Abstract
The aim of the present study is to investigate the production of antioxidant peptides during milk fermentation with co-culture of Lactic Acid Bacteria (LAB) and yeast. Five LAB strains, previously screened with higher hydrolysis activity and <em>Debaryomyces hansenii</em> H2 which isolated from Tibet kefir were used in the study. The peptides separated from fermented milk were analysed antioxidant activity with DPPH radical scavenging, hydroxyl radical scavenging, chelation of metal ions and reducing power assays. The growth of <em>Streptococcus</em>. <em>thermophilus</em>, <em>Lactobacillus</em>. <em>delbrueckii</em> ssp. bulgaricus and <em>Lactococcus</em>. <em>lactis</em> was enhanced with co-cultures and L. acidophilus was inhibited in co-culture with yeast. In co-culture with yeast, a significant decrease of the acidity was observed among all the fermentation and the pH reached higher values than in single LAB cultures. Except for <em>L.delbrueckii</em> ssp. bulgaricus, there was no significant difference of protein hydrolysis with other test LAB strains between co-culture and single culture. The co-incubation of LAB with the yeast developed a stronger antioxidant activity in DPPH radical and hydroxyl radical scavenging and no significant (p>0.05) difference in chelation of metal ions. The reducing power of <em>L. delbrueckii</em> ssp. bulgaricus and <em>L. helveticus</em> in co-culture was significant higher than those of single culture.
Highlights
Reactive Oxygen Species (ROS) and free radicals are highly reactive molecules with one or more unpaired electrons, which can directly attack biological macromolecules, including DNA, RNA, protein and other substances and eventually cause cell injury (Behrend et al, 2003)
The growth of S. thermophilus, L.delbrueckii ssp. bulgaricus and Lc. lactis was enhanced with co-cultures
Compared to the viable counts reached at 6.64 log cfu/mL in single yeast culture, D. hansenii H2 was inhibited by all Lactic Acid Bacteria (LAB) strains and the final counts was in range of 5.54-6.38 log cfu/mL
Summary
Reactive Oxygen Species (ROS) and free radicals are highly reactive molecules with one or more unpaired electrons, which can directly attack biological macromolecules, including DNA, RNA, protein and other substances and eventually cause cell injury (Behrend et al, 2003). Food containing antioxidant substances, which can reduced the reactive activity of ROS and free radicals, may be used to help the human body to reduce oxidative damage. Especially the Caseins, are a source of antioxidant peptides obtained either by enzymatic hydrolysis or by fermentation. The antioxidant activity of milk protein hydrolysates and individual peptides released after hydrolysis have been reported by several studies (Hernandez-Ledesma et al, 2005; Rival et al, 2001a, b). The antioxidant peptides have been identified in fermented milk with lactic acid bacteria and these peptides had an important role in the oxidative stability of yoghurt (Abubakr et al, 2012; Virtanen et al, 2007)
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