Compounds with the ability to inhibit angiotensin-converting enzyme (ACE) are used medically to treat human hypertension. The presence of such compounds naturally in food is potentially useful for treating the disease state. The goal of this study was to screen lactic acid bacteria, including species commonly used as dairy starter cultures, for the ability to produce new potent ACE-inhibiting peptides during milk fermentation. Strains of Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus delbrueckii ssp. bulgaricus, Lactobacillus helveticus, Lactobacillus paracasei, Lactococcus lactis, Leuconostoc mesenteroides, and Pediococcus acidilactici were tested in this study. Additionally, a symbiotic consortium of yeast and bacteria, used commercially to produce kombucha tea, was tested. Commercially sterile milk was inoculated with lactic acid bacteria strains and kombucha culture and incubated at 37°C for up to 72 h, and the liberation of ACE-inhibiting compounds during fermentation was monitored. Fermented milk was centrifuged and the supernatant (crude extract) was subjected to ultrafiltration using 3- and 10-kDa cut-off filters. Crude and ultrafiltered extracts were tested for ACE-inhibitory activity. The 10-kDa filtrate resulting from L. casei ATCC 7469 and kombucha culture fermentations (72 h) showed the highest ACE-inhibitory activity. Two-step purification of these filtrates was done using HPLC equipped with a reverse-phase column. Analysis of HPLC-purified fractions by liquid chromatography-mass spectrometry/mass spectrometry identified several new peptides with potent ACE-inhibitory activities. Some of these peptides were synthesized, and their ACE-inhibitory activities were confirmed. Use of organisms producing these unique peptides in food fermentations could contribute positively to human health.

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Synbiotic-drinkable yoghurt was produced by using some new probiotic bacteria and enriched with 1% oat. The resultant synbiotic-drinkable yoghurts were stored at 5°C and analyzed for physico-chemical, rheological, microbiological and sensory properties when fresh and after 7, 14 and 21 days. The obtained results cleared that the acid development of probiotic bacteria revealed that control sample (C1) without probiotic strains or oat and yoghurt with Bifidobacterium breve (B) recorded the highest pH values, while yoghurt with Lactobacillus acidophilus (A) recorded the lowest pH during the fermentation of yoghurt. The chemical composition of the produced yoghurt indicated slightly decreases in carbohydrates and pH values, Moreover there were significantly increased in TS, protein, fat and titratable acidity contents during cold storage. On the other hand, WSN (%), diacetyle (ppm) and viscosity (cp) significantly increased in the fortified treatments comparing to the unfortified control (C1). The total viable cell counts of TBC, LAB, Streptococcus thermophilus and probiotic bacteria (log cfu/ml) increased during cold storage through the first 7 days then they decreased thereafter gradually till the end of storage period. Generally, it can be found that enriched synbioticdrinkable yoghurt treatments with different probiotic strains and oat had higher viable counts compared to control (C1); there was an improvement of sensory properties by adding probiotic bacteria and oat.

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