Effects of Processing Conditions During Manufacture on Retronasal-Aroma Compounds from a Milk Coffee Drink

To develop a ready-to-drink (RTD) milk coffee retaining the original coffee flavor, the effects of processing conditions during manufacture on retronasal-arma (RA) compounds from the milk coffee were investigated by gas chromatography-mass spectrometry using an RA simulator (RAS). Thirteen of 46 detected compounds in the RAS effluent (RAS compounds) decreased significantly following pH adjustment of coffee (from pH 5.1 to 6.8) and 5 compounds increased. RAS compounds from coffee tended to decrease through the pH adjustment and subsequent sterilization. Significantly higher amounts of 13 RAS compounds were released from the milk coffee produced using a blending-after-sterilization (BAS) process without the pH adjustment than from that using a blending-before-sterilization (BBS) process with the pH adjustment. In BAS-processed milk coffee, significantly lower amounts of 8 high-volatility compounds and 1H-pyrrole were released from coffee containing infusion-sterilized (INF) milk than from coffee containing plate-sterilized (PLT) milk, whereas 3 low-volatility compounds were released significantly more from coffee using PLT milk. Principal component analysis revealed that the effect of the manufacturing process (BAS, BBS, or homemade (blending unsterilized coffee without pH adjustment with sterilized milk)) on milk coffee volatiles was larger than that of the sterilization method (INF or PLT) for milk, and that the sterilization method could result in different RAS volatile characteristics in BAS and homemade processes. In conclusion, a BAS process was found to be superior to a BBS process for the manufacture of an RTD milk coffee that retains volatile characteristics similar to that of a homemade milk coffee. Practical Application: Ready-to-drink (RTD) milk coffee manufactured using the conventional blending-before-sterilization process does not retain its original coffee flavor due to pH adjustment of the coffee during the process. The new blending-after-sterilization (BAS) process enabled the production of RTD milk coffee whose volatiles are closer to that of homemade milk coffee, as demonstrated by the results of RAS-GC-MS analysis. The BAS process has already been applied to the manufacture of RTD milk coffees in Japan.