Browsing by Author "Beukes, Martine"
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- ItemEffect of stone and roller milling on physicochemical, functional and structural properties of sifted wheat flour(Stellenbosch : Stellenbosch University, 2021-03) Beukes, Martine; Manley, Marena; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.ENGLISH ABSTRACT: Stone milling, which is one of the oldest forms of wheat flour milling, makes use of two stones to grind wheat grain to a flour. Stone milling is often associated with whole wheat flour, however a range of stone milled flour, including white flour, is found in supermarkets and other retail points across South Africa. Very few studies have focussed on white stone milled flour, and this study set out to provide fundamental knowledge regarding this. The first research chapter studied the effect of stone and roller milling on the physicochemical, functional and structural properties of white flour. Two hard wheat grain samples, i.e. a South African commercial wheat cultivar and an imported Canadian commercial blend, were milled using stone and roller milling methods. The results obtained from the samples indicated that the milling methods used often had the largest effect on the flour samples, larger than the wheat types or the interaction of wheat type and milling method. Sieving the stone ground wheat meal through a 212 μm sieve (as per South African wheat flour regulations) proved ineffective in removing the bran particles, as indicated by the significantly darker colour and significantly higher ash content compared to the roller milled flour. The sifted stone milled flour had an extremely low flour yield compared to the roller milled flour. This may be because the stone mill crushes the entire wheat kernel to produce a whole wheat flour and does not separate the bran and endosperm as is the case with the break system of a roller mill. The ash content of the sifted stone milled flour was significantly higher than that of the refined roller milled flour. The stone milled flour also had a significantly higher water absorption capacity than the roller milled flour, which was due to the significantly smaller median flour particle size, higher starch damage and ash content. The higher ash content suggests a higher aleurone and bran content, thus a higher arabinoxylan content and water absorption capacity. Stone milled samples had significantly higher falling numbers than roller milled samples. Significant differences between stone and roller milled flour for both wheat samples were seen for the alveograph P (tenacity), L (extensibility), P/L (curve configuration ratio) and W (deformation energy). The tenacity and curve configuration ratio were significantly higher, and the extensibility and deformation significantly lower for stone milled flour compared to the roller milled flour. The mixograph midline peak time and peak height were mostly affected by the wheat types, however the stone milled flour samples had significantly lower values for both these aspects compared to the roller milled samples. The pasting properties obtained with the Rapid Visco Analyser (RVA) also significantly differed between milling methods: the stone milled flour had lower pasting viscosities and peak time, but a higher pasting temperature. The scanning electron micrographs (SEM) provided insight into the qualitative aspects of the flour samples and illustrated that stone milled flour samples were less uniform with visible mechanical damage to the starch granules. The second research chapter aimed to determine the adherence of three commercial stone milled flour samples and one roller milled sample to South African wheat flour and fortification regulations. The samples were sourced from points of retail in the Western Cape, South Africa, and the moisture content, ash content, bran content, crude protein content, CIELab colour and presence of iron were determined. The protein content suggests that the flour samples could be suitable for bread production, yet the bran content of the stone milled flour samples were too high to be classified as white bread wheat flour. The packaging of the roller milled flour samples indicated that the products were fortified with micronutrients, yet one batch did not indicate a presence of iron. None of the stone milled samples indicated a presence of iron, nor did the packaging contain fortification claims or information as stipulated in the regulations.