The use of lactoperoxidase for the bleaching of fluid whey

摘要

Lactoperoxidase (LP) is the second most abundant enzyme in bovine milk and has been used in conjunc-tion with hydrogen peroxide (H_2O_2) and thiocyanate (SCN~-) to work as an antimicrobial in raw milk where pasteurization is not feasible. Thiocyanate is naturally present and the lactoperoxidase system purportedly can be used to bleach dairy products, such as whey, with the addition of very little H_2O_2 to the system. This study had 3 objectives: 1) to quantify the amount of H_2O_2 necessary for bleaching of fluid whey using the LP system, 2) to monitor LP activity from raw milk through manufacture of liquid whey, and 3) to compare the flavor of whey protein concentrate 80% (WPC80) bleached by the LP system to that bleached by tra-ditional H_2O_2 bleaching. Cheddar cheese whey with annatto (15 mL of annatto/454 kg of milk, annatto with 3% wt/vol norbixin content) was manufactured using a standard Cheddar cheesemaking procedure. Various levels of H_2O_2 (5-100 mg/kg) were added to fluid whey to determine the optimum concentration of H_2O_2 for LP activity, which was measured using an established colorimetric method. In subsequent experi-ments, fat-separated whey was bleached for 1 h with 250 mg of H_2O_2/kg (traditional) or 20 mg of H_2O_2/ kg (LP system). The WPC80 was manufactured from whey bleached with 250 mg of H_2O_2/kg or 20 mg of H_2O_2/kg. All samples were subjected to color analy-sis (Hunter color values and norbixin extraction) and proximate analysis (fat, protein, and moisture). Sensory and instrumental volatile analyses were conducted on WPC80. Optimal LP bleaching in fluid whey occurred with the addition of 20 mg of H_2O_2/kg. Bleaching of fluid whey at either 35 or 50℃ for 1 h with LP resulted in >99% norbixin destruction compared with 32 or 47% destruction from bleaching with 250 mg of H_2O_2/ kg, at 35 or 50℃ for 1 h, respectively. Higher aroma intensity and increased lipid oxidation compounds were documented in WPC80 from bleached whey compared with WPC80 from unbleached whey. Monitoring of LP activity throughout cheese and whey manufacture showed that LP activity sharply decreased after 30 min of bleaching (17.01 ± 1.4 to <1 U/mL), suggesting that sufficient bleaching takes place in a very short amount of time. Lactoperoxidase averaged 13.01 ± 0.7 U/mL in unpasteurized, fat-separated liquid whey and 138.6 ± 11.9 U/mL in concentrated retentate (11% solids). Lactoperoxidase may be a viable alternative for chemi-cal whey bleaching.