Browsing by Subject "fermented"

Proteins contribute to network structures in foods not only when soluble as monomers but as various meso-scaled structures. The aim of the work was firstly to investigate the effects of heating and high pressure homogenization on colloidal properties and stability of plant protein dispersions, in particular soy and oat proteins. Secondly, aim was to test gelation properties of soy and oat proteins by fermentation using lactic acid bacteria. Results showed that when dispersed in milk permeate, soy protein isolate and oat protein concentrate powders were sedimenting fastly unless high pressure homogenization was applied. Particle size measurement also showed starch granules (average size 5 μm) existed in oat protein concentrate. In gelation study, gelation point varied from pH 6.0 to 5.5 depending on the soy protein content in the milk-soy mixture. As casein has lowest isoelectric point (compared to ~5.5 of oat globulin and soy), gelation takes place at lower pH value in milk-only gels. Confocal Laser Scanning Microscope (CLSM) pictures demonstrated a difference in gel network; the higher the soy protein content, the denser the protein network was. Texture analysis showed no significant (p<0.05) difference in firmness of soy or milk gels. However, soy- skim milk 75:25 and 50:50 mixtures were slightly weaker. Oat protein in ratio of 50:50 (oat-milk) could not form a gel and even with 25:75 ratio, the gel was considerably weak. The storage experiment showed that water retention was improved by addition of soy protein. Firmness of soy protein gels also increased in storage. The panelists in the sensory panel had very scattered opinions on the given samples but found sample with soy- skim milk 50:50 most generally appealing. In conclusion soy proteins formed a denser gel network compared to milk proteins when fermented with lactic acid bacteria. Mixing soy protein isolate with skim milk improved water retention in fermented gels during storage. Sensory wise addition of 50 % soy protein to the product was found generally appealing even when comparing to the skim milk sample. Oat protein formed a gel when added 25 % only. The effect of other compounds (for example starch in oat) could be one of the structure weakening factors.