Effect of cultivar and roller milling process on the level of phenolic compounds in Italian durum wheat

Phenolic compounds have many favourable effects on human health, arising from their antioxidant activity and capacity to protect critical macromolecules (such as chromosomal DNA, structural proteins and enzymes, low-density lipoproteins, and membrane lipids) from damages induced by active species of oxygen (Dreosti, 2000; Heim et al., 2002). The external layers of wheat caryopses contain interesting levels of various phenolic compounds, and bran extracts have a recognised antioxidant activity and are capable to inhibit lipid peroxidation in human low-density lipoprotein in vitro (Yu et al., 2005). Pasta, both dry and fresh (the latter showing a moisture level of 24-30%), stands out among the wheat-based foods for its typical sensory properties, able to be combined with a wide range of dressings. It is consumed mostly in Italy, but is known and appreciated all over the world. To fulfill nutritional expectations of consumers, whole-wheat pasta is also produced, although in amounts definitely lower than conventional pasta. It shows higher contents of fibre, vitamins and antioxidant substances than conventional pasta, but its consistency can be affected by bran fibre, which interferes with the gluten network (Sivam et al., 2010). The aim of this work has been to assess the feasibility of enrichment of fresh pasta with fluid extracts of phenolic compounds derived from bran. In this way, we intended to produce pasta with increased antioxidant properties, without the technological drawbacks of bran fibre. In particular, the aspects referring to dough characteristics (strength and tenacity to extensibility ratio, determined by Chopin alveograph) and sensory properties of final product have been considered and analysed. Methods involved quantitative descriptive sensory analysis, aroma profiling by Solid Phase Micro Extraction of volatile compounds coupled to Gas Chromatography/Mass Spectroscopy (SPME-GC/MS), and colorimetric determinations. Moreover, various extracting methods and different enrichment levels were evaluated. Every trial was performed in triplicate and submitted to statistical analysis. Regarding the extracting solvents, a preliminary evaluation indicated higher extracting capability of methanol, compared to acetone and ethanol, but only ethanol-derived extracts were selected for the enrichment trials due to their intended edible use. The obtained results indicated that all the extracting methods involving basic hydrolysis lead to higher concentrations of phenolic compounds (with an extracting capability of about 5 mg phenolic compounds, expressed as gallic acid, per g dry bran), as determined by Folin Ciocalteau reaction followed by spectrophotometric measures at 765 nm. However, the subsequent step of neutralization of the same extracting procedure produced NaCl or KCl, which affected the dough characteristics and altered the sensory characteristics of the final products, profiled by considering bulkiness, stickiness, firmness, salty taste, bitter taste, and wholemeal aroma. In particular, a significantly higher value (P < 0.05) of tenacity to extensibility ratio (alveographic P/L) was observed in dough enriched with hydrolised bran extracts, respect to control dough obtained by adding only water. Besides, significantly higher values of firmness, salty taste and wholemeal aroma were observed in pasta enriched with the same hydrolised extracts, while bitter taste did not appear significantly different, at P < 0.05. The colorimetric analysis showed that also colour of enriched pasta was significantly different from that of control, with higher values of both yellow index (b*) and brown index (100 – L). Better results were obtained by avoiding the initial hydrolysis step, which lead to enriched fresh pasta with sensory properties similar to the conventional types, but with enhanced antioxidant activity. In particular, saltiness and consistency were not statistically different from control, while the colorimetric indices appeared higher than in control, with a more intense brownish tone. Also the dough did not show significant differences in the alveographic P/L value (P < 0.05). The aroma profile, determined by SPME-GC/MS analysis of volatile compounds, appeared relatively poor, under the quantitative and qualitative point of view, respect to the usual profile of other cereal-based foods, such as bread. In particular, it was mainly characterized by alcohols (i.e. 1-butanol, 1-pentanol, 1-esanol) and aldehydes (esanal, eptanal, acetaldehyde). In fact, the origin of the volatile compounds observed was essentially imputable to oxidative phenomena related to kneading, in the absence of important biochemical reactions of fermentative or thermal nature due to leavening or baking. In conclusion, this research demonstrated the feasibility of the production of fresh pasta enriched with phenolic compounds derived from bran, assumed that the preliminary preparation of the edible phenolic extract carefully takes into account the best balance between extraction yield and technologic drawbacks