Franco Pedreschi

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 (0.8×0.8×5cm) which were blanched at 75°C for 10min. Unblanched strips were used as the control. Control or blanched strips were then dried at 85°C for 10min and immediately partially fried at 175°C for 1min. Finally, frozen par-fried potatoes were fried at 175°C for 3min 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 370μg/kg of acrylamide and the final frying determined French fries with 2075μg/kg of acrylamide. When control potato strips were treated with a 10000 ASNU/l asparaginase solution at 40°C for 20min, 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, 10min) in an 10000 ASNU/l asparaginase solution at 40°C for 20min is an effective way to reduce acrylamide formation after frying by reducing the amount of one of its important precursors such as asparagine.

Current issues in dietary acrylamide: formation, mitigation and risk assessment

Acrylamide (AA) is known as a neurotoxin in humans and it is classified as a probable human carcinogen by the International Agency of Research on Cancer. AA is produced as by-product of the Maillard reaction in starchy foods processed at high temperatures (>120 °C). This review includes the investigation of AA precursors, mechanisms of AA formation and AA mitigation technologies in potato, cereal and coffee products. Additionally, most relevant issues of AA risk assessment are discussed. New technologies tested from laboratory to industrial scale face, as a major challenge, the reduction of AA content of browned food, while still maintaining its attractive organoleptic properties. Reducing sugars such as glucose and fructose are the major contributors to AA in potato-based products. On the other hand, the limiting substrate of AA formation in cereals and coffee is the free amino acid asparagine. For some products the addition of glycine or asparaginase reduces AA formation during baking. Since, for potatoes, the limiting substrate is reducing sugars, increases in sugar content in potatoes during storage then introduce some difficulties and potentially quite large variations in the AA content of the final product. Sugars in potatoes may be reduced by blanching. Levels of AA in different foods show large variations and no general upper limit is easily applicable, since some formation will always occur. Current policy is that practical measures should be taken voluntarily to reduce AA formation in vulnerable foods since AA is considered a health risk at the concentrations found in foods.

Some Changes in Potato Chips During Frying Observed by Confocal Laser Scanning Microscopy (CLSM)

Confocal laser scanning microscopy (CLSM) was used in fluorescence mode for oil and cell wall detection, and in reflective mode to observe the surface morphology of potato chips. Oil distribution in chips fried at 170°C in oil mixed with the thermoresistant probe Nile Red was studied as the crust developed during frying. Oil was trapped only in intercellular spaces for short frying times while at longer times it was strongly linked to the developed crust microstructure (not only in intercellular spaces but also over some cells) and not easily extractable by hexane washing. Chips infiltrated with a solution of the dye Congo Red (CR) before frying revealed drastic changes in cell walls but no signs of rupture during frying at the magnification used in this research (20X). Topographical data acquired by CLSM in reflective mode confirmed that several cells are broken during the cutting operation. Image representation of the reconstructed surface of a fried chip (170°C, 3 min) allowed observe oil location in potato surface after frying.

Modeling Water Loss During Frying of Potato Slices

The effect of blanching and drying on water loss and oil uptake during potato slice frying was studied. Two pretreatments were carried out for the slices: (i) blanching in hot water at 85°C for 3.5 min; (ii) blanching in hot water at 85°C for 3.5 min and then, air-dried until a moisture content of 60 % (wet basis) was obtained. A control treatment, consisting of unblanched potato slices not air-dried was also conducted. After the pretreatments, potato slices were deep-fried in sunflower oil at 120, 150, and 180°C. With respect to the control treatment, blanching provided an increase while blanching-drying a decrease of the oil uptake. Two models, based on Ficks law, were used to describe water loss during frying. The first one is the classic model with an effective moisture diffusion coefficient, which assumed a constant value. The second model considers that the diffusion coefficient varies during the frying process. The variable diffusivity model adjusted the experimental data much better than the constant diffusivity model did. The effective moisture diffusion coefficient, in the variable diffusivity model, increased with frying time and temperature and behaved very similar for both control and blanched slices, while the increase of this coefficient was considerable higher for the blanched-dried slices. The development of a more porous structure with less oil content in the case of blanched-dried slices could explain this fact.

Frying of Potatoes: Physical, Chemical, and Microstructural Changes

Frying is one of the oldest unit operations and is used not only in industry but also at home. The most commonly fried vegetable is potato, for important commercial products such as potato chips, par-fried potatoes, and french fries. Quality parameters of interest for fried potatoes include physical and chemical properties such as color, mechanical properties (e.g., crispness, hardness, etc.), structural properties (e.g., porosity and roughness), oil content, and water content, among others. Some chemical contaminants such as acrylamide and furan are heat-generated during the frying of potato slices or strips, leading to final fried pieces with considerable amounts of these contaminants. The controllable variables in industrial frying processes are generally potato variety, oil type, frying time, and frying temperature. Therefore, the study of the quality changes during frying is critical because knowledge regarding kinetics parameters will enable prediction of the final quality in fried potatoes and improvements in the final product value by selecting properly the processing conditions. Finally, modern techniques such as computer vision provide valuable tools to quantify and predict physical and chemical properties of potato pieces during frying in a fast and noninvasive way. In addition, computer vision can allow us to classify fried potatoes in different quality classes previously determined by sensorial panels.

Volume measurement method of potato chips

Abstract A simple method is proposed to quantify volume of potato chips by measuring the displaced volume of a finely granular material (rape seeds) by the volume of the chips. Firstly, compaction of the seeds was studied to evaluate the reproducibility and accuracy of the technique. The results obtained indicate an encouraging potential of the technique to estimate the apparent volume of potato chips and give some indications of variation of chip apparent density with some important technological parameters such as chip thickness, frying temperature, and pre-treatment of the slices before frying (e.g., blanching). This technique showed that the apparent volume of un-blanched potato slices increased clearly (P=0.007) with frying temperature (from 120°C to 190°C) until the chips reached final moisture contents <3% (wet basis). For 180 and 190°C, the final apparent volume of these samples indicated that the chips expanded in ∼6% beyond its original volume before frying (14.1 mL). For potato slices blanched in hot water (80°C and 3.5 min) and fried under the same temperature intervals and conditions, this trend was not statistically significant (P=0.088), and the average apparent volume of the chips was 10.9 mL which correspond as an average to a shrinkage of ∼23%.

Furan occurrence in starchy food model systems processed at high temperatures: effect of ascorbic acid and heating conditions.

Furan, a potential carcinogen, has been detected in highly consumed starchy foods, such as bread and snacks; however, research on furan generation in these food matrixes has not been undertaken, thus far. The present study explored the effect of ascorbic acid addition and cooking methods (frying and baking) over furan occurrence and its relation with the non-enzymatic browning in a wheat flour starchy food model system. Results showed that furan generation significantly increased in the presence of ascorbic acid after 7 min of heating (p < 0.05). The strongest effect was observed for baked products. Additionally, the furan content in fried products increased with the increase of the oil uptake levels. As for Maillard reactions, in general, the furan level in all samples linearly correlated with their degree of non-enzymatic browning, represented by L* and a* color parameters (e.g., wheat flour baked samples showed a R(2) of 0.88 and 0.87 for L* and a*, respectively), when the sample moisture content decreased during heating.

Physical properties of emulsion-based hydroxypropyl methylcellulose/whey protein isolate (HPMC/WPI) edible films

The objective of this research was to study the effect of the film microstructure of oil-in-water emulsions stabilized by hydroxypropyl methyl cellulose/whey protein isolate (HPMC/WPI) with or without sodium dodecyl sulfate (SDS) over physical properties of HPMC/WPI emulsion-based films. The films were prepared with different HPMC/WPI-oil-SDS combinations (%w/w for 100g of dispersion): HPMC; WPI; HPMC/1WPI-0.5-SDS; HPMC/1WPI-1; HPMC/2WPI-0.5; HPMC/2WPI-1-SDS. Physical properties of films were evaluated. The results showed no statistical differences (p>0.05) between the thicknesses of EFs (0.156 ± 0.004 mm). The effect of oil content and incorporation of SDS showed the inverse trend for WI and ΔE, the increasing order of change, for WI and ΔE, among the formulation evaluated was: HPMC/1WPI-1>HPMC/2WPI-0.5>HPMC/2WPI-1.0-SDS≈HPMC/1WPI-0.5-SDS≈WPI>HPMC for WI and HPMC/1WPI-0.5-SDS>HPMC/2WPI-1.0-SDS>HPMC/2WPI-0.5>HPMC/1WPI-1 for ΔE, respectively. The addition of oil and SDS decreased the TS and EB, because oil addition into EF induces the development of structural discontinuities, producing an EF with less chain mobility, and consequently, with less flexibility and resistance to fracture.

Using RGB Image Processing for Designing an Alginate Edible Film

The use of edible films to coat food products is a technique that allows for an extended shelf-life. One of the most widely used polymers is calcium alginate. However, this polymer can modify the original food color and the perception by consumers. The objective was to design an alginate film based principally on color changes using a RGB color model. Edible films were prepared with sodium alginate and glycerol as plasticizer, cross-linking the polymer with calcium. Dry and hydrated states of the edible films were studied. Film thickness was directly proportional to surface concentration and increased with hydration. There is a zone in which the color does not change with alginate surface concentration and another where the color is directly proportional to it. This latter scenario is not a consequence of structural changes or the degree of hydration. Results showed a range where the color was not modified by the alginate concentration; hence, an optimal surface concentration was determined as a design parameter. Edible films made using the optimal surface concentration would not mask microbial contamination and have good physical properties (water vapor transmission and swelling) compared with other surface concentrations. In addition, it was possible to model alginate surface concentration as a function of surface color using mathematical tools (clustering, linear regression, and support vector machine), allowing one to study the optimal use of the edible films.

CHARACTERIZATION OF THE SURFACE PROPERTIES OF CHOCOLATE USING SCALE-SENSITIVE FRACTAL ANALYSIS

ABSTRACT A scanning laser microscope was used at its highest resolution (25 µm) to study the surface of three kinds of commercial chocolate. Data of measured surfaces were analyzed by scale-sensitive fractal analysis (SSFA) using linear and area tiling (length-scale and area-scale analysis) and by conventional statistical analyses for roughness. Area-scale and length-scale fractal complexities (Lsfc and Asfc) and the smooth-rough crossover (SRC) derived from SSFA proved adequate to characterize the surface roughness of chocolate and changes in topography as a result of bloom. The three chocolate surfaces analyzed had similar values of Asfc, Lsfc and ARa. Nestlé milk chocolate presented significant higher values of SRC than those corresponding to the other two kinds of chocolate analyzed (e.g., 0.051 mm2 vs. 0.038 and 0.037 mm2 in the case of area-scale sensitive analysis) implying a rougher surface.