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.     

Non-enzymatic browning and estimated acrylamide in roots,tubers and plantain products

Acrylamide has been discovered in foods, especially high carbohydrate foods that are dry-cooked (baked, fried or roasted) at high temperatures which also create the conditions for non-enzymatic browning. Baking, frying and roasting are common food preparation methods in Ghana. Fifteen different high carbohydrate foods in Ghana, that undergo dry-cooking, have been investigated for non-enzymatic browning and acrylamide production. The products that showed notable non-enzymatic browning and acrylamide levels include fried sweet potato, plantain chips from the fresh produce, with their respective non-enzymatic browning and acrylamide values as 0.095 ± 0.006 optical density (OD), 1043 ± 47.6 parts per billion (ppb); 0.034 ± 0.03 OD, 568 ± 22.9 ppb. Roots and tuber products had relatively high non-enzymatic browning and acrylamide levels while plantain products showed low levels of non-enzymatic browning and acrylamide.     

The effect of asparaginase on acrylamide formation in French fries

Acrylamide formation in French fries was investigated in relation to blanching and asparaginase soaking treatments before final frying. Par-fried potatoes of Bintje variety were prepared by cutting strips (0.8 × 0.8 × 5 cm) which were blanched at 75 °C for 10 min. Unblanched strips were used as the control. Control or blanched strips were then dried at 85 °C for 10 min and immediately partially fried at 175 °C for 1 min. Finally, frozen par-fried potatoes were fried at 175 °C for 3 min to obtain French fries. Pre-drying of raw or blanched potato strips did not generate acrylamide formation as expected. Partial frying of pre-dried control potato strips generated 370 μg/kg of acrylamide and the final frying determined French fries with 2075 μg/kg of acrylamide. When control potato strips were treated with a 10000 ASNU/l asparaginase solution at 40 °C for 20 min, the acrylamide formation in French fries was reduced by 30%. When blanched potato strips were treated in the same way, the produced French fries have 60% less acrylamide content than blanched strips without the enzyme treatment. Soaking of blanched potato strips (75 °C, 10 min) in an 10000 ASNU/l asparaginase solution at 40 °C for 20 min is an effective way to reduce acrylamide formation after frying by reducing the amount of one of its important precursors such as asparagine.     

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.     

Effect of microwave pre-thawing of frozen potato strips on acrylamide level and quality of French fries

The objective of this study was to reduce frying time, and hence acrylamide level of French fries by microwave pre-thawing of frozen potato strips. Effect of this pre-treatment on acrylamide content and quality attributes of French fries was determined. Frozen par-fried potato strips (8.5 × 8.5 × 70 mm) were thawed in a microwave oven prior to final frying in sunflower oil at 170, 180, and 190 °C. Potato strips that were final fried without pre-thawing were considered as the control. Acrylamide analysis was performed by liquid chromatography–mass spectrometry (LC–MS) method. Microwave pre-thawing of frozen strips reduced the acrylamide level of French fries by 10% (from 17.7 to 15.9 ng/g), 89% (from 72.1 to 8.0 ng/g), and 64% (from 50.5 to 18.4 ng/g) for frying at 170, 180, and 190 °C, respectively, in comparison to the control samples. Quality attributes (texture, color, and oil content) of pre-treated strips were found to be comparable to those of the control.     

Characterization of chlorophyll degradation in banana and plantain during ripening at high temperature

Bananas fail to fully degreen when ripening at tropical temperatures, but this abnormal symptom does not occur in plantain. To elucidate the temperature effect on banana degreening, comparison of the colour change and chlorophyll degradation pathway between banana and plantain during ripening at 20 or 30 °C was carried out. Compared to bananas ripening at 20 °C and plantains at 20 °C or 30 °C, bananas at 30 °C contained significantly higher levels of chlorophylls, chlorophyllide a and pheophorbide a at the end of the ripening process, linearly correlating to the colour scores of a^∗, b^∗ and Hue angle. Whilst higher chlorophyllase activity was recorded in both banana and plantain at 30 °C as to the fruits at 20 °C, 30 °C inhibited Mg-dechelatase activity in banana, but not in plantain. The reduction of Mg-dechelatase activity in banana peel at 30 °C may contribute to repressed chlorophyll degradation and lead to uneven degreening.     

Extrusion of a hard-to-cook bean (Phaseolus vulgaris L.) and quality protein maize (Zea mays L.) flour blend

Heated extrusion was tested as an alternative process for incorporating “hard-to-cook” beans into food products. A 3² factorial design was used to evaluate extrusion conditions for a 40/60 (w/w) blend of “hard-to-cook” beans and quality protein maize. Tested extrusion variables were temperature (155, 170 and 185 °C) and moisture content (15.5, 17.5 and 19.5 g/100 g). Screw speed was fixed at 130 rpm. The extrudates obtained at 155 and 170 °C with 15.5% moisture had the best physical characteristics and were chosen for comparative analysis of nutritional changes between the unprocessed “hard-to-cook” bean/quality protein maize flour blend and the resulting extrudates. In vitro protein digestibility was higher in the extrudates (80%) than in the flour blend (76%). In vitro starch digestibility was higher at 155 °C (89%) and 170 °C (92%) than in the flour blend (12%). Processing conditions decreased dietary fibre content by 38% at 155 °C and 44% at 170 °C.     

The kinetics of acrylamide formation/elimination in asparagine–glucose systems at different initial reactant concentrations and ratios

The effect of initial reactant concentration and ratio on the kinetics of acrylamide formation and elimination was studied using diluted asparagine–glucose model systems, heated at temperatures between 120 and 200 °C. By means of single response modelling, acrylamide concentrations measured could be modelled using a simplified kinetic model, in which acrylamide formation and elimination reactions were included. Changing the reactant concentration in equimolar systems did not affect significantly the kinetic parameters (k_Fref and E_aF) for acrylamide formation, whereas the rate constant for acrylamide elimination increased with increasing reactant concentration, in the range from 0.01 M to 0.125 M. Modifying the reactant ratio, while keeping one of the reactants at a fixed concentration (0.125 M), did not affect the estimated parameters as compared to the equimolar system. In addition, multiresponse modelling was applied on three model systems with a different initial reactant ratio. Besides acrylamide, the concentration of the reactants and fructose and the level of browning were quantified. By means of deduction, a mechanistic model was proposed which was able to model all responses simultaneously in an adequate way. It appeared that caramelisation has a predominant role in browning, however, only in the system with an excess of sugar. The corresponding kinetic parameters estimated were in some cases significantly different, but in the same order of magnitude.     

Correlations of carotene with sensory attributes in carrots under different storage conditions

The all-trans-α-, all-trans-β-, and cis-carotene content, measured by HPLC–DAD and the main sensory attributes in two carrot varieties, of the years 2002 and 2003, during storage at 4 °C, 20 °C, −18 °C and −25 °C were determined. At 4 °C, increase of the total carotene content of 8% and 23% were found in the 1st and in the 2nd harvest year, respectively within 14 days of storage. Deep-frozen carrots were characterized as more “juicy”, less “tender”, “aromatic” and “sweet” compared to fresh carrots in both harvest years. Sensory attributes and chemical data were correlated, and it was shown that the carotene content was positively correlated with the attribute fibrous texture and negatively correlated with the attribute tender texture.     

Survival of Pseudomonas fluorescens on beef carcass surfaces in a commercial abattoir

The influence of a commercial chilling process (18 h at 10 °C followed by up to 78 h at 2 °C) on Pseudomonas fluorescens inoculated on beef carcass surfaces at four sites, neck (NE), outside round (OR), brisket (BR) and foreshank/brisket (FB) before chilling (“hot inoculated”) or after chilling for 24 h (“cold inoculated”) was investigated. Pseudomonas counts increased significantly at all sites on “hot inoculated” carcasses during storage, but on “cold inoculated” carcasses, counts declined or remained unchanged. On hot and cold inoculated carcasses, differences in Pseudomonas growth or survival were demonstrated between sites. No clear relationships were observed between Pseudomonas growth or survival and chiller relative humidity (RH) or surface water activity (a_w) at the different sites. These results were unexpected, and are discussed in relation to environmental factors that affect the growth/survival of P. fluorescens on carcass surfaces during chilling i.e. temperature, RH, and the relationship of these parameters to surface water activity (a_w).     

An experimental set-up for studying acrylamide formation in potato crisps

The objective of this work was to set up lab-scale equipment for production of crisps mimicking industrial conditions. Slices of Saturna potatoes were deep-fat fried for 2-4.5 min at 160 °C. A solid phase extraction method for acrylamide from potato crisps was used, and the extraction recovery was calculated to 95%. Acrylamide was analysed using liquid chromatography tandem mass spectrometry. The relative standard deviation was below 3% for analyses performed on the same day and below 5% for inter-day analyses. The limit of quantification was estimated to be 160 μg/kg potato crisps. The colour of potato slices was determined using a digital imaging method and related to the acrylamide content. There were tendencies that L*(lightness) decreased and that that a*(redness) and b*(yellowness) increased with increasing acrylamide content. In another experiment, potatoes with different glucose levels were fried for 4 min but no significant difference in acrylamide content (2200-2800 μg/kg) was observed. The experiment was repeated after three months of storage. The levels of acrylamide increased significantly to 8200-13200 μg/kg. The potatoes had been fertilized with different levels of nitrogen, but no relation was found between the nitrogen supplied and the acrylamide content. The experimental set-up was shown to give realistic and reproducible experimental data, regarding colour, water content and acrylamide levels. It will be used together with the analytical methods as a platform for further research on the formation of acrylamide.     

Moisture sorption isotherms – Experimental and mathematical investigations of orange (Citrus sinensis) peel and leaves

The aims of this work were to determine chemical composition and sorption isotherms of Tunisian orange peel and leaves of the “Maltaise” variety. These by-products were found to be rich in fibre, soluble sugars, protein, minerals and phenols. The equilibrium moisture contents of “Maltaise” peel and leaves were measured using the static gravimetric method at three temperatures (40, 50 and 60 °C) and in wide range of water activity (0.109–0.891). Desorption and adsorption data of peel and leaves were best fitted by the Peleg model at 40, 50 and 60 °C. The net isosteric heats of desorption and adsorption were determined from sorption isotherms. For both peel and leaves, the net isosteric heat of desorption was higher than the net isosteric heat of adsorption and both decreased continuously with increasing of the equilibrium moisture content.     

Higher acrylamide contents in French fries prepared from “fresh” prefabricates

A recent campaign indicated that French fries prepared from fresh prefabricates stored at about 4 °C had a double acrylamide content compared to those from frozen products. During storage at 4 °C, reducing sugars were liberated which enhance acrylamide formation. Even with boiling water, blanching did not completely inactivate the alpha amylase. Pre-frying was more effective, but conditions of 170 °C/60 s, as often applied, were still only at the borderline of suppressing liberation of reducing sugar. It is concluded that processing conditions of fresh prefabricates for potato products like French fries and roasted or baked products should be revisited to prevent liberation of reducing sugar during storage and enhanced acrylamide formation.     

Initial evaluation of a field-friendly incubation procedure for the colorimetric assay of cassava linamarase

The Cooke colorimetric assay of cassava linamarase activity is temperature- and time-inflexible, making “real time” monitoring of linamarase activity in remote cassava-processing sites practically impossible. A modified incubation procedure is described, in which the 30 °C linamarase incubation step is terminated through acidification, yielding a stable cyanohydrin solution. Using partially purified linamarase as a “standard extract”, the solution – held for up to 21 days at ambient/refrigeration temperatures before colorimetry – showed reductions of up to 21% compared with the standard Cooke assay. In a separate trial, a strong linear relationship (r² > 0.95) was observed between recorded linamarase activity values and incubation temperature in the 25–40 °C range, indicating that incubation may take place in remote processing sites without a water bath, and resulting data may reliably be adjusted in keeping with the standard 30 °C incubation assay. The novel procedure thus appears to offer a satisfactory “field-friendly” means of assaying linamarase activity.     

Quantitative analysis of acrylamide in tea by liquid chromatography coupled with electrospray ionization tandem mass spectrometry

An effective sample preparation procedure was optimized and a liquid chromatography–tandem mass spectrometry (LC–MS/MS) was developed for the quantitative analysis of acrylamide in tea. [¹³C₃]-acrylamide was used as internal standard. Acrylamide was extracted at 25 °C for 20 min by 10 ml water followed by 10 ml acetonitrile, and then 4 g of magnesium sulfate and 0.5 g of sodium chloride were added to the above mixture under stirring thoroughly. In order to increase the response of acrylamide, 9 ml acetonitrile layer was taken and concentrated to 0.5 ml. Solid-phase extraction with an Oasis MCX cartridge was carried out for clean-up. The limit of detection (LOD) and limit of quantification (LOQ) were 1 and 5 ng/ml, respectively. The recovery efficiency of the extraction procedure ranged between 74% and 79%. The levels of acrylamide in 30 tea samples were less than 100 ng/g. Black, oolong, white and yellow tea samples had quite low acrylamide contents (<20 ng/g). Higher acrylamide levels occurred in baked, roasted, and one sun-dried green tea samples (46–94 ng/g).     

A bench-scale high-shear wet-milling test for wheat flour

Bench-scale wet-milling tests for wheat flour are available for the traditional processes of Martin and Batter, but tests for the high-shear processes of Alfa-Laval/Raisio, Hydrocyclone, and High-Pressure Disintegration are few in number. In this study, critical processing parameters of a high-shear wet-milling process, namely high-shear mixing, gluten-aging, and gluten-washing steps, were investigated using response surface methodology, and those parameters led to a bench-scale wet-milling test starting with a “highly sheared flour–water dispersion” (HS-FWD). Optimum conditions for the test were: a water–flour ratio (db) of 1.7, water temperature of 35 °C, and homogenizer speed of 6000 rpm for 2.0 min in the high-shear mixing step, a temperature of 40 °C for 20 min in the gluten-aging step, and gluten-washing of 2.0 min in the Glutomatic system. The HS-FWD wet-milling test with high level of repeatability was capable of discriminating wet-milling qualities of several hard, soft, and coarsely ground wheat flours.     

Correlations of ingredients with sensory attributes in green beans and peas under different storage conditions

The total ascorbic acid contents and the antioxidant capacity in green beans and in peas were measured during deep-frozen storage and compared to storage at 4 °C and 20 °C. In green beans only, the flavonols quercetin and kaempferol were measured. The results were correlated with sensory attributes which were evaluated at the same storage stages. The total ascorbic acid content is a good parameter for the storage time of both vegetables and showed, for peas, a positive correlation with the attribute “sweet taste” and a negative correlation with the attribute “musty” odour. The total ascorbic acid content of green beans was positively correlated with a “squeaky” texture and negatively with a “musty” taste. The flavonol content and the antioxidant capacity were more stable during the storage process and showed less correlation with sensory attributes.     

Lipase-catalysed synthesis of natural aroma-active 2-phenylethyl esters in coconut cream

The aim of this research was to study the feasibility of biosynthesising natural aroma-active 2-phenylethyl esters in coconut cream via biocatalysis. Five commercial fungal lipases (Palatase 20 000L, Lipase AYS “Amano”, Lipase A “Amano” 12, Piccantase A and Piccantase AN) were screened for their ability to produce 2-phenylethyl hexanoate and 2-phenylethyl octanoate from coconut cream supplemented with natural 2-phenylethanol. Palatase 20 000L and Lipase AYS “Amano” showed the greatest potential for the synthesis of 2-phenylethyl esters. The biosynthetic reaction by the lipase Palatase 20 000L was further studied under different temperature, pH, enzyme and substrate concentrations, with maximum ester synthesis obtained at 9% v/v 2-phenylethanol and 2.15–8.60 mg enzyme protein/100 ml of reaction mixture. A temperature range of 30–53 °C and a pH range of 5.2–8.5 had little effect on the lipase Palatase activity, respectively. The ester-synthesising reaction appeared to proceed by both alcoholysis and esterification.     

Acrylamide formation in different batter formulations during microwave frying

Acrylamide, a probable human carcinogen, is found to be formed in a wide range of fried foods. In this study, the effects of microwave frying on acrylamide formation in the coating part of chicken were investigated. It was also aimed to determine the effects of various flour types (soy, chickpea and rice flour) in batter formulations on the acrylamide formation and on the color of fried chicken. Usage of all flour types except soy flour resulted in approximately the same moisture content and color development after 1.5 min of microwave frying. Acrylamide contents of batter parts of 1.5 min microwave fried samples having different flours were similar. Microwave frying provided lower acrylamide content and lighter color as compared to those fried conventionally for 5 min for all types of flours. This reduction in acrylamide level was the highest (34.5%) for rice flour containing batter.     

Effects of composition on fat rheology and crystallisation

The crystallisation behaviour of three fat blends, comprising a commercial shortening, a blend of fats with a very low trans fatty acid content (“low-trans”) and a blend including hardened rapeseed oil with a relatively high trans fatty acid content (“high-trans”) was studied. Molten fats were lowered to a temperature of 31 °C and stirred for 0, 15, 30, 45 and 60 min. Samples were removed and their rheological properties studied, using a controlled stress rheometer, employing a frequency sweep procedure. Effects of the progressive crystallisation at 31 °C on the melting profile of fat samples removed from the stirred vessel and solidified at −20 °C were also studied by differential scanning calorimetry (DSC).