Milk is an oil-in-water emulsion, with the fat globules dispersed in a continuous skimmilk phase. If raw milk were left to stand, however, the fat would rise and form a cream layer. Homogenization is a mechanical treatment of the fat globules in milk brought about by passing milk under high pressure through a tiny orifice, which results in a decrease in the average diameter and an increase in number and surface area, of the fat globules. The net result, from a practical view, is a much reduced tendency for creaming of fat globules. Three factors contribute to this enhanced stability of homogenized milk: a decrease in the mean diameter of the fat globules (a factor in Stokes Law), a decrease in the size distribution of the fat globules (causing the speed of rise to be similar for the majority of globules such that they don’t tend to cluster during creaming), and an increase in density of the globules (bringing them closer to the continuous phase) oweing to the adsorption of a protein membrane. In addition, heat pasteurization breaks down the cryo-globulin complex, which tends to cluster fat globules causing them to rise.
The main purpose of the experiment was to separate the cream of raw milk by using Disk-Bowl centrifuge. The main principle of separation depends on density differences between fat and liquid phases. Fat is found as emulsion in the milk. The diameter of the fat globules is significant. By increasing diameter of globules, separation of fat becomes easier. As well we introduced the homogenization that primarily causes disruptions of fat globules into much smaller ones. Consequently it diminishes creaming and may also diminish the tendency of globules to clump or coalesce.
Özet: Homojenizasyon işlemi süt ürünlerinde yağ stabilizasyonu amacıyla kullanılan yaygın uygulamalardan birisidir. Bu çalışmada sütler 5 farklı basınç (0, 3.5, 7, 10.5 ve 14 MPa) uygulanarak homojenize edilmiş ve bu sütlerden Kaşar peyniri yapımının, peynirlerin çeşitli özelliklerine etkisi araştırılmıştır. Homojenizasyon basıncının artmasına bağlı olarak yağ globulleri küçülmüş (p<0.01), peynir verimi ise artmıştır (p<0.01). Homojenizasyon işlemi, Kaşar örneklerinin yağ, kurumaddede yağ (p<0.01), yağsız peynirde nem ve asitlik (p<0.05) değerlerini yükseltmiş, kurumaddede protein, kül, tuz ve pH değerlerini ise önemli düzeyde (p<0.05) düşürmüştür. Kurumadde ve protein değerleri bu uygulamadan önemli derecede etkilenmemiştir (p>0.05). Homojenizasyon basıncının artmasına bağlı olarak aminonitrojen oranlarının arttığı (p<0.05), lipoliz değerlerinin ise düştüğü belirlenmiştir (p<0.05). Mikrobiyolojik özelliklerden maya-küf sayısı basınç arttıkça azalmış (p<0.05), toplam aerobik ve laktik asit bakterileri ise uygulamadan etkilenmemiştir (p>0.05). Homojenizasyon işlemi peynir örneklerinin renklerini beyazlattığından, renk-görünüş açısından homojenize örneklerin puanları düşmüş (p<0.01), diğer özellikler yönünden bir farklılık oluşmamıştır (p>0.05).
The Effect of Different Homogenization Pressures on Chemical, Biochemical, Microbiological, and Sensorial Properties of Kashar Cheese
Abstact: Homogenization process is a common application for fat stabilization in dairy industry. In this study, cheese-milks were homogenized at 5 different pressures (0, 3.5, 7, 10.5 and 14 MPa), and the effect of cheese making with these milks on various cheese properties was investigated. Depending on increase in homogenization pressure, diameter of fat globules decreased (p<0.01) and cheese yield increased (p<0.01). While homogenization process caused an increase in fat, fat in dry matter (p<0.01), moisture in non-fat dry matter and titratable acidity (p<0.05), protein in dry matter, ash, salt and pH values declined by increment of homogenization pressure (p<0.05). Dry matter and protein contents of cheese samples were not significantly affected from this application (p>0.05). It was determined that, amino nitrogen ratio increased and lipolysis values decreased (p<0.05) depending on increase in homogenization pressure. Mould-yeast counts decreased in homogenized samples (p<0.05), however total aerobic and lactic acid bacteria counts were not influenced by these applications. Colour and appearance points of homogenized cheese samples were found lower than control as a result of whitening effect of homogenization, but there was no difference in points of flavour and body-texture properties.