A study on the impact of physical disruption and reforming on cheese texture
Fiziksel parçalama ve reformasyonun peynirin tekstürel özelliklerine etkileri üzerine bir çalışma
- Tez No: 839371
- Danışmanlar: PROF. DR. JOHN LUCEY
- Tez Türü: Doktora
- Konular: Gıda Mühendisliği, Food Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2012
- Dil: İngilizce
- Üniversite: University of Wisconsin-Madison
- Enstitü: Yurtdışı Enstitü
- Ana Bilim Dalı: Gıda Bilimleri Ana Bilim Dalı
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 250
Özet
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Özet (Çeviri)
In this study, mechanical reforming of non-fat, low-fat and full-fat cheese was investigated. Our first goal was to understand the mechanisms of cheese reformation. In the context of this study, we adopted the word reform to mean the process of breaking the cheese into pieces and putting it together to form a cheese block, which may or may not, differ from its original form. The resulting cheese from that process may also remain intact or fail to be reformed. Our second goal was to determine how reforming influences the functional properties and texture of cheese. Reforming the cheese is a novel technique. No study has yet been published on how this process influences the texture of low-fat cheese, what factors promote fusion between cheese particles after reforming, and under what conditions cheese will mostly reform. We wanted to know how, to what extent, and under what conditions, cheese fuses and sticks back together when it is reformed. We know the physical and chemical properties of cheese and how cheese matrix is initially formed from milk. Interactions involved in the transition of milk to cheese can help us to understand the factors that are responsible for the reformation of the cheese network. Cheese is essentially a protein matrix held together by the interactions between caseins (i.e., hydrophobic, electrostatic and Van der Waals interactions, hydrogen bonds and ion bridges). Each casein molecule in cheese can be simply viewed as a block copolymer with their segregated hydrophobic and hydrophilic regions offering several interaction pathways with other caseins to form polymers. Factors that influence the strength of the interactions and bonds between caseins should also determine the level/degree of fusion between cheese particles after reforming. We wanted to alter the strength of those interactions and bonds to see how they would affect the affinity of caseins to stick back together again when we reform the cheese. The question was; would the caseins assemble again as they did in the initial cheese making process? If all of the interactions and bonds restore, then we assume that there would be no difference in texture between the reformed and the original cheese. In the course of this study, the impact of grating size, temperature, pH and use of different types of emulsifiers on the reformability of cheese were evaluated by examining the texture, rheology, melt properties and visual appearance of cheese samples before and after reforming process. Cheese was ground up/ shredded by a food processor/ shredder and then pressed back together to be reformed. Reformation was done by cold extrusion under vacuum using an extruder in dairy plant while in laboratory scale experiments by manual pressing. The impact of the scale of the disruption on cheese protein network was investigated by grating cheese into different sizes (9, 6, 3 and 1.5 mm) before reforming. Non-fat cheese bases were used in this trial to eliminate the contribution of fat on reforming and to see if reforming can help reduce the textural problems caused by fat removal. Grating and reforming the non-fat cheese reduced its hardness. The size of the particles used for grating did influence the texture properties of reformed cheese with bigger shred sizes giving higher hardness values. All reformed cheese samples exhibited higher degree of flow than the cheese base, while size of the grating did not influence the meltability. Our trials on the impact of reforming temperature (4, 18 or 30°C) on the reformability and texture properties of non-fat cheese showed that, when cheese was reformed at higher temperatures the cheese had softer texture. A vacuum extruder was used for reforming the cheese samples. Reforming the cheese at higher temperatures produced a smooth cheese with a softer texture. Reducing the pH of low-fat cheese from pH 6.2 to 5.3 brought about a 93% recovery in hardness and about 86% recovery in dynamic moduli of the reformed cheese compared to the cheese base. Microscopy and texture test results showed that cheese fused and reformed better at low pH values, i.e., with greater levels of colloidal calcium phosphate (CCP) solubilisation. At high pH, i.e. 6.2, reforming the cheese reduced its hardness and storage modulus while making it more meltable which was attributed to the presence of weaker interactions and incomplete recovery of the bonds between caseins after the reforming process. Impact of different types of emulsifiers (anionic emulsifiers: citric acid esters of monoglycerides (CITREM), diacetyl tartaric acid esters of monoglycerides (DATEM), sodium stearoyl lactylate (SSL), zwitterionic: lecithin and non-ionic: distilled monoglycerides (DM), lactic acid esters of monoglycerides (LACTEM), acetic acid esters of monoglycerides (ACETEM) and sorbitan tristearate (STS) on reforming aged low-fat and full-fat Cheddar cheese was investigated. Non-ionic emulsifiers did not alter the texture of full-fat cheese except for the addition of STS for texture properties at low temperatures, while they increased the meltability of the full fat cheese. Use of non-ionic emulsifiers seemed to make the low-fat cheese more prone to fracture during compression except for STS. As for the anionic emulsifiers, SSL reduced the hardness of low-fat cheese and made it very sticky and soft. CITREM, DATEM and STS appeared to produce firmer cheese. The use of DATEM and SSL resulted in cheese that had exhibited significantly lower loss tangent maximum compared to control cheese. The overall results of this study suggested that reforming cheese created a weaker/softer cheese protein network through the physical disruption of bonds and interactions. There was a partial recovery of the bonds and interactions in all cheese samples when shreds were repressed back into cheese blocks. Grating and reforming the cheese imparted some level of discontinuity to the protein matrix that was easier to compress and thus was better to chew down. Temperature used for reforming influenced cheese fusion and the final textural properties of the cheese. Increase in temperature increased the hydrophobic interactions, and accompanied by the greater bond mobility, which promoted the fusion of the cheese particles. Cheeses reformed at higher temperatures (~30ºC) were still softer than cheeses reformed at low temperature after 1 week of cold storage probably due to the incomplete recovery of the bonds and interactions that were broken as heated. At low pH, cheese fusion was greater since the solubilization of CCP crosslinks with the decrease in pH increased bond mobility of caseins. Anionic emulsifiers changed the texture properties of the reformed cheese, probably due to their strong interaction with caseins through their charged groups. Addition of emulsifiers during reforming resulted in differences between the full-fat and low-fat cheese especially with the use of more hydrophobic non-ionic emulsifiers, which was probably due to their higher affinity to interact with fat rather than proteins. While low-fat cheese reformed with non-ionic emulsifiers did not show any difference in meltability as compared to control, they increased the degree of flow in full-fat cheese.
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