Survival of probiotic adjunct cultures in cheese and challenges in their enumeration using selective media

Various selective media for enumerating probiotic and cheese cultures were screened, with 6 media then used to study survival of probiotic bacteria in full-fat and low-fat Cheddar cheese. Commercial strains of Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus paracasei, or Bifidobacterium lactis were added as probiotic adjuncts. The selective media, designed to promote growth of certain lactic acid bacteria (LAB) over others or to differentiate between LAB, were used to detect individual LAB types during cheese storage. Commercial strains of Lactococcus, Lactobacillus, and Bifidobacterium spp. were initially screened on the 6 selective media along with nonstarter LAB (NSLAB) isolates. The microbial flora of the cheeses was analyzed during 9 mo of storage at 6°C. Many NSLAB were able to grow on media presumed selective for Lactococcus, Bifidobacterium spp., or Lb. acidophilus, which became apparent after 90 d of cheese storage, Between 90 and 120 d of storage, bacterial counts changed on media selective for Bifidobacterium spp., suggesting growth of NSLAB. Appearance of NSLAB on Lb. casei selective media [de man, Rogosa, and Sharpe (MRS) + vancomycin] occurred sooner (30 d) in low-fat cheese than in full-fat control cheeses. Differentiation between NSLAB and Lactococcus was achieved by counting after 18 to 24 h when the NSLAB colonies were only pinpoint in size. Growth of NSLAB on the various selective media during aging means that probiotic adjunct cultures added during cheesemaking can only be enumerated with confidence on selective media for up to 3 or 4 mo. After this time, growth of NSLAB obfuscates enumeration of probiotic adjuncts. When adjunct Lb. casei or Lb. paracasei cultures are added during cheesemaking, they appear to remain at high numbers for a long time (9 mo) when counted on MRS + vancomycin medium, but a reasonable probability exists that they have been overtaken by NSLAB, which also grow readily on this medium. Enumeration using multiple selective media can provide insight into whether it is the actual adjunct culture or a NSLAB strain that is being enumerated.     

Assessing the proteolytic and lipolytic activities of single strains of mesophilic lactobacilli as adjunct cultures using a Caciotta cheese model system

Seventeen strains of mesophilic lactic acid bacteria, isolated from cheese (non-starter lactic acid bacteria, NSLAB) or sourdough, were used individually as adjunct cultures in a Caciotta cheese model system. Adjunct cultures were monitored by randomly amplified polymorphic DNA analysis and their cell counts mainly varied from ca. 9.0 to 8.0 log cfu g⁻¹ throughout 36 days of ripening. Adjunct cultures influenced differently cheese proteolysis. Both NSLAB and sourdough strains caused an extensive secondary proteolysis; however, some NSLAB strains produced the highest concentration of free amino acids. Principal component analysis (PCA) differentiated cheeses manufactured with NSLAB strains Lactobacillus parabuckneri B₉F_ST, Lb. paracasei B₆₁F₅, Lb. curvatus 2768 and Lb. rhamnosus ATCC 7469 based on the accumulation of Lys, Glu, Phe, Hist, Asp and Met. Assessment of cheese lipolysis showed that: (i) highest concentrations of free fatty acids (FFA) were found with NSLAB strains Lb. rhamnosus ATCC 7469 and Lb. casei subsp. pseudoplantarum 2742 (ca. 10 500 mg kg⁻¹); (ii) PCA differentiated cheeses manufactured with NSLAB strains Lb. rhamnosus ATCC 7469 and Lb. casei subsp. pseudoplantarum 2742 based on the accumulation of palmitic (C16:0) and linoleic (C18:2) acids, and those with Lb. curvatus 2768 and Lb. parabuckneri B₉F_ST based on the high concentration of short chain FFA; (iii) the cheese made with sourdough strain Lb. sanfranciscensis CB1 had the highest levels of unsaturated FFA.     

Extension of Tosèla cheese shelf-life using non-starter lactic acid bacteria

Six strains of non-starter lactic acid bacteria (NSLAB) were used to extend the shelf-life of the fresh cheese Tosèla manufactured with pasteurised cows’ milk. The acidification kinetics of three Lactobacillus paracasei, one Lactobacillus rhamnosus and two Streptococcus macedonicus were studied in synthetic milk medium. Lb. paracasei NdP78 and NdP88 and S. macedonicus NdP1 and PB14-1 showed an interesting acidifying capacity and were further characterised for growth in UHT milk and production of antimicrobial compounds. Lb. paracasei NdP78 and S. macedonicus NdP1 grew more than 2 log cycles in 6 h. Lb. paracasei NdP78 was also found to produce a bacteriocin-like inhibitory substance (BLIS) active against Listeria monocytogenes. The four NSLAB strains (singly or in combination) were used to produce experimental pilot-scale cheeses which were compared by a panel. The cheese manufactured with the mixed culture Lb. paracasei NdP78 - S. macedonicus NdP1 was the most appreciated for its sensory properties. The cheeses produced at factory-scale showed higher concentrations of lactobacilli (7.90 log CFU/g) and streptococci (6.10 log CFU/g), but a lower development of coliforms (3.10 log CFU/g) and staphylococci (2.78 log CFU/g) than control cheese (4.86, 4.89, 4.93 and 5.00 log CFU/g of lactobacilli, streptococci, coliforms and staphylococci, respectively) processed without NSLAB addition. The food pathogens Salmonella spp. and Listeria monocytogenes were never detected. The dominance of the species inoculated was demonstrated by denaturing gradient gel electrophoresis (DGGE), whereas strain recognition was evaluated by randomly amplified polymorphic DNA (RAPD)-PCR. From the results obtained, Lb. paracasei NdP78 and S. macedonicus NdP1 were able to persist during the storage of Tosèla cheese and their combination influenced positively the sensory characteristics and shelf-life of the final product.     

Investigation of the ability of dairy nonstarter lactic acid bacteria to grow using cell lysates of other lactic acid bacteria as the exclusive source of nutrients

A new device named a cell sonicated substrate membrane system (CSSMS), consisting of a tissue culture insert that supplies nutrients, in the form of starter lactic acid bacteria (SLAB) lysate extract, through a polycarbonate membrane which isolates it from the nonstarter lactic acid bacteria (NSLAB) inoculum and serves as a support for bacterial growth, was developed. The CSSMS was used to demonstrate that the Lactobacillus helveticus SLAB lysate provides sufficient nutrients to allow the growth of L. casei and L. rhamnosus NSLAB in vitro. The results support the hypothesis that NSLAB could grow in aged cheese using only SLAB cell lysate as nutrients.     

Ripening of Cheddar cheese made from blends of raw and pasteurised milk

Cheddar cheeses were made from pasteurised milk (P), raw milk (R) or pasteurised milk to which 10 (PR10), 5 (PR5) or 1 (PR1) % of raw milk had been added. Non-starter lactic acid bacteria (NSLAB) were not detectable in P cheese in the first month of ripening, at which stage PR1, PR5, PR10 and R cheeses had 10⁴, 10⁵, 10⁶ and 10⁷ cfu NSLAB g⁻¹, respectively. After ripening for 4 months, the number of NSLAB was 1–2 log cycles lower in P cheese than in all other cheeses. Urea–polyacrylamide gel electrophoretograms of water-soluble and insoluble fractions of cheeses and reverse-phase HPLC chromatograms of 70% (v/v) ethanol-soluble as well as -insoluble fractions of WSF were essentially similar in all cheeses. The concentration of amino acids were pro rata the number of NSLAB and were the highest in R cheese and the lowest in P cheese throughout ripening. Free fatty acids and most of the fatty acid esters in 4-month old cheeses were higher in PR1, PR5, PR10 and R cheeses than in P cheese. Commercial graders awarded the highest flavour scores to 4-month-old PR1 cheeses and the lowest to P or R cheese. An expert panel of sensory assessors awarded increasingly higher scores for fruity/sweet and pungent aroma as the level of raw milk increased. The trend for aroma intensity and perceived maturity was R>PR10>PP5>PR1>P. The NSLAB from raw milk appeared to influence the ripening and quality 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

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.     

Application of Lactobacillus amylovorus as an antifungal adjunct to extend the shelf-life of Cheddar cheese

Lactobacillus amylovorus DSM 19280 is an antifungal strain that is inhibitory to a range of fungi including Penicillium expansum, Penicillium roqueforti, Aspergillus niger, Aspergillus fumigatus and Fusarium culmorum. In this study, the strain was used as an adjunct culture in a Cheddar cheese model system. During the ripening period, P. expansum spores were applied to the cheese surface to mimic fungal contamination. The presence of the antifungal L. amylovorus adjunct resulted in a four-day delay in appearance of Penicillium growth on the cheese in comparison to the adjunct-free control. When cheeses were exposed to natural airborne fungi, the presence of the adjunct resulted in a six-day delay in the appearance of mycelia on the cheese surface. Significantly, its presence had no detectable negative impact on cheese quality. The results indicate that the strain could have an application for extending the shelf-life of cheeses which are prone to fungal spoilage.     

Technological properties of candidate probiotic Lactobacillus plantarum strains

The study of new probiotic strains for their technological relevance and use in dairy products is important for trade and industry. Eight Lactobacillus plantarum strains isolated from Bulgarian cheeses and selected for their potential probiotic properties were characterized. In vitro tests with the API ZYM system revealed high aminopeptidase and phosphatase activity, and weak lipolytic activity. The L. plantarum strains showed also a weak proteolytic activity and were characterized as slow variants on the base of their coagulation ability. They maintained high viability in fermented milk over extended shelf-times at refrigerated temperature and demonstrated a good adaptation to 6% NaCl. Among the preservatives, only calcium propionate did not affect the growth of L. plantarum. The highest concentrations used of potassium sorbate (0.5 and 1%) and nisaplin (0.02%) decreased the bacterial growth. One L. plantarum strain was tested as an adjunct to commercially available formula for cream cheese. This candidate probiotic culture withstood the technological processing and retained high number of 10⁷ cfu g^?1 at the end of the 3 months storage period at 4 °C.     

Nonstarter lactic acid bacteria biofilms and calcium lactate crystals in Cheddar cheese

A sanitized cheese plant was swabbed for the presence of nonstarter lactic acid bacteria (NSLAB) biofilms. Swabs were analyzed to determine the sources and microorganisms responsible for contamination. In pilot plant experiments, cheese vats filled with standard cheese milk (lactose:protein = 1.47) and ultrafiltered cheese milk (lactose:protein = 1.23) were inoculated with Lactococcus lactis ssp. cremoris starter culture (8 log cfu/mL) with or without Lactobacillus curvatus or Pediococci acidilactici as adjunct cultures (2 log cfu/mL). Cheddar cheeses were aged at 7.2 or 10°C for 168 d. The raw milk silo, ultrafiltration unit, cheddaring belt, and cheese tower had NSLAB biofilms ranging from 2 to 4 log cfu/100 cm². The population of Lb. curvatus reached 8 log cfu/g, whereas P. acidilactici reached 7 log cfu/g of experimental Cheddar cheese in 14 d. Higher NSLAB counts were observed in the first 14 d of aging in cheese stored at 10°C compared with that stored at 7.2°C. However, microbial counts decreased more quickly in Cheddar cheeses aged at 10°C compared with 7.2°C after 28 d. In cheeses without specific adjunct cultures (Lb. curvatus or P. acidilactici), calcium lactate crystals were not observed within 168 d. However, crystals were observed after only 56 d in cheeses containing Lb. curvatus, which also had increased concentration of d(−)-lactic acid compared with control cheeses. Our research shows that low levels of contamination with certain NSLAB can result in calcium lactate crystals, regardless of lactose:protein ratio.     

Biochemical,microbial and sensory evaluation of white soft cheese made from cow and lupin milk

The aim of the present study was to evaluate some physicochemical, microbiological and sensory properties of fresh and matured (75 days) soft cheeses made with mixtures of cow milk and 0, 25, 50 and 75 mL/100 mL of lupin milk. A remarkable increase in cheese yield was observed with increasing the level of lupin milk to the mixture. Compared to cow milk cheese, the protein content was significantly (P ≤ 0.05) increased while ash was decreased with the increase in the level of lupin milk for both fresh and matured cheese. However, fat content, total solids and acidity were increased only for fresh cheese and decreased for mature one compared to that of cow milk. The pH showed significant (P ≤ 0.05) reduction when the levels of lupin milk increased for fresh cheese while for matured cheese it slightly decreased. The total bacterial count is within the range that naturally exists in milk containing foods. The others microorganisms such as fungi, mold, Escherichia coli, and Salmonella were not existed in both types of cheese. Regardless of cheese color, incorporation of lupin milk at low concentration (25 mL/100 mL) significantly (P ≤ 0.05) enhanced the taste, texture, flavor, and overall acceptability of both fresh and mature cheese.     

Discrimination of commercial Caciocavallo cheeses on the basis of the diversity of lactic microflora and primary proteolysis

A wide variety of semi-hard pasta-filata cheese fall under the common name “Caciocavallo”, including Caciocavallo Silano, a Protected Denomination of Origin (PDO) cheese produced in Southern Italy. Multivariate analysis techniques were used to investigate the specificity of Caciocavallo Silano PDO cheeses within the area of production and to compare them with cheeses of similar denomination or cheeses produced with similar technology. The composition of lactic acid bacteria (LAB) communities at the species level and the primary proteolysis of commercial cheeses were assessed. A high variability was observed in the composition of LAB communities, and no clear relationship was found with either the region of origin or the cheese denomination. However, the microflora of PDO cheeses was less heterogeneous than that of non-PDO cheeses and composed mainly of non-starter lactic acid bacteria (NSLAB) such as Lactobacillus paracasei, L. fermentum, and L. plantarum. A high diversity in the proteolytic pattern of the cheeses was also found. This diversity was associated with the trends observed in the community of LAB populating each of the cheeses. The main problems concerning the protection of the denomination are discussed.     

Antifungal activity of Meyerozyma guilliermondii: Identification of active compounds synthesized during dough fermentation and their effect on long-term storage of wheat bread

Preliminarily, 146 strains of yeasts were screened for the antifungal activity toward the indicator Penicillium roqueforti DPPMAF1. The strain Meyerozyma guilliermondii LCF1353 was selected and used for dough fermentation. The water/salt soluble extract of the dough was analyzed by HPLC and GC/MS-SPME. The synthesis of the extracellular cell wall-degrading enzyme β-1,3-glucanase and ethyl-acetate was shown. The effect on conidia germination mainly suggested a fungistatic activity. M. guilliermondii LCF1353 was used as starter for dough fermentation in combination with Wickeramomyces anomalus 1695 and Lactobacillus plantarum 1A7, which were previously selected for antifungal activity. The growth of the strains was monitored by plate count and molecular techniques, and competitive or antagonistic interactions among them were excluded. Bread started with the combination of M. guilliermondii LCF1353, W. anomalus LCF1695 and L. plantarum 1A7 showed a more prolonged shelf life compared to the other breads. Fungal growth was delayed at least until 14 days of storage, under conditions of high artificial inoculum. The bread manufactured with the above combination showed good chemical and textural characteristics and, as shown by sensory analysis, it was appreciated for elasticity, color and taste.     

Production and Characterization of an Antifungal Compound (3-Phenyllactic Acid) Produced by <Emphasis Type="Italic">Lactobacillus plantarum</Emphasis> Strain

The Lactobacillus plantarum strain was isolated from grass silage that produces a broad spectrum of antifungal compound, active against food and feed-borne filamentous fungi in agar plate assay. Aspergillus fumigatus and Rhizopus stolonifer were the most sensitive among molds. No inhibitory activity could be detected against mold Penicillium roqueforti. Enhanced antifungal activity was observed at 30 °C in pH 6.5. Minimum inhibitory concentration values against fungal cultures were ranged from 6.5 to 12.0 mg/ml for commercial 3-phenyllactic acid. The production of antifungal compound phenyllactic acid (PLA), lactic acid, and acetic acid by L. plantarum strain was also investigated. Structure characterization of the antifungal compound was carried out by nuclear magnetic resonance spectroscopy, infrared spectroscopy, and gas chromatography. The produced compound (PLA) acted as a fungistatic and delayed the growth of a variety of fungal contaminants.     

Phenotypic and genotypic characterization of non-starter Lactobacillus species diversity in Indian Cheddar cheese

A total of 243 non-starter lactobacilli were isolated from 12 premium quality Indian Cheddar cheese samples ripened for different periods and in different plant conditions. They were classified up to species level using mainly sugar fermentation assay and PCR. Based upon phenotypes, a maximum of 46.50% were classified as Lactobacillus paracasei, followed by 34.98% isolates as Lactobacillus plantarum. Only 3.29% were classified as Lactobacillus rhamnosus and 4.12% as Lactobacillus delbrueckii species, while 22 (9.05%) isolates (of which 16 L. plantarum/Lactobacillus paraplantarum and 6 Lactobacillus delbrueckii ssp. lactis/Lactobacillus crispatus) could not be designated to a single species. One isolate of Lactobacillus coryniformis ssp. coryniformis was isolated for the first time from Cheddar cheese (0.41%) while 1.65% isolates remained unidentified. Mostly, the tentative characterization based on phenotype, could be confirmed by PCR targeting rRNA. Those isolate groups which could not be tested in PCR, or resembled with more than one species in their phenotypic traits, could be resolved by the BLAST homology analysis of the partial tuf gene sequences of few representative isolates.     

Effect of biopolymers containing natamycin against Aspergillus niger and Penicillium roquefortii on fresh kashar cheese

Fungal spoilage during refrigerated storage is one of the main safety and quality‐related problems for dairy products. The effect of wheat gluten (WG) and methyl cellulose (MC) biopolymers containing natamycin (NA) on the growth of Aspergillus niger and Penicillium roquefortii on the surface of fresh kashar cheese during storage at 10 °C for 30 days was investigated. Wrapping of A. niger‐inoculated cheese with MC films containing 5–20 mg NA per 10 g resulted in approximately 2‐log reductions in spore count. Two mg NA per 10 g included into WG films was sufficient to eliminate A. niger on the surface of cheese. However, MC and WG films containing NA did not cause any significant decrease in P. roquefortii count on the cheese surface. Therefore, especially use WG films in dairy applications could be an effective way of controlling A. niger growth on these products.     

Evaluation of antimicrobial and physical properties of edible film based on carboxymethyl cellulose containing potassium sorbate on some mycotoxigenic Aspergillus species in fresh pistachios

Active packaging is a relatively novel concept of packaging that changes the conditions of the packaged food to extend its shelf-life and improve its safety. In this study, antimicrobial effects of carboxymethyl cellulose based-edible film containing potassium sorbate as an antimicrobial agent were studied against Aspergillus flavus (PTCC-5004), Aspergillus parasiticus (PTCC-5286) and A. parasiticus (PTCC-5018) by using agar diffusion assay. Results showed suitable inhibition effects against A. parasiticus (PTCC-5286) and A. flavus (PTCC-5004) in comparison with A. parasiticus (PTCC-5018). Pistachios were coated with this edible antimicrobial film containing three concentrations of sorbate (1, 0.5 and 0.25 g/100 mL film solution); all concentrations showed no growth of molds. Tensile strength values of films with potassium sorbate, decreased when compared to control, and film’s flexibility, was 28.82 percent for 3 g/100 mL sorbate, while higher concentration of sorbate, decreased the flexibility. The water vapor permeability values (WVP) of films were determined to be 1.18 (g mm/m² day kPa) for films plasticized with glycerol, without sorbate while WVP values for the films containing 1 and 2 g/100 mL sorbate increased to 3.77 and 15.5 (g mm/m² day kPa), respectively. The observed glass transition temperature (T_G) depression for these polymer blends was related to the plasticizer content (water, polyethylene, and glycerol), especially water.     

Manufacture of low-fat Cheddar cheese by exopolysaccharide-producing Lactobacillus plantarum JLK0142 and its functional properties

This study aimed to evaluate the effect of exopolysaccharide (EPS)-producing Lactobacillus plantarum JLK0142 on the ripening characteristics and in vitro health-promoting benefits of low-fat Cheddar cheese. Three batches of cheese were made by employing a non-EPS–producing cheese starter (control), in combination with Lb. plantarum JLK0142 as an adjunct and the purified EPS as an ingredient. Lactobacillus plantarum JLK0142 survived well in cheese, with counts of 7.99 log cfu/g after 90 d of ripening. All experimental cheeses (with adjunct culture or EPS ingredient) had higher moisture, proteolysis, and sensory scores, and lower hardness and cohesiveness compared with the control cheese. Water-soluble extracts from the experimental cheeses outperformed that of the control in scavenging 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS), and hydroxyl radicals, and inhibiting α-amylase, angiotensin-converting enzyme, and HT-29 tumor cell growth. Therefore, incorporation of the EPS-producing culture of Lb. plantarum JLK0142 is promising for improvement of low-fat cheese quality and bioactivities.     

Technological and probiotic role of adjunct cultures of non-starter lactobacilli in soft cheeses

The influence of two cheese-isolated Lactobacillus strains on cheese composition, acceptability and probiotic capacity was assessed. Soft cheeses with and without the addition of Lactobacillus plantarum I91 or Lactobacillus paracasei I90 were prepared. Gross composition was assessed and secondary proteolysis was described by soluble fractions and free amino acids profiles. Acceptability was determined by a panel of 98 non-trained consumers. Cheeses harboring added Lactobacillus strains were also studied in vivo to evaluate their probiotic capacity. Gross composition of the cheeses was similar for control and treated (Lactobacillus-added) cheeses. Peptidolysis increased in cheeses with added lactobacilli, which was evidenced by a higher free amino acid content. Overall, the acceptability of the cheeses was good: 65%–80% of the consumers said that they “liked very much” or “liked” the cheeses. Cheeses with L. plantarum I91 showed the highest changes in composition and proteolysis and were the most accepted ones. On the contrary, composition of cheeses with L. paracasei I90 was similar to that of the controls, but these samples were less accepted than cheeses without lactobacilli. The oral administration of cheese containing L. plantarum I91 or L. paracasei I90 proved to be safe and able to enhance the number of IgA + cells in the small intestine lamina propria of mice. The use of selected strains of NSLAB exerted a technological and probiotic role: it contributed to the standardization of cheese quality and induced benefic health effects at the gut mucosa in vivo.     

Influence of high-pressure processing (HPP) on physico-chemical properties of fresh cheese

Freshly prepared rennet-coagulated soft cheese was high-pressure (HP) treated at up to 291 MPa and 29 min and using a full 2-factor central composite design of experiment, its physico-chemical properties (colour, fat, lipid oxidation, moisture and protein content, pH, and texture) were examined. HP treatment influenced significantly (p < 0.05) the colour, fat, moisture, lipid oxidation, hardness and adhesiveness of the fresh cheese. Fat content increased apparently as moisture decreased significantly after HP treatment of above 100 MPa. Increased pressures reduced lipid oxidation but increased yellowness although the latter showed more effect over redness in the HP-treated fresh cheese. Also, increased pressures increased hardness, decreased acidity and adhesiveness in HP-treated fresh cheese although increased exposure was found to increase acidity.Industrial relevanceHigh isostatic pressure for processing fresh cheese is yet to be adopted on an industrial scale. There is a need for research to provide evidence that improved properties of fresh cheese can be realized. The effects of HPP on rennet-coagulated soft Scottish cheese are investigated and the data from this study have provided points where optimized characteristic properties of HPP fresh cheese can be attained, which can serve as a lead for HPP users on fresh cheese.     

Proteolytic and other hydrolytic enzyme activities in non-starter lactic acid bacteria (NSLAB) isolated from cheddar cheese manufactured in the United Kingdom

The populations of non-starter lactic acid bacteria (NSLAB) in a selection of 15 good-quality UK-manufactured Cheddar cheeses that had been matured for 6-9 months ranged from 10⁵ to 10⁷ bacteria g⁻¹. Fifteen different species of lactic acid bacteria were identified using commercially-available identification systems. The species isolated most frequently were Lactobacillus paracasei subsp. paracasei and Lb. plantarum; 10 other species were isolated from two or more cheeses and three species were recovered from only a single cheese. There were marked differences in the NSLAB populations of the cheeses produced by different UK manufacturers, and differences were also apparent in the populations of two cheeses produced on different occasions at the same creamery. Forty-one isolates, selected to include all the species identified and the dominant strains present in cheeses produced at several different creameries, were screened for activities of 34 proteolytic, five glycoside hydrolase and five esterolytic enzymes. All the NSLAB possessed a wide range of hydrolytic enzymes and therefore had the potential to contribute at some stage to the development of cheese flavour during the maturation and ripening period. Inter-species and strain differences in enzyme profiles and levels of activity were apparent and were determinants for the non-random selection of NSLAB for use as adjunct cultures in subsequent cheese-making trials. The breakdown of diagnostic substrates was indicative of the presence of multiple proteinase, tripeptidase, dipeptidase (including prolinase- and prolidase-like), dipeptidyl peptidase, prolyl, proline, aspartyl, pyroglutamyl (pyrrolidone-carboxyl) and general aminopeptidase activities.