Production of conjugated fatty acids in probiotic-fermented walnut milk with the addition of lipase

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Walnut milk is rich in linoleic acid (LA) and linolenic acid (LNA) in the form of triglycerides. Four LAB strains capable of converting LA and LNA could grow to 9.0 lg CFU/mL in walnut milk. However, no conjugated fatty acids were detected. Lipase was added to release LA and LNA and then LAB was inoculated to ferment walnut milk. However, conjugated linoleic acid (CLA) and conjugated linolenic acid (CLNA) were only detected in walnut milk inoculated with Bifidobacterium breve CCFM683. When 60 U/mL lipase was added, the total amount of conjugated fatty acids reached 1.33 ± 0.01 mg/mL with conversion rates of 5.0% and 11.3% for CLA and CLNA, respectively. By monitoring the fermentation progress, the amount of conjugated fatty acids could reach a maximum of 2.30 ± 0.01 mg/mL at 20 h (p < 0.05). When 20 U/mL lipase was added, the amount of conjugated fatty acids in fermented walnut milk reached 1.58 mg/mL and conversion rates increased to 7.2% and 21.6% for CLA and CLNA, respectively. Thus, adding lipase can realize the conversion of CLA and CLNA in walnut milk and reducing the amount of lipase and hydrolysis time is beneficial to improve the conversion rates, but total amount is reduced.