Quality and potential health benefits of wraps made from wheat low grade flour with added xanthan gum

Abstract

Wraps are an unleavened, flat, and circular bread that is 1- 2 mm thick. White bread flour made from wheat is extensively used in the manufacture of wraps in South Africa. Low grade flour is a by product of milling and can be used as a cheaper alternative to white bread flour. Its high phenolic content and associated antioxidant activity may offer potential health benefits such as reduction in the risk of lifestyle diseases related to oxidative stress. In addition, its relatively higher dietary fibre content offers potential anti-diabetic properties unlike white bread flour which has a high glycaemic index. However the weak gluten quality of low grade flour can compromise the dough rheological properties and quality of wraps. Xanthan gum can improve weak gluten quality by mimicking the viscoelastic properties of gluten. Xanthan is also known to improve the quality of baked products. The objective of this research was to produce a health beneficial wrap of good quality using low grade flour with added xanthan gum. Low grade wheat flour was used to manufacture wraps. Xanthan gum (0.5% and 0.25% (w/w)) was added to low grade flour. The dough rheological properties of the flour, the quality, and shelf life of the wraps were determined. White bread flour was used as a reference sample in this research. Water absorption, and Farinograph mixing stability of low grade flour increased with increasing concentration of xanthan gum. Low grade flour with 0.5% xanthan gum had similar mixing stability to white bread flour. Mixing tolerance index (MTI) of low grade flour decreased with addition of xanthan gum, and the MTI of low grade flour with 0.25% xanthan gum was similar to white bread flour. At 50% flour hydration (constant hydration), as well as at flour hydration according to Farinograph water absorption (adapted hydration), the dough tenacity of low grade flour was increased by the addition of xanthan gum, while the dough extensibility was decreased by xanthan gum addition. At adapted hydration, the dough extensibility of low grade flour with 0.5% xanthan gum was similar to the dough extensibility of white bread flour. The P/L ratio expresses the relationship between the dough strength, and the dough extensibility. The P/L ratio of low grade flour with 0.5% xanthan gum had a value of 0.5 which makes it suitable for bread making. The pasting viscosities of low grade flour increased with the addition of xanthan gum. Wraps made from low grade flour did not puff during baking. Xanthan gum addition however did improve puffing in wraps made from low grade flour. The puffing of wraps made from low grade flour with 0.5% xanthan gum was similar to the puffing of wraps made from white bread flour. Wraps could only be stored for three days before mould growth was visible. Wraps made from low grade flour with 0.25% xanthan gum had the lowest rollability score, a lower modulus and higher extensibility over time. On day 0, all wraps exhibited a B-type crystallinity as determined by X-Ray diffractometer. The % crystallinity of all wraps increased over storage time. Percent crystallinity increased from 5% to 11.6% for wraps made from white bread flour; for wraps made from low grade flour it increased from 7% to 11%; for wraps made from low grade flour; with added xanthan gum (0.25%) it increased from 7% to 12%, and for wraps made from low grade flour with added xanthan gum (0.5%) it increased from 5.1% to 13%. A thermogram peak on the DSC was only visible on day 3 of storage between 95 and 102◦C for the wrap made from white bread flour. The total phenolic content and antioxidant activity of wraps made from low grade flour were higher than those of wraps made from white bread flour. Simulated gastro-intestinal digests of the wraps had higher total phenolic content and antioxidant activity than the acidified methanol extract. The relatively higher total phenolic content and antioxidant activity of wraps made from low grade flour indicates that they may offer potential health benefits. Low grade flour however produces a poor quality wrap, with a reduced shelf life. Addition of xanthan gum to low grade flour improves dough rheology, as well as the quality of wraps. This is possibly due to the interactions which occur between xanthan gum and wheat proteins, as well as between xanthan gum with the amylose of the starch molecule. The wraps with 0.25% xanthan gum produce wraps with a better quality.