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Effect of pasture feeding and lactation stage on the biochemical composition of goat milk and cheese flavor

K. A. Soryal, S. Zeng, B. Min, S. Hart, K. Tesfai, and T. Sahlu

E (Kika) de la Garza Institute for Goat Research, Langston University, Langston, OK

This study was to examine the effect of pasture feeding with different levels of concentrate and lactation stage on milk fatty acids and cheese characteristics. Twenty lactating Alpine goats were randomly assigned into four groups. Group A was confined, fed alfalfa hay and supplemented with 0.66 kg concentrate (per 1 kg of milk over 1.5 kg/day) (Control). The three pasture groups with different levels of concentrate were B (0.66 kg/d), C (0.33 kg/d), and D (no supplementation). Two batches of milk (10 kg) were collected monthly for processing into a soft cheese, Egyptian Domiati, from April through September 2001. Milk samples were analyzed for fat, protein, lactose, and TS, and cheese samples were organoleptically scored. Results indicated that the overall mean values of short chain (C6, C8, C10; SCFA) and long chain (C12, C14, C16, C18, C18:1, C18:2, and C18:3; LCFA) fatty acids in milk were 0.98 and 6.79 mg/g, respectively. Both SCFA and LCFA contents in goat milk were affected (P < 0.001) by stage of lactation. SCFA concentration for D was lower, 0.83 mg/g than for A, B, and C (1.04, 1.02, and 1.04 mg/g, respectively). However, LCFA content in B (7.34 mg/g) was higher (P < 0.05) than in D (6.28 mg/g). SCFA (1.7 mg/g) and LCFA (9.2 mg/g) in the early lactation were greater (P < 0.001) than in mid- to late lactation (0.7-1.2 and 6.0-8.1 mg/g, respectively). Milk fat content was positively correlated with milk protein (r = 0.42, P < 0.01), TS (r =0.87, P < 0.001), and cheese yield (r = 0.60; P < 0.001) but was negatively correlated with flavor score (r = -0.33; P < 0.01). Milk protein was positively correlated with TS (r = 0.68, P < 0.001) and cheese yield (r = 0.38; P < 0.05). SCFA and LCFA concentrations in milk were positively correlated (r = 0.7; P < 0.001). In conclusion, the best cheese flavor was obtained with milk from groups receiving little or no supplemented concentrate (C and D) in mid-lactation when LCFA and TS contents in milk were low.


 

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