Effect of mannoproteins on red wine colour stability: new insights from collaborative OIV work

Since 2005, mannoproteins (MPs) have been authorised by the European Community (EU, regulation 2165/2005) as an additive for tartaric and protein stabilisation. However, their effect on colour stabilisation in red wine is still a matter for debate in research due to the nature of the product, timing, dose, and wine variety. In recent years, the International Organisation of Vine and Wine (OIV) expert working group has been carrying out collaborative work to elucidate the role of MPs in red wine. The aim of the present work is to show the results of the third year of a study in which five laboratories performed the same analyses on the same wines. Three mannoproteins (A, B, C) at two concentrations (20-40 g/hL) were added to two wines (French and Italian). The equilibration period was one week at cellar temperature (15-18 °C). The wines were then analysed at two aging time points: after one month and five months. The analyses consisted of a cold stability test, CIEL*a*b* coordinates, colour parameters (Abs 420-520-620 nm), and a copigmentation index. An analysis of individual anthocyanins and the characterisation of the MPs was also carried out. Results were expressed as the means of four repetitions carried out in five laboratories. Besides slight variations in colorant intensity and CIEL*a*b* coordinates, none of the wines showed differences visible to the human eye. MPs seem to prevent the loss or degradation of molecular anthocyanins at one month aging. The copigmentation index seemed to increase depending mainly on MP typology, with no difference between the two tested doses, indicating that the 20 g/hL concentration may be appropriate for these wines. The stability of the colouring matter was always observed after the MP treatment. However, the multivariate analyses revealed that after five months of aging the MP-C was the most effective for both wines. Finally, the effect on stability of the colouring matter is MP-dependent, the mannose content (>80 %) and molecular weight (37 < kDa < 79) being the critical factors for the effectiveness of MPs in red wine colour stability.