Studies On The Characteristics Of Beer Foam Proteins And Its Preparation

There are so many factors to effect the formation and retention of beer foam, of which foam protein is the most important one. The quality of beer foam is attributed to the characteristics and number of foam proteins to a great extent. In this paper, the difference of protein composition and characteristics, including molecular distribution, surface hydrophobicity, amino acid composition and so on in beer and its foam were studied systematically. Then according to preceding surveys, with a series of processes of alkaline dissolving & acid depositing, enzymatic modification and foam separation in turn, preparing the functional foam proteins as beer additive to improve beer foam was studied in succession.Compared with the original beer, the liquid from beer foam has higher concentration of total proteins from 0.057-0.147mg/mL, and the exceeding parts are mainly high molecular weight proteins (MW>5,000Da). Furthermore, the concentration of HMWP in foam liquid has higher linear relativity to beer head retention value than that in original beer, which indicated the near relationship and high coherence between HMWP (MW>5,000Da) and foam proteins, and the rationality and validity of Bradford method as a way to determine the concentration of foam proteins.The enriching degree of HMWP into foam implied how many contributions made by HMWP to the formation and retention of beer foam. The enriching ability of HMWP can be changed by foam additives, which have less influence than the inherent properties of HMWP. As the result, the quality of beer foam proteins can be estimated by its enriching ability. Malt is the only obvious origin of foam proteins in beer, which quality and functional characteristics are determined by the original malt necessarily, while the brewing processes are the means to express and retain these potential qualities as fully as possible, so the enriching ability of HMWP can also embody the problems in malt quality or brewing process.Studies on gel chromatogram with Superdex G75 column visibly showed that the amount of high molecular weight proteins (MW>5,000Da) in foam liquid are much larger than that in residual beer after foaming, which accorded with the results measured with Bradford method. From the analysis of amino acid components, we found that strong hydrophobic amino acids of proteins in foam liquid increased when compared with that in residual beer after foaming, for instance, leucine increased 20.3 percent, phenylalanine increased 19.5 percent and isoleucine 19.4 percent respectively, which implied that these strong hydrophobic amino acids play a great part in beer foam.After separation of beer proteins by hydrophobic interaction chromatogram, four fractionations marked F1, F2, F3 and F4 were obtained according to their hydrophobicity. Studies showed that foam ability of these fractionations increasing along with their hydrophobicity, which implied that the strong hydrophobic proteins isolated by HIC resemble proteins in foam after foaming separation, both are close to pure foam proteins.Through SDS-PAGE gel electrophoresis of proteins isolated by HIC, we found that the weakest hydrophobic fractionation F1 has low molecular weight distribution (MW<5,000), which indicated that there would be some connections between molecular weight distribution of proteins an its hydrophobicity. The other fractionations with stronger but different hydrophobicity have the similar molecular weight distribution, which was explained presumably that in the course of malting and brewing, molecule of proteins originated from barley were modified, which caused the change of its structure and surface hydrophobicity resultingly in the condition of invariable molecular weight.Preparation of foam proteins used in beer was studied in this paper. The raw material is soy defatted protein. After three main processes of alkali dissolving & acid depositing, enzymatic modification and foam separation, the protein production with good solubility and foamability were obtained, which can be used in beer to improve...