Effects of herd diet, protein fortification and coagulation conditions on in-vat curd syneretic properties and ripening profiles of Maasdam cheese

This thesis describes a series of studies undertaken to underpin developments in the Irish cheese industry, particularly an increased interest in the potential of achieving market advantage through the promotion of grass- or pasture-fed products. However, a knowledge gap exists in terms of the impact of herd diet on the processing characteristics and on the ripening and sensory properties of resultant cheeses. Similarly, the industry has moved to produce more continental-type cheeses in an effort to diversify from predominantly Cheddar manufacture. Thus, there is a further research requirement for information regarding the manufacture of continental-type cheese such as Masadam from a seasonal Irish milk supply, and the application of process modifications such as membrane filtration in the manufacture of such cheeses. This research focused initially on characterizing the cheesemaking properties of milk and the physico-chemical, ripening and sensory properties of Maasdam cheese derived from a herd fed indoors on total mixed ration (TMR) and herds fed outdoors on either perennial rye grass (GRA) or perennial rye grass with white clover (CLO). Furthermore, the effects of protein-standardization of milk on cheesemaking properties, e.g., rennet coagulation, in-vat curd moisture loss kinetics and curd microstructure at different set temperatures were also investigated. There was a minimal feed-induced variation on in-vat curd moisture loss kinetics, final Maasdam cheese yield, recovery of fat and protein, physico-chemical composition, and proteolysis and biochemical changes (such as propionate and lactate) during 150 d of ripening. The principal differences noted were in colour, with GRA or CLO cheeses being less white and more yellow, and TMR cheeses being more white. Maasdam cheeses made from the milk of the TMR-fed herd had higher levels of linoleic acid (C18:2) and palmitic acid (although the difference in palmitic acid content was not significant), compared to pasture-derived cheese and this translated into a firmer texture in the mouth from TMR cheeses. A detailed investigation of the metabolic profile of cheese samples using nuclear magnetic resonance and gas chromatography-mass spectrometry showed that TMR-derived cheese samples had higher levels of citrate, while GRA or CLO cheeses had higher levels of toluene, thus providing a potential chemical fingerprint for differentiation between cheeses based on feeding systems. The coagulation properties of milk concentrated to protein levels of 4, 5 or 6% at 28, 32 or 36°C were also characterized. It was concluded that cheese producers would need to focus on optimizing the cutting window, based on milk protein level and coagulation temperature, to attain uniform curd rigidity on completion of the cutting cycle. However, the coagulation time and cutting process for milk with 5% protein at 28°C was similar to that observed for milk of 4% protein coagulated at 32°C, due to similar levels of curd firmness and curd firming rate in these gels. Curd from milk concentrated to 6% protein had a dense protein network compared to that with 4% protein, as observed by transmission and scanning electron microscopy, and the curds from the former milk contained lower levels of moisture during stirring compared to the latter. An increased coagulum cut size is required to achieve a uniform curd moisture content when milk protein levels are increased by standardization (4 to 6%). However, breakage of curd particles of size >6 mm3 from milk concentrated to >5% milk was excessive, which significantly influenced the curd moisture loss kinetics during stirring. Overall, a fundamental understanding of coagulation and curd syneresis properties was gained in terms of the application of ultrafiltration for milk protein concentration, which can be applied to reduce the impact of seasonal variability in milk composition for cheesemaking. This research generated fundamental knowledge which may be useful to achieve greater consistency in cheese manufacture and in achieving diversification of the Irish cheese industry through the manufacture of Maasdam type and other continental cheese types of consistent quality from a predominantly grass-fed milk production system