Manufacturing natural blue colorant from genipin-crosslinked milk proteins: Does the heat treatment applied to raw milk influence the production of blue compounds?

Abstract

The production of an innovative food ingredient obtained from unripe Genipa americana L. pulp and milk was studied in this paper. Natural blue compounds were produced from the crosslinking between genipin and milk proteins. They are a promising ingredient for the natural food colorant sector. In this regard, this paper aimed to evaluate the impact of heat treatments applied to raw milk on the production of blue compounds. Thermal treatments could change the milk protein conformation and the exposition of their amine groups affecting the crosslinking with genipin. For this, raw milk was subjected to different thermal treatments such as low-temperature and long-time (LTLT; 60 °C/30 min), high-temperature and short-time (HTST; 72 °C/15 s), ultra-high temperature (UHT; 145 °C/2 s), and spray drying (SD; inlet and outlet temperature: 165 and 79 °C, respectively). Thermally treated milk samples were used as solvents for the genipin extraction from unripe genipap pulp and suppliers of proteins to produce blue compounds. Blue colorants milk-based were compared concerning their FTIR spectra, free-genipin content, and color attributes. High temperatures impacted protein conformation, reducing the number of primary amines available for crosslinking. Free-genipin content after the reaction step was a good crosslinking indicator. The HTST-treated milk produced the bluest colorant due to its higher number of primary amines available to react with genipin. Our findings demonstrated that the heat treatment applied to raw milk could influence the production of blue compounds. These results are useful for the enhancement of the manufacturing process of natural blue food colorants.

Keywords

• Milk pasteurization
• Spray drying
• Casein
• Commercial sterilization