Proteolysis
Proteolysis in cheese samples was assessed at 60-d intervals during ripening using HPLC, following the procedure detailed by Hickey et al. (2006) and modi- fied by Rulikowska et al. (2013). Five grams of cheese was homogenized in 20 mL of 0.1 M citrate buffer at pH 3.6 at 40°C for 1 h to separate the fat. The whole suspension was centrifuged at 3,000 × g for 30 min at 4°C. The resulting pellet (100 mg) was dissociated in 5 mL of disassociating solution and held in a water bath at 40°C for 1 h with periodic mixing. This mixture was then centrifuged at 20,000 × g for 10 min at room tem- perature and filtered through a nylon 0.45-mm syringe filter. An aliquot of 20 mL was injected into a Shimadzu liquid chromatograph (LC-10 AT VP series; Shimadzu Corp., Kyoto, Japan) with a UV-visible detector at 214 nm (Shimadzu Corp.). Separation was achieved using a gradient of 2 mobile phases: (A) 90% water and 10% acetonitrile with 0.1% trifluoroacetic acid and (B) 90% acetonitrile and 10% water with 0.1% trifluoroacetic acid at a flow rate of 0.8 mL/min. The gradient was 75% A for 12 min, reduced to 51% A over 31 min, a fur- ther reduction to 20% A over the next 13 min, held at 20% A for another 3 min, and then an increase to 75% A over 3 min and held at this concentration for a further 2 min; the total run time was 54 min. The column was a C4 Jupiter 5 mm 300 A column (Shimadzu Corp.).
ProteolysisProteolysis in cheese samples was assessed at 60-d intervals during ripening using HPLC, following the procedure detailed by Hickey et al. (2006) and modi- fied by Rulikowska et al. (2013). Five grams of cheese was homogenized in 20 mL of 0.1 M citrate buffer at pH 3.6 at 40°C for 1 h to separate the fat. The whole suspension was centrifuged at 3,000 × g for 30 min at 4°C. The resulting pellet (100 mg) was dissociated in 5 mL of disassociating solution and held in a water bath at 40°C for 1 h with periodic mixing. This mixture was then centrifuged at 20,000 × g for 10 min at room tem- perature and filtered through a nylon 0.45-mm syringe filter. An aliquot of 20 mL was injected into a Shimadzu liquid chromatograph (LC-10 AT VP series; Shimadzu Corp., Kyoto, Japan) with a UV-visible detector at 214 nm (Shimadzu Corp.). Separation was achieved using a gradient of 2 mobile phases: (A) 90% water and 10% acetonitrile with 0.1% trifluoroacetic acid and (B) 90% acetonitrile and 10% water with 0.1% trifluoroacetic acid at a flow rate of 0.8 mL/min. The gradient was 75% A for 12 min, reduced to 51% A over 31 min, a fur- ther reduction to 20% A over the next 13 min, held at 20% A for another 3 min, and then an increase to 75% A over 3 min and held at this concentration for a further 2 min; the total run time was 54 min. The column was a C4 Jupiter 5 mm 300 A column (Shimadzu Corp.).
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