Jean M. Banks

Comparison of the microbiological, compositional, biochemical, volatile profile and sensory characteristics of three Italian PDO ewes’ milk cheeses

Abstract Three batches of three Italian ewes’ milk cheeses (Canestrato Pugliese, Fiore Sardo and Pecorino Romano), which were manufactured under the Protected Denomination of Origin (PDO), were compared for microbiological, compositional, biochemical, volatile profile and sensory characteristics. After ca. 1 year of ripening, the three cheeses had a complex microbial population, composed mainly of non-starter lactic acid bacteria (NSLAB); several species of mesophilic lactobacilli and enterococci were identified. Pecorino Romano had a very high level of NaCl, 8.7±0.1% w/w. The level of pH 4.6-soluble nitrogen increased in the order: Canestrato Pugliese>Fiore Sardo>Pecorino Romano. Urea-PAGE electrophoresis showed that the hydrolysis of α s1 -casein was more consistent than β -casein. RP-HPLC profiles of the ethanol-soluble and ethanol-insoluble fractions of the pH 4.6-soluble nitrogen showed differences between the cheeses which agreed with the content of free amino acids. Glutamic acid, histidine, valine, isoleucine, leucine and phenylalanine were the free amino acids present at the highest levels in all the cheeses. Sixty-two volatile components were identified by Gas Chromatography-Mass Spectrometry analysis of steam distillates of the cheeses. The volatile profile of the three cheeses differed significantly. Esters were the main volatiles in the Canestrato Pugliese cheese but were the lowest in Fiore Sardo cheese. Ketones and alcohols were the principal class of volatile components in Fiore Sardo and Pecorino Romano cheeses, respectively. Lactones and products of the breakdown of the sulphur-containing amino acids were found at considerable levels in all cheeses, but aldehydes were present at low levels. Only 30 carboxylic acids were identified; Canestrato Pugliese had the highest content of total acids. Butanoic, hexanoic, octanoic and decanoic acids represented the 30–33% of the total carboxylic acids in the cheeses. The cheeses were subjected to descriptive sensory analysis; 19 discriminating and 2 descriptive attributes were analysed by Principal Component Analysis (PCA). The sensory characteristics of the three ewes’ milk cheeses were distinct.

Enhancement of amino acid catabolism in Cheddar cheese using α-ketoglutarate : amino acid degradation in relation to volatile compounds and aroma character

The effectiveness of the transaminase acceptor α-ketoglutarate in enhancing amino acid catabolism and manipulating the aroma profile of Cheddar cheese has been studied. Utilisation of α-ketoglutarate, catabolism of amino acids, volatiles production, and aroma profile of the cheese were monitored after 6, 12 and 24 weeks ripening. Glutamate and GABA were considerably enhanced on addition of the transaminase acceptor while levels of phenylalanine, leucine, isoleucine, alanine, valine, methionine and threonine were reduced. Addition of α-ketoglutarate increased volatile components originating from the catabolism of branched chain and aromatic amino acids. These compounds included acetic, propanoic, 2-methylpropanoic and 3-methylbutanoic acids, 3-methylbutanol, phenylacetaldehyde and benzaldehyde. Additionally enhanced production of 3-OH-2-butanone was evident. Addition of α-ketoglutarate increased aroma intensity, creamy and fruity aromas. Effects obtained must be verified by tasting cheeses made with food grade α-ketoglutarate, but results suggest potential benefits in accelerated maturation, low fat systems and manipulation of flavour profiles.

Energy sources of non-starter lactic acid bacteria isolated from Cheddar cheese

Abstract The range of carbon sources available in cheese curd during maturation that could be used as energy and growth substrates by 60 cultures of non-starter lactic acid bacteria isolated from Cheddar cheese was determined by the detection of tetrazolium salt reduction in Biolog MT1 microplates ™ . There were marked inter-species and strain differences in the range of carbon substrates catabolized by the 11 Lactobacillus spp. and 2 Weissella spp. examined. Sugars were used widely among the NSLAB with 90, 100 and 85% of the isolates metabolizing lactose, glucose and galactose, respectively. In addition, ribose, N -acetyl-galactosamine and sialic acid, potentially derived from nucleic acid and casein deglycosylation, were catabolized by 58, 48 and 22% of the isolates, respectively. Lactic acid was also a potential substrate for 15% of the isolates but Tween 80 was not an effective substrate. Although 50% of the NSLAB removed citric acid from the growth medium it was not an independent energy source. Peptides and amino acids were also catabolized by up to 27% of the NSLAB provided that an exogenous source of α -ketoglutaric acid was present to facilitate the aminotransferase-mediated transamination degradative pathway. The MT1 microplate method facilitates the rapid screening for isolates able to establish in the cheese curd and for the detection of specific metabolic activities in isolates undergoing evaluation for use as adjunct cultures in cheesemaking trials.

Sensory properties of Cheddar cheese: changes during maturation

Abstract The aroma, flavour and texture of 16 samples of commercial Cheddar cheese have been profiled after ripening at 10 °C for 3, 4, 6, 8, 10 and 12 months. Systematic changes in sensory character have been studied and the main changes during maturation identified. Although sensory character changed slowly during ripening, assessment early in the maturation period was an unreliable estimate of ultimate sensory character. Progressive changes in Cheddar aroma and flavour, creamy flavour, acid flavour and mouth-coating character were noted during ripening. Changes in minor components of aroma and flavour were also observed but, on average, were small. Two samples eventually developed marked rancid character and another became excessively bitter. The relation between gross composition of the cheese and sensory properties was investigated. In the early stages of ripening, the ratings for Cheddar flavour and mouth-coating character were associated with the salt content of the cheese and with the concentration of fat in dry matter. However, as the cheese matured these associations weakened.

Volatile components in steam distillates of Cheddar cheese as indicator indices of cheese maturity, flavour and odour

Abstract Chemical analyses were carried out on 12 samples of commercial Cheddar cheese differing widely in perceived maturity. Quantitative descriptive analysis of the cheeses has been previously reported elsewhere. Protein breakdown was estimated by selective fractionation of the water soluble components. Steam distillates of the cheese were also prepared. The volatiles in the steam distillates were fractionated by gas liquid chromatography and 31 peaks identified by mass spectrometry. Multivariate calibration was used to derive equations relating the sensory attributes to the chemical assay. Perceived maturity, intensity of cheddar cheese flavour and acid flavour were modelled with a high degree of fit. As a result, the chemical analyses employed offer considerable potential for objective assessment of key quality attributes of Cheddar cheese.

Variability of the species and strain phenotype composition of the non-starter lactic acid bacterial population of cheddar cheese manufactured in a commercial creamery

Abstract The non-starter lactic acid bacteria (NSLAB) present in cheddar cheese manufactured in a commercial creamery was monitored phenotypically to the strain level over a period of 12 months to examine the effects of maturity status and manufacturing practices on the composition of the population. Five Lactobacillus spp. and Leuconostoc lactis were identified among the 459 isolates selected. The predominant NSLAB, Lactobacillus paracasei and Lactobacillus brevis , were present in 59 and 31% of the cheeses examined and represented 52.7 and 25.8%, respectively, of the isolates identified. Among the NSLAB screened 71 different phenotypic profiles were identified and these included 26 biotypes of Lb. paracasei , 14 Lb. brevis , 11 Lactobacillus plantarum , 10 Lactobacillus curvatus and 7 Leuc. lactis . The average number of strains recovered from a cheese was 3.9±2.1 and ranged from 1 to 11. Although approximately 70% of the cheese samples were dominated by three or less strains the NSLAB populations were heterogeneous and the majority (61.5%) were comprised of four or more strains of one or more species. Only 30 of the biotypes were recovered from more than one population. There was no evidence for the repeated recurrence of any of the strains isolated although some of the Lb. paracasei strains were present intermittently in cheeses throughout the 12-month manufacturing period. Six Lb. brevis strains also recurred in some of the cheeses produced in a limited period during the autumn. Pronounced shifts in the species complement and strain profile occurred during maturation, while the average number of strains present in the cheese decreased with increasing maturity. Microbiological examination of the NSLAB population of cheese either produced in different vats during the same production run or manufactured in the same vat but in different production runs (vat fills) indicated that the number of strains common to paired samples from two vats or a single vat in successive production runs was only 1.7±1.4 and 1.5±1.2, respectively, and confirmed the inherent variability that exists, both within and between production runs, in the non-starter population of cheese manufactured in a commercial creamery.

Aminopeptidase and Dipeptidyl Peptidase Activity of Lactobacillus spp. and Non-starter Lactic Acid Bacteria (NSLAB) isolated from Cheddar Cheese

The complexity of the peptidolytic enzyme systems of a variety (67 strains) of non-lactococcal dairy lactic acid bacteria was established. Diagnostic substrate hydrolysis by cell lysates confirmed the widespread occurrence of general aminopeptidase and dipeptidyl peptidase activities; lower levels of other more specific aminopeptidases were also indicated. Inhibitor studies demonstrated that more than one type of leucyl aminopeptidase and dipeptidyl peptidase were present in cell lysates. Although both activities were susceptible to metallo- and serine-type inhibitors, the predominant aminopeptidase activity was associated with the metalloenzyme group whereas the principal dipeptidyl peptidase activity was mediated by serine-type protease action. Some characteristics of individual enzymes comprising the aminopeptidase and dipeptidyl peptidase activity were determined for components separated by polyacrylamide gel electrophoresis and located in situ in the gel by activity staining with amidomethylcoumarin substrates. Three individual aminopeptidases with apparent molecular masses of 95, 44 and 30 kDa and a multimer (≥180 kDa) were detected. The 95 kDa and 44 kDa enzymes were metalloenzymes whereas the 30 kDa enzyme was a serine peptidase. The 95 kDa component thus resembled pepN while the 44 and 30 kDa enzymes exhibited some characteristics of an infrequently described LAB metallodipeptidase and serine prolyl aminopeptidase, respectively. Two serine dipeptidyl peptidases, with apparent molecular masses of 88 and 125 kDa, were also detected after PAGE. The 88 kDa enzyme resembled X-prolyl-dipeptidyl aminopeptidase (pepX); the 125 kDa enzyme, not previously characterized in LAB, occurred widely among bacteria from this group. The lactobacilli, and other dairy lactic acid bacteria examined, have a complex of enzymes involved in peptide turnover, several enzymes of which have a commonality within the group.

A comparison of the flavour and texture of Cheddar cheese of factory or farmhouse origin

Diversity in the flavour and texture of Cheddar cheese was studied in 34 samples of factory or farmhouse origin. Sensory profiles were measured using an integrated Design, Data capture and Sensory Profiling Protocol (DDASPP). The main differences in character of the cheese were between the sub-set of farmhouse cheeses manufactured from raw milk and cheese made from pasteurised milk. Raw milk cheese was more intensely flavoured than conventional product, but was notable for elevated ratings for atypical flavours such as rancid, bitter and unclean. In general, farmhouse cheese showed excessively wide variations in composition which were also associated with atypical flavour or texture. Within factory-made products there was little distinction between samples of Scottish, English, Irish and Canadian origin. However, mature samples of New Zealand Cheddar were of a slightly different character. No strong relations between the sensory properties and composition of the cheese could be deduced. Nevertheless, as expected, the extent of proteolysis and moisture in non-fat solids content of the samples were associated with differences in flavour and texture.

Cheddar Cheese Flavour and Chemical Indices: Changes During Maturation

In many ways, Cheddar cheese is like wine. Its final character is determined not only by the initial composition of the product but also by the biochemical and chemical changes which occur during maturation. The cheese technologist is faced with the problem of harnessing these complex reactions to produce cheese which has a clear identity. That is, a Cheddar cheese should be quite different from a Jarlsberg. Moreover, the product must be consistent or the consumer will be confused. For example, mature Cheddar cheese should always have a flavour level and balance which meets the customer’s expectations.