Application of metabolomics to assess milk quality and traceability

Milk is a foodstuff widely consumed around the world originating from a variety of different species, animal management and production systems. In recent years, consumers have placed a much greater emphasis on the authenticity and origin of some food products often willing to pay a premium price for such products that is, for example 'Grass-Fed Dairy'. Therefore, it is important to establish methods to assess both quality and authentication of milk and dairy products for increased food security and consumer protection. Accordingly, NMR-based, GC–MS-based, and LC–MS-based metabolomics have been established as useful tools in the analysis of dairy products, such as raw and processed milk. This short-review provides an updated and critical overview on the most useful metabolomics-based platforms and the most useful multivariate statistical tools available for metabolomic data interpretation

The application of process analytical technologies (PAT) to the dairy industry for real time product characterization - process viscometry

peer-reviewedThe ideal PAT tool is an inline instrument that can monitor and measure process parameters simultaneously in real time while operating in a highly automated environment. Instruments must be of sanitary design, operate robustly within the full process cycle (production and cleaning). Inline determination of the rheological properties of moving fluids (i.e. dairy concentrates) is one of the process parameters where PAT tools can be add real value in terms of optimising process control. Measurement of process viscosity is crucial in the monitoring and control of a variety of concentration processes in the dairy industry. Continuous monitoring of the rheological behaviour of the fluid can allow for optimisation of the process e.g. pumping (avoid pump blockage and failure), evaporation (limit fouling and maximise water removal) and spray drying (avoidance of nozzle fouling). This review concentrates on the state of the art developments being made in the area of process viscometry

Effect of cow feeding system on the quality and constituents of raw milk, dairy products and the rumen

The overall aim of this thesis was to investigate the effects of pasture versus conventional indoor cow feeding systems on the composition, quality and characteristics of milk, dairy products and rumen microbiota. Initially the effects of perennial ryegrass (GRS), perennial ryegrass and white clover pasture (CLV) and total mixed ration (TMR) feeding of cows on the composition and nutritional quality of raw milk throughout an entire lactation was examined (Chapter 2). Cow diet was shown to have a significant effect (P < 0.05) on both the macrocomposition and fatty acid content of milk throughout lactation. Milk from pasture fed cows had significantly higher (P < 0.05) concentrations of fat, protein, true protein and casein. Pasture derived milk was shown to have significantly higher (P < 0.05) content of conjugated linoleic acid and omega 3 fatty acids while TMR derived milk had significantly higher (P < 0.05) palmitic acid and omega 6 fatty acids. The aim of Chapter 3 was to examine the effects of different feeding systems on the composition, quality and sensory properties of mid lactation sweet cream butter. The nutritional composition of butters was improved by pasture feeding. Alterations in the fatty acid composition of butter between feeding systems contributed to significant differences in textural and thermal properties of the butters. Volatile analysis of butter by GC-MS identified 25 compounds present in each of the butters, five of which differed significantly (P < 0.05) based on feeding system. Chapter 4 examined the effects of diet on the composition, quality and sensory properties of Cheddar cheese throughout nine months of ripening. This study demonstrated the benefits of pasture derived feeding systems for production of Cheddar cheeses with enhanced nutritional and rheological quality compared with TMR feeding system. Pasture derived feeding systems were shown to produce Cheddar cheeses more yellow in colour than that of TMR, which was positively correlated with cheese β-carotene content. Feeding system had a significant effect on the fatty acid composition of the cheeses. Differences in the cheese fatty acid content were correlated with alterations to the Cheddar cheese rheological properties. Feeding system and ripening time had a significant effect on the volatile profile of the Cheddar cheeses. Principal component analysis of average fatty acid profiles in milk, butter and Cheddar cheese showed clear separation of the products from the grazed pasture-based diets to that of a TMR system throughout lactation, offering insight into the ability to verify pasture derived milk and products by fatty acid profiling. In Chapter 5, 16s RNA MiSeq sequencing was applied to both solid and liquid fractions of cow rumen to examine the effect of cows feeding system on the rumen microbiota. There was a clear separation between the liquid and solid fractions. No major differences in the rumen microbiota composition between cows exposed to different diets was found, which is likely as a result of a shortened adaptation period. It is also clear that the majority of the rumen microbiota is still undiscovered. As such, further work is required to fully understand the effects of these diets on the rumen microbiota and its functionality. Untargeted 1 H-NMR was used to examine the effects of cows feeding system on the rumen and milk metabolome (Chapter 6). Our results show that feeding system impacted significantly on both the rumen and milk metabolome. This study has highlighted that 1 H-NMR metabolomics coupled with multivariate analysis is capable of distinguishing both rumen-fluids and milk samples derived from cows on different feeding systems. Finally, Chapter 7 discusses the major findings and general conclusions arising from the studies presented in this thesis

Influence of Supplemental Feed Choice for Pasture-Based Cows on the Fatty Acid and Volatile Profile of Milk

peer-reviewedThe purpose of this study was to examine the impact of a variety of supplemental feeds on the composition and quality of milk in a pasture-based dairy system. Four pasture-supplemented feeding systems were compared: Group 1 supplementation with 16% crude protein parlour concentrate (CONC); Group 2 supplementation with palm kernel expeller plus parlour concentrate (PKE); Group 3 supplemented with soya hulls plus parlour concentrate (SOYA); Group 4 was supplemented with molassed beet pulp plus parlour concentrate (BEET). Supplemental feeding system was demonstrated to have a significant effect on the size of native casein micelles and the gelation properties of milks. While CONC feeding produced significantly higher casein micelle size, gel strength (Young’s Modulus) was significantly negatively correlated with casein micelle size. Supplemental feeding system had a significant effect on a number of fatty acids (FA) and indices derived therefrom, including total saturated and unsaturated fatty acids, de novo produced FA, omega 3, and omega 6 FA. The volatile profile of milks was also affected by supplemental feed choice, whereby multivariate analysis demonstrated that the CONC diet was distinctly different to that of the PALM, SOYA, and BEET milks. Multivariate analysis demonstrated that it is possible to distinguish milks from different pasture-supplemented feeding systems by their FA profile

The Proportion of Fermented Milk in Dehydrated Fermented Milk–Parboiled Wheat Composites Significantly Affects Their Composition, Pasting Behaviour, and Flow Properties on Reconstitution

Peer reviewedDairy and cereal are frequently combined to create composite foods with enhanced nutritional benefits. Dehydrated fermented milk–wheat composites (FMWC) were prepared by blending fermented milk (FM) and parboiled wheat (W), incubating at 35 °C for 24 h, drying at 46 °C for 48 h, and milling to 1 mm. Increasing the weight ratio of FM to W from 1.5 to 4.0 resulted in reductions in total solids (from 96 to 92%) and starch (from 52 to 39%), and increases in protein (15.2–18.9%), fat (3.7–5.9%), lactose (6.4–11.4%), and lactic acid (2.7–4.2%). FMWC need to be reconstituted prior to consumption. The water-holding capacity, pasting viscosity, and setback viscosity of the reconstituted FMWC (16.7% total solids) decreased with the ratio of FM to W. The reconstituted FMWC exhibited pseudoplastic flow behaviour on shearing from 18 to 120 s−1. Increasing the FM:W ratio coincided with a lower yield stress, consistency index, and viscosity at 120 s−1. The results demonstrate the critical impact of the FM:W ratio on the composition, pasting behavior, and consistency of the reconstituted FMWC. The difference in consistency associated with varying the FM:W ratio is likely to impact on satiety and nutrient value of the FMWCs

Comparison of the nutritional composition of experimental fermented milk:wheat bulgur blends and commercially available kishk and tarhana products

peer-reviewedDried, fermented blends of dairy products and cereals, such as kishk and tarhana, are foodstuffs traditionally consumed in many regions as they possess good nutritional qualities and extended storage stability. This study examined the nutritional composition of kishk or tarhana type products and compared with experimental blends of fermented milk and wheat bulgur containing 60–80% milk. The blends with higher milk contents had levels of protein (18.9%) and fat (5.8%) at the concentrations specified in fortified blended foods as outlined by the World Food Program. Higher milk contents were also associated with higher contents of calcium (323.2 mg/100 g), phosphorus (335.3 mg/100 g), vitamin A (486.7 µg/100 g) and α-tocopherol (174.5 µg/100 g). The nutritional content of the experimental fermented milk:wheat bulgur blends compared favourably with that of the commercial samples. These blends may be suitable as base products, to be fortified with micronutrients, for the development of fortified blended foods (FBFs) for humanitarian distribution

Physicochemical properties of whole milk powder derived from cows fed pasture or total mixed ration diets

peer-reviewedThis study examined the effect of dietary factors on compositional and functional properties of whole milk powder (WMP) produced from bovine milk. Raw milk samples were obtained from 3 groups of 18 Holstein Friesian spring-calving cows randomly assigned to diets based on perennial ryegrass (GRS), perennial ryegrass/white clover sward (CLV), and total mixed ration (TMR). Raw milks obtained in late lactation were subsequently standardized for fat, heat-treated (90°C for 30 s), evaporated, and homogenized before spray drying. The WMP produced from each diet were analyzed to determine differences in color, particle size distribution, heat coagulation time, yogurt gelation, texture profile, and protein profile due to each diet. Significant differences in heat coagulation time were observed between the CLV and TMR samples, whereas color values were significantly different between GRS and TMR samples. No significant differences in gross composition, protein profile, or whey protein nitrogen index were found between the 3 WMP samples. Average D90 values (the particle size at which 90% of the particles were smaller than the specified size) for fat globules were significantly lower in the TMR sample compared with the GRS and CLV samples. Yogurts produced from GRS- and CLV-derived WMP had significantly higher elastic moduli (G′) than those produced from TMR-derived WMP. Similarly, texture profile analysis revealed significantly higher firmness values in yogurt samples derived from CLV compared with TMR samples. Our data characterize the effect of these diets on the composition and functional properties of fat-standardized WMP, suggesting better yogurt functionality and thermal stability in WMP derived from pasture-based bovine diets

The “Grass-Fed” Milk Story: Understanding the Impact of Pasture Feeding on the Composition and Quality of Bovine Milk

peer-reviewedMilk is a highly nutritious food that contains an array of macro and micro components, scientifically proven to be beneficial to human health. While the composition of milk is influenced by a variety of factors, such as genetics, health, lactation stage etc., the animal’s diet remains a key mechanism by which its nutrition and processing characteristics can be altered. Pasture feeding has been demonstrated to have a positive impact on the nutrient profile of milk, increasing the content of some beneficial nutrients such as Omega-3 polyunsaturated fatty acids, vaccenic acid, and conjugated linoleic acid (CLA), while reducing the levels of Omega-6 fatty acids and palmitic acid. These resultant alterations to the nutritional profile of “Grass-Fed” milk resonate with consumers that desire healthy, “natural”, and sustainable dairy products. This review provides a comprehensive comparison of the impact that pasture and non-pasture feeding systems have on bovine milk composition from a nutritional and functional (processability) perspective, highlighting factors that will be of interest to dairy farmers, processors, and consumers

Effect of different forage types on the volatile and sensory properties of bovine milk

peer-reviewedThe effect of 3 diets (grass, grass/clover, and total mixed ration) on the volatile and sensory properties of bovine milk was assessed over an entire lactation season. Little evidence was found of direct transfer of terpenes into raw milk from the different diets, and it is likely that the monocultures of ryegrass used with and without white clover were factors as these contained very few terpenes. Evidence of direct transfer of nonterpene volatiles from forage to the subsequent raw milks was probable; however, differences in the protein carbohydrate availability and digestion in the rumen appeared to have a greater contribution to volatile profiles. Pasteurization significantly altered the volatile profiles of all milks. A direct link between the milk fatty acid content, forage, and volatile products of lipid oxidation was also evident and differences in fatty acid content of milk due to forage may also have influenced the viscosity perception of milk. Irish sensory assessors preferred pasteurized milk produced from grass-fed cows, with least preference from milk produced from total mixed ration diets. β-Carotene content was significantly higher in milks derived from grass or grass/clover and appears to have directly influenced color perception. Toluene and p-cresol are both degradation products of β-carotene and along with β-carotene were identified as potential biomarkers for milk derived from pasture. The only correlation that appeared to influence the flavor of milk as determined using ranked descriptive analysis was p-cresol. P-Cresol appears to be responsible for the barnyard aroma of milk and is also likely derived from the deamination and decarboxylation of tryptophan and tyrosine due to the higher levels of available protein in the grass and grass/clover diets. The highest levels of p-cresol were in the grass/clover diets and are likely due to the degradation of the isoflavone formononetin in the rumen, which is present in white clover swards.This work was funded by the Department of Agriculture, Fisheries and Food, under the Food Institutional Research Measure; Sensory Network Ireland Reference 13SN401

Effect of pH and heat treatment on viscosity and heat coagulation properties of milk protein concentrate

peer-reviewedThe effect of pH, adjusted using either hydrochloric acid (HCl), citric acid or sodium hydroxide, on calcium ion (Ca2+) activity, and consequent changes in viscosity and heat coagulation time (HCT) of milk protein concentrate (MPC) was investigated. Reducing the pH of MPC dispersions resulted in a reduction in their viscosity, which subsequently increased during heat treatment. The maximum heat stability of MPC was observed at pH 6.7. Reducing the pH of MPC from 6.7 to 6.2 resulted in a significant (P < 0.05) increase in Ca2+ activity, and reduction in HCT. Such changes were more extensive using HCl compared with citric acid. Increasing the pH greater than 6.7 also led to a reduction in HCT but a decrease in Ca2+ activity. These results demonstrate the importance of pH adjustment, and choice of acidulant, on Ca2+ activity, viscosity, and heat coagulation properties of MPC concentrates during processing