Processing and properties of toffee

Toffee is a hard-textured confectionery product which is made by boiling together sugar, milk, and fat to a certain temperature. The aim of this study was to determine the suitability and effect of seven kinds of dairy powders in toffee processing. The recipes based on dry dairy powder content of 8.8% (1st series), and protein content of 3.5% with constant solid content compensated by sucrose (2nd series). Dairy powders used in this research were: skim milk powder (SMP); butter milk powder (BMP); whole milk powder (WMP); lactose-free skim milk powder (LF-SMP); lactose-free whole milk powder (LF-WMP); 40% demineralized whey powder (D40); and 70% demineralized whey powder (D70). Color, mechanical properties, water content, water activity (aw), and glass transition temperature (Tg) of final toffee samples were analyzed. Mechanical properties were examined after one week storage as well. The data obtained were analyzed by MATLAB and SPSS. In both series, toffees made of LF-SMP showed darkest color, and those containing WMP had lightest color. Higher water content and aw in the 2nd series resulted in softer and more sticky toffees than in the 1st series. Increasing content of protein and lactose increased the hardness of toffee in the 1st series. In the 2nd series, sucrose crystals produced gritty texture of toffee, leading to decreasing hardness and stiffness of toffee, but increasing stickiness. After one week storage, all the toffees became harder and more sticky. Toffees made from lactose free dairy powders always showed higher tendency to flow and deformation than the others, indicating the function of lactose in stability of toffee. In conclusion, increasing content of protein and lactose increased the hardness of toffee. Increasing content of protein and reducing sugar led to darker color of toffee. Higher water content and aw decreased hardness, stiffness, and stability of toffee, but increased stickiness. Increasing the content of sucrose decreased the hardness, stiffness, and stability of toffee as well. SMP showed highest suitability among seven kinds of dairy powders in toffee manufacture. BMP and WMP were also possible to be dairy source in the recipe of toffee. Lactose-free milk powder was not a good choice to form stable toffee.