The present invention provides a lactic acid bacterium which has high proteolysis activity and thus has excellent peptide production ability and/or amino acid production ability. The present invention also provides fermented milk which contains an amino acid and/or a peptide at high concentration and has a good flavor. The present invention specifically provides a lactic acid bacterium belonging to the genus Lactobacillus helveticus, which is characterized by having at least one of the following properties (a)-(d). (a) The lactic acid bacterium produces 25 &mgrmol/ml or more of a free amino acid by fermenting animal milk. (b) The lactic acid bacterium produces 8.5 mg/ml or more of a peptide by fermenting animal milk. (c) The lactic acid bacterium produces XP peptide and/or XPP peptide in a total amount of 260 &mgrg/ml or more by fermenting animal milk. (d) The amount of IPP peptide and VPP peptide per acidity of fermented milk that is obtained by fermenting animal milk at 30-34 DEG C (inclusive) is 6.0 mg/g or more in terms of VPP.本發明提供一種具有高蛋白質分解活性,且肽生成能力及/或胺基酸生成能力優異之乳酸菌。本發明提供一種高濃度地含有胺基酸及/或肽,且風味良好之醱酵乳。具體而言,本發明提供一種屬於瑞士乳酸菌之乳酸菌,其特徵在於具有以下(a)~(d)中之至少1種性質:(a)藉由使獸乳醱酵而生成25 μmol/ml以上之游離胺基酸;(b)藉由使獸乳醱酵而生成8.5 mg/ml以上之肽;(c)藉由使獸乳醱酵而生成總量為260 μg/ml以上之XP肽及/或XPP肽;(d)使獸乳於30℃以上34℃以下醱酵所獲得之醱酵乳之單位酸度之IPP肽及VPP肽的量以VPP換算量計為6.0 mg/g以上。(無元件符號說明)
