Abstract
Thirty-five different lactic acid bacteria (LAB) strains were screened for their conjugated linoleic acid (CLA) isomers (C18:2 cis-9, trans-11 and C18:2 trans-10, cis-12) producing ability from linoleic acid (LA) in sheep’s milk. Preliminary experiments revealed that Lactobacillus delbrüeckii ssp. bulgaricus 2230 and Streptococcus thermophilus St 360 among the screened strains had the highest CLA-producing ability. This two strains were assayed in an 11-run fractional factorial design to investigate the effect of four variables included glucose, powdered sheep milk, LA and inoculum ratio on CLA production in a sheep’s milk yogurt. The optimum conditions for producing the highest levels of CLA (42.86%) were obtained by adding 10.00 mg/mL of glucose, 30.00 mg/mL of powdered sheep milk, 0.90 mg/mL of LA and a 1:2 (St:Lb) ratio of bacterial strains in the inoculum. This CLA-rich sheep’s milk yogurt could be an important supplementary food source for increasing the CLA in the human diet.
Highlights
Bovine milk is the most commonly consumed type of milk
Ovine milk is favored in terms of fatty acids (FA); they have a high proportion of saturated fatty acids (SFA) with both short and medium chains (Corrêa, Rohenkohl, & Osório, 2014; Mayer & Fiechter, 2012)
L. bulgaricus strains were cultured in Man Rogosa Sharpe (MRS) medium (Merck, Darmstadt, Germany) and S. thermophilus strains were cultured in M17 medium (HiMedia, Mumbai, India) with incubation at 37 oC and 42 oC, respectively, for 48 h under anaerobic conditions
Summary
Bovine milk is the most commonly consumed type of milk. In many countries, milk from other animal species is a significant share of the milk consumed. Compared to bovine and caprine milk, ovine milk is richer in fat, proteins, ash, calcium, iron, manganese, phosphorus, zinc, all essential amino acids, most vitamins, medium-chain fatty acids and monounsaturated fatty acids (MUFA) (Balthazar et al, 2015; Park, 2007). Ovine milk is favored in terms of fatty acids (FA); they have a high proportion of saturated fatty acids (SFA) with both short and medium chains (Corrêa, Rohenkohl, & Osório, 2014; Mayer & Fiechter, 2012). Ovine milk has the highest conjugated linoleic acid (CLA) content (i.e. 1.08% of ovine against 1.01% and 0.65% of bovine and caprine milks respectively) and 3.21% of linoleic acid (LA) (Jahreis et al, 1999)
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