Effectiveness of modified zeolites as adsorbent materials for frying oils

Natural zeolite was modified by four different techniques namely using Tween80, β‐cyclodextrine and olive mill waste water at RT and hydrochloric acid at 110°C, and then modified zeolites were used as adsorbent materials in six consecutive days dough frying with refined hazelnut oil. Some parameters in the oil samples of control and experimental groups were measured and the ranges were determined as following; total polar materials (TPM)‐chromatography (4.09–70.22%), free acidity (0.16–1.19%), smoke point (221.50–184.00°C), conjugated dienoic acids (0.36–2.19%), L value (35.65–52.15), a* value (?0.18–5.98), b* value (?3.73–10.40), turbidity (0.70–10.40 NTU), viscosity (67.67–825.50 cP), and oil absorbed by the dough (5.10–8.85%). The results of this study have shown that both natural zeolite and modified zeolites have different level of activities as frying oil adsorbent materials. The best results were achieved with Tween80 modified zeolite for the TPMs, free acidity, instrumental color values, smoke point, and conjugated dienoic acid measurements. Similarly better result for turbidity was with olive mill waste water modified zeolite and for viscosity was with hydrochloric acid modified zeolite. It was determined that adsorbent treatment did not affect fat absorption level of fried dough. Practical applications : The results of this study have shown that natural zeolite modification with different techniques can improve its adsorption capacity significantly. In this respect, utilization of modified zeolite for frying oil recovery applications can be an industrially sound practice since natural zeolite is a very cheap and easily found material.     

No Evidence Found for Diels–Alder Reaction Products in Soybean Oil Oxidized at the Frying Temperature by NMR Study

It has been generally accepted that the Diels–Alder reaction mechanism is one of the major reaction mechanisms to produce dimers and polymers during heating process of vegetable oil. Soybean oil oxidized at 180 °C for 24 h with 1.45 surface area-to-volume ratio showed 36 % polymer peak area in gel permeation chromatogram. However, the NMR DEPT (Distortionless Enhancement by Polarization Transfer) 135 spectrum did not show any signals of possible Diels–Alder products. A fraction separated from the oxidized soybean oil by column chromatography contained 98 % polymers, but again, showed no signals of proposed Diels–Alder products in the DEPT 135 spectrum. Methyl oleate and triolein without a diene required for the Diels–Alder reaction produced 27 and 63 % of total polymers, respectively, under the same condition. This indicates that the polymers must be produced by reactions other than the Diels–Alder reaction for these oils. This study shows that the Diels–Alder reaction is not the major reaction to produce polymers during oxidation of soybean oil, within the DEPT 135 spectroscopy sensitivity level, about 5 mol %.     

Effect of Tocopherols on the Anti-Polymerization Activity of Oryzanol and Corn Steryl Ferulates in Soybean Oil

Steryl ferulates (SFs) are ferulic acid esters of phytosterols and/or triterpene alcohols which have potential as frying oil antioxidants. The objective of this study was to evaluate the anti-polymerization and antioxidant activity at frying temperatures of corn steryl ferulates (CSFs), rice steryl ferulates (oryzanol), and a mixture of CSFs with oryzanol, alone and with tocopherols. Antioxidant activity was measured by the reduction of polymerized triacylglycerol formation, and loss of olefinic and bisallylic protons from fatty acid double bonds by ¹H NMR. CSFs and oryzanol slowed the oxidation and polymerization of soybean oil triacylglycerols heated to 180 °C more effectively than a mixture of alpha and gamma tocopherols. CSFs were more effective at preventing polymerization than oryzanol, but when oryzanol was combined with tocopherols, they all had similar antioxidant activity. In addition, tocopherols had a protective effect on SFs. Corn SFs were degraded more quickly during heating than oryzanol, however, the phytosterol constituents of corn SFs, sitostanol and campestanol, were actually more resistant to degradation compared to the phytosterol constituents of rice SFs. Results demonstrate that corn and rice SFs may be effective antioxidants for use in frying oils, and that their activity is enhanced in the presence of tocopherols.     

MODELING WATER LOSS DURING FRYING OF POTATO STRIPS: EFFECT OF SOLUTE IMPREGNATION

ABSTRACT

The effect of solute impregnation on water loss and oil uptake during potato strip frying was studied. Blanched potato strips were impregnated at 25°C by soaking in a solution of sucrose–NaCl–water, 20–5–75% by weight. After rinsing and air drying, strips were deep fried in sunflower oil at 160, 170 and 180°C. A control treatment, consisting of potato strips blanched but not soaked and later air dried was also conducted. Solute impregnation provided a decrease of the oil uptake. Two models, based on Fick's law were used to describe water loss during frying. The first one is the classic model with an effective moisture diffusion coefficient assumed a constant value. The second model considers that diffusion coefficient varies during the frying process. For a given frying temperature, constant diffusion coefficient for control potatoes resulted in lower values than the impregnated ones. The variable diffusivity model showed a two-stage behavior: during the first stage of frying, diffusion coefficient increased with frying temperatures, but from a given time on an inverse behavior began. This last fact was found to be related to an increase of the measured peak force needed to penetrate the potato crust.     

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 frying oils on the postprandial endoplasmic reticulum stress in obese people

The addition of antioxidants to frying oil reduces postprandial oxidative stress and the inflammatory response. ER stress may trigger both inflammation and oxidative stress processes. We aimed to determine the biological effects of the intake of four models of frying oils on postprandial ER stress in peripheral blood mononuclear cells. Twenty obese people received four breakfasts following a randomized crossover design, consisting of muffins made with different oils (virgin olive oil (VOO), sunflower oil (SFO), and a mixture of seed oils (SFO/canola oil) with either dimethylpolysiloxane (SOD) or natural antioxidants from olives (SOP) added), which were previously subjected to 20 heating cycles. ER stress was assessed by measuring the mRNA levels of sXBP1, BiP, CRT, and CNX in peripheral blood mononuclear cells. Our study showed that the intake of the muffins made with SFO induced the postprandial increase of the mRNA levels of the ER stress‐sensor sXBP1, and the ER stress related chaperones BiP and CRT (all p‐values <0.05). The harmful effects associated with the use of SFO as frying oil, in terms of inflammatory response and postprandial oxidative stress, may be partially mediated by the induction of postprandial ER stress.     

Aldehydes contained in edible oils of a very different nature after prolonged heating at frying temperature: Presence of toxic oxygenated α,β unsaturated aldehydes

The evolution of the abundance of the different types of aldehydes, including those that are genotoxic and cytotoxic, oxygenated α,β unsaturated, in the headspace of extra virgin olive, sunflower and virgin linseed oils, submitted to frying temperature for prolonged periods of time, in a discontinuous industrial fryer, was analysed. Very close relationships were found between the abundance of the aldehydes in the three oils at a certain heating time and the original oil composition in the main components. The equations that related these parameters, which can be used for predictive purposes, show not only which acyl group each aldehyde comes from, but also its quantitative influence. This is the first time that the presence of 4-oxo-(E)-2-decenal, and 4-oxo-(E)-2-undecenal have been detected, not only in frying oils, but also in foods. Furthermore, the concentration of aldehydes such as 4-hydroxy-(E)-2-nonenal, (E)-4,5-epoxy-(E)-2-decenal, 4-hydroxy-(E)-2-hexenal, and 4-oxo-(E)-2-nonenal have been determined simultaneously for the first time in these edible oils submitted to frying temperature. The fact that significant concentrations of these toxic compounds were found in some oils before the oil reached 25% of the polar compounds is a cause of concern for human health.     

Influence of natural antioxidants on the formation of trans‐fatty‐acid isomers during heat treatment of sunflower oil

The intake of foods containing trans fatty acids (TFAs) can have deleterious effects on human health, mainly on the cardiovascular system. Thus, it is important to consider the processes that form TFAs in foods, and the alternatives to minimise their formation. The influence of two added natural antioxidants on TFA formation during heat treatment (120 h at 180°C) of sunflower vegetable oil were examined: rosemary extract (Rosmarinus officinalis L.) (1 g per kg oil) and lutein (0.1 g per kg oil). Changes in FA composition were determined using Ag‐ion SPE and gas–liquid chromatography, with total polar compounds determined using dielectric constant measurements and the index of atherogenicity was calculated. Total TFAs with ≥1 trans double bond increased from 0.91 to 1.71% in control samples; this increase was significantly less with both rosemary extract (1.55%) and lutein (1.43%) additions. Among the individual TFAs, significant increases were seen for C18:1,t‐9, C18:2,t‐9,t‐12 and C18:2,c‐9,t‐12/9‐t,12‐c. Polar compounds also increased, with the highest concentrations in control samples, and significantly less with both rosemary extract and lutein additions. According to results of our study, we can summarize that addition of lutein have greater effect on reduction of TFA formation than rosemary extract. Practical applications: Antioxidants, particularly from plants, are widely used in the food industry. They can provide benefits in food preparation, including improving colour, odour and stability, acting as acid regulators and natural preservatives. They have also become accepted by customers and consumers, and so indirectly they have had effects on consumer perception. Addition of natural antioxidants such as rosemary extract is usually limited by the sensory characteristics of the food, with one study showing that addition of rosemary extract at 1–3 g per kg vegetable oil is recommended. The effects of antioxidants on the formation of TFAs in vegetable oils has not been well studied in the literature. Among the already known benefits, the use of such antioxidants as functional ingredients in lipid technologies might reduce the formation of TFAs during thermal treatment.     

Modelling of energy flows in potato crisp frying processes

Food frying is very energy intensive and in industrial potato crisp production lines frying is responsible for more than 90% of the total energy consumption of the process. This paper considers the energy flows in crisp frying using a First Law of Thermodynamics modelling approach which was verified against data from a potato crisp production line. The results indicate that for the frying process considered, most of the energy used is associated with the evaporation of water present in the potato and on the surface of potato slices. The remainder is from evaporation of frying oil and air of the ventilation system and heat losses from the fryer wall surfaces by convection and radiation. The frying oil is heated by an industrial gas furnace and the efficiency of this process was calculated to be 84%. The efficiency of the overall frying process which was found to be of the order of 70% can be improved by employing exhaust heat recovery and optimising other operating and control parameters such as exhaust gas recirculation.     

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.