Proteolytic and textural changes of semi-hard goat cheese during ripening in oil

Tijekom zrenja sira dolazi do proteolize koja podrazumijeva razgradnju micela kazeina do peptida i slobodnih aminokiselina pomoću proteolitičkih enzima. Pri tome zbog smanjenja aktiviteta vode i povećanja pH vrijednosti sira dolazi do omekšavanja teksture sira. Jedno od složenih senzorskih svojstava sira koje određuje njegovu kvalitetu i prepoznatljivost je tekstura. Sir neprestano gubi vlagu čime se proces proteolize usporava. Pretpostavlja se da čuvanje sira u ulju usmjerava proteolitičke reakcije sprječavanjem gubitka vlage tijekom zrenja sira, čime se mijenja i njegova tekstura. Stoga je cilj ovog rada istražiti utjecaj zrenja sira u ulju na proteolitičke i teksturne promjene polutvrdog kozjeg sira te utvrditi njihovu međusobnu povezanost. Istraživanje je provedeno u tri ponavljanja/šarže u pilot pogonu Zavoda za mljekarstvo. Proizvedeni sirevi iste šarže podijeljeni su u dvije grupe obzirom na način zrenja: 1) zrenje na zraku (kontrolna grupa) 2) zrenje u ulju nakon 10 dana zrenja na zraku. Zrenje sira trajalo je 60 dana. Za zrenje u ulju se koristila mješavina ekstra djevičanskog mljetskog maslinovog ulja i rafiniranog suncokretovog ulja (50:50). Uzorkovanje sira provelo se 0., 10., 20., 30., 45. i 60. dana zrenja. Fizikalno-kemijske analize sira uključivale su određivanje sadržaja suhe tvari i proteina te pH vrijednosti i aktiviteta vode. Proteolitičke promjene u siru praćene su određivanjem udjela frakcije dušika topljive u vodi (WSN %TN) i 12 %-tnoj trikloroctenoj kiselini (TCA-SN %TN). Tekstura sira određena je teksturnim analizatorom. Sadržaj suhe tvari i proteina je u siru koji je zrio u ulju bio značajno (p=0,01) manji u odnosu na sir koji je zrio na policama, dok su proteolitičke promjene, odnosno vrijednosti WSN%TN i TCA-SN%TN bile značajno (p=0,01) veće kod sira koji je zrio u ulju. Čvrstoća i lomljivost kod sira koji je zrio u ulju značajno (p<0,05) su manje nego kod sira koji je zrio na zraku, a deformacija u točki loma značajno (p=0,01) veća. Zrenje sira u ulju sprječava gubitak vlage što povoljno djeluje na teksturu sira čime se omogućuje njegova konzumacija u periodima godine kada nema proizvodnje kozjeg mlijeka s obzirom na sezonski karakter proizvodnje kozjeg mlijeka.During cheese maturation, proteolysis occurs, which entails the degradation of casein micelles to peptides and free amino acids by proteolytic enzymes. At the same time, due to a decrease in water activity and an increase in the pH of the cheese, the texture of the cheese softens. One of complex sensory property of cheese that determines its quality and distinctiveness is texture. During maturation, the cheese constantly loses moisture, thereby slowing down the process of proteolysis. It is assumed that storing of cheese in oil directs proteolytic reactions, preventing moisture loss during cheese maturation, thereby changing the texture of the cheese. Thus, the aim of this research is to study the effect of ripening in oil on proteolytic and textural changes of semi-hard goat cheese and to determine their relationship. Three batches of cheese were produced in the pilot plant of the Department of Dairy Science. The cheeses produced in one batch were divided into two groups according to the method of ripening: 1) ripening in air (control group) 2) ripening in oil after 10 days of ripening in air. The total duration of ripening was 60 days. A mixture of Mljet’s extra virgin olive oil and refined sunflower oil (50:50 ratio) was used for cheese ripening. Chesse sampling was carried out on the 0th, 10th, 20th, 30th, 45th and 60th day of ripening. Physico-chemical analysis of cheese included determination of dry matter and protein content, as well as pH and water activity. Proteolytic changes in cheese were controlled by determining the proportion of water-soluble nitrogen fraction (WSN %TN) and 12% trichloroacetic acid (TCA-SN %TN). The texture of the cheese was determined by texture analyser. The content of dry matter and protein in cheese ripened in oil was significantly (p=0,01) lower than in cheese matured in air, while proteolytic changes (WSN%TN and TCA-SN%TN) were significantly (p=0,01) higher in cheese matured in oil. The firmness and fracturability of cheese matured in oil was significantly (p