improvement of the emulsifying properties of farsi gum (amygdalus scoparia spach) through maillard-type conjugation with β-lactoglobulin

introduction: hydrocolloids are widely used in food systems as an emulsifying or stabilizing agent. one way to improve the emulsifying properties of hydrocolloids is complexation with proteins. in general, protein and hydrocolloid components may be combined together by either a) covalent bonding (conjugates) or b) electrostatic complexing. conjugates can be efficiently prepared during the storage of freeze-dried or spray-dried powders of protein- hydrocolloid mixtures if stored at appropriate temperature and relative humidity. farsi gum (fg) is a natural gum that exudated from mountain almond trees (amygdalus scoparia spach). in this study, blg (β-lactoglobulin)-fg conjugates were prepared by dry heat treatment at different blg/fg mixing ratios (1:1, 1:2 and 2:1) and emulsifying properties of these conjugates were characterized. materials and methods: firstly, blg and fg were dry mixed at blg/fg (1:1, 1:2 and 2:1) weight mixing ratios. the blg-fg mixtures were incubated at 60 ºc for a period of 1-14 days in desiccators containing saturated nacl (to have 75 % relative humidity). formation of blg-fg conjugates was confirmed by sds-page. with the advancement of maillard reaction, amadori and browning compounds formation was determined by the absorbance at 304 nm and 420 nm, respectively. creaming index (ci) was assessed by determining the height of serum layer developed during storage (at 30 min intervals for 180 min) in emulsion (0.5 wt. % total biopolymer and 25% v/v o/w). the emulsion activity index (eai) and emulsion stability index (esi) were determined by turbidimetric technique at 500 nm absorbance. in addition, the effect of storage (3 days) at accelerated condition (40 ºc) and freeze-thaw treatment on droplet size distribution of emulsions (1.5 wt. % total biopolymer and 40 % v/v o/w) were evaluated by static light scattering. finally, microstructure of blg-fg emulsion was captured by light microscopy. statistical analysis of the all data was carried out using sas 9.1 with significance defined at p 0.05) effect on eai. however, esi was significantly increased over time and esi of 2-week incubated blg-fg conjugate was significantly different (p<0.05) from others (control, 0 hour, 2 and 6 days). during 3 day-storage of emulsions at 40 ºc, average droplet sizes of fg, ga, blg-fg conjugates at 1:1, 1:2, and 2:1 weight mixing ratios were altered from 34.36 to 34.76 μm, 34.18 to 33.79 μm, 17.87 to 17.76 μm, 31.30 to 34.46 μm, and 25.07 to 24.52 μm, respectively. on the other hand, the average droplet size of emulsions after freeze-thaw treatment of fg, blg-fg conjugates at 1:1, 1:2, and 2:1 weight mixing ratios was increased from 34.36 to 80.96 μm, 17.87 to 57.49 μm, 31.30 to 100.45 μm, and 25.07 to 70.32 μm, respectively. after freeze-thaw treatment, emulsion prepared with ga was broken down and oiling-off was observed. based on droplet size distribution of emulsions, results showed that blg:fg (1:1) conjugate had better emulsion stability with finer droplet size compared with other blg/fg mixing ratios (1:2 and 2:1), native fg and gum arabic. moreover, microscopic features of emulsions were a suitable evidence for improvement of emulsifying properties of fg. it is clear from the above discussion that the blg-fg conjugates (1:1, 1:2 and 2:1) performed much better than native fg and ga alone at the same emulsifier/oil ratio (1.5 wt. % total biopolymer and 40 % v/v oil). conclusion: emulsion prepared with the blg-fg conjugates at 1:1 weight mixing ratio exhibited a lower initial mean droplet diameter between others (blg/fg at 1:2 and 2:1 weight mixing ratios, native fg, ga). therefore, blg-fg conjugates (1:1) have the potential for use as an effective emulsifier in emulsion formulation. however, finding the right reaction condition is necessary (time and temperature) in further researches.