, they are not willing to sacrifice organoleptic properties. Vacuum frying might be an alternative for the production of nutritious, healthy, palatable, and novel snacks. The objective of this review is to discuss the effect of atmospheric deep-fat frying on the main microstructural components and quality parameters of fried food, to understand how quality can be improved by lowering the operating pressure and, therefore, the processing temperature.     

煎炸油在薯片煎炸过程中的品质变化

以煎炸油为研究对象,以薯片为煎炸原料,研究煎炸油煎炸过程中理化指标变化及各指标间的相关性。结果表明:在煎炸过程中,煎炸油的折光指数、色泽、酸值、羰基值和极性值均随时间的延长而增大;过氧化值随着煎炸时间延长先增大后逐渐减小;碘值随时间的延长而降低;比重、黏度、皂化值在煎炸过程中的变化无明显规律。酸值、羰基值、极性值、色泽和折光指数彼此之间有极显著的正相关性,且相关系数均大于0.9;煎炸油极性值的变化可通过色泽和酸值进行预测。     

Thermophysical Properties of Okara During Drying

The simulation of heat transfer during thermal treatments of foods requires the knowledge of thermophysical properties of the material. In this study some thermophysical properties of okara, such as density, specific heat, thermal conductivity, thermal diffusivity, heat transfer coefficient, and mass transfer coefficient, were obtained during a drying process. Okara was extruded in the shape of spherical pellets and then dried in a fixed bed dryer from 78% of moisture content (w.b.) until 3%. During the drying process, the water content and the temperature of the samples were periodically measured. The thermal properties were obtained from empirical correlations found in the literature, which use the okara centesimal composition, analyzed in a laboratory, and the relative humidity and velocity of the drying air, measured during the process. The results in this study showed that it is possible to estimate the thermal properties cited using the experimental moisture content history and the centesimal composition of the food.     

Determination of heat transfer coefficient during high pressure frying of potatoes

Besides traditional atmospheric frying, high pressure (super-atmospheric) frying might be an alternative approach to the frying of food products. In this study, convective heat transfer coefficient during atmospheric and high pressure frying was compared. For this purpose, a pressure cooker was modified to allow the immersion of a sample into frying oil under pressure and temperature measurement of sample and oil. Heat transfer coefficient versus frying time was determined on potato slabs using changes of total mass of the experimental set-up. At the pressure of 2 bar, the results showed an almost doubled heat transfer coefficient compared to the atmospheric pressure frying. The knowledge of heat transfer coefficient during pressure frying is expected to allow accurate determination of temperature distribution and hence the kinetic calculations to lead to development of an alternative frying process.     

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.     

Physical and thermal properties of potato chips during vacuum frying

Vacuum frying (1.33 kPa), with the aid of a de-oiling mechanism, was used to produce low-fat potato chips.The kinetics of oil absorption and oil distribution in the potato chips was studied so that effectiveness of the de-oiling system could be established. Non-linear regression was used to fit the experimental data to the models used to describe oil absorption in potato chips with time.Moisture content, oil content, microstructure, diameter and thickness expansion, bulk density, true density, and porosity of chips fried at different temperatures (120, 130, and 140 °C) was performed to evaluate the effect of process temperature on the product. The convective heat transfer coefficient at the oil-chip interface was determined for the same temperature range.The final oil content of the potato chips was 0.072 ± 0.004, 0.062 ± 0.003, and 0.059 ± 0.003 g/g solid for frying temperatures of 120, 130, and 140 °C, respectively. These values are lower (80-87% less) than those found in the not de-oiled potato chips, which indicates that the de-oiling mechanism is crucial in vacuum frying processing. A significant difference (P < 0.05) was observed in oil content and oil distribution within temperatures. The rate of change in product quality attributes was greatly affected by temperature; however, the final values of moisture content, bulk density, true density, porosity, diameter shrinkage, and thickness expansion were not affected by temperature.During vacuum frying, the convective heat transfer coefficient changed considerably as frying progressed; moreover, it increased with temperature reaching a maximum between 2200 and 2650 W/m² K depending on frying temperature.     

Applying an intelligent model and sensitivity analysis to inspect mass transfer kinetics,shrinkage and crust color changes of deep-fat fried ostrich meat cubes

The objectives of this study were to use image analysis and artificial neural network (ANN) to predict mass transfer kinetics as well as color changes and shrinkage of deep-fat fried ostrich meat cubes. Two generalized feedforward networks were separately developed by using the operation conditions as inputs. Results based on the highest numerical quantities of the correlation coefficients between the experimental versus predicted values, showed proper fitting. Sensitivity analysis results of selected ANNs showed that among the input variables, frying temperature was the most sensitive to moisture content (MC) and fat content (FC) compared to other variables. Sensitivity analysis results of selected ANNs showed that MC and FC were the most sensitive to frying temperature compared to other input variables. Similarly, for the second ANN architecture, microwave power density was the most impressive variable having the maximum influence on both shrinkage percentage and color changes.     

养殖大黄鱼低温真空油炸的工艺

养殖大黄鱼肉鲜味美,将其加工制成油炸方便食品,可以拓宽大黄鱼加工方式,改善其加工品质,提高大黄鱼的经济价值,丰富我国鱼类的市场品种,满足广大不同消费群体的需求.本文以新鲜大黄鱼为原料,采用低温真空油炸技术进行处理,试验得出大黄鱼低温真空炸鱼食品生产的最佳工艺条件为:在真空度为0.03MPa.温度为145℃下油炸120 s,此时,生产出的大黄鱼休闲食品,颜色金黄透明,鱼肉软硬适中,口感好,其蛋白质含量≥80%,水分含量≤6%.     

子芋真空油炸最佳工艺研究

本文研究子芋油炸时的工艺特性,包括：油炸温度、真空度、时间和原料厚度对子芋重要营养成分α型VE的保存,美拉德反应程度以及产品酥脆度的影响,提出将真空油炸技术应用于多子芋酥产品的加工,采用正交试验筛选真空油炸工艺条件。所选出的最佳工艺条件为：真空度0．0825Mpa,油炸温度110℃,油炸时间15min,原料厚度0．8cm。按此生产的产品品质远胜于常压油炸产品,并且原料的重要在养成分α型VE的保存率比常压油炸产品高3倍,产品理化和卫生指标符合食品卫生标准。     

Vacuum frying process of gilthead sea bream (Sparus aurata) fillets

Vacuum frying was tested as an alternative technique to develop low oil content fried gilthead sea bream fillets. Three oil temperatures for vacuum frying (90, 100, and 110 °C) were considered. For each temperature the times investigated were 1, 2, 3, 4, 5, 6, 8 and 10 min. To compare the effect of vacuum frying to atmospheric frying on the characteristics of gilthead sea bream fillets and frying rate, treatment at 165 °C was considered. The effect of oil temperature and pressure conditions on the drying process and oil absorption of sea bream fillets was investigated. Other product attributes such as shrinkage and colour were analyzed. Atmospheric frying (165 °C) produces a greater decrease in the mass of the fillets than vacuum frying treatment. Compared with atmospheric frying, oil content of vacuum-fried fish fillets was lower. After ten minutes of treatment the values obtained for vacuum frying were 0.14 ± 0.01 g_oil/g_{dry solid}, 0.18 ± 0.02 g_oil/g_{dry solid} and 0.12 ± 0.01 g_oil/g_{dry solid} for 90 °C, 100 °C and 110 °C respectively and 0.27 ± 0.01 g_oil/g_{dry solid} for traditional frying at 165 °C. Atmospheric frying was the treatment that produced the greatest shrinkage in the fillets reaching values of 36.8% with respect to the fresh sample after ten minutes of treatment. For vacuum treatments shrinkage values ranged between 23.7% and 33.0% at 100 °C and 110 °C respectively after 10 min of frying. According to the results, the vacuum treated samples became lighter, less greener and more yellow.

Industrial relevance

Healthy products are a tendency in the international market. Vacuum frying offers some advantages that can include: the preservation of natural colour and flavours of the products due to low temperature and low oxygen content during the process (better than with conventional deep fat frying), and has less adverse effects on oil quality. The use of this technology on fish products can improve the problems of market saturation at the present time for some species like gilthead sea bream (Sparus aurata).     

Color Development in a Model System During Frying: Role of Individual Amino Acids and Sugars

The color of fried potato products is limited by reducing sugars, but can be affected by free amino acids. Filter paper discs saturated with solutions of amino acids in combination with glucose, fructose and sucrose were fried in oil to investigate color formation. Four phases of color development were identified; equilibrium, lag, rapid and slow phase, corresponding to the water content of the system. Lysine, 7-aminobutyric acid and glycine produced most color and glutamic acid least. Fry color of glucose and fructose systems was very similar, but sucrose systems produced less color. Glucose and fructose systems were not affected by pH changes, but there was a slight effect on sucrose systems.     

Influence of temperature on heat transfer coefficient during moderate vacuum deep-fat frying

The objective of this study is to analyze the influence of temperature and reduced pressure on the convective heat transfer coefficient, h, during frying of products with different area/volume ratio. h was determined from surface temperature and moisture loss experimental data during frying of potato cylinders and “churros”, at different oil temperatures (100, 120 and 140 °C) and moderate vacuum (19.5–25.9 kPa). The results obtained during vacuum frying were compared with those obtained at atmospheric pressure, both for the same oil temperature (140 °C) and for the same thermal gradient (40 °C). During frying, h changes considerably, reaching a maximum between 700–1600 Wm⁻² K⁻¹ in vacuum frying and 800–2000 Wm⁻² K⁻¹ in atmospheric frying. To quantify the effect of oil temperature, pressure and size of the product on h, a parameter called “bubbling efficiency”, BE, was defined. BE relates the bubble departure radius and the area/volume ratio of the product. An equation (the derivative of the Gompertz function) was proposed to estimate the mean heat convective coefficients for each frying condition as a function of BE (R² = 0.957). The relation between h and BE shows a maximum corresponding to an optimal bubbling pattern. Most of the vacuum frying settings are outside this optimum, being affected by the insulation effect of bubbles covering the surface.     

Use of Artificial Neural Network to Predict Temperature, Moisture, and Fat in Slab-Shaped Foods with Edible Coatings During Deep-Fat Frying

ABSTRACT: An artificial neural network (ANN) was developed to predict heat and mass transfer during deep-fat frying of infinite slab-shaped foods coated with edible films. Frying time, slab half-thickness, film thickness, food initial temperature, oil temperature, moisture diffusivity of food and film, fat diffusivity through food and film, thermal diffusivity of food, heat transfer coefficient, initial moisture content of food, and initial fat content of food (mf_o) were inputs. Temperature at the center (T₁), average temperature (T_ave), fat content (mf_ave), and moisture content (m_ave) of food were outputs. Four ANNs with 50 nodes each in 2 hidden layers with learning rate = 0.7 and momentum = 0.7 provided most accurate outputs, that is maximum absolute errors for T₁ and T_ave were < 1.2 °C, < 0.004 db for m_ave, and < 0.003 db for mf_ave. The predictions of mf varied linearly with mf.     

蛋白面包贮藏期间理化指标的变化

测定了20℃条件下蛋白面包和酵母面包的理化指标的变化。通过水分含量、水分活度、自由水含量、结合水含量、支链淀粉结晶度、硬度和弹性的测定,得出蛋白面包与酵母面包相比具有较好的品质,在贮藏期间抗老化效果较好,并可延长货架期。为研制新型蛋白面包提供理论参考。     

Modeling deep-fat frying for control of acrylamide reaction in plantain

This paper discusses the possibility of controlling acrylamide formation/elimination reactions in plantain during frying. A 2D model including heat and vapor transfer and acrylamide reactions was developed. The model was validated against experimental data, consisting of the plantain core temperature and average water and acrylamide contents. Validations were made on two different typical plantain-based foods, i.e. “tajadas” (thick product) and “tostones” (thin product), in which the acrylamide contents were found to be 0.24 and 0.44 mg kg⁻¹ (fat-free dry basis), respectively. The simulations highlighted that non-isothermal heat treatment is a good strategy to reduce the acrylamide content (up to 50% reduction). However, controlling the asparagine content in the raw material through maturity stage selection or by implementing immersion pretreatments is an easier way to mitigate the acrylamide net amount in plantain products.     

真空回潮对烟叶质量的影响

为验证真空回潮过程对烟叶质量的影响,在同一条件下,对高中低3个档次有代表性的9种主料烟叶进行了使用与不使用真空回潮机处理的重复试验验证和对比分析。结果表明,与不使用真空回潮机相比,使用真空回潮机的烟叶碎片率较低;烟叶的总糖、还原糖、总碱和糖碱比有所降低,而总氮、钾和氯变化不明显;对中低档烟叶的香气质和香气量没有明显影响,但减少杂气,降低刺激性效果明显;高档烟叶的香气量和烟气浓度稍有降低,但杂气减少,刺激性降低。     

Optimisation of lipase-catalysed interesterification reaction for modulating rheological and heat transfer properties of frying oil

The present work reports the optimisation of enzyme interesterification reaction of rice bran oil (RBO) and refined, bleached, deodorized, palm olein (RBDPO) blend using immobilized 1,3-specific lipase, to improve the kinematic viscosity and heat transfer coefficient of oil, important for characterising heat transfer during the frying process. Four variables, namely RBO (20–80%) in RBO–RBDPO blend, reaction temperature (25–65 °C), enzyme concentration (1–13%, w/w) and reaction time (1–13 h) were selected and optimised using response surface methodology (RSM) coupled with central composite rotatable design (CCRD). The optimisation results predicted that optimum reaction conditions for preparing enzyme interesterified oil, having minimum kinematic viscosity (2.63 × 10⁻⁶ m² s⁻¹) and maximum heat transfer coefficient (262.0 Wm⁻² °C⁻¹) were at 62% RBO, temperature 65 °C, enzyme concentration 10% (w/w) and time 6.4 h. The predicted values were validated experimentally and corroborated with DSC melting profile and triacylglycerol molecular species data. This investigation could help snack food industries to develop suitable oils for frying operations.     

Effects of Heating,Vacuum Drying and Steeping on Gelatinization Properties and Dynamic Viscoelasticity of Various Starches

Starches having A‐ and B‐type X‐ray diffraction patterns (A‐ and B‐type starches) were modified by heating at 120 °C for 2 h (HT), vacuum drying at room temperature for 20 h (VD) and steeping at 50 °C for 20 h (ST). The properties of starches were compared using differential scanning calorimetry (DSC) and dynamic viscoelasticity behavior during heat processing (G' behavior). As observed by DSC, HT rarely changed the gelatinization properties for A‐type starches, but decreased the gelatinization temperatures and enthalpies (ΔH) for B‐type starches. A shift of the X‐ray diffractograms from B‐type to A‐type patterns was not detected after HT. Similar changes in gelatinization properties were observed for B‐type starches after VD. ST increased the gelatinization temperatures and also narrowed the gelatinization temperature range irrespective of crystal type. Both HT and VD decreased the peak temperature (T_p) in G' behavior and increased the peak G' value for B‐type starches. ST increased T_p and also decreased the peak G' value irrespective of starch crystal type. G' values after reaching T_p — which indicate the viscoelasticity of the swollen starch granules without breakdown — showed significant increases only for B‐type starches after HT.     

Physicochemical and fatty acid characteristics of stewed pork as affected by cooking method and time

This study was designed to investigate the effects of cooking on physicochemical and fatty acid characteristics of stewed pork. Pre‐fried or raw pork belly cubes were stewed for 60, 90, 120, 150 or 180 min. After cooking, proximate chemical composition, texture, sensory evaluation, lipid oxidation, fatty acid profiles and cholesterol content were determined. Prolonged cooking time resulted in higher percentages of dry matter, fat and fat loss in stewed cubes (P < 0.01), and pre‐frying also increased fat loss. Tenderness and elasticity values of texture profile analysis and sensory scores were the highest for the cubes stewed for 180 min or by pre‐frying combined with stewing for 150 min. Pre‐frying and extended cooking time significantly increased lipid oxidation (P < 0.01). Cooking modified fatty acid profiles which altered the derived cardiovascular indices, and reduced cholesterol content. Prolonged stewing improved eating quality and most nutritional values of pork belly.