Quality of milk protein in dairy farms from Southeastern region of Brazil
Abstract
The quality of milk protein is related to the capacity of milk being processed or not, called thermal stability. Unstable Non Acid Milk is characterized by low casein stability that results in precipitation during alcohol test without presence of acidity on milk sample and determines great damages. This study had the objective of diagnosing protein quality and occurrence of Unstable Non Acid Milk on raw milk produced by dairy farms of the Southeast ern region of Brazil. For investigation of occurrence, 201 dairy farms were chosen and received a trained technician to collect milk samples monthly. During one year 2,970 milk samples delivered in dairy plants were evaluated for milk quality (fat, protein , lactose, solids non fat, somatic cell count and total bacterial count) and for protein quality in terms of thermal stability using titratable acidity, alcohol test and pH. As a result, it was observed that 7% from 52 million liters of processed milk were classified as Unstable Non Acid Milk. There wasn’t relationship between occurrence of Unstable Non Acid Milk and milk production level. However, occurrence displayed a variation throughout months during the year, being the final of fall the highest incidence of the problem. The milk identified as Unstable Non Acid Milk showed changes on milk composition, in special for lactose, what can describe a possible relation between the problem and nutritional practices, more specific related to carbohydrate metabolism, what can help to find the prevention and/or control the problem of thermal stability related to milk protein.
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Introduction
Protein is currently the most valued component of milk in the majority of countries. The appreciation of this element over the fat can explain the huge increase in cheese consumption and encouraging the reduction of the consumption of animal fat about the relationship to health [1].
The importance of protein levels is directly related to industrial performance, mainly cheeses. Others aspects such as protein quality must be emphasized and also associated to industrial incomes during the processing of milk. Protein quality refers mainly the capacity to withstand thermal processing, in other words, the thermal stability of milk. During this process, several changes occur and the most important thing was associated with the structures of proteins, including casein micelles [2]. So, stability is directly related to milk capacity to resist the coagulation by heat, and thus, its ability to thermal processing.
The estimation of the milk thermal stability can be possible achieved through the alcohol test or alizarol [1]. This test is widely used in dairy as a way to accept or decline milk at the moment of its arrival at the platform in industries or even at dairy farm. The occurrence of milk with thermal instability, diagnosed by this test, is a problem found in various regions of Brazil which results in inappropriate raw materials for the dairy production, representing losses for the entire dairy chain [3].
Most of problems with thermal instability are related to milk with high acidity due to the high bacterial contamination. However, the problem may also be associated to the stability of milk protein, known as Unstable Non Acid Milk. Milk classified as Unstable Non Acid Milk have normal pH and titratable acidity, low bacterial and somatic cell count but, the coagulation is positive on the alcohol test.
The occurrence of this problem is still poorly investigated due to the complexity of factors involved in thermal stability of milk and their random occurrence, encouraging studies for the knowledge in the control and/or preventive measures. In view of the points analyzed in relation to milk protein, the aim of this study was to detect the Unstable Non Acid Milk produced and sent to the dairy industries in southeastern of Brazil. This study was grounded according to the characteristics of milk composition, seasonal variation and occurrence.
Conclusion
Finally, the 52 million liters of milk processed, 7% were classified as Unstable Non Acid Milk . This results in about 3,5 million liters of milk involved with low -quality protein, varying its occurrence throughout the months of the year, especially in the early fall and late winter. The problem named Unstable Non Acid Milk has close relation with nutritional management, particularly for the metabolism of carbohydrate that is an important matter to find the prevention and / or control the problem.
