Studies on the Impact of Durum Wheat Bran and Bran Protein Extract on Nutritional and Technological Aspects of Pasta and Bread

Abstract

<p>Wheat bran is the main by-product of the wheat milling industry. This product is dense in nutrients and bioactive compounds and these have been shown to have an important role in reducing the risk of several diseases, like cardiovascular diseases and type 2 diabetes. However, inclusion of wheat bran alone in cereal based foods can produce undesirable impacts on sensory and textural properties making them less attractive to consumers with bran being used more for animal than human food. This project aimed to see if better uses of wheat bran are possible and focused on:</p> <p>(i) Extraction of proteins from wheat bran to incorporate into pasta and bread to enrich their nutritional value while maintaining acceptable quality. These proteins were extracted from fine durum wheat bran using alkaline extraction (pH 9.5) and isoelectric precipitation to generate a wheat bran protein concentrate (WBPC). WBPC exhibited high protein content (~61%) with good protein yield 20.5–24.8% and contains essential amino acids, especially those limiting amino acids in cereals (lysine and threonine). WBPC retained some phenolic acids, but at an eightfold lower quantity than in bran and retained about half the antioxidant activity (DPPH) of bran while enriched with phytosterol (9.01 mg/g) content compared with wheat bran (1.88 mg/g). WBPC showed excellent functional properties in terms of high solubility over a wide pH range and good water and fat absorption capacity. The main protein components of WBPC were albumin and globulin proteins. The effects of addition of WBPC to pasta and bread was determined. Incorporation of pasta with WBPC at 0-20% level of replacement enhanced the nutritional and functional properties of pasta in terms of increasing the protein content of pasta from 12.3 ± 0.07 g/100 g in the control to 12.7 ± 0.07-23.4 ± 0.28 g/100 g at 1-20% level of incorporation. Total essential amino acids of enriched pasta increased from 3.76 g/100 g in the control to 3.94-7.59 g/100 g at 1-20% level of addition. Enriched pasta with WBPC showed enhancement in phytosterol, phenolic acids and antioxidant capacity compared with the control pasta. The in vitro starch digestion of pasta was not affected by WBPC addition. Overall pasta quality was acceptable up to 10% WBPC and superior to wholemeal pasta, especially in appearance. However, bread with WBPC was very sensitive even at 1% addition showing inferior bread loaf volume and texture.</p> <p>(ii) Reduction of wheat bran particle size was another attempt to find better ways to utilise bran in pasta and bread. Seven durum wheat bran fractions were obtained by milling and sieving (coarse, fine, 425, 315, 250, 180 µm and <180 µm) and were characterised for their physicochemical and phytochemical properties. These fractions were added to pasta and bread formulations to determine if they provide a better balance of nutritional benefit with product quality compared to using coarse bran alone in these foods. Fine bran fractions (FB, 180 and<180 µm) showed higher protein content than coarse fractions with highest protein content in <180 µm. Reduction of bran particle size resulted in significant changes in bran functionality. The fraction 425 revealed the highest content of phenolic acids and the least was <180, while the fractions FB and 180 showed the highest levels of phytosterol. The antioxidant capacity of bran was not affected by particle size reduction of bran. Incorporation of bran fractions into pasta revealed significant improvements in functional properties of pasta. Bran imparted increased antioxidants, ferulic acid and phytosterols. The different bran fractions had minimal impact on these measures except for ferulic acid, which was higher in larger particles (425 and 315). Finer fractions (FB, 180 and <180 µm) showed a lower cooking loss and higher firmness than coarser fractions (CB, 425, 315, 250) and also a more desirable appearance than other fractions. However, pasta quality was affected by bran additions, especially at 20%. Bread incorporated with bran fractions at 10% was evaluated. Bran fractions negatively impacted bread loaf volume, colour and texture with coarse bran having the least impact.</p>