Changes in free and bound fractions of aroma compounds of four Vitis vinifera cultivars at the last ripening stages.

The volatile composition of white Agudelo, Blancolexitimo, Godello and red Serradelo cultivars (NW Spain) harvested at two different stages of ripening have been evaluated. C(6)-compounds, alcohols, volatile fatty acids, monoterpenes, C(13)-norisoprenoids, volatile phenols and carbonyl compounds were identified and quantified in free and glycosidically bound forms by gas chromatography-mass spectrometry (GC-MS). The total volatile concentration showed a significant increase between the two ripening stages studied for all cultivars. The free volatile composition increased during maturity for Godello and Serradelo cultivars; however the glycosidically bound concentration increases for all cultivars with exception of B. lexitimo. Free C(6)-compounds ((E)-2-hexanal, 1-hexanol and (E)-2-hexen-1-ol) and bound alcohols (benzyl alcohol and 2-phenylethanol) showed the highest concentrations of volatile compounds for all grape cultivars in the two dates studied. Godello cultivar showed the highest change of volatile concentration between two ripening dates because of the high value of free C(6)-compounds. B. lexitimo was the most terpene-rich cultivar at the last ripening stage due to linalool; however C(13)-norisoprenoids in free form were detected in low concentrations for all cultivars but not in Godello and B. lexitimo cultivars at the last ripening stage. Free hexanoic acid increased during ripening in all cultivars. The evolution of volatiles during ripening of grape juice from the cultivars studied was not proportional to the changes in sugar content, which shows that the technological and aromatic maturities did not occur at the same time in these cultivars. The results also showed the cultivar * ripening date interaction for all, free and bound, groups of compounds.

Relationship between hydroxycinnamic acid content, lignin composition and digestibility of maize silages in sheep.

Cell wall-bound hydroxycinnamic acids and the composition of lignin were studied in relation to the digestibility of a collection of 91 maize silages in wethers. Total lignin and guaiacyl content showed the highest correlation coefficients with digestibility. Using the above-mentioned chemical parameters, eight equations were also developed to predict digestibility. The prediction of organic matter digestibility produced a high adjusted R2 value (0.487) using total lignin, guaiacyl, esterified ferulic acid and esterified p-coumaric acid content as predictors. The prediction of in vivo dry matter digestibility produced a higher adjusted R2 value (0.516) using the same variables as predictors. Cell wall digestibility depends on a multiplicity of factors and it is not possible to attribute a causal effect on in vivo digestibility to any single factor. However, total lignin, guaiacyl and p-coumaric acid content emerge as good predictors of digestibility.

Digestibility of silages in relation to their hydroxycinnamic acid content and lignin composition.

BACKGROUND: The effectiveness of the analysis of cell wall-bound hydroxycinnamic acids and the composition of lignin to evaluate the in vivo digestibility of a silage collection with unknown botanical composition was evaluated. RESULTS: Syringyl units content and total etherified phenols showed the highest correlation coefficients with in vivo dry matter digestibility (IVDMD) (r = - 0.792 and r = - 0.703, respectively), while guaiacyl units and total phenols showed the highest correlation coefficients with in vivo organic matter digestibility (IVOMD) (r = - 0.871 and r = - 0.817, respectively). Using the above-mentioned chemical parameters, 10 equations were also developed to predict in vivo digestibility. The prediction of IVDMD produced a high adjusted R(2) value (0.710) using syringyl, total lignin, etherified total phenols, esterified ferulic acid and total phenol content as predictors. The prediction of IVOMD produced a higher adjusted R(2) value (0.821) using guaiacyl, total phenols, total ferulic acid and etherified p-coumaric acid content as predictors. CONCLUSION: Cell wall digestibility depends on a multiplicity of factors and it is not possible to attribute a causal effect on in vivo digestibility to any single factor. However, syringyl and guaiacyl content and etherified phenols emerge as good predictors of digestibility.