AbstractsBiology & Animal Science

Microstructure and surface characterization of fried batter coatings

by Jamshid Rahimi




Institution: McGill University
Department: Department of Bioresource Engineering
Degree: PhD
Year: 2015
Keywords: Agriculture - Food Science and Technology
Record ID: 2062091
Full text PDF: http://digitool.library.mcgill.ca/thesisfile130567.pdf


Abstract

Two different sets of batter systems were used. First, wheat flour batter was pre-heated at different temperatures namely 60, 70, and 80ºC for 10 min. The batter samples were then deep fried at 180±2°C in canola oil. Batter pre-heated at 60ºC showed higher moisture content, lower fat content and lower porosity than non-pre-heated batter and batters pre-heated at 70 and 80ºC. Therefore 60ºC pre-heating temperature was chosen to study the effect of different batter formulations (namely 100 g wheat flour to 0 g rice flour, 75 g to 25 g, 50 g to 50 g, 25 g to 75 g, and 0 g to 100 g) on moisture and fat content, and porosity. Furthermore, the effect of batter formulations and pre-drying times on different fractions of fat in fried batter was studied. Different mathematical models for predicting moisture diffusivity and oil transfer during frying were evaluated. Batter with 100 g wheat flour was found to have higher surface fat and total fat contents, while its penetrated fat content was lower than that with other batters. Batter with no pre-drying showed higher surface, penetrated and total fat content than other systems. Moisture diffusivity ranged between 5.47×10-6 and 7.38 ×10-6 m2/min. Page model was found as the best fit model to evaluate the oil transfer rate constants. The influence of batter formulation and pre-drying time on different fraction of inter-particle spaces in fried batter that are occupied by air, moisture, or fat was evaluated. Higher rice flour content in batter significantly increased the fraction of inter-particle spaces occupied by air (SOA), and decreased the fraction of spaces occupied by moisture (SOM) and fat (SOF). Longer pre-drying times showed greater fraction of spaces occupied by air, and smaller fraction of spaces occupied by moisture and fat. SOA, SOM, and SOF of the batter systems ranged from 2.20 to 46.03%, 2.55 to 47.07%, and 0.35 to 11.11%, respectively. Surface characteristic of fried batters when prepared from different combination of wheat and rice flours was investigated. Parameters such as the total number, mean area, the biggest area, ratio and roundness of the generated ruptures on the coating surface after frying were used to characterize the microstructure of fried batters. Batters formulated only with wheat flour showed the highest number of ruptures whereas batters formulated only with rice flour showed the least. Roundness of the ruptures ranged from 0.19 to 0.35. The higher the amount of rice flour used in the formulation of batter, the higher the area of holes and cracks generated on surface. Fractal dimension (FD) and lacunarity were applied to study the structure and irregularities of surface of batters with different formulations during frying. Using scanning electron microscopy, images of batter surfaces were captured, and analyzed via FracLac plug-in that was applied in ImageJ software. FD ranged between 2.79 and 2.82. Application of higher amount of wheat flour in batter preparation resulted in higher FD values compared to batters with higher amount of rice…