The influence of a seasonal milk supply on the biochemical and sensory properties of Cheddar cheese

The impact of seasonal calving systems with varying pasture allowance on Cheddar cheese composition, nutritional quality and ripening characteristics

The objective of this study was to examine the impact of stage of lactation (early, mid and late) and proportion of pasture in the cows diet (high: GRS, medium: PMR and no: TMR) on the composition and quality of Cheddar cheese. Triplicate trials were carried out in each stage of lactation, and milk protein and fat contents were standardized for Cheddar cheese manufacture at pilot scale. As cheese milks were standardized for milk fat and protein contents, gross composition did not differ as a result of diet. Fatty acid profiles of GRS cheese were significantly different from TMR, while PMR profiles were less distinct and more similar to both GRS and TMR profiles, as illustrated by partial least squares discriminatory analysis. Fatty acids including CLA C18:2 cis-9, trans-11, C22:1 n-9 and C18:3 n-3 were most influential in this separation of profiles. Fatty acid profiling revealed that GRS derived cheese contained higher proportions of nutrients considered beneficial for human health including higher proportions of unsaturated fatty acids and omega-3 fatty acids. A biomarker model utilizing the proportions of 5 fatty acids was constructed and was effective at distinguishing between cheese of GRS, TMR and PMR feeding systems. Proportions of ρ-κ-casein, αs2-casein and αs1-casein in cheese also differed between diets while proportions of ρ-κ-casein, αs1-casein and β-casein were lowest in late lactation cheese. The impact of diet was less influential compared with that of stage of lactation on the ripening characteristics of cheese. An index of primary proteolysis was highest in late lactation cheese. The peptides derived from the proteolysis of κ-casein and β-casein and levels of secondary proteolysis, in particular, the proportions of 12 free amino acids were most influenced by stage of lactation. Overall this study demonstrated the effects of increasing pasture allowance and stage of lactation on the nutritional quality and ripening properties of Cheddar cheese.

Impact of feeding regimes and lactation stage on sensory attributes of Cheddar cheese

This study investigated the effects of diet and stage of lactation (SOL) on sensory profiles, texture, volatile profiles, and colour of Cheddar cheese. Cheddar cheese was manufactured from early-, mid-, and late-lactation milk obtained from seasonally calved cows (n = 54). Cows were assigned a diet; group 1: perennial ryegrass (GRS), group 2: total mixed ration (TMR), and group 3: partial mixed ration (PMR). Instrumental analysis was performed at 270 days (mature Cheddar). Sensory evaluation took place after 548 days (extra mature Cheddar). Toluene was the only volatile compound that was significantly influenced by diet. The trained panel rated early-lactation cheese as stronger than mid- and late- for cowy/barny flavour and late-lactation cheese as sweeter than early- and mid-lactation cheese. Mid-lactation cheese was liked least overall. Early-lactation cheeses were rated higher for 'crumbly' texture than mid- and late. Diet affected consumer ratings, with GRS and PMR cheese rated as more intense than TMR for flavour, aftertaste, and saltiness. Consumers reported that TMR cheese was lighter in colour compared to GRS cheese, which was supported by instrumental analysis. Consumers perceived GRS as more springy and less crumbly than TMR and PMR, while Texture Profile Analysis indicated that TMR was harder than GRS. Consumer segmentation was observed with two clear preference groups, one preferring GRS and one preferring TMR. For both groups, 'taste' seemed to be the main driver of liking, highlighting that consumer preference is most impacted by individual taste preferences.

Effect of seasonal variations on the acid gelation of milk

We investigated the effect of seasonal variations on the acid gelation properties of bovine milk in a seasonal-calving New Zealand herd for 2 full milking seasons. We tested the formation of acid gels in 2 milk systems: unstandardized skim milk and standardized whole milk (4.6% protein, 4.0% fat). For unstandardized skim milk, late-season milk acid gels had a longer gelation time and a lower gelation pH than early- and mid-season milk acid gels, but we found no consistent seasonal variation in the final storage modulus. For standardized milk, late-season milk had the most inferior acid gelation properties during the year, including the lowest final storage modulus, the lowest gelation pH, and the longest gelation time. Standardization alleviated but did not eliminate the prolonged gelation time of late-season milk. These results indicated that the physicochemical properties of seasonal milk contributed greatly to its acid gelation, independent of differences in protein content. Standardization was not adequate to stabilize the acid gelation properties of late-season milk. Desirable acid gelation properties correlated with lower glycosylated κ-casein content, lower β-lactoglobulin:α-lactalbumin ratio, lower extent of whey protein-casein micelle association, and lower total calcium and ionic calcium content. We discuss the possible effects of the correlating variables on the acid gelation properties of seasonal milk. Natural variations in the glycosylation degree of κ-casein might play an important role in acid gel structural development by altering the electrostatic and hydrophobic interactions among the milk proteins.

Composition, coagulation characteristics, and cheese making capacity of yak milk

Yak is one of the few species of which the rennet-coagulated cheese making characteristics of its milk are still not well understood. This study investigated composition and rennet-induced coagulation properties of milk from 17 individual yak cows in comparison with milk from 32 individual Holstein cows. Yak cows produced milk with generally higher concentrations of milk components. The concentrations of fat, protein, solids-not-fat (SNF), and calcium in yak milk were 1.89-, 1.68-, 1.46-, and 2-fold those in Holstein milk, respectively. The hydrodynamic radii of casein micelles (187.25 nm) and chymosin-induced paracasein (1,620 nm) were about twice the sizes of those found in Holstein milk. Higher concentrations of calcium in yak milk, together with larger sizes of casein micelles, explains the reason for its fast rate of curd formation and firmer curd texture. Optical microrheology analysis also showed that Ca²⁺ concentration had greater influence on the coagulation of yak milk than on Holstein milk. Cheese making trials with yak and Holstein milk proved the higher cheese yield of yak milk: 1.67-fold that of Holstein milk. Therefore, yak milk could be a suitable source of milk for enzyme-coagulated cheese making.

Estimating the impact of somatic cell count on the value of milk utilising parameters obtained from the published literature

The impact of mastitis on milk value per litre independent of the effect of mastitis on milk volume, was quantified for Ireland using a meta-analysis and a processing sector model. Changes in raw milk composition, cheese processing and composition associated with increased bulk milk somatic cell count (BMSCC) were incorporated into the model. Processing costs and market values were representative of current industry values. It was assumed that as BMSCC increased (i) milk fat and milk protein increased and milk lactose decreased, (ii) fat and protein recoveries decreased, (iii) cheese protein decreased and cheese moisture increased. Five BMSCC categories were examined from ⩽100 000 to >400 000 cells/ml. The analysis showed that as BMSCC increased the production quantities reduced. An increase in BMSCC from 100 000 to >400 000 cells/ml saw a reduction in net revenue of 3·2% per annum (€51·3 million) which corresponded to a reduction in the value of raw milk of €0·0096 cents/l.

Encapsulation of a Lactic Acid Bacteria Cell-Free Extract in Liposomes and Use in Cheddar Cheese Ripening

A concentrated form of cell free extract (CFE) derived from attenuated Lactococcus lactis supsb. lactis 303 CFE was encapsulated in liposomes prepared from two different proliposome preparations (Prolipo Duo and Prolipo S) using microfluidization. Entrapment efficiencies of 19.7 % (Prolipo S) and 14.0 % (Prolipo Duo) were achieved and the preparations mixed in the ratio 4 (Prolipo Duo):1 (Prolipo S). Cheddar cheese trials were undertaken evaluating the performance of CFE entrapped in liposomes, empty liposomes and free CFE in comparison to a control cheese without any CFE or liposomes. Identical volumes of liposome and amounts of CFE were used in triplicate trials. The inclusion of liposomes did not adversely impact on cheese composition water activity, or microbiology. Entrapment of CFE in liposomes reduced loss of CFE to the whey. No significant differences were evident in proteolysis or expressed PepX activity during ripening in comparison to the cheeses containing free CFE, empty liposomes or the control, as the liposomes did not degrade during ripening. This result highlights the potential of liposomes to minimize losses of encapsulated enzymes into the whey during cheese production but also highlights the need to optimize the hydrophobicity, zeta potential, size and composition of the liposomes to maximize their use as vectors for enzyme addition in cheese to augment ripening.

Proteomic study of proteolysis during ripening of Cheddar cheese made from milk over a lactation cycle

Milk for cheese production in Ireland is predominantly produced by pasture-fed spring-calving herds. Consequently, there are marked seasonal changes in milk composition, which arise from the interactive lactational, dietary and environmental factors. In this study, Cheddar cheese was manufactured on a laboratory scale from milk taken from a spring calving herd, over a 9-month lactation cycle between early April and early December. Plasmin activity of 6-months-old Cheddar cheese samples generally decreased over ripening time. One-dimensional urea-polyacrylamide gel electrophoresis (PAGE) of cheese samples taken after 6 months of ripening showed an extensive hydrolysis of caseins, with the fastest hydrolysis of αs1-caseins in cheeses made in August. A proteomic comparison between cheeses produced from milk taken in April, August and December showed a reduction in levels of β-casein and appearance of additional products, corresponding to low molecular weight hydrolysis products of the caseins. This study has demonstrated that a seasonal milk supply causes compositional differences in Cheddar cheese, and that proteomic tools are helpful in understanding the impact of those differences.

Seasonal and wastewater stream variation of trace organic compounds in a dairy processing plant aerobic bioreactor

Bioreactors are often an integral part of dairy factory efforts to reduce the biological oxygen demand of their wastewater. In this study, infeed, mixed liquor and supernatant samples of an aerobic bioreactor used by a dairy factory in South-Eastern Australia were analyzed for nutrients and organic compounds using gas chromatography-mass spectrometry and physicochemical analyses. Despite different concentrations of organic inputs into the bioreactor, nutrients and trace organic compounds were reduced significantly (i.e. average concentration of trace organic compounds: infeed=1681 μg/L; mixed liquor=257 μg/L; supernatant=23 μg/L). However, during one sampling period the bioreactor was adversely affected by the organic loading. Trace organic compounds in the samples were predominantly fatty acids associated with animal products. The analyses suggest that it is possible to trace a disruptive input (i.e. infeed with high organic carbon concentrations) into an aerobic bioreactor by measuring concentrations of fatty acids or ammonia.

Discrimination of seasonality in cheeses by near-infrared technology

BACKGROUND

Owing to the importance of the season of collection of milk for cheese quality, a study was made of the usefulness of near-infrared spectroscopy (NIRS) for discriminating the seasonal origin (winter or summer) of milk and quantifying the fat content of cheeses, since fat is one of the components most affected by the season of collection of milk for the elaboration of cheeses.

RESULTS

In the internal validation, 96% of samples from winter milk and 97% of samples from summer milk were correctly classified, while in the external validation the prediction rate of samples correctly classified was 92%. Moreover, quantitative models allowed the determination of fat in winter, summer and winter + summer cheeses.

CONCLUSION

Rapid prediction of the fat content of cheeses and the seasonal origin (winter or summer) of milk was achieved using NIRS without previous destruction or treatment of samples.

Lipolysis in Cheddar Cheese Made from Raw, Thermized, and Pasteurized Milks

The evolution of free fatty acids (FFA) was monitored over 168 d of ripening in Cheddar cheeses manufactured from good quality raw milk (RM), thermized milk (TM; 65 degrees C x 15 s), and pasteurized milk (PM; 72 degrees C x 15 s). Heat treatment of the milk reduced the level and diversity of raw milk microflora and extensively or wholly inactivated lipoprotein lipase (LPL) activity. Indigenous milk enzymes or proteases from RM microflora influenced secondary proteolysis in TM and RM cheeses. Differences in FFA in the RM, TM, and PM influenced the levels of FFA in the subsequent cheeses at 1 d, despite significant losses of FFA to the whey during manufacture. Starter esterases appear to be the main contributors of lipolysis in all cheeses, with LPL contributing during production and ripening in RM and, to a lesser extent, in TM cheeses. Indigenous milk microflora and nonstarter lactic acid bacteria appear to have a minor contribution to lipolysis particularly in PM cheeses. Lipolytic activity of starter esterases, LPL, and indigenous raw milk microflora appeared to be limited by substrate accessibility or environmental conditions over ripening.

Starter bacteria are the prime agents of lipolysis in cheddar cheese

To assess the contribution of starter lactic acid bacteria (LAB) to lipolysis in Cheddar cheese, the evolution of free fatty acids (FFAs) was monitored in Cheddar cheeses manufactured from pasteurized milks with or without starter. Starter-free cheeses were acidified by a combination of lactic acid and glucono-delta-lactone. Starter cultures were found to actively produce FFAs in the cheese vat, and mean levels of FFAs were significantly higher in starter cheeses over ripening. The contribution of nonstarter LAB toward lipolysis appears minimal, especially in starter-acidified cheeses. It is postulated that the moderate increases in FFAs in Cheddar cheese are primarily due to lack of access of esterase of LAB to suitable lipid substrate. The results of this study indicate that starter esterases are the primary contributors to lipolysis in Cheddar cheese made from good quality pasteurized milk.