Assessment of proteolysis and lipolysis in cheeses made using artisanal lamb rennet paste

Abstract

Rennet paste contains chymosin and pepsin as major enzymatic coagulant, and lipolytic enzymes such as pre-gastric lipase (PGL) and gastric lipase (GL), able to release free fatty acids during cheese ripening. Main factors influencing rennet paste features are diet (milk feeding, weaning) and slaughter age. Little is known about the effects of probiotic addition to milk substitute on the microbial and enzyme feature of rennet, and thus on the characteristics of cheese. In the present study the effects of different rennet pastes on the Pecorino foggiano cheese in terms of proteolytic and lipolytic characteristics were investigated. Twenty-four lambs were divided into six groups of four according to a 3x2 factorial design with lambs being subjected to three different feeding systems: mother suckling (MS), artificial rearing (AR), and artificial rearing with Lactobacillus acidophilus (Strain DSM 20079; DSMZ, Braunshweig-Germany; cells were suspended in milk replacer at the concentration of 7log ₁₀ cfu ml-¹) supplementation (ARLb) and slaughtered at 20d and 40d for each feeding treatment. Lambs’ abomasa were processed according to a traditional protocol to obtain rennet paste used for ovine cheese production. The extent of proteolysis and lipolysis in the cheese was monitored by determining the levels of free amino acids (FAAs) and free fatty acids (FFAs) in cheeses at 60 days of ripening. Total FAAs detected in MS cheeses was higher (P<0.05) than in other experimental cheeses, at both age of slaughtering of lambs. FAAs can be substrate for successive flavor forming reactions which convert FAA to various alcohols, aldehydes, acids, esters. Lowest levels of total FAA in ARLb cheeses could be related to the highest lactic microflora loads in rennet paste. In fact, in a previous note the supplementation of milk replacer with Lb. acidophilus was found to influence the growth dynamics of lactic acid bacteria in the rennet paste, with greater lactobacilli cell loads in cheese in the first stages of ripening. A reduction of individual FFA in cheese was observed in all treatments passing from 20 to 40 days of slaughtering of lambs. The most abundant free fatty acid were: butyric acid (C4:0), caproic acid (C6:0), palmitic acid (C16:0), oleic acid (C18:1) and linoleic acid (C18:2) according to milk fatty acid content and other work on ovine cheese. ARLb cheeses displayed higher levels of short chain FFA (C4:0-C10:0) and medium chain FFA (C12:0-C16:0) than MS cheeses, at 20 and 40 days, probably due to the impact of the diet on lipolytic enzymes in the rennet paste. When lambs are feed milk supplemented with Lb. acidophilus rennet paste is enriched in pregastric lipases able to release preferentially short-chain FFA. In conclusion, diet and age of slaughtering of lambs were found to influence the enzyme profile in rennet paste and thus the proteolytic and lipolytic patterns of cheese at 60 days of ripening.