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Background : : : : The increase in the goat’s milk production chain has been intensified in recent years. However, little is known about the quality characteristics of goat’s milk. In this sense, the present assay aimed to evaluate the physical parameters of goat’s milk: titratable acidity, alcohol and heat stability and its possible relations. Materials, Methods & Results : 71 samples of Saanen and Alpine goat’s milk were collected during the second lactation phase. In the milk samples were determined the titratable acidity and thermal and alcohol stability. Besides milk samples, date of individual milk production, race, date of birth and order of birth were collected. The titratable acidity values ranged between 11 and 20°D. The median stability of alcohol 52oGL was verified and 76.4% of the samples presented an alcohol stability in which the graduation was lower than 60oGL. A low negative (r = - 0.1914) and non significant (P = 0.1073) correlation was determined between milk production and alcohol stability. In addition to this, a low negative (r = - 0.05702) non-significant (P = 0.6223) correlation between alcohol stability and acidity, measured in Dornic degrees was determined; however, these results did not present a significant association between each other (k = - 0.006). During the clot-on boiling test, a coagulation rate of 39.46% (30/76) from the samples was observed, from which 32% (16/50) was originated from Saanen goats and 53.85% (14/26) from Alpine goats. Discussion : At the time of milking, the acidity of the goat milk varies from 12 to 14oD. This natural acidity is determined by lactation stage and, at the end of this, the acidity is from 16 to 18oD in bulk tank milk. However, in this study, the samples were related to the individual milk production and that may result in different values. Studies have shown significant differences in mean values of acidity according to race, ranging between 12 and 23oD; similar to those observed in this study, but with less individual variability. Data on the stability of goat milk are scarce and the large number of samples that showed no precipitation with alcohol 50°GL is close to the values found in a previous study (40 and 44oGL). Similarly, there are few data on the thermal stability in goat milk. In bulk tank milk samples the thermal stability was determined to 124.5 and 133oC. However, in another study, a low stability of milk coagulation occurs at temperatures from 92 to 110oC. The low thermal stability may be related to the physic-chemical properties of goat milk like protein concentrations and pH. Another factor to consider is that due to its protein composition, the micelles of goat’s milk are less hydrated than those of cow’s milk. This factor, coupled with the highest level of milk proteins and calcium, give to the goat milk a lower thermal stability. It was found that the stability test to alcohol has no correlation with the acidity and contains a wide variability, considering the individual goat milk. Other studies, aiming at correlating the alcohol and heat instability proof to the overall net production of milk in the industrial manufacturing of dairy products, should be performed, considering the growth of the market of caprine dairy products in Brazil.

O objetivo deste trabalho foi avaliar o efeito da restrição alimentar na incidência do leite instável não-ácido (LINA) e na composição do leite de vacas Jersey. Foi realizado um experimento piloto de indução ao LINA, com oito vacas Jersey em lactação, confinadas e separadas em dois grupos, às quais havia sido fornecida uma dieta equilibrada ad libitum. Em dois períodos de 18 dias, foram fornecidos dois tratamentos com 100 e 60% das exigências nutricionais. Foram realizados os testes de acidez titulável e do álcool 76%; pH, densidade, crioscopia, caseína, gordura, proteína bruta, lactose, extrato seco total, número de células somáticas e produção de leite foram determinados. A restrição alimentar aumenta a ocorrência de LINA e diminui a produção de leite e a quantidade total dos componentes produzidos; entretanto, não altera os teores dos componentes lácteos. The objective of this work was to evaluate the effects of feed restriction on unstable nonacid milk occurrence and milk composition of Jersey cows. A pilot trial of feed restriction was conducted with eight lactating Jersey cows. Animals were confined and allocated to two groups which received a balanced diet ad libitum. They received sequentially two treatments, at different periods: 100 and 60% of nutritional requirements. Milk was analyzed for titrated acidity and precipitation at alcohol test 76%; pH, density, cryoscopy, casein, fat, crude protein, lactose, total solids, number of somatic cells and milk production were determined. Feed restriction increases unstable nonacid milk occurrence, reduces milk production and amount of components; however, it does not change the concentration of the milky components.