Barley lipid transfer protein 1 is involved in beer foam formation.

Sorensen, S.B., Bech, L.M., Muldbjerg, M., Beenfeldt, T. and Breddam, K.

Abstract
Beer foam generated by gas sparging in a glass foam tower, using nitrogen saturated with water vapour, was diluted with distilled water to the original beer volume and passed through the foam tower again, then rediluted and passed through again. The foam finally obtained (about 35% of the original quantity of beer foam) was separated into two fractions of different molecular weight (MW) by gel filtration. Analysis showed that the high MW fraction consisted mainly of carbohydrate, with a protein content of 10% (predominantly an albumin of MW 40000 Dalton, originating from barley and known as protein Z) while the low MW fraction was mostly protein, over half of which was identified as a barley lipid transport protein (MW 9700 Dalton) designated LTP1, but which also included fragments of hordein and glutelin. Foaming trials showed that the low MW fraction was responsible for the capacity to form foam, while the high MW fraction helped to prolong the life of the foam once formed. A mixture of the two fractions in proportions and concentrations similar to those in the original beer was able to form a good stable foam. When LTP1 was separated from the other proteins of the low MW fraction, the foam formed from pure LTP1 was very unstable, while that of the other protein fraction lasted much longer. LTP1 extracted from raw barley was found to be much less effective at forming foam than that from beer, indicating that it undergoes some change during malting and/or brewing.
Keywords : barley beer foam foam stability protein