Accelerated Cheddar Cheese Ripening with an Aminopeptidase Fraction from Squid Hepatopancreas

ABSTRACT: An aminopeptidase (AP) fraction from squid (Illex illecebrosus) hepatopancreas was added to Cheddarcheese at 2 levels, and its influence on ripening indices was determined for up to 3-mo storage at 11 °C. Twocommercial enzymes (Neutrase ® and Flavourzyme ) were similarly tested. Cheese with the higher level of squid APcontained more soluble N, amino acids, and Cheddar flavor after 1 mo, but it developed defects in texture andbitterness as ripening progressed. Cheese with less squid AP did not differ from the control with respect to allripening indices over 3-mo storage. Ripening Cheddar contains cysteine protease inhibitor(s) that inhibit low levelsof squid AP but not Neutrase ® and Flavourzyme.Keywords: Cheddar cheese, acceleration, aminopeptidases, squid hepatopancreas, ripening Introduction C HEDDAR CHEESE REQUIRES A LONG PERIOD OF TIME TO DEVELOP the full flavor and texture of ripened cheese. Thus, the oper-ating and capital costs for aging cheese represent a significantportion of the production cost for Cheddar cheese manufacture.Shortening the ripening time through a low-cost method will re-duce the cost of cheese for the producer and the consumer.Cheddar cheese ripening, a very complex biochemical process,is mainly affected by the rate and extent of proteolysis (Fox 1989;Fox and others 1993). Many investigators have examined the roleof proteolytic enzymes in Cheddar cheese ripening (Broadbentand others 1998; Kim and others 1994; Trepanier and others 1992;Wilkinson and others 1994). The use of proteases to acceleratecheese ripening is promising because of their specific action andpotential for low production cost. Proteases are separated into 2main groups: endoproteinases and exopeptidases. Endoprotein-ases cleave the polypeptide chain at specific susceptible peptidebonds within the chain, while exopeptidases hydrolyze 1 or a fewamino acid(s) at a time from either the N terminal (aminopepti-dases) or C terminal (carboxypeptidases) of the polypeptide.Adding proteolytic enzymes to cheese may accelerate the de-velopment of typical Cheddar cheese flavor, but it may alsocause undesirable changes in cheese quality. A high ratio of en-doproteinase to exopeptidase activity produces crumbly, soft-textured cheeses (Law and Wigmore 1982). Excessive endopro-teinase activity also may cause bitterness due to thepreponderance of aromatic and hydrophobic amino-acid resi-dues of -casein (Morihara 1974). On the other hand, exopepti-dases catalyze the formation of free amino acids, many of whichserve as flavor precursors in aged Cheddar, for example, glutamicacid, leucine, and methionine (Puchades and others 1989). Thedevelopment of Cheddar cheese flavor also results from the deg-radation of sulfur amino acids, that is, the formation of methion-al and methanethiol from methionine (Fox and others 1995). Theavailability of an enzyme preparation with a high ratio of exopep-tidase to endoproteinase activity could aid ripening with mini-mal development of texture defects and bitterness. Microbialaminopeptidases have gained considerable attention recently asagents of the normal cheese ripening process (De Palencia andothers 1997; Gobbetti and others 1995a; Miyakawa and others1994; Rul and others 1994). Izawa and others (1997) successfullyused the AP from