Raw milk chemical composition and its variations at tank level in dairy plants of the VIII, IX and X regions of Chile

Abstract

Monthly milk samples collected for a 1-year period (June/96 - May 97) from bulk tanks of 16 dairy plants of the VIII, IX and X Regions (about 85% of the national reception) were analyzed to evaluate their main components which may be considered in schemes of payment of milk to the producer.
The average composition (n = 192), range and coefficient of variation (CV) were: fat (3.53 ± 0.02; 2.70-4.33; 7.04); protein (3.51 ± 0.01; 3,20 - 3.95; 3.64), casein (2.82 ± 0.01; 2.03 - 3.33; 5.77; whey protein (0.68 ± 0.01; 0.54 - 0.92; 8.82); lactose (4.91 ± 0.02; 4.26 - 5.57; 5.15); total solids (11.94 ± 0.02; 10.31 - 12.86; 2.89) and solids-non-fat (8.42 ± 0.02; 7.37 - 9.07; 3.32), respectively. Whey protein and fat showed the highest variation during the year referred to coefficient of variation, in spite of the considered volume (milk of dairy plant tanks); the lowest variation was showed by the total solid parameters.
A significant statistical correlation was observed (P < 0.01) among total solids with lactose, fat, protein and casein, also casein with lactose and total protein. A multiple lineal regression equation was determined to estimate total solids in relation to lactose, fat and protein (TS = 1.67619 + 0.260215 Lac + 0.606474 MG + 1.95457 Prot). Also total solids were estimated in relation to fat and protein (TS = 6.68026 + 0.709519 MG + 0.788243 Prot). Both equations showed a significant statistical correlation (P < 0.01) between variables, with an estimated standard error of 0.07377 and 0.275451, respectively. Thus, the first equation is more accurate.
From the results previously obtained, it is highly recommendable to know the milk normal variaton at a regional level, to define schemes of payment of milk to producers.