Confocal Laser Scanning Microscopy and Image Analysis for Elucidating Crumb and Crust Microstructure of Bran-Enriched South African Fried Dough and Batter

Oluwatoyin O Onipe,Daniso Beswa,Afam I O Jideani

doi:10.3390/foods9050605

Oluwatoyin O Onipe, Daniso Beswa + Show 1 more

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https://doi.org/10.3390/foods9050605

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Abstract

A double staining protocol for image acquisition using confocal microscopy (CLSM) coupled with image analysis was employed to elucidate the crust and cross-sectional properties of fried dough. Penetrated oil by image analysis (POia), porosity and pore features were quantified from the cross-section micrographs. Crust surface roughness was measured using fractal metrics and fat content was determined by solvent extraction using the American Association of Cereal Chemists method. Crumb porosity ranged between 54.94%–81.84% and reduced (p < 0.05) with bran addition. Crumb pore sizes ranged from 0–475 µm with <1 circularity, indicating elliptical shape. POia values were notably higher (p < 0.05) than PO by Soxhlet extraction (POsox), except for wheat bran (WB) fried dough where the values of POia and POsox were closely ranked. The linear effect of initial moisture content and bran concentration showed a significant impact on the image properties. The mean fractal dimension (FD) decreased as initial moisture increased. The addition of WB caused a significant reduction in the FD of fried dough, while the opposite effect was noted for its oat bran counterpart. Due to non-collinearity of image properties (FD, POia and porosity), data were fitted to cubic polynomial regression with R2 values > 0.70. CLSM and image analysis were effective in measuring oil absorption and interpreting crumb properties of fried dough. The protocol used in this study can be applied to other thick deep-fried foods for qualitative observation and quantitative measurement of a specific physical or chemical property.

Highlights

IntroductionThe transformation of dough and batter into magwinya encompasses vital microstructural changes highly dependent on processing conditions such as mixing, and dough development, fermentation (bubble formation as a result of CO2 release in the dough/batter), moulding of dough and/or scooping of batter and thermal treatment (frying)
The transformation of dough and batter into magwinya encompasses vital microstructural changes highly dependent on processing conditions such as mixing, and dough development, fermentation, moulding of dough and/or scooping of batter and thermal treatment
This paper presents the first study on the quantitative analysis of magwinya crumb and crust properties determined from confocal micrographs

Summary

Introduction

The transformation of dough and batter into magwinya encompasses vital microstructural changes highly dependent on processing conditions such as mixing, and dough development, fermentation (bubble formation as a result of CO2 release in the dough/batter), moulding of dough and/or scooping of batter and thermal treatment (frying). Foods 2020, 9, 605 quality changes to the texture of the foods, such as crust formation, pore size distribution and porosity measurement, have all been estimated using image analysis [5]. The CLSM choice in visualisation of changes in fried foods is due to its ability to produce images with clear contrast, differentiating one food component (fat, protein or carbohydrates) from the other and from the empty pores. This is achieved using dyes specific to a food component and simultaneously viewing these components. The choice of fluorophore depends on its affinity to the food component of interest, emission spectra, and behaviour in the food matrix [4,7]

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