Investigating the Impact of Distiller's dried grains with Solubles on the Quality of Milk and Swiss Cheese
Late blowing in Swiss cheese, a result of unwanted gas production during ripening, is unacceptable to consumers, is impossible to slice, and causes economic loss to manufacturers. Cheese processors have raised concerns that feeding distiller’s dried grains with soluble (DDGS) to cows leads to this defect, in part because of Clostridium tyrobutyricum. In this study, the effect of feeding DDGS on composition and quality of milk and Swiss cheese was studied. Thirty healthy mid-lactation ISU Dairy Farm Holstein cows were assigned randomly to one of three dietary treatment groups (10 cows per treatment group): (1) total mixed ration (TMR) with no DDGS, (2) TMR with 10% substitution with DDGS, and (3) TMR with 20% DDGS. One complete milking from all cows within a treatment was collected and pooled for cheese making trials, twice within each of three month-long treatment periods. Additionally, individual milk samples from three milkings of a day were collected weekly, and proximate analysis was carried out on pooled individual milk samples. Cheese milk was filtered, standardized to 0.88 fat:protein, and pasteurized before addition of starter cultures and coagulant. Curds were cut, fore-worked, worked, and post-worked according to a baby Swiss cheese recipe, followed by pressing and brining (100C, 12hrs). The 3.5 kg blocks were vacuum packed and allowed to ripen (100C, 7 days; then 220C, 21days), then cooled (40C, 60 days). The milk and DDGS were analyzed for C. tyrobutyricum using selective media. After incubation up to 48 hours in modified RCM lactate medium, tubes containing DDGS did not show gas formation, whereas most of the tubes containing milk showed gas formation, which indicates that DDGS were not the source of C. tyrobutyricum. Milk fat content decreased as % DDGS in diet increased (p < 0.05). Solids nonfat, protein, and lactose content of milk of cows fed 10% and 20% DDGS were only slightly higher than from control diet. After ripening (> 60 days), baby Swiss cheese had typical propionic acid Swiss cheese aroma. Regardless of diet treatment, pinholes, slits, and cracks were seen throughout most cheeses. DDGS feeding increased the amount of long chain unsaturated fatty acids and decreased short chain and most medium chain fatty acids. Although feeding cows DDGS modified milk composition and subsequent cheese composition, DDGS alone should not be blamed as a source for C. tyrobutyricumor for late blowing in Swiss cheese.
Keywords: C.tyrobutyricum, Swiss-cheese