Correlation of Protein Contents and Milk Temperatures, with Milk Density of Friesian Holstein (FH) Cow in Ngablak District of Magelang Regency Central Java

Indicators of milk quality commonly used by the Milk Processing Industry (MPI) is the milk density (MD). Some factors that influence the milk density is milk protein in the form of casein and milk temperatures. This study aims to examine the correlation between protein content and milk temperature to milk density. The material used was 90 lactating FH cows in the II - III of lactation period and 2 – 3 of lactation months. The analysis used is simple linear correlation regression. The results showed that the increase in protein content caused an increase in the milk density by 73.48%. The decreased in temperature caused an increase in the milk density by 5.25%. Protein content and milk temperature to milk density had a significants correlation value (P <0.01). The overall calculation shows that there is a relationship between the protein content and milk temperature to milk density. Protein content with milk density, shows a very strong positive correlation. The milk temperature and the milk density shows a very strong negative correlation. The conclusion is that there is a positive relationship between protein content to milk density, and a negative relationship between milk temperature to milk density. The higher the protein content, the higher the milk density. The lower the milk temperature, the higher the milk density value.


Introduction
Friesian Holstein (FH) is very commonly cultivated in Indonesia as a milk-producing cow. The average milk production of FH cows is 2,000 -2,500 liters in one lactation period. High milk production causes FH cows to be cultivated more in Indonesia as milk producers (Syarief and Sumoprastowo, 1990). FH cows have a predominantly black and white striped coat color, and sometimes red and white stripes are found. The size of the head is relatively long, straight and wide, with a relatively short horn shape and curving forward. FH cows have a docile temperament and are relatively calm (Siregar, 1993).
Milk is a white liquid which contains complete nutrients in the form of protein, lactose, fat, several vitamins, minerals, and hormones that are excreted by the mammary glands in adult female mammals which act as food for their children (Guetouache et al., 2014). Milk

Results and Discussion
Based on the analysis of the milk quality (protein content, milk temperature, and milk density) that has been carried out, the results of the analysis are as shown in Table 1.  Amino acids and peptides that are formed from natural protein digestion will be Tabel 2. The regression equation, correlation coefficient (r), coefficient of determination (R 2 ) between protein content (PC) to true milk density (TMD), and milk temperature (MT) to measured milk density (MMD).

Protein Contents and True Milk Density
Based on the data in Table 2 Protein content (PC) of 2.63% is low (Table   1.), but it can increase the true milk density (TMD). This is because the protein in the total solid milk has a large enough molecular weight, causing an increase in true milk density (TMD). Lestari and Soesilo (2017) stated that the α-casein, β-casein, and κcasein bands were 32, 24, and 19 kDa in size, respectively. Saputra (2018) states that protein is part of the total solid of milk or milk solid material. It is confirmed by Vidiyanto et al. (2015) that the total solid milk is the main factor affecting the high density of milk.

Density
Based on the data in Lowering the temperature of the milk will cause the compaction of several components of milk, such as water and milk fat. In accordance with the opinion of Sutrisna et al. (2014), a decrease in milk temperature will lead to the compaction of fat globules. The density of fat that is compacted will be greater than that of fat in the liquid state. Gabas et al. (2012), shows that the higher the milk temperature, the lower the milk density.
The value of the correlation coefficient (r) and determination (R2) is low, because in addition to decreasing the temperature of the milk causes an increase in the measured milk density (MMD), heating (temperature increase) of milk will also cause an increase in the measured milk density (MMD). This is because the water content in the milk is evaporated, thus increasing the proportion of the total solid of milk. This is explained by Miskiyah (2011) which states that there will be water evaporation in heated milk, thereby increasing the density of the milk.

Conclusion
Protein content (PC) has a very strong positive correlation to the milk density (MD). The higher the milk protein content, the higher the milk density. Milk temperature (MT) has a weak negative correlation with milk density. The lower the temperature of the milk, the higher the density of the milk.