Document Type : Research Article
Authors
Ferdowsi University of Mashhad
Abstract
Introduction:Deep fat frying is a cooking method where oil is used as the heat transfer medium, in direct contact with food at a temperature above boiling point of water. The aim of this process is to combine short cooking times with unique characteristics. It also involves heat and mass transfer simultaneously. During frying time, the mass transfer is characterized by the dynamics moisture loss from the food and the fat uptake into the food. There is some experimental evidence showing that water loss and oil absorption are correlated and progress with specific kinetic. In the meantime, oil uptake of product is an important issue, affecting the nutritional and organoleptic qualities of fried foods. However, one problem associated with fried foods is the considerable amount of oil absorbed during the deep frying process. It is affected by oil temperature, frying time, initial water content of food ingredients, product surface area, the ratios of product weight to frying oil volume, pretreatments and many other factors. So far, several approaches have been suggested for decreasing oil uptake during deep frying of fried foods. One way to decrease oil absorption in foods is referred to batter coating. In this regard, the ingredients and flow behavior's properties of batter are the most important parameters to determine the performance of batter coating and reduction of oil uptake in the final product. In the batter formulations, proteins and gums can be used as important and effective components, because they have great water bonding and barrier properties, which has strong impact on reduction of oil uptake during frying. Therefore, the objective of the present study was to assess the effects of replacement of Godume shahri seed gum (0.5 and 1%) or soy protein isolates (2 and 4 %), as part of the wheat flour in batter formulation, on rheology of batter, batter pickup and mass transfer kinetic parameters during deep frying of chicken nuggets.
Materials and method:
Raw materials including fresh chicken breasts, onion, salt, hot pepper, wheat flour, baking powder, and 100% pure sunflower oil were purchased from local markets. SPI (92% protein. w/w, db) were obtained from FSL Co. The batter formulations consisted of wheat flour, salt (1.5% w/w, db), baking powder (0.5% w/w, db), SPI (2 and 4% w/v, db) and Godume shahri seed gum (0.5 and 1%). For all samples, water/dry mix proportion had always been 5:3.
Rheological properties of the batters were carried out using a Bohlin rotational Viscometer. For each test, shear rate increased from 0 to 300 s−1. The flow behavior index (n) and consistency coefficient (k) values were computed by fitting the power law model.
The chicken nuggets, containing a mixture of chicken breast meat (88%), onions (10 %), Pepper (0.5%) and salt (1.5 %) were prepared in slab shapes using a manually operated cutting device. The dimensions of the chicken nuggets were about 4.5 cm (length) × 2.6 cm (width) ×1.1 cm (thickness) (±0.2 cm). Batter pickups (%) were calculated by the weight difference between the chicken nuggets after coating to the weight of chicken nuggets before coating.
Deep frying was performed in programmable deep fat fryer contained 1.5 L refined sunflower oil. Samples were placed in a wire basket and then submerged for the required times of zero, 1, 2, 3, 4 and 5 minutes at 150 ◦C, 170 ◦C, and 190 ◦C. Oil and moisture content of the chicken nuggets were determined by standard techniques. For modeling moisture and oil transfer phenomena in fried chicken nuggets, Fick’s law of diffusion and a first order kinetic model were used respectively.
Results and Discussion:Results showed that Godume shahri seedgum had more effect on apparent viscosity compared with soy protein isolates. Polysaccharidic structure of Godume shahri seed gum prepares high number of hydroxyl groups. Hydrodynamic interactions between polar and hydrophobic groups trap most of the free water and consequently increase batter viscosity. All batters showed shear thinning behaviour (n≥0.529). The power law model was adequately suitable to describe the flow behavior of the batters (R2≥0.994). Coating uptake at the surface of nuggets was significantly affected by the batter consistency. The consistency index for batter containing gum was high and therefore the coating uptake was higher for these samples. The maximum moisture loss rate and the effective diffusion coefficient obtained for chicken nuggets coated with only batter. Addition of soy protein isolates and Godume shahri seed gum to batter formulation, decreased the Deff to 3.55-5.46×10-8 m2/s and 3.38-5.32×10-8m2/s, respectively. This can be attributed to the effect of different batter formulations and special functions of gum and protein. The activation energy to remove moisture and oil absorptionwere 10.79 (kJ/mol) and -7.91(kJ/mol) for the control sample, 13.37-17.64 (kJ/mol) and -5.90 to -9.18 (kJ/mol) for soy protein isolates and 11.9-14.7 (kJ/mol) and -7.56 to-10.30 (kJ/mol) for Godume shahri seed gum, respectively.
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