# Advance on the Capitalization of Grape Peels By-Product in Common Wheat Pasta
## 3 Results
### Relations between Characteristics  
Pearson's correlations coefficients (Table 5) were obtained to evaluate the relations between the studied characteristics. Significant very strong correlations (\(p<0.05\)) were obtained between cooking loss and crude ash (\(r=0.92\)), crude fat (\(r=0.92\)), crude protein (\(r=-0.92\)), crude fiber (\(r=0.95\)). Color parameters (\(L^{*}\), \(a^{*}\) and \(b^{*}\)) were strongly correlated with the chemical composition of pasta (\(p<0.05\)), except with moisture and carbohydrates, positive correlations being observed between \(L^{*}\) and crude protein (\(r=0.99\)), \(a^{*}\) and crude ash (\(r=0.92\)), crude fat (\(r=0.92\)), crude fiber (\(r=0.86\)), total polyphenols (\(r=0.82\)) and resistant starch (\(r=0.99\)), \(b^{*}\) and crude protein (\(r=0.98\)), while negative correlations were obtained between \(L^{*}\) and crude ash (\(r=-0.99\)), crude fiber (\(r=-0.99\)), crude fat (\(r=-0.99\)), total polyphenols (\(r=-0.95\)) and resistant starch (\(r=-0.89\)), between \(a^{*}\) and crude protein (\(r=-0.92\)) and between \(b^{*}\) and crude ash (\(r=-0.98\)), crude fat (\(r=-0.98\)), crude fiber (\(r=-0.99\)), total polyphenols (\(r=-0.98\)) and resistant starch (\(r=-0.82\)) content. A strong positive correlation significant at \(p<0.05\) was observed between total polyphenols content and resistant starch (\(r=0.83\)). The total polyphenols and starch content were significantly correlated (\(p<0.05\)) with the proximate composition, except moisture and carbohydrates. Furthermore, the chemical composition of the added ingredient had a major impact on dough texture which is given by the interactions between proteins, starch, lipids, fibers and sugars. Grape peel sugars could have a great contribution to dough cohesiveness increase since they could form bridges between starch and protein molecules [38]. Resilience was found to be directly influenced by protein quality, presence of soluble fiber and water availability [39]. Thus, the competition of gluten proteins with grape peel particles for water could have been a possible explanation of dough resilience decrease. Pasta proximate composition was influenced by grape peel flour incorporation, significant changes in crude ash, crude fat and carbohydrates being observed. The intake of nutrients of grape peel flour determined the increase of final product ash and fat, while the protein content showed a slight decrease. Similar reduction in protein content and increase in ash was reported for durum wheat pasta enriched with apple flour which could be due to the dilution effect of wheat protein [40]. The carbohydrates content decrease was in line with the results reported by [PERSON] et al. [41] which showed that the addition of grape skin lowered muffins carbohydrates values. One of the most important contribution of grape peel flour is to the raise of pasta fiber content, total polyphenols content and resistant starch. It is well known that grape peels are rich sources of soluble and insoluble dietary fibers and polyphenols such as flavonoids, hydroxybenzoic, hydroxycinnamic acids, flavanols, tyrosol and condensed tannins [42; 43]. The strong correlation (\(r=0.83\), \(p<0.05\)) obtained between polyphenols and resistant starch content support the hypothesis of starch digestibility changes caused by polyphenols presence. [PERSON] et al. [44] demonstrated that polyphenols play an important role in the rate and the extent of starch digestion. Resistant starch formation could be promoted by the presence of polyphenols [45], the interactions between starch and polyphenols resulting in insoluble complexes development [46]. Furthermore, the phenolic compounds presence can raise resistant starch content due to the appearance of non-covalent phenolic/starch interactions and/or to the inhibition of digestive enzymes [44; 45]. Total polyphenols and fiber content were correlated to pasta cooking loss increase (\(r=0.99\) and \(r=0.95\) respectively at \(p<0.05\)). Similar raise was reported by [PERSON] et al.