Use of autolytic starter systems to accelerate the ripening of Cheddar cheese

Abstract

The rapid release of intracellular enzymes due to autolysis of lactic acid bacteria in the cheese matrix post-manufacture is thought to play a role in the acceleration of cheese ripening. To investigate this hypothesis Cheddar cheese was manufactured using three related starter systems which varied with respect to their autolytic properties. Starter system A contained a blend of two Lactococcus lactis strains (223 and 227) which had a low level of autolysis. System B was identical to A but included an adjunct of a highly autolytic strain of Lactobacillus helveticus (DPC4571). System C consisted only of strain DPC4571 as starter. The cheeses were evaluated during ripening for key ripening indices including autolysis of starter cells by release of intracellular marker enzyme lactate dehydrogenase (LDH), composition, proteolysis and flavour development by descriptive sensory analysis. Populations of Lb. helveticus DPC4571 decreased rapidly in cheeses B and C and were not detected by 8 weeks. The level of starter culture autolysis proceeded in the order C≫B>A. Levels of proteolysis were elevated in cheeses B and C relative to A. Principal component analysis of the sensory data separated the character of cheese A from that of cheeses B and C. Cheeses B and C developed a unique ‘balanced’ ‘strong’ flavour early in ripening with a ‘caramel’ and ‘musty’ odour and ‘sweet’ ‘astringent’ flavour compared to cheese A. Hierarchical cluster analysis grouped C at 2 months with B at 6 and 8 months reflecting accelerated flavour development. Proteolytic and sensory data support the hypothesis that autolysis accelerates the rate of cheese ripening.

Introduction

A period of ripening is required for flavour development in most cheese types and can extend up to 1–2 years for some hard cheese varieties. Attempts to shorten the ripening time using a range of ripening systems have had varying degrees of success (Law, 2001). Approaches which have been used include the addition of exogenous enzymes or cheese slurries to the curd, use of modified or novel starters or starter adjunct cultures and elevated ripening temperatures (Wilkinson, 1993). With advancing technology and changing markets, new goals for ripening systems are emerging. These include: flavour improvement of low fat cheeses, enhancement of flavour intensity, production of fast ripening cheeses for use in processed cheese products, the development of new uniquely flavoured cheeses, and improvement in flavour consistency.

Many studies have reported the inclusion of various strains of lactobacilli as adjuncts to improve flavour development and accelerate cheese ripening. In general, such adjuncts modified proteolysis, resulting in the formation of high concentrations of free amino acids (FAA) and improved flavour compared to the control cheese (Broome, Krause, & Hickey, 1990; Trepanier, Simard, & Lee, 1991; McSweeney, Fox, Lucey, Jordan, & Cogan, 1993; Lane & Fox, 1996; Crow, Curry, & Hayes, 2 (1996), Lynch, McSweeney, Fox, Cogan, & Drinan (1997); Crow, Curry, & Hayes, 2001). The use of adjuncts in addition to normal starter cultures in cheese-making can result in higher concentrations of enzymes in cheese, without concomitant overproduction of lactic acid in the vat.

The proteolytic system of lactococci and lactobacilli consists of an extracellular proteinase (Prt P), and a range of intracellular peptidases including: oligoendopeptidases (Pep O, Pep F), general aminopeptidases (Pep N, Pep C, Pep G), glutamyl aminopeptidase (Pep A), pyrolidone carboxylyl peptidase (PCP), prolyl-dipeptidyl aminopeptidase (Pep X), proline iminopeptidase (Pep I), aminopeptidase P (Pep P), prolinase (Pep R), prolidase (Pep Q), general dipeptidase (Pep V) and general tripeptidase (Pep T) (Christensen, Dudley, Pederson, & Steele, 1999). The action of these endo- and exopeptidases leads to the production of oligopeptides and FAA, which are in turn flavour precursors (Visser, 1977a; Visser & de Groot-Mostert, 1977b; Law, 1984; Fox & Wallace, 1997). The proteolytic system of lactobacilli is less well studied than that of lactococci but, in general, both possess similar proteinases and peptidases (Sousa, Ardö, & McSweeney, 2001). Many of these peptidases have been isolated and purified although their cellular location has not been unequivocably defined. However, it is likely to be similar to the peptidases of lactococci which were shown to be intracellular (Kunji, Mierau, Hagting, Poolman, & Konings, 1996; Laan, Haverkort, de Leij, & Konings, 1996). Cell lysis is therefore a necessary step to release the cytoplasmic peptidases into the cheese curd and allow access to their substrates. The earlier the peptidases are released, through lysis, the sooner they can participate in proteolysis and, hence, accelerate ripening. According to Law (2001), the rate and extent of starter culture lysis in young cheese is linked positively to the quality and rate of development of flavour in Cheddar cheese.

Previous studies have shown that starter lysis in cheese results in an increase in the concentration of FAA and to a decrease in bitterness (Chapot-Chartier, Deniel, Rousseau, Vassal, & Gripon (1975a), Bie & Sjöström (1975b); Chapot-Chartier, Deniel, Rousseau, Vassal, & Gripon, 1994; Wilkinson, Guinee, O’Callaghan, & Fox, 1994; Crow et al., 1995a; Crow, Martley, Coolbear, & Roundhill, 1995b; O’Donovan, Wilkinson, Guinee, & Fox, 1996; Kawabata et al., 1997). Hence, the selection of highly autolytic strains for cheese manufacture not only appears to be a means to accelerate the development of cheese flavour but also to potentially improve its sensory characteristics. In a review of the autolysis of thermophilic lactobacilli, Lortal, Lemée, and Valence (1997) suggested that the intracellular location of peptidases can, through autolysis, influence the final flavour of several kinds of cheese.

In a series of studies, El Soda, Madkor, and Tong (1999) and Madkor, El Soda, and Tong (1999), Madkor, El Soda, and Tong (1999 (2000) investigated the potential of several strains of Lb. helveticus as adjuncts in cheese ripening. These researchers characterised the autolytic rate and enzymatic activities in buffer systems and found great variability between strains. They predicted that strains with high levels of peptidase activities as well as high autolytic levels may have a significant impact on cheese ripening. In cheese slurry systems (incubated at 32°C for 5 d) the use of such strains resulted in proteolytic and lipolytic changes resembling that of a 3 month old mild flavoured cheese. Using attenuated cells of Lb. helveticus as an adjunct in Cheddar cheese, they found significantly higher levels of free amino nitrogen, and flavour development without a detrimental effect on cheese texture or quality.

Drake, Boyleston, Spence, and Swanson (1996), El Soda, Madkor, and Tong (1999) investigated the use of a strain of Lb. helveticus WSU19 as an adjunct in full-fat and reduced-fat Cheddar cheese. They concluded that inclusion of this strain increased proteolysis, significantly enhanced flavour scores and reduced bitterness after 3 and 6 months of ripening. Kiernan, Beresford, O’Cuinn, and Jordan (2000) investigated autolysis of lactobacilli during Cheddar cheese ripening. Cheese was manufactured using a blend of Lactococcus lactis subsp. lactis 303 and L. lactis subsp. cremoris 227 as starter and single strains of mesophilic lactobacilli or Lb. helveticus DPC4571 as starter adjunct. It was concluded that strains of mesophilic lactobacilli did not autolyse during cheese ripening while Lb. helveticus 4571 did. Fenelon, Beresford, and Guinee (2002) compared the use of six different bacterial culture systems for the production of reduced-fat Cheddar cheese. Lb. helveticus DPC4571 was added as an adjunct to the experimental cheeses. These workers concluded that the use of thermophilic adjuncts containing Lb. helveticus could impart novel flavour attributes, and improve the acceptability of, reduced-fat Cheddar cheese.

The objective of the work described in this report was to investigate the potential to accelerate Cheddar cheese ripening and enhance flavour development by the use of a known highly autolytic strain of Lb. helveticus DPC4571.